Three Approaches to Miniaturize Bandpass Filters in a Coaxial Cavity

For high-power sub-6 GHz communication systems, the miniaturization of filters is an emerging trend. This paper summarizes three strategies for downsizing coaxial cavity filters based on the principle of resonant cavity miniaturization. First, the feed probes are lengthened to reduce the cavity filter's transverse size; second, the coaxial inner conductor is shortened to reduce the cavity filter's longitudinal size; and third, a high dielectric constant dielectric is loaded into the resonant cavity to reduce the cavity filter's overall size. The paper introduces the guiding concepts of the three approaches and validates the viability of the methods using simulation and measurement results.