P-Band Transmission Coefficient Measurement of Small-Size Planar Transparent Materials

This article proposes a frequency-domain method based on the cross-ratio (CR) invariance principle for measuring the transmission coefficients of small-size planar transparent materials (TMs) at P-band (0.3–1 GHz). The proposed method achieves accurate measurement of materials under tests (MUTs) using three calibration standards with known transmission coefficients. This method effectively eliminates two limitations of the free-space method at P-band: insufficient temporal resolution and dependence on large-size samples. To further improve the accuracy of the proposed method, a multipoint CR method is proposed. The multipoint CR method uses additional calibration standards to construct multiple calibration triplets. Corresponding weights are assigned to each triplet based on the law of uncertainty propagation. The weighted average of the results from all triplets is then calculated to determine the final transmission coefficient of the MUT. A measurement setup is developed to verify the validity, accuracy, and repeatability of the proposed method through both simulation and measurement of three different types of materials.