Triple-Band Cavity Bandpass Filters

This paper presents a new class of cavity-based triple-band filters employing resonators that support three operation modes. The proposed triple-band filters do not require junctions and can achieve an equivalent Chebyshev performance with fewer cavities, thus significantly reducing the footprint when compared to traditional approaches. The filter facilitates a systematic design approach starting from the coupling-matrix generation to the overall response optimization. The concept is potentially applicable to most triple-mode resonators and is demonstrated in this paper using waveguide and dielectric resonators. The first design is an inline structure employing elliptical waveguide cavities, whereas the second design is a folded structure using rectangular waveguide cavities. The third design is implemented by dielectric loaded cavity resonators. All the proposed triple-band filter designs offer high Q and allow for independent control of each frequency and coupling parameter. To verify the concept, three triple-band filter examples with different realizations are designed, manufactured, and tested to allow comparisons.