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15-08-2011
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Noise Coupling Effects in Aperture Arrays

Submitter: Bert Woestenburg, Laurens Bakker
Description: The effect of noise coupling in aperture arrays, discussed in the AJDI of July 29, 2011 has been studied in more detail. Simulated noise coupling contributions at 1400 MHz for a full two-dimensional scan are presented here for one polarization of the 49-element Apertif array in the two-dimensional plot, showing relatively low noise coupling over a large scan range. One-dimensional scans in the direction with the smallest change in noise coupling (east-west), as well as for the perpendicular direction show that the noise coupling contributions remain below 10 K for scan angles up to 60 in the east-west direction and below 14 K over the full scan range. In the north-south direction a maximum value of 13 K for the noise coupling at 1400 MHz was calculated at 45, increasing to 50 K for scanning near the horizon, illustrated in the accompanying figure.

This result underlines that the increase in measured system noise temperature at large scan angles, discussed in the AJDI of July 29, 2011 is caused by noise pick up at the horizon. With the inclusion of the noise coupling contributions in the model for the aperture array system noise temperature, measured and simulated system noise temperatures for small scan angles are almost identical (within the measurement accuracy of 5 K).

This confirms the validity of the models, with the active reflection coefficient being the only variable as a function of scan angle. More details may be found in a paper by Woestenburg, Bakker and Ivashina, accepted for publication in IEEE Transactions on Antennas and Propagation.
Copyright: ASTRON
 
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