Topology Optimization of Conical-Beam Antennas Exploiting Rotational Symmetry

Microstrip conical-beam antennas are designed by the topology optimization of metallic patches combining the discrete optimization of vias. The antennas are designed to be angular-periodic structures with eight identical sectors, which makes the rotational symmetric radiation pattern more easily to be achieved and the optimization problem much easier to be solved. A restarting technique is introduced for the circular polarization design case, where the high cross-polarization discrimination (XPD) is hard to be realized. By increasing the weight of cross-polarization penalization function after the optimization restarts, much higher XPD is achieved compared to that of the antennas optimized with fixed subobjective weighting factors. By this method, two conical-beam antennas, which are linearly polarized and left-handed circularly polarized antennas, respectively, are designed. Simulated and measured results show that the antennas have expected conical shape radiation patterns, good matching, and high polarization purities.