Inter-element Distance Research Articles

Design and Optimization of Sparse Planar Antenna Arrays for Wireless 3-D Local Positioning Systems

In this paper the design and measurement verification of optimized planar sparse arrays for use in wireless localization applications are presented. Existing literature on array optimization has mainly been concerned with arrays intended for imaging applications. As the array requirements for 3-D localization in multipath environments are essentially different, we made an analysis of the array parameters important for this specific application. The set of challenging practically relevant requirements for the optimization of the planar array layout was defined, including a restriction to a small number of antennas and minimal interelement distance bigger than $\lambda /2$ . An adapted multi-objective particle swarm optimization stochastic algorithm was employed to optimize array for the robust and precise direction of arrival of a single source inside a wide angular scan range up to ±60° in azimuth and elevation planes. Two optimized receive arrays consisting of eight patches were manufactured and measured to present the trade-off achieved under the desired requirements. The effects of optimized array parameters on the performance of 3-D positioning are validated by angle measurements in an anechoic chamber and different indoor scenarios.

Array element localization using multidimensional scaling (MDS) and matrix completion, with comparisons to more conventional non-linear least squares optimization

Multidimensional scaling (MDS) is an approach from the social sciences which was invented to project qualitative notions of distance onto 2D or 3D coordinate axes to provide visual displays for clustering purposes. As it turns out, this provides a viable algorithm for array element localization. When we calibrate an array using acoustic or RF ranging signals we measure inter-element distances and form a Euclidean Distance Matrix (EDM), and then convert them to 3D orthogonal coordinates. MDS converts the EDM to AEL coordinates. This process has some drawbacks. We may not get all the inter-element distances, because our ranging signals may have limited detection ranges, or because of obstructions to the line of sight. Also, it is not clear how to incorporate knowledge of unequal measurement errors among the EDM entries. Matrix completion is an approach from compressed sensing that allows us to perform the MDS paradigm, despite missing values in the EDM. We will present simulations for typical AEL scenarios and compare AEL results from MDS and matrix completion with results obtained using non-linear least squares optimization.

DOA estimation for sparse nested MIMO radar with velocity receive sensor array

Direction of arrival (DOA) estimation for sparse nested MIMO radar with velocity receive sensor array is studied, and an algorithm based on extended unitary root multiple signal classification (MUSIC) is proposed. The nested MIMO radar utilizes sparse transmit array and velocity receive array with nested inter-element distances, which can make the final virtual array to be a long and sparse velocity sensor array. After exploiting unitary transformation to transform the data into real-valued one, an extended root MUSIC based method is developed to decompose the angle estimation into high-resolution but ambiguous and low-resolution but unambiguous DOA estimations, which are automatically paired. Thereafter, the ambiguous estimation is used to recover all possible DOAs, and the unambiguous DOA estimation is used as a reference to resolve the estimation ambiguity problem. Compared to conventional methods, the proposed algorithm requires no peak search, maintains larger aperture and achieves better DOA estimation performance. The simulation results verify the effectiveness of our approach.

Sidelobe Reduction in a Planar Array using Genetic Algorithm under Backlobe Reduction Condition

The peak sidelobe level (PSL) minimizing amplitude weights for planar array, with 3D beamforming under the backlobe level reduction (BLL) condition is proposed. Binary genetic algorithm (BGA) is performed on the amplitude weights to achieve low PSL. BLL reduction condition for the inter-element distance between the antenna elements is applied to achieve reduced BLL. Earlier studies only focus on minimizing sidelobe level of planar array. BLL reduction condition has not yet been applied for planar array case. Hence a different way of achieving the amplitude weights to reduce PSL with 3D beamforming using BGA, under the BLL reduction condition is proposed in this paper. Obtained PSL and BLL for planar array by applying optimized weights under BLL condition is -20.89 dB and -2.37 dB respectively. PSL is reduced by 8.84 dB compared to uniform planar array. BLL is reduced by 2.37 dB compared to planar array discussed in existing research work.

