Field theory-based design and optimization of compact multiple gap coupled microstrip filter with loaded stub

This paper presents a field theory-oriented CAD model with a circuit-based optimization algorithm for the design of a class of integrated gap-coupled microstrip filters. These filters consist of multiple stub-loaded line resonators that are coupled through gaps. The proposed technique is based on a platform of unified lumped circuit network characterizing gap-coupled structures. The lumped circuit parameters are accurately obtained by the use of a newly proposed “Short-Open Calibration” (SOC) technique that is self-consistently accommodated in a full-wave method of moments (MoM). A 3-pole bandpass filter with the bandwidth of 1.2% is designed and the prediction of its optimized characteristics agrees well with simulated results from the HP Momentum