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.

5

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