Abstract
This thesis presents various work done towards achieving miniaturization of circuits at microwave and millimetre-wave frequencies. Included are techniques for the characterization of dielectric materials, mainly low temperature co-fired ceramic (LTCC) and barium strontium titanate (BST), using a free space method at frequencies between 145 GHz and 200 GHz. Data from the measurements provided new information on the performance of dielectric materials at high millimetre-wave frequencies. A new method to characterize dual-layer materials is also introduced in the thesis. Using BST as a distributed varactor, a new, miniature tuneable bandpass filter was developed. Measured results from the filter show a very significant improvement in performance compared to other similar structures, reported elsewhere. Other work on the theme of miniature components included the development of a narrowband bandpass filter at 150 GHz, using rectangular waveguide as a prototype for an LTCC design. In this filter work the design procedures commonly used at lower frequencies were modified to give optimum results at high mm-wave frequencies. The effect of miniaturizing the area occupied by microwave and mm-wave circuits was also investigated. This lead to new information on the optimum spacing of circuit interconnections, and on the effectiveness of isolation structures, for both single and multilayer circuits, operating over a given frequency range.