Beamforming Applications Research Articles

Joint time-frequency analysis on space-time-coding digital metasurfaces

Space-time and time-varying metastructures have attracted a lot of research interest in recent years. On the other hand, digital programmable metasurfaces have also gained great attention owing to their powerful capabilities in controlling electromagnetic (EM) fields and waves in real time, which is very suitable for implementing spatiotemporal modulations in a digital manner. Accordingly, space-time-coding (STC) digital metasurfaces have recently been proposed to realize advanced manipulations of EM wavefronts and digital information, allowing simultaneous control of propagation directions in the space domain and harmonic distributions in the frequency domain. However, their instantaneous responses and the connection between the time- and frequency-domain characteristics have not yet been fully revealed. Here, we present a joint time-frequency analysis method to revisit STC digital metasurfaces, in which the time-domain instantaneous scattering patterns and frequency-domain equivalent excitations are investigated to analyze the spatial-spectral distributions of the modulated waves. This joint time-frequency analysis method helps to better explain the basic working principle of STC digital metasurfaces and is expected to facilitate more applications in wireless communications, radar, imaging, and beamforming.

A Microwave Photonics True-Time-Delay System Using Carrier Compensation Technique Based on Wavelength Division Multiplexing

A novel microwave photonic true-time-delay (TTD) system using carrier compensation technology is proposed and experimentally demonstrated. Wavelength division multiplexing combines ten lasers into a single beam. We separate one channel from the laser as a compensating carrier, and the compensation carrier is combined with the time-delayed optical signals to be detected. Meanwhile, sideband signals are amplified effectively thanks to carrier-suppressed double-sideband (CS-DSB) modulation. Therefore, the power of both the central optical carriers and sidebands is guaranteed, which produces a better beat frequency result than the TTD system without carrier compensation. The simulation results confirm that the signal amplitude has an order of magnitude improvement due to the compensation. With employing the delay fibers based on multiple-fiber Bragg gratings (MFBGs), the experimental delay and response time reach 90.160 μs and 160.80 ns. The proposed technique can find applications in time-delay beamforming of phased array antennas (PAAs).

Optical phased array with on-chip phase calibration.

Optical phased arrays (OPAs) with phase-monitoring and phase-control capabilities are necessary for robust and accurate beamforming applications. This paper demonstrates an on-chip integrated phase calibration system where compact phase interrogator structures and readout photodiodes are implemented within the OPA architecture. This enables phase-error correction for high-fidelity beam-steering with linear complexity calibration. A 32-channel OPA with 2.5-µm pitch is fabricated in an Si-SiN photonic stack. The readout is done with silicon photon-assisted tunneling detectors (PATDs) for sub-bandgap light detection with no-process change. After the model-based calibration procedure, the beam emitted by the OPA exhibits a sidelobe suppression ratio (SLSR) of -11 dB and a beam divergence of 0.97° × 0.58° at 1.55-µm input wavelength. Wavelength-dependent calibration and tuning are also performed, allowing full 2D beam steering and arbitrary pattern generation with a low complexity algorithm.

Modified Huber M-Estimate Function-Based Distributed Constrained Adaptive Filtering Algorithm Over Sensor Network

Most of the existing distributed adaptive filtering algorithms over wireless sensor networks (WSNs) are developed, aiming to solve unconstrained network optimization problems. However, in practice, the weight coefficients of the filter may need to satisfy a set of linear equations. Thus, a distributed adaptive algorithm that can solve the sensor network optimization problem under constraints is needed. Considering the possible impulsive interference in the observed signals, a novel robust distributed constrained adaptive algorithm called diffusion constrained least mean M-estimate (D-CLMM) is proposed by using the modified Huber function (MHF), which endows the network robustness to impulsive noise. The transient, steady-state performances and stability of the proposed D-CLMM are studied with the aid of some commonly used assumptions and verified by computer simulations. Moreover, the effectiveness of D-CLMM is verified in distributed parameter estimation and beamforming applications in non-Gaussian noise environments.

