60

Chapter 3

METHODOLOGY AND

EXPERIMENTAL SETUP

3.1 Introduction

In this chapter methodology, experimental setup and equipment

used for the present work is described. The simulation of monopole

antennas is carried out by using Mentor Graphics IE3D simulation

software of version 14.65 in University Science Instrumentation Centre,

Gulbarga University, Gulbarga-585106. This was sponsored by UGC,

New Delhi under Major Research Project. The whole experimental work

of monopole antennas is carried out by using German make Rohde and

Schwarz(R&S) Vector Network Analyzer(VNA) of ZVK model (10 MHz - 40

GHz) in the Microwave Electronics Research Laboratory (MERL),

Department of Post Graduate Studies and Research in Applied

Electronics, Gulbarga University, Gulbarga-585106.

3.2 IE3D software

Electromagnetic (EM) simulation is an advanced technology to

yield high accuracy analysis and design of complicated microwave and

RF printed circuits, antennas, high speed digital circuits, microwave and

millimeter-wave integrated circuits (MMICs) and other electronic

components. IE3D is an integrated full wave EM simulation and

optimization package for the analysis and design of 3-D planar

microwave circuits, MMIC, RFIC, RFID, antennas, digital circuits and

high frequency printed circuits boards (PCB). It is the most versatile, easy

to use, efficient and accurate EM simulation tool.

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3.2.1 Basic theory and implementation

IE3D is a full-wave EM solver. It solves the Maxwell equations,

which governs the macro electromagnetic phenomenon. It solves the

Maxwell‟s equations in an integral form through the use of Green‟s

functions. It can model both the electric current on a metallic structure

and a magnetic current representing the field distribution on a metallic

aperture.

In IE3D, we adopt a triangular and rectangular mixed meshing

scheme and apply the non-uniform basis functions. As a non-uniform

meshing based simulator, it approaches a problem in a better way. A

user draws a circuit as a group of arbitrarily shaped polygons on a layout

editor first. Then, the simulator tries to fit a non-uniform triangular and

rectangular mesh in to the circuit. The non-uniform meshing scheme is

more flexible, efficient and accurate, than the uniform meshing scheme.

It creates significantly fewer cells and unknowns than uniform grid based

meshing.

The exciting thing is that close boundary Green‟s function

formulation and uniform meshing are implemented in to the IE3D. Users

are offered with the maximum flexibility and capability with the uniform

meshing for open boundary, close boundary and periodic boundary

conditions. Periodic boundary condition is used to model large phase

arrays.

3.2.2 IE3D Application programs

The IE3D package consists of the seven major application

programs.

MGRID : It is the major layout editor for conditions of a structure. It

allows a user to create and edit a structure as polygons and vertices.

IE3DLIBRARY: The object oriented schematic layout editor for

parameterized modeling and editing.

AGIF : The advanced automatic geometry modeling tool to create fill 3D

IE3D models directly from GDSII files.

62

IE3DOS: It is the EM simulator or simulation engine for numerical

analysis. It is a DOS-style command line application.

IE3D: The IE3D dialog displaying the progress of an IE3D simulation or

optimization.

PATTERNVIEW: Post processor for radiation pattern visualization and

post processing.

ADIX: It is the optional ACIS/DXF? GDSII/GERBER format converter.

To perform an EM simulation, user has to start from the layout editor

MGRID. On MGRID, a circuit has to be drawn as a group of polygons.

After the construction of circuit, the simulator engine IE3D can be

invoked. The simulation result is saved into a file compatible with the

Agilent/Eesof Touchstone format.

The saved file can be imported into other popular commercial

nodal network or circuit simulators such as the ADS from Agilent/Eesof

or Microwave office from Applied Wave Research. The simulation result

can also be displayed and processed by schematic editor MOUDA. One of

the major disadvantages is that the field and current distributions from a

simulated structure are accessible to users which are valuable to circuit

and antenna designers.

