An In-Line Waveguide-to-Microstrip Transition Using Radial-Shaped Probe

In this letter, an in-line waveguide-to-microstrip transition at Ka-band is presented. It utilizes a radial-shaped probe a quarter-wavelength away from the waveguide short-back, which is also used as a support for the microstrip substrate, to terminate the TE₁₀ mode of the standard waveguide. This printed structure is easy to fabricate and convenient to be installed in the waveguide cavity with a split-block configuration. A test module at Ka-band is designed and fabricated. It provides a return loss better than 10 dB from 26.5 to 38.5 GHz and an insertion loss of 1.2 to 2 dB within a wide frequency range from 26.5 to 36.2 GHz with a low cost, easy to fabricate printed structure. The measured results show good agreement with the simulated ones.