Super‐resolution orbital angular momentum based radar targets detection

Abstract

Radiating twisted beams, Orbital Angular Momentum (OAM) based radar provides a new perspective for present radar techniques. However, estimation methods now used has a demerit of resolution. Thus, we raised Multiple Signal Classification (MUSIC) algorithm to improve resolution ability based on this innovative concept. The echo model based on uniform circular array (UCA) for MUSIC was first built. In contrast to uncorrelated signals in classical MUSIC algorithm, echo signals from targets are fully coherent with each other. Spatial smoothing technique was subsequently utilized in OAM regime to tackle it. Simulation results showed the super-resolution capacity of MUSIC to detect objectives compared to the traditional Fast Fourier Transform (FFT) method. Introduction: Orbital Angular Momentum (OAM) has been widely studied in optic regime regarding imaging, microscopic particle and communication [1,2]. While radio OAM had not been explored until Bo. Thide et al. first proved the effectiveness of OAM generating in a low-frequency band in [3]. The numerous orthogonal helical beams entitle OAM a larger freedom degree, benefiting high capacity of communication and enriching radar targets more information. Recent work on radio OAM consists of two parts, i.e. antennas design to produce twisted beams and OAM multiplexing in communication system. Several approaches including circular array [4-6], spiral phase plate [7-8], higher resonate mode [9] are employed to engender electromagnetic vortex. Meanwhile, OAM multiplexing from simulations to outdoor experiments [10-12] were conducted to attain a high-capacity communication. Radar based on this concept had not attracted much attention until Guo et al. [13] first proposed OAM based target detection model, opening a new perspective for existing radar techniques. Such system generates various twisted beams to illuminate targets as shown in Fig.1 and receive echo signals in a reverse way. By making a Fast Fourier Transform (FFT) or back projection of received signals, this scheme manifests azimuthal resolution ability without relative moves or beams scanning. Additionally, no complex waveform is needed for this scenario. Later, [14] further extended the detection model to Multiple-in-multiple-out (MIMO) and Multiple-in-single-out (MISO) modes. Besides, two-dimension imaging method by exploiting OAM and frequency diversity was studied as well. Both papers utilized traditional methods like FFT and black projection to make estimations of azimuth angle. To gain a high resolution, numerous samples in OAM domain are required, thus increasing complexity of the system. Therefore, super-resolution techniques based on OAM radar detection are in demand. This paper built the model and derived spatial smoothing multiple signal classification (MUSIC) [15] algorithm to gain super-resolution estimations of targets.

Orbital Angular Momentum Waves: Generation, Detection, and Emerging Applications

“…Due to the existence of the Rayleigh limit, traditional radar imaging algorithms can only provide limited azimuth resolution. Some efficient algorithms have been proposed for OAM-based super-resolution radar imaging, such as UCAA-based autoregressive models and power spectral density (PSD) estimation algorithm [187], UCAA-based echo models and multiple signal classification (MUSIC) algorithm [188], [189], estimating signal parameter via rotational invariance techniques (ESPRIT) algorithm [190] and least squares algorithms [191], [192].…”

Sidelobe Suppression and Beam Collimation in the Generation of Vortex Electromagnetic Waves for Radar Imaging

“…However, OAM multiplexing in the wireless communication has also caused controversy [5]. For radar detection and imaging realms, the helical phase-front can be exploited to improve the resolution of the cross-range profile of the target [6]- [8]. In [7], [9], the concentric uniform circular arrays are designed to adjust the main-lobe directions of the OAM beams with different modes.…”

Reflective Metasurface for Vortex Wave Generating and Divergence Reducing in X-Band

“…Over the years, there are many progressive explorations on the application of vortex wave in multidisciplinary field such as communications [12], detection [13] and imaging [14] for its obvious advantages. The generation of vortex wave is the basis for the application of vortex wave.…”