an antennae system for a detector . the antennae system includes a two - dimensional electro - magnetic transmitter array that has an x number of transmitter elements , and a two - dimensional electro - magnetic receiver array that has a y number of receiver elements . the two - dimensional electro - magnetic transmitter and receiver arrays have a spatial relationship such that at least one subset of the two - dimensional electro - magnetic transmitter and receiver arrays forms a regular array of spatial displacements of z pairwise combinations of transmitter and receiver elements , where z is greater than the sum of x and y .