Array Antenna Designs for the SKA-AAlo Eloy de Lera Acedo 1 AAVP 2010, Cambridge, UK. 10/12/10

Overview 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 2

Frequency band: 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

4 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 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

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6 f = 200 MHz

7 E-plane ~ 35 dB

8 Danzer configuration

9 E-plane ~ 15 dB

10 Infinite array simulations to optimize the sensitivity of a unit cell containing a bow-tie antenna. Bow-tie Low-Frequency Ultra- Wideband antenna Optimization: Distance between elements Antenna size Angle of arms LNA: Fmin = 0.2 dB, Rn = 10 Ω, Zopt = 200 Ω, Zamp = 200 Ω E-plane +/-45 4dB Size: 60x60x30 cm

11 Software validation

12 Reflection coefficient – no optimized antenna Common mode issues are important and can be studied in scaled prototypes. And scaled prototypes are important!

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14 Toothed log-periodic antenna (BLU- 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

15 Simulations LNA: Using 2 Avago atf54143 (50K min noise temp, Rn = 5 Ω, Zopt = 200 Ω, Zamp = 200 Ω)

16 Prototypes Scaled array (under construction) 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.

17 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 e/o Power conditioning Solar panel Energy storage Elements: MHz Analogue ADC: 1GS/s Data Control Sync m all optical

Conclusions 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 – 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? 18

Conclusions 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? 19

20 End Thank you