Single Beam Pattern Research Articles

A liquid crystal-based multi-bit terahertz reconfigurable intelligent surface

Recently, the growing interest in reconfigurable intelligent surface (RIS) technology has spurred extensive research on its utilization in the terahertz (THz) regime. The reconfiguration of the THz field empowered by the RIS holds great significance for various practical RIS-aided implementations at THz frequencies. In this study, we present a multi-bit liquid crystal-based RIS that allows for the programmable control of THz waves. The proposed RIS is characterized by an achievable 3-bit working state as well as a near 270° maximum phase shift around 0.28 THz. This high degree of freedom in manipulating the phase of the reflected field provides flexibility in terahertz spatial beam reconfigurations. We show that the terahertz single-beam pattern can be steered continuously from 5° to 55° toward the desired angles while also allowing the adjustment of the beam number and beamwidth. Through this demonstration, we aim to contribute to the advancement of RIS technologies in the terahertz regime, paving the way for various RIS-aided applications such as THz wireless communications and beyond.

Efficient Phase-Only Dual- and Multi-Beam Pattern Synthesis With Accurate Beam Direction and Power Control Employing Partitioned Iterative FFT

In this communication, a novel phase-only method based on a partitioned iterative Fourier transform (PIFT) is presented to efficiently synthesize dual- and multibeam patterns for uniformly spaced linear and planar arrays. To achieve accurate mainlobe peak directions, the PIFT integrates a partitioned beam calibration strategy into the IFT to successively calibrate the beams by partitioning the multibeam pattern into single-beam patterns and calibrating them individually. Besides, the peak powers of the multiple beams are precisely controlled through proper mainlobe corrections. Several numerical examples of synthesizing dual- and multibeam patterns with accurately controlled peak directions and beam powers as well as reduced sidelobe levels (SLLs) are presented to demonstrate the effectiveness and efficiency of the proposed method. Synthesized results are validated with full-wave simulation. Comparisons with other phase-only methods are also presented to show the superiority of the proposed method.

Hilbert-Coding Metasurface for Diverse Electromagnetic Controls.

Metamaterials, or metasurfaces, allow the flexible and efficient manipulation of electromagnetic (EM) wave. Although the passive coding metasurfaces have achieved a great deal of functionality, they also need a complex design process. In this paper, we propose Hilbert-coding metasurfaces for flexible and convenient EM regulation by arranging Hilbert-coding metamaterial units of different orders. To demonstrate this behavior, we designed 12 metasurfaces, then fabricated and measured 6 samples. Validation results on 6 Hilbert-coding metasurfaces show the deflection angles of the four single beam patterns obtained are about 21°, 13°, 12°, and 39°, with energy values of 7.75 dB, 7.3 dB, 7.2 dB, and 7.7 dB, respectively, and the deflection angles of the dual-beam patterns are 28.5° and 20° with energy values of 10.05 dB and 11.4 dB, respectively. The results are quite consistent with the simulation data, further confirming the feasibility of our idea. In addition, there are potential applications in Wireless Communications and Radar-imaging, like EM beam scanning and EM field energy distribution control in communication and imaging scenarios.

1-Bit dual-polarized ultrathin lens antennas based on Huygens’ metasurface

In this paper 1-bit dual-polarized ultra-thin lens antennas are presented based on Huygens’ principle. The unit cell provides two-state transmission phase compensation for dual-polarized waves. By tuning state 0 away from resonance and state 1 near Huygens’ resonance, the 180° transmission phase difference between the two states is achieved. In the frequency range of 27.5–28.5 GHz, the transmission phase difference between the two states of the unit cell is 180° ± 20°, and the transmission amplitude is greater than −2 dB. Using the proposed unit cell, three ultrathin 1-bit Huygens’ metasurface antennas comprising 33 × 33 unit cells with single beams pointing separately at 0°, 15°, and 30° are designed, fabricated and measured. Simulated and measured results show that the proposed 1-bit transmitarray antenna can achieve single-beam patterns, which is useful for the development of reconfigurable transmission and digital metasurface antennas in the future.

Data-Driven Beam Management With Angular Domain Information for mmWave UAV Networks

Unmanned aerial vehicles (UAVs) have extensive civilian and military applications, but establishing a UAV network providing high data rate communications with low delay is a challenge. Millimeter wave (mmWave), with its high bandwidth nature, can be adopted in the UAV network to achieve high speed data transfer. However, it is difficult to establish and maintain the mmWave communication links due to the mobility of UAVs. In this paper, a beam management scheme utilizing angular domain information (ADI) is proposed to rapidly establish and reliably maintain the communication links for the mmWave UAV network. Firstly, Gaussian process machine learning (GPML)-enabled position prediction is proposed to facilitate coarse-ADI acquisition through the proposed UAV clustering algorithm. Then, with the proposed confined-ADI acquisition which removes the redundancy in the coarse-ADI acquisition, fast beam tracking with respectively the single-beam pattern and the multi-beam pattern is achieved. Finally, a data-driven beam pattern selection scheme is proposed for improving the spectrum efficiency. Simulation results verify the outstanding performance of the proposed beam management for mmWave UAV networks.

