Ferrite tuner with polycrystalline CaV garnet

We made a stripline-type ferrite tuner with polycrystalline CaV garnet at UHF band. The properties of the ferrite disk were first evaluated in a bandstop filter configuration. The effective line width was measured as a function of both frequency and over the band 100-4000 MHz, and we discussed the necessary conditions for making a narrow filter with small insertion loss at low frequency. The coupling theory of the ferrite tuner together with the theoretical equation of the external Q are presented. The experimental values of the external Q almost coincides with the theoretical ones. Tests of this tuner resulted in an insertion loss is 1.9-2.5 dB, a bandwidth of 20-30 MHz, and an attenuation at the image frequency of more than 30 dB. The performance of higher modes is also discussed.