The IE3D package consists of the seven major application

programs:

MGRID: It is the major layout editor for construction of a structure. It

allows a user to create and edit a structure as polygons and vertices. It

has full control over the detail shapes and locations of geometry. Starting

from V14, MGRID is renamed as IE3D EM Design System. It has

integrated layout editing, s-parameters visualization and post processing,

current distribution visualization, near-field and far-field post processing

and visualization. It also has Fas EM Design Kit for real-time full-wave

EM tuning and optimization.

63

IE3D LIBRARY: The object-oriented schematic-layout editor for

parameterized geometry modeling and editing. With the introduction of

Fast EM Design Kit for real-time EM tuning, optimization and synthesis,

parameterization becomes necessarily needed and extremely important

for IE3D full-wave design. Parameterization is available on the major

IE3D layout editor MGRID. However, it is limited to vertices and polygons

levels. High-level parameterization can be done on IE3DLIBRARY. To

make IE3DLIBRARY more flexible, we have introduced Boolean objects

and void objects.

The new introduction makes IE3DLIBRARY much more capable in

generating sophisticated parameterized models. IE3DLIBRARY is

relatively easy to use because no many commands are involved. Detailed

discussion on using IE3DLIBRARY can be found from other electronic

documentations.

AGIF: The advanced automatic geometry modeling tool to create full-3D

IE3D models directly from GDSII files, Cadence Virtuoso and Cadence

Allegro.

IE3DOS: It is the EM simulator or simulation engine for numerical

analysis. It is a DOS-style command line application. It is called in the

background by the IE3D dialog to perform an EM simulation. It is

normally hidden from the customers. IE3DOS supports Win32, Win64,

Linux32 and Linux64. The 64-bit editions allow users to solve large

structures.

IE3D: The IE3D dialog displaying the progress of an IE3D simulation or

optimization. The IE3D engine is actually in IE3DOS while IE3D is only

the shell for displaying the progress. The IE3D dialog is also integrated

into MGRID and IE3DLIBRARY.

MODUA: MODUA is the schematic editor for parameter display and nodal

circuit simulation.

64

Most of its capabilities are integrated into MGRID in V14. Mixed

EM and circuit co-simulation is still the unique feature on MODUA while

other S-parameter display and post processing features are integrated

into MGRID.

PATTERNVIEW: Post processor for radiation pattern visualization and

post processing. All functionalities of PATTERNVIEW are integrated into

MGRID in V14.

ADIX: It is the optional ACIS/DXF/GDSII/GERBER format converter. All

functionalities of ADIX are integrated into MGRID for those users choose

the ADIX option.

To perform an EM simulation, a user can start from layout editor

MGRID, IE3DLIBRARY or AGIF. The most fundamental one is the MGRID

layout editor. On MGRID, you draw a structure as a group of polygons.

After you finish constructing the structure as polygons and defining ports

on it, you can invoke the simulation engine IE3D to perform an EM

simulation. The simulation result is saved into a file compatible with the

Agilent/EEs of Touchstone format. The saved file can be imported into

other popular commercial nodal network or circuit simulators such as

the ADS from Agilent/EEs of or Microwave Office from Applied Wave

Research. The simulation result is also saved into the IE3D geometry file

(.geo or 1-8 .ie3). They can be visualized and post-processed on MGRID,

MODUA, IE3DLIBRARY and AGIF of the IE3D package. MODUA is a

program similar to the Agilent/EEs of Touchstone except it does not have

a library with large number of elements. MODUA actually does not need

such a library because any simulation result files and pre-simulated

geometry files from MGRID can be used as modules in MODUA.

A user can also define lumped elements, such as R, L, C, M

(mutual inductor), open circuit, short circuit and ideal connection, on

MODUA to do an EM and circuit co-simulation. Before V14, MODUA is

automatically invoked by IE3D to display the solved s-parameters after a

65

simulation. Starting from V14, users can use MGRID to do visualization

and post processing. The only functionality MODUA has while MGRID

does not have is circuit simulation. If no E Mand circuit co-simulation

and optimization are involved, users even don‟t need MODUA on IE3D

V14.

