Wave dispersion measurements of helically corrugated waveguides using a Vector Network Analyser

斯特拉斯克莱德大学已研制出X波段(8.2 GHz~12.4 GHz)回旋管行波放大器、振荡器和微波脉冲压缩器。本提案旨在研究螺旋波纹波导的使用，以研究这一概念在更高的Ka频段(26.5 GHz到40 GHz)和W频段(75 GHz到110 GHz)的可扩展性。当一个人寻求提高频率时，两个实质性的问题立即出现，即要求制造足够精确的轮廓和足够光滑的表面，以产生所需的色散特性和可容忍的损失。在迄今研究过的较低X波段频率下，已使用数控铣床来生产所需的3D表面，但在较高频率下，按比例减小的公差加上刀具接触间隙的减小将禁止这项技术。因此，该项目将研究现有的替代制造技术，包括液压和机械成形、电铸、铸造和火花侵蚀，所有这些技术都与电抛光和薄表面电镀相结合。制作的波导节将由矢量网络分析仪(VNA)进行测量。VNA将被用来测量螺旋结构的波色散，方法是比较辐射相角的主值随频率的变化，因为它通过已知长度的波导传播。对放大器和振荡器相互作用区和螺旋压缩器段的波色散进行了测量，并与理论和模型的预测进行了比较。

Gyrotron travelling wave amplifiers, oscillators and microwave pulse compressors based on helically corrugated waveguides have been developed at the University of Strathclyde at X-band Frequencies (8.2GHz to 12.4GHz). This proposal intends to study the use of helically corrugated waveguides to investigate the scalability of this concept to higher Ka-band (26.5GHz to 40GHz) and W-band (75GHz to 110GHz) frequencies. Two substantial problems immediately present themselves as one looks to increase the frequency, namely the requirements to fabricate an adequately accurate profile with a sufficiently smooth surface to produce the required dispersive properties with a tolerable loss. At the lower Xband frequencies hitherto investigated CNC mills have been used to produce the required 3D surface, but at higher frequencies the proportionately reduced tolerances plus the reduced clearances for tool access will prohibit this technique. The project will therefore investigate the alternative fabrication techniques available, including hydraulic and mechanical forming, electroforming, casting and spark erosion, all combined with electropolishing and thin surface plating. The fabricated waveguide sections will be measured by a Vector Network Analyser (VNA). The VNA will be used to measure the wave dispersion of helical structures by comparing the evolution of the principle value of the phase angle of the radiation as a function of frequency as it propagates through a known length of the waveguide. Measurements of the wave dispersion of amplifier and oscillator interaction regions and helical compressor sections will be benchmarked and compared with the predictions of theory and modelling.