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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
ATMS INDIA
2015
1/27/2015
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Introduction to CATRs (characteristics & analysis)
(1/11)
3
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:
Introduction to CATRs (characteristics & analysis)
(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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Introduction to CATRs (characteristics & analysis)
(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
Introduction to CATRs (characteristics & analysis)
(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
Introduction to CATRs (characteristics & analysis)
(5/11)
7
yQZ
xQZ
Quality of antenna measurements
Polarization field purity in the QZ
Cross polar amplitude level
EΘ field component
measured
zQZ
-30 -60 [dB]
QZ
Introduction to CATRs (characteristics & analysis)
(6/11)
8
yQZ
xQZ zQZ
Quality of antenna measurements
Polarization field purity in the QZ
Cross polar amplitude level
Eφ field component
measured -30 -60 [dB]
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1/27/2015
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Introduction to CATRs (characteristics & analysis)
(7/11)
9
yQZ
xQZ
Antenna under
Test
Quality of antenna measurements
Polarization field purity in the QZ
Cross polar amplitude level
Cross polar measurement accuracy also depends on
Antenna size and position in the QZ
-30 -60 [dB]
Introduction to CATRs (characteristics & analysis)
(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
ATMS INDIA
2015
1/27/2015
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Introduction to CATRs (characteristics & analysis)
(9/11)
11 11
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
Introduction to CATRs (characteristics & analysis)
(10/11)
12 12
CATRs analysis and design improvements by modern tools
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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Introduction to CATRs (characteristics & analysis)
(11/11)
13 13
Cross polar (horizontal) field component in the QZ
Vertical polarization feed
CATRs analysis and design improvements by modern tools
Example of CATRs analysis by using MoM
dB (V/m) Time-domain amplitude variation
Polarization performances in parabolic reflectors
(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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Polarization performances in parabolic reflectors
(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
Polarization performances in parabolic reflectors
(3/8)
16
x
y
F z
n ico
Erco
y
x
icx
Γv
yf
xf zf
Eco
16
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
ATMS INDIA
2015
1/27/2015
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Polarization performances in parabolic reflectors
(4/8)
17 17
Aperture plane
Secondary cross polar component induced by
asymmetry of primary radiation pattern
Example – dipole feed source
Co-polar field component
Polarization performances in parabolic reflectors
(5/8)
18 18
y
x
F
n
yf
xf
Γv
Erco
x φ
Eco
Eco φ
ico
icx z zf
Eco and Ecx defined according to the Ludwig’s third
definition wrt to (xf , yf , zf) coordinate system
Secondary cross polar component not induced by
symmetric primary radiation pattern in center-fed parabolic reflectors
ATMS INDIA
2015
1/27/2015
10
Polarization performances in parabolic reflectors
(6/8)
19 19
y
x
F z
n
yf
xf
Γv
Erco
x
zf
φ Eco
Eco φ
ico
icx
Ercx
Ecx
Ecx
Secondary cross polar component induced by
feed axis zf not coincident with the axis of reflector z
Eco and Ecx defined according to the Ludwig’s third
definition wrt to (xf , yf , zf) coordinate system
Plane of symmetry of reflector
Polarization performances in parabolic reflectors
(7/8)
20 20
y
x
F
yf
xf
zf Eco
Γv
φ'
Eco φ'
ico
icx
Erco
Ercx n
z
Secondary cross polar component induced by
feed axis zf not coincident with the axis of reflector z
Eco and Ecx defined according to the Ludwig’s third
definition wrt to (xf , yf , zf) coordinate system
Plane of symmetry of reflector
x
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2015
1/27/2015
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Polarization performances in parabolic reflectors
(8/8)
21 21
y
x
F
yf
xf
zf
z
n ico Eco
icx
Erco
y
x
Secondary cross polar component induced by
feed axis zf not coincident with the axis of reflector z
Eco and Ecx defined according to the Ludwig’s third
definition wrt to (xf , yf , zf) coordinate system
Plane of symmetry of reflector
Cross polarization proprieties in CATRs
(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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1/27/2015
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Cross polarization proprieties in CATRs
(2/18)
23 23
Amplitude
Phase shift (wrt co-polar phase)
