Use of Group Delay of Sub-Circuits in Optimization of Wideband Large-Scale Bandpass Filters and Diplexers

A new method is proposed for the design of large-scale wideband resonator-coupled bandpass filters and diplexers. Corrected group delay responses of sub-circuits in combination with space mapping are used to compute the physical dimensions from the coupling matrix model. The coupling matrices are designed using the available theories. The method is based on dividing the structures into many sub-circuits and calculating the group delay responses of the reflection from which the coupling parameters and cavities' resonant frequencies can be extracted. Using a linear space mapping, the structures are optimized efficiently. Depending on the structure's complexity, few to no full-wave optimization is needed to tune the structures to the true designated filtering function. Bandpass filters and diplexers with bandwidths up to approximately 22% have been designed successfully using the proposed approach. A novel stacked cascaded quadruplet filter has been developed using this method. The design of wideband all-pole filters and diplexers are addressed in the paper.