S-Band Antenna Array - uu.diva-portal.org322886/FULLTEXT01.pdf · S-Band Antenna Array Master...

53
UPTEC F10 020 Examensarbete 30 hp Mars 2010 S-Band Antenna Array Mathias Dalevi

Transcript of S-Band Antenna Array - uu.diva-portal.org322886/FULLTEXT01.pdf · S-Band Antenna Array Master...

UPTEC F10 020

Examensarbete 30 hpMars 2010

S-Band Antenna Array

Mathias Dalevi

Teknisk- naturvetenskaplig fakultet UTH-enheten Besöksadress: Ångströmlaboratoriet Lägerhyddsvägen 1 Hus 4, Plan 0 Postadress: Box 536 751 21 Uppsala Telefon: 018 – 471 30 03 Telefax: 018 – 471 30 00 Hemsida: http://www.teknat.uu.se/student

Abstract

S-Band Antenna Array

Mathias Dalevi

This report presents concepts for a planar active electronically scannedantenna(AESA). The goal of the project was to devlop a low-weight, low profile, thin,S-band antenna with wide-scan angle capabilities. In the final concept the serviceaspects of the T/R-modules was also taken into acount in order to allow easy and fastreplacements of these components. The antenna was designed and optimised usingthe commercial software Ansoft HFSS. A prototype of the antenna was constructedand later measured and verified. The final concept is a 2m×2m antenna with anestimated weight of around 320 kg, around 11 cm thick (where the thickness of theantenna element is 1.76 cm) and has a maximum scan angle range of more than 45degrees (with <–10dB active reflection) in the frequency band 3–3.5 GHz.

Sponsor: Saab Electronic Defense SystemsISSN: 1401-5757, UPTEC F10 020Examinator: Thomas NybergÄmnesgranskare: Roger KarlssonHandledare: Hanna Isaksson

COMPANY UNCLASSIFIED

MASTER THESIS

I

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

I

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

S-Band Antenna Array

Master Thesis By

Mathias Dalevi

The work has been carried out at Saab Electronic Defense Systems

Mölndal

Mentor: Hanna Isaksson

Examiner: Thomas Nyberg

Reviewer: Roger Karlsson

COMPANY UNCLASSIFIED

MASTER THESIS

II

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

II

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

COMPANY UNCLASSIFIED

MASTER THESIS

III

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

III

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Abstract

This report presents concepts for a planar active electronically scanned

antenna(AESA). The goal of the project was to devlop a low-weight, low

profile, thin, S-band antenna with wide-scan angle capabilities. In the final

concept the service aspects of the T/R-modules was also taken into acount in

order to allow easy and fast replacements of these components. The antenna

was designed and optimised using the commercial software Ansoft HFSS. A

prototype of the antenna was constructed and later measured and verified. The

final concept is a 2m×2m antenna with an estimated weight of around 320 kg,

around 11 cm thick (where the thickness of the antenna element is 1.76 cm)

and has a maximum scan angle range of more than 45 degrees (with <–10dB

active reflection) in the frequency band 3–3.5 GHz.

COMPANY UNCLASSIFIED

MASTER THESIS

IV

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

IV

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Populärvetenskaplig Sammanfattning

Det här arbetet presenterar koncept för en aktiv elektronisk styrd

antenn(AESA). Arbetet är ett sammarbete mellan två examenarbeten,

elektriska och mekaniska koncept, där de elektriska koncepten innefattar

framtagning och optimering av antennelementen. Målet med projektet var att

ta fram en plan, lätt och tunn AESA med stora utstyrningsmöjligheter i S-

bandet mellan 3–3.5 GHz.

En AESA har många fördelar jämfört med en konventionell mekaniskt styrd

antenn eftersom den kan rikta in loben elektriskt och därmed snabbare scanna

av ett område. Detta är möjligt eftersom varje antennelement styrs av sin egen

T/R-modul (sändar/mottagar-modul). Loben styrs genom att individuellt

kontrollera fasen av strömmen på varje antennelement. Det går även att

kontrollera amplituden av strömmen vid varje antennelement vilket ger

möjigheter som att motverka störningar, få mindre sidlober eller en smalare

respektive bredare lob mm. Att varje element styrs av sin egen modul gör även

systemet mer pålitligt eftersom det fortfarande skulle fungera trots att en

sändar/mottagar-modul gått sönder.

Arbetet inleddes med en litteraturstudie där olika koncept undersöktes och

utvärderades för att sedan gå vidare med det mest lovande konceptet som var

en aperture kopplad stackad patch. Antennelementet designades och

optimerades med EM-simulatorprogrammet Ansoft HFSS v11.2 där elementet

realiserades med periodiska randvillkor och optimerades med en olinjär

programmeringsmetod. Efter optimeringen konstruerades en prototyp av

antennen bestående av 10×10 element som sedan verifierades och testades.

Resultatet av det simulerade antennelementet visar utstyrningsmöjligheter på

mer än 45 grader i varje plan med reflektioner på mindre än –10dB i bandet

mellan 3–3.5 GHz. De uppmätta resultaten på prototypen skiljer sig något från

de simulerade resultaten på prototypen och visar en något bättre prestanda.

COMPANY UNCLASSIFIED

MASTER THESIS

V

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

V

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Preface

This master thesis project has been carried out at Saab Electronic Defense

Systems at Lackarebäck, Gothenburg, in the period September-February. It is

the concluding part of the masterprogram of Engineering Physics at Uppsala

University. I like to thank all the co-workers at Saab Electronic Defence

Systems for their help and support throughout the project and especially my

mentor Hanna Isaksson and Jonas Wingård (co-worker). Finally I would like

to thank Lovisa Björklund for making this project possible and giving me the

opportunity to realize it at Saab Electronic Defence Systems.

COMPANY UNCLASSIFIED

MASTER THESIS

VI

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

VI

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Abbreviations

HFSS – HIGH FREQUENCY STRUCTURE SIMULATOR AESA – ACTIVE ELECTRONICALLY SCANNED ANTENNA PCB – PRINTED CIRCUIT BOARD VSWR – VOLTAGE STANDING WAVE RATIO TRM – TRANSMIT RECEIVE MODULE

COMPANY UNCLASSIFIED

MASTER THESIS

VII

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

VII

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Contents

1 Introduction .......................................................................................... 1 1.1 Background .............................................................................. 1 1.2 Goal specification ..................................................................... 1

2 Basic Radar Theory ............................................................................. 2

3 Antenna theory ..................................................................................... 4 3.1 Antenna Array .......................................................................... 4 3.2 Microstrip patch element .......................................................... 5 3.3 Aperture coupled patch ............................................................ 7 3.4 Surface-wave coupling ............................................................. 8 3.5 Grating lobes ............................................................................ 9 3.6 Wide angle impedance match .................................................. 9

4 Concept and design ........................................................................... 10 4.1 Overall antenna geometry ...................................................... 10 4.2 Antenna concept .................................................................... 11 4.3 Aperture coupled stacked patch design .................................. 12 4.4 Antenna feed .......................................................................... 15 4.5 Aperture coupled stacked patch final version ......................... 17 4.6 Quarter wave patches ............................................................ 21 4.7 Meander patch ....................................................................... 22

