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This paper introduces an advanced meta-heuristic optimization technique, namely, Atom Search Optimization (ASO) for the synthesis of linear and planar arrays. Synthesis of array antenna is a traditional electromagnetic problem. Investigations have been made by many researchers on synthesis of various antennas by applying several algorithms. ASO is a global optimization algorithm based on atom dynamics in dealing with different challenging problems. The ASO is applied to the array synthesis of the symmetric and asymmetric linear array antennas. To verify the effectiveness of the ASO algorithm, a comparative analysis of simulation results and published results for linear arrays has been made. The ASO optimized non uniform amplitude coefficients have been applied to the ON elements of the two ring concentric circular array. A comparative analysis with Firefly algorithm (FA) and Flower Pollination Algorithm (FPA) show the proposed algorithm is a comprehensive optimization algorithm in antenna array pattern synthesis.

Since most studies for estimating an angle-of-arrival (AOA) based on the antenna array have considered the antenna array with a single configuration, they are not proper to simultaneously estimate AOAs of multiple signals with various frequencies. In this paper, we introduce a cascade AOA estimation technique consisting of CAPON and Beamspace Multiple Signal Classification (MUSIC), based on a Combined Array Antenna (CAA) with Uniform Rectangular Frame Array (URFA) and Uniform Circular Array (UCA), for enhancing the above problem. In addition, we provide the computational complexity analysis for showing the low computational complexity of this technique comparing to the conventional technique.

A wideband monostatic simultaneous transmit and receive (STAR) antenna subsystem with high isolation and co-horizontally polarized (Co-HP) omnidirectional radiation is presented. The antenna subsystem consists of a STAR antenna and a beamforming network (BFN). The STAR antenna consists of a planar circular array having four printed dipole elements surrounded by two groups of parasitic strips. The parasitic strips are used to improve the impedance bandwidth and reduce the gain variation in transmit (TX) and receive (RX) modes. To achieve high isolation, the four ports of the STAR antenna are excited with two orthogonal phase modes for TX and RX using the BFN. The BFN is a six-port network consisting of two 180° hybrid couplers, one 90° hybrid coupler, and a Wilkinson power divider. The 180° hybrid coupler is elaborately designed with low imbalances since it is most key to achieve high TX/RX isolation. Measured results show the proposed STAR subsystem achieves a TX/RX overlapping IMBW of 4.71-6.2 GHz, and a 40-dB TX/RX isolation bandwidth of 4.81-5.88 GHz, while maintaining horizontally polarized omnidirectional radiation patterns for TX and RX over the entire operating frequency band.

For multiplex beams of orbital angular momentum (OAM), we propose a two-looped concentric uniform circular array (CUCA) consisting of sequentially rotated circular polarization (CP) triangle patches. Generally speaking, the rotation of the CP antenna makes feeding networks free of narrow-band phase shifters. Further investigations also reveal that CP performances of elements and the rotation parameters (including directions and centers) are critical factors. Moreover, adopting the triangle patches makes the array compact and wideband. A demonstration with 12 elements is designed and fabricated, whose radius is only 0.760. Simulations and measurements suggest that it could emit circularly polarized vortex waves of modes -1 and -2 at the X band simultaneously, and its bandwidth is about 8.7%.

In the theoretical part of this work, a calibration strategy for both phase and amplitude calibration of rotating equispaced circular array based on redundant space calibration was introduced. It avoids the challenging implementation of conventional noise-injection networks, especially for a large-scale array, by using the strong self-consistency accomplished by array rotation. This study presents comprehensive simulation results of the proposed calibration strategy, where calibration residuals and image reconstruction errors are evaluated. The phase calibration shows outstanding performance, while the amplitude calibration is found to be biased due to the logarithms used to linearize the system of calibration equations, and the resulting image reconstruction bias is scene-dependent. A bias correction method is proposed accordingly, which requires an a priori regional brightness temperature within the observation scene. The performance of both phase and amplitude calibration take advantage of increasing the number of elements, which promises the system scalability for high spatial resolution applications., The authors would like to thank the anonymous editor and reviewers for their constructive comments and suggestions. This collaboration was also supported by the Joint Ph.D. Training Program from the University of Chinese Academy of Sciences.

