Explicit Size-Reduction of Circularly Polarized Antennas through Constrained Optimization with Penalty Factor Adjustment

Modern communication systems of high data capacity incorporate circular polarization (CP) as the preferred antenna radiation field configuration. In many applications, integration of the system circuitry with antennas imposes size limitations on CP radiators, which makes their development process a challenging endeavor. This can be mitigated by means of simulation-driven design, specifically, constrained numerical optimization. Majority of the performance-related constraints are expensive to evaluate, i.e. require full-wave electromagnetic (EM) analysis of the system. Their practical handling can be realized using a penalty function approach, where the primary objective (antenna size reduction) is complemented by contributions proportional to properly quantified constraint violations. The coefficients determining the contribution of the penalty terms are normally set up using designer's experience, which is unlikely to render their optimum values in terms of the achievable miniaturization rates as well as constraint satisfaction. This paper proposes a procedure for automated penalty factor adjustment in the course of the optimization process. Our methodology seeks for the most suitable coefficient levels based on the detected constraint violations and feasibility status of the design. It is validated using two CP antenna structures. The results demonstrate a possibility of a precise constraint control as well as superior miniaturization rates as compared to the manual penalty term setup.