A Rapid Method for Arbitrary Microstrip Structures using the FFT-Algorithm

A rapid method is presented to calculate microstrip structures with arbitrary shape embedded in multilayered dielectric. The current is divided into small rectangular subdomains and is approximated with triangular basis functions in x- and y- direction. A modified Galerkin procedure is applied in spectral domain. The coupling integrals of the generalized impedance matrix are split into a very fast converging part and a remainder, which is solved by the FFT procedure. The method is applied to edge coupled microstrip antennas but is also capable to deal with arbitrarily shaped microstrip structures. The time saving factor is about 10 compared to the conventional numerical integration. Current distribution and input impedance is derived. Accuracy of the computed techniques presented is verified experimentally.