A Dual Polarised Wideband Planar Phased
Array for Radio Astronomy
Dr David Zhang and Prof. A. K. Brown
School of Electrical and Electronic Engineering
The University of Manchester
Email: david.zhang@manchester.ac.uk
NAM 2012, 27-30 March 2012
The University of Manchester
Outline
A brief review of wide-band aperture array
antenna design
AA-mid Antenna design for PrepSKA
Conclusions and future work
NAM 2012, 27-30 March 2012
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The SKA mid-frequency array
• The requirement is for approaching two octaves
of bandwidth (400MHz to 1.4 GHz)
• A scan angle of at least +/-45degs
• Polarimetry is required on the radio astronomical
sources so that two orthogonal polarisations are
needed
NAM 2012, 27-30 March 2012
The University of Manchester
A brief review of wide-band aperture
array antenna design
NAM 2012, 27-30 March 2012
The University of Manchester
• Three structures have been compared in both theory
and in hardware:
– Vivaldi antenna
• A structure developed by ASTRON using a thin metallised foil
known as FLOTT
– A modified Bunny Ear antenna incorporating comb line
chokes[1]
• All aluminium laser cut structure
– A planar antenna using coupled ring radiators termed ORA
(Octagonal Ring Antenna,[2])
• Implemented using polystyrene dielectric and thin copper radiating
rings
1.
2.
Y. Zhang, A. K. Brown, “Bunny Ear Combline Antennas for Compact Wide-Band Dual-Polarized Aperture Array,”
IEEE Transactions on Antennas and Propagation, Vol. 59, No. 8, pp. 3071-3075, August 2011.
Y. Zhang, A. K. Brown, “Octagonal Ring Antenna for a Compact Dual-Polarized Aperture Array,” IEEE
Transactions on Antennas and Propagation, Vol. 59, No. 10, pp. 3927-3932, October 2011.
NAM 2012, 27-30 March 2012
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Aperture Array Antennas
Operating frequency band:
300MHz-1GHz, ±45o scan angle
FLOTT: (a)(d)
BECA: (b)(e)
ORA: (c)(f)
NAM 2012, 27-30 March 2012
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Active reflection coefficient
0
FLOTT
BECA
ORA
Reflection coefficient (dB)
-5
-10
-15
-20
-25
-30
-35
0.25
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0.4
0.6
0.8
Frequency (GHz)
The University of Manchester
1
Three candidate designs
(16×
×16 finite arrays)
FLOTT
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BECA
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ORA
Cross polarisation in the intercardinal plane
at 1 GHz, based on the finite array
measurement for the centre element
0
ORA
FLOTT
BECA
Cross polarisation (dB)
-5
-10
D-plane
45o Cut
-15
-20
-25
-30
-35
0
5
10 15
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20 25 30 35
Angle (deg)
40 45 50 55
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60
0
0
-1
-1
-2
-2
Log Mag (dB)
Log Mag (dB)
Scanned element pattern for the
centre element of the finite array
-3
FLOTT, 1 GHz, Simulated
FLOTT, 1 GHz, Measured
BECA, 1 GHz, Measured
ORA, 1 GHz, Measured
FLOTT, 700 MHz, Measured
-4
-5
-6
-50
-40
-30
-20
-10
0
10
Angle (deg)
20
FLOTT, 1 GHz, Simulated
FLOTT, 1 GHz, Measured
BECA, 1 GHz, Measured
ORA, 1GHz, Measured
FLOTT, 700 MHz, Measured
-4
-5
30
E-plane (0o Cut)
NAM 2012, 27-30 March 2012
-3
40
50
-6
-50
-40
-30
-20
-10
0
10
Angle (deg)
20
30
H-plane (90o Cut)
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40
50
Design Summary
Tapered slot antenna shows a higher cross
polarization in the inter-cardinal plane (45o-plane)
A long tapered slotline is needed to produce a
broad frequency bandwidth, as a result, the
radiation pattern can be narrow at the high end of
frequency band
ORA exhibits a broad radiation pattern and a
smooth cross polarisation performance over the
entire scan range
NAM 2012, 27-30 March 2012
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AA-mid Antenna Design for PrepSKA
The target Operating frequency band:
400MHz-1.4GHz, ±45o scan angle
NAM 2012, 27-30 March 2012
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The element separation for the AA-mid aperture array
The feeding methods of ORA
The ORA finite array analysis
NAM 2012, 27-30 March 2012
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Maximum element spacing (mm)
Element separation for AA-Mid
250
240
230
λ/(1+sinθmax),θmax=30
o
o
ORA element spacing with 30 scan
220
210
200
λ/(1+sinθmax),θmax=45
o
o
ORA element spacing with 45 scan
190
180
170
160
150
140
130
120
110
100
0.8
0.9
1
1.1
1.2
1.3
1.4
High frequency (GHz)
