Présentation PowerPoint - atmsindia.orgatmsindia.org/tech_papers/2015/ATMStutorial_Cross polar...

ATMS INDIA

2015

1/27/2015

1

Cross polar reduction feeds in single

reflector CATR ATMS 2015 – Hotel Park Bangalore, India, 2th February, 2015

A. Riccardi

Introduction to CATRs (characteristics & analysis)

Polarization performances in parabolic reflectors

Cross polarization proprieties in CATRs

The conjugate matched feed array

Concept

Design

Simulation

Proof-of-the-concept measurements

Conclusions

OVERVIEW

2

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(1/11)

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Compact Antenna Test Ranges (CATRs) are collimating

systems for antenna measurements

Off-set single reflector or dual parabolic reflectors

with treated edges

Dual reflector CATR

Single reflector CATR

Serrations Rolled-edge

Mini CATR

Example of CATR configurations:


(2/11)

4

CATRs provide nearly plane wave in the

near-field region - Quiet Zone (QZ)

Orthogonal components are measured

yQZ

xQZ zQZ

EΘ field component

measured

Antenna under

Test

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(3/11)

5

yQZ

xQZ zQZ

Eφ field component

measured

Antenna under

Test

CATRs provide nearly plane wave in the

near-field region - Quiet Zone (QZ)

Orthogonal components are measured

Co-polar amplitude


(4/11)

6

yQZ

xQZ zQZ

0 -1

Quality of antenna measurements

Co-polar (amplitude/phase) field uniformity in the QZ

Quality parameters:

Taper

Ripple

[dB]

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QZ


(5/11)

7

yQZ

xQZ


Polarization field purity in the QZ

Cross polar amplitude level

EΘ field component

measured

zQZ

-30 -60 [dB]

QZ


(6/11)

8

yQZ

xQZ zQZ




Eφ field component

measured -30 -60 [dB]

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(7/11)

9

yQZ

xQZ

Antenna under

Test




Cross polar measurement accuracy also depends on

Antenna size and position in the QZ

-30 -60 [dB]


(8/11)

10

Compensated dual reflector vs single reflector CATR have

similar performances with main differences on:

Cross polar discrimination: >40dB vs >25-30dB.

Price and complexity: High vs Low

Compensated dual reflector CATR Single reflector CATR

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CATRs analysis and design improvements by modern tools

Example of CATR analysis by using MoM

Peak amplitude distribution

Time-domain amplitude variation Electric density current - vertical component

Vertical feed polarization source

-38.7

-88.7

dB (A/m)

dB (A/m)

-38.7

-39.7


(10/11)

12 12


Example of CATRs analysis by using MoM

Time-domain amplitude variation

Vertical feed polarization source

-38.7

-88.7

dB (A/m) Electric density current - horizontal component

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Cross polar (horizontal) field component in the QZ

Vertical polarization feed


Example of CATRs analysis by using MoM

dB (V/m) Time-domain amplitude variation


(1/8)

14 14

y

x

F

yf

xf

Γv

z zf ΓH

Secondary cross polar component will not be induced if

primary radiation pattern is symmetric and

feed axis zf is coincident with the axis of reflector z

T.-S. Chu, R. H. Turrin, “Depolarization Proprieties of Offset Reflector Antennas”, IEEE Transactions on Antennas and Propagation, Vol. AP- 21, No. 3, May 1973.

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(2/8)

15 15

y

x

F z

n

yf

xf

Γv

Erco

x

zf

Ercx

Ecx

φ Eco

Eco φ

Ecx

ico

icx

y

Eco and Ecx defined according to the Ludwig’s third

definition wrt to (xf , yf , zf) coordinate system

Secondary cross polar component induced by

asymmetry of primary radiation pattern


(3/8)

16

x

y

F z

n ico

Erco

y

x

icx

Γv

yf

xf zf

Eco

16





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(4/8)

17 17

Aperture plane



Example – dipole feed source

Co-polar field component


(5/8)

18 18

y

x

F

n

yf

xf

Γv

Erco

x φ

Eco

Eco φ

ico

icx z zf



Secondary cross polar component not induced by

symmetric primary radiation pattern in center-fed parabolic reflectors

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(6/8)

19 19

y

x

F z

n

yf

xf

Γv

Erco

x

zf

φ Eco

Eco φ

ico

icx

Ercx

Ecx

Ecx


feed axis zf not coincident with the axis of reflector z



Plane of symmetry of reflector


(7/8)