In contrast to the popular multimode orbital angular momentum (OAM) generation method that uses uniform circular array combined with phase shifter network, time-modulated circular array (TMCA) does not require multiple radio frequency chains and costly analog devices and it requires only switches. In this article, an arbitrary-order OAM generation and beam steering method for TMCA is proposed, which incorporates the existing integer-order OAM generation and beam steering method as a special case. Furthermore, we analyze the effect of elements on–off ordering on the generation of OAM beams, and prove that sequential ordering has the lowest power consumption. Finally, the effectiveness of the proposed methods is validated through electromagnetic simulations.

Orbit Angular Momentum (OAM) is a potential candidate for next-generation short-distance line-of-sight wireless communication, it is assumed that the channels associated with different OAM modes are orthogonal. When there are misalignments between transmitter and receiver arrays, the assumption is incorrect. In this paper, we propose the methods to estimate the array misalignment values in the OAM-based communication system for Uniform Circular Array (UCA) in transmitter and receiver. It is shown that, when the pilot signals are transmitted in a single or all OAM modes, the absolute value of the received signal can be approximated by the polynomial functions of misalignment angle. By solving these functions, the misalignment angle can be estimated. The proposed methods are theoretically analyzed and tested for OAM Index Modulation (OAM-IM)-based communication system, The obtained results indicate that the proposed methods improve the OAM-IM based communication system in the presence of array misalignments problem.

Mutual coupling between the space-borne antenna has an essential impact on the communication characteristics of a wireless link to submerged submarines. In this article, the mutual coupling between antennas of a circular array in an anisotropic plasma over a very low-frequency (VLF: 3–30 kHz) range is investigated. An expansion of the currents into phase modes enables us to develop an efficient method to analyze the mutual coupling between antennas. The $N$ -coupled integral equations for antennas of an array are first derived with full consideration of the mutual coupling effect. By making use of the phase modes combined with the method of moment (MoM), the $N$ -coupled integral equations are decomposed into independent ones and solved for each phase mode. Computations and discussions show that the self and mutual impedances of antennas are increased with the geomagnetic field tilt angle. Moreover, the mutual impedance is decreased with the increasing electrical separation, thereby indicating that the mutual coupling effect is weakened as the separation increases. The accuracy of the proposed method is verified by comparing the computed results with experiments and simulation using commercial electromagnetics software FEKO.

Objective: Traditional endoscopic ultrasonography (EUS), which uses one-dimensional (1-D) curvilinear or radial/circular transducers, cannot achieve dynamic elevational focusing, and the slice thickness is not sufficient. The purpose of this study was to design and fabricate a 1.5-dimensional (1.5-D) circular array transducer to achieve dynamic elevational focusing in EUS in vivo . Methods : An 84 × 5 element 1.5-D circular array transducer was successfully developed and characterized in this study. It was fabricated with PZT-5H 1-3 composite that attained a high-electromechanical coupling factor and low-acoustic impedance. The acoustic field distribution was measured with different transmission modes to validate the 1.5-D elevational beam focusing capability. The imaging performance of the 84 × 5 element 1.5-D circular array transducer was evaluated by two wire phantoms, an agar-based cyst phantom, an ex vivo swine pancreas, and an in vivo rhesus macaque rectum based on multifocal ray-line imaging method with five-row elevational beam steering. Results : It was demonstrated that the transducer exhibited a central frequency of 6.47 MHz with an average bandwidth of 50%, a two-way insertion loss of 23 dB, and crosstalk of Conclusion : Dynamic elevational focusing and the enhancement of the slice thickness in EUS were obtained with a 1.5-D circular array transducer. Significance : This study promotes the development of multirow and two-dimensional array EUS probes for a more precise clinical diagnosis and treatment.

