D-band Directly Coupled Bandpass Filter Based on Micro-coaxial Structure

This article presents a novel class of directly coupled resonators bandpass filter with a wide stopband performance based on rectangular micro-coaxial line, utilizing additive manufacturing technologies. The resonators are composed of rectangular micro-coaxial lines, with supports working as the coupling elements between them. The proposed structure is relatively easy to fabricate using additive manufacturing (AM). The use of rectangular micro-coaxial lines exploits a very small cross section, which can be useful for some applications, such as filters that conform to an existing device. In addition, in order to reduce transmission losses, the dielectric inside the coaxial line is air, which means that the inner conductor must be sustained by utilizing some supports. Although these supports can be either dielectric or metallic, they should be as small as possible so as to avoid interfering the filter response in this design, or they should simply be part of the filter. In this article, the second solution has been adopted, as a result, the metallic supports act as the coupling elements among resonators.