Compact Dual-band Bandpass Filter Based on Dual-coaxial Resonators

keywords:dual-band bandpass filter  double coaxial resonator  compact size  controllable frequency  controllable bandwidth

Abstract:A compact dual-band bandpass filter based on dual-coaxial resonators is proposed in this paper. The dual-coaxial resonator is constructed by embedding one coaxial resonator into the other one, where the conductive post of one coaxial resonator acts as the metallic shielding of the other resonator. Accordingly, a dual-mode resonator is obtained almost without increasing the size as compared to the conventional single-mode coaxial resonator. By investigating the control of resonant frequencies of the dualcoaxial resonator and the control of coupling coefficient between two resonators, separate control of the excitation of two resonant modes and the coupling coefficient between two resonators are achieved. Then, a dual-band bandpass filter with controllable passband frequencies and bandwidths is realized. The measured center frequencies are 2. 73 GHz and 3. 19 GHz, the insertion losses are 0. 92 dB and 0. 75 dB, and the 3 dB fractional bandwidths are 5. 0% and 3. 4%. A transmission zero is generated at the frequency between the two passbands, achieving a good dual-passband filtering response.