Parallel-plate mode suppression in a slot coupled microstrip antenna with a triplate line feed

Experimental and numerical considerations on parallel-plate mode suppression have been performed on a slot-coupled microstrip antenna with a triplate line feed. In the measurements, the effect of multiple reflection of the parallel-plate mode is caused by the edge of the dielectric substrate. We have proposed a technique to solve the problems concerning multiple reflection, and obtained good agreement between measurements and calculations. Measured results demonstrate the effective performance of the configuration with a shunt-stub in the isolated geometries. We have also performed considerations numerically on mutual coupling due to the parallel-plate mode in the array configuration with two elements. Numerical results indicate drastic suppression of the mutual coupling due to the parallel-mode in comparison with the conventional configuration