A Double L-Shaped 4-D MIMO Radar Array With Optimal Subspace-Based Angular Resolution

Abstract

This article presents an optimal angular resolution array design method for 4-D multiple-input and multiple-output (MIMO) radar systems, leveraging subspace-based direction-of-arrival (DOA) estimation algorithms. In MIMO radar, the array configuration is a key factor determining angular resolution. Among various topologies, the L-shaped structure provides a favorable balance between aperture use and noise robustness. Specifically, for a uniform planar array, the angular resolution improves with larger apertures along two orthogonal axes, while the L-shaped configuration achieves the best angular antinoise performance under the same aperture size. To maximize the virtual L-shaped aperture, both the transmit and receive arrays are configured in identical L-shaped orientations, forming a virtual array that preserves the optimal structure. Detailed modeling of angular resolution for 1-D linear and 2-D planar arrays is conducted, introducing an angular resolution discriminant (ARD) to evaluate the angular performance of different configurations. The impact of noise on array signals is explored, along with the concept of redundant elements. By combining the ARD with the properties of redundant elements, the double L-shaped array design is shown to achieve optimal angular resolution in both the theta and phi planes using subspace-based methods. Following the proposed approach, a 4T8R MIMO radar prototype is designed and fabricated, demonstrating angular resolutions of 8.4° and 6.1° in the theta and phi planes, respectively. Several indoor multitarget detection experiments highlight the proposed technique’s potential for indoor tracking and multipeople vital sign monitoring applications. The proposed technique is well-suited for super-resolution subspace-based angle estimation algorithms, providing a balance between simplicity and low computational complexity. This array design approach provides a solid theoretical foundation for future 4-D millimeter-wave radar applications.