Nonseparable Nth-band filters as overlapping-subarray tapers

In a receive array "overlapped subarrays" refers to an array output formed as a weighted sum of subarray outputs themselves formed as identically weighted combinations of the outputs of overlapping element subsets. The system array factor becomes a product of two array factors with different periods, one associated with each sum, just as the frequency response of a two-stage IFIR filter in a DSP system is the product of two frequency responses with different periods. It is well known that an Nth-band filter can be the most efficient choice for an IFIR filter\´s first stage, but the corresponding array idea appears unknown. Design examples apply modern optimization to nonseparable tapers, with three of four examples featuring Nth-band subarray tapers. Whether an Nth-band approach is best is not settled here and is properly context dependent: designs should be carried out both ways and compared. Further, a very small subarray taper can easily be Nth-band entirely by accident, so designers should be aware of the associated array-factor features that necessarily result and cannot be optimized away.