Planar/Waveguide Quasi-Elliptic Linear-Phase Filters Using Mixed Cascaded Frequency-Dependent Triplets With Extracted Pole Sections

This article presents two types of planar/waveguide quasi-elliptic linear-phase filters using mixed cascade frequency-dependent triplets (FDTs) and extracted pole sections (EPSs). Specifically, we propose the circuit synthesis and planar/waveguide realization techniques for quasi-elliptic linear-phase filters using the cascaded FDT and EPS. The circuit synthesis for the proposed filters avoids the complex matrix rotation and special scaling procedures compared with the general matrix synthesis and is directly compatible with lumped-element-based integrated circuit design. Besides, it permits cascading of FDTs and singlet sections thus effectively forming the pseudo-elliptic filter with a linear phase. For physical realization, we present new TEM- and TE-mode coupling configurations, and therefore, the mathematical models can be realized in practice with simple and practical structures. Finally, we present the complete design procedures of the planar configuration cascading two FDTs and waveguide structure cascading two EPSs and FDT to validate the theory.