Modified Compact High-Q Coaxial Cavity Resonator With Its Applications

This article presents a method to modify the coaxial resonator by bending the inner cylinder coaxial into the gradient dumbbell shape coaxial. The new coaxial resonator, gradient dumbbell coaxial resonator (GDCR), could provide very compact sizes while remaining high-quality factors (Q
u
). Then the GDCR resonator was deployed to design a four-pole bandpass filter (BPF) centred at 3.5 GHz with a fractional bandwidth (FBW) of 5.71%, and a pair of symmetrical transmission zeros (TZs) located at 3.27 and 3.64 GHz for demonstration. The TZs were generated by introducing the capacitive-dominant cross-coupling between resonator 1 and resonator 4, which avoids using the support material as the conventional methods. The theoretical responses were also given for comparison, which showed a good agreement with simulated ones.