Enhanced feeds in focal plane imaging array systems: Off focus configurations

The performances of focal plane arrays that implement multi-beam coverage from a single reflector antenna are usually reduced by conflicting requirements on the feed elements. Dense packing is required to minimize the beam separation, while typically large apertures provide the high feed directivity which in turn translates in low spill over losses from the reflector. In this paper the use of a dielectric super-layer is proposed to shape the radiation pattern of each feed so that the spill over from the reflector is reduced without increasing the dimensions of each aperture. A prototype with 19 wave-guides arranged in a hexagonal lattice has been designed. The simulated embedded patterns provide an increase of the edge of coverage gain, with respect to the free space case, of at least 1dB in an operating bandwidth of ap6%. Moreover when a frequency and polarization reuse scheme is adopted the increase in the edge of coverage is 2.1 dB leading to a fully efficient use of the reflector.