Link-Level Analysis of a Multiservice Indoor Distributed Antenna System [Wireless Corner

In this article, the link-level performance of a multiservice indoor distributed antenna system (MS-IDAS) in an indoor-hotspot scenario is studied. A low-profile broadband antenna is proposed as the access point (AP) antenna, and then it is used as an identical array element for constructing two-and three-port multipleinput, and multiple-output (MIMO) antennas. The proposed MS-IDAS antenna covers various IEEE 802.11 standards within 2-6 GHz, and its link-level simulations are performed at 5 GHz for the 802.11n protocol. The error-rate performances of the three-element MIMO antenna is analyzed in WINNER indoor scenarios by using simulated-channelimpulse response (CIR). In a typical indoor-hotspot room with dimensions of 20 m x 20 m x 10 m, the wallmounted MS-IDAS antenna shows better coverage than the ceilingmounted case. In addition, the proposed MIMO antenna outperforms a uniform linear-dipole array with the same interelement distance in terms of error-rate performance.

Design of a compact MIMO antenna with pattern diversity for WLAN application

AbstractThe multiple input multiple output (MIMO) antenna consists of two printed inverted‐F antennas whose interelement distance is 7 mm. The isolation of the MIMO antenna is improved since the ground plane is modified to achieve a pattern diversity effect. The measurement results, such as impedance bandwidth, mutual coupling coefficient, radiation pattern were identified as having good performance. The MIMO antenna is further evaluated with an evaluation criterion that includes correlation coefficient and diversity gain, and results indicate successful isolation and diversity performance. All of the results demonstrate that the proposed MIMO antenna is compatible with wireless communication products.

An iterated local search algorithm for the minimum differential dispersion problem

Given a set of n elements separated by a pairwise distance matrix, the minimum differential dispersion problem (Min-Diff DP) aims to identify a subset of m elements (m < n) such that the difference between the maximum sum and the minimum sum of the inter-element distances between any two chosen elements is minimized. We propose an effective iterated local search (denoted by ILS_MinDiff) for Min-Diff DP. To ensure an effective exploration and exploitation of the search space, ILS_MinDiff iterates through three sequential search phases: a fast descent-based neighborhood search phase to find a local optimum from a given starting solution, a local optima exploring phase to visit nearby high-quality solutions around a given local optimum, and a local optima escaping phase to move away from the current search region. Experimental results on six data sets of 190 benchmark instances demonstrate that ILS_MinDiff competes favorably with the state-of-the-art algorithms by finding 131 improved best results (new upper bounds).

Generalization of Directivity Expressions for Antenna Arrays

This communication identifies and proposes the generalized templates of directivity expressions for antenna arrays with identical omnidirectional and isotropic elements. Parameters of this expression are the element patterns, interelement distances, and the complex excitation coefficients of all elements. It is further shown that the proposed expression can also satisfactorily calculate the directivity of antenna elements. Examples show the efficiency of the proposed expressions in terms of computational speed, accuracy, and memory requirement. Simpson's 1/3rd rule is followed for numerical pattern integration.

A Dual-Band Feed Network for Series-Fed Antenna Arrays Using Extended Composite Right/Left-Handed Transmission Lines

In this paper, extended composite right/left-handed (E-CRLH) structures are studied to design multiband microwave devices. As an example, a three-way series power divider (SPD) is designed. The overall effects of the E-CRLH structures, as the feeding networks of the antenna arrays, on the antenna arrays main-beam variations are investigated. We also design and implement two antenna arrays with $N=3$ elements and the same interelement distances each fed by a distinct three-way SPD. The radiation patterns of the antennas are examined. Simulation and measurement results demonstrate that the desired main-beam squinting of the antenna array could be obtained by engineering the parameters of the feeding network instead of adjusting the interelement distances.

Theoretical and practical limits of superdirective antenna arrays

Abstract Some applications as Wireless Power Transfer (WPT) require compact and directive antennas. However, Electrically Small Antennas (ESAs) have low efficiencies and quasi-isotropic radiation patterns. Superdirective ESA arrays can be an interesting solution to cope with both constraints (the compactness and the directivity). In this paper, the theoretical and practical limits of superdirective antennas will be presented. These limits can be summarized by the directivity sensitivity toward the excitation coefficients changes and the radiation efficiency decrement as the inter-element decreases. The need for negative resistances is also a practical limit for transforming these arrays into parasitic ones. The necessary trade-offs between the antenna total dimensions (the number of elements and the inter-element distance) and the attainable directivity and efficiency are also analyzed throughout this paper.

