Free-space measurement of bi-axial anisotropic materials
This paper presents an extension of the free-space method for measurement of bi-axial anisotropic material at microwave frequencies. In this method, four complex transverse constitutive parameters are directly computed from the reflection and transmission coefficients of a planar sample in free space for a normally incident plane wave with two polarizations. By using the measured amplitudes of the reflection and transmission coefficients of a planar sample at six incident angles with two polarizations, two complex longitudinal constitutive parameters are obtained by finding the solution to minimize the properly designed objective function under the suitable judging criterion. The numerical trials are carried out for a high-loss material by joining random errors to simulate the real measurement condition, which verifies the validity of this method.
A free-space method for measurement of dielectric constants and loss tangents at microwave frequencies
For measurements of dielectric properties of planar slabs of ceramic and composite materials, the authors have developed a free-space measurement system in the frequency range of 14.5-17.5 GHz. The key components of the measurement system are a pair of spot-focusing horn lens antennas, a network analyzer, and a computer. Because of the far-field focusing ability of horn lens antennas, the free-space measurements can be made at microwave frequencies in a relatively compact and simple measurement setup. The time-domain gating feature of the network analyzer and the thru, reflect, and line calibration technique were used to eliminate the effects of undesirable multiple reflections. The dielectric constants and loss tangents were measured for standard materials such as fused quartz, Teflon, and polyvinylchloride (PVC). Dielectric properties for Teflon and PVC were also measured in a waveguide medium for purposes of comparison with the free-space method. >
MEASUREMENT OF THE COMPLEX DIELECTRIC CONSTANT OF LIQUIDS AT CENTIMETER AND MILLIMETER WAVELENGTHS
The measurement of the complex dielectric constant of lossy liquids in the millimeter and centimeter wave region by a free-space technique is described. The method involves the measurement of absorption per wavelength and of reflectance at normal incidence. Families of curves are given for the relations between these two quantities and the real and imaginary parts of the complex dielectric constant. Results for ethyl and methyl alcohol at 9 and 13 mm. wavelength are compared with those obtained by waveguide techniques.