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Far- and Near-Field Channel Measurements and Characterization in the Terahertz Band Using a Virtual Antenna Array

Yiqin Wang, Shu Sun, Chong Han

TL;DR

This work tackles the challenge of characterizing far- and near-field THz channels for extremely large-scale antenna arrays. It presents a measurement framework using a THz virtual antenna array to perform wideband MISO experiments with UPAs up to 4096 elements in the 260–320 GHz band, validating non-linear near-field phase behavior and the Rayleigh criterion for phase error. A cross-field path loss model is proposed to unify FF and NF behavior across the UPA, with parameters that have physical interpretation and fit well to the data (MSE ≈ 0.0022). The findings advance THz ELAA channel modeling and offer a practical tool for designing and analyzing THz MIMO systems, while noting the need for further measurements across different distances and frequencies to generalize the model.

Abstract

Extremely large-scale antenna array (ELAA) technologies consisting of ultra-massive multiple-input-multiple-output (UM-MIMO) or reconfigurable intelligent surfaces (RISs), are emerging to meet the demand of wireless systems in sixth-generation and beyond communications for enhanced coverage and extreme data rates up to Terabits per second. For ELAA operating at Terahertz (THz) frequencies, the Rayleigh distance expands, and users are likely to be located in both far-field (FF) and near-field (NF) regions. On one hand, new features like NF propagation and spatial non-stationarity need to be characterized. On the other hand, the transition of properties near the FF and NF boundary is worth exploring. In this paper, a complete experimental analysis of far- and near-field channel characteristics using a THz virtual antenna array is provided based on measurement of the multi-input-single-output channel with the virtual uniform planar array (UPA) structure of at most 4096 elements. In particular, non-linear phase change is observed in the NF, and the Rayleigh criterion regarding the maximum phase error is verified. Then, a new cross-field path loss model is proposed, which characterizes the power change at antenna elements in the UPA and is compatible with both FF and NF cases.

Far- and Near-Field Channel Measurements and Characterization in the Terahertz Band Using a Virtual Antenna Array

TL;DR

This work tackles the challenge of characterizing far- and near-field THz channels for extremely large-scale antenna arrays. It presents a measurement framework using a THz virtual antenna array to perform wideband MISO experiments with UPAs up to 4096 elements in the 260–320 GHz band, validating non-linear near-field phase behavior and the Rayleigh criterion for phase error. A cross-field path loss model is proposed to unify FF and NF behavior across the UPA, with parameters that have physical interpretation and fit well to the data (MSE ≈ 0.0022). The findings advance THz ELAA channel modeling and offer a practical tool for designing and analyzing THz MIMO systems, while noting the need for further measurements across different distances and frequencies to generalize the model.

Abstract

Extremely large-scale antenna array (ELAA) technologies consisting of ultra-massive multiple-input-multiple-output (UM-MIMO) or reconfigurable intelligent surfaces (RISs), are emerging to meet the demand of wireless systems in sixth-generation and beyond communications for enhanced coverage and extreme data rates up to Terabits per second. For ELAA operating at Terahertz (THz) frequencies, the Rayleigh distance expands, and users are likely to be located in both far-field (FF) and near-field (NF) regions. On one hand, new features like NF propagation and spatial non-stationarity need to be characterized. On the other hand, the transition of properties near the FF and NF boundary is worth exploring. In this paper, a complete experimental analysis of far- and near-field channel characteristics using a THz virtual antenna array is provided based on measurement of the multi-input-single-output channel with the virtual uniform planar array (UPA) structure of at most 4096 elements. In particular, non-linear phase change is observed in the NF, and the Rayleigh criterion regarding the maximum phase error is verified. Then, a new cross-field path loss model is proposed, which characterizes the power change at antenna elements in the UPA and is compatible with both FF and NF cases.
Paper Structure (9 sections, 2 equations, 3 figures, 3 tables)

This paper contains 9 sections, 2 equations, 3 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Channel Measurement Campaign
  3. Channel Measurement System
  4. Measurement Deployment
  5. Measurement Results
  6. Channel impulse response
  7. Path loss
  8. Phase
  9. Conclusion

Figures (3)

  • Figure 1: Overview of the MISO measurement.
  • Figure 2: CIR at the UPA center.
  • Figure 3: Path gain of the LoS ray across the UPA. Gray dots represent the measurement result, and the colored surface represents the model fitting result.