Design and Analysis of a Proof-of-Concept Checkered-Network Compressive Array

Compressive arrays have recently been proposed as a new technique for reducing the number of controls in a beamforming system for a given array aperture, promising improved performance over existing thinned-array and subarray techniques. Checkered networks, feed networks consisting of interconnected couplers and fixed phase shifters, have been suggested for realizing the required overlapped subarrays. Although a checkered network has previously been implemented in microstrip, an integrated compressive array, comprising both the antenna elements and the feed network, is required to demonstrate the practical feasibility of such systems. Results for the first successfully manufactured checkered-network compressive array with integrated antenna elements are presented, thereby showing that compressive arrays are promising for use in a variety of real-world beamforming applications. Analysis of the results shows that steered-beam squint is a greater issue than previously assumed, and design guidelines are presented for minimizing the risk of excessive steered-beam squint in manufactured compressive arrays.

Slow Light Mode at the Degenerate Band Edge for True Time Delay Applications

Tuneable true time delay device is designed at the degenerate band edge (DBE) by using two coupled periodic silicon ridge waveguides. The holes of the two ridge waveguides are well-tuned to let four modes couple and degenerate at the bandgap providing a slow light mode (the DBE mode). Transfer matrix method is utilized to trace and verify the slow light mode in the device. A 25-unit cell device ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10~ \boldsymbol {\mu m}$ </tex-math></inline-formula> length device) is constructed to realize the slow mode at the DBE with 70% transmission and 42.5 ps signal delay over 130 GHz dispersion free bandwidth. Liquid crystal cladding layer is incorporated to provide continuous control of the slow mode velocity around the DBE resonance for UWB antenna array beamforming applications.

Huygens' Metasurface With Stable Transmission Response Under Wide Range of Incidence Angle

Metasurfaces, as two-dimensional (2-D) metamaterials, show great potentials in electromagnetic wave manipulation. Here, an angular nondispersive transmission-type Huygens’ meta-atom, made up of an I-shaped metal patch and a square split ring, is proposed for wide incidence angle holographic metasurfaces. Nine varieties of the Huygens’ meta-atom with high transmission amplitude (higher than 0.9) and stable transmission phase (vary less than 10°) under transverse magnetic wave illumination from 0° to 60° are selected. To verify the performance of the meta-atoms proposed, two holographic metasurfaces are simulated and fabricated to reconstitute identical holographic images under normal and oblique linearly polarized wave illuminations, respectively. The experimental demonstrations show imaging efficiencies higher than 48.28% with signal-to-noise ratio as high as 22.57. Our designs provide a solution for angular nondispersive metasurface designs, which suggest great practical applications in beamforming, and information storage systems.

A compact size wide‐angle 3 × 3 substrate integrate waveguide Butler matrix for Ku‐band applications

In this paper, an array antenna fed by a novel double layer 3 × 3 Butler matrix for Ku-band application was presented. An antipodal Vivaldi antenna (AVA) with dielectric lens was suggested as radiating elements. AVA has a broadband specification along with directive stable patterns at operational bandwidth. Combinational structure of substrate integrated waveguide topology by modified radiating element (AVAs) results to miniaturized size and acceptable radiation efficiency in whole of Ku-Band. Presented array covers frequency range of 13–17.5 GHz (30%) with average gain of 14.2 dBi. The proposed beam-steering antenna with compact size and good performance is capable to cover an angle range from −39 to 38° in whole operation frequency. This structure with unique configuration and specification can be a good candidate for beam-forming application for wireless devices.

