Anisotropic Permittivity Measurement Using a Strip Air Line System

A strip air line system for measuring anisotropic materials in the band from 0.3 to 1 GHz is proposed. The multireflect-thru method is used to calibrate the measurement system in the whole band with a single strip air line. In the strip air line, the TEM mode propagates along the strip in the material under test (MUT). Therefore, it is possible to accurately measure the permittivity of anisotropic materials with the strip air line. Since a small portion of the electric field is parallel to the ground plane around two edges of the strip, the measured property is not purely along one direction. To obtain higher accuracy, with the help of linear combination, the properties along two directions are disentangled by two measurements. The validity and the accuracy of the system for measuring anisotropy are verified by simulation results and the measurement results of polytetrafluoroethylene (PTFE) and two anisotropic materials.