array antenna designs for the ska-aalo eloy de lera acedo 1 aavp 2010, cambridge, uk. 10/12/10
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Array Antenna Designs for Array Antenna Designs for the SKA-AAlothe SKA-AAlo
Eloy de Lera Acedo
1AAVP 2010, Cambridge, UK. 10/12/10
OverviewOverview
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
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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 requirementsSKA-AAlo antenna requirements3
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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!
Antenna simulation in AA Antenna simulation in AA environment (Sensitivity)environment (Sensitivity)
[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.
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6
-40 -20 0 20 40-80
-70
-60
-50
-40
-30
-20
-10
0
(º)
dB
MBF + BaselinesSingle element pattern + array factorError
f = 200 MHz
2
2
sin
10
),(max
),(),(log10
MBF
gleMBF
E
EEe
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-50 0 50
-60
-50
-40
-30
-20
-10
(º)
dBW
EEP's meanSingle element patternError
E-plane
2
sin10 ),(),(log10 glemean EEe
~ 35 dB
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1 1.5 2 2.50
200
400
600
800
1000
1200
Distance to nearest element normalized to the antenna's diameter D
Num
ber
of e
lem
ents
Danzer configuration
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E-plane
2
sin10 ),(),(log10 glemean EEe
-50 0 50
-60
-50
-40
-30
-20
-10
(º)
dBW
EEP's meanSingle element patternError
~ 15 dB
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Infinite array simulations to optimize the sensitivity of a unit cell containing a bow-tie antenna.
Bow-tie Low-Frequency Ultra-Bow-tie Low-Frequency Ultra-Wideband antennaWideband antenna
Optimization: Distance between elements Antenna size Angle of arms
180 200 220 250 270
10-2
Aef
f/Tsy
s [m
2 /K]
Freq [MHz]
= 0o
= 10o
= 20o
= 30o
= 40o
= 50o
= 60o
LNA: Fmin = 0.2 dB, Rn = 10 Ω, Zopt = 200 Ω, Zamp = 200 Ω
E-plane +/-45 deg @ 4dBSize: 60x60x30 cm
11Software validationSoftware validation
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0 0.5 1 1.5 2 2.5 3 3.5-25
-20
-15
-10
-5
0
Freq /GHz
S /
dB
MeasurementSimulation
Reflection coefficient – no optimized antenna
Common mode issues are importantand can be studied in scaled prototypes.
And scaled prototypes are important!
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-80 -60 -40 -20 0 20 40 60 80-25
-20
-15
-10
-5
0
Angle /degrees
Mag
/dB
Measured E-plane normalized power pattern @ 910 MHz
MeasurementSimulation
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Toothed log-periodic antenna (BLU-Toothed log-periodic antenna (BLU-tooth???)tooth???)
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
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Simulations LNA: Using 2 Avago atf54143 (50K
min noise temp, Rn = 5 Ω, Zopt = 200 Ω, Zamp = 200 Ω)
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PrototypesPrototypes
Scaled array(under construction)
0 0.5 1 1.5 2 2.50
0.2
0.4
0.6
0.8
1
1.2
Scaled Array Antenna Positions
X (m)
Y (
m)
P1
P2
P3
P4
P5
P6P7
P8
P9
P10
Array characteristics
• Initially 10 elements over a ground plane. Then: 50 elements, more?
• Differential feeding.
• Sparse array of single-polarized antennas?
Main aims
• 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.
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Real size array (2011):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 of dual-polarized antennas.
Main aims
• To test and characterize real SKA–AAlo parts: Antennas, baluns-LNAs, cables, digitalisation, power, back-end, etc.
• To do some simple observations with SKA-AAlo technology in 2011.
e/o
e/o
e/o
Powerconditioning
Solar panel
Energy storage
Elements:70-450MHz
Analogue
ADC: 1GS/s
Data
Control
Sync.
50-100m all optical
Conclusions and Future workConclusions and Future work
1. Element candidate getting there. (BLU, BLU-tooth – what polarization purity do we need?).
2. Infinite array simulations done. Finite array simulations done*. (effect of LNA in simulations can taken into account). * More need to be done as well. Important: Accurate simulations of GND, 2-pol and differential feeding.
3. Build single (scaled?) prototype and measure Z and pattern done. (To validate simulations).
4. 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?
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Conclusions and Future workConclusions and Future work
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?
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20EndEnd
Thank you