One of the major advantages of EM simulation is that the field and

current distributions from a simulated structure are accessible to the

users. Information on the current and field distribution in a structure

can be valuable to circuit and antenna designers. On the IE3D, you can

optionally save the current distribution file in a simulation. The current

distribution file can be accessed on MGRID V14 while opening the

geometry file. You can visualize the vector and scalar current

distribution. You can also do an animation on the current distribution.

You can find the radiation patterns and other parameters from the

current distribution on MGRID. Finally, the radiation patterns can be

visualized and post-processed on either MGRID or PATTERNVIEW. You

can display the 3D patterns, 2D patterns, merge different patterns, find

array radiation patterns, and find the transfer functions between the

transmitting (Tx) antenna and the receiving (Rx) antenna. You can

display and process the parameters of linearly polarized and circularly

polarized antennas. On MGRID, you can also calculate and visualize near

field distribution on the structure. Some users may have a geometry

constructed using other tools. The MGRID can import and export in

GDSII and CIF formats in the standard version. The optional ADIX

converter allows a user to import and export geometry in AutoCAD DXF

format (for 2D or 3D), ACIS format (for 3D) and GERBER format. ADIX is

fully integrated into MGRID. When the ADIX optional is enabled, MGRID

is able to import and export in GDSII, CIF, DXF, ACIS and GERBER

formats. Table 3.1 shows the functionalities of the IE3D software as given

below.

66

Table 3.1 Functionalities

FUNCTIONALITY

AND CAPABILITY

GENERAL SPECIAL CAPABILITY

OR EXPLANATION

Microstrip Circuits Yes Multiple dielectrics, lossy and finite

ground Plane

Stripline Circuits Yes Accurate modeling of finite strip

thickness

Co-planar

Waveguide (CPW)

Yes Finite thickness, lossy ground, finite

or infinite ground plane

Slot-line

Structures

Yes Magnetic current modeling for infinite

ground plane and electric current

modeling for finite ground plane.

Suspended

Stripline and Other

Multilayer Planar

Circuits

Yes No limit on the number of dielectric

and

metallic layers

High Speed Digital

Packaging and

Signal Integrity

Yes RLCG equivalent circuit extraction in

SPICE format, simulation of SPICE file

in frequency domain for verification

and confirmation

Printed Circuits on

Lossy Silicon

Substrate

Yes IE3D‟s Green‟s functions include all

the losses in the dielectrics and

metals.

HTS

Superconductor

Circuits

Yes Modeling of skin effect and high

dielectric Permittivity

Coaxial Circuits

and Shielded Strip-

line

Circuits

Yes modeling of any multiple conductor

transmission line systems of arbitrary

cross-section shape

Microstrip

Antennas

Yes Edge fed, probe-fed, proximity coupled

fed and aperture coupled fed, no

limitation on number of feeds and

vertical pins.

67

Wire Antennas Yes Dipoles, loop antennas, cylindrical

helix and conical helix antennas,

quadrifilar antennas. It provides more

accurate modeling than the typical

wire antenna algorithms.

RF Antennas Yes Inverted antennas, spiral antennas

and any other antennas with planar

and 3D metallic structures

Plane-wave

Incident and RCS

Problems

Yes Calculate monostatic and bistatic

radar cross-section (RCS)

3D Capability

Metallic Structures

Yes Vertical and conical via holes, air

bridges, 3D interconnect, no

limitation on the shape and

configuration of a 3D structure

3D Dielectric

Structures

Yes Patch antennas with finite substrate,

wire bonds in inhomogeneous

dielectric environment.

Arbitrarily Shaped

Structures

Yes No limitation on the shape and

orientation of planar and 3D

structures, meshing structure

efficiently without limited by uniform

grids

Open Structures Yes Capture all the radiation and coupling

effects

Closed Structures Yes Electric and magnetic walls emulating

enclosures. Exact boxed Green‟s

functions are implemented in the

IE3D 8.0 for precise modeling of

enclosed structures.

