This thesis presents the designs and measurement performance of nine SU-8 micromachined waveguide circuits operating at WR-10 band (75-110 GHz), WR-3 band (220-325 GHz) and WR-1.5 band (500-750 GHz). Two thick SU-8 photoresist micromachining processes, namely, the separate single-layer process and the joint two-layer process, are developed to fabricate these terahertz waveguide circuits. In order to achieve accurate and secure interconnections with measurement network analyzers, two calibrated measurement methods for micromachined waveguide circuits are proposed. The measurement performance of these micromachined circuits is excellent in terms of very low insertion loss. The design of multiple-passband filters using coupling matrix optimisation is also discussed in this thesis. The optimisation is performed on the coupling matrix and a genetic algorithm (GA) is employed to generate initial values for the control variables for a subsequent local optimisation (sequential quadratic programming - SQP search). The novel cost function presented in this thesis measures the difference of the frequency locations of reflection and transmission zeros between the response produced by the coupling matrix and the ideal response. An eighth-order X-band dual-band waveguide filter with all capacitive coupling irises is fabricated and measured to verify the design technique.
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