Sub-Terahertz (sub-THz) (i.e., 100-300 GHz) communication is envisioned as one of the key components for future beyond fifth-generation (B5G) communication systems due to its large untapped bandwidth. Sub-THz channel measurements are essential for building accurate and realistic sub-THz channel models. Virtual antenna array (VAA) scheme has been widely employed for radio channel sounding purposes in the literature. However, its application for the W-band (i.e., 75-110 GHz) has been rarely discussed due to system phase instability issues. To tackle this problem, a long-range phase-compensated vector network analyzer (VNA)-based channel sounder at the Wband is proposed. First, the back-to-back measurement of the developed channel sounder is carried out with the presence of cable bending, where the initial phase variation beyond 180 • range due to cable effects can be well corrected to within 10 • range with the proposed phase-compensation scheme, clearly validating its effectiveness. To examine how well it works in practical deployment scenarios, the proposed channel sounder is then employed for channel sounding with two measurement distances, covering both near-field (with a line-of-sight (LoS) distance of 7.3 m) and long-range (with a LoS distance of 84.5 m) cases. Based on the measured data, a high-resolution channel parameter estimator is applied to extract the channel multipath parameters for the large-scale VAA at the W-band, both in the near-field and long-range scenarios, respectively. The highresolution algorithm was extended to support virtual arrays composed of both omnidirectional antenna and directive antenna in this work. The conventional directional scanning scheme (DSS) measurement is adopted as the reference measurement to validate the effectiveness and robustness of the developed channel sounder. In the end, to demonstrate the state-of-art channel sounding capabilities of the developed channel sounder, ultra-wideband (UWB) channel measurements at 104.5 GHz with 11 GHz bandwidth using the VAA scheme are conducted in a hall scenario with the measurement range up to 58 m with omnidirectional antennas, and the channel parameters are extracted using the validated high-resolution channel parameter estimator for channel modeling purposes.
