Mingtuan Lin

Improved OAM-Based Radar Targets Detection Using Uniform Concentric Circular Arrays

Without any relative moves or beam scanning, the novel Orbital-Angular-Momentum- (OAM-) based radar targets detection technique using uniform concentric circular arrays (UCCAs) shows the azimuthal estimation ability, which provides new perspective for radar system design. However, the main estimation method, that is, Fast Fourier Transform (FFT), under this scheme suffers from low resolution. As a solution, this paper rebuilds the OAM-based radar targets detection model and introduces the multiple signal classification (MUSIC) algorithm to improve the resolution for detecting targets within the main lobes. The spatial smoothing technique is proposed to tackle the coherent problem brought by the proposed model. Analytical study and simulation demonstrate the superresolution estimation capacity the MUSIC algorithm can achieve for detecting targets within the main lobes. The performance of the MUSIC algorithm to detect targets not illuminated by the main lobes is further evaluated. Despite the fact that MUSIC algorithm loses the resolution advantage under this case, its estimation is more robust than that of the FFT method. Overall, the proposed MUSIC algorithm for the OAM-based radar system demonstrates the superresolution ability for detecting targets within the main lobes and good robustness for targets out of the main lobes.

Performance Analyses of the Radio Orbital Angular Momentum Steering Technique Based on Ka-Band Antenna

The misalignment in the orbital angular momentum- (OAM-) based system would distort the radiation patterns of twisted beams carrying OAM, consequently making the OAM-based communication infeasible. To tackle the misalignment problem, a radio OAM steering technique based on a uniform circular array (UCA) is illustrated. Subsequently, simulations are conducted to explore the influence of the OAM steering on the OAM mode quality and transmission performance. Furthermore, UCAs working at Ka-band with formulated feeding networks are designed and fabricated to analyze the performance of the OAM steering. The influences of OAM steering on mode quality and orthogonality are then evaluated in the experiment. Overall, the analyses of OAM steering technique are beneficial for the development of radio OAM study.

Theoretical Analyses and Design of Circular Array to Generate Orbital Angular Momentum

Uniform circular array (UCA) is a pioneering approach to generate radio twisted beams carrying orbital angular momentum (OAM). However, faulty antenna elements in a UCA could render the array into an imperfect UCA (IUCA), consequently creating distortion for OAM-based communication or radar systems. To analyze the effects of an IUCA on generating OAM, elementary wave function and wave transformation are derived to obtain field equations of a general circular array. Further derivation of IUCA shows that the field of an IUCA is a superposition of OAM modes, which is caused by polluted orthogonalities of OAM modes. To achieve pure OAM modes, the orthogonal matching pursuit algorithm, the convex optimization tool, and the analytical solution are employed to design a feeding network to retrieve the orthogonal property at the cost of strong gain loss. Then, the reduced constraints method is proposed for the IUCA to achieve high-purity and low-loss OAM mode. Finally, four circular arrays with different shapes are explored for limited installation space to generate twisted beams.

Rotary way to resolve ambiguity for planar array

In this paper we address a novel method of eliminating ambiguity for planar array. It is known that ambiguity appears in the direction of arrivals (DOA) estimation when the aperture of the array is large enough. We propose a method of rotating the array to solve the ambiguity problem. Firstly, we use multiple signal classical algorithm (MUSIC) to estimate DOA. Then we rotate an angle of the array and use MUSIC again to obtain the spatial spectrum. Later, a rotary MUSIC (R-MUSIC) algorithm defined as root of two spectrums product is proposed, which can suppress pseudo peaks of spectrum. Furthermore, an Improved R-MUSIC (IR-MUSIC) is raised to improve the performance. Finally, simulation results for circular array show that the rotary method of resolving ambiguity is feasible and effective. And we also evaluate the suppression performance for different rotation angles.

Experiment of ka-band orbital angular momentum steering technique

The Orbital Angular Momentum-(OAM-) based system exhibits high potential to realize speedy communication for short-range application, which requires the transmitter and receiver should be strictly aligned to each other. For misaligned system, it would distort the helical phase profile and intensity pattern of twisted beams carrying OAM. In this paper, Ka-band radio OAM steering technique by employing traditional beams steering method is demonstrated to tackle the misalignment problem. Experiment shows a good conservation of OAM mode after steering.

Single-Layer SIW corrugated technique for gain enhancement

A single-layer corrugated antenna based on substrate integrated waveguide (SIW) technique working at Ka-band is designed in this paper. Unlike traditional metallic corrugated method and multiple-layer SIW corrugated technique, the proposed antenna, with a lower profile and simpler fabrication, employs the SIW slot as the feeder and SIW grooves to enhance the radiation. Simulation demonstrates a 6.8 dB gain improvement for single SIW slot surrounded by periodic SIW grooves. Furthermore, the SIW slot array is implemented to achieve a higher gain. The fabricated antenna has a low reflection less than 10 dB from 26.4 GHz to 28.2 GHz and an enhanced gain up to 18 dB, showing a good agreement with the simulation results.

DOA ambiguity suppressing by rotating the array

Enlightened by nonlinear property of the pseudo direction of arrivals (DOA) estimation, a rotary method by rotating the array is used to suppress ambiguity. By employing the multiple signal classical algorithm (MUSIC), the DOA is estimated before and after the rotation. Taking advantage of two estimations, a rotary MUSIC is defined to reduce the ambiguity, as well as the improved R-MUSIC. With simulations, it has been proved that the proposed rotary method have a great suppression of ambiguity. In comparison with traditional sparse array method of eliminating ambiguity, the proposed rotary method has greater ambiguity suppression and can work in a wider frequency band.

The SVA-MUSIC Algorithm Based on a Simple Vector Array

The MUSIC algorithm based on a vector array can estimate the direction of arrivals (DOA) and polarization parameters with the impinging signals carrying the polarization information. The conventional vector unit consists of two orthogonal dipoles which are always not orthogonal since the isolation between two dipoles is not ideal. Moreover the design of the two orthogonal dipoles is always complex. In this paper, a simple vector array (SVA) is proposed to overcome the disadvantage of the conventional vector array (CVA). Instead of using two orthogonal dipoles, the vector sensor unit only includes one dipole in such a SVA with the adjacent unit orthogonal. The SVA-MUSIC algorithm based on a SVA is also proposed in the paper. The simulation results presented in the paper prove its feasibility and show that the SVA-MUSIC algorithm has a better resolution and performance than the CSA-MUSIC (Conventional Scalar Array MUSIC).