Angle-Estimation Bias and Coupling-Model Accuracy Requirements for Mutual-Coupling Compensation in 77 GHz Automotive Radar: A Simulation Study
Md Nadim Hosain1, Anup Chandra Sagor2, Md Emadur Rahman Ekra1*, Ashikur Mollik1
Abstract
Mutual coupling between closely spaced receive elements biases angle-of-arrival (AoA) estimates in automotive radar, and digital compensation removes this bias only if the assumed coupling matrix is accurate. In this study, we quantify how accurate it must be. We model an eight-element, half-wavelength patch array on Rogers RO3003 inside a complete 77 GHz FMCW chain (1 GHz chirp, 512 × 128 data cube, CA-CFAR) and compare conventional beamforming with inverse-matrix decoupling and a normalized coupled-manifold beamformer. Coupling is represented by a reduced banded model (−12 dB adjacent coupling) and, as a network-consistent benchmark, by impedance-derived coupling of half-wavelength dipoles. We show analytically that the bias equals the amplitude-weighted least-squares slope of the excess element phase; this predictor matches exact estimates within 0.004°. Without compensation, the bias reaches 0.97°, or 0.45 m of lateral error at 28.5 m, and dominates the error because the per-channel SNR after integration exceeds 20 dB for vehicle-sized targets. With an exact matrix, both estimators remove the bias, follow the Cramér–Rao bound, and cost under 0.3 dB of SNR. With an inexact matrix, the residual bias grows linearly with the coupling error: a 20% magnitude error leaves 9–19% of the bias, and a 10° phase error leaves 10–51%, depending on the coupling phase. A three-parameter banded fit fails on the network-consistent benchmark (1.99° of 2.23° remains), whereas a Toeplitz fit leaves 0.15°. Calibrating a Toeplitz-structured response from 13 angles holds the 95th-percentile residual below 0.2° at about 31 dB calibration SNR. All results are simulation-based; full-wave extraction and measurement remain necessary.
Keywords
automotive radar; FMCW radar; 77 GHz; array calibration; Cramér-Rao bound
Cite This Article
Hosain, M. N., Sagor, A. C., Ekra, M. E. R., Mollik, A. (2026). Angle-Estimation Bias and Coupling-Model Accuracy Requirements for Mutual-Coupling Compensation in 77 GHz Automotive Radar: A Simulation Study. International Journal of Scientific Advances (IJSCIA), Volume 7| Issue 6: Nov – Dec 2026, Pages 919-930. URL: https://www.ijscia.com/wp-content/uploads/2026/11/Volume7-Issue6-Nov-Dec-No.1113-919-930.pdf
Volume 7 | Issue 6: Nov – Dec 2026
