Dielectric resonance in nickel ferrite for K and Ka-band filters

Abstract

The nature of dielectric resonance and its utility for a magnetic field tunable band-pass filter have been studied in a polycrys- talline disk of nickel ferrite. The lowest order dielectric resonance mani- fests as two modes corresponding to clockwise and counter-clockwise polarization of the microwave fields. Under the influence of a static magnetic field perpendicular to the disk plane, one of the modes show a decrease in frequency whereas the other shows an increase in frequency. With increasing H, the frequency separation increases. Band-pass filters for operation at 19, 30, and 35 GHz have been designed and character- ized. The filter central frequency has been controlled with proper choice of disk dimensions. The filter frequency is tuned with H, by 2-7%. As the filter frequency is well above the ferromagnetic resonance frequency expected for the static magnetic fields, the overall losses are small with the insertion loss ranging from 2 to 5 dB. Theoretical estimates of H- tuning of dielectric resonance and pass-band are much higher than measured values, indicative of potential for further improvement in filter performance. The ferrite filters are of importance for use in the K and Ka-band communication devices. V C 2014 Wiley Periodicals, Inc. Micro- wave Opt Technol Lett 56:814-818, 2014; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.28195 tunable band-pass filter in the K- and Ka-frequency bands are discussed here. The filter has the advantage of low insertion loss, ranging from 4 to 6 dB, and excellent power handling capability (expected for dielectric resonators) and moderate H- tuning that is possible only for ferrites. The filter can be tuned by 2-7% of the central frequency with H. A theory is discussed here for H-tuning of the ferrite dielectric resonator and tuning of the filter pass-band. It is shown that estimated tuning ranges are much higher than the measured values and could be indicative of potential for further improvement in the tuning range and characteristics of the filter. 2. EXPERIMENT