Some methods of analysis of a probe-fed microstrip disk antenna

The authors present three methods (with increasing complexity) of incorporating the gap capacitance of the probe basis into the input impedance calculation of a probe-fed antenna. They are the variational formula, the mode-matching method, and the mode-matching method with a diaphragm. It is noted that in the previous approach the gap capacitance of the probe base that shunts the input impedance of the microstrip antenna is not included in the input impedance. Under the single-mode approximation, the mode-matching methods are identical to the variational formula. However, when a diaphragm is present, the single-mode approximation is insufficient. Therefore, the variational formula is inaccurate when a diaphragm exists. The theory shows that the effect of the gap capacitance at the coaxial aperture on the input impedance of the microstrip antenna is important when the dielectric substrate is thick. The theories agree well with experimental data with no fudge factors.<>