SKA AAVP Antenna Array developments at University of Cambridge
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Transcript SKA AAVP Antenna Array developments at University of Cambridge
Array Antenna Designs for
the SKA-AAlo
Eloy de Lera Acedo
AAVP 2010, Cambridge, UK. 10/12/10
1
SKA-AAlo antenna requirements
Mutual coupling simulation
Bow-tie element design (BLU antenna)
Software validation
A better design: BLU-tooth antenna
Prototypes
Future work and conclusions
Overview
2
Frequency band: 70 - 450 MHz
Dual polarization
Wide field: +/- 45 deg.
Controlled sidelobes
Immersed in an AA sparse/random? array
Sky noise limited
Easily deployable
Low cost
Self-powered elements?
SKA-AAlo antenna requirements
3
Motivation:
◦ Irregular arrays (random, spiral, etc…) are not so easily characterized
with commercial software. It allows us to analyze LNA effects in the EM
simulation.
◦ Based on MoM + MBFs and the interpolation technique presented in
[1], where the computation of interactions between MBFs is carried out
by interpolating exact data obtained on a simple grid. Array size:
SKA-AAlo is OK!
[1] D. Gonzalez-Ovejero and C. Craeye, “Fast computation of Macro Basis
Functions interactions in non-uniform arrays,” in Proc. IEEE AP-S Soc. Int. Symp.,
San Diego, CA, Jul. 2008.
Antenna simulation in AA
environment (Sensitivity)
4
5
2
E MBF ( , ) Esin gle ( , )
e 10 log10
2
max E MBF ( , )
f = 200 MHz
0
-10
-20
dB
-30
-40
-50
-60
MBF + Baselines
Single element pattern + array factor
Error
-70
-80
-40
-20
0
(º)
20
40
6
2
e 10 log10 E mean ( , ) Esin gle ( , )
E-plane
-10
dBW
-20
~ 35 dB
EEP's mean
Single element pattern
Error
-30
-40
-50
-60
-50
0
(º)
50
7
Danzer configuration
1200
Number of elements
1000
800
600
400
200
0
1
1.5
2
2.5
Distance to nearest element normalized to the antenna's diameter D
8
2
e 10 log10 E mean ( , ) Esin gle ( , )
E-plane
-10
~ 15 dB
dBW
-20
-30
-40
-50
EEP's mean
Single element pattern
Error
-60
-50
0
(º)
50
9
Infinite array simulations to optimize the sensitivity of a
unit cell containing a bow-tie antenna.
E-plane +/-45 deg @ 4dB
Size: 60x60x30 cm
Optimization:
Distance between elements
Antenna size
Angle of arms
LNA: Fmin = 0.2 dB, Rn = 10
Ω, Zopt = 200 Ω, Zamp = 200 Ω
o
-2
10
=0
o
= 10
o
= 20
o
[m2/K]
= 30
o
= 40
o
eff sys
= 50
o
A /T
= 60
180
200
220
Freq [MHz]
Bow-tie Low-Frequency UltraWideband antenna
250
270
10
Software validation
11
0
Measurement
Simulation
-5
S /dB
-10
-15
-20
Reflection coefficient – no optimized antenna
-25
0
0.5
1
1.5
2
2.5
3
3.5
Freq /GHz
Common mode issues are important
and can be studied in scaled prototypes.
And scaled prototypes are important!
12
Measured E-plane normalized power pattern @ 910 MHz
0
Measurement
Simulation
Mag /dB
-5
-10
-15
-20
-25
-80
-60
-40
-20
0
Angle /degrees
20
40
60
80
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High gain: As much as +/- 45 deg with around 7 dBi
(in progress). Do we need different?
Easily constructed in a dual pol. configuration.
Close to ground.
Full BW coverage (sky noise limited up to at least 300
MHz).
Improves low freq. T wrt BLU antenna.
Size: 170x170x70 cm
Toothed log-periodic antenna (BLUtooth???)
14
Simulations
LNA: Using 2 Avago atf54143 (50K
min noise temp, Rn = 5 Ω, Zopt =
200 Ω, Zamp = 200 Ω)
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Scaled array
(under construction)
Array characteristics
• Initially 10 elements over a ground
plane. Then: 50 elements, more?
Scaled Array Antenna Positions
1.2
1
• Differential feeding.
P3
P10
Y (m)
0.8
P9
P7
P2
P6
0.6
P8
P1
• Sparse array of single-polarized
antennas?
P5
0.4
P4
0.2
0
0
0.5
1
1.5
2
2.5
Main aims
X (m)
• To validate the home-made MoM
code for full EM simulation of
SKA stations. Code developed by
UCL Belgium and Cambridge.
• Characterization of antenna
elements and mutual coupling.
• Characterization of common–
mode currents.
Prototypes
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Real size array (2011):
Elements:
70-450MHz
Solar panel
Array characteristics
• 8,10? non-scaled elements over a
realistic ground plane (metallic mesh).
• Feed with a SKA differential LNA
and/or a balun+single-ended LNA +
other SKA technology.
• Sparse array
antennas.
of
Power
conditioning
Energy
storage
dual-polarized
Main aims
• To test and characterize real SKA–
AAlo parts: Antennas, baluns-LNAs,
cables, digitalisation, power, backend, etc.
• To do some simple observations
with SKA-AAlo technology in 2011.
ADC: 1GS/s
50-100m all
optical
e/o
Data
e/o
Control
e/o
Sync.
Analogue
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1.
Element candidate getting there.
2.
Infinite array simulations done. Finite array
simulations done*. (effect of LNA in simulations can
what polarization purity do we need?).
(BLU, BLU-tooth –
taken into account). * More need to be done as well. Important:
Accurate simulations of GND, 2-pol and differential feeding.
3.
4.
Build single (scaled?) prototype and measure Z
and pattern done. (To validate simulations).
Build scaled array prototype – under
construction. (Mutual coupling, array performance in
simulations.)
5.
Build real size element array prototype – 2011.
We need: baluns/LNAs, Analogue, ground
plane, cables, power,... And a back-end to test
it. Then: realistic SKA- AAlo measurements
(noise, etc.). What tests do we need and when?
Conclusions and Future work
18
Antenna element is getting close to the
final design.
Prototypes are important. Scaled
prototypes are important! And accurate
measurements as well.
Let’s talk about Sensitivity.
Practical issues NOW: feeding, dual
polarizations, etc.
Frequency range?
FoV?
Conclusions and Future work
19
Thank you
End
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