A Decoupling-based Approach for Signature Estimation of Wideband XL MIMO-FMCW Radars

Abstract

Modern radars employing wideband signals and extremely large (XL) multiple-input multiple-output (MIMO) arrays can significantly improve range and angular resolution. However, when large bandwidth and array aperture are used simultaneously, the spatial delay across the array becomes comparable to the radar range resolution, leading to the spatial wideband effect (SWE). The SWE introduces several distortions including range migration (range squint), beam squint, and range-angle coupling (RAC), which spread the target response in the range-angle domain and may cause physically separated targets to overlap and mask each other. In this work, we propose a decoupling-based target detection and parameter estimation framework for MIMO frequency modulated continuous wave (FMCW) radar. The proposed method reformulates the joint range-angle estimation problem as a decoupled sequential frequency estimation problem, where the two-dimensional (2D) estimation is carried out through successive one-dimensional (1D) super-resolution estimations. Specifically, we employ orthogonal matching pursuit (OMP) to perform sparse recovery-based range and angle estimation with high resolution. The proposed decoupling strategy is further extended to spatial wideband XL-MIMO FMCW radar systems, enabling reliable detection and separation of targets even when their responses overlap due to severe RAC. Simulation results demonstrate that the proposed approach accurately detects multiple targets and successfully resolves overlapping target responses in the presence of SWE, outperforming conventional Fourier transform and clustering-based methods.

Figures (5)

• Figure 1: Uniform linear array corresponding to virtual elements of XL-MIMO radar
• Figure 2: Illustration of signal distortions in XL-MIMO FMCW radar systems. (a) range–angle map showing dual wideband spread due to RAC. (b) frequency-dependent beam squint effect (c) range migration effect across the large antenna array.
• Figure 3: Illustration of proposed decoupling-based signature estimation (a) joint range–angle map with three targets across two range bins (b) range profile revealing two resolvable bins (c) angular profile at the first bin with a single target (d) angular profile at the second bin with two targets.
• Figure 4: Range–angle maps and clustering results for three targets under different configurations, demonstrating the impact of SWE on target separability.
• Figure 5: Detection of targets in the range--angle domain using the proposed decoupling-based low-index method (a) angular frequency domain response showing successful detection of all target DoAs. (b)--(d) corresponding beat frequency responses for each detected DoA, clearly separating the overlapping targets in the range domain.