Periodic Structures Yes Periodical walls to emulating

periodical structures such as infinite

array. Exact periodic Green‟s

functions are implemented into the

68

IE3D 8.0 for precise modeling of

periodic structures.

Number of Ports

and Port Location

No limit Offer different de-embedding schemes

for different situation: extension

schemes for high accuracy, localized

for highly packed circuits, differential

feed for structure without an infinite

ground plane. No limitation on port

location and orientation.

Lumped Elements

and

Layout Level

Simulation

Yes Lumped elements defined in both the

layout and schematic editors, s-

parameter files incorporated for mixed

EM and nodal simulation

Electromagnetic

Optimization

Yes Automatic adjusting the location of

polygon vertices to fine tune

structures

Mixed

Electromagnetic

and Network

Optimization

Yes The MGRID+MODUA+IE3D allow

mixed electromagnetic and network

simulation and optimization.

Back Simulation Yes Users are allowed to extract the effect

of a geometry portion out of a

simulation of a larger geometry. The

extra portion is excluded from the

final results.

Number of

Conductor Layers

No limit A user can define as many conductor

layers as the user likes

Different

Conductor

Property in a

Circuit

Yes A user can define the conductor as

normal conductor, HTS

superconductor, or thin film resistor.

Metallic Thickness

Modeling

Yes The actual geometry of a thick

metallic structure can be modeled,

taking into consideration of the skin

69

effect

Number of

Dielectric Layers

No limit General formulation and

implementation of Green‟s functions

for unlimited number of dielectric

layers

Complex Dielectric

Constant (εr),

Permeability (μr)

and Conductivity

(σ)

Yes Complex εr, μr and σ available for

both the dielectric layers and the

metallic strips.

Frequency

dependent metallic

and substrate

parameters

Yes A user is allowed to define the

complex εr, μr and σ

Thin Dielectric

Layers

Yes Tested for thin dielectric layers down

to 0.1 microns in MMICs.

High Dielectric

Constant Material

Yes Tested for dielectric constant up to

1000 in HTS circuits

MIM Capacitors Yes Optionally meshing the coupling

plates into small cells for accurate

modeling; aligning the meshing on

both plates; automatic creation of

meshed MIM capacitor with or

without vias.

Spiral Inductors Yes Easy one-step construction of

rectangular and circular spiral

inductor, modeling of finite thick

metal traces, modeling of air-bridges,

modeling of lossy ground plane

Interactive Graphic

Input of Geometry

Yes Flexible mouse input and keyboard

input of polygon vertices, strong 2D

and 3D geometry checking

Convenient

Geometry Editing

Yes Copy, move, polygon and vertex

elevation, automatic cutting of

70

overlapped polygons, digging holes in

geometry, polygon connectivity

checking, etc.

3D Structure

Display in

Geometry

Editing

Yes 3D display is a great help to 3D

geometry Editing

Automatic

Generation of

Geometry

Yes One step parameterized constructions

of vias, wire-bonds, circles, rings,

curve-structures, spheres, fans,

conical and cylindrical helix

antennas, cylindrical tubes, probe-

feed proximity, slots, etc.

Parameter Display Yes Data list, linear graph and Smith

Chart display of S, Y, Z-parameters,

VSWR, lumped element equivalent

circuits.

Comparison of

Results

Yes Display multiple simulation and

measurement results simultaneously

Curve-fitting and

Interpolation

Yes Curve-fitting simulation data to yield

smooth Result

Nodal Circuit

Simulation

Yes Connect two or more s-parameter

modules or lumped elements together

using idealized connection

Calculation of Port

Information with

Loading

Yes The MODUA allows a user to calculate

the voltage, current and waves at all

the ports under different excitation

and load conditions.

Equivalent Circuit

Extraction

Yes Calculate RLCG equivalent circuit for

transmission line model, find the

parameter values for equivalent

circuit created by users

Frequency

Dependent

Yes The MODUA allows extraction of

frequency dependent equivalent

71

Equivalent Circuit

Extraction

circuit extraction.

