High Selectivity Cylindrical Cavity Dual-Band Bandpass Filter With Stepped Cylinders

In this brief, a quad-mode cylindrical cavity dual-band bandpass filter (CCDBPF) is proposed. Two stepped cylinders are located at the top and bottom of the cylindrical cavity. Two low-order resonant modes are generated because of two stepped cylinders, and they constitute the first passband. Two high-order modes are the low-order modes of the cylindrical cavity itself, which constitute the second passband. The center frequencies of two passbands are 1.61 GHz and 2.61 GHz, respectively. Two passbands can be independently adjusted. The first passband can be adjusted from 1.55 to 1.67GHz with insertion loss of 0.13-0.15 dB. The second passband can be adjusted from 2.48 to 2.67 GHz with low insertion loss of 0.1-0.2dB. The frequency selectivity is improved because of four transmission zeros (TZs) at 1.49 GHz, 1.89 GHz, 2.52 GHz, and 2.89 GHz. Since the stepped cylinders introduce a low-frequency passband, the miniaturization of the CCDBPF is realized. Finally, the CCDBPF is fabricated and measured. The measured frequency responses are coincident with the simulated results.