A modified transmission line model for cavity backed microstrip antennas

Spatial power combining of many MMIC amplifiers at millimeter wave frequencies using a fixed array of microstrip antenna elements places unique demands on the dielectric media. The substrate must be relatively thick to allow space for MMIC placement, must provide rather high thermal conductivity to dissipate MMIC heat, and be of high dielectric constant to shrink the circuit element dimensions. Presently, microstrip antenna models require a low dielectric constant substrate to be valid. This paper presents a modified transmission line model based on the model of Pues and Van de Capelle (1984) which addresses the problems of thick, high dielectric constant substrates as applied to proximity coupled, cavity backed microstrip antenna elements. The goal of the model was to guide the design of a microstrip array antenna suitable for a spatial power combined module.