AbstractA formula for the resonance frequencies of circular microstrip patch antennas for 30 TMnmmodes is developed by the curve‐fitting technique from computed data of existing theory. The formula is found to be within about ± 1.3% error of the theoretical results. For this formula, it is not necessary to compute the zeros of the derivative of the Bessel function. The formula is expressed in a simple algebraic form to be appropriate for the computer‐aided design (CAD) of microstrip antennas. © 1993 John Wiley&Sons