Low-Profile Miniaturized Coaxial Cavity Resonators and Filters

A new class of coaxial cavity filters with low-profile is proposed. The additional benefits of the technology include: volume reduction, high performance, and superior spurious free-response. The proposed resonator consists of a cavity enclosure and three metallic conductors; an outer hollow cylinder, an inner hollow cylinder protruding the cavity from the opposite side of the first conductor and a third metallic post. The operation principle of the resonator is demonstrated by means of an equivalent lumped element circuit. The circuit allows for a fast and efficient initial design of the resonators. Full-wave optimization is required to produce the final configuration of the filters. Experimental results validate the analysis. The electrical length of the experimental resonators is as low as l0/16. The measured insertion loss of the 5 pole filter is 0.92 dB at 722 MHz. Experimental results show a spurious free response of the order of 7.6 times for the fabricated filter.