In this paper, the antenna array appropriate topologies and configurations are investigated to reduce the impact of large gain variation between array elements that is produced due to the mutual coupling. Moreover, the most appropriate antenna array topology that can realize a maximum system throughput and achieve fairness between users in terms of their spectral efficiency is determined. Our analysis focuses on the comparison between various array geometries (uniform planar array (UPA), circular array (CA), conformal array (CfA), uniform planar circular array (UPCA), centric planar circular array (CPCA) and, finally, conical array (CoA)) with half-wavelength dipole elements. The simulation results show that UPA, CA, and CfA have total efficiency around 96 % at 2.6 G H z . Moreover, all the proposed geometries have achieved Envelope Correlation Coefficient (ECC) less than 0.5, and high Diversity Gain (DG) that makes it suitable for MIMO. The CfA geometry has been elected as the most suitable topology, which can provide minimum gain variation, maximum system throughput, and achieve fairness between users’ spectral efficiency. Finally, curl antenna is considered in the designed antenna array to study the effect of antenna gain pattern. Two array geometries have been designed using the curl antenna, which are the UPA and the CfA. The CfA curl has insertion loss - 30 d B between the edge elements and achieve fairness index between the users up to 0.98733 . Moreover, the results show that curl antenna geometries can achieve higher system throughput compared to half-wavelength dipole based array geometries.

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 HE21 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 $l=\pm 1$ , which have a relatively low divergence angle of ±9° and high gain of around 13 dBi.

In this paper, an improved array factor of the concentric uniform circular array (CUCA) antenna is proposed for the orbital angular momentum (OAM) vortex beam optimization design. From the perspective of the radiation pattern’s power conservation principle, a correction factor is introduced to the conventional array factor of CUCA. Then, based on the improved array factor, by adjusting the rings’ radii parameters of the CUCA, we optimize the vortex beam’s sidelobe level through the generic algorithm (GA). Two different CUCA antenna model are calculated as examples to further illustrate the effectiveness of the improved array factor. Subsequently, an electromagnetic simulation model of two rings CUCA antenna is built at C band for generating low sidelobe vortex beam carrying OAM mode. The electromagnetic simulation model of the designed CUCA antenna is also fabricated and measured. The corresponding antenna far-field vortex beam radiation pattern and near-field vortex wave electric field distributions are measured. The simulation results and the measurement results are in good agreement. The proposed designs of antenna and OAM vortex beam regulation are expected to be used for 5G and 6G communications applications

The orbital angular momentum (OAM)-based communication systems may face severe transmission problems when the transmit and receive uniform circular array pairs are blocked. In this paper, a promising technique named intelligent reflecting surface (IRS) is proposed to help alleviate blockages and provide alternative line-of-sight links. To maximize the achievable rate of the IRS-assisted OAM communication systems, we optimize its transmit power allocation along with the IRS's reflecting phase shifts, and propose an alternative optimization-based algorithm to solve the resulting optimization problem with coupled variables and non-convex structure. Specifically, the proposed algorithm obtains a closed-form solution to the transmit power allocation by applying the majorization-minimization and $\ell _1$ -ball projection approaches, and obtain the locally optimal solution to the IRS's reflecting phase shifts by applying the weighted minimum mean square error-based fixed point iteration approach. Simulation results demonstrate the superiority of our proposed algorithm over existing baseline algorithms and also show its robust stability to the oblique angle errors.

Deploying a high-frequency (HF) radar on one anchored floating platform for the maneuverability appears to be a good alternative. In this case, because the yaw rotation during one coherent integration time may be rather large, an effective method to get precise direction-of-arrival (DOA) estimations is important for reliable ocean surface current mapping. In this article, we propose an adaptive data channel conversion method to compensate for this kind of rotation. In this method, radar data can be converted from rotating antenna channels into pseudo-fixed beam channels by following the minimum-mean-square-error rule between the wanted pseudo-fixed beam and a reference beam. Simulations with a uniform circular array and one kind of yaw rotation, the range of which is ${\text{90}^{\circ}}$ , are conducted. After compensation, the DOA estimation of one simulated object becomes unbiased and performs nearly as good as that on a fixed platform. Besides, the high root-mean-square errors of radial ocean currents, caused by the yaw rotation, also decrease. Furthermore, we introduce a field experiment of one anchored floating HF radar, during which the DOA estimations of two onshore radars’ direct waves improved drastically. The field ocean currents, deduced from this floating HF radar, also indicate the feasibility of the proposed method. This method offers a new idea to compensate for a floating platform's yaw rotation and can help introduce the traditional onshore HF radar to a much more flexible offshore scenario.