Numerical analysis of vibroacoustic beamforming gains for acoustic source detection inside a pipe conveying turbulent flow

This study concerns a monitoring technique based on vibration measurements for identifying the presence of an acoustic source in a fluid-filled pipe conveying turbulent flow. In such situation, the source-induced vibrations can be smeared with the flow-induced vibrations, which hinders the source detection. To increase the signal-to-noise ratio (SNR), beamforming techniques can be applied to the vibrations measured by an array of accelerometers mounted on the pipe. However, the current problem is more complex and challenging than most typical beamforming applications due to strong fluid–structure coupling and to the presence of resonant modes and internal flow excitations. Numerical vibroacoustic methods are presented to predict the vibratory response of a pipe excited by a monopole source and/or a turbulent boundary layer (TBL). The cross-spectral matrices of the computed radial accelerations induced by the monopole source to be detected and by the TBL are used for assessing the performance of two vibroacoustic beamforming techniques. The array gains using both, the conventional and the MaxSNR beamforming approaches are estimated. Results indicate superior performance of the MaxSNR, which leads to significantly higher array gain.

Photonic Beamforming for 5G and Beyond: A Review of True Time Delay Devices Enabling Ultra-Wideband Beamforming for mmWave Communications

The next generations of wireless communications are promising high capacity, low latency, and high throughput, enabled by millimeter wave spectrum. Beamforming and beam steering are key requirements for millimeter wave systems due to the fundamental limitations of such high frequencies. Traditional phased array antennas are narrow band and conventional beamforming techniques are too bulky, energy hungry, and expensive to integrate into consumer electronics. Therefore, new approaches of beamforming and beamsteering are required for 5G and beyond due to shortcomings of existing technologies. Here we present a comprehensive review of the photonic true time delay units for application in beamforming of next generations of wireless communications. The prospects and progress of several photonic techniques are discussed here along with their challenges. The fundamental focus of this endeavor will be on the on-chip Silicon-on-Insulator based approaches which enable utilizing conventional CMOS fabrication process for integration with other optical components for compact photonic integrated circuit.

Mutual Interference of Automotive OFDM Radars—Analysis and Countermeasures

Due to its noise-like signal property, digital orthogonal frequency-division multiplexing (OFDM) radars are often assumed to be robust against interference. While a lot of research has been carried out for interference between different modulation schemes, the mechanisms of interference from OFDM to OFDM radars have been barely addressed. This paper provides a thorough analysis of mutual OFDM to OFDM interference based on radar measurements using a 4x4 77 GHz multiple-input multiple-output (MIMO) OFDM radar prototype. The effects of interference are described both qualitatively and quantitatively for cyclic-prefix and stepped-carrier OFDM. Second, it is shown that conventional mitigation methods in the spectrogram are not suitable due to the random coding of cyclic-prefix OFDM. As an alternative, the application of adaptive beamforming is proposed and two realization possibilities are provided. Finally, new mitigation strategies in the modulation domain are proposed. They allow to shape interference to specific range-Doppler cells, yielding an interference-free range-velocity map for the area of interest. Additionally, the method may be used as the basis to enable simple conventional interference mitigation strategies.

Analytical design for full-space spatial power dividers using metagratings

We present a rigorous theoretical framework for designing full-space spatial power dividers using metagratings. In our study, the current restrictions of spatial power dividing platforms such as reflection-only performance, operating at normal incidence, and small reflection/refraction angles have been totally relaxed. A modal expansion analysis based on the Floquet–Bloch theorem is established so that a discrete set of spatial harmonics is considered in both reflection and transmission sides of a compound metallic grating in which the unknown coefficients are calculated by applying proper boundary conditions. By eliminating the unwanted scattering harmonics, the proposed metagrating has the ability to realize different functionalities from perfect anomalous refraction to reflection/transmission spatial power dividing, without resorting to full-wave numerical optimizations. Our findings not only offer possibilities to realize arbitrary spatial power dividers but also reveal a simple platform for beam-forming applications.

