波导-同轴线的脊型转换器设计与测试

射频测量系统中经常会用到波导-同轴线转换器，主要是利用其将射频器件的波导端口转换成能够直接接入测量仪器的50 Ω同轴线。本文设计的648 MHz/WR1500波导同轴转换器主要用于CSNS升级工程（CSNS-II）超导直线射频器件的测量。利用切比雪夫脊型阶梯阻抗变换和探针耦合的方式实现波导到同轴线的转换。对脊加载波导和不连续同轴线分别进行了分析，得到最优尺寸。为了提高测量精度，设计的波导-同轴线转换器具有低插入损耗、低驻波比和宽带宽等特性。最后对生产的转换器进行了测试，测试结果与仿真结果相近，能够满足作为测量器件的使用要求。

Design and test of device for transition from ridge waveguide to coaxial line

Waveguide to coaxial line transtion is often used in RF measurement systems. To measure the network parameters of these RF devices with a vector network analyzer and other instruments, the transtion is indispensable to convert the waveguide ports of the RF devices to 50 Ω coaxial line which can directly access the network analyzer. The 648 MHz/WR1500 transformer designed in this paper is mainly used for the measurement of the superconducting linac RF devices at the China Spallation Neutron Source (CSNS) upgrading phase (CSNS-II). In this paper Chebyshev ridge ladder impedance transformation and probe coupling are adopted to complete waveguide to coaxial line transition. The ridge loaded waveguide and discontinuous coaxial line are analyzed respectively, and the optimal size is obtained. The designed transformer has the characteristics of low insertion loss, low VSWR and wide bandwidth to achieve high measurement accuracy. At last, the transition device is tested, and the test results are close to the simulation results, which can meet the requirements of being a measuring device.