Design and calibration of a wideband TEM-cell for material characterization

Abstract

A wideband TEM-cell is designed for dielectric measurements to operate over a 50 MHz - 800 MHz frequency range by using transmission/reflection method. This cell is compact, easy to fabricate, and useful for measuring porous samples such as concrete. The classic dielectric measurement setup is usually based on rectangular TE10-mode waveguides which become very large, expensive, and non-practical for lower frequencies. As for a classic coaxial cell, non-uniformity of the electromagnetic field and the difficulty to obtain sample in a toroidal shape for coaxial cells are overcome using the proposed TEM-cell. Wideband matching is performed using a coaxial to waveguide connector based on a tapering technique. A specific calibration is used and the complex permittivity and permeability are calculated from the measured S-parameters. Preliminary experimental results are presented.