Ferrite Tuned Dual-Mode Dielectric Resonator Filters

This paper is devoted to the design of a novel technique for ferrite tuning of dielectric loaded, dual-mode cavity filters. This is dealt with in two specific areas: i) Improving the technique to realize a high -Q, low loss, dielectric-loaded, dual-mode cavity band-pass filter, using the hybrid HEM_11delta mode, ii) Developing techniques to obtain a wide range tuning mechanism, using ferrite materials. The designed dual-mode filters offer unloaded Q_u of more than 10,000 with an insertion loss less than 1 dB. It is shown that ferrite tuning is possible either at below resonance or at the above resonance state, depending upon the strength of the applied DC magnetic field. Experimental results showed that due to its lower saturation magnetization yttrium garnet offers a wider tuning range compared with nickel ferrite. An accurate mathematical model has been developed, for the analysis and study of dielectric resonators, axially loaded with a ferrite rod. The technique presented can also be used to accurately determine the resonant frequencies of different modes of dielectric resonators (including hybrid modes) both of disc or ring form housed in a cylindrical cavity. Theoretical and practical results are in good agreement