Epsrc Doctoral Training Grant | Garner, Jason

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) [1]. 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 [2].
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.
References:
[1] 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.
[2] 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.