Configuring a sparse aperture antenna for spaceborne MTI radar

Sparse arrays provide potential for improving the minimum detectable velocity (over 3 m/s improvement for sidelooking radar) of spaceborne moving target indication radar for a given physical aperture. This paper examines the benefits and some of the challenges resulting from employing sparse arrays: grating lobes introduce ambiguities that may create Doppler blind zones; area coverage rate may reduce due to a narrower antenna main beam for coherent transmission; and intrinsic clutter motion may reduce the usable fraction of the Doppler space. We consider the application of orthogonal transmit waveforms to increase area coverage rate, as well as frequency diversity and aperiodic subarray spacings to mitigate Doppler blind zones.