Microstrip disk antennas, Part II: The problem of surface wave radiation by dielectric truncation

The far zone fields radiated from a microstrip disk antenna with a truncated dielectric layer were obtained using the cavity model with magnetic side walls, the dyadic Green's functions are stratified media, and the integral representation analysis of the fields in the complex plane. It is shown that the truncation of the dielectric is responsible for the ondulations observed in the radiation patterns of these antennas and that they result from the interference of the space wave fields with those radiated as a consequence of the incidence of the surface wave into the truncation region. It is suggested that this interference problem may be alleviated by truncating the dielectric as far as possible from the antenna elements and by using lower values of dielectric thickness to disk radius ratios
d/a
, and of dielectric relative permittivities
\epsilon_{r}
.