Phased Array Theory Research Articles

Reflectarrays and Metasurface Reflectors as Diffraction Gratings: A tutorial

Reconfigurable reflectors have significant potential in future telecommunication systems, and approaches to the design and realization of full and tunable reflection control are now actively studied. Reflectarrays, being the classical approach to realize scanning reflectors, are based on the phased-array theory (the so-called generalized reflection law) and physical optics approximation of the reflection response. To overcome the limitations of the reflectarray technology, researchers actively study inhomogeneous metasurfaces, using the theory of diffraction gratings. To make these devices tunable and fully realize their potential, it is necessary to unify the two approaches and study reconfigurable reflectors from a unified point of view. Here, we offer a tutorial on reflectarrays and metasurface reflectors, explaining their common fundamental properties that stem from the diffraction theory. This tutorial is suitable for graduate and postgraduate students and hopefully will help to develop deeper understanding of both phased arrays and diffraction gratings.

On-demand harmonic wave suppression in non-Hermitian space-time-periodic phased arrays

Phased arrays have been a cornerstone of non-destructive evaluation, sonar communications, and medical imaging for years. Conventional arrays work by imparting a static phase gradient across a set of transducers to steer a self-created wavefront in a desired direction. Most recently, space-time-periodic (STP) phased arrays have been explored in the context of multi-harmonic wave beaming. Owing to the STP phase profile, multiple scattered harmonics of a single-frequency input are generated which propagate simultaneously in different directional lanes. Each of these lanes is characterized by a principal angle and a distinct frequency signature that can be computationally predicted. However, owing to the Hermitian (real) nature of the spatiotemporal phase gradient, waves emergent from the array are still bound to propagate simultaneously along up- and down-converted directions with a perfectly symmetric energy distribution. Seeking to push this boundary, this paper presents a class of non-Hermitian STP phased arrays which exercise a degree of unprecedented control over the transmitted waves through an interplay between gain, loss, and coupling between its individual components. A complex phase profile under two special symmetries, parity-time (PT) and anti-PT, is introduced that enables the modulation of the amplitude of various harmonics and decouples up- and down-converted harmonics of the same order. We show that these arrays provide on-demand suppression of either up- or down-converted harmonics at an exceptional point—a degeneracy in the parameter space where the system’s eigenvalues and eigenvectors coalesce. An experimental prototype of the non-Hermitian array is constructed to illustrate the selective directional suppression via time-transient measurements of the out-of-plane displacements of an elastic substrate via laser vibrometry. The theory of non-Hermitian phased arrays and their experimental realization unlock rich opportunities in precise elastoacoustic wave manipulation that can be tailored for a diverse range of engineering applications.

Analysis of Exponential Frequency-Diverse Array for Short-Range Beam-Focusing Technology

The frequency-diverse array (FDA) is a promising technology because of its angle- and range-dependent beam pattern. The FDA has unique properties, such as beam scanning and focusing, which are difficult to achieve using the conventional phased antenna array theory. In this study, the relationship between range and frequency increment is analyzed, and the fundamental operation principle of FDA is thoroughly investigated. The effect of coupling among antenna elements is also discussed to analyze the FDA theory. Furthermore, a novel exponential FDA method for short-range beam focusing is presented based on the proposed FDA analysis method. The proposed method has been investigated through various case studies and applied to research efforts on FDA methods. The FDA design procedures and analysis methods are also presented in this article.

주파수 다양성 배열 기술을 이용한 근거리 3차원 빔 집중 기술

The frequency diverse array (FDA) is a promising technology owing to its angle-range-dependent beam pattern. The FDA possesses unique properties such as beam scanning and focusing, which are difficult to achieve using the conventional phased antenna array theory. Herein, the relationship between range and frequency increment was analyzed, and the fundamental operation principle of FDA was investigated. Further, a novel exponential FDA method for short-range beam focusing was presented based on the proposed FDA analysis method. The proposed method was investigated through various case studies and applied to research efforts on FDA methods.

Multi-dimensional and large-sized optical phased array for space laser communication

In this study, we propose a novel multi-dimensional and large-sized optical phased array theory for space laser communication that addresses the theoretical limitations of the conventional optical phased array. We theoretically analyzed the principle of this phased array technology. The results of simulation and laboratory experiment clearly showed it can realize the large scanning angle and high optical gain required for communication. The novel optical phased array theory is of great significance to the revolution of miniaturization and networking in the field of space laser communication.

