Design and Validation of the Phase-Compensated Long-Range Sub-THz VNA-Based Channel Sounder

Abstract

This paper presents the first vector network analyzer (VNA)-based sub-Terahertz (sub-THz) phase-compensated channel sounder at 220-330 GHz using radio-over-fiber (RoF) techniques that could enable long-range phase-coherent measurements. The optical cable solution enables long-range channel measurements at sub-THz bands, since it can effectively minimize the cable loss. This paper also proposes a novel phase compensation scheme to stabilize the phase variations introduced by optical fiber of the channel sounder to enable its application in multichannel/antenna measurements. This proposed channel sounder is validated in back-to-back measurements under two optical cable conditions, i.e., with presence of thermal changes and mechanical stress. The phase variation introduced by the cable effects in the system is shown to be over 400 • in 220-330 GHz, compared to 15 • at 220-288 GHz and 37 • in 288-330 GHz after compensation, respectively, demonstrating the robustness and effectiveness of the developed channel sounder in practice. The developed system, which has a dynamic range of 106.7 dB, can support measurement range up to 300 m (limited by the optical cable length in our system and subject to over-the-air signal transmission loss in practical environment).

Design and Validation of a Multilink Phase- Compensated Long-Range Ultrawideband VNA-Based Channel Sounder

“…However, due to the unstable phase performance of the fiber, the phase information of these channel frequency responses is inaccurate, which means that the high-resolution algorithms cannot be applied to the measurement data when the VAA concept is adopted. Phase-compensation scheme has been validated at 1-50 GHz in [19], [37], and at 300 GHz in [20], and the measurement results in those papers demonstrate the practicality and effectiveness of the phase compensation principle and structure. However, the phase compensation scheme is only validated in single-input-single-output channel sounders.…”

“…Comparison of the proposed sounder and the state-of-theart channel sounders is discussed as follows. The channel sounders in [15], [19], [20], [42], [43] are VNA-based channel sounders. A multi-link channel sounder is presented in [15] at 28 GHz with 4 GHz bandwidth.…”

“…However, the phase of the signal in the fiber is inherently sensitive to the thermal change and mechanical stress of the fiber cables [34], [35], limiting its application for phase-coherent measurements, e.g., VAA-based channel measurements, which is widely used for spatial channel measurements at mmWave bands [15]. To enable phase-coherent ultrawideband channel measurements in the long-range scenarios, phase compensation strategies were presented in [19], [20], [36], [37]. The phase compensation scheme using the bidirectional strategy was applied in the VNA-based channel sounder using RoF techniques up to 30 GHz in [19] and extended to 50 GHz in [37].…”

“…The phase compensation scheme using the bidirectional strategy was applied in the VNA-based channel sounder using RoF techniques up to 30 GHz in [19] and extended to 50 GHz in [37]. Furthermore, the phase compensation scheme is extended to sub-THz frequency bands, i.e., 220-330 GHz in [20] and compensated phase variation is up to 15 • compared to over 400 • before phase compensation. The results in the literature demonstrate the effectiveness of the phase compensation strategy for VNAbased channel sounders.…”

On the Phase-Compensated Long-Range VNA-based Channel Sounder for sub-6 GHz, mmWave and sub-THz frequency bands

“…Phase compensation schemes can be applied to stabilize the phase of the VNA-based channel sounder at sub-6 GHz, mmWave and sub-Terahertz (sub-THz) bands [3], [10]- [12]. The phase compensation scheme in [10] is directly implemented using microwave circulators and radio frequency (RF) cables at sub-6 GHz bands, and using circulators and E/O and O/E conversion units for channel sounder at 1-30 GHz [3] and 1-50 GHz [11], respectively.…”