A Microwave Measurement Technique for Complex Constitutive Parameters

A technique was developed for the measurement of complex constitutive parameters of thin slabs of radiation absorbing material. Parameters include the real and imaginary components of the permittivity and permeability. The conductivity was lumped into a composite imaginary permittivity component through the loss tangent. The homogeneity of the material across the slabs surface and the ability of this technique to locate areas where the parameters deviate from the average was also examined. The transmission coefficients of the slabs were measured at several angles of incidence using a 180 degree, bistatic configuration. This permitted a computer program to solve the nonlinear system of transmission equations for the desired parameter values. The technique and computer program are applicable to measurements taken at either perpendicular or parallel polarization, and takes advantage of prior known material qualities, nonmagnetic or lossless, to reduce the order of the system. Measurements were taken at 94 GHz using a Gunn phase-locked oscillator as a source. A pair of conical horn-lens antennas and a Scientific Atlanta 1783 Programmable microwave receiver were the primary pieces of equipment required. Theses.