3D Current

Distribution

Display

Yes Display 2D vector current, 3D current

density animation, 3D average current

density display

3D radiation

pattern display

Yes 3D pattern, 3D mapped pattern, 2D

pattern and 2D polar pattern for both

linear and circular polarized

antennas, axial ratio display, display

of radiation parameters such as

directivity, radiated power

Radiation

Parameter

Frequency

Response Display

Yes The PATTERNVIEW allows display of

frequency response display of

radiation parameters

Radiation Pattern

Phase Display

Yes The PATTERNVIEW allows displaying

the phase of a pattern.

Radiation Pattern

Comparison

Yes The PATTERNVIEW allows

comparison of radiation patterns at

different frequencies and from

different structures.

Radiation Patterns

of Loaded

Antennas

Yes The IE3D allows users to calculate the

radiation patterns of antennas with

lumped elements.

General Radiation

Patterns

Yes The IE3D 10.0 allows users to

calculate an Nport structure‟s

patterns without the excitations

defined. The pattern for the specified

excitation can be readily obtained in

the display time. It allows tuning of

antenna patterns by changing the

excitations only.

72

Pattern

Optimization

Yes The IE3D 7.0 allows optimization of

radiation patterns and parameters.

Pattern Rotation Yes You can rotate the patterns from

CURVIEW or PATTERNVIEW. This

feature is very important for wireless

applications because rotation of

antennas is frequently encountered.

Real Ground Effect

on Pattern

Yes The CURVIEW and PATTERNVIEW

allow the users to add the effects of

the real ground to the pattern.

Pattern Merging Yes The PATTERNVIEW allows merging of

radiation patterns from individual

radiators. This feature allows

calculation of radiation pattern from a

very large structure divided into

smaller sub-structures for field

simulation.

3D Near Field

Display

Yes Display scalar potentials, vector

potentials, E-fields, H-fields and

Pointing vectors as curves and 3D

graphs.

Save High Quality

Bitmap File

Yes Save colorful current distribution,

radiation Pattern or near field pictures

in bitmap files.

Display Current

and Field with

Different

Excitation and

Load Conditions

Yes Easy investigation of circular

polarization, antenna with integrated

source.

S-parameter files

compatible with Agilent/EEsof ®

Yes

73

RLCG Equivalent

Circuit SPICE

Compatible

Yes RLCG segments extracted at single

low frequency for low frequency

applications

Frequency

Independent Wide

Band

Equivalent Circuit

Extraction in

SPICE

format.

Yes* This feature is in the optional

MDSPICE. The MDSPICE converts an

N-port wide-band s-parameters file

into a RLC network with perfectly

matching

S-parameters.

Frequency

Dependent

Equivalent Circuit

Extraction and

Visualization

Yes Available on MGRID, IE3DLIBRARY

and MODUA on IE3D V12.

Time-Domain

Simulations on

S-Parameters

Yes* The MDSPICE simulator allows high

accuracy SPICE simulation based

upon the s-parameters from IE3D

GDSII, DXF, ACIS,

GERBER and CIF

Bi-direction

Conversion

Yes* CIF and GDSII formats are built-in.

DXF; ACIS and GERBER formats are

optional.

EM Tuning,

Optimization and

Synthesis

Yes Users can do full-wave EM tuning,

optimization and synthesis real-time

at design time on MGRID and IE3D

LIBRARY.

3.3 Vector Network Analyzer

A Vector Network analyzer is a test system that enables the RF

performance of radio frequency (RF) and microwave devices to be

characterized in terms of network scattering parameters or S-parameters.

The key element is that it can measure both amplitude and phase. Only

with knowledge of phase and magnitudes from a VNA circuit models be

developed that will enables complete simulation to be under taken.

74

Hence, the information provided by this is used to ensure that the RF

design of the circuit is optimized to provide the best performance.

