S -parameter de-embedding technique for accurate impedance characterisation in radiometry

Accurate impedance characterisation is a prerequisite for reliable radiometric noise power measurements. This work is framed in an approach of non-contact temperature measurements of weakly conductive objects within enclosed cavities. The presented method adapts a de-embedding technique based on S -parameter analysis. The technique enables precise determination of the antenna and low-noise amplifier (LNA) input impedances. Both parameters are essential for scaling measured noise powers and accounting for intrinsic LNA noise. Printed circuit boards (PCBs) were fabricated as devices under test (DUT) and half devices under test (HUT). Reference capacitors were incorporated at defined planes to establish calibration conditions. The symmetry of the DUT was verified using vector network analyser measurements in the 0.2–1 GHz range. This ensures the validity of the de-embedding central reference impedances. The proposed algorithm was applied to experimental data and validated against analytically generated reference models. The results demonstrate excellent agreement between de-embedded and theoretical S -parameters. DUT and HUT structures provide a robust basis for calibration in a novel self-calibrating radiometer. This approach eliminates the need for repeated in situ impedance measurements, thereby enabling accurate, efficient, and scalable radiometric applications.