Wideband Tuning of the Tunneling Frequency in a Narrowed Epsilon-Near-Zero Channel

We propose a design of foam epsilon-near-zero (ENZ) waveguide with E- and H-plane step discontinuities at the same waveguide cross section. This enables using channel dielectric permittivity greater than the permittivity in input waveguides, which is required for foam ENZ waveguide realization. A method for wideband tuning of tunneling frequency by changing the length of two longitudinal slots was also proposed and experimentally verified. Simulated tuning range is 1.06 GHz, which is in a good agreement with experimentally achieved 0.99 GHz. This tuning range is accompanied by amplitude decrease of 1.6 dB.