Design and Diagnosis of Wideband Coupled-Resonator Bandpass Filters

A method for circuit elements parameter extraction of wideband filters from their electromagnetic (EM) simulated response is presented. A combline-like resonator for filter realization is introduced. Several possible electric and magnetic coupling structures are investigated. The equivalent lumped element circuit has electric and magnetic couplings modeled by capacitors and inductors instead of frequency-independent reactance or impedance inverters. The parameter extraction method of direct-coupled-resonator filters is developed and is applied to symmetric canonical filters. For filters with nonadjacent spurious couplings, optimization is used to extract the lumped element parameters to reproduce the EM simulated response. Excellent agreement between the EM simulation, lumped elements extracted responses and measurements is obtained. Filter synthesis is carried out by an optimization process. Several filter designs are presented to illustrate the design procedure and validate the circuit modeling. Measured results of an eight-pole filter verified the design process.