Designing Cross-Coupled Microstrip Bandpass Filter Based Coupling Matrix Optimization Technique

Abstract

This research article presents a novel compact cross-coupled bandpass filter (BPF) microstrip operating at 1.2 GHz. The proposed filter is designed and developed by coupling the RLC resonator and TL transmission line circuits excited by a symmetrical microstrip feed line (MSL). The fractional bandwidth (FBW) of the filter is found to be 12.83%. The equivalent lumped circuit model of the filter is obtained from AWR Designer. By decomposing the filter into separate entities for individual electromagnetic (EM) simulation via the High Frequency Structure Simulator (HFSS) and the equivalent lumped circuit model of the filter is obtained in AWR designer this approach achieves computational efficiency facilitating the extraction of key parameters aligned to specified general coupling matrix (CM). All these parameters from the overall response of the filter are used in the Chebychev approximation method models at the second and fourth order. The transmission zeros are close to the bandpass edge. The proposed filter has a reflection loss(|S11|) less than -25 dB and an insertion loss (-|S21|) less than 0.21dB. Besides the filter has strong and varying group delay response over the entire bandwidth from 1.15 GHz to 1.3 GHz. The proposed bandpass filter also shows good stopband rejection (being greater than 25 dB) and |S11|< -0.1 dB from 1.35 GHz to 1.75 GHz and sharp decrease in bandwidth at the hard shoulder. All simulated results are extracted via the HFSS simulator method based on finite element FEM. All results produced by AWR design software have a close similarity with the results simulated and optimized by HFSS. © 2024 Elsevier B.V. All rights reserved.