Analytical Calculation of Impedance Matching for Probe-Fed Microstrip Patch Antennas

The goal of this article is to present an analytical solution to the feeding mechanism for a microstrip patch antenna fed by a vertical probe. The feeding mechanism employs a circular capacitive structure to improve the impedance matching, specifically for microstrip patch antennas on thick dielectrics. A circuit model is introduced to find the design parameters. The circuit model includes a series inductor associated with the feeding probe, a parallel plate radial microstrip line, a series radial gap capacitor and an RLC resonator as the patch antenna. A closed form impedance transformation is generated for the parallel plate radial microstrip line. The result of a Schwarz-Christoffel mapping is used to find the radial gap capacitor. The full-wave simulation and measured results are compared with the model and display good agreement.