WiFi channel state information (CSI) is a key enabler of precise radio sensing applications for commercially available off-the-shelf hardware. By utilizing colocated WiFi devices, this article aims to perform Angle-of-Arrival (AoA) estimation as one instance of radio sensing. However, unsynchronized local oscillators (LOs) in a WiFi network can cause carrier frequency offsets and sampling frequency offsets, which can lead to imperfect CSI. To this end, we propose a wired LO clocking scheme to eliminate residual impairments on regular WiFi transceivers. By utilizing a common oscillator, we transform a standard WiFi setup to a frequency-aligned transceiver architecture across several colocated devices. Building upon the proposed scheme, we present a detailed investigation of hardware-related impairments and environmental conditions. In particular, we are the first to investigate the temperature-dependent behavior of the CSI phase across multiple devices. We validate the performance in a lab setup as well as in a real-world application assembly, namely, a nine-antenna uniform circular array for AoA estimation. Furthermore, we show that with only a single received packet and minor hardware adjustments, we are able to obtain the AoA of a WiFi transmitter with a mean absolute error of 1.5° in line-of-sight conditions and 19.9° in strong multipath living room conditions.

As a pathbreaking approach to generate orbital angular momentum (OAM) beam, uniform circular array (UCA) has been extensively researched and applied. However, the impact of the imperfect UCA (IUCA) converted from a UCA with the position of antenna elements on the purity of the generated OAM beam is rarely considered. In order to verify the effect of position deviation on the OAM beam, this letter deduces the analysis model of the IUCA and the OAM mode purity model. The OAM mode purity refers to the weight of the intensity of the “expected OAM mode.” Numerical simulation results show that the OAM beam generated by IUCA is a superposition of OAM beams with a series of different modes, and this results in a certain OAM beam received being contaminated. Compared with the radius deviation, the azimuth deviation of antenna elements has more obvious influence on the OAM mode purity. Moreover, low-mode OAM beams are more suitable for long-distance transmission. Properly increasing the antenna array radius can improve the purity of high-order OAM modes.

Azimuthal centrosymmetry in an array grid is typically associated with arrays that are circular, concentric, cylindrical, spherical, or hemispherical. However, a recently proposed alternative combines an azimuthal circular array with a linear vertical array. For this elegantly simple new array grid's use in the direction-of-arrival estimation, this article advances array-design insights to meet a given estimation–precision threshold, by examining the tradeoff between the azimuth-angle Cramer–Rao bound vis-a-vis the polar-angle Cramer–Rao bound in a proposed two-step design procedure.

The conventional calibration methods only took into account the mutual coupling (MC) and the gain/phase error. However, the antenna element pattern could also be an important factor in calibration as the antenna element pattern could be direction-dependent. This letter proposes a calibration method to jointly estimate array errors and antenna element patterns for the uniform circular array (UCA). The array errors are composed of MC and gain/phase error. The antenna patterns of different elements are presumed rotationally similar due to the structure of the UCA. The simulation and field experiments demonstrated the effectiveness of the proposed method.

Electromagnetic (EM) vortex can realize high resolution imaging in forward-looking observation geometry without relative motion between the radar system and targets. However, the current research about EM vortex imaging only exploits integral orbital angular momentum (OAM) beams, which limit the application in the real scene with the existence of noise. An EM vortex enhanced imaging method based on fractional OAM beams is proposed against noise effect in this letter. Firstl the generation method of fractional OAM beams with phase distribution of nonintegral OAM mode is proposed using uniform circular array, and the corresponding features are analyzed. Subsequently, the imaging model and scheme with fractional OAM beams are provided and the principle for enhancing imaging performance is derived. Finally, results by Monte Carlo simulations demonstrate that the proposed vortex imaging method based on fractional OAM beams is robust against noise effect and can achieve better imaging performance in low signal-to-noise ratio (SNR) environment, which is of prospect for overcoming the shortage of poor imaging performance in low OAM order and complex noise scenario. This letter benefits the development of EM vortex imaging.

