Front-to-back ratio improvement of a microstrip patch antenna using an isolated soft surface structure

A microstrip patch antenna fabricated on a substrate, shows significant performance degradation by surface waves. Particularly when the patch antenna is printed on high dielectric substrates or thick substrate, its front-to-back ratio is considerably affected. Various solutions for the surface wave suppression such as photonic bandgap (PBG), electromagnetic bandgap (EBG), micromachining technology and complex artificial soft surfaces, which requires considerable area to form a bandgap structure. In microstrip patch antenna design, the size of ground plane is limited. To solve this problem, we propose new isolated soft surfaces structure which does not share the ground plane of a patch. By removing the ground plane edges of the patch and forming soft surfaces within the bare substrate, the front-to-back ratio of a patch antenna significantly improved. A numerical investigation is presented for a patch antenna surrounded by the proposed new soft surface structure and the effectiveness of the soft surface in terms of front-to back ratio improvement is verified by its implementation. It is shown that the broadside gain of a patch antenna can be decreased by about 1 dBi while the backside level can be increased by about 11 dBi. As a result, the improvement for the front-to-back ratio of a patch antenna can be increased to about 10 dB through the use of the proposed new soft surface structure.