Reduction of grating lobes for slot antenna array at 60 GHz using multilayer spatial angular filter

A 2 × 2 planar slot antenna array is designed at 60 GHz. The slots are excited by a printed corporative feeding network based on the ridge gap waveguide (RGW) technology. Such a network, requires more than a full wavelength spacing between the slots, which cause excitation of undesired grating lobes. In order to reduce the grating lobes level, multilayer dielectric superstrates are placed above the slot antenna array. The multilayer superstrates act as a spatial angular filter, which filters out antenna radiation except in the main beam region. In the case of placing the 2×2 array elements, 1.1λ apart, numerical results show that the grating lobes are significantly reduced outside the ± 26° range.