Multi-Mode Dielectric Resonator Filters

Abstract

Dielectric resonator (DR) filters are widely used in microwave communications due to their small size and high Q-factor. Multi-mode filters offer a further level of miniaturisation. A new multi-mode dielectric resonator filter is presented in this thesis. The TE11d dual-mode DR offers an 11% size reduction ratio compared with a coaxial air-filled filter with the same unloaded Q-factor (Qu) and about 820 MHz spurious separation from the fundamental frequency 1.95 GHz. Two coupling techniques are applied in the TE11d filter configuration. These are: ceramic puck/probe in contact and etching holes through the ceramic puck for probe installation. A 4th order Chebyshev filter dual-mode DR filter has been simulated and fabricated using each technique. The results show a good agreement between the simulation and measurement with half spurious-free window compared with non-loaded cavity. In the etching method, the spurious-free window and the Qu improved compared with unpatterned ceramic puck. The inline structure filter provides an extra improvement in the spurious window base for the planar configuration. Another approach to the dual-mode DR filter has been studied in this work. A HE11 dual-mode with ceramic puck placed at the base of the cavity presents a good size reduction ratio and acceptable spurious window. The mathematical model shows that transmission zeros (TZs) can be generated in all orientation cases of the inter-resonator coupling hole. The control range of the TZs positions was from 40 MHz from the centre frequency. A good agreement was obtained between the simulation and the measurement results. A triple-mode DR filter with two-piece of the ceramic puck in parallel has been presented. The one cavity approach offers a high Q-factor with 400 MHz suppression. A coaxial probe was used for the input/output coupling and the etching hole through the ceramic puck for inter-resonator coupling. A 3rd order Chebyshev DR filter was simulated and fabricated with two TZs on the upper sideband. The practical results show prospects in application of the filter for miniaturised microwave communications