Fast and Robust Characterization of Dielectric Slabs Using Rectangular Waveguides

TL;DR

This paper introduces a new waveguide measurement method for dielectric slabs that extends outside waveguides, enabling accurate permittivity characterization of arbitrarily shaped samples across microwave to sub-terahertz frequencies.

Contribution

The paper presents a novel approach using an equivalent Pi-circuit model to measure dielectric permittivity of irregularly shaped slabs without precise sample shaping.

Findings

Equivalent shunt impedance depends only on permittivity, not shape or position.

Method is effective for medium- and high-loss dielectrics.

Applicable from microwave to sub-terahertz frequencies.

Abstract

Waveguide characterization of dielectric materials is a convenient and broadband approach for measuring dielectric constant. In conventional microwave measurements, material samples are usually mechanically shaped to fit the waveguide opening and measured in closed waveguides. This method is not practical for millimeter-wave and sub-millimeter-wave measurements where the waveguide openings become tiny, and it is rather difficult to shape the sample to exactly the same dimensions as the waveguide cross-section. In this paper, we present a method that allows one to measure arbitrarily shaped dielectric slabs that extend outside waveguides. In this method, the measured sample is placed between two waveguide flanges, creating a discontinuity. The measurement system is characterized as an equivalent Pi-circuit, and the circuit elements of the Pi-circuit are extracted from the scattering parameters. We have found that the equivalent shunt impedance of the measured sample is only determined by the material permittivity and is rather insensitive to the sample shape, position, sizes, and other structural details of the discontinuity. This feature can be leveraged for accurate measurements of permittivity. The proposed method is very useful for measuring the permittivity of medium-loss and high-loss dielectrics from microwave to sub-terahertz frequencies.