Automatic measurement of permittivity and permeability at microwave frequencies using normal and oblique free-wave incidence with focused beam

A free-wave method for determining the dielectric and magnetic properties of materials from reflection measurements made at normal incidence and transmission measurements made at normal and oblique incidence is proposed. The method combines frequency domain measurements and time domain (TD) analysis and uses polarization to avoid typical ambiguities in the results. Varying the incident angle and the polarization, measurements were made in the X-band. The technique was validated by comparing the results obtained with those from well-established waveguide techniques. A focusing assembly makes it possible to measure relatively small samples, thus avoiding diffraction problems. It also improves the ambiguity-solving procedure proposed for the technique. The measurement procedure is fully automated by using the HP8510 network analyzer controlled by an HP362 computer, which also processes the data. Results for low-loss dielectrics such as teflon, nylon, and polymethyl methacrylate (PMMA) and for microwave-absorbing materials are reported.