Vector Network Analyzer measures the magnitude and phase

characteristics of networks such as amplifiers filters, attenuators and

antennas etc. It compares the incident signal that leaves the analyzer

with either the signal that is transmitted through the test device or the

signal that is reflected from its input. In this dissertation antenna

measurement work is carried out using German make VNA ZVK (10 MHz-

40GHz) which is shown in Fig. 3.1. The instrument is basically 2-port,

4-channel analyzer consisting of test set, reference oscillator, signal

generator, first and second local oscillator, front-end, converter (A/D),

measurement control unit and a front panel as shown in Fig. 3.2.

The logical variables used at the microwave frequency are traveling

waves rather than total voltage and total currents. The basic task of

network analyzer is the measurement of S-parameters. These

S-parameters are expressed as

b1 = S11.a1+S12.a2

b2 = S21.a1+S22.a2

For S-parameter subscript “ij”, j is the port that is excited (the

input port) and „i‟ is the output port. Thus S11 refers to the ratio of signal

that reflects from port one for a signal incident on port one. Parameters

S11 and S22 are refers to as reflection co-efficient because they only refer

to what happens at a single port, while S12 and S21 are refers to as

transmission co-efficient because they refer to what happens from on

port to another.

75

Fig. 3.1 Vector Network Analyzer

Some of the characteristics and features of VNA ZVK are as

follows:

1. Distinguishing features:

Four receiver channels

Bidirectional.

Standard calibration methods plus R & S calibration

methods for test fixtures, circuit broadband

76

Fig. 3.2 Measurement Control Unit

Importance of VNA measurements:

Measuring both magnitude and phase of components is important

for several reasons. First, both measurements are required to fully

characterize a linear network and ensure distortion-free transmission. To

design efficient matching networks, complex impedance must be

measured. Engineers developing models for computer aided-engineering

(CAE) circuit simulation programs require magnitude and phase data for

accurate models.

In addition, time-domain characterization requires magnitude and

phase information in order to perform an inverse-Fourier transform.

Vector error correction, which improves measurement accuracy by

removing the effects of inherent measurement system errors, requires

both magnitude and phase data to build an effective error model. Phase-

77

measurement capability is very important even for scalar measurements

such as return loss, in order to achieve a high level of accuracy.

Basic measurement task:

The basic measurement task of a network analyzer is to determine

the linear characteristics of a device under test (DUT), characterized by

the scattering parameters, as a function of frequency. In most cases the

DUTs to be examined will have two ports, i.e. an input and an output.

For this reason network analyzers usually have two test ports (port 1 and

port2), to which DUTs are connected by cable.

For overall determination of the scattering matrix [S] of a two-port,

four measurements are necessary for each frequency point, i.e. a

reflection measurement at the input and output of the DUT and

transmission measurement in the forward and reverse direction. For this

purpose the network analyzer applies a RF test signal to the DUT

alternately via port 1 and port 2, measures the signal reflected or

transmitted by the DUT, and is thus able, using the defining equations

for scattering parameters, to determine all four S parameters of the two-

port as shown in Fig. 3.1. Thus it can perform the basic measurement

task. Every network analyzer is composed of the three subsystems as

shown in Fig. 3.2.

1. A signal source for generating the test signal.

2. An S parameter test set for separating the different signal

components.

3. A receiver that receives the different signal components evaluates

and displays them. The number of receiver channels, in this case

is four, corresponds to the number of signal components provided

by the test set.

The scattering parameters, since they are either measured directly

or formed by ratios of wave quantities that are measured directly, are the

primary measured quantities of a network analyzer. Due to their

78

definition they are complex. They can be converted to derived measured

quantities, for example the complex impedance or admittance, as well as

scalar quantities like voltage standing wave ratio (VSWR) or group delay.

The reflection coefficient can also be displayed with respect to a

propagation time or distance axis by transforming from frequency into

time domain.

