Design of Coupled-Resonator Filtering Network With Asymmetric Arbitrary Group-Delay Response and Frequency-Variant Coupling

A class of RF-analog-signal-processing passive circuits with bandpass filtering behavior and arbitrary prescribed group-delay characteristics is reported. The proposed approach is based on a cross-coupled-resonator network with frequency-dependent coupling to realize both symmetrical and asymmetrical frequency-variation patterns for the phase response. The synthesis procedure exploits a gradient-based optimization technique of the characteristic polynomials and a dispersive-coupling-matrix formulation to achieve the prescribed group-delay function. For illustration purposes, a third-order cross-coupled-resonator filter example in a triplet scheme with one dispersive coupling and linear-type group-delay frequency-variation profile is synthesized. A 2-GHz microstrip prototype of this example is also developed and tested to experimentally verify the devised design principle.