5 Prototype ............................................................................................ 22 5.1 Antenna parts ......................................................................... 22 5.2 Mechanical parts .................................................................... 25

6 Result .................................................................................................. 26 6.1 Simulated Results of the prototype ......................................... 28 6.2 Simulated results of the optimized antenna ............................ 30 6.3 General measurement theory ................................................. 32 6.4 Measured Results .................................................................. 33

7 Conclusion and discussion ............................................................... 40

8 Future Recommendations ................................................................. 40

References ................................................................................................... 41

Appendix ..................................................................................................... 43 A.1 Material ................................................................................. 43 A.2 Connector ............................................................................... 43 A.3 Radar bands ........................................................................... 44

COMPANY UNCLASSIFIED

MASTER THESIS

1

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

1

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

1 Introduction

1.1 Background

This work is done as a master thesis at Saab Electronic Defense Systems in

Gothenburg and the goal is to develop new electronic concepts for Active

Electronically Scanned Antennas (AESA). The work is done together with

Christian Norinder and Fredrik Övgård who are responsible for the mechanical

concept of the antenna. Since the development of electronical and mechanical

solutions of an antenna system such as an AESA are equally important and

highly depend on each other, me, Fredrik and Christian worked closely

toghether in order to optimize with regard to both aspects.

An Active Electronically Scanned Antenna (AESA) consist of a number of

antenna elements aligned in an array. By controlling the phase in each antenna

element it is possible to steer the electromagnetic field that propagates from

the antenna. In other words this could be explained as scanning the beam or

steering the beam [1]. By controlling the amplitude in each element it is

possible to shape the beam, supress sidelobes, supress jamming signals etc.

The ability to control the phase and the amplitude is made possible by having

a transmit/receive-module (T/R-module) behind every element of the array.

Since each element is controlled by a T/R-module, the system will have a

graceful degradation, i.e. if one T/R-module would stop functioning the

system would not shut down.

Important electrical performance parameters for an AESA are bandwith, scan

angle, standing wave ratio (SWR), antenna gain, polarization, etc. Important

mechanical properties are heat generation (cooling), stiffness, weight,

accessibility to the T/R-modules and thickness.

When AESA antennas first were introduced to the market it was an expensive

technology and only considered as a solution when there was a big financial

support and no other solutions were good enough, e.g. fighter air-plane radars.

During the 1990’s the technology had matured to the extent that AESAs were

competitive to projects with limited budgets [2]. This has resulted in great

improvement of the performance of these systems due to the AESA’s many

advantages.

1.2 Goal specification

The goal of this project was to develop concepts for a planar, low-weight, low

profile, S-band, active electronically scanned antenna. Much freedom was

given to the designer, however properties that were required was specified at

COMPANY UNCLASSIFIED

MASTER THESIS

2

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

2

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

the beginning of the project as well as some goals. The specified goals and

properties of the antenna can be seen in Table 1.1 and the properties and their

consequence are explained below. There are many different types of antenna elements that can be used in an

AESA but for this project only planar elements were considered. Advantages

with planar elements are that they have lower profile compared to other

elements such as noches and this is an advantage especially when there is a

demand for high structural integration. One type of planar elements are

microstrip patch elements which will be brought up and explained in this

report. The ambition in this project was to develop an AESA antenna

operating in the S-band (see Appendix A3 for definition) capable of scan

angles greater than 45 degrees in every direction and maximum antenna

element thickness of 3cm. It was also desirable to develop mechanical

solutions that can simplify the service procedure of the T/R-modules, to

develop an antenna with low profile and at the same time limit the total weight

of the antennasystem to around 500 kg, see Table 1.1.

Table 1.1: The requirements for the project.

2 Basic Radar Theory

Radar uses electromagnetic radiation in order to detect and locate reflecting

objects [1]. The technique is basically to send a signal and if the signal returns,

the comparing of the echo signal with the original signal can give the location,

speed, and size of the object. The maximum range of the radar can be

determined by the radar range Equation (2.1)

ANTENNA ELEMENT

(ELECTRICAL)

ANTENNA SYSTEM

(MECHANICAL)

OTHER

<3 cm thick ~500 kg Design that allows for an easy way to switch T/R-modules

>45 degrees scan angle

~2x2 meter2 Scalable

0.5 GHz bandwidth in S-band with active reflection < −10dB

Planar Cost-effective

COMPANY UNCLASSIFIED

MASTER THESIS

3

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

3

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

22

2

222

44

,1

wff

t

r

R

De

P

P. (2.1)

Where Pr is the received power of the antenna, Pt is the transmitted power

from the antenna, σ is radar cross section, eff is the efficiency of the antenna, Г

is the reflection coefficient, D(θ,ϕ) is the directivity of the antenna, λ is the

wavelength, R is the distance between the antenna and the target, ρw is the

polarisation unit vector of the scattered wave and ρ is the polarization of the

antenna.

An AESA steers the antenna beam electronically which means that it can

direct its beam much faster than the conventional mechanically steered

antenna. An AESA consists of different subsystems in which each subsystem

contributes to the performance of the antenna. The subsystems in an AESA are

radiating elements (antenna elements), T/R modules, exciter, distribution

network and receiver, see Figure 2.1. The properties of each subsystem and the

interface between the subsystems are important and affect the overall antenna

performance.

The distribution network in an AESA is a multilayer PCB which task is to

distribute the signals to the right locations. The T/R-modules transmits and

receives the signals and are directly connected to the antenna elements. Since

the received signals are weak when they return to the antenna it is important

that the T/R-modules are located very close to the antennas in order to

minimize losses.

In a conventional radar (without taking into account improvements which can

be made with signal-processing) the resolution is determined by the

beamwidth of the antenna [1]. When there is a need to track fast moving

objects, such as missiles or airplanes, the resolution of a conventional radar is

not good enough. In order to improve the resolution a sum and a difference

channel can be used to perform a mono pulse measurement.

COMPANY UNCLASSIFIED

MASTER THESIS

4

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

4

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 2.1: A simple illustration of the subsystem of a radar.

3 Antenna theory

3.1 Antenna Array

The radiation characteristics of an array are determined by different factors. To

make the theory easier, an ideal case is assumed where every element in the

array have the same radiation characteristics.

The radiation of the array can then be controlled by a number of design

parameters: the geometrical configuration of the overall array, the relative

displacement between the elements, the excitation amplitude and phase of the

different elements and the relative pattern of the individual elements [3]. The

ability to control these parameters independently will yield good control of the

radiation pattern of the antenna. The total field for an array is given by

AFEFEtotal . (3.1)

Where EF is the element factor which is the radiation characteristic for an

individual element and AF is the array factor which depends on the relative

distance between the elements, the excitation phase and the excitation

amplitude. For a rectangular array with the elements spaced a distance dx in

the x-direction and spaced a distance dy in the y-direction (see Figure 3.1 for

geometry) the array factor is given by

COMPANY UNCLASSIFIED

MASTER THESIS

5

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

5

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

)))cos(sin()(1(

1 1

)))cos(sin()(1(

11yyxx

kdnjN

n

M

m

kdmj

mn eeIIAF

. (3.2)

Where βx and βy are the progressive phase shift between elements in the x-

direction and the y-direction, Im1 is the excitation coefficient in the x-direction

and I1n is the excitation coefficient in the y-direction.

