An Analysis of Arbitrarily Shaped Microstrip Antennas Including Surface Wave Effects

The accurate determination of surface currents in microstrip planar antennas requires the solution of a two-dimensional singular integral equation of electric type (EFIE). The first problem encountered when solving this equation numerically, is the obtention of a fast and accurate algorithm for evaluating its kernel. This kernel is given by a combination of Sommerfeld-like integrals where the surface wave phenomena are automatically included, and standard computer integration routines are unable to evaluate it. A second problem is the implementation of an efficient moment method. This task is very delicate because the kernel is singular. In particular, the self (diagonal) terms of the moment matrix must be carefully evaluated. Also, the modelling of the coaxial feed probe offers considerable difficulties which have been overcame by using Richmond´s reaction method. This paper presents a coherent numerical approach to solve these problems and to calculate the current distribution in microstrip antennas of arbitrary shape.