Feed reactance of rectangular microstrip patch antenna with probe feed

The input impedance of a microstrip patch antenna is an important design parameter, which controls the radiated power and impedance bandwidth. In the case of a probe fed patch antenna, the total input impedance consists of the probe reactance in series with the patch impedance. Good models for calculating patch impedance are available, but models for the probe feed appear to consider only the inductive reactance. The authors show that the total feed reactance in fact consists of two components i.e. the inductive reactance of the probe plus the capacitive reactance between the patch and the ground plane. The results show that when both the reactance components are taken into account, the agreement between the calculated and measured results is excellent