Assessing the Impact of Data Filtering Techniques on Material Characterization at Millimeter-Wave Frequencies

This article reports on an investigation into data filtering techniques for material characterization using a commercially available WR-15 (50-75 GHz) material characterization kit (MCK). The MCK uses a guided free-space method (operating like the conventional quasi-optical focused beam system) that enables measurement of S-parameters of dielectrics using a vector network analyzer (VNA). Multiple reflections and resonances exist in the MCK and they cannot be readily eliminated by calibration. To minimize these effects on extracting dielectric constant and loss tangent from the measured S-parameters, data filtering techniques (e.g., Savitzky-Golay filter and time-gating) can be adopted. A comparison of the measurement results using these two techniques was carried out on five common dielectric materials. Generally, the results obtained using these two filtering techniques are consistent with each other, and the Savitzky-Golay filter offers better performance in the scenario where the specimen quality is not ideal. Three specimens were also measured using an open resonator (operating at 36 GHz). There is generally good agreement between the results from the MCK and the open resonator.