Refraction of Flexural Waves by Ultra-Broadband Achromatic Meta-Slab With Wavelength-Dependent Phase Shifts

Abstract Great progress has been made in modulating flexural waves by elastic metasurfaces. Most of the proposed elastic metasurfaces suffer from chromatic aberration, limited in a narrow bandwidth around the designed frequency. In this paper, overcoming the chromatic aberration, an ultra-broadband achromatic meta-slab (UAM) with subunits of gradient thickness is proposed to realize the refraction angle unchanged with the incident frequency. Based on the phase compensation principle, wavelength-dependent phase shifts for the UAM that realize achromaticity are obtained. In order to verify the effectiveness of the theoretical design, the transmitted wavefields are solved according to the phased array theory, and the results correspond with those obtained by the finite element (FE) simulations and experiments, which show that the refraction angle is unchanged for incident frequencies from 2 kHz to 8 kHz. Besides, the UAM is extended into a periodic meta-slab, and multifrequency achromaticity is realized. Our designed meta-slabs overcome the chromatic aberration by simple configurations, which have significance in the applications of vibration control, vibrational energy harvesting, and health monitoring.

3D-printed meta-slab for focusing flexural waves in broadband

Focusing of elastic waves by meta-structures is of considerable significance in energy harvesting. However, meeting both high transmission and wide bandwidth for these meta-structures is a challenge. In this paper, we propose a 3D-printed meta-slab with shuttle-like subunits with gradually varying thickness to focus incident flexural waves in broadband. Shuttle-like subunits have high transmission performance and frequency-dependent phase shifts. Based on these subunits, the meta-slab is designed by the mechanism of phase compensation, which makes the focal position unchanged with the incident frequencies. The wave fields of the transmitted region are obtained by the phased array theory and measured by the experiments. Their results are consistent and demonstrate well the focus ability of the meta-slab. Our design effectively concentrates the energy of broadband flexural waves, providing a new approach for energy harvesting.

Manipulating spatial directivity of acoustic scattering from a submerged cylinder by means of annular grooves

An annular groove (AG) structure with depth gradient is proposed which can manipulate the spatial distribution of the acoustic scattering field for a finite rigid cylinder in water. An analytical analysis is given for better understanding the underlying mechanism of the abnormal scattered wave, which can be accomplished by using the phased array theory. When the plane acoustic wave is normally incident, the scattering acoustic wave in the transverse direction of the cylinder deflects, which is due to the interaction between the phase delay modulated by the AG structure with varying groove depths and the Bragg scattering of adjacent grooves. The finite element method is used to calculate the acoustic scattering field of a finite rigid cylinder with annular grooves and obtain the frequency and spatial distribution characteristics. How the structural parameters such as depth, gradient, and duty ratio of the annular grooves affect the acoustic scattering field is discussed in detail. The results show that the target strength in the transverse direction decreases linearly with duty ratio increasing while the target strength in the deflection direction of the acoustic wave increases with the duty ratio until <i>δ</i> = 30%, after which it remains almost constant. When the incident acoustic wave is fixed, the acoustic scattering wave of the AG cylinder can be deflected by designing the gradient appropriately, and the deflection direction is independent of the frequency. Numerical and experimental results for a cylinder with multiple annular-groove units show that the spatial directivity of the scattering field of the grooved cylinder changes, and the target strength is enhanced at six pre-designed deflection angles. Meanwhile, the deflected acoustic wave has a certain width and the interference among periodic structures of the AG units exists, which makes the spatial directivity of the scattering field of the cylinder equalize and changes the scattering characteristics of the cylinder, thereby providing a theoretical basis for designing three-dimensional underwater objects each with an acoustic stealth.

A fractional phase-coding strategy for terahertz beam patterning on digital metasurfaces.

Coding metasurfaces have drawn great attention for its digital wave manipulation in deep subwavelength-scale in the last decade, more sophisticated and flexible coding strategies suitable for terahertz wavefront manipulations are becoming more urgently demanded. Due to its rigidity in phase gradient division, both phase gradient metasurfaces and conventional phase coding technique lack the flexibility to expand applications in a large field of view and accurate targeting. This study presents a generalized coding method by precisely reconfiguring the array factor based on the phased array theory and metasurface concept, which can be applied for anomalous scattering and ultrafine radiation patterning. According to our quantitative analysis on the relationship between the deflected angles and the supercell spacing, a fractional coding method for arbitrary phase gradient distribution has been attained by logically discretizing the spacing scale of supercells. By switching on different coding sequences or incident frequencies, a single beam to multiple beam scanning in an expanded angular range with minimal step can be achieved on the fractional phase-coding metasurfaces. As a proof of concept, the 2-bit coding metasurfaces arranged by four fractional coding sequences have been fabricated and measured, demonstrating a consecutive single-beam steering pattern ranging from 22° to 74° in 0.34-0.5 THz. Crosswise verified by the good accordance among numerical prediction, simulation and experiment, the proposed coding strategy paves a path to delicate beam regulation for high-resolution imaging and detection.