Figure 3.1: Geometry of a planar array configuration with the elements

positioned in a rectangular lattice. Adapted from Balanis, 2005 [3].

3.2 Microstrip patch element

Microstrip patch elements have advantages such as low profile, low cost, easy

manufacturing, and low weight, see Balanis, 2005 [3] for details. However,

there are disadvantages such as a narrow bandwidth. The most simple

configuration of a microstrip patch antenna consist of a thin metallic strip

placed on top of a dielectric layer placed above a ground plane (thin metallic

layer), see Figure 3.2.

COMPANY UNCLASSIFIED

MASTER THESIS

6

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

6

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 3.2: The basic configuration of a microstrip patch with a microstrip

feeding arrangement. After Balanis, 2005 [3].

The microstrip patch in Figure 3.2 has a bandwidth of around 1-3% which is

quite narrow. There are some ways to enhance the bandwidth at the expense of

a more complicated structure and it is feasible to obtain a bandwidth of about

90% when scanning the antenna at broadside [4]. A stacked patch has higher

bandwidth and consists of two or more radiating patch elements, the original

patch and the parasitic stacked patch. The stacked patch is placed on top of a

new dielectric layer above the original patch. This will enhance the bandwidth

to about 14% because a new resonance frequency is introduced. By using an

electromagnetic simulation program, for example ansoft HFSS, it is possible

to optimise the dimension of the patch and the stacked patch and in this way

achieve a greater bandwidth.

There are some guidelines when designing a microstrip element and the

procedure according to the transmission line model is explained below [3].

First determine the shape of the microstrip patch such as rectangular or

circular etc. The rectangular shape is the most widely used geometry and

depending on the shape of the patch, the design procedure varies.

Here a rectangular patch is assumed and the first step of the design is to

specify the desired frequency (f), the height (h) of the substrate and the

dielectric constant of the substrate (εr). The choice of εr and h is important for

the performance of the antenna patch. εr normally lies in the interval 2.2<

εr<12 and h normally lies in the interval 0.003λ0< h<0.05λ0 where λ0 is the

wavelength of the electromagnetic wave propagating from the patch at its

resonance frequency f.

As a rule of thumb the initial value for the width of the patch that normally

leads to efficient radiating characteristics can be calculated from

COMPANY UNCLASSIFIED

MASTER THESIS

7

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

7

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

21

0

1

2

2

rrf

CW

. (3.3)

Because of the finite dimension of the patch, the electromagnetic fields along

the edges undergo fringing which basically means that the antenna looks

longer from an electromagnetic point of view. This affects the resonance

frequency of the patch. The extent of the fringing depends on the ratio W/h

together with the dielectric constant of the substrate εr, where W is the width of

the patch and h is the height of the substrate.

Since W/h is large for microstrip patches, the fringing depends mainly of the

dielectric constant εr. When W/h>1 the effective electric constant is

2

1

, 1212

)1(

2

)1(

W

hrreffr

. (3.4)

When the effective dielectric constant is known it is possible to calculate the

effective length of the patch according to

8.0)258.0

264.03.0

412.0

,

,

h

W

h

W

h

L

effr

effr

(3.5)

LLLeff 2. (3.6)

It should be noted that the transmission line model is not very accurate and by

calculating the dimension of the patch according to this model, the resonance

frequency will probably deviate from the desired one. This model is therefore

best used in order to calculate initial values which are later optimised in an

electromagnetic simulation program.

3.3 Aperture coupled patch

Another way to enhance the bandwidth is to use a more complicated feeding

structure, for example, aperture coupling or proximity coupling. The aperture

coupled feeding structure illustrated in Figure 3.3 consists of five layers.

COMPANY UNCLASSIFIED

MASTER THESIS

8

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

8

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

The 1st layer is a ground plane, the 2

nd layer is a dielectric, the 3

rd layer is

prepreg dielectric (thin dielectric that is used to bond the 2nd

and 4th

layers

together), the 4th

layer is another dielectric and the 5th

layer is another ground

plane. The 2nd

layer has a microstrip line on top of it which is used as a

feeding point for the structure.

The 5th layer is a ground plane with a slot which is excited by the microstrip

line in the 2nd

layer. This feeding structure could then be used to feed a patch

which would be placed on top of a third dielectric layer placed above the

ground plane with the slot. This configuration introduces a quite complex

feeding structure but the gain will be a bandwidth of around 14% for a single

patch

Figure 3.3: Aperture coupled configuration.

To further enhance the bandwidth it is possible to use an aperture coupled

stacked patch configuration. By using this configuration it is possible to obtain

a bandwidth of around 90%. The common denominator, between all

bandwidth-enhancement techniques is a more complex, less compact structure.

3.4 Surface-wave coupling

A problem with patch antennas is that they excite surface-waves, which are

guided by the substrate and the ground plane. In array applications, the

surface-wave coupling between antenna elements could severely degrade the

performance of the antenna. According to Nikolic, 2005 [5], this coupling

becomes important when the normalized electrical thickness h/λ0 of the

substrate has a value that fulfill the relation

COMPANY UNCLASSIFIED

MASTER THESIS

9

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

9

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

r

h

2

3.0

0

. (3.7)

When Equation.(3.7) is satisfied it is important to suppress these surface-

waves in order to improve the performance of the antenna. This can be done

by enclosing each antenna in a cavity which in the simplest way is done by

surrounding each antenna with metalized via-holes that are in contact with a

ground plane.

3.5 Grating lobes

A grating lobe is defined as a maxima other than the principal maxima of

radiation that occurs when the spacing between elements are large enough

(larger than λ/2) to permit in-phase addition of radiated fields in more than one

direction [3]. Assume a one dimensional array with N isotropic radiating

elements, uniform excitation and a spacing of distance dy (see Figure 3.1). The

the criterion for no grating lobes is then given by

)sin(1

1

0

yd. (3.8)

Where θ0 is the scan angle and λ is the wavelength of the highest frequency of

the operating band.

3.6 Wide angle impedance match

When scanning an array in different directions the reflection coefficient

changes.

This phenomenon results in degradation of the performance of the antenna

array. One approach to solve this problem is to use a Wide Angle Impedance

Match (WAIM) layer spaced in front of the array [6]. A WAIM layer consist

of one or several dielectric layers that match the reflection coefficient to wider

scan angles which improves the scanning capabilities of the antenna. A WAIM

layer could be the radome of the antenna.

COMPANY UNCLASSIFIED

MASTER THESIS

10

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

10

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

4 Concept and design

4.1 Overall antenna geometry

When designing an AESA there are basically two different architectures that

can be chosen, the tile-architecture or the brick-architecture. The different

architectures describe the orientation of the T/R-modules relative the antenna

elements. When using the tile-architecture, the T/R-modules are parallel to the

antenna elements and when using the brick-architecture the T/R-modules are

positioned perpendicular to the antenna elements. In this project several

concepts involving both brick and tile architectures have been considered but

the concept that was most promising uses tile-architecture

The most promising tile-concept has T/R-modules connected to the antenna

elements through double-sided T/R-modules (see Figure 4.1) which makes this

concept very thin and the main reason why this concept was chosen.

