The aim of the project is to design passive waveguide coupling components for high frequency gyro-amplifiers. The project focussed on a 94 GHz amplifier, with potential applications in a Cloud Profiling Radar weather monitoring system, and a 372 GHz amplifier, designed as a proof-of-principle device for proton-enhanced NMR imaging.
A rectangular-to-circular T-junction input coupler with a stepped waveguide reflector for a 94 GHz gyro-travelling wave amplifier (gyro-TWA) was designed using numerical modelling. The component was manufactured through a spark erosion technique and tested on a Vector Network Analyser (VNA) . The passive component was applied to existing active and passive components to form an amplifier system. A feed signal was fed into the cavity through the waveguide coupler and an experimental examination of the device was performed. The bandwidth and the output signal magnitude from the gyro-TWA was recorded.
A comparison of two input couplers for a fundamental mode 372 GHz gyro-amplifier was made. A rectangular-to-circular T-junction coupler and a multiple-hole input coupler were numerically modelled. A high transmission from the rectangular input waveguide to the circular cross-section cavity feed waveguide was achieved; however, the high transmission operation of the two couplers was shown to be dependent on strict tolerances being applied to the parameters during manufacture. A comparison of the input coupler designs and a discussion of the manufacturing tolerance effect on the coupler performance were presented .
To ease the manufacturing tolerance effect on the waveguide coupler performance, a higher order mode (HOM) input coupler was designed to couple to an 8-fold helically corrugated interaction waveguide (HCIW). The design of the coupler incorporated a power splitting section which equally divides the incident wave into two discrete in-phase signals. The coupler was designed with waveguide bends to ensure the two signals arrived at the interaction cavity at the same time. A numerical model of the component was constructed and a detailed analysis of transmission performance with parametric variation was performed. A prototype design of the HOM input coupler was manufactured at 90 – 96 GHz, using the component as the input and output section to test the transmission and reflection of the waveguide channels on a VNA. A journal paper discussing the design, manufacture and testing of the waveguide component is currently being drafted.
 L. Zhang, W. He, C. R. Donaldson, J. R. Garner, P. McElhinney and A. W. Cross, “Design and measurement of a broadband sidewall coupler for a gyro-TWA,” IEEE Trans. Microw. Theory Techn., vol. 63, no. 6, pp. 3183-3190, Oct. 2015.
 J. R. Garner, L. Zhang, C. R. Donaldson, A. W. Cross and W. He, “Design Study of a Fundamental Mode Input Coupler for a 372-GHz Gyro-TWA I: Rectangular-to-Circular Coupling Methods,” IEEE Trans. Electron Devices, vol. 63, no. 1, pp. 497 - 503, Jan. 2016.