New computation of the resonant frequency of a tunable equilateral triangular microstrip patch

A new dynamic permittivity expression is formulated to be used in the cavity analysis to determine the resonant frequency of an equilateral triangular microstrip patch. The proper sidelength extension expressions are given for low and high substrate permittivity cases. Better accuracy with respect to the moment method and other previous models is obtained for various structural parameters and operational modes. The proposed computation is also extended for the analysis of the two-layer structure in order to determine the air-gap tuning effect on the resonant frequency.