Compact dual-band bandpass filter using stub-loaded multiple-mode resonator

A compact dual-band bandpass filter using the proposed stub-loaded multiple-mode resonator (MMR) is presented. This MMR is formed by loading three open-ended stubs in shunt to a simple uniform impedance resonator in center and two symmetrical locations, respectively. By properly adjusting the lengths of these stubs, the first two resonant modes of this MMR can be allocated within one band while the third and fourth resonant modes can be allocated within another band. It results in the formulation of a novel dual-band bandpass filter with compact-size and high isolation between passbands by introducing the source-load coupling. Simulated and measured results are found in good agreement with each other, showing high rejection level between passbands.