Microwave Cavity Filters are widely used in RF systems for high Q signal filtering. But their bulky sizes at lower operating frequencies make them quite inconvenient to be used especially in the frequency range 1-4 GHz, which is the range of most of the commercial wireless applications. This thesis work aims to enhance the usability of cavity filters in these lower frequency ranges, by exploring a unique reentrant structure for the cavity filter design. The study further explores the use of superconductors in the design to for improve the performance of the filters by reducing the associated losses. After verifying the basic workability of the concept, a coupled reentrant cavity filter design is proposed with an equivalent high Q.
To develop high-quality rf components for wireless telecommunications, we have processed single-domain YBCO of various dimensions and geometry for the device applications including high-Q resonators and filters. In this development, a critical parameter, the surface resistance, R s , of single-domain YBCO has been measured in wide ranges of temperature and magnetic field. We have found that the Pippard model can best describe the well oxygenated crystal, indicating the high-quality of single-domain YBCO. However, such scaling breaks down when the oxygen structural disorders are introduced into the sample. A fundamentally different scaling behaviour is observed, which is closely related to the structural defects of oxygen. We report such a behaviour and discuss the possible underlying mechanism.
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