This paper presents the generation of modes of angular momentum of the orbital type using a proposed array antenna fed with Rotman lens of multiple layers of compact size. The gain of orbital angul...

The analysis of scanning range for both planar and circular array antenna in 5G application is presented in this research paper. Radiation pattern and scanning angle range of these antenna arrays and enhanced for RF receiver front-end application. A single array consists of various subarrays which represents vertical and horizontal linear arrays of radiators. These radiating elements have prescribed magnitude and phase distribution. They determined the range and shape of radiation pattern in both vertical and horizontal directions. Analysis of directive properties and range of scanning angle of those arrays shows that for small base stations, adaptive arrays with 5 subarrays, the circular configuration is more preferred as compared to planar array, because planar configuration has limitation with scanning angle 120°. Due to different geometry with some degree of curvature, circular configuration allows the beam steering in wider angular range up to 150°. It has wider beam and less directivity as compared to planar array.

This paper proposes a multiple signal classification (MUSIC) framework for direction-of-arrival estimation by combining multiple circular arrays in the circular-harmonics domain. We jointly transform the received signals of all sub-arrays into the circular harmonics domain to generate a set of sound field coefficients containing the direction information of the sound sources. These coefficients are then formulated in a form in which MUSIC algorithm can be applied. Compared with the conventional circular-harmonics-domain localization methods, which are based on a single circular array, the proposed method can provide sufficient spatial resolution over different frequency ranges by adjusting the distribution of sub-arrays. Furthermore, the mean square error of the estimated sound field coefficients is derived for guiding this adjustment. Numerical simulation results indicate that a reasonable distribution of sub-arrays can effectively avoid the performance degradation caused by the zeros of Bessel functions, which is an inherent problem of the modal array signal processing. Simulation and experimental results with different configuration parameters demonstrate that the proposed method provides a better localization performance compared to the state-of-the-art methods.

In this letter, we present a dual-polarized orbital angular momentum multiple-input.multiple-output (OAM-MIMO) with uniform circular arrays (UCAs) that achieves a transmission rate of over 200 Gb/s. We design and evaluate the properties of microstrip antennas on 28 GHz band and then fabricate the antennas and implement them on a transmitter and receiver with four UCAs disposed concentrically. Each UCA consists of 16 microstrip antenna elements and is connected to a Butler matrix that can generate and separate five OAM modes (±2, ±1, and 0). There is also a center antenna capable of transmitting mode 0, so the total number of antenna elements is 65 and 21 streams can be transmitted simultaneously. In order to maximize the transmission capacity, we use polarization multiplexing. We conduct two data transmission experiments at a distance of 10 m. In the experiment of virtual dual-polarized OAM-MIMO transmission, we achieved approximately 110 Gb/s transmission for both polarizations. In the experiment of 21 streams, simultaneous transmission of dual-polarized OAM-MIMO, the result of 201.5 Gb/s was achieved.

The super-high-frequency band is used in the fifth-generation (5G) mobile communication system, and the introduction of massive multiple-input–multiple-output (MIMO) to 5G is being considered. In an environment with substantial propagation loss, such as that in the case of millimeter waves, massive MIMO can realize beamforming according to the position of terminal stations. Therefore, it is important to understand the direction of arrival of millimeter waves. In this letter, we clarify the relationship between power, delay time, and direction of arrival while focusing on the horizontal direction, using a 48-element massive array in the 20 GHz band in urban Japan. In addition, we obtain direction-of-arrival (DoA) estimation results using an iterative reduction threshold algorithm (ISTA), which is based on compressed sensing. It is shown that the dominant path can be estimated by using the ISTA even with approximately five elements.

In this letter, a method is proposed for synthesizing sparse concentric ring arrays that use a minimum number of uniformly excited aperiodic concentric rings to match a predefined reference pattern. An auxiliary layout of concentric rings based on the Bessel function approximation of the circular array pattern is first synthesized using the off-grid compressive sensing framework and convex optimization to match the reference pattern using a minimum number of rings. Then, a density tapering technique is used to replace each ring with a ring of uniformly spaced isotropic radiating elements. Simulations were carried out to assess the effectiveness of the proposed method.

