Resonant frequency of equilateral triangular microstrip antenna with and without air gap

A tunable equilateral triangular microstrip patch (ETMP) antenna with a variable air gap between the substrate and the ground plane has been studied theoretically and experimentally. Calculated resonant frequencies for different air gap heights have been verified with measurements of a coax-fed antenna. The tunability of the antenna as a function of the air gap height is studied theoretically showing over 200% tunable range of an ETMP with 50 mm side length printed on a substrate with ε_r=10.5. The computed results for the antennas with zero air gap height are compared with a standard spectral domain moment method analysis supported by other previously reported experiments. Very close agreement is revealed in all comparisons.