CSA-based acoustic beamforming for the contribution analysis of air-borne tyre noise

The contributions of air-borne tyre noise to the overall interior noise sources of a vehicle were investigated using an acoustic beamforming technique based on the conditioned spectral analysis (CSA). This was realised using a set of accelerometers located at the various sources to measure the reference signals of these sources and, these reference signals were then applied successively in the CSA to eliminate the linear effects of these reference signals from the array microphone signals being processed. CSA is a signal separation technique that can be used for multi-reference purposes. In the CSA technique, multi-reference signals can be used to modify the original cross-spectral matrix of array microphone signals, and the combination of the acoustic beamforming method with CSA results in a powerful technique that can be used to separate sound maps into components of different mechanisms. In this paper, different signal separation techniques and their applications in acoustic beamforming are introduced. CSA-based acoustic beamforming is then proposed. The efficacy of the CSA-based acoustic beamforming was examined experimentally. Finally, the CSA-based acoustic beamforming was applied to the interior noise source localization of a vehicle to estimate the contributions from the air-borne tyre noise and other noise sources to the overall interior sound maps.

Large-scale true-time-delay remote beamforming with EO frequency combs and multicore fiber.

Optical true-time-delay (OTTD) beamforming is a promising solution to support the ultra-broadband radio access network. However, large-scale antenna arrays set at remote radio units require the OTTD counterpart to have corresponding larger-scale channel numbers. Here, we demonstrate an OTTD remote beamforming network with a record 287 channel number using electro-optic frequency combs and multicore fiber. Our proposed scheme can generate beams for both one-dimensional and two-dimensional antenna arrays. We highlight that using multicore fiber not only increases the channel numbers but also supports remote beamforming. We estimate the long-term stability of this remote beamforming network, and 1-ps-level relative time delay variation in 2 h is obtained when using multicore fiber. It is one order of magnitude better than using parallel single-mode fibers. Thus, highly stable beamforming is achieved. These results pave the way for the application of OTTD beamforming in 5G and beyond networks.

Circularly polarized hybrid mode substrate integrated waveguide antenna for two quadrant scanning beamforming applications for 5G

Electromagnetic band gap (EBG) based two ports multiple-input and multiple-output (MIMO) substrate integrated waveguide (SIW) antenna for two quadrant beamforming applications using metasurfaces is addressed. A novel SIW structure is employed to achieve beamforming. This work comprises two types of vias having different diameters and lengths in order to achieve multibeam in the first and second quadrant with 120° coverage. Two cross slots tilted at ± 45 ° are etched on top of the structure. The width variation of one of the cross slots achieved beam scanning in first quadrant with coverage of 90°. Additionally, four circular slots are etched on the top metallic layer to improve the axial ratio and the gain of the antenna. Apart from that, two diagonally etched slots help to enhance the gain and radiation properties of the antenna. Furthermore, to get the good mutual coupling and isolation between the two ports, EBG unit cells are deployed on the ground. The proposed antenna shows good right hand circularly polarized radiation within the band with the help of metasurfaces (MS) deployed on an extended part of the substrate. MS also improves the return loss bandwidth. In the end, the diversity properties of the MIMO have been studied as well. The proposed antenna shows good performance in all respects for 5G applications.

Circularly polarized hybrid mode substrate integrated waveguide antenna for two quadrant scanning beamforming applications for 5G

Electromagnetic band gap (EBG) based two ports multiple-input and multiple-output (MIMO) substrate integrated waveguide (SIW) antenna for two quadrant beamforming applications using metasurfaces (MS) is addressed. A novel SIW structure is employed to achieve beamforming. This work comprises two types of vias having different diameters and lengths in order to achieve multibeam in the first and second quadrant with 120° coverage. Two cross slots tilted at ± 45 ° are etched on top of the structure. The width variation of one of the cross slots achieved beam scanning in first quadrant with coverage of 90°. Additionally, four circular slots are etched on the top metallic layer to improve the axial ratio and the gain of the antenna. Apart from that, two diagonally etched slots help to enhance the gain and radiation properties of the antenna. Furthermore, to get the good mutual coupling and isolation between the two ports, EBG unit cells are deployed on the ground. The proposed antenna shows good right hand circularly polarized radiation within the band with the help of MS deployed on an extended part of the substrate. MS also improves the return loss bandwidth. In the end, the diversity properties of the MIMO have been studied as well. The proposed antenna shows good performance in all respects for 5G applications.

