On the Modeling and Multi-objective Optimization Design of Compact Planar Ultra-wideband Impedance Transformer

Abstract

A versatile scheme for design of planar ultra-wideband impedance transformer is proposed by using fragment-type structures (FTS) for modeling and MOEA/D-GO for optimization. To improve the optimization efficiency, non-uniform FTS cells are applied. To find the optimal planar FTS transformer, two objective functions characterizing the return loss and the insertion loss of the impedance transformer, respectively, are defined on a ultra-wide bandwidth. For demonstration, a 25-ohm to 50-ohm FTS impedance transformer is designed, which acquires reflection coefficient lower than -20 dB and extra insertion loss less than 0.27 dB in ultra-wide frequency band of 0.89-5.00 GHz.