Dielectric resonator bandstop filters

Dielectric resonators have been widely employed in wireless and satellite communication systems due to their inherently large Q allowing them to fashion low loss and narrow bandwidth filters. Recent progress has adopted these resonators in applications requiring low volume and mass for demanding specifications. The technology at present consists of an assortment of bandpass filters using dielectric resonators but there is little published material on bandstop filters employing such resonators. Bandstop filters are desirable to suppress frequencies at the front end of wireless communication systems. To meet future demands, it is imperative to reduce the costs of these filters in both volume and weight using dielectric
resonators.

This thesis presents compact mono-mode and dual-mode bandstop dielectric resonator structures. The former consists of a dielectric-loaded waveguide cavity filter that offers a miniaturised version to typical cavity dielectric resonator filters requiring high unloaded Qs. The niono-mode filter described is ideal for relaxed specifications requiring a lower Q resonator to replace common coaxial resonator filters. For applications requiring high bandwidth, this resonator is improved
by coupling a dielectric ring resonator to a coaxial transmission line. A novel dual-mode bandstop resonator is developed taking advantage of the geometry of a cylindrical puck within a single shielded cavity to create two degenerate modes with equal resonant frequency, effectively replacing two mono-mode cavities. Miniaturisation is achieved by sitting the dielectric puck at the base of the
cavity and correct phase separation between the orthogonal modes is produced from a curved uniform transmission line.

The mode behaviour is observed in the physical realisations using a 3D FEM solver. Advanced filtering functions using prescribed reflection zeros is demonstrated with the simulation of a dual-cavity, dual-mode bandstop resonator where inter- and intra- cavity couplings are controlled. The miniaturisation techniques discussed in this thesis will provide cost-reduction for microwave communication
systems requiring high- Q bandstop filters.