On the front-end design of mid-frequency aperture array for square kilometre array

Complementary to the conventional dish radio telescopes, aperture arrays provide a technically attractive approach to achieve a large field of view and flexibility in observational parameters e.g. Sky area vs. bandwidth. Designs of both aperture array elements and overall geometry for the SKA Mid Frequency Aperture Array are presented here, together with resulting trade-offs. The paper reports the latest developments of global efforts on the front-end design of Mid-Frequency Aperture Array, not attempting to make technology selections, as the priority of sciences and the time for implementing Mid-Frequency Aperture Array is yet to be fully confirmed. Different on-going front-end solutions are introduced, particularly crossed ring antenna array with a planar structure is explored in more detail as it is less known in the community. Key performances of the candidate front-end technologies are addressed by examining the prototypes. The objective of the collaborative study is to increase technology readiness for implementation of Mid-Frequency Aperture Array in the future.