Design guidelines of substrate-integrated cavity backed patch antennas

A set of substrate-integrated cavity-backed patch antennas of alternative topologies is proposed. Using the substrate-integrated waveguide (SIW) technology, the cavity backing the patch is emulated using array of plated through via holes. The proposed topologies have the potential to widen the inherent limited bandwidth of the conventional patch from typically 2% to about 15% depending on the height of the backing cavity. Additionally, the cavity enhances the antenna gain by about 2 dB, as the cavity is very effective in suppressing the unwanted surface waves, thus improving the radiation efficiency. Meanwhile, the proposed SIW topology has a low fabrication cost, as the whole structure could be attained using conventional printed circuit board processing. Design parameters of the SIW cavities are thoroughly investigated in this study, demonstrating their leakage characteristics. Four different structures are investigated corresponding to the different combinations of rectangular or circular patches backed by rectangular or circular SIW cavities. Detailed design guidelines are presented for the SIW cavities to ensure minimum leakage losses and for the radiating elements to achieve a desired fractional bandwidth. Based on experimental prototypes, a thorough comparative study between the four different topologies is presented demonstrating the attractive characteristics of each topology as far as gain, bandwidth, cross-pol level and mutual coupling.