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
13





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)
15
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
16

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
17
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
20