Microwave transversal six-band bandpass planar filter for multi-standard wireless applications

An approach to design microwave multi-band bandpass planar filters with an arbitrary number of passbands is proposed. It is based on the generalization of a previously-reported transversal filter structure to synthesize multi-band responses. This filter topology, by means of signal-interference techniques, allows frequency-selective transfer functions with multiple passbands separated by inter-band transmission zeros to be derived. Analytical equations and guidelines for the theoretical design of the described multi-band bandpass filter configuration are given. Moreover, its practical viability is verified through the construction and testing of a six-band bandpass microstrip prototype. To the authors' knowledge, no other filter solution with such a plurality of passbands has been experimentally proven to date.