This paper compares the uniform circular array based orbital angular momentum (UCA-OAM) scheme, which enables spatial multiplexing transmission of data symbols via multiple OAM modes, with the UCA-MIMO scheme through numerical analysis and simulation in terms of spectral efficiency and feedback over-head. Specifically, based on the relations between the eigenmodes of the UCA-SVD-MIMO system and the modes of UCA-OAM system as well as the capacity formula, the channel capacities of the two systems are compared for the cases where equal power allocation and waterfilling power allocation are employed, and then the effectiveness of the analytical results are verified through simulation.

Multitransmitter structure can improve the misalignment tolerance of wireless power transfer (WPT) system, but some new problems such as a sharp drop in transmission efficiency will occur when the receiver moves to the boundary situation between transmitters. It is very crucial to solve this problem for an efficient and stable WPT system. In this article, a flexible combination multitransmitter coupling structure based on hexagonal array coil and auxiliary switch is proposed, and the coupling characteristics under misalignment conditions has been deeply analyzed with mutual inductance model. Unlike using coupling coefficient, a convenient switching control strategy is proposed based on the primary current to activate the optimal coil working mode, and the experimental results favorably verified the theoretical analysis. Compared with the circular array coil and the square array coil, the proposed coupling structure and control method can greatly improve the transmission efficiency of the WPT system at the coil boundary, and has stronger robustness under different misalignment conditions.

Inhabited isolated areas require independent power systems called isolated microgrids. Conventional protection schemes are not suitable for isolated microgrids due to their dependence on significant fault current. This article introduces an adaptive differential feature-based protection scheme for fault detection and faulty phase identification for isolated microgrids. Instead of differential currents, it proposes differential features, where edge computing is used to extract the features at point of measurement. The most informative one-dimensional feature is extracted from each phase at both ends of the line. The line differential feature is compared with an adaptive threshold to perform fault detection. The threshold is updated every second and is immune to system noises. Faulty phase identification is performed with a logical comparison. An in-memory circular buffer is proposed to store the local features in case of communication delay. Communication and synchronization are experimentally validated, and the worst-case latency is reported along with individual processing time for data acquisition, feature extraction, communication, and fault detection. Extensive validations are done with IEC-based and IEEE 13-node-based isolated microgrid. The test results are compared with state-of-the-art methods and proved that the proposed scheme is practical to be adopted in real- world isolated microgrids of different sizes and topologies.

Aiming at the problem of vertical target coordinate measurement when two projectors were touching the target at the same time, a two-target identification method of circular array photoelectric detection system was proposed. A circular detection array was formed by using photodetectors, and three fan-shaped linear lasers with all luminescence angles of 60° were uniformly arranged on circular detection array to form a detection light curtain. When the two projectiles passed through detection light screen at the same time, six projectiles would be generated on the circular detection array. The central position of the six projectiles would be identified through the signal processing circuit. Finally, the target coordinates of two projectiles would be calculated by system projectile hitting coordinate measurement formula. On the basis of the theory of system measurement, the coordinate measurement model of the projectile hitting target was established, and the coordinate measurement error was analyzed and simulated. The simulation results show that the maximum standard deviation of the X coordinate measurement error is 2.7 mm and the maximum standard deviation of the Y coordinate measurement error is 0.6 mm when the target surface is 1 m×1 m. The experimental results show that the standard deviation of X coordinate measurement error is 2.22 mm and Y coordinate measurement error is 1.98 mm when the target surface is 1 m×1 m. Therefore, the system proposed can effectively measure the target coordinates of double projectors with a projectile diameter of 4.5 mm or above.

