Dielectric resonators with BT (BaTiO₃), TiO₂, and ZrO₂ powders without using the rare earth oxide powders were fabricated for the target relative permittivity of between 30 and 40 and the filter characteristics of metal cavity filter with the dielectric resonators inside were evaluated. Powder characteristics such as particle size distributions and specific surface areas were measured for the composing raw powders to evaluate the powder states. After measuring and comparing the relative permittivity and dielectric losses of the dielectrics of three different compositions, the specific composition was determined (BT:TiO₂:ZrO₂=1:4:1 in mole) and the dielectric resonators were fabricated with that composition, which shows relative permittivity of around 35. The powder characteristics of mixed powders with the determined composition were also evaluated to investigate any agglomerates possibly formed in the process of powder mixing. Dielectric resonators were fabricated by the powder compaction (compaction pressure: 31 MPa) and firing method. The peak firing temperature was 1,300℃ and the holding time at the peak temperature was 3 hours. After firing, cylindrical resonators with one end closed were mechanically machined to eliminate any size differences in dielectric resonator which can be caused by the shrinkage difference during each firing process of resonator fabrication. After measuring the resonator characteristic in the frequency range from 3.6 GHz to 3.8 GHz by changing the height of dielectric resonator, the height of the resonator was determined to be 11.7 mm. Finally, filter characteristics of TM (Transverse Magnetic) mode metal cavity filters with the dielectric inside were measured and evaluated. The metal cavity filters with the dielectric resonators showed the insertion losses of below 1 dB with the band widths of 200 MHz and over 20 dB return losses from 3.6 GHz to 3.8 GHz, whose filter characteristics well satisfied the requirements of the band pass filters for the base stations and it was proved that the dielectrics using the proposed composition could be used as dielectric resonator.