1-D Electronic Beam-Steering Partially Reflective Surface Antenna

A 1-D electronic beam-steering partially reflective surface (PRS) antenna using a new reconfigurable PRS unit cell is proposed in this paper. The proposed work addresses the challenge to achieve a large beam steering angle with small gain variation and a small number of active/lumped elements by using a reconfigurable PRS superstrate only. The PRS unit cell consists of two back-to-back T-shaped strips with one PIN diode inserted between them and a pair of trapezoid patches (a rectangular patch and a pair of triangle parasitic patches). Beam steering is achieved by controlling the different states of PIN diodes. Thanks to the trapezoid patches, the proposed unit cell can generate a larger phase difference between different states, thereby leading to a larger beam steering angle. Furthermore, due to the addition of more degrees of freedom in the proposed unit cell, the phase difference can be easily manipulated. Moreover, since the T-shaped strips in each unit cell is connected with adjacent ones, the biasing network is very simple without needing a large number of lumped elements and dc biasing lines. The beam steering property is analyzed by using phased array theory. An antenna prototype with a main beam direction towards 0°, -18° and 18° operating at 5.5 GHz in the H-plane is fabricated and measured. Good agreement between the predicted simulation and measurement results for the input reflection coefficients and radiation patterns is achieved, which validates the feasibility of the design. The measured realized gains are over 11 dBi for all states with a 0.8 dBi gain variation.

Broadband acoustic phased array with subwavelength active tube array

Acoustic metasurfaces provide a way to manipulate wavefronts at anomalous reflection or refraction angles through subwavelength structures. Here, based on the generalized Snell's refraction law for acoustic metasurfaces and the classical acoustic phased array (PA) theory, a broadband acoustic PA with a subwavelength active tube array has been proposed to form a special acoustic beam and to determine the directivity characteristics of the acoustic source. Theoretical analysis shows that the dispersionless wavefront manipulation can be realized by the gradient model of the active tube array, and a wide working frequency band can be obtained in practical applications from the simulated and experimental results. The numerical results of forming a special acoustic beam and establishing an acoustic focus model with an arbitrary focal position are consistent with the theoretical predictions. The experimental results agree well with the simulated results in the model of forming the acoustic beam of 45°. By combining acoustic metamaterials and conventional acoustic PA, the model of the active tube array paves a way to design a composite acoustic PA with high radiation efficiency and system robustness without the need for any complex circuit control system. This design concept is expected to be used in the design of ultrasonic therapy devices and high-efficiency transducers.

UHF antenna array arrangement optimization for partial discharge direction finding in air-insulted substation based on phased array theory

Ultra-high-frequency (UHF) antenna array system is applied to detect and locate partial discharge (PD) sources in air-insulated substation (AIS). Time-difference localization algorithm is generally adopted in such system in which the antenna array is of large scale. In this paper, the phased array theory from radar field is introduced to estimate the direction-of-arrival (DOA) of PD source to reduce the array size. The DOA estimation results are calculated by two-sided correlation transformation (TCT) focusing algorithm and multiple signal classification (MUSIC) algorithm. Based on that, the optimum arrangement of antenna array is investigated considering both high directional accuracy and small array size. The DOA estimation performances of three array geometries namely uniform linear array (ULA), uniform circular array (UCA) and uniform Y-shaped array are compared through Cramer-Rao lower bound (CRLB), numerical simulation and experimental testing. Moreover, the number of elements and element spacing are optimized. The results indicate that 4-elements UCA with 0.2m element spacing is the optimum array arrangement for PD location in AIS.

All-plasmonic Optical Phased Array Integrated on a Thin-film Platform

Optical phased arrays have been demonstrated to enable a variety of applications ranging from high-speed on-chip communications to vertical surface emitting lasers. Despite the prosperities of the researches on optical phased arrays, presently, the reported designs of optical phased arrays are based on silicon photonics while plasmonic-based optical phased arrays have not been demonstrated yet. In this paper, a passive plasmonic optical phased array is proposed and experimentally demonstrated. The beam of the proposed plasmonic optical phased array is steerable in the far-field area and a high directivity can be achieved. In addition, radio frequency phased array theory is demonstrated to be applicable to the description of the coupling conditions of the delocalized surface plasmons in optical phased arrays and thus the gap between the phased arrays at two distinctly different wavelengths can be bridged. The potential applications of the proposed plasmonic phased arrays include on-chip optical wireless nanolinks, optical interconnections and integrated plasmonic lasers.