Figure 4.1: Illustration of how the T/R-modules would be connected to the

distribution network when normal SMP-connectors are used.

Normally a radar-system is designed so that behind the antenna elements there

are T/R-modules and behind the T/R-modules there is a distribution network.

This design makes it difficult to reach the T/R-modules in order to perform

maintenance work. Therefore, the decision was made to place the distribution

network in front of the T/R-modules which makes the service procedure of the

T/R-modules easier. It also makes is possible to combine the antenna elements

and the distribution network into one solid piece which will contribute to the

stability of the antenna and simplify the manufacture. Another advantage is

that the contact connecting the T/R-modules with the antenna elements could

be removed (see Section 4.4).

Antenna element

Distribution network

SMP connector cccocontact

TRM

COMPANY UNCLASSIFIED

MASTER THESIS

11

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

11

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

4.2 Antenna concept

At the beginning of the project, literature was studied in order to investigate

what kind of antenna elements that would be suitable for this project. After

carefully considering the three most interesting elements, the aperture coupled

stacked patch was chosen to be the element on which simulations was to be

performed.

Important design issues were the array lattice geometry and the inter element

spacing. The choice of the inter element distance depends on the highest

operating frequency but should also be chosen so that there are no grating

lobes, see Equation.(3.8). After some research and discussions with the project

members the decision was made to use a triangular lattice, see Figure 4.2. A

triangular lattice was chosen because it minimizes the amount of T/R-modules

in the antenna array [1].

This means that less T/R-modules are required for an analogous performance

and therefore a more cost-effective solution is obtained. The downside of

choosing a triangular lattice is a more complicated geometry. In this project,

the inter-element spacing was chosen to be around half of the wavelength λ

corresponding to the highest frequency in the operating band.

Figure 4.2: Illustration of the geometry of the triangular lattice used in this

project. From Skolnik, 1990 [7].

The three antenna elements chosen after the literature study were an aperture

coupled stacked patch, a quarter-wave patch and a meander patch element.

COMPANY UNCLASSIFIED

MASTER THESIS

12

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

12

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

A quarter-wave patch is smaller than a λ/2 patch. Smaller elements means that

the mutual coupling between the elements could be reduced which enables a

wider scan angle capability in one of the planes. Another good property is the

wide beamwidth. The reason not to choose this element was that because of

the connection of the element to the ground plane there will be an anti-

symmetrical current distribution which will contribute to higher cross-

polarization of the field. For some applications it may be desirable to have

very low cross-polarization. Another reason not to choose the quarter-wave

patch was that there has been few published report on this element in array

applications.

The meander element was interesting mainly because of a published report

from a group in India that illustrated properties necessary in this project, i.e. S-

band, wide scan angle up to 60 degrees and low profile [9]. After careful

consideration, the decision was made to leave this element due to doubts

concerning the feasibility of obtaining these properties with the given element.

The aperture coupled stacked patch was developed by FOI [8] and good result

had been obtained, both in simulations and in practice. Another group from

Italy [4] had also obtained good result from simulation with a similar element.

These two observations were the major reasons of choosing this type of

element.

4.3 Aperture coupled stacked patch design

The aperture coupled stacked patch was the chosen element after the literature

study and the design of the antenna element has been carried out in the

commercial software Ansoft HFSS v11.2. The element has been simulated

with periodic boundary conditions (infinite array) and has been optimised with

a non linear programming method. The design procedure for this element is

explained below.

The first step in the design procedure for this antenna element was to begin

with an element that already was designed before that had properties that were

required for this project. In this case the antenna that FOI had developed [8]

was used as a starting point when recreating and simulating the model in

HFSS, see Figure 4.3 and Figure 4.4. This element has been designed for both

vertical and horizontal polarization but in this project only one polarization has

been used.

COMPANY UNCLASSIFIED

MASTER THESIS

13

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

13

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 4.3: Original antenna element that was used as starting point in the

design [8]. The black bolded lines represents layers of copper (patch and

ground plane), the red bolded lines represents microstrip lines (fork).

Figure 4.4: Illustration of the feeding arrangement from the element which

originates from [8].The structure is constructed to radiate two polarizations,

vertical and horizontal. It consists of two perpendicular microstrip-forks and

two perpendicular H-slots.

Rogers 4350 (r = 3.48)

Rogers 4403 (r = 3.17)

Rogers 4450B (r = 3.58)

Rogers RT/duroid (r = 2.2)

Rohacell HF 71 (r = 1.09)

0.76

0.25

1.14

1.2

0.51

[mm]

COMPANY UNCLASSIFIED

MASTER THESIS

14

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

14

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

The element was first recreated for the frequencies that the element originally

had been designed for (X-band and Ku-band). The second step was to rescale

the element to work in the S-band and this was done by multiplying all the

dimensions of the element with a scaling factor Sf which was calculated with

Equation.(4.1)

)_(

)_(

elementdesiredf

elementoriginalfS f . (4.1)

Where f(original_element) is the highest frequency of the operating band for

the original antenna element and f(desired_element) is the highest frequency

of the operating band for the desired antenna element.

It was found that there was a complex dependence between the feeding

arrangement and the lower patch. This means that the element behaved

differently after the scaling-adjustment of the patch dimensions and

optimization of the element was required in order to make it function in a

similar way as before. The element was then placed into a triangular lattice.

This was followed by optimizing the different dimensions of the element: the

dimension of the feeding fork, the thickness of the dielectric layers, the

placement of the via-holes, the dimension of the H-slot and the dimensions of

the patches (see Figure 4.9 and Figure 4.10 for illustration of the element).

A parameter that greatly influences the performance of the element is the

width of the two parallel striplines, which build up the fork. This parameter

influences the impedance of the fork and since it is directly connected to the

feeding structure it is important that they are matched, i.e. they have the same

impedance. Another example are the heights of the first two dielectric layers,

which build up the feeding structure (see Figure 3.3). This influence can be

explained by the importance of the positioning of the fork relative to the

ground plane with the H-slot and the patches, this is important for the coupling

of the different parts of the element. Other important parameters are the

dimensions of the lower and upper patches and their positioning relative one

another. It was important that these parameters were optimized since these

dimensions greatly would influence the performance of the antenna. The next

step in the design was to take the mechanical aspects under more careful

consideration since this project has intended to produce a low-weight solution.

To reduce the weight of the antenna element, the thickness of the dielectric

layers were reduced and replaced by a low-weight distance material called

Rohacell, which from an electromagnetic point of view behaves as air. Since

Rohacell is electrically shorter than the dielectric material it replaced, the new

Rohacell layers had to be thicker.

COMPANY UNCLASSIFIED

MASTER THESIS

15

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

15

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

The feeding arrangement had to be re-optimized with the rohacell layer

because it turned out that there was a dependence of the positioning of the

feeding arrangement as well. After the procedure of reducing the weight of the

element it was time to replace some of the dielectric layers that was used in the

element.

