Constrained optimisation for generating gain‐bandwidth design trade‐offs of wideband unidirectional antennas

Abstract

Broadband unidirectional antennas realised in microstrip technology find applications in many wireless communication systems. One of their design challenges is the necessity of handling multiple performance figures which is difficult when using traditional design methods, largely based on parameter sweeping. This work presents a simple optimisation-based framework that permits generation of gain-bandwidth trade-off designs for this class of antenna structures. The proposed methodology exploits sequentially executed constrained optimisation runs which produce maximum-gain designs across the range of prescribed target impedance bandwidths. To control the latter, design constraints are imposed on the reflection response but also on gain variability to ensure flat in-band characteristics. For the sake of demonstration, an example compact wideband quasi-Yagi antenna is considered for which a set of trade-off designs is obtained with the impedance bandwidth varied from 9 to over 54%, and corresponding gain levels from 7.4 dB to around 5.5 dB, which determines the antenna capabilities in terms of these performance figures. The approach proposed in this work can be utilised as a design aid as well as a tool for quantitative performance comparison of different (alternative) antenna topologies.