20 20

y

x

F

yf

xf

zf Eco

Γv

φ'

Eco φ'

ico

icx

Erco

Ercx n

z






x

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(8/8)

21 21

y

x

F

yf

xf

zf

z

n ico Eco

icx

Erco

y

x







(1/18)

22 22

yQZ

XQZ Eco

y

x

xf

yf

zf

Cross-polar field induced by single reflector CATR

Side-fed (or floor-fed) configurations

Horizontal co-polar component in the QZ

z

Plane of symmetry

of reflector

yf

xf Plane of symmetry

of reflector

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(2/18)

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Amplitude

Phase shift (wrt co-polar phase)

0°

180°





(3/18)

24 24

yQZ

XQZ

Eco

y

x

xf

yf

zf

z



Vertical co-polar component in the QZ

Plane of symmetry

of reflector

yf

xf Plane of symmetry

of reflector

XQZ

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(4/18)

25 25


180°

0°

Amplitude





(5/18)

26 26

F

yf

xf

zf

z

n ico Eco

icx



y

x

Erco

y

Ercx


Secondary cross polar component also in the plane of symmetry

because of different reference polarizations orientation between primary

and secondary pattern (with respect to plane of symmetry of reflector)

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y

x

Plane of symmetry

of reflector

yQZ

XQZ

yf zf

xf

Ecx

Secondary cross polar component also in the plane of symmetry

because of different reference polarizations orientation between primary

and secondary pattern (with respect to plane of symmetry of reflector)

z

φ

yf

xf

XQZ Eco


(7/18)

28 28

y

x

yQZ

yf zf

xf


Diagonal-fed configurations


Plane of symmetry

of reflector z

φ

yf

xf

φ

XQZ Eco

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(8/18)

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Amplitude




180°

0°



(9/18)

30 30

y

x

yQZ

XQZ

yf zf

xf




Plane of symmetry

of reflector

Eco

z

φ

yf

xf

φ

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(10/18)

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Amplitude




180°

0°



(11/18)

32

Amplitude

32

Cross-polar field induced by uncompensated

dual-reflector CATR


yQZ xQZ

yf

xf


0°

180°

Reflector S Cylindrical parabolic

reflector wrt vertical plane

Reflector M Cylindrical parabolic

reflector wrt horizontal plane

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(12/18)

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Amplitude

33

yQZ

yf

xf


180°

0°

Cross-polar field induced by uncompensated

dual-reflector CATR






xQZ


(13/18)

34 34

yQZ

yf

xf

Cross-polar field not induced by compensated

dual-reflector CATR


Amplitude

Reflector S parabolic reflector

Reflector M Parabolic reflector

xQZ

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yf

xf


dual-reflector CATR


Co-polar amplitude From reflector S

0°

180°

Cx-polar phase shift (wrt co-polar phase)

Cx-polar amplitude

Amplitude


(15/18)

36 36

yQZ


dual-reflector CATR


Co-polar amplitude from Reflector S


180°

0°

xQZ

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(16/18)

37 37

yQZ

yf

xf


dual-reflector CATR


Amplitude

Reflector S parabolic reflector

Reflector M Parabolic reflector

xQZ


(17/18)

38 38

yf

xf


dual-reflector CATR


Co-polar amplitude

0°

180°

Cx-polar phase shift (wrt co-polar phase)

Cx-polar amplitude

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Amplitude


(18/18)

39 39

yQZ


dual-reflector CATR


Co-polar amplitude from Reflector S


180°

0°

xQZ

Modern cross polar cancellation techniques

(1/2)

40

Polarization grids have been proposed to mitigate the

induced cross polar from the reflector.

A different polarization grid is needed for each polarization.

M. A. J. Griendt, V. J. Vokurka, “Polarization grids for applications in compact antenna test ranges”, 15th Annual Antenna Measurement Techniques Association Symposium, AMTA, October 1993, Dallas, Texas.

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Modern cross polar cancellation techniques

(2/2)

41

Higher order mode horns have been proposed to mitigate

the induced cross polar from the reflector.

The higher order mode excitation is very narrow band and

limited to one polarization.

