For realize these measurements, a characterization bench based on the principle of measurement in free space was used. As shown below, the sample to be characterized is placed between two horn antennas fitted with focusing lenses.
The reflection and transmission coefficients are measured using a vector network analyzer and the dielectric parameters of the sample are extracted using different algorithms.
Several sets of horn antennas cover a wide frequency band, from 6 GHz to 42 GHz.
The characterized samples are plans with a format of 300 mm x 300 mm. The free space test rig is calibrated using a TRL (through/reflect/line) method.
The typical measurement accuracy of this bench after calibration at normal incidence is +/- 0.025dB and +/- 0.5° in phase over the entire frequency range.
These tests measure the S parameters in transmission/reflection of the samples. The test rig for each frequency band is calibrated such that the phase reference planes are placed at the faces of the sample.
The sample is placed at the level of the phase reference planes without the presence of a metal plate. Finally, the complex permittivity ε and the complex permeability µ of the samples are extracted from measurements of the coefficients of transmission S11 and reflection S21.