Experimental Verification of Below-Cutoff Propagation in Miniaturized Circular Waveguides Using Anisotropic ENNZ Metamaterial Liners

TL;DR

This study experimentally verifies that miniaturized circular waveguides with anisotropic ENNZ metamaterial liners can support below-cutoff transmission, significantly enhancing signal propagation at frequencies below natural cutoff.

Contribution

It introduces a simple printed-circuit design for anisotropic ENNZ liners and validates their effectiveness through experimental and simulation results, advancing miniaturized waveguide technology.

Findings

Below-cutoff transmission is achieved with ENNZ liners.

The liner's anisotropic parameters accurately predict cutoff reduction.

Experimental results agree with simulations.

Abstract

This paper presents experimental verification of below-cutoff transmission through miniaturized waveguides whose interior is coated with a thin anisotropic metamaterial liner possessing epsilon-negative and near-zero (ENNZ) properties. These liners are realized using a simple, printed-circuit implementation based on inductively loaded wires, and introduce an HE$_{11}$ mode well below the natural cutoff frequency. The inclusion of the liner is shown to substantially improve the transmission between two embedded shielded-loop sources. A homogenization scheme is developed to characterize the liner's anisotropic effective-medium parameters, which is shown to accurately describe a set of frequency-reduced cutoffs. The fabrication of the lined waveguide is discussed, and the experimental and simulated transmission results are shown to be in agreement.