K. Bahadori, and Y. Rahmat-Samii, “Tri-Mode Horn Feeds Revisited: Cross-Pol Reduction in Compact Offset Reflector Antennas”, IEEE Transactions on Antennas and Propagation, vol. 57, no. 9, September 2009

The conjugate matched feed array – concept

(1/15)

42 42

High cross-polar discrimination

below -40dB

for any single reflector CATR

configuration (side-fed, floor-fed and

diagonal fed) and uncompensated

dual-reflector CATRs

over 1.5:1 band with scalable design

for dual orthogonal polarizations

Characteristics:

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(2/15)

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Central element, (co-feed)

provides high quality co-polar

component in the QZ

Cx-polarized side elements (cx-

feeds) provide conjugate field

matching for cancelling the

cross-polar component induced

in the QZ

Description:

-30 -60 [dB]

0 -1 [dB]


(3/15)

44 44

yQZ

Eco

y

x

xf

xf

zf

z

Cross-polar field compensation by using the conjugate

matched feed array

Side-fed configuration / Floor-fed configuration


Plane of symmetry

of reflector

Plane of symmetry

of reflector

XQZ

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(4/15)

45

0°

180°


45

Amplitude


matched feed array




(5/15)

46 46

Amplitude Amplitude


matched feed array



-30 -60 [dB]

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The conjugated matched feed array – concept

(6/15)

47 47

yQZ Eco

y

x

xf

xf

zf

z


matched feed array



Plane of symmetry

of reflector

Plane of symmetry

of reflector

XQZ


(7/15)

48 48

0°

180°



matched feed array



Amplitude

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(8/15)

49 49

Amplitude Amplitude


matched feed array



-30 -60 [dB]


(9/15)

50 50

y

x

yQZ

yf zf

xf

Plane of symmetry

of reflector z


matched feed array

Diagonal-fed configuration


yf

xf

φ

φ

Feed axis XQZ

Eco

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(10/15)

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180°

0°


51


matched feed array




(11/15)

52 52


matched feed array



Amplitude Amplitude

-30 -60 [dB]

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(12/15)

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y

x

yQZ

yf zf

xf

Eco

z

Plane of symmetry

of reflector

φ

53


matched feed array



xf

yf φ

Feed axis XQZ


(13/15)

54 54

Amplitude


matched feed array



180°

0°


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(14/15)

55 55

yQZ

yf

xf

Amplitude


matched feed array in uncompensated dual-reflector CATR






xQZ


(15/15)

56 56

yQZ

yf

xf

Amplitude


matched feed array in uncompensated dual-reflector CATR






xQZ

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The conjugate matched feed array – design (1/2)

57

Aperture size of the co-feed:

for high quality QZ co-polar component (lowest frequency constrain)

Very low cross-polar component produced by co-feed in the array

57

Cx-feed distance

Distance between cx-feeds for cross polar

cancellation below the target of -40dB,

trade-off:

Cross polar cancellation performance (highest

frequency constrain)

Cross polar component of co-feed due to

coupling

The conjugate matched feed array – design (2/2)

58 58

Fre

qu

en

cy [G

Hz]

Nearly identical field

distribution

Discrepancies

Frequency dependent

Frequency independent

1.5

0:1

Ba

nd

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The conjugate matched feed array – simulation

(1/3)

59 59

MoM PO MoM - Current amplitude

distribution (courtesy of

IDS spa)

Primary field evaluation – Full wave

simulation

[10.0, 15.0]GHz

QZ field numerical evaluation - PO calculations with

Serration modelling

Serration modelling validation


(2/3)

60 60

GO PO

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(3/3)

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Frequency [GHz]

10.0 12.5 15.0

Compensated cross polar field in the QZ [-60, -40]dB below

the peak of the co-polar component


(1/2)

62 62

Single-polarized

[10.0, 12.5] GHz

Measurements (filtered) before compensation

Measurements (filtered) after Compensation

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(2/2)

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MoM simulation Measurements (filtered) after

Compensation

Conclusions

64 64

A wide-band, conjugate matched feed concept has been

developed and validated for common single reflector

CATR, achieving cross polarization discrimination

>40dB over a bandwidth of 1.5:1 for simultaneous

orthogonal polarization.

A proof-of-the-concept demonstrator (CXR), in

single polarization with 1.25:1 bandwidth, has

been designed and manufactured.

Measurements in a standard CATR confirm the

concept of cross polar reduction in the QZ and

validate the numerical results.

A prototype of the CXR has been designed achieving

(numerically) cross polarization discrimination below

40dB for simultaneous orthogonal polarization and

covering the band of 1.6:1.

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65

Thank you for your attention

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