Single channel FMCW radar in moving scenario

Single channel frequency modulated continuous wave(FMCW) radar is attracting considerable critical attention in recent years due to its small size and low cost. However, the velocity-angle coupling problem occurs in a moving scenario, which eventually leads to obstacles for the application of beamforming. For this problem, the paper proposes a motion compensation method, and based on this method, a single channel FMCW radar signal processing flow is proposed. Numerical and experimental results are provided to validate the proposed method. It is suggested that the velocity-angle coupling problem can be effectively solved by the proposed motion compensation method, and moving targets can be effectively detected by using this single channel FMCW radar signal processing flow.

A Polarity Alignment Method for Group-Averaging of Event-Related Neural Signals at Source Level in MEG Beamforming Applications.

Brain waveforms reconstructed at source level, like in beamforming, suffer polarity indeterminacy, which precludes direct group averaging of associated waveforms. We describe a polarity alignment method as an alternative of averaging rectified (i.e. absolute value) waveforms. Using MEG from an auditory localisation task, we compare the ability of the two approaches to enable signal detection in the primary auditory cortex over increasing sample size. The two methods are comparable in signal detection sensitivity, but the alignment method preserves group-average polarity alternation.

Direction finding and beamforming using cylindrical array of dipole antennas in the presence of cylindrical scatterer/reflector including the mutual coupling effect

Three-dimensional dipole arrays are normally used at the proximity of a reflective structure. Filamentary short-circuited dipoles are proposed to model the effect of the reflector structure. The computational burden is significantly reduced by using mutual impedance matrices. An analytical method of modelling the effect of the cylindrical reflector in a three-dimensional cylindrical geometry of dipole antenna arrays is introduced both for direction finding and beamforming applications in the presence of mutual coupling. The results of the implementation of the MUSIC (multiple signal classification) direction-finding algorithm show that the proposed model for accounting the cylindrical reflector, in the presence of a mutual coupling effect, has the required efficiency and reduced root-mean-square-error (RMSE). Monte-Carlo simulations for the beamforming algorithm are conducted to evaluate the signal-to-interference ratio (SIR) values in the presence of a cylindrical reflector and the results show that the model has the desired performance. The whole process of beamforming and pattern generation has been verified through high-frequency structural simulator (HFSS) simulation. The simplicity, adequate precision and low computational cost of this method can be appropriately used in the cylindrical reflector/scatterer in three-dimensional geometries, especially for base station applications.

Robust Three-Microphone Speech Source Localization Using Randomized Singular Value Decomposition.

Direction-of-arrival (DOA) estimation is a fundamental technique in array signal processing due to its wide applications in beamforming, speech enhancement and many other assistive speech processing technologies. In this paper, we devise a novel DOA technique based on randomized singular value decomposition (RSVD) to improve the performance of non-uniform non-linear microphone arrays (NUNLA). The accurate and efficient singular value decomposition of large data matrices is computationally challenging, and randomization provides an effective tool for performing matrix approximation, therefore, the developed DOA estimation utilizes a modified dictionary-based RSVD method for localizing single speech sources under low signal-to-noise ratios (SNR). Unlike previous methods developed for uniform linear microphone arrays, the proposed approach with L-shaped three microphone setup has no ‘left-right’ ambiguity. We present the performance of our proposed method in comparison to other techniques. The demonstrated experiments shows at-least 20% performance improvement using simulated data and 25% performance improvement using real data when compared with similar DoA estimation techniques for NUNLA. The proposed method exploits frame-based online time delay of arrival (TDOA) measurements which facilitates the proposed algorithm to run on real-time devices. We also show an efficient real-time implementation of the proposed method on a Pixel 3 Android smartphone using its built-in three microphones for hearing aid applications.