Low-profile design of dual-frequency and dual-polarised triangular microstrip antennas

A single-feed triangular microstrip patch antenna that can be operated at two distinct resonant modes is proposed. The two resonant modes can radiate an omnidirectional dipole-like pattern with linear polarisation and a broadside pattern with circular polarisation, respectively. To achieve the required frequency ratio of the two operating frequency bands, several designs of the proposed antennas with different substrate thickness and patch sizes are studied. In addition, these designs can easily obtain a 50 (omega) input impedance without any additional matching circuit. Details of the antenna design and obtained performance are presented.