RT/duroid 5880 which was used initially is a Teflon based material and it is

difficult to attach it to other materials with glue. This means that if this

material would have been used the antenna would have been difficult to

assemble. The materials Rogers 4350B and FR-4 were chosen instead because

they function well in the operating frequency range used in this project, they

are easy to assemble and they are used widely in industry which makes it fast

and easy to order and receive the materials. The next step was to introduce a

more practical arrangement to feed the microstrip fork. Until this point, the

feed had been a coaxial probe which is impractical to manufacture.

4.4 Antenna feed

The antenna feed consist of a metalized via hole, called a signal-via, which

connect the microstrip fork with a SMP connector. The signal-via goes

through the Rogers 4350B layers to a etched pattern at the lower ground plane,

see Figure 4.5. This pattern is connected to the SMP-connector which enables

the signal to go from the SMP-conncector to the microstrip fork.

Figure 4.5: The figure shows the etched pattern in the ground plane which is

used in the prototype (the vertical lines doesn’t represent an etched pattern

and should be interpreted as part of the ground plane. The signal-via is

indicated by the grey dot. The distance between the pad and the ground plane

is 0.250 mm in the prototype but has been adjusted to around 0.110 mm for the

optimized element.

In order to prevent parallel plate modes from propagating it was necessary to

enclose each antenna element in a cavity. This was done by surrounding each

antenna element with metallised via-holes which connect the lower ground

plane and the ground plane with the H-slot. In the simulations, the vias that

build up the cavity were simulated as perfect conducting sheets in order to

reduce the complexity of the system.

COMPANY UNCLASSIFIED

MASTER THESIS

16

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

16

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

The connection transition used in the prototype is different from the one that

would be used when designing the whole antenna system, i.e. with distribution

network and TR-modules. The distribution network and the antenna elements

will be made as one solid piece which will contribute to the stiffness of the

antenna and make the manufacture simpler. A stiffer antenna will need less

supporting materials and the antenna will therefore be lighter.

The SMP-connectors, see Figure 4.1, will be replaced with another kind of

RF-connector, see Figure 4.6, which will reduce the number of RF-connectors

used in the system. In the prototype, a SMP-connector is used to feed the

antenna element through a signal-via which is connected to the microstrip

fork. When the distribution network is added the idea is that the signal-via will

go all the way from the upper Rogers4350B layer (the dielectric layer right

underneath the ground plane with the H-slot) down to the other side of the

distribution network. The signal-via is then connected to a RF-connector

which is mounted on the distribution network and finally the RF-connector is

connected to a T/R-module.

The RF-connector is a kind of computer connector (see Figure 4.6) which is

able to process both power and several RF-signals in one unit which means

that instead of using several SMP-connectors and a power supplier it would

only be necessary to use one computer connector. By using the computer

connector the complexity of the system could be reduced and a more cost-

effective solution would be provided. The explanation for this is that 4 SMP-

connectors costs much more than 1 computer contact. The computer contacts

also serve the purpose of holding the T/R-modules which means that no

additional structure is needed for this.

When designing this system it will be necessary to widen the signal-via which

goes through the antenna and the distribution network. This is necessary in

order to guaranty a fully metalized via-hole because its diameter d has to fulfil

the relation

hd 7 . (4.2)

Where h is the height of the signal-via and d is the diameter.

COMPANY UNCLASSIFIED

MASTER THESIS

17

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

17

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 4.6: Illustration of the computer-contact which is used instead of the 4

SMP-connectors in Figure 4.1.

4.5 Aperture coupled stacked patch final version

The final version of the aperture coupled stacked patch consists of several

layers as shown in Figure 4.10 where the first layer is a Rogers 4350B

dielectric layer placed above a ground plane with a microstrip fork etched on

top of it, (see Figure 4.7 for optimized dimensions of the fork).

The next layer is another Rogers 4350B layer which has a ground plane with

an H-slot on top of it, see Figure 4.8 for optimized dimensions of the H-slot.

From the ground plane with the H-slot to the other ground plane, near the

edges there are metallised via holes that connect the two ground planes to each

other. In this way the lower structure (red in Figure 4.9) becomes a cavity that

isolates the individual elements from unwanted radiation from neighbouring

elements. This cavity also prevents that unwanted parallel modes will occur.

The next layer is a layer of rohacell which is followed by a Rogers 4350B

dielectric layer with a microstrip patch on top of it. The structure then

continues with a layer of rohacell and above the rohacell there is a layer of FR-

4 with a stacked patch at its bottom side, see Figure 4.9 and Figure 4.10 for

geometry.

In addition of holding the stacked patch, the FR-4 could work as a radome, i.e.

a protecting layer against weather conditions. However in most cases it will be

necessary to place a conventional radome on top of the element because the

antenna will not be stiff enough in order to allow for building the complete

2×2 meter2 system. A conventional radome means that there is a quarter

wavelength of rohacell with a protective layer on top of it such as FR-4.

COMPANY UNCLASSIFIED

MASTER THESIS

18

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

18

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

The quarter-wavelength of the distance-material is required so that the

radiation not will be exposed of humidity and other weather related conditions

because it could affect the radiation characteristics of the antenna. The radome

for this antenna will apart from making the antenna more solid and protecting

it from weather conditions, also serve as a WAIM-layer, see Section 3.6. This

means that the radome will help the antenna to be matched for high scan

angles and boost its performance. Note that the dielectric constant of the

rohacell in the radome has another value than the other rohacell, see Figure

4.10. The ultimate 2 mm layer of FR-4 can with advantages be switched to

another material called cyanate ester which has both better mechanical and

electrical properties than FR-4.

Figure 4.7: The optimised dimensions of the microstrip fork. Both the red lines

and the parts which are enclosed by the red lines build up the microstrip fork.

14mm

1.46 mm

mm

1.66mm

2.09mm

COMPANY UNCLASSIFIED

MASTER THESIS

19

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

19

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 4.8: The optimized dimensions for the H-slot. Both the red lines and the

parts that are enclosed by the red lines are part of the slot.

Figure 4.9: A transparent view of the aperture coupled stacked patch

configuration.

16.054mm

2.45 mm

21.25mm

COMPANY UNCLASSIFIED

MASTER THESIS

20

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

20

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 4.10: Illustration of the layers of the Aperture coupled stacked patch

configuration and the distribution network (light-green bottom plate).

Apparaturkopplad

stackad patch

Thickness (without

distribution network and

radome) =17.589 mm

Ground-plane of copper

(black)

Thickness=0,052 mm

Rogers 4350B: (red)

Thickness=2,388 mm

Rogers4450B: (green)

Thickness=0,102 mm

Rogers 4350B: (red)

Thickness=0.946 mm

Ground-plane of copper

(black)

Thickness=0,035 mm

Rohacell: ( εr=1.09,

white)

Thickness=4,7 mm

Patch of copper

Thickness=0.017 mm

Rogers4350B: (red)

Thickness=0,762 mm

Rohacell: ( εr=1.09,

white)

Thickness=8,17 mm

FR-4: (purple)

Thickness=0,4 mm

Patch of copper

Thickness=0.017 mm

Distribution-network

12 lager Rogers 4350B

Thickness=3mm, (light-

green)

Radome:

FR-4(or cyanate ester):

Thickness= 2mm.

