Synthesis of Cross-Coupled Resonator Filters With Frequency-Dependent Coupling Using Comprehensive Learning Particle Swarm Optimization

This paper presents the synthesis of cross-coupled resonator filters with frequency-dependent coupling. The elements of the coupling matrix are found using comprehensive learning particle swarm optimization (CLPSO). The application of CLPSO in filter synthesis is illustrated with four examples involving third- and fourth-order generalized Chebyshev filters with frequency-dependent cross-coupling where the resonators are arranged in triplet and quadruplet configurations. An extra transmission zero (TZ) can be produced below or above the passband by introducing frequency-dependent coupling in comparison to classical approaches. The frequency responses of the synthesized filters are presented.