Magnetic sensor arrays have been employed to measure currents for multicore cables due to their advantages of compact size, lightweight, low power consumption, and large dynamic range. However, the existing methods are applicable only to cases where the cable must be perpendicular to the sensor array plane due to the lack of capability of the 2-D magnetic field model to consider conductor inclination. To solve this problem, this article presents a method using a circular array of single-axis magnetic sensors to measure magnetic fields along and perpendicular to the sensor array plane. A 3-D magnetic field model that involves conductor incline angles is first derived. On the basis of the derived model, two main steps are performed to realize current sensing. First, an off-site calibration method is used to calibrate magnetic sensor parameters, including sensor position, orientation, gain factor, and phase shift. Second, not only the conductor currents and positions but also the incline angles are simultaneously calculated based on the detected magnetic fields and calibrated sensor parameters. Both steps are formulated as nonlinear least-square problems and solved efficiently. Both simulation and experiment are performed to demonstrate the superiority of the proposed method compared to the existing ones based on the 2-D magnetic field model when inclinations are introduced. The proposed method may have the potential for designing a clamp-on current sensor dedicated to multicore cables similar to hand-held current probes with a relatively large inner diameter for single-conductor systems.

A uniform linear array (ULA) or a multi-element planar array composed of uniform linear arrays is the main applied research array for direction-of-arrival (DOA) estimation in array signal processing. In recent years, the uniform circular array (UCA) is getting more attention because of its consistent azimuthal beam resolution, but the DOA estimation algorithm of a UCA is complex and difficult to implement. To solve this problem, a UCA positioning method based on virtual interpolation and subarray rotation (VISAR) is proposed. This method effectively reduces the computational complexity of DOA estimation for a UCA, and the simulation analysis of the algorithm shows that in terms of positioning performance, the proposed algorithm is better than the existing virtual interpolation algorithms in the case of a low signal-to-noise ratio (SNR).

A strong signal through the antenna sidelobes can be interpreted as a main lobe signal and may cause a major angle error in the direction finding system. An auxiliary antenna channel in the Maisel’s sidelobe blanking system increases the cost, and the method using each boresight error (BSE) of the monopulse and interferometer causes many errors in the real antenna. In this paper, a sidelobe recognition method applicable to a wideband uniform circular array without auxiliary antenna channel is proposed. Four boresight errors are obtained from monopulse and interferometer in the circular array and then the maximum value of differences between boresight errors is taken and is compared to the optimal threshold value. The results have the effect of reducing errors occurring in the sidelobe region while maintaining the performance in the main lobe region. To validate the proposed method, a circular array antenna with eight wideband microstrip antennas is designed and manufactured. As a result, there is a significant improvement in the error rate compared to the existing method. It is confirmed that there is no error when the threshold value is from 0.5 ° to 0.7 ° at 6, 9, and 12 GHz, and the error rate is less than about 1 % when the threshold value is between 0.4 ° and 1.0 °.

A method of focused delivery of ultrasonic energy to a given point inside a biological object using a circular antenna array is proposed. The functional diagram of a multielement circular array with alternating emitting and receiving elements is presented. The channels of emitting elements contain controlled phase shift modules and all receiving elements are connected to the summator. The possibility of ultrasonic energy focusing is shown by means of modeling of the circular array operation with allowance for the wave propagation in two media. The result of focusing is estimated with allowance for the interface between two media. It is assumed that the two media differ in the propagation speed of the ultrasonic wave. The presence of two media on the propagation path of the ultrasonic wave leads to defocusing and shift of the focus position.

In this letter, we propose to exploit the array motion of sparse circular arrays (SCA) on a rotating platform to increase the degrees of freedom (DOF) (i.e. the number of unique spatial lags) associated with the rotating array when compared to the array on a fixed platform. This increases the total number of sources that can be resolved by the rotating SCA with the same amount of physical sensors. The signal model for the combined synthetic array before and after a unit rotation motion is derived together with the closed-form expression for the increase in the DOF of a rotating nested sparse circular array (NSCA). A new modified NSCA is proposed and it is shown that the DOF of the proposed sparse array is higher than the conventional NSCA under motion with the same number of sensors. A simulation study is carried out to estimate the direction of arrival (DOA) of signals in a sensing environment that is assumed to be stationary over array motion of unit rotation and it verifies the effectiveness of array motion to increase the DOF of an SCA. The simulations also show the improved performance of the proposed NSCA.