Heuristic solution approaches for the maximum minsum dispersion problem

The Maximum Minsum Dispersion Problem (Max-Minsum DP) is a strongly NP-Hard problem that belongs to the family of equitable dispersion problems. When dealing with dispersion, the operations research literature has focused on optimizing efficiency-based objectives while neglecting, for the most part, measures of equity. The most common efficiency-based functions are the sum of the inter-element distances or the minimum inter-element distance. Equitable dispersion problems, on the other hand, attempt to address the balance between efficiency and equity when selecting a subset of elements from a larger set. The objective of the Max-Minsum DP is to maximize the minimum aggregate dispersion among the chosen elements. We develop tabu search and GRASP solution procedures for this problem and compare them against the best in the literature. We also apply LocalSolver, a commercially available black-box optimizer, to compare our results. Our computational experiments show that we are able to establish new benchmarks in the solution of the Max-Minsum DP.

Classification and optimization of beam responses synthesized from non-uniformly spaced linear arrays

A probability distribution for the element positions on a linear array is derived so as to match a target beam pattern that approximates a Dolph-Chebychev array. The random beam responses generated from such a configuration exhibit a mean profile in observation angle that is invariant with element size N but the variance decays as 1/N. The beam responses are classified considering the N-1 inter-element distances as features that control the deviation from the mean beam profile and the variance of the class. The inter-element distance constraints are incorporated in a computational model of the firefly algorithm (FA) designed to optimize the location of the array elements that match the target beam pattern. The FA consists of a set of fireflies, representing arrays, which move through the solution space with directed movement based on each fireflies' fitness and random movement to ensure adequate exploration and avoid local minima. The fitness function is a combination of a target beam-width, side-lobe lev...

Using ambient noise correlations for relocating drifting sensor networks

A drifting sensor network, such as hydrophones mounted on autonomous underwater vehicles or drifting buoys, can be used as a random volumetric array for locating underwater acoustic sources. However, navigational uncertainties of mobile platforms underwater limit the positioning accuracy of their acoustic sensors. Precise positioning is required to perform coherent processing for sound source localization using this random volumetric array. It has been shown that ambient ocean noise correlations between fixed receivers can provide additional inter-element distance information to perform array element self-localization [Sabra et al., IEEE J.Ocean Eng., 30 (2005)]. An extension of this approach for an array of drifting sensors will be proposed by optimizing the required averaging duration to account for sensor drift motion. Performance of this proposed approach will be demonstrated using at-sea data collected in the Long Island Sound.

A New Technique for the Analysis of Energy Coupling and Exchange in General Antenna Systems

This paper provides a deeper insight into the nature of electromagnetic interactions by studying practical settings of strong and weak mutual coupling involving typical antenna elements coupled through the near field. We develop new techniques capable of analyzing the dynamic structure of generic antenna–antenna interactions by describing how energy exchange is divided between propagating and nonpropagating parts in a way reflecting the geometrical shapes and interelement distances of the coupled antennas. The proposed method is implemented through a special method-of-moment (MoM) numerical model and is used to give information about how energy is localized between antennas or electromagnetic objects, which is directly related to the physics of complex systems and the problem of energy storage, transfer, and manipulations. The work utilizes some recent developments in which a spectral near-field theory and the antenna current Green’s function formalism were proposed to analyze and describe general electromagnetic systems. The present formulation is developed in conjunction with the special MoM implementation to generate various numerical illustrations and new field energy density pictures combined with analysis of the physics of near-field coupling as revealed through the new results. The technique realized here can be easily integrated into existing full-wave solvers such as MoM to provide systematic pictures of near-field interactions and coupling with more comprehensive and detailed information compared with conventional port parameters such as the S-matrix. The method is suitable for applications such as near-field detection, energy transfer, and near-field communications, besides its fundamental importance for mutual coupling in antenna arrays in general.

No priming for global motion in crowding.

