Optimized design of single feed circularly polarized microstrip patch antennas

Perturbed square ring slot with reconfigurable polarization

“…This technique has the drawbacks of requiring two feed lines as well as a hybrid network of some kind to provide the necessary phase shift. Single feed circular polarization has been realized in microstrip antennas through the introduction of a perturbation in opposing corners of the antenna [5][6][7]. These perturbations introduce a second near-degenerate mode.…”