Analysis of Low Frequency Phased Array Stations Dr. Nima Razavi-Ghods Dr. Eloy de Lera Acedo Cambridge AAVP 2010, 09/12/10 1

Overview Phased array design parameters AA-lo station configuration studies (regular vs. random) Randomisation of elements Simulations to compute T A and A/T (geometries, weighting, element types) Future work and conclusions 2

Factors Affecting Beam on the Sky Array size (fundamental limit on Aeff/Tsys) Array geometry (main and side-lobe profile) ◦Fully filled grids (regular lattice) ◦Sparse or thinned grids ◦Truly randomised grids Antenna element response (scan/polarisation response, matching, mutual coupling) Operating frequency, processing bandwidth, integration time Weighting schemes (main beam and side-lobe profile) ◦Spatial windows (e.g. Hamming, Gaussian, Kaiser) ◦Side-lobe profile control (e.g. Dolph-Chebyshev/Taylor, Fourier design method) ◦Adaptive nulling Back-end processing ◦Fully digital core (any weighting in single or multiple stages) ◦First level analogue (some limitations in response)

Antenna Array Geometries 4

Random Vs. Regular 5 Sky (Haslam) Lat = 28.59S, Long = E Date: 01/01/2020, Time 19.33h Triangular Lattice Beam 10,000 elements, d = 0.8

Random Vs. Regular 6 Sky (Haslam) Lat = 28.59S, Long = E Date: 01/01/2020, Time 19.33h Random Lattice Beam 10,000 elements

Randomised Array: AA-lo 7 d = /3 : 2

Randomisation algorithm 8 Fixed min. distance Variable min. distance

Simulations to compute T A 9 T A was analysed as the beam tracked 3 cold patches on the sky over four and half hours. Array factor based simulations carried computed using NFFT. AA-lo Station ~10k elements. 6 Geometries: regular, triangular, sparse random, thinned, concentric rings, and fully random. 4 minimum inter-element separations: 0.5, 0.8, 1, 2. 3 Weights: Uniform, Taylor and Dolph-Chebyshev (SLL = 35 dB) 3 Element types.

SKA AA-lo observable Sky 10 Region 1: 09 h 07 m 12 s 0000’46’’, Region 2: 04 h 03 m 36 s -3448’00’’ Region 3: 04 h 45 m 00 s -6100’00’’ R1 R2 R3

Results for T A : Region 1 11

Results for T A : Region 2 12

Results for A/T: Region 1 13

Results for A/T: Region 2 14

Taylor Weighting (SLL = 35 dB) 15

16 AA-lo Observable Sky

Low Gain vs. High Gain Element 17

Xarray Tool: MATLAB GUI 18

Future work and collaborations Main objective: SKA simulator Faster and more accurate simulations of the station beam based on MBF approach (collaboration with UCL). Computation framework for station simulator (collaboration with Oxford). Further analysis of beam synthesis techniques and weight calibration. Design of optimal geometry, e.g. far out versus close in side-lobes. 19

Thank You. 20