Signals and Telecommunication Journal L. Djouablia 1,*, A. Labbani2, A. Benghalia3 4 1 2015 Using a combined approach, the effect of air gap tuning on the resonant frequency and radiation field of an equitriangular microstrip antenna is presented in this paper. An equilateral triangular patch is implemented on an isotropic dielectric with an air gap inserted under this one in order to estimate the influence of an air gap on radiation antenna’s characteristics. The problem is analysed in spectral domain using the moment method and an electric field integral equation combined with a mathematical approach. However, the dyadic Green’s functions corresponding to the proposed structure are developed and the Fourier transform of basis current components are calculated mathematically using “the reference element” method. A numerical result shows that the change in resonant frequency, bandwidth and radiation field of the antenna is due primarily to a small disturbance of the air gap thickness and consequently substrate’s equivalent permittivity.