Besides the display of a measured quantity as a function of

frequency, one may often also be interested in its dependence on

generator level at constant frequency or how it changes with time at a

fixed frequency and a fixed generator level. These measurements can be

made in a level or time sweep mode. Note the difference between time

sweep domain transformations. Instruments can measure S-parameters

in complex form that means, with amplitude and phase information, are

referred to as vector network analyzers.

Proceeding in the direction of signal flow, the first major

component of the instrument is the crystal-controlled reference oscillator

in the synthesizer subsystem. From this the test signal and all LO signals

are derived. It must be possible to set the frequency of the test signal

generator over several decades. So one takes a synthesizer generator with

a frequency range of one octave for example, and generates the remaining

bands by doubling, division and for low frequencies by down conversion

with an auxiliary oscillator. At the input of the test set there is an

electronic RF switch which, in bidirectional operation of the network

analyzer, alternately switches the generator signal to the VSWR bridges

at port 1 and port 2 at each frequency point. In the unidirectional mode it

stays in one position. Power splitters, inserted between the VSWR bridges

and the RF switch, couple out the reference signals a1 and a2 which are

a measure of the waves incident to the bridges and thus to the DUT. The

signal components b1 and b2 which are transmitted or reflected by the

DUT connected between the two test ports PORT1 and PORT2, are

applied to the test set outputs via the VSWR bridges.

79

Linear Non-linear Frequency

converting

S-

parameters

Compression

point

Mixer

measurements

Group

delay

Interception

point

Any harmonics

Impedance - Intermodulation

Admittance - Arbitrary frequency

conversion

The characteristics like VSWR, input impedance and return loss

will be measured using this network analyzer. The basic block diagram of

Vector Network analyzer is as shown in Fig. 3.3.

Fig. 3.3 Basic block diagram of Vector Network Analyzer

80

3.4 Radiation pattern measurement system

Radiation pattern is a graph, which shows the variation in actual

field strength of radiated or received power with respect to the reference

antenna. The information contain in the radiation pattern of an antenna

is beamwidth, side lobe level, location of side lobes and positions of null

etc.

The radiation pattern measurement setup is as shown in Fig. 3.4.

The distance R between the transmitting and receiving antennas is given

by,

R ≥

22D

where, D is the broad dimension of the pyramidal horn and is the

operating wavelength in cm.

In the present study the turn-table method is used to measure the

radiation pattern of device under test (DUT). Here DUT, which is a

monopole antenna, is kept in the receiving mode and the reference

antenna, which is a pyramidal horn antenna, kept in the transmitting

mode.

The two antennas are placed so as to face each other and then,

keeping the position of transmitting antenna fixed, the receiving antenna

is rotated around its axis, to change the angle in steps of degrees. At each

angle the received power is measured. The graph is plotted for azimuth

angle verses normalized power, which gives radiation pattern of DUT.

The turn-table measurement setup shown in Fig. 3.4 is specially

designed for the measurement of antenna radiation pattern by

Sophisticated Test and Instrumentation Center (STIC), Cochin University

of Science and Technology, Cochin. The system is totally automatic and

computer controlled and mainly consists of two units, namely positioner

control system (S310C) and antenna positioner (S310P). The S310C is

micro controller based turn-table controller, which can work as a stand-

alone unit or can be controlled from a computer. The S310C is designed

81

to control the S310 series positioner, which are all stepper motor driven.

The receiving part of Fig. 3.4 consisting of Computer, S310P, S310C,

device under test (DUT), crystal detector and Power meter.

The device under test is connected in the receiving mode in Fig.3.3,

the reference antenna (i.e. pyramidal horn) is kept at a certain distance

away from the receiving antenna by satisfying the formula R≥

22D,

where R is the distance between transmitting and receiving antenna, D is

the broader diameter of antenna and is the operating wavelength. The

transmitting and receiving antennas are aligned properly before taking

the measurements for obtaining maximum on-axis power. The microwave

source at the transmitting section is energized and is tuned for the

desired frequency.