Radome:

FR-4: (purple)

(or cyanate ester)

Thickness= 2mm

Rohacell (εr=1.5, white):

Thickness =20 mm

COMPANY UNCLASSIFIED

MASTER THESIS

21

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

21

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

4.6 Quarter wave patches

A quarter-wave patch, also called a planar inverted-F antenna (PIFA-antenna)

is illustrated in Figure 4.11. The quarter-wave patch is put together in the same

way as a regular patch with the difference that a shortening pin is used to

terminate the patch to the ground plane at a point where the electrical field of

the resonant mode is zero [10]. By shortening the patch it is possible to reduce

the length of the patch to a quarter-wavelength. Holub and Milan, 2008 [11]

has shows that with menaderly folded shorted-patches it is possible to reduce

the length of the patch with up to λ/16. However, these configurations are too

complex and not practical for array applications because these elements have a

narrower bandwidth and the degree of freedom when designing these elements

are reduced. Conclusively, it would not be possible, for example, to put

together an aperture coupled stacked λ/16 patch. It should be possible to put

together an aperture coupled stacked quarter wave patch without complicating

the element too much and this could be done by shortening the patch with a

metalized via that connect the ground-plane with the H-slot to the patch. This

configuration is more complicated than the regular configuration which has

been investigated during this project and one interesting thing to investigate is

how much the metalized via would change, if at all, the performance of the

antenna. Another downside of using a quarter-wave patch is that the material

between the ground-plane and the patch has to be a dielectric material

compatible to PCB-technology.

This means that it is not possible to use the low-weight distance material

rohacell which has been used in this project. This will increase the weight of

the antenna and if this parameter of the antenna needs to be minimized this is

probably not a good solution. Another good property which has been

published by Chair el al, 1999 [12] was big bandwidth improvement

compared to the half-wave patch and another bad property was the high cross-

polarisation of the field, especially in the H-plane [12].

Figure 4.11: A simple quarter-wave patch configuration. From Waterhouse,

1995 [10].

COMPANY UNCLASSIFIED

MASTER THESIS

22

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

22

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

4.7 Meander patch

As mentioned earlier, a meander-patch was considered in the literature-study,

see Figure 4.12. The specific element considered by Beenamole et al., 2007

[9] doesn’t have the qualities required for this project but the possibility to use

this element in a more complicated configuration with broader bandwidth

could be very interesting. An example of a configuration which would be

suitable is the aperture coupled stacked meander patch configuration which

there haven’t, to the author’s knowledge, been any published reports of. The

aperture coupled stacked meander-patch is like the regular aperture coupled

stacked patch configuration with the difference that the lower or upper patch is

switched to a meander-patch instead of the regular patch. However, there is a

problem with the dimensions of the meander-patch considered by Beenamole

et al., 2007 [9] because it is too large to fit in the available space in the

antenna geometry.

Figure 4.12: Dimension and geometry of the meander-patch considered in the

literature-study From Beenamole et al., 2007 [9] .

5 Prototype

5.1 Antenna parts

The patch, the stacked patch and the feeding-substrate are all manufactured

with printed circuit board technology (PCB-technology), see Figure 4.10 for

illustration of the different layers of the element. To place an order of the

PCBs, a blueprint of the three boards has been made in the commercial

software Allegro, Figure 5.1 and Figure 5.2 show the blueprint of the PCB

which contain the feeding arrangement of the antenna.

COMPANY UNCLASSIFIED

MASTER THESIS

23

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

23

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

The company Teltex has been selected to manufacture the PCBs. The

materials that have been chosen for this project are Rogers 4350B and FR-4.

They function well in the operating frequency range and they are used widely

in industry which makes it fast and easy to order and receive the material from

Teltex.

The thickness of the material comes with standardised thicknesses which limit

the design freedom of the antenna. One standard thickness of the Rogers

4350B material had been mixed up with another material called Rogers 4003C

when it was delivered to Teltex and in order to speed-up the delivery of the

product it was necessary to switch this specific PCB to the new material. This

switch has caused changes to both the mechanical and electrical properties of

the antenna, however since the material has similar properties as the original

Rogers 4350B material, the changes are small enough to be acceptable. When

the PCBs were obtained from Teltex, the SMP-connectors were surface-

mounted on the feeding-substrate in the production-facility at Saab Electronic

Defense Systems. Some problems were encountered here due to the large

dimension of the PCB and due to the fact that the PCB had an error in its

design but these problems were solved.

The rohacell-sheets that were used in this project are called HF71 and the

company Hagema was selected to slice the rohacell into pieces according to

Figure 4.10. Hagema was also chosen to manufacture the aluminium sheets

which support the antenna structure, see Section 5.2. When the RF-connectors

had been mounted it was time for the rohacell, the mechanics and the PCBs to

be attached together with very strong glue at the workshop of Saab Electronic

Defense Systems. In order to glue all pieces together in an accurate way, two

reference-holes have been made at the edges of every piece of the antenna, see

Figure 5.2. By placing a pin in each hole it is possible to glue the pieces of the

antenna in a precise way.

COMPANY UNCLASSIFIED

MASTER THESIS

24

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

24

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 5.1: The PCB containing the pattern of the fork and via-holes (green).

The two boards in Figure 5.1 and Figure 5.2 were from the beginning two

separate circuit-boards but in a later stage they have been bonded together

with a prepreg material called Rogers 4450B that has similar properties as the

two boards. This will create a transition region in the material which is

anisotropic with varying thickness and dielectric constant. Since this antenna

is constructed for the S-band, the wavelength should be long enough so that

these irregularities will not have a major impact of the performance of the

antenna but nonetheless it will have a measurable effect. Another comment

regarding the antenna element in the middle of the first row and the antenna

element in the middle of the 10th

row is that these elements could be

functioning differently in comparison to the other elements. The reason for

this is that when the PCBs were manufactured, the machine required that there

were two holes in the PCBs and since the size of the antenna array was close

to the actual panel-size available, the drilled holes will be very close to these

two antenna elements and they might be affected by it.

COMPANY UNCLASSIFIED

MASTER THESIS

25

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

25

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 5.2: The board containing the pattern of the upper ground plane with

H-slots.

5.2 Mechanical parts

Behind the antenna elements there is a 2 mm thick aluminium-sheet in order to

make the prototype more solid. The aluminium sheet was attached to the

antenna elements with glue. Attached at the corners of the sheet there are

supporting structures (see Figure 5.3) which are compatible with the interface

at Saabs measurement room A15 but they also provide the possibility to attach

the antenna to a table for demonstration purposes or for other measurement

purposes. In addition to these there are some “dummy” T/R-modules mounted

on the antenna, see Figure 5.3, which serve the purpose of demonstrating the

manner in which the real T/R modules would be attached to the antenna.

