Input impedance of a probe-fed stacked circular microstrip antenna

The input impedance of a microstrip antenna consisting of two circular microstrip disks in a stacked configuration driven by a coaxial probe is investigated. A rigorous analysis is performed using a dyadic Green´s function formulation whereby the mixed boundary value problem is reduced to a set of coupled vector integral equations using the vector Hankel transform. Galerkin´s method is used in the spectral domain, using two sets of disk current expansions. One set is based on the complete set of orthogonal modes of the magnetic cavity, and the other uses Chebyshev polynomials with the proper edge condition for the disk currents. An additional term is added to the disk current expansion to model the current properly in the vicinity of the probe/disk junction. The input impedance of the antenna, including the probe self-impedance, is calculated as a function of the layered parameters and the ratio of the two disk radii. Disk current distributions and radiation patterns are presented. The calculated results are shown to be in good agreement with experimental data