Microwave Dual-Band Bandpass Planar Filters Based on Generalized Branch-Line Hybrids

A new class of microwave dual-band bandpass planar filter is reported. It uses an original generalized branch-line hybrid topology devised here, operating as dual-passband transversal filtering section. This type of filter network, under feedforward signal-interaction concepts, enables dual-band bandpass filtering actions with transmission zeros to be generated. Some design formulas and guidelines helping to synthesize the proposed dual-passband transversal filtering section are given. Furthermore, to prove its practical viability, theoretical, simulated and experimental results of two manufactured sharp-rejection dual-band bandpass microstrip filter prototypes are shown.