Automated design of circularly polarized microstrip patch antennas with improved axial ratio

A novel procedure for automated simulation-driven tuning of circularly polarized (CP) microstrip patch antennas (MPA) for improved axial ratio (AR) is presented. Our approach specifically addresses the CP MPAs exited through dual inputs which are driven by branch line couplers of unequal power splits. Our procedure allows for the improvement of AR over the required range of operating frequencies. The procedure, implemented in a part with numerical optimization, is governed by a closed form formulas computing an appropriate unequal amplitude excitation of the MPA of interest. The required excitations are implemented with microstrip branch line couplers. Numerical optimization addresses the effect of coupling (through the feed) of the entire MPA-feed circuit. In this paper, the approach is illustrated with a numerical example of a probe-fed MPA. Moreover, our methodology has also been demonstrated to work for MPAs with open-end microstrip inputs. Numerical validation is carried out using full-wave simulations of the entire MPA-feed circuits.