0°
180°
Cross-polar field induced by single reflector CATR
Side-fed (or floor-fed) configurations
Horizontal co-polar component in the QZ
Cross polarization proprieties in CATRs
(3/18)
24 24
yQZ
XQZ
Eco
y
x
xf
yf
zf
z
Cross-polar field induced by single reflector CATR
Side-fed (or floor-fed) configurations
Vertical co-polar component in the QZ
Plane of symmetry
of reflector
yf
xf Plane of symmetry
of reflector
XQZ
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1/27/2015
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Cross polarization proprieties in CATRs
(4/18)
25 25
Phase shift (wrt co-polar phase)
180°
0°
Amplitude
Cross-polar field induced by single reflector CATR
Side-fed (or floor-fed) configurations
Vertical co-polar component in the QZ
Cross polarization proprieties in CATRs
(5/18)
26 26
F
yf
xf
zf
z
n ico Eco
icx
Eco and Ecx defined according to the Ludwig’s third
definition wrt to (xf , yf , zf) coordinate system
y
x
Erco
y
Ercx
Plane of symmetry of reflector
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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Cross polarization proprieties in CATRs
(6/18)
27 27
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
Cross polarization proprieties in CATRs
(7/18)
28 28
y
x
yQZ
yf zf
xf
Cross-polar field induced by single reflector CATR
Diagonal-fed configurations
Horizontal co-polar component in the QZ
Plane of symmetry
of reflector z
φ
yf
xf
φ
XQZ Eco
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1/27/2015
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Cross polarization proprieties in CATRs
(8/18)
29 29
Amplitude
Cross-polar field induced by single reflector CATR
Diagonal-fed configurations
Horizontal co-polar component in the QZ
180°
0°
Phase shift (wrt co-polar phase)
Cross polarization proprieties in CATRs
(9/18)
30 30
y
x
yQZ
XQZ
yf zf
xf
Cross-polar field induced by single reflector CATR
Diagonal-fed configurations
Vertical co-polar component in the QZ
Plane of symmetry
of reflector
Eco
z
φ
yf
xf
φ
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2015
1/27/2015
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Cross polarization proprieties in CATRs
(10/18)
31 31
Amplitude
Cross-polar field induced by single reflector CATR
Diagonal-fed configurations
Vertical co-polar component in the QZ
180°
0°
Phase shift (wrt co-polar phase)
Cross polarization proprieties in CATRs
(11/18)
32
Amplitude
32
Cross-polar field induced by uncompensated
dual-reflector CATR
Horizontal co-polar component in the QZ
yQZ xQZ
yf
xf
Phase shift (wrt co-polar phase)
0°
180°
Reflector S Cylindrical parabolic
reflector wrt vertical plane
Reflector M Cylindrical parabolic
reflector wrt horizontal plane
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1/27/2015
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Cross polarization proprieties in CATRs
(12/18)
33
Amplitude
33
yQZ
yf
xf
Phase shift (wrt co-polar phase)
180°
0°
Cross-polar field induced by uncompensated
dual-reflector CATR
Vertical co-polar component in the QZ
Reflector S Cylindrical parabolic
reflector wrt vertical plane
Reflector M Cylindrical parabolic
reflector wrt horizontal plane
xQZ
Cross polarization proprieties in CATRs
(13/18)
34 34
yQZ
yf
xf
Cross-polar field not induced by compensated
dual-reflector CATR
Horizontal co-polar component in the QZ
Amplitude
Reflector S parabolic reflector
Reflector M Parabolic reflector
xQZ
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1/27/2015
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Cross polarization proprieties in CATRs
(14/18)
35 35
yf
xf
Cross-polar field not induced by compensated
dual-reflector CATR
Horizontal co-polar component in the QZ
Co-polar amplitude From reflector S
0°
180°
Cx-polar phase shift (wrt co-polar phase)
Cx-polar amplitude
Amplitude
Cross polarization proprieties in CATRs
(15/18)
36 36
yQZ
Cross-polar field not induced by compensated
dual-reflector CATR
Horizontal co-polar component in the QZ
Co-polar amplitude from Reflector S
Phase shift (wrt co-polar phase)
180°
0°
xQZ
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1/27/2015
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Cross polarization proprieties in CATRs
(16/18)
37 37
yQZ
yf
xf
Cross-polar field not induced by compensated
dual-reflector CATR
Vertical co-polar component in the QZ
Amplitude
Reflector S parabolic reflector
Reflector M Parabolic reflector
xQZ
Cross polarization proprieties in CATRs
(17/18)
38 38
yf
xf
Cross-polar field not induced by compensated
dual-reflector CATR
Vertical co-polar component in the QZ
Co-polar amplitude
0°
180°
Cx-polar phase shift (wrt co-polar phase)
Cx-polar amplitude
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Amplitude
Cross polarization proprieties in CATRs
(18/18)
39 39
yQZ
