Three-Dimensional Target Parameter Estimation Method Based on Limited-Mode Vortex Electromagnetic Wave Radar

Compared with traditional radar systems, the vortex electromagnetic wave (VEMW) radar based on orbital angular momentum (OAM) provides additional degrees of freedom for target detection. However, most existing VEMW radar imaging and parameter estimation methods rely on a large number of OAM modes, which significantly increases the hardware cost and complexity of the system. Moreover, the introduction of high-order modes causes the main lobe of the VEMW to deviate from the region of interest while reducing the system’s robustness to noise, severely limiting its practical engineering applications. To address these limitations, this study proposes a three-dimensional target parameter estimation method based on limited OAM modes. First, a forward-looking imaging geometric model of the VEMW radar is constructed, and pulse compression technology is used to extract the target’s range information. Subsequently, the echo ratio between the sum and difference beams of dual OAM modes is constructed, and the symmetry of the Bessel function is utilized to estimate the target’s azimuth angle information. Finally, the echo signal ratio of adjacent OAM modes is constructed, and the recurrence property of the Bessel function is used to estimate the target’s elevation angle information. Furthermore, for a dual-target scenario within the same range bin, the echo signal ratio of adjacent OAM modes is constructed, and the target parameters are estimated by exploiting the phase difference characteristics of the echoes. In addition, this paper derives the Cramér–Rao lower bound for azimuth and elevation angle estimation and compares the root mean square error of the proposed closed-form three-dimensional estimation method with the theoretical lower bound. Numerical simulations and microwave anechoic chamber experiments show that the proposed method achieves reliable three-dimensional parameter estimation in multitarget and noisy environments, thereby verifying its effectiveness and engineering feasibility.