An in-line coaxial-to-circular waveguide transition at X band

A wideband transition from the coaxial TEM mode to the TM₀₁ mode of the circular waveguide with in-line input-output architecture is proposed in this paper. The transition employs multi-stage stepped impedance transformer to achieve wideband responses. Both mode transition and impedance matching characteristics are discussed in the paper. A demonstrator is developed and validated experimentally. As compared with some recently published reports, a better performance is observed. Moreover, the developed transition could facilitate the mechanical fabrication more easily. It can be found wide applications such as the circular waveguide based slot array antenna, the nondestructive detection, cracks inside the conductive pipes, and so on.