Array Theory Research Articles

Pattern Reconfigurable, Low-Profile, Vertically Polarized, ZOR-Metasurface Antenna for 5G Application

A novel miniaturized, aperture-shared, vertically polarized (VP), zeroth-order resonance (ZOR)-based, metasurface antenna with pattern reconfigurability is proposed for sub-6 GHz fifth-generation (5G) application in this article. By exploring an aperture-shared ZOR metasurface with only four p-i-n diodes, the proposed pattern reconfigurable metasurface radiator can be operated at nine radiation states (one omnidirectional beam and eight scanning beams with 45° step). This novel reconfigurable ZOR metasurface is analyzed by equivalent circuit, array theory, and field distribution. To validate the proposed working principles and design guidelines, this VP metasurface-based pattern reconfigurable antenna with a low profile of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.05\lambda _{0}$ </tex-math></inline-formula> is fabricated and measured. It exhibits an 11.5% overlapped −10 dB impedance bandwidth (3.40–3.8 GHz, well covering B42/B43 LTE bands) and a 4.5 dBi peak gain in different radiation states. With the advantages of a miniaturized size (low profile), broadband, flexible pattern switching capacity, good radiation performance, and simple design, it is well poised for space-limited sub-6 GHz microcell applications.

두 가지 개구구조의 투과 단면적에 대한 일반적인 표현식의 타당성: 단일 공진 개구 구조와 비공진 개구의 유한 주기구조

For an electromagnetic plane wave that is normally incident upon an aperture or aperture array in an infinite perfectly electrical conducting plane, the validity of the general expression for the transmission cross-section as a measure of the transmitted power through the aperture or aperture array is investigated for the following two cases: first, for a single transmission resonant aperture (TRA) such as a complementary split ring resonator, which is larger than Bethe’s small magnetic dipole; second, for the finite periodic array of a non-TRA such as the usual circular or rectangular apertures aligned along the E-plane direction corresponding to the parallel configuration in terms of the terminology of the electrical dipole array theory. To validate the investigation, the proposed expression is applied to a general aperture distribution, and the results are compared with the results obtained using the Rao–Wilton–Glisson method for the above two cases of aperture distributions. Consequently, it is discovered that for the finite array of non-TRAs, the E-plane aperture array produces an improved directive for the field than the H-plane aperture array used as the Huygens source. This observation may aid in understanding the underlying physics of the two-slot model for rectangular microstrip antennas and the basic 1D linear array as a minimal system exhibiting the extraordinary optical transmission phenomena in 2D aperture arrays.

Performance analysis of spectrum sensing based on distributed satellite clusters under perturbation

In this paper, we investigate the spectrum sensing performance of a distributed satellite clusters (DSC) under perturbation, aiming to enhance the sensing ability of weak signals in the coexistence of strong and weak signals. Specifically, we propose a cooperative beamforming (BF) algorithm though random antenna array theory to fit the location characteristic of DSC and derive the average far-field beam pattern under perturbation. Then, a constrained optimization problem with maximizing the signal to interference plus noise ratio (SINR) is modeled to obtain the BF weight vectors, and an approximate expression of SINR is presented in the presence of the mismatch of signal steering vector. Finally, we derive the closed-form expression of the detection probability for the considered DSC over Shadowed-Rician fading channels. Simulation results are provided to validate our theoretical analysis and to characterize the impact of various parameters on the system performance.

Generation of arbitrarily directed split beams with a reflective metasurface.

We present a new, to the best of our knowledge, formalism in the design of metasurface beamsplitters with arbitrarily chosen split beam directions. This technique is based on the well-established array theory; in particular the Fourier transform method of array synthesis, to cast an obliquely incident plane wave to multiple designer-selected scattering directions. To show the efficacy of this approach, a beamsplitting metasurface reflector is designed and verified experimentally and numerically. The metasurface is fabricated by screen-printing patterns of metallic rectangular-shaped resonators of conductive ink onto a ground plane-backed substrate. The beamsplitting characteristics are quantified using a simple free-space transmit/receive horn system operating at 10.525 GHz. It is shown that the presented design technique accurately predicts the scattering properties of the fabricated metasurface and is a useful method for electromagnetic wave manipulation.

