A ${\rm TM}_{01}$ Mode Monoblock Dielectric Filter

A novel TM₀₁ monoblock dielectric filter is presented in this paper. The proposed filter is made from a single piece of ceramic with silver-plated external surfaces and a metallic lid for hosting tuning screws. The dominant TM₀₁ mode is supported by a centered dielectric rod with one end short-circuited. Not requiring a metallic housing and dielectric resonator mounting fixture, the filter maximizes the space utilization, achieves an optimal Q factor for a given volume, and provides a high mechanical and thermal stability. One prototype filter operating at 2.6 GHz with 50-MHz bandwidth is designed, fabricated, and measured. To demonstrate its superiorities in terms of Q factor and thermal stability, a metal coaxial filter of the same size working at the same frequency and bandwidth is fabricated and measured as well. The measured unloaded Q factor of the monoblock dielectric filter and the metal coaxial filter are about 3000 and 1800, respectively. Furthermore, the frequency drift due to temperature change for the proposed monoblock dielectric filter is -2.7 ppm/ °C while that of its coaxial counterpart is -14.2 ppm/ °C. More detailed design considerations for such monoblock filters are also given.