Resonant frequency of higher order modes for circular microstrip antennas

A modified expression for calculating the resonant frequency for higher order modes of a circular microstrip antenna is presented in this paper. It is found that by using the cavity model analysis to calculate the frequency for higher order modes, the frequency difference between the theoretical and measured values increases as the order of the mode increases. This discrepancy is eliminated by generalizing the expression for resonant frequency in the cavity model to include the mode order and thus modifying the effective capacitance used in the analysis. The theoretical results obtained are in excellent agreement with the experimental values.