A Transmission-Reflection Method for Complex Permittivity Measurement Using a Planar Sensor
We present a contact method for the complex permittivity measurement of materials based on a two-port microwave sensor over a frequency range of 3–4 GHz. The proposed sensor is composed of a 3-dB directional coupler with the direct and coupled ports each connecting an open-ended transmission line. Two simple un-calibrated scattering parameters are required to extract the complex permittivity of the materials under test (MUT). One is for the empty sensor, and the other is for the MUT loaded on the sensor. Additionally, the relation expression between complex permittivity and measured scattering parameters is presented. Some experiments were carried out over the whole frequency range. The results agree well with the resonant method. This transmission-reflection method can provide a highly accurate measurement for only requirement of amplitude information of the S-parameters. To low-loss materials, the relative errors of the calculated results are less than 4% for real part and 6% for imaginary part of permittivity in comparisons with the literature data.