Moment method analysis of an aperture coupled microstrip antenna with multilayer superstrate

Microstrip patch antennas are often required to operate in non-homogeneous layered structures, they may, for example, have a single cover layer to protect them from environmental hazards. For the application presented in this paper the antenna is required to operate on the inside of a vehicle windscreen, where the laminated glass acts as a three layered dielectric superstrate on the antenna and will significantly affect its performance. The ideal feed system for this type of antenna is an aperture coupled arrangement which requires no physical contact between the antenna and feed. The microstrip feedline on the lower surface of the bottom substrate is coupled electromagnetically through a small aperture in the ground plane to the patch on the upper surface of the upper substrate. This paper presents a moment method analysis of this structure to determine the input impedance and far field radiation pattern