Circular Ring Array Research Articles

EZR-MZR Resonators for Compact Low-Profile Omnidirectional Circular-Polarized Antenna Design

New zeroth-order resonator (ZOR): the curved EZR-MZR resonator [epsilon-zero resonance (EZR) and mu-zero resonance (MZR)] was proposed for circular-polarized (CP) antenna design with low-profile and omnidirectional characteristics. The proposed curved EZR-MZR resonator has two orthogonal polarizations with 90° phase difference (PD). By forming four resonators in a circular ring array, the MZR can be characterized as a magnetic dipole. Then, the unidirectional pattern of the horizontal polarization was transformed to be omnidirectional while the EZR with vertical polarization can be characterized as an electric dipole and it radiates omnidirectional pattern. As the PD of the vertical and the horizontal polarizations is inherently 90°, the allying of the two orthogonal polarizations leads to a CP radiation with an omnidirectional pattern. To feed the resonators with uniform amplitude and phase, a feeding network with four equal radial arms is used. The proposed omnidirectional CP antenna has the advantages of low profile from ZOR characteristics and high design efficiency from the inherent 90° PD between the orthogonal polarizations. A prototype with resonant frequency of 1.544 GHz was designed with a diameter of 57 mm (0.29 $\lambda _{r}$ , $\lambda _{r}$ is the free space wavelength of the resonant frequency) and a height of 4 mm (0.02 $\lambda _{r}$ ).

Voltage-tunable terahertz metamaterial based on liquid crystal material for bandpass filters and phase shifters

ABSTRACTIn this paper, we proposed a voltage-tunable terahertz metamatrial, which is composed of the circular-ring deep-slot array fabricated by UV-LIGA process to form a controlled cavity embedded with the liquid crystal (LC). By changing the biased voltage, the transmission peak of the terahertz metamaterial can be continuously tuned within a frequency range of 38 GHz. Moreover, this metamaterial can work over a wide range of incident and polarization angle for both TE and TM waves due structure symmetry. In addition, a differential phase of 74° is obtained at 0.45 THz by tuning the biased voltage. Therefore, our results open new opportunities for the tunable THz bandpass filters and phase shifters.

Optimal Synthesis of Shaped Beams Through Concentric Ring Isophoric Sparse Arrays

An innovative deterministic approach to the optimal power synthesis of mask-constrained shaped beams through the concentric-ring isophoric sparse arrays is presented. The design procedure exploits at best the state-of-the-art techniques, respectively, available in the cases of circular-ring isophoric arrays radiating pencil beams and of linear isophoric arrays generating shaped beams. The technique avoids the exploitation of global-optimization algorithms and allows us to significantly outperform all the (few) available procedures.

DOA and Polarization Estimation Based on Sparse COLD Array

Direction of arrival (DOA) ambiguity influences the performance of array signal processing. To address this problem, a DOA and polarization estimation method is proposed in this paper. Based on sparse uniform concentric semi-circular array consisting of concentred orthogonal loop and dipole pairs, the actual array steering vector can be transformed into a virtual one without additional computation. By applying dot division and dot product operation to outer and inner circular ring array spatial steering vectors, two new spatial steering vectors of arrays whose inter-element spacing are less and much larger than half wavelength are obtained respectively, the cyclic phase ambiguity is disambiguated effectively. In the proposed algorithm, all the array elements (actual and virtual) contribute toward the derivation of both the coarse estimations and the fine estimations, thereby achieving full exploitation of the entire physical aperture, the estimation precision is herein improved.

An ultrathin quad-band polarization-insensitive wide-angle metamaterial absorber

In this article, an ultrathin quad-band polarization-insensitive wide-angle metamaterial absorber has been presented. The proposed structure consists of a periodic array of concentric square and circular rings imprinted on grounded FR-4 dielectric substrate. The simulated result shows that the structure has four discrete absorption peaks at 3.91, 5.16, 7.10, and 9.16 GHz with peak absorptivities of 99.35, 98.04, 99.85, and 99.78%, respectively. The proposed structure is symmetric in design providing nearly unity absorption for all polarization angles under normal incidence. It also shows high absorption (∼90%) for wide incident angles upto 45° for both transverse electric and transverse magnetic polarizations. By illustrating surface current distribution, the absorption mechanism of different parts of the proposed structure has been analyzed. Finally, the structure has been fabricated and the measured results are in good agreement with the simulated responses. The designed quad-band absorber is easy to manufacture and can be used in various potential applications. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:697–702, 2015

Design of thinned concentric circular antenna arrays using firefly algorithm

Firefly algorithm (FA) is a nature inspired computing algorithm based on the behaviour of fireflies. It is a kind of stochastic meta-heuristic algorithm that can be used for various engineering optimisation problems. This study presents application of FA for the design of thinned multiple concentric circular antenna arrays. The aim is to achieve an array of uniformly excited isotropic elements that will generate a pencil beam pattern in the vertical plane with minimum side lobe level (SLL). Two different cases have been considered in this study for thinning of concentric circular (ring) arrays using FA. The first case is with uniform inter-element spacing fixed at 0.5λ or its multiple and the second case with optimum inter-element spacing or its multiple. The thinning percentage of the array is kept equal to or more than 50% and the beamwidth is kept equal to or less than that of a fully populated, uniformly excited and 0.5λ spaced ring array of same number of elements and rings. The results obtained are compared with previous published results, which show the effectiveness of this approach.

Side Lobe Reduction of Concentric Thinned Antenna Array Using Evolutionary Algorithms

This paper presents how to thin an concentric circular ring array antenna optimally using evolutionary algorithms. In order to obtain lower Sidelobe level (SLL) form a large antenna array in different azimuth planes, various types of optimization algorithms have been used. A pattern synthesis method based on thinning is presented to generate a pencil beam pattern from a concentric ring array of isotropic antennas. It is obtained by finding out optimum sets of elements state using GA, PSO and DE in four azimuth planes . Results clearly show the effectiveness of the proposed method. Keywords: concentric circular ring array, genetic algorithm (GA), differential evolution Algorithm (DE), particle swarm optimization Algorithm (PSO), peak sidelobe level (peak SLL), thinned array

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.

An Effective Deterministic Procedure for the Synthesis of Shaped Beams by Means of Uniform-Amplitude Linear Sparse Arrays

A rigorous deterministic approach is proposed for the mask-constrained power pattern synthesis of shaped beams through one-dimensional sparse arrays having uniform-amplitude excitations (and variable phases). The approach includes the well known density taper procedure as a special case. The corresponding technique, which exploits an analytical formulation of the problem and convex programming routines, results in fast computation and is able to achieve optimal solutions without recurring to any global optimization. Numerical results assessing the capabilities of the proposed design method are provided, opening the way to the development of an effective approach for the synthesis of circularly symmetric shaped beams via uniformly-excited circular ring arrays.

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.

OPTIMIZATION OF NON-UNIFORM CIRCULAR ARRAYS WITH COVARIANCE MATRIX ADAPTATION EVOLUTIONARY STRATEGY

In this paper, a covariance matrix adaptation evolutionary strategy (CMA-ES) is employed for optimization design of non-uniform circular antenna arrays. To achieve minimum sidelobe levels with the constraint of a speciflc flrst null beamwidth, the CMA-ES is utilized to flnd out the optimal weights and geometry of the circular array. The three various circular ring arrays are solved via CMA-ES, and the results are presented for arrays of varying conflgurations. The design results obtained with CMA-ES are compared to the existing array designs in the literature and to those found by the other evolutionary algorithms. Comparison with the results of other algorithms reveals the superiority of the CMA-ES.

Comparative study of magnetization reversal process between rectangular and circular thin film rings

The magnetization reversal processes of rectangular and circular permalloy ring arrays are compared. Rectangular rings reverse via two different processes, one of which includes the formation of a vortex state. The corners of the rectangular rings affect domain wall pinning and reverse domain nucleation processes and alter the field values for the two major transitions between magnetic states as compared to a circular ring. The effects of film thickness are also investigated. Micromagnetic simulations are compared with the experiment results.

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.

Magnetic pinning of flux lattice in superconducting-nanomagnet hybrids

Strong superconducting pinning effects are observed from magnetic landscapes produced by arrays of circular rings with varying magnetic remanent states. The collective and the background pinning of superconducting Nb films is strongly enhanced by the stray magnetic field produced by an array of circular Ni rings magnetized to form “onion” (bidomain) states. On the other hand, when the same rings are magnetized into vortex (flux-closed) states, or are randomly magnetized, the superconducting pinning is much smaller. The greatest pinning is produced when the superconducting vortex lattice motion is along a direction in which there is a strong magnetic field variation.

SYNTHESIS OF THINNED PLANAR CONCENTRIC CIRCULAR ANTENNA ARRAYS --- A DIFFERENTIAL EVOLUTIONARY APPROACH

Circular antenna array design is one of the most important electromagnetic optimization problems of current interest. The problem of designing a large multiple concentric planar thinned circular ring arrays of uniformly excited isotropic antennas is considered in this paper. This antenna must generate a pencil beam pattern in the vertical plane along with minimized side lobe level (SLL). In this paper, we present an optimization method based on an improved variant of one of the most powerful real parameter optimizers of current interest, called Difierential Evolution (DE). Two sets of difierent cases have been studied here. First set deals with thinned array design with the goal to achieve number of switched ofi elements equal to 220 or more. The other set contains design of array while maintaining side lobe level (SLL) below a flxed value. Both set contains two types of design, one with uniform inter-element spacing flxed at 0.5‚ and the other with optimum uniform inter-element spacing. The half-power beam width of the synthesized pattern is attempted to maintain flxed at the value equal to that of a fully populated array with uniform spacing of 0.5‚. Simulation results of the designed thinned arrays are compared with a fully populated array for all the cases to illustrate the efiectiveness of our proposed method.

Ultra-Low-Sidelobe-Level Concentric-Ring-Array Pattern Synthesis Using Bessel Neural Networks [Antenna Designer's Notebook

The present paper proposes a new approach to constrained optimal pattern synthesis for a circular ring array with ultra-Iow-sidelobe levels. The approach uses an artificial neural network (ANN) with hidden Bessel activation functions, trained using the Levenberg-Marquardt (LM) algorithm. The proposed approach is capable of producing minimal sidelobe levels for an arbitrary pattern shape using only a few iterations, and without high memory requirements as compared to existing alternatives.

NOVEL FRACTAL ANTENNA ARRAYS FOR SATELLITE NETWORKS: CIRCULAR RING SIERPINSKI CARPET ARRAYS OPTIMIZED BY GENETIC ALGORITHMS

A novel fractal antenna-array type is proposed. The design is based on the Sierpinski rectangular carpet concept. However, the generator is a circular ring area, fllled with radiating elements, so the higher stages of the fractal development produce large arrays of circular rings which, besides the high directivity, have the advantage of the almost uniform azimuthal radiation pattern, attribute that many applications require. The introduced arrays can operate as direct radiating multi-beam phased arrays and meet the requirements of satellite communications links: high End of Coverage (EOC) directivity, low Side Lobe Level (SLL) and high Career to Interference ratio (C=I). These operational indices were further optimized by a synthesized multi-objective and multi-dimensional Genetic Algorithm (GA) which, additionally, gave arrays no more than 120 elements.

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.