A design of 79 GHz band coaxial waveguide transition using finline built on high-permittivity substrate

We have put a lot of effort into development of a 79 GHz band range finder and have seen that a coaxial waveguide transition using a finline built on a high-permittivity substrate is required. Then, we attempted to design a 79 GHz band coaxial waveguide transition using finline built on alumina substrate (relative permittivity 10). The goal of the performance is less than -10 dB of |S₁₁| at the frequency from 74 GHz to 84 GHz. In this paper, we focus on the gap between the outer side curves of the finlines. As a result, we have found that the gap between the outer side curves of the finlines has the optimal value. At the moment, based on the optimal value, we are producing the coaxial waveguide transition using finline.