In a demo board, the main function of a de-embedding line is to eliminate the impact of non-Device Under Test (DUT) components—such as test fixtures and connecting lines—on measurement results, thereby obtaining the performance parameters of the DUT itself more accurately.

In high-frequency circuit testing, the DUT on a demo board usually needs to be connected to test instruments (e.g., vector network analyzers) via test fixtures and connecting lines. These test fixtures and connecting lines introduce additional losses, reflections, and phase shifts, which can affect the accuracy of DUT measurements. Through a specific circuit structure and measurement method, the de-embedding line removes the influence of these non-DUT components from the overall measurement results. For example, by measuring the characteristic parameters of the de-embedding line itself, its impact on the signal can then be subtracted from the overall measurement results (which include the fixture and DUT) during data processing. This ensures that the measurement results more truly reflect the DUT’s performance, enabling accurate acquisition of parameters such as the DUT’s impedance, insertion loss, and reflection coefficient.