There is psychophysical evidence that low-level priming, e.g., from oriented gratings, as well as high-level semantic priming, survives crowding. We investigated priming for global translational motion in crowded and noncrowded conditions. The results indicated that reliable motion priming occurs in the noncrowded condition, but motion priming does not survive crowding. Crowding persisted despite variations in the direction of the flankers with respect to the prime's direction. Motion priming was still absent under crowding when 85% of the flankers moved in the same direction as the prime. Crowding also persisted despite variations in the speed of the flankers relative to the prime even when the flankers' speed was four times slower than the speed of the prime. However, a priming effect was evident when the prime's spatial location was precued and its distance to the flankers increased, suggesting a release from crowding. These results suggest that transient attention induced by precueing the spatial location of the prime may improve subjects' ability to discriminate its direction. Spatial cueing could act to decrease the integration field, thereby diminishing the influence of nearby distracters. In an additional experiment in which we used fewer flankers, we found a priming effect under conditions in which the interelement distance varied between flankers and prime. Overall, the results suggest that motion priming is strongly affected by crowding, but transient attention can partially retrieve such facilitation.

Design procedure of UHF RFID reader antennas based on ETSI and FCC standards

This paper presents the design procedure of two ultra-high-frequency radio frequency identification reader antennas used in searching tagged items. They consist of microstrip arrays with alternating orthogonal dipoles, which are fed in series by a pair of microstrip lines. The dipoles are designed properly to provide the required bandwidth. The inter-element distance is adjusted to the center frequency, where the elements provide in-phase excitation and create two orthogonal electric-field components that give beams with direction diversity. Simulated results show that the return loss bandwidth (RL &gt; 13 dB) of the first antenna design covers the required frequency band of ETSI (865–868 MHz) standard. In addition, simulated and measured results of the second antenna design indicate that the return loss bandwidth covers both the frequency bands of european telecommunications standards institute (ETSI) and federal communications commission (FCC) (865–928 MHz) standards. Regarding the coverage volume in the vicinity of the antenna, it was deduced that both antennas can read tagged items in a semi-cylindrical volume that extends to a radius of more than 50 cm. Finally, a case study of reading tagged books in front of a library cabinet with six shelves has been presented.

Inter-element orientation and distance influence the duration of persistent contour integration.

Contour integration is a fundamental form of perceptual organization. We introduce a new method of studying the mechanisms responsible for contour integration. This method capitalizes on the perceptual persistence of contours under conditions of impending camouflage. Observers viewed arrays of randomly arranged line segments upon which circular contours comprised of similar line segments were superimposed via abrupt onset. Crucially, these contours remained visible for up to a few seconds following onset, but eventually disappeared due to the camouflaging effects of surrounding background line segments. Our main finding was that the duration of contour visibility depended on the distance and degree of co-alignment between adjacent contour segments such that relatively dense smooth contours persisted longest. The stimulus-related effects reported here parallel similar results from contour detection studies, and complement previous reported top–down influences on contour persistence (Strother et al., 2011). We propose that persistent contour visibility reflects the sustained activity of recurrent processing loops within and between visual cortical areas involved in contour integration and other important stages of visual object recognition.

Low‐cost Ku‐band dual‐polarized and beam switchable cross‐type antenna array for satellite communications

ABSTRACTA dual‐polarized and beam switchable patch antenna array, which works well along the entire Ku‐band (10.6–12.7 GHz) is introduced in this article. The proposed array is formed with cross‐type antenna unit cell and fed by a balanced power division network with microstrip lines. By tuning the length of paths in the feeding network, phase differences taking place among units, therefore, beam‐shifting could be obviously observed on the measured radiation patterns. It is worth while noting that, as patch sharing technique is used in the array arrangement, not only the interelement distance is significantly decreased but also the beam‐shifting angle is distinctly enlarged in the case of same phase‐shifting. The proposed antenna can be easily fabricated on very low‐cost Teflon substrate with printing circuit technology, which might be a good candidate for direct broadcast from satellite reception antenna. In this article, the configuration of an experimental 1 × 4 array and its measured S‐parameters and radiation characteristics will be given. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2656–2659, 2014

Magnetostatic interaction of permalloy rectangles exhibiting a Landau state investigated by magnetotransport of single rectangles

We study the magnetostatic interaction of submicron $\mathrm{Ni}{}_{81}$$\mathrm{Fe}{}_{19}$ rectangles arranged in a linear chain by measuring the anