Concentric Circular Array Research Articles

FAST SYNTHESIS OF LARGE PLANAR ARRAYS USING ACTIVE ELEMENT PATTERN METHOD AND FINE-GRAINED PARALLEL MICRO-GENETIC ALGORITHM

A radiation pattern synthesis technique for large planar arrays with active element pattern (AEP) method and flne-grained parallel micro-genetic algorithm (FGPMGA) is presented. Based on the AEP method, the mutual coupling between array elements can be taken into account. Analysis problems of large rectangular and triangular grid planar arrays are divided into small linear array problems. And for a multiple concentric circular ring array, we only need to obtain one-sixth of all AEPs. So computational cost is greatly reduced. Large planar arrays with low side lobe level (SLL) can be achieved via optimizing the excitation amplitudes and phases. In order to reduce the global optimization time, the FGPMGA is used. This technique is applied to design 256-element rectangular grid, 200- element triangular grid and 4-circle 60-element concentric circular ring E-shaped patch antenna arrays. The radiation patterns calculated by the AEP method show good agreements with those by using CST Microwave Studio.

PATTERN SYNTHESIS OF CONCENTRIC CIRCULAR ANTENNA ARRAY BY NONLINEAR LEAST-SQUARE METHOD

An improved nonlinear least-square method is presented in this paper. This method changes the traditional least-square method's shortness of being sensitive to its initial conditions. Pattern synthesis for concentric circular arrays using nonlinear least-square method is introduced. The excitation amplitudes and phases of the array elements are optimized. This method can make the design of the feeding network much easier because the excitation amplitudes of the elements placed on the same ring are equal. The number of parameters to be optimized is reduced which leads to a faster simulation speed and makes the simulation results much more accurate. Also, the cost of designing the feeding network is reduced. The simulation results show the good agreement between the synthesized and desired radiation pattern. Also, the peak side lobe level (PSLL) of the synthesized radiation pattern is quite low.

Holey-Metal Lenses: Sieving Single Modes with Proper Phases

We study a planar, holey-metal lens made as a set of concentric circular arrays (rings) of nanoscale holes milled in a subwavelength-thick metal film. Each nanohole-a finite-length, circular, single-mode waveguide with a radius-dependent mode index-is used as a phase-shifting element. Our experimental results confirm that the focusing properties of our polarization-independent, holey-metal lens milled in a 380-nm-thick gold film and illuminated with 531 nm light fits the analytical model well. The proposed concept could offer an alternative to conventional refraction microlenses and open up a vital path toward on-chip or fiber-end planar photonic devices for biosensing and imaging.

Thinning of concentric two-ring circular array antenna using fire fly algorithm

The paper describes the application of novel meta-heuristics of the fire fly algorithm for reduction of the maximum Side Lobe Level (SLL) with specific First Null Beam Width (FNBW) of thinned two-ring Uniform Concentric Circular Arrays (UCCA) of isotropic elements. The effect of thinning is analyzed in the four subsequent examples using uniform and non-uniform excitations for different FNBW. Optimization is carried out without and with prefixing the value of the percentage of thinning. The UCCA containing 35 and 70 elements in the two successive concentric rings is optimized using FFA. The example using non-uniform excitation is proved more efficient to reduce SLL for same FNBW. Simulation results show the SLL performance improves as we chose the FNBW wider in the designing problem. Fixing the percentage of thinning at a higher value increases the power efficiency of the feeding network with little compromise on the design specifications. The non-uniformly excited thinned concentric array is again optimized using two more state-of-the-art algorithms, namely, Particle Swarm Optimization (PSO) and Differential Evolution (DE) to compare the effectiveness of each algorithm in a statistically meaningful way. Design results using fire fly algorithm shows better performances compared to PSO and DE provided the same number of function evaluation has been considered for all the algorithms.

Synthesis of thinned planar concentric circular antenna arrays using biogeography-based optimisation

This study presents a novel optimisation algorithm biogeography-based optimisation (BBO) for thinning large multiple concentric circular ring arrays. The objective is to achieve an array of uniformly excited isotropic antennas that will generate a narrow beam with minimum relative sidelobe level (SLL). BBO is a new comprehensive force based on the science of biogeography. Biogeography is the schoolwork of geographical allotment of biological organisms. BBO utilises migration operator to share information between the problem solutions. The problem solutions are known as habitats and sharing of features is called migration. In this study, the authors propose pattern synthesis method to reduce the SLLs with narrow beamwidth (BW) by making the ring array thinned using the BBO algorithm. The thinning percentage of the array is kept equal to or more than 50% and the BW is kept equal to or less than that of a fully populated, uniformly excited and 0.5λw, spaced concentric circular ring array of same number of elements and rings. The results obtained are compared with previous published results of modified particle swarm optimisation and differential evolution with global and local neighbourhoods.

A Subspace-Based Compensation Method for the Mutual Coupling in Concentric Circular Ring Arrays for Near-Field Source Localisation

We propose a technique for compensating the effect of mutual coupling on parameter estimation that is suitable with any subspace-based super-resolution algorithms. A Concentric circular ring array (CCRA) formed using thin dipole antennas in the receiving mode is employed to estimate the parameters of electromagnetic sources located in the radiating near field of the array. A CCRA geometry that obtains a lowest Cramer-Rao lower bound (CRLB) in the presence of array mutual coupling is chosen for investigation. The mutual coupling among antenna elements of the array would affect the orthogonality of subspaces when MUSIC or ESPRIT algorithms are used for parameter estimation. The proposed method obtains a compensation matrix that restores the orthogonality between the subspaces there by improving the accuracy of estimation. To avoid three-dimensional searches, the range parameter is estimated using a cross-correlation-based method. Numerical simulation using a full-wave electromagnetic (EM) solver is employed to demonstrate the effectiveness of the proposed compensation approach.

Thinned Concentric Circular Antenna Array Synthesis using Particle Swarm Optimization

This paper presents an optimal thinning of a large multiple concentric circular ring arrays of uniformly excited isotropic antennas based on Particle Swarm Optimization method. Circular Antenna Array (CAA) has gained immense popularity in the field of communications nowadays. It has proved to be a better alternative over other types of antenna array configuration due to its all-azimuth scan capability, and the beam pattern which can be kept invariant. In this paper, a 9 ringed Concentric Circular Antenna Array (CCAA) with central element feeding is considered. Extensive simulation results justify the optimization efficacy of the proposed approach for antenna array synthesis. The simulation results show that the number of effective antenna elements can be brought down from 279 to 139 with simultaneous reduction in Side Lobe Level by 20.37dB relative to the main beam with a fixed half power beamwidth using PSO. Real coded Genetic Algorithm (RGA) as well is also adopted to compare the results of PSO algorithm.

Optimizing circular ring arrays for forward-looking IVUS imaging.

Forward-looking (FL) catheter-based imaging systems are highly desirable for guiding interventions in intra- vascular ultrasound (IVUS) applications. One of the main challenges of array-based FL-IVUS systems is the large channel count, which results in increased system complexity. Synthetic phased-array processing with a reduced firing count simplifies the front-end and, hence, can enable 3-D real-time imaging. Recently, we have investigated dual-ring arrays suitable for IVUS imaging, in which the two concentric circular arrays are used separately as transmit (Tx) and receive (Rx) arrays. In this study, we present different optimized array designs based on dual and single circular rings which are suitable for synthetic phased-array processing with a reduced number of firings. To obtain an optimal firing set that produces low side lobes in the wideband response, we use a simulated annealing algorithm. In the simulations, we use 1.2-mm-diameter array configurations with 64 Tx and 58 Rx elements, a center frequency of 20 MHz and fractional bandwidths of 50% and 80%. The results show that optimized dual-ring arrays provide 8 dB improvements in peak near side-lobe level with no widening in the main lobe width when compared with full and other sparse co-arrays.

A Self-Calibration Algorithm for Concentric-UCA in the Presence of Mutual Coupling

A self-calibration algorithm for concentric uniform circular arrays (C-UCA) in the presence of mutual coupling is presented. The proposed algorithm can simultaneously estimate the directions of arrival (DOA) of signal sources and coupling coefficients of antenna array with a calibration source. It not only can calibrate the mutual coupling of the inner sub-arrays, but also can compensate for the mutual coupling between sub-arrays. Compared with conventional self-calibration algorithm based on iterative alternating minimization technique, the proposed algorithm transforms joint estimation about DOA and mutual coupling coefficients into cascaded estimation, which means that the parameters can be obtained by one dimensional spectrum peak search. The proposed self-calibration algorithm has high estimation precision and low computational burden. Simulation results show the effectiveness of the presented method.

Perceiving Spatial Relations via Attentional Tracking and Shifting

Perceiving which of a scene's objects are adjacent may require selecting them with a limited-capacity attentional process. Previous results support this notion [1-3] but leave open whether the process operates simultaneously on several objects or proceeds one by one. With arrays of colored discs moving together, we first tested the effect of moving the discs faster than the speed limit for following them with attentional selection [4]. At these high speeds, participants could identify which colors were present and determine whether identical arrays were aligned or offset by one disc. They could not, however, apprehend which colors in the arrays were adjacent, indicating that attentional selection is required for this judgment. If selection operates serially to determine which colors are neighbors, then after the color of one disc is identified, attention must shift to the adjacent disc. As a result of the motion, attention might occasionally miss its target and land on the trailing disc. We cued attention to first select one or the other of a pair of discs and found the pattern of errors predicted. Perceiving these spatial relationships evidently requires selecting and processing objects one by one and is only possible at low object speeds.

Synthesis of Planar Arrays With Elements in Concentric Rings

The circular symmetry of concentric ring arrays becomes an advantage for situations where the radiation patterns are symmetric in the azimuthal direction. For planar arrays with elements in an equispaced grid, the fast Fourier transform can be applied in the calculations involved between the array factor and the source distribution. However, for circular arrays the elements are in a non-equispaced grid, making the application of fast computation algorithms difficult. Therefore, two techniques are proposed to synthesize circular arrays. The first one provides the control of the pattern by sampling the array factor. In this case, the fast Fourier transform can be applied. The windows technique is also utilized to control the sidelobe levels and the ripple structure of the shaped beam. The second technique considers the symmetric nature of concentric circular arrays and the control of the array factor is performed imposing some specific points of the pattern.

Concentric Circular Array Antenna Null Steering Synthesis by Using Modified Hybrid Ant Colony System Algorithm

In this article, a hybrid optimization method has been proposed consisting of modified ant colony systems (ACSs) and constrained nonlinear programming (NLP) to solve the problems of null synthesis of concentric rings circular array antenna consist of parallel center feeding dipoles elements with two complex nonlinear optimization problems. In the first problem, a synthesis of concentric circular array radiation pattern with many interface signals is considered. In the second problem, the hybrid optimization algorithm is used to achieve wide nulls in the concentric circular array radiation pattern. The optimization process is achieved by finding the optimal values of the excitation coefficients of each element in the circular rings array. Several examples are considered here to verify the validity of this method. The results obtained by this method show that it is possible to obtain an array radiation pattern with wide null width of 90 o with a depth equal to -60dB and two nulls on both sides of the main lobe with about -112.9 dB depth level. Comparisons were made between the results of this proposed method and the results obtained by many other evolutionary optimization algorithms, and it is clearly shown that this method is more efficient and flexible in solving the problems of concentric circular array antenna performance optimization.

COMPARATIVE PERFORMANCE OF GRAVITATIONAL SEARCH ALGORITHM AND MODIFIED PARTICLE SWARM OPTIMIZATION ALGORITHM FOR SYNTHESIS OF THINNED SCANNED CONCENTRIC RING ARRAY ANTENNA

Scanning a planar array in the x-z plane directs the beam peak to any direction ofi the broadside along the same plane. Reduction of sidelobe level in concentric ring array of isotropic antennas scanned in the x-z plane result in a wide flrst null beamwidth (FNBW). In this paper, the authors propose pattern synthesis methods to reduce the sidelobe levels with flxed FNBW by making the scanned array thinned based on two difierent global optimization algorithms, namely Gravitational Search Algorithm (GSA) and modifled Particle Swarm Optimization (PSO) algorithm. The thinning percentage of the array is kept more than 45 percent and the flrst null beamwidth (FNBW) is kept equal to or less than that of a fully populated, uniformly excited and 0:5‚ spaced concentric circular ring array of same scanning angle and same number of elements and rings.

Estimating Rayleigh wave particle motion from three-component array analysis of ambient vibrations

SUMMARY Several methods have been proposed in the past years to extract the Rayleigh wave ellipticity from horizontal-to-vertical spectral ratios of single station ambient noise recordings. The disadvantage of this set of techniques is the difficulty in clearly identifying and separating the contribution of higher modes. In most cases, only the fundamental mode of ellipticity can be identified. Moreover, it is generally difficult to correct for the energy of SH and Love waves present in the horizontal components of the ambient vibration wavefield. We introduce a new methodology to retrieve Rayleigh wave ellipticity using high-resolution frequency–wavenumber array analysis. The technique is applied to the three components of motion and is based on the assumption that an amplitude maximum in the f–k cross-spectrum must represent the true power amplitude of the corresponding signal. In the case of Rayleigh waves, therefore, the ratio between maxima obtained from the horizontal (radial-polarized) and vertical components of motion will also represent the frequency-dependent ellipticity function. Consequently, if we can identify the Rayleigh dispersion curves of several modes on the f–k plane, then the corresponding modal ellipticity patterns can also be separated and extracted. To test the approach, synthetic and real data sets were processed. In all tested cases, a reliable estimation of segments of the fundamental mode ellipticity was obtained. The identification of higher modes is possible in most cases. The quality of results depends on the selected array geometry and the signal-to-noise ratio, with a major improvement achieved by increasing the number of receivers employed during the survey. An experiment conducted in the town of Visp (Switzerland) allowed the retrieval of portions of ellipticity curves up to the second Rayleigh higher mode, using two concentric circular array configurations of 14 and 11 receivers each.

Synthesis of Thinned Multiple Concentric Circular Ring Array Antennas using Particle Swarm Optimization

In this paper, we propose an optimization method based on Particle Swarm Optimization (PSO) algorithm for thinning a large multiple concentric circular ring array of uniformly excited isotropic antennas and generate a pencil beam in the vertical plane with minimum relative side lobe level (SLL). The half-power beam width of the pattern is attempted to make equal to that of a fully populated array of same size and shape. The synthesis is performed with a standard particle swarm optimization technique as well as with an improved version of standard PSO. Simulation results of the proposed thinned array are compared with a fully populated array to illustrate the effectiveness of our proposed method.

SYNTHESIS OF THINNED PLANAR CIRCULAR ARRAY ANTENNAS USING MODIFIED PARTICLE SWARM OPTIMIZATION

In this paper, the authors present an optimization method based on modifled Particle Swarm Optimization (PSO) algorithm for thinning large multiple concentric circular ring arrays of uniformly excited isotropic antennas that will generate a pencil beam in the vertical plane with minimum relative side lobe level (SLL). Two difierent cases have been studied, one with flxed uniform inter-element spacing and another with optimum uniform inter-element spacing. In both the cases, the number of switched ofi elements is made equal to 220 or more. The half- power beam width of the synthesized pattern is attempted to make equal to that of a fully populated array with uniform spacing of 0:5‚. Simulation results of the proposed thinned arrays are compared with a fully populated array to illustrate the efiectiveness of our proposed method.

Concentric circular arrays of Josephson junctions as dressed models of granular superconductors

An extended dressed Josephson network model is adopted to study the quantitative magnetic behaviour of three-dimensional granular systems. The model consists of a stack of collections of N concentric circular arrays of small identical Josephson junctions, each two adjacent elements of the stack being superconductively coupled by additional Josephson junctions. The low-field magnetic response of granular superconductors is simulated by means of the proposed model.

Adaptive Beamforming Using Frequency Invariant Uniform Concentric Circular Arrays

This paper proposes new adaptive beamforming algorithms for a class of uniform concentric circular arrays (UCCAs) having near-frequency invariant characteristics. The basic principle of the UCCA frequency invariant beamformer (FIB) is to transform the received signals to the phase mode representation and remove the frequency dependence of individual phase modes through the use of a digital beamforming or compensation network. As a result, the far field pattern of the array is electronic steerable and is approximately invariant over a wider range of frequencies than the uniform circular arrays (UCAs). The beampattern is governed by a small set of variable beamformer weights. Based on the minimum variance distortionless response (MVDR) and generalized sidelobe canceller (GSC) methods, new recursive adaptive beamforming algorithms for UCCA-FIB are proposed. In addition, robust versions of these adaptive beamforming algorithms for mitigating direction-of-arrival (DOA) and sensor position errors are developed. Simulation results show that the proposed adaptive UCCA-FIBs converge much faster and reach a considerable lower steady-state error than conventional broadband UCCA beamformers without using the compensation network. Since fewer variable multipliers are required in the proposed algorithms, it also leads to lower arithmetic complexity and faster tracking performance than conventional methods.

An approach for low sidelobe beamforming in uniform concentric circular arrays

In this paper, a new tapered beamforming function for sidelobe reduction in the uniform concentric circular arrays (UCCA) is proposed. This technique is based on tapering the current amplitudes of the rings in the array, where all elements in an individual ring are weighted in amplitude by the same value and the weight values of different rings are determined by a function that has a normalized-gaussian probability density function variation. This novel tapering window is optimized in its parameters to have the lowest possible sidelobe level that may reach 43 dB below the main lobe and these optimum weights are found to be function of the number of elements of the innermost ring and the number of rings in the array. The proposed tapering window can be modified to compensate the gain reduction due to tapering when compared with the uniform feeding case.

Adaptive Beamforming and DOA Estimation Using Uniform Concentric Spherical Arrays with Frequency Invariant Characteristics

This paper proposes a new digital beamformer for uniform concentric spherical array (UCSA) having nearly frequency invariant (FI) characteristics. The basic principle is to transform the received signals to the phase mode and remove the frequency dependency of the individual phase mode through the use of a digital beamforming network. It is shown that the far field pattern of the array is determined by a set of weights and it is approximately invariant over a wide range of frequencies. FI UCSAs are electronic steerable in both the azimuth and elevation angles, unlike their concentric circular array counterpart. The frequency invariant characteristic of the FI UCSA also makes it possible to design separately the compensation network and beamformer weighting coefficients. The design of the compensation network is formulated as a second order cone programming (SOCP) problem and is solved optimally for minimax criterion. Thanks to the frequency invariant characteristic, traditional narrow band adaptive beamforming algorithms such as minimum variance beamforming (MVB) can be applied to the FI UCSA. Also, traditional narrow band 2-D direction of arrival (DOA) estimation algorithms such as unitary ESPRIT can be extended to broadband DOA estimation using FI UCSA. Simulation results show that the proposed adaptive beamformer using FI UCSA can obtain a higher output signal to inference plus noise ratio over the conventional tapped-delay line approach. Simulation results also show that FI UCSA has uniform beampattern and resolution around 360° in both azimuth and elevation angles, unlike FI uniform concentric circular array. The usefulness of the proposed UCSA-FIB in broadband 2-D DOA estimation is also verified by computer simulation.