Explicit Size-Reduction of Circularly Polarized Antennas Through Constrained Optimization With Penalty Factor Adjustment

Marzieh Mahrokh,Slawomir Koziel

doi:10.1109/access.2021.3114996

Abstract

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.

Highlights

With the growing demands for reliable high-capacity data transfer, an increasing attention has been given to incorporation of circular polarization (CP) antennas into modern communication systems
The continuing trend towards miniaturization enforces CP antennas to be compatible with space constraints in applications such as Aerospace and Synthetic Aperture Radar (SAR) [3], Global Positioning System (GPS) [4], picosatellites [5], 5G communication systems [6], or wearable and on-body devices
The verification case studies include two CP antennas optimized for minimum size with the constraints imposed on their axial ratio and reflection responses

Summary

INTRODUCTION

With the growing demands for reliable high-capacity data transfer, an increasing attention has been given to incorporation of CP antennas into modern communication systems. Several miniaturization techniques based on topological modifications of the antenna structure have been proposed, including the use of slots and fractals [7], defected ground structure [8], fractal metasurfaces and fractal resonators [9], or mushrooms and reactive impedance surfaces (RIS) [10] These techniques have been successful in working out a compromise between the compact size and performance figures of CP antenna. Therein, properly quantified constraint violations appear as additional terms complementing the main objective The efficacy of this approach relies on the proper adjustment of the penalty factors. Other approaches include feasible space boundary exploration procedure [26], or alternating the sizereduction- and constraint-improvement-oriented search steps [27] In all these cases, the performance of the optimization process depends on a proper manual selection of the penalty factors. EXPLICIT SIZE-REDUCTION THROUGH CONSTRAINED OPTIMIZATION This section recalls a formulation of EM-driven antenna size reduction problem, as well as outlines the standard trustregion-based algorithm employed as the main optimization engine

PROBLEM FORMULATION

TRUST-REGION GRADIENT BASED ALGORITHM

DEMONSTRATION CASE STUDIES

CONCLUSION