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The maximum
element spacing in
the array is limited
by the appearance of
grating lobes, and
the electromagnetic
interactions between
the elements with
scan, the resulting
numbers are not
normally the same
The infinite ORA array with
125 mm element separation
0
Broadside
27o Diagonal plane
-5
36o Diagonal plane
Reflection coefficient (dB)
-10
45o Diagonal plane
-15
-20
-25
-30
-35
-40
-45
0.3
0.4
0.5
0.6
0.7
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0.8 0.9
1
Frequency (GHz)
1.1
1.2
1.3
1.4
1.5
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The infinite ORA array with
125mm element separation
0
Reflection coefficient (dB)
-5
-10
-15
-20
-25
-30
-35
Broadside
-40
45o E-plane
-45
0.3
45o H-plane
0.4 0.5
0.6 0.7
0.8 0.9 1 1.1
Frequency (GHz)
1.2
1.3 1.4
1.5
400MHz-1350MHz, maximum 45o scan angle
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The infinite ORA array with 112
mm element separation
0
Broadside
Reflection coefficient (dB)
-5
-10
45o E-plane
45o H-plane
-15
-20
-25
-30
-35
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5
Frequency (GHz)
450MHz-1400MHz, maximum 45o scan angle
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Feeding methods for ORA
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Coplanar waveguide feed for
EM measurements, SKADS
50 ohms single-ended
output, feasible for
radiation pattern
measurement, but this
balun can be lossy!
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Single-ended and differential
feeding methods
The single-ended stripline
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Differential coaxial cable feeding
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ORA performance with 50ohms
stripline feed, 112mm
0
Reflection coefficient (dB)
-5
-10
-15
-20
-25
Broadside
-30
45o E-plane
45o H-plane
-35
0.3
0.4
NAM 2012, 27-30 March 2012
0.5
0.6
0.7
0.8 0.9
1
1.1
Frequency (GHz)
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1.2
1.3
1.4
1.5
ORA performance with
differential coaxial cable feeds,
112mm element spacing
0
Broadside
Reflection coefficient (dB)
45o E-plane
-5
45o H-plane
-10
-15
-20
-25
0.4
0.5
NAM 2012, 27-30 March 2012
0.6
0.7
0.8 0.9
1
Frequency (GHz)
1.1
The University of Manchester
1.2
1.3
1.4
The ORA Finite Array Analysis
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The passive reflection coefficient
for ORA with the stripline feed
0
The centre element in a
5×5 array with all the rest
elements are loaded
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Reflection coefficient (dB)
5 × 5 finite array, the centre element
-5
-10
-15
-20
-25
-30
0.4
0.5
0.6
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0.7
0.8 0.9
1
1.1
Frequency (GHz)
1.2
1.3
1.4
Surface current on the conducting
sheets for a single element excitation
400MHz
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900MHz
1400MHz
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Single-ended Stripline feed for the 5×5
subarray of the 10×10 finite array tile
The active reflection coefficient
0
Active reflection coefficient (dB)
-5
-10
-15
-20
-25
-30
-35
-40
0.4
NAM 2012, 27-30 March 2012
5 ×5 finite array, simulated
infinite array, simulated
5 ×5 subarray in a 10×10 finite array, measured
0.5
0.6
0.7
0.8 0.9
1
Frequency (GHz)
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1.1
1.2
1.3
1.4
Differential feeding method, passive
reflection coefficient measured
Element 13
Element 1
0
Element 13
Element 1
Reflection coeffcient (dB)
-5
-10
-15
-20
-25
-30
-35
0.4
NAM 2012, 27-30 March 2012
0.5
0.6
0.7
0.8
0.9
1
Frequency (GHz)
The University of Manchester
1.1
1.2
1.3
1.4
Conclusions
• Three different structures have been designed and
performance compared
– The Vivaldi is well known and provides broadband performance
• It suffers from potentially high cross-polarisation in the inter-cardinal planes
• Care must be taken to avoid narrow frequency resonances in the input
impedence
– BECA offers slightly improved cross polarisation and less
susceptibility to input resonances but is potentially more
complex
– ORA provides a planar array alternative which is promising, has
low scan loss and lower cross-polarisation with potentially
simpler construction but requires further investigation for large
scale manufacture
NAM 2012, 27-30 March 2012
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Thank you very much!
NAM 2012, 27-30 March 2012
The University of Manchester