Grating lobe suppression by a parasitic dipole layer over a waveguide transverse slot array with reflection-canceling posts

A unit element consisting of a transverse slot, a post and a pair of parasitic dipoles is proposed for an application in the bore-sight beam antenna array to suppress grating lobes with minimum unit reflection at the waveguide input. The unit is designed with suitable dipole position and dimensions to suppress radiation in the directions of grating lobes in a transverse slot array and with suitable diameter and position of the post to minimize input reflection. The reflection and radiation characteristics of the unit are analyzed by the method of moments (MoM). It is found that larger reflection of a transverse slot can be reduced below -20 dB while its uniform pattern can be suppressed by more than 20 dB in the direction of the grating lobes.