In the local mode the operator can directly enter the angular

positions in degrees in order to position the turn-table. The arrows keys

provided on the front panel of S310C can be used to position the turn-

table manually. The DUT is connected to the crystal detector through

SMA and waveguide to co-axial connector. The output of crystal detector

is fed to the power meter to measure the received power at different

angles.

With the execution of the software developed by STIC, the radiation

pattern of DUT connected in the receiving mode will be measured

automatically. The obtained data can be stored at various data files and

the plot of radiation pattern is obtained using Origin-6.1 software. With

the help of this facility the radiation pattern measurement can be made

quickly with more accuracy.

82

Transmitting section Receiving section

VNA

Universal

Horn antenna

Tripod stand

(STIC S310C)

POSITIONER CONTROLLER

Fig. 3.4 Radiation Pattern Measurement System

3.5 Fabrication of proposed antennas

The fabrication of the monopole antenna is the most important

artwork after designed in the Auto CAD-2004. A laser print out of the

artwork is taken. The print dimension was achieved on one side of the

single sided PCB using photolithographic process. The fabrication

process of PRMA is shown in Fig. 3.5. In development of artwork of PRMA

accuracy is maintained up to eight decimal points. Accuracy is vital at

this stage and depending on the complexity and dimensions of the PRMA

Power

Meter

POSITIONER

(STIC S310P)

DUT

83

either full or enlarged scale artwork should be prepared on stabiline or

Rubylith film or prepared on butter paper. Using the precision cutting

blade of a manually operated co-ordinal graph the opaque layer of the

stabiline or Rubylith is cut to the proper geometry and can be removed to

produce either a positive or negative representation of the PRMA.

The design dimensions and tolerances are verified on a coordinate

axis measuring instrument using optical scanning. Enlarged artwork

should be photo reduced using a high precession camera to produce high

resolution negative, which is later used for exposing the photo resists.

The laminate should be cleared using the substrate manufacturer

recommended, procedure to insure proper adhesion of the photo resist

and the necessary resolution in the photo development process. The

photo resist is now applied to both sides of the laminate using laminator;

the laminate is then allowed to attain normal at room temperature prior

to exposure and development. The photographic negative must be now

linked in very close contact with the poly ethylene cover sheet of the

applied photo resist using a vacuum frame copy board or other

technique, to assure the feed line resolution required. With exposure to

proper wave length of light, polymerization of the exposed photo resist

occurs making it insoluble in the developer solution. The both side of

PRMA is exposed completely without a mask, since the copper file is

retained to act as a ground plate. The protective polythene cover sheet of

the photo resist is removed and the antenna is now developed in a

developer, which removes the soluble photo resist material. Visual

inspection is needed to assure proper development of rectangular

monopole antenna.

When these steps are completed, the antenna is ready for etching.

This is the critical step and required considerable care does that proper

etch rates are achieved. After etching photo resist is removed using a

strip line solution visual and optical inspection should be carried out to

ensure a good product and to ensure performance with dimensional to

84

Fig. 3.5 Fabrication process

Selection of substrate material

Design

Master drawing

Negative film development

Resist application

Laminate cleaning

Photocopy

Artwork layout

Resist exposure

Resist development

Etching

Inspection

Bounding

Finishing

85

tolerances, with a final acceptance or rejection being based on resonant

frequency, radiation pattern and impedance measurement.

For acceptable units, the edges are smoothened and the antenna is

reinserted in water and dried. If desired, a thermal cover bonding may be

applied by placing a bonding film between the laminates does to be

bounded out placing these between tooling plates. Dowel pins can be

used for alignment and the assembly is then heated under pressure until

the bonding temperature is reached.

The assembly is allowed to cool under pressure below the melting point

of the bonding film and the laminate is then removed for inspection. The

above procedure comprises the general steps necessary in producing a

microstrip rectangular monopole antenna. The substance used for the

various process Ex. Cleaning, etching or the tools used for matching etc.,

depends on the substrate choose.

The design procedure and results of the monopole antennas are

discussed in the next chapter.