MICROWAVE SUPERCONDUCTOR FILTERS

Abstract

The end-coupled filter is wisely used in narrowband microwave systems. However, when filter bandwidth increases, higher coupling capacitances are required in filter realization. This causes filter gap size to become too small to realize due to tolerances in fabrication. This thesis introduces an edge-end-coupled filter which, by improving the coupling between filter resonators, provides a significant relaxation in stringent gap dimensions of higher bandwidth end-coupled filters. A design methodology has been developed and successfully used to design and fabricate a microwave filter at 4.9 GHz with a 5% bandwidth. Planar filters exhibit excessive loss as frequency increases. The filter loss is attributed to finite conductivity of the conductor materials used. Introduction of thin-film high temperature superconductor (HTS) can result in reduction of the conductor loss. This thesis covers HTS filter design, implementation and measurement. Thee edge-end-coupled filter topology was used for these filters. Passband distortion problems in the design of a 10 GHz HTS filter were solved by replacing half-wavelength resonators with full-wavelength resonators. However, this method introduced unwanted harmonics at 5 GHz and 15 GHz. These were eliminated by means of a stopband structure consisting of quarter-wavelength open stubs.