Second-order beams of two-dimensional slot arrays

Second-order beams in the space patterns of two-dimensional slot array antennas may far exceed the sidelobe level and therefore increase the susceptibility of a search radar to jamming or to spurious target echoes. These beams arise from the nonuniform orientation of successive slots; i.e., alternating inclination or displacement with respect to the waveguide axis. In this paper, expressions are derived for the positions of the second-order beams and for their amplitudes relative to the main beam. Experimental verification of these expressions is presented for two-dimensional arrays of edge, series, and shunt slots. Methods for suppressing the second-order beams are discussed.