Microstrip disk antennas. I - Efficiency of space wave launching.

The behavior of space, surface and leaky waves in microstrip antennas and the effects on the efficiency of space wave launching are studied theoretically, along with the effects of the physical characteristics of the dielectric layer over the antenna ground plane. Since the waves are excited in an antenna substrate, the radiated fields are expressed in terms of the cavity model with magnetic sidewalls and dyadic Green's function in stratified media. The contributions of space and surface waves are quantified and efficiency and directivity values are determined as functions of the antenna dimensions. Truncations in the dielectric are shown to cause undulations in the antenna radiation patterns, arising from the interference of space wave fields with fields produced when the surface wave is incident in the truncation region. Truncating the dielectric as far as possible from the antenna elements and implementing lower dielectric values in the disk radius ratios and the dielectric relative to the permittivities could reduce the interference problem.