Enhancement of circular polarization output in square patch microstrip antennas

FDTD simulations of the resonant modes in microsnip square patch antennas fed by one microstrip line were used to develop antenna designs with enhanced circular polarization (CP). Besides the conventional cut corner, the new designs include additional microstrip supporting the antenna symmetry with respect to the diagonal of the square patch. Analysis of the mode splitting phenomena in the antennas was used to find the optimal corner cut and the feed point location. Measurements of near- and far-fields, as well as axial ratio of the prototypes, confirmed the possibility to obtain with high quality CP in a wide frequency band for the designed antenna.