Thinned Planar Aperture Array with High Polarization Purity for SKA

Abstract

APID5181637. For large scale array applications such as the Mid-Frequency Aperture Array (MFAA) of the Square Kilometre Array (SKA) telescope, a regular type grid can result in over 20 million array elements to fulfill the sensitivity requirement. Such a fully filled array has an essentially flat effective area with frequency and can provide excellent control of the radiation pattern, particularly the sidelobe level (SLL). Thinning techniques undersample the aperture to reduce the number of elements required, and hence overall system cost, whilst maintaining angular resolution. In principal, the effective area now becomes a function of frequency, depending on the number and type of elements used and their layout. This is also true of sidelobe levels, particularly at wider angular regions. Initially a mathematical model on aperture arrays has been used to develop the thinning algorithms with the goal of exploring how much thinning could be used without significantly effecting the fully filled array performance for a MFAA application. The robustness of the thinning strategy developed is verified by a full wave simulation on finite array using a broadband planar interconnected array approach. This type of array lends itself to economic production of large scale arrays. A thinned array version can in principal be easily implemented although has not been previously reported in the literature. It is confirmed that the total number of elements can be reduced by 7% without a significant impact on overall array performance compared to a fully filled array. Polarization purity is one of the most stringent requirements for future radio telescopes. The polarization performance of the thinned planar array is analyzed including the intrinsic cross polarization ratio and the polarization orthogonality.