HackMan: hacking commodity millimeter-wave hardware for a measurement study

The extremely high frequency of Millimeter-Wave technology warrants Gbps throughput for the next-generation wireless communication systems, but mmWave signals also suffer from severe path loss due to high attenuation. To compensate for this loss, mmWave radios establish communication links via directional beams so as to increase channel gains and communication range. Until recently, the measurement studies on mmWave technology were mainly based on prototypes built from band-limited Software Defined Radio, which could not characterize performance in realistic settings. Latest studies using commodity hardware reports straightforward measurements on the impact of environment settings but did not present deep analysis on the correlations of low-layer information. Meanwhile, those studies lack the ability to configure commodity devices under controlled settings, for instance, a single beam pattern for experimentation, thus failing to perform deeper analysis on low-layer protocol parameters. In this paper, we conduct extensive measurements in typical indoor settings, utilizing 802.11ad-compliant commodity hardware. Different from earlier studies, we hack the firmware and gain the privilege to modify physical layer settings online, enabling us to gain more insights under controlled settings. Essentially, we have demonstrated that (1) Signal-to-Noise Ratio, the criteria for beam control, may not be positively correlated with throughput, (2) sticking to a single beam pattern during data transmission can lead to both channel gains and throughput improvement, and (3) only independent cross-links could interfere with each other while multi-links coordinated by one AP experience no interference. These insights lead us to rethink the existing beam control policy.

Single-Beam 1 Bit Reflective Metasurface Using Prephased Unit Cells for Normally Incident Plane Waves

A single-beam prephased 1 bit reflective metasurface is proposed to achieve single-beam patterns under normally incident plane waves. Theoretical analysis and numerical simulations are presented to show that, under normally incident waves, single-beam patterns can be achieved by introducing a fixed prephase distribution with two values in the 1 bit metasurface. Compared with conventional 1 bit reflective metasurfaces, the proposed scheme alleviates the inherent limitation of single-beam patterns on 1 bit reflective metasurfaces under normally incident plane waves. To verify the proposed scheme, a 1 bit unit cell is designed with a 180°±25° phase difference between the two states for frequencies ranging from 34.3 to 49.9 GHz, and a layer-stacking method is proposed to achieve two prephases with a 90° phase difference. As an example, three 1 bit reflective metasurfaces comprising 20 × 20 unit cells with single beams pointing separately at 0°, 15°, and 30° are designed and measured over frequencies of 37.0 to 41.0 GHz; the measured sidelobe levels are less than -7.8 dB. Simulated and measured results show that the proposed prephased 1 bit metasurface can achieve single-beam patterns under normally incident plane waves.

Deep learning enabled superfast and accurate M2 evaluation for fiber beams.

We introduce deep learning technique to predict the beam propagation factor M2 of the laser beams emitting from few-mode fiber for the first time, to the best of our knowledge. The deep convolutional neural network (CNN) is trained with paired data of simulated near-field beam patterns and their calculated M2 value, aiming at learning a fast and accurate mapping from the former to the latter. The trained deep CNN can then be utilized to evaluate M2 of the fiber beams from single beam patterns. The results of simulated testing samples have shown that our scheme can achieve an averaged prediction error smaller than 2% even when up to 10 eigenmodes are involved in the fiber. The error becomes slightly larger when heavy noises are added into the input beam patterns but still smaller than 2.5%, which further proves the accuracy and robustness of our method. Furthermore, the M2 estimation takes only about 5 ms for a prepared beam pattern with one forward pass, which can be adopted for real-time M2 determination with only one supporting Charge-Coupled Device (CCD). The experimental results further prove the feasibility of our scheme. Moreover, the method we proposed can be confidently extended to other kinds of beams provided that adequate training samples are accessible. Deep learning paves the way to superfast and accurate M2 evaluation with very low experimental efforts.

Simultaneous Generation of Complex Structured Curve Beam.

At present, people are using holographic technologies to shape complex optical beams for both fundamental research and practical applications. However, most of the reported works are focusing on the generation of a single beam pattern based on the computer-generated hologram (CGH). In this paper, we present a method for simultaneously shaping the multiple beam lattice where the intensity and phase of each individual beam can be prescribed along an arbitrary geometric curve. The CGH that is responsible for each individual beam is calculated by using the holographic beam shaping technique, afterwards all the CGHs are multiplexed and encoded into one phase-only hologram by adding respective linear phase grating such that different curves are appeared in different positions of the focal regions. We experimentally prove that the simultaneous generation of multiple beams can be readily achieved. The generated beams are especially useful for applications such as multitasking micro-machining and optical trapping.

