Extraction of the Wideband Dielectric Properties of a Material Layer Using Measured Natural Frequencies

A new experimental technique for determining the complex permittivity of a dielectric material is introduced. A conductor-backed dielectric sheet is illuminated by a transient plane wave in a free-space measurement range and the temporal reflected field is analyzed as a natural mode series. By comparing the natural frequencies extracted from the response to those found theoretically using a simple dispersion model, the permittivity of the sheet may be determined over a broad band of frequencies. Since the natural frequencies are not affected by the waveform of the incident field, they remain a robust descriptor of the permittivity even after the requisite calibration steps. Examples of the low-loss dielectrics polyvinyl chloride, acrylic, and garolite are examined.