Coaxial-to-Waveguide Matching With $\varepsilon$-Near-Zero Ultranarrow Channels and Bends

We propose the use of metamaterial-inspired ultranarrow channels at cutoff to realize an interesting matching between a coaxial antenna and a waveguide. The anomalous properties of a channel at cutoff, analogous to those of zero permittivity materials, allow a simple matching design, valid for arbitrary waveguides, with large degrees of freedom in terms of geometry, length and possible bending of the connecting channel. Moreover, the static-like properties of the channel allow such matching, independent of the relative position of the antenna and possible bending and abruptions along the channel.