Cross-polar field not induced by compensated
dual-reflector CATR
Vertical co-polar component in the QZ
Co-polar amplitude from Reflector S
Phase shift (wrt co-polar phase)
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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The conjugate matched feed array – concept
(2/15)
43
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]
The conjugate matched feed array – concept
(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
Horizontal co-polar component in the QZ
Plane of symmetry
of reflector
Plane of symmetry
of reflector
XQZ
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The conjugate matched feed array – concept
(4/15)
45
0°
180°
Phase shift (wrt co-polar phase)
45
Amplitude
Cross-polar field compensation by using the conjugate
matched feed array
Side-fed configuration / Floor-fed configuration
Horizontal co-polar component in the QZ
The conjugate matched feed array – concept
(5/15)
46 46
Amplitude Amplitude
Cross-polar field compensation by using the conjugate
matched feed array
Side-fed configuration / Floor-fed configuration
Horizontal co-polar component in the QZ
-30 -60 [dB]
ATMS INDIA
2015
1/27/2015
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The conjugated matched feed array – concept
(6/15)
47 47
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
Vertical co-polar component in the QZ
Plane of symmetry
of reflector
Plane of symmetry
of reflector
XQZ
The conjugate matched feed array – concept
(7/15)
48 48
0°
180°
Phase shift (wrt co-polar phase)
Cross-polar field compensation by using the conjugate
matched feed array
Side-fed configuration / Floor-fed configuration
Vertical co-polar component in the QZ
Amplitude
ATMS INDIA
2015
1/27/2015
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The conjugate matched feed array – concept
(8/15)
49 49
Amplitude Amplitude
Cross-polar field compensation by using the conjugate
matched feed array
Side-fed configuration / Floor-fed configuration
Vertical co-polar component in the QZ
-30 -60 [dB]
The conjugate matched feed array – concept
(9/15)
50 50
y
x
yQZ
yf zf
xf
Plane of symmetry
of reflector z
Cross-polar field compensation by using the conjugate
matched feed array
Diagonal-fed configuration
Horizontal co-polar component in the QZ
yf
xf
φ
φ
Feed axis XQZ
Eco
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The conjugate matched feed array – concept
(10/15)
51
180°
0°
Phase shift (wrt co-polar phase)
51
Cross-polar field compensation by using the conjugate
matched feed array
Diagonal-fed configuration
Horizontal co-polar component in the QZ
The conjugate matched feed array – concept
(11/15)
52 52
Cross-polar field compensation by using the conjugate
matched feed array
Diagonal-fed configuration
Horizontal co-polar component in the QZ
Amplitude Amplitude
-30 -60 [dB]
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1/27/2015
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The conjugate matched feed array – concept
(12/15)
53
y
x
yQZ
yf zf
xf
Eco
z
Plane of symmetry
of reflector
φ
53
Cross-polar field compensation by using the conjugate
matched feed array
Diagonal-fed configuration
Vertical co-polar component in the QZ
xf
yf φ
Feed axis XQZ
The conjugate matched feed array – concept
(13/15)
54 54
Amplitude
Cross-polar field compensation by using the conjugate
matched feed array
Diagonal-fed configuration
Vertical co-polar component in the QZ
180°
0°
Phase shift (wrt co-polar phase)
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The conjugate matched feed array – concept
(14/15)
55 55
yQZ
yf
xf
Amplitude
Cross-polar field compensation by using the conjugate
matched feed array in uncompensated dual-reflector CATR
Horizontal co-polar component in the QZ
Reflector S Cylindrical parabolic
reflector wrt vertical plane
Reflector M Cylindrical parabolic
reflector wrt horizontal plane
xQZ
The conjugate matched feed array – concept
(15/15)
56 56
yQZ
yf
xf
Amplitude
Cross-polar field compensation by using the conjugate
matched feed array in uncompensated dual-reflector CATR
Vertical co-polar component in the QZ
Reflector S Cylindrical parabolic
reflector wrt vertical plane
Reflector M Cylindrical parabolic
reflector wrt horizontal plane
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
The conjugate matched feed array – simulation
(2/3)
60 60
GO PO
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The conjugate matched feed array – simulation
(3/3)
61 61
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
Proof-of-the-concept measurements
(1/2)
62 62
Single-polarized
[10.0, 12.5] GHz
Measurements (filtered) before compensation
Measurements (filtered) after Compensation
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Proof-of-the-concept measurements
(2/2)
63 63
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