Dual-band microstrip coupled filters with hybrid coupling paths

This work proposes a novel dual-band microstrip coupled filter based on the traditional single-band coupled filter theory. This filter has a single set of resonators arranged carefully to generate different coupling paths at the two bands, such that the filter of each band can be designed independently. A dual-band transformer that matches different load impedances at the two bands is also developed for application in a tapped feed configuration, thus introducing an extra controllable transmission zero. Simulation and measurement results of a dual-band filter operated at 2.4 and 5.2 GHz demonstrate that the proposed filter is feasible.