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 where the mixed boundary value problem is reduced to a set of coupled vector integral equations using the vector Hankel transform. Galerkin's method is employed in the spectral domain where two sets of disk current expansions are used. One set is based on the complete set of orthogonal modes of the magnetic cavity, and the other employs Chebyshev polynomials with the proper edge condition for the disk currents. An additional term is added to the disk current expansion to properly model the current in the vicinity of the probe/disk junction. The input impedance of the stacked microstrip 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 also presented. The calculated results are compared with experimental data and shown to be in good agreement.