Dual-Band Bandpass Coaxial Cavity Filters With Controllable Center Frequencies and Bandwidths Using F-Shaped Resonators

In this study, a novel dual-band bandpass coaxial cavity filter with large design freedoms for center frequencies and bandwidths is proposed by introducing F-shaped dual-mode resonators. Each F-shaped dual-mode resonator is capacitively loaded with two tuning screws for simultaneously tuning two frequencies. A dual-iris structure is implemented for the couplings between the two dual-mode resonators, with two screws applied to enhance the couplings. A dual-disc capacitive coupling is implemented at the input and output ports. By introducing these structures, the frequencies and bandwidths of the two passbands can have large design freedoms. A third-order dual-band filter at 0.845 GHz/1.790 GHz with bandwidths of 12 MHz/26 MHz is also designed, fabricated, and measured. Low insertion losses of 0.4 dB and 0.35 dB are achieved at the passbands. In comparison with planar dual-band bandpass filters, the filter presented in this study offers lower insertion losses and more convenience in filter tuning.