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The purpose of this paper is to introduce a fast and simple method to calculate an estimation of parameters of interest of microstrip antennas, such as the resonance frequencies for example.

The Trefftz collocation method will be used to solve the governing differential equations of the problem. This method uses trial functions that satisfy, in a certain region the governing differential equations. Complete sets of solutions of such equations are required so that completeness and convergence can be guaranteed. The values of the wavenumbers for which the solution of the governing equation is unbounded, are those correspondent to the resonance frequencies of the antenna. After finding the wavenumbers, with the help of empirical correction formulas (because of the effect of the fringing field), the actual resonance frequencies are determined.

The Trefftz collocation method was found to be a very simple, fast and accurate method for the computation of the electric field under the patch of a microstrip antenna. Results obtained from this method showed excellent accuracy with less computational effort than other methods previously used.

Although the resonance wavenumbers may be accurate for any shape of antenna (because of the method convergence), the resonance frequencies might not be so accurate for irregular shapes since the parameters of the empirical formulas are approximated. Also the resonant cavity model is only valid for antennas made of thin substrates.

This formulation of the Trefftz method was for the first time applied to this problem, showing promising results.