Joint Sparsity-Based Range-Angle-Dependent Beampattern Synthesis for Frequency Diverse Array

For frequency diverse array (FDA) range-angle-dependent beampattern synthesis, the objective is to obtain the desired beampattern performance using fewer antenna elements or smaller aperture. This paper proposes a FDA single-beam pattern synthesis by joint $\ell _{1}$ -norm minimization and convex optimization in the beginning. A virtual uniform FDA array with small element spacing and corresponding frequency increment is created first. Then, we formulate the array pattern synthesis (APS) problem as finding a joint sparse weight vector, which can be obtained by solving a convex optimization problem with the joint sparse constraint between angle dimension weight vector and range dimension weight vector, where some small entries of the vector can be regarded as zeros without significantly changing the array pattern performance. The antenna elements corresponding to the mapping positions of nonzero values of the joint sparse weight vector are placed to form a non-uniform FDA. Finally, convex optimization is further conducted to obtain the optimal weight vector of the non-uniform FDA. Besides, we expand the idea to FDA multi-beam pattern synthesis based on the convex optimization problem with joint sparse constraint between angle dimension weight matrix and range dimension weight matrix. Numerical examples are provided to verify the efficiency of achieving the desired radiation pattern with the fewer antenna elements, and better APS performance for given array elements.

Source Geometry Optimization for Hemispherical Radiation Pattern Coverage

Single beam patterns radiated by linear sources degrade as their maxima points toward endfire direction. Different source geometries are, therefore, to be investigated and compared to achieve better angular coverage. We choose to perform this by analyzing the characteristics of the linear operator connecting the current source to the far field in a simplified two-dimensional (2-D) geometry through its singular value decomposition (SVD). Two indexes are introduced and found useful to achieve geometry optimization. First, the case of continuous sources is examined and then the results are extended to discrete (array) sources. It is found that, while the best solution is a conformal semicircumference source, linear sources arranged at angles provide nearly identical single beam patterns pointing in different directions to provide a hemispherical coverage.

Testing spatial co-prime sampling theory

An array of sensors can be used to estimate the direction of arrival of a narrowband signal in the far field with the use of conventional beamforming. In order to avoid spatial aliasing, the distance between the sensors have to be d ≤ λ/2 apart. This is analogous to the Nyquist theorem for sampling in time with fs= 2fo. Co-Prime arrays are non-uniform arrays that can predict what a uniform array with an aperture of L = M×N total sensors can using fewer sensors; they have a total number of sensors L = M + N—1 while maintaining an aperture of M×N sensors in a full uniform line array with λ/2 spacing between elements. Each subarray is uniform linear, equally spaced by Nλ/2 or M λ/2 and then combined to create a non-uniform linear array. The result with the different inter-element spacing between the subarrays is grating lobes in different locations with the exception of the true DOA. Conventional beamforming is done with both subarrays and the outputs are then multiplied together to yield a single beam pattern. The theory to this will be tested using a uniform array of 30 sensors and selecting the data from certain sensors to achieve co-prime sampling.

Design, Simulation, and Experimental Study of Far-Field Beam-Forming Techniques Using Conformal Waveguide Arrays

Phased-array antennas have been employed for decades in numerous applications, such as radar, cellular communications, and satellite systems. Satellite links, for example, may require high-gain microwave beams with overall wide area coverage. Phased-array antennas for such an application can typically control position and beam width of individual sectoral patterns within the coverage region. This article presents an economical alternative in a conformal array antenna of open-ended rectangular waveguides, which can generate either multi-beam or single-beam patterns by switching control to different radiator configurations within the array structure. In the implementation to be presented, the conformal array property is realized by an axial shift of the array elements. This provides additional control over multi-beam coverage area and intensity taper. In this article, four array configurations are presented with experimental and simulated results that are shown to be in close agreement.

Recent progress in laser fusion research at Osaka University: Uniformity and stability issues*

Improvement of laser irradiation uniformity in the Gekko XII system [IEEE J. Quantum Electron. QE-17, 1639 (1981)], both single beam pattern and power balance, is discussed. Substantial reduction of laser absorption nonuniformity is obtained for spherical harmonic modes greater than 15 by introducing spectrally dispersed amplified spontaneous emission. No perturbation growth is observed in flat foils accelerated by spectrally dispersed amplified spontaneous emission. Dependences of laser absorption uniformity on beam pattern and power imbalance are investigated in detail. The design goal of the power imbalance in the precision Gekko XII system is 3% in peak to valley, and laser absorption nonuniformity is estimated to be a few percent. Growth of hydrodynamic instabilities is analyzed for high convergence ratio implosions in the precision Gekko XII system.

Back-Face Only Electrical Connections of Thickness Mode Piezoelectric Transducers

The radiation patterns of disk transducers connected in a recently reported novel manner by Laughlin, Drews, and Wilson is studied. In this connection, the back-face plating of a transducer is divided into two electrodes which constitute the only transducer-to- transceiver connection, and a dual-beam radiation pattern resulted. However, we found that repolarizing one half of the transducer re- stored a single beam pattern. This method of connection and regionally repolarizing the piezoelectric transducer appears highly advantageous for use in fabrication of both miniature transducers and various trans- ducer arrays (e.g., linear, annular, and matrix).