A low profile cylindrical cavity dual-band bandpass filter with short-circuited metal pillars

This paper presents a low profile cylindrical cavity quadruple-mode dual-band bandpass filter. Five short-circuited metal pillars are loaded in a cylindrical cavity to change the electric field distributions of the original resonant modes. The changed TM010 mode and TM110+ mode form the first passband, and the changed TM110- mode and TM210+ mode form the second passband. The center frequencies of the two passbands are 3.05 GHz and 3.59 GHz, with relative bandwidths of 1.72% and 2.5%, respectively. The first passband can be adjusted independently, and the stopband range of the proposed bandpass filter is relatively wide. By using the degenerate modes, two transmission zeros are introduced to improve the selectivity of the proposed bandpass filter. The use of TMmn0 mode effectively reduces the height of the cavity. The fabricated cavity bandpass filter is measured, and the measured results are accordance with the simulated ones.