Spatial Impedance in mmWave Antenna Characterization: Revisiting Far-Field Criteria

This study presents a theoretical framework for evaluating electromagnetic field behavior in free-space antenna measurements, especially at mmWave frequencies. By analyzing spatial wave impedance and its deviation from the intrinsic free-space value, the paper challenges traditional far-field criteria and proposes regime-aware validation for compact range setups. The results are applicable to mmWave radar, automotive antenna testing, and near-to-far-field transformation strategies. # Spatial Impedance in mmWave Antenna Characterization: Revisiting Far-Field Criteria This is version **v1.0**, intended as the initial submission to **EuMW 2026**. The manuscript investigates the physical limitations of conventional far-field assumptions in mmWave antenna measurements, focusing on the spatial structure of wave impedance \( Z(r) \). It proposes a calibration-aware framework grounded in the analytical behavior of reactive and radiative field components, using the Hertzian dipole as a theoretical reference. --- ## Version History - **v1.0 (2026-01-14)** Initial submission version prepared for EuMW 2026. - Trimmed to 4 pages in compliance with EuMW guidelines - Figure 1 condensed into a single composite image (a–c) - Reflector circularity and \( Z(r) \neq Z_0 \) emphasized - References reduced from 12 to 8; wording tightened throughout - Acknowledgment and Conclusion sections compressed for clarity - Fully LaTeX-compliant under EuMW IEEEtran template - **v1.1 (2026-01-19)** - file name changed (delete "EuMW")