A reflective-type, quasi-optical metasurface filter

We introduce a new technique for designing quasi-optical, reflective-type spatial filters. The proposed filter is a reflective metasurface with a one dimensional, frequency-dependent phase gradient along the aperture. By careful design of each unit cell of the metasurface, the phase shift gradient provided by the adjacent unit cells can be engineered to steer the beam towards a desired, anomalous reflection direction over the passband region of the filter. Outside of that range, the phase shift gradient required to produce the anomalous reflection is not present and hence, the wave is reflected towards the specular reflection direction. This way, the metasurface acts as a reflective filter in a quasi-optical system where the detector is placed along the direction of anomalous reflection. The spectral selectivity of this filter is determined by the frequency dispersion of the metasurface's phase response. Based on this principle, a prototype of the proposed metasurface filter, which operates at 10 GHz and has a bandwidth of 3%, is designed. The device is modeled using a combination of theoretical analysis using the phased-array theory and full-wave electromagnetic simulations. A prototype of this device is also fabricated and characterized using a free-space measurement system. Experimental results agree well with the simulations.

Near-Field Ultrasonic Phased Array Deflection Focusing Based CFRP Wing Box Structural Health Monitoring

Near-field ultrasonic phased array theory is researched and utilized in the carbon-fiber wing box to identify the damage in the structure. Near-field ultrasonic phased array based structural health monitoring is researched to overcome the limitation of the far-field ultrasonic phased array in monitoring scope. The time delay of the theory and the process of the damage identification method are researched in detail. The recognition result is shown in a mapped image. The proposed method is applied in carbon fiber-reinforced polymer (CFRP) wing box to monitor the load in the structure. The experimental results show that the near-field ultrasonic phased array based structural health monitoring method is effective to identify the load position in the structure.

Design of Pattern Reconfigurable Antennas Based on a Two—Element Dipole Array Model

A new method for pattern reconfigurable antenna (PRA) design is introduced on the basis of a two-element dipole array model in this communication. Firstly, a two-element dipole array loaded with varactor diodes is analyzed in detail. The two dipoles of the array are folded to form a square and the reconfigurable pattern characteristics of the array can be still explained by the phased array theory. And then, based on the two-element dipole array model, a patch top-loaded monopole antenna is proposed to design the PRA (denoted as PTMPRA). Applying the field equivalence principle, the antenna radiation can be analyzed with two couples of magnetic dipoles. The phase of the magnetic dipoles may be adjusted by the loaded varactor diodes, and the antenna can reconfigure the patterns in two orthogonal planes. The antenna is fabricated and measured. The studies validate that the new method for designing pattern reconfigurable patch antenna is simple and efficient.

3-D Imaging Based Ultrasonic Phased Array Theory for Composite Structure Damage Identification

The Lamb wave phased array theory is utilized to analysis the damage scattered signals to identify the structure defect. The damage scattered signals are gotten by comparing the health signals with the damage signals. Phased array theory based structural health monitoring can scan the structure in a certain range of 0°~180° by controlling the time delay of the excitation signals and the response signals. The processed signals in monitoring direction is shown on 3-D imaging to express the damage location in the structure. The method is verified by the experiment on the composite structure and the result shows that the Lamb wave phased array method can detect the damage in the composite structure and the 3-D image clearly displays the structure damage location.

Research on Parallel PZT Phased Array Based Structural Health Monitoring in CFPR

Phased array theroy can controll the Lamb wave beem steering in certain range by adding the time delay to the signals. Phased array theory is used to identify the damge in the structure. One dimensional PZT array is restricted in monitoring distance. Two parellel PZT sensors arrays are utilized to monitor the CFPR structure to extend the monitoring distance and to improve the precision of the damage locatilization. The experiment is done on the CFPR structure by using two parellel PZT arrays to detect the damage in the structure. The results of the experiment is shown on the mapped image. Gray-scale in the mapped image from dark to light corresponds to the signal amplitude from low to high. The highlight of the mapped image is the damage location in the structure. The monitoring results in the CFPR structure by two parellel PZT arrays is accurate and identical.

Implement of Lamb Wave Using PZT Phased Arrays for Structural Health Monitoring

Phased array theory is analyzed. The PZT phased array is applied in SHM for the Al plate to identify the hole in the structure. The Lamb wave beam steering is controlled by adding the time delay to the signals. The structure can be scanned in half plane by using the phased array theory to control the Lamb wave beam steering. The damage in the structure can be recognized and localized by the phased array method. The identification result is shown on mapped image. The phased array damage localization method is verified by the experiment and the result shows that the method is effective to recognize the hole damage in the structure.

Screw Loosening Monitoring in UAV Wing Box Based on Phased Array Theory

Phased array theory was utilized in the unmanned aerial vehicle (UAV) wing box to identify the screw loosening in the structure. Phased array theory could well control the beam steering of Lamb wave to the desired directions to scan the structure for damage recognition. The time delay in special direction was calculated for the beam steering of the signal. The recognition result was shown on a mapped image.