COMPANY UNCLASSIFIED

MASTER THESIS

26

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

26

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 5.3: Illustration of the fully assembled prototype as seen from the

back/rear

6 Result

The goals of the project were to design a low-weight, thin, S-band antenna

with 0.5 GHz bandwidth with scan angle capabilities of at least 45 degrees at

every plane with less than −10dB reflections see Table 1.1. The actual result of

the project can be seen in Table 6.1.

COMPANY UNCLASSIFIED

MASTER THESIS

27

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

27

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Table 6.1: The table illustrates the result of the project.

Thickness of antenna element

Bandwidth (S11=−10dB) when scanning up to 40 degrees

Weight

Antenna Properties

1.76 cm 0.5 GHz 317 kg

By comparing Table 6.1 with Table 1.1, the conclusion that the goal of less

than 3 cm thick antenna element has been fulfilled with good marginal which

also is the case of the total weight of the antenna. The simulated results of scan

angle capabilities of 45 degrees at every plane has not been reached for the

prototype; however they have been fulfilled with some adjustments of the

element, as is shown in Section 8. For the prototype the antenna is only

capable of scan angles up to 40 degrees in the H-plane and more than 45

degrees in the E-plane. This result could have been better but since this project

was carried out as a master thesis, there wasn’t enough time to finish the

optimisation of the antenna element in time before the deadline for prototype

manufacturing had been reached. In Table 6.2 the calculations for the weight

of the total system is presented.

Table 6.2: The table shows the estimated masses for different parts of the

antenna.

Mass [kg]

Calculated values

Contacts 2.4

Antenna layer structure 112

Layer structure support frame 6.6

TRM:s 39

Estimated values

TRM covers 2

Cooling structure 10

Exciter & Receivers 70

Cabling 20

Fans 15

Power distribution box 5

Heat exchanger 35

Total mass 317

Required max mass 500

Allowed maximum mass for remaining parts 183

COMPANY UNCLASSIFIED

MASTER THESIS

28

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

28

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

6.1 Simulated Results of the prototype

Figure 6.1: Active reflection coefficient (S11) for different scan angles for H-

plane.

As illustrated in Figure 6.1, the reflection coefficient S11 for the E-plane in the

frequency range of interest is below −10dB for scan angles up to 40 degrees

and around −8.5dB when scanning 45 degrees. This result is below the goal of

scanning-capabilities of at least 45 degrees.

COMPANY UNCLASSIFIED

MASTER THESIS

29

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

29

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 6.2: Active reflection coefficient (S11) for different scan angles for D-

plane (diagonal plane).

The reason to show the diagonal-plane is that the antenna elements are

positioned in a triangular lattice and sometimes when this is the case,

performance is degraded in this plane. This is not the result in this case as

illustrated by Figure 6.2. As illustrated in Figure 6.2, the reflection coefficient

S11 for the D-plane is below −10dB in the frequency range of interest when

scanning the array 45 degrees and below −8dB when scanning 60 degrees.

COMPANY UNCLASSIFIED

MASTER THESIS

30

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

30

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 6.3: Active reflection coefficient (S11) for different scan angles for E-

plane.

As illustrated in Figure 6.3, the reflection coefficient S11 for the H-plane is

below −10dB in the frequency range of interest when scanning the array 45

degrees and below −8.9dB when scanning 60 degrees.

6.2 Simulated results of the optimized antenna

The simulated results of the optimised antenna have better performance than

the results of the prototype and it is possible to scan the antenna 48 degrees or

more in all the planes.

COMPANY UNCLASSIFIED

MASTER THESIS

31

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

31

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 6.4: Simulated results of the active reflection coefficient for the

optimised antenna in the H-plane shows scan angle capabilities of up to 48

degrees.

Figure 6.5: Simulated results of the active reflection coefficient for the

optimised antenna in the D-plane illustrate scan angle capabilities of more

than 45 degrees.

COMPANY UNCLASSIFIED

MASTER THESIS

32

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

32

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 6.6: Simulated results of the active reflection coefficient for the

optimised antenna in the E-plane illustrate scan angle capabilities of more

than 45 degrees.

6.3 General measurement theory

The driving impedance of an antenna element in an array has two parts, the

self impedance and the mutual impedance (which is caused by other elements

in the array or by interfering obstacles), see [3]. The sum of all contributions

of an individual antenna elements impedance is called the active reflection

coefficient, Γa. To measure Γ

a one must measure the coupling between all the

antenna elements in the array, see [13]. In order to measure the coupling

between 2 elements in an array it is necessary to terminate all the other

elements to 50 ohm and then measure the S-parameters from the two ports of

the network analyser, S11, S12, S21 and S22. To measure the active reflection

coefficient for one element one must measure and sum the coupling between

this element and all other elements of the array. So, for example, to measure Γa

for one antenna element in an array of 100 elements it is necessary to perform

99 measurements.

The results which HFSS illustrates are of the active reflection coefficient.

HFSS uses periodic boundary condition which means that an infinite number

of antenna elements are assumed in the model. So how well the measured

results coincide with the simulated results depends on the accuracy of the

simulated model and on how many elements there are in the array.

COMPANY UNCLASSIFIED

MASTER THESIS

33

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

33

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

The active reflection coefficient is given by

m

n

n nm

m

ma

mV

VS

V

V

,

. (6.1)

Where Vm− is the backward going wave in element m, Vm

+ is the complex

voltage feeding element m and Sm,n is the coupling between element m and n.

6.4 Measured Results

Figure 6.7 shows the coupling between the 45:th element and all the other

elements in the array. It illustrates that the coupling is very symmetrical and

lower than −23dB. The figures 6.11−6.19 show that there is a difference

between the simulated results and the measured results. The explanations for

the differences are mainly due to two effects. First, the simulated results are

based on a on a simplified model which is a little different from reality.

Second, the model assumes an infinite array while the prototype consists of a

finite number of elements.

Figure 6.7: Measured results of the coupling between the 45:th element and

all other elements in the array, the coupling is given in dB.

COMPANY UNCLASSIFIED

MASTER THESIS

34

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

34

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 6.8: The figure shows the reflection of the different scan angles θ in the

H-plane. The figure indicates scan angle capabilities of more than 45 degrees.

Figure 6.9: The figure shows the reflection of the different scan angles θ in the

D-plane. The figure indicates scan angle capabilities of more than 45 degrees.

COMPANY UNCLASSIFIED

MASTER THESIS

35

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

35

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 6.10: The figure shows the reflection of the different scan angles θ in

the E-plane. The figure indicates scan angle capabilities of more than 45

degrees.

Figure 6.11: Comparison of the simulated and measured results for the

prototype.

COMPANY UNCLASSIFIED

MASTER THESIS

36

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

36

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 6.12: Comparison of the simulated and measured results for the

prototype.

Figure 6.13: Comparison of the simulated and measured results for the

prototype.

COMPANY UNCLASSIFIED

MASTER THESIS

37

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

37

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 6.14: Comparison of the simulated and measured results for the

prototype.

Figure 6.15: Comparison of the simulated and measured results for the

prototype.

COMPANY UNCLASSIFIED

MASTER THESIS

38

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

38

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 6.16: Comparison of the simulated and measured results for the

prototype.