Multimodal Orbital Angular Momentum Data Model Based on Mechanically Reconfigurable Arrays and Neural Networks.

Multimodal orbital angular momentum is a research hotspot in the field of electromagnetic wave communication. How to accurately detect and identify multimodal orbital angular momentum data is a current academic problem. Based on the theory of mechanically reconfigurable arrays and neural networks, the purity, detection method, and transmission and reception of orbital angular momentum vortex waves are modeled in this paper. Through the network identification of the dynamic model of the three-degree-of-freedom reconfigurable manipulator, the paper takes the identification result and the control input of the single neuron PID as the input of the system control torque of the manipulator and realizes the reconfigurable manipulator. In the simulation process, the local approximation effect of the nonlinear control system used is very ideal. The single neuron PID controller overcomes the shortcomings of time-consuming and unsatisfactory control accuracy caused by the constant parameter of the traditional PID controller and realizes the circular loop. On the other hand, at the point of interest of the human eye, its resolution value is the largest, and its value gradually decreases as the distance from the pit increases. The experimental results show that the three-transmitting and three-receiving orbital angular momentum vortex wave transceiver system based on the mechanically reconfigurable array and neural network theory is relatively complete, and the transmission coefficient between the same modes reaches 0.827, which is much higher than that between different modes. On this basis, the modal purity, detection method, and reception of orbital angular momentum are studied accordingly. At the same time, the damage to the microscopic particles can be greatly reduced. At the same time, the information delay is reduced to 8.25%, which effectively improves the isolation characteristics of different modal orbital angular momentum channels and promotes the communication transmission of multimodal signals.

Multi beam scanning programmable metasurface using miniaturized unit cells for 5G applications

This paper proposes a programmable reflective metasurface with a miniaturized unit cell that actively controls the scattered waves for achieving steerable multibeam radiation in sub-6 GHz 5G communication systems. The design uses array theory to provide the required phase shifts for various multibeam radiation patterns. The reconfigurability of the metasurface phase profile is attained by voltage-controlled varactor diodes embedded in the structure. Then, different unit cell arrangements are employed to achieve multibeam functionality where Pianoboard and Chessboard configurations provide one and two-dimensional multi beams, respectively. It turns out steerable multibeam radiation is achieved by dynamically change the dimension of the super unit cells. The reliability of the results is verified through analytical and numerical approaches. Moreover, the comparisons show that the proposed unit cell has more miniaturized size rather than the conventional cells, resulting in a better approximation for the ideally continuous phase profile identified by the generalized Snell’s law.

Standing-Wave Feeding for High-Gain Linear Dielectric Resonator Antenna (DRA) Array.

A novel feeding method for linear DRA arrays is presented, illuminating the use of the power divider, transitions, and launchers, and keeping uniform excitation to array elements. This results in a high-gain DRA array with low losses with a design that is simple, compact and inexpensive. The proposed feeding method is based on exciting standing waves using discrete metallic patches in a simple design procedure. Two arrays with two and four DRA elements are presented as a proof of concept, which provide high gains of 12 and , respectively, which are close to the theoretical limit based on array theory. The radiation efficiency for both arrays is about 93%, which is equal to the array element efficiency, confirming that the feeding method does not add losses as in the case of standard methods. To facilitate the fabrication process, the entire array structure is 3D-printed, which significantly decreases the complexity of fabrication and alignment. Compared to state-of-the-art feeding techniques, the proposed method provides higher gain and higher efficiency with a smaller electrical size.

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.

