Characterization of Sub-THz Channel Sounding Systems in OTA Measurement Scenarios Using a Vector Network Analyzer

Understanding the hardware impairments and the effect of the postprocessing algorithms on an unknown channel sounder (CS) requires a comparison with a calibrated instrument with a known error model. In this study, we use a vector network analyzer (VNA) with error models and theoretical calculations to characterize two correlation-based, purpose-designed CS test instruments operating around 200 and 300 GHz, respectively. We conducted a series of controlled measurements, including both line-of-sight (LoS) and nonline-of-sight (NLoS) scenarios. Key aspects investigated include VNA calibration accuracy, noise performance, and power delay profile (PDP) peak magnitude and delay drift. For the correlation-based CSs, we investigate the impact of dc offset and in-phase and quadrature (IQ) imbalance on measurements. The measurement scenarios enabled detailed characterization of the antennas under test, the VNA’s nonlinearity, and the total spectrum of the CSs. We examined the feasible bandwidth in terms of PDP path gain and delay deviations, comparing results with VNA measurements to ensure accuracy. Additionally, multipath measurements using various reflectors provided insights into the system’s response to different multipath components, presenting the influence of reflectors on path gain and measurement uncertainties. Some of the findings demonstrated combined uncertainties of ±0.22 and ±0.51 dB for the WR05 and WR03 VNA measurements, respectively. The CS measurements displayed a standard deviation of 0.4 dB and 0.3 both before and after applying the Hann window for 5 GHz bandwidth for the WR05 band. At the WR03 CS 5-GHz bandwidth, the deviations were 1.4 and 1 dB before and after applying the Hann window, respectively.