Triple-Mode Wideband Bandpass Filter Using Stub-Loaded Resonators

This article presents a triple-mode wideband filter using stub-loaded resonators (SLR). The structure of the filter is simple. Two metal cylinders are loaded in a rectangular cavity to form a SLR, in which the vertical metal cylinder is short-circuited with the top wall of the cavity, and the horizontal metal cylinder is short-circuited with the side wall of the cavity. The probe and SLR feed three new TEM resonant modes. The center frequency and FBW of the filter are 4.285GHz and 50.6%, respectively. The lowest resonant frequency of the rectangular cavity is 8.89GHz, so the filter realized minimization. Adjusting the height of the vertical metal cylinder can influence the resonant frequency of mode 1 and mode 3, resulting the bandwidth is adjustable. The coupling matrix of the filter is synthesized, and the synthesized result are in good agreement with the simulated result.