On the resonant frequencies of dual-band patch antennas

A square patch radiator supports both TM₀₁ and TM₁₀ modes with equal resonant frequencies. Feeding the patch in its diagonal can excite both modes with equal amplitudes and phases. By utilising this property, an effective technique is proposed to realise dual-band dual-polarised patch antenna. While the lower resonant frequency can be calculated using an existing analytical formula, an expression of the higher resonant frequency is still missing in the literature. To this end, an approximate expression of the higher resonant frequency is devised using the equivalent transmission line model in this work. It is a function of the distance between the shorting post and the feeding location. In order to validate the accuracy of the expression, three different antenna configurations are designed and manufactured. Good agreements between theoretical, simulated, and measured results are observed.