Figure 6.17: Comparison of the simulated and measured results for the

prototype.

COMPANY UNCLASSIFIED

MASTER THESIS

39

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

39

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Figure 6.18: Comparison of the simulated and measured results for the

prototype

Figure 6.19: Comparison of the simulated and measured results for the

prototype

COMPANY UNCLASSIFIED

MASTER THESIS

40

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

40

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

7 Conclusion and discussion

A thin, low weight, S-band AESA with high scan angle capabilities has been

designed, optimised, manufactured and later measured and verified. All the

goals, both mechanical and electrical, which was stated at the beginning of the

project has been fulfilled.

In summary the project started with a literature study in order to investigate

what type of antenna elements that would be suitable for this project. Once an

appropriate element was found, the next step was to design and perform

simulations of the antenna. When the simulations were completed, the parts

for the prototype were ordered and the preparation for all the steps in the

constructions of it was made. Once the prototype was completed,

measurements of the active reflection coefficient were performed. The results

of the measurements indicates a scan angle range of around 45 degrees (with

<–10dB active reflection) in the frequency band 3–3.5 GHz. The thickness of

the antenna without taking into account the radome is around 1.76cm and the

total weight for the 2m×2m antenna is estimated to around 320 kg.

The measured results of the active reflection coefficient show the same

behaviour as the simulated results but they do not match exactly, see Figures

6.11-6.19. This is explained by the fact that the simulated results are realised

with periodic boundary conditions, i.e. an infinite array is assumed while the

prototype in which the measured results come from is finite with 10 rows × 10

columns of antenna elements.

8 Future Recommendations

A very simple adjustment can be made in order to improve the performance of

the antenna and that is to adjust the separation between the pad which connect

the SMP-connector to the antenna element and the ground plane, see Figure

4.5. In the prototype this separation is 0.250 mm but that is unnecessary wide

and by adjusting it to slightly above 0.110 mm, which is the case of the

optimised element, the performance of the antenna improves. The performance

also improves when a WAIM-layer is positioned in front of the antenna, see

Section 3.6. The WAIM-layer also functions as a radome, a protective layer

against weather conditions and is necessary in order to improve the stiffness of

the antenna. When these two changes have been made the antenna can be

scanned more than 45 degrees in the H-plane and about 60 degrees in the E-

plane.

COMPANY UNCLASSIFIED

MASTER THESIS

41

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

41

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

To make the simulated results more alike the measured results changes in the

model can be made in order to make the model more alike the prototype. One

change to make is to model the via-holes which enclose the feeding-structure

more accurate. One could also use more points in the simulation and further

increase the resolution.

These changes will make the model more complex and the time to simulate

will take much longer time.

References

[1] Skolnik Merrill L., Introduction to Radar Systems 3rd

edition.

McGraw-Hill Higher Education, 2001.

[2] Parker D, Zimmerman D. C., Phased arrays-part1: theory and

architectures. IEEE Transactions on Microwave Theory and

Techniques. Vol. 50, Issue 3:678–687, 2002.

[3] Balanis C. A., Antenna Theory, 3rd

edition. John Wiley & Sons, 2005.

[4] Tallini D, Galli A, Ciattaglia M, Infante L, De Luca A, Cicolani M., A

new low-profile wide-scan phased array for UWB applications.

Proceedings of Antennas and Propagation 2007. EuCAP 2007.

[5] Nikolic M. M, Djordjevic A. R, Nehorai A., Microstrip Antennas With

Suppressed Radiation in Horizontal Directions and Reduced Coupling.

IEEE Transactions on Antennas and Propagation. Vol. 53, No. 11, pp

3469–3475, November 2005.

[6] Magill E. G, Wheeler H. A., Wide-Angle Impedance Matching of a

Planar Array Antenna by a Dielectric Sheet. IEEE Transactions on

Antennas and propagation Volume 14, Issue 1:49 – 53, Jan. 1966.

[7] Skolnik, Merrill L., Radar Handbook (2nd

Edition). McGraw-Hill,

1990. Online version available at: http://knovel.com.proxy.lib.chalmers.se/web/portal/browse/display?_EXT_KNOVEL_DISPLAY_bookid=701&VerticalID=0. Accessed 2010-02-01.

COMPANY UNCLASSIFIED

MASTER THESIS

42

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

42

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

[8] Huss L-G, Gunnarsson R, Andersson P, Erickson R., A wideband,

wide angle scan, microstrip array antenna element. Proceedings of the

EURAD, 2005.

[9] Beenamole, K. S, Kutiyal, P. N. S, Revankar, U. K, Pandharipande

V.M., Compact planar microstrip antenna element for wide-scan angle

active phased arrays. Proceedings of Antennas and Propagation, 2007.

EuCAP 2007. pp 1-3.

[10] Waterhouse R., Small microstrip patch antenna. Electronics letters.

Vol. 31. No. 8, 1995.

[11] Holub, Alois, Polívka, Milan., A novel microstrip patch antenna

miniaturization technique: A meanderly folded shorted-patch.

Microwave Techniques. Vol. 23-24. pp. 1-4, 2008.

[12] Chair, R., Lee, K. F., Luk. K. M., Bandwidth and cross-polarization

characteristics of quarter-wave shorted patch antennas. Microwave and

optical technology letters. Vol. 22, No. 2, 1999.

[13] Svennson, B., Lanne, M., Verification of an active phased array using

single element measurments. First AMTA Europe Symposium, 2006.

COMPANY UNCLASSIFIED

MASTER THESIS

43

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

43

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

Appendix

A.1 Material

Table A.1: Table shows the properties of some of the different material

which were considered during the project.

Material εr Dissipation loss factor tan(δ)@10GHz

Density [g/cm

3]

Coefficient of thermal expansion(x)

Coefficient of thermal expansion(y)

Coefficient of thermal expansion(z)

FR-4 4.8 1.9

Roger4350B 3.48 0.0037 1.86 14 16 35

Rogers4003C 3.38 0.0027 1.79 11 14 46

Rogers4450B 3.54 0.004 1.86 19 17 50

RT/Duroid 5880

2.2 0.0009 2.2

Rohacell 71 HF

1.09 0.0038 0.075

Copper 1 0 8.94 16.7 16.7

A.2 Connector

The SMP-connector used for the prototype is called rpt368405/3. The regular

footprints for the connector can be used.

COMPANY UNCLASSIFIED

MASTER THESIS

44

Prepared (also subject responsible if other) No.

OEG PUH Mathias Dalevi 83/03631-1/FCK11507 en Approved Checked Date Rev Reference

OEG PUH (LOVISA BJÖRKLUND) WHANISA 2010-05-27 A

44

This

docu

men

t an

d t

he

info

rmat

ion c

onta

ined

her

ein i

s th

e

pro

per

ty o

f S

aab A

B a

nd m

ust

not

be

use

d,

dis

close

d o

r al

tere

d

wit

hout

Saa

b A

B p

rior

wri

tten

conse

nt.

A.3 Radar bands

Table A.3: The definition of the radar-bands according to IEEE definitions.

From Balanis, 2005 [3].