Waveguide modal analysis of single and stacked probe-fed microstrip antennas with circular geometries

This paper presents a waveguide modal analysis of single and stacked microstrip antennas with circular geometries. Single and stacked circular, annular-ring, and annular-ring-loaded circular microstrip antennas fed by an off-centered coaxial line are considered. Both the substrate and superstrate are assumed to be uniaxially anisotropic. The waveguide modal analysis is realised by introducing a large cylindrical wall to enclose the patch antenna. The effects of the feeding probe and the finite thickness of patches are rigorously taken into account in the analysis. Moreover, it is also an efficient technique since the complicated multilayered microstrip antenna problem is simply treated as a waveguide junction cascading problem, which can be efficiently solved by the modal expansion method. Numerical results for the input impedance of single and stacked circular and annular-ring-loaded circular microstrip antennas are compared with experimental data measured by others. Good agreement is achieved.