Array Signal Processing on Distributed Acoustic Sensing Data: Directivity Effects in Slowness Space

AbstractDistributed Acoustic Sensing (DAS) involves the transmission of laser pulses along a fiber‐optic cable. These pulses are backscattered at fiber inhomogeneities and again detected by the same interrogator unit that emits the pulses. Elastic deformation along the fiber causes phase shifts in the backscattered laser pulses which are converted to spatially averaged strain measurements, typically at regular fiber intervals. DAS systems provide the potential to employ array processing algorithms. However, there are certain differences between DAS and conventional sensors. While seismic sensors typically record the directional particle displacement, velocity, or acceleration, the DAS axial strain is inherently proportional to the spatial gradient of the axial cable displacement. DAS is therefore insensitive to broadside displacement, for example, broadside P‐waves. In classical delay‐and‐sum beamforming, the array response function is the far‐field response on a horizontal slowness (or wavenumber) grid. However, for geometrically non‐linear DAS layouts, the angle between wavefront and cable varies, requiring the analysis of a steered response that varies with the direction of arrival. This contrasts with the traditional array response function which is given in terms of slowness difference between arrival and steering. This paper provides a framework for DAS steered response estimation accounting also for cable directivity and gauge‐length averaging – hereby demonstrating the applicability of DAS in array seismology and to assess DAS design aspects. It bridges a gap between DAS and array theory frameworks and communities, facilitating increased employment of DAS as a seismic array, while providing building blocks for the development of DAS array design tools.

Imaginary couplings in non-Hermitian coupled-mode theory: Effects on exceptional points of optical resonators

Exceptional point (EP) degeneracies in coupled cavities with gain and loss provide on-chip photonic devices with unconventional features and performance. However, such systems with realistic structures often miss the exact EPs even in simulation, and the mechanism of this EP disruption has yet to be thoroughly identified. Here, we extend the coupled-mode theory of one-dimensional non-Hermitian resonator arrays to study the effects of the imaginary part of the inter-cavity coupling, which is a second-order term and attributed to material amplification, absorption, and radiation. By taking an appropriate gauge for the model, we clarify that the imaginary coupling components have a symmetric form in the effective Hamiltonian and hence represent non-Hermiticity. These additional factors can lift the gain- and loss-based EP degeneracies. However, they are proportional to the sum of the imaginary permittivities for involved cavity pairs. Thus, when the amplification and absorption of adjacent cavities are balanced, their contribution to the imaginary coupling is canceled, and the EP singularity can be restored. Radiation-induced imaginary couplings measure the change in net radiation loss by the interference between cavity modes. Their impact on the EP can also be counteracted by small cavity resonance detuning even in loss-biased cases. We show and analyze eligible simulation examples based on photonic crystal nanocavities, and highlight design of an ideal EP degeneracy that is protected by generalized PT symmetry and induced by radiation.

A Mechanically Rollable Reflectarray With Beam-Scanning Capabilities

A novel 1-D beam-steerable reflectarray antenna (RA) is proposed for the Ku-band. The RA aperture consists of 24×48 variable size square patch elements printed on a flexible plastic substrate. The aperture is wrapped around two cylinders to create a 12λ×12λ illumination window at the operating frequency of 14 GHz. Beam-steering is achieved by mechanically rolling the aperture. To mitigate antenna pattern degradation, an aperture phase distribution optimization technique is presented. The performance of this RA system is studied analytically using array theory. The effects of aperture size and unit-cell size are also discussed. The performance of the proposed RA is validated using simulations and measurements. The results illustrate that our design achieves 1-D beam-steering from -21∘ to +21∘ in the elevation plane while maintaining towards the broadside direction a maximum realized gain of 25.1 dBi. In this beam-scanning range, the gain variation is less than 1.5 dB, beamwidth variation is less than 1.6∘, and the side lobe level is maintained below -15 dB. In summary, the main advantage of our design is its ability to steer its high gain beam without using complicated feed networks or complex mechanical systems. Such antennas are especially needed in SmallSat and space applications.

