PARALLEL-PLATE MODE SUPPRESSION IN A SLOT-COUPLED MICROSTRIP ANTENNA WITH A TRIPLATE LINE FEED

A triplate type slot coupled microstrip antenna provides an antenna fo r which the feed circuit can be multilayered. In this paper, we presen t an analytical discussion concerning suppression of leakage power in the parallel plate mode. The method of analysis used is the spectral d omain moment method, for which a full-wave analysis is possible. It is shown that the rate of the parallel plate mode versus the input power takes a minimum at the resonant frequency of the patch itself due to the series resonance of the patch. This phenomenon is discussed by mea ns of an equivalent circuit. The input impedance at this resonant freq uency is low, so that matching cannot be obtained by the adjustment of the element alone. In order to use the above phenomenon as a suppress ion method for the parallel plate mode, a structure with a parallel st ub is proposed. It is experimentally demonstrated that this structure is effective for suppression of the parallel plate mode. (C) 1998 Scri pta Technica.