A High-Power Low-Loss Continuously Tunable Bandpass Filter With Transversely Biased Ferrite-Loaded Coaxial Resonators

This paper presents a technology for high-power lowlosscontinuously tunable RF filters demonstrated by the exampleof a two-pole coupled-resonator filter. The resonators are shortenedcoaxial cavities loaded with ferrite inserts, where an externallyapplied transverse dc magnetic bias controls the center frequency.The filter is analyzed by simulations that take into accountthe inhomogeneity of the bias field. A prototype is manufacturedand tested, exhibiting a tuning span of 41% in which theunloaded factor varies in the range from 1223 to 2425. Goodcorrespondance is observed between simulation and measurementresults. Furthermore, the power-handling capability of the filter isdiscussed and the ionization breakdown limit under normal conditionsis estimated to be 800 W. The filter’s linearity is characterizedby a standard two-tone test, where the level of the third-order passiveintermodulation product is observed to be 53.1 dBm at aninput fundamental tone level of 2 43 dBm.