Time-Varying Signal Propagation at Sub-THz Frequencies Using a Vector Network Analyzer

Vector network analyzers (VNAs) are primarily designed to measure time-invariant networks by capturing the complex voltage response at discrete frequency points within a sample window defined by the intermediate frequency bandwidth (IFBW). The interval between frequency steps is determined by factors such as the selected IFBW and the total number of frequency points, which will result in the overall measurement duration. This conventional approach presents challenges when measuring time-varying transmissions, as changes in the waveform must be considered throughout the entire measurement period. To address this challenge, we investigate methods to adapt signal acquisition for time-varying signals, evaluating the feasibility and limitations of using VNAs for this purpose. We analyze the sweep duration and evaluate a segmented sweep, conducting experimental verification to establish a measurement scenario. This scenario aims to improve our understanding of time-varying measurements and to apply it to other much more dynamic channel-sounding systems, enabling estimation of associated measurement uncertainties. We present the measurement setup, mathematical analysis to simulate the scenario, and time intervals obtained for each measured segment at varying velocities, considering the actual position at each frequency step.