Design of Real-Valued Wideband Beamformers Using an Adaptive-Array-Theory-Inspired WLS: Theory and Algorithm

The weighted least squares (WLS)-based beamformer design can achieve flexible beampattern control via adjusting the WLS weighting function inspired by the adaptive array theory (AAT). Nevertheless, the weighting function is conventionally adjusted in an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ad hoc</i> way, and precise beampattern control cannot be guaranteed. Although an analytical solution for the weighting function adjustment was proposed very recently, it is only applicable to complex-valued narrowband beamformers. In some applications such as acoustic/seismic array processing, however, real-valued wideband beamformers are required, since acoustic/seismic signals are usually unmodulated, real-valued and wideband. This paper studies the theory and design of real-valued wideband beamformers using an AAT-inspired WLS, which can achieve precise wideband beampattern control. The main contributions of this paper include: i) we theoretically prove the existence of the WLS weighting function for the real-valued wideband beamformers to achieve precise control of wideband beampatterns, and derive the corresponding analytical solutions; ii) we provide the insights into the impact of the weighting function on the cost function, which is useful to find the optimum solution for the weighting function among multiple feasible solutions; and iii) we propose an algorithm for the design of real-valued wideband beamformers using the proposed AAT-inspired WLS, which does not require to fine-tune any user parameters, and can guarantee precise control of wideband beampatterns as demonstrated by the simulation results.

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.

Design and Optimization of Ultrasound Phased Arrays for Large-Scale Ultrasound Neuromodulation.

Low-intensity transcranial focused ultrasound stimulation (tFUS), as a noninvasive neuromodulation modality, has shown to be effective in animals and even humans with improved millimeter-scale spatial resolution compared to its noninvasive counterparts. But conventional tFUS systems are built with bulky single-element ultrasound (US) transducers that must be mechanically moved to change the stimulation target. To achieve large-scale ultrasound neuromodulation (USN) within a given tissue volume, a US transducer array should electronically be driven in a beamforming fashion (known as US phased array) to steer focused ultrasound beams towards different neural targets. This paper presents the theory and design methodology of US phased arrays for USN at a large scale. For a given tissue volume and sonication frequency (f), the optimal geometry of a US phased array is found with an iterative design procedure that maximizes a figure of merit (FoM) and minimizes side/grating lobes (avoiding off-target stimulation). The proposed FoM provides a balance between the power efficiency and spatial resolution of a US array in USN. A design example of a US phased array has been presented for USN in a rat's brain with an optimized linear US array. In measurements, the fabricated US phased array with 16 elements (16.7×7.7×2 mm3), driven by 150 V (peak-peak) pulses at f = 833.3 kHz, could generate a focused US beam with a lateral resolution of 1.6 mm and pressure output of 1.15 MPa at a focal distance of 12 mm. The capability of the US phased array in beam steering and focusing from -60o to 60o angles was also verified in measurements.

A Low-Divergence Circularly Polarized Dual-Mode OAM Antenna Based on Higher Order Laguerre–Gaussian Modes

An open resonator antenna for orbital angular momentum (OAM) generation and dual-mode application is proposed. The excitation of OAM mode is deduced by the open resonator theory and the circular array theory. In the cavity, eight aperture coupled patch antenna elements are used to excite two higher-order Laguerre-Gaussian HE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> modes with a 90° phase difference. Verifying by simulation and experiment, the proposed low-profile antenna can radiate left-hand or right-hand circularly polarized waves of OAM modes l=±1, which have a relatively low divergence angle of ±9° and high gain of around 13 dBi.

Analysis of Omnidirectional Antenna Systems Using Cavity Model

Vertically polarized omnidirectional antenna system (VPOAS) and horizontally polarized omnidirectional antenna system (HPOAS) are designed and theoretically analyzed at 2.2 GHz for NAG-Missile telemetry. Theoretical formulations of far-zone field patterns are derived using the cavity model in conjunction with array theory, equivalence theorem, and image theory. The derived radiation patterns are plotted using MATLAB software. The proposed antenna is simulated using CST software and fabricated to validate the derived results. The proposed antenna systems are resonating at 2.22 GHz with 32 MHz impedance bandwidth and peak gain of 4.15 and 5.37 dBi for VPOAS and HPOAS, respectively.

Evaluating Gyratory Compaction Characteristics of Unbound Permeable Aggregate Base Materials from Meso-Scale Particle Movement Measured by Smart Sensing Technology.

The quality of compaction of unbound aggregate materials with permeable gradation plays a vital role in their field performance; however, there are currently few unanimously accepted techniques or quality control criteria available for ensuring adequate compaction of such materials in either laboratory or field applications. This paper presented testing results of a laboratory gyratory compaction study where the combinations of gyratory parameters were properly designed using the orthogonal array theory. Innovative real-time particle motion sensors were employed to record particle movement characteristics during the compaction process and provide a meso-scale explanation about compaction mechanisms. Particle abrasion and breakage were also quantified from particle shape digitized from the three-dimensional (3D) laser scanner before and after compaction. The optimal combination of gyratory parameters that yields the best compaction performance was determined from the orthogonal testing results with the relative importance of major influencing parameters ranked accordingly. Meso-scale particle movement at the upper center and center side positions of the specimen are promising indicators of compaction quality. The gyratory compaction process can be consistently divided into three distinct stages according to both macro-scale performance indicators and meso-scale particle movement characteristics. A statistically significant bi-linear relationship was found to exist between relative breakage index and maximum abrasion depth, whereas the quality of compaction and the extent of particle breakage appear to be positively correlated, thus necessitating the cost-effective balance between them. The results of this study could provide technical insights and guidance to field compaction of unbound permeable aggregates.

MPARC: A fast beampattern synthesis algorithm based on adaptive array theory

This paper presents a multi-point array response control (MPARC) algorithm to realize fast beampattern synthesis. The MPARC algorithm stems from adaptive array theory, and it can adjust the array response at multiple angles, either simultaneously or individually. The designed weights are constructed as a linear combination of an initial weight vector and multiple steering vectors multiplied by different complex factors. Since the update of the designed weights would change the beampattern in the entire spatial domain, the minimum pattern distortion criterion is established to design the complex factors, and a closed-form weight vector is obtained. Moreover, a pattern synthesis scheme based on the MPARC algorithm is presented to synthesize focused and shaped beampatterns efficiently. The comparison with the existing oblique projection-based algorithms shows that the presented MPARC algorithm can achieve multi-point response adjustment with much lower computational complexity, and the angle omission problem is addressed in this paper. Numerical results are provided to demonstrate the performance of the MPARC algorithm in array response control and the efficiency in pattern synthesis.

Analysis and modelling of rampart line antennas

A new, efficient, and accurate analytical model is introduced for estimating the beam direction of rampart line antennas with microstrip radiators that can change beam direction with feeding frequency. The model takes its origins from 1-D array theory, in which the bends represent the radiating elements, and the interconnecting lines represent the phase shifters. A mathematical expression accounting for the equivalent length of the bends for the correct estimation of the distance between the radiators is introduced. The model was tested for various substrate relative permittivity values ranging from 2.9 to 6.45. This model can be used for arbitrary rampart line configurations by providing the equivalent dipole direction, depending on the orientation of the bends. An alternative geometry was proposed to reduce the coupling between the parallel line segments. A prototype operating in a bandwidth of 1 GHz around 7.8 GHz was realized on a Rogers RO4350B high-frequency laminate with a thickness of 1.524 mm. Both the radiation pattern and the reflection coefficient were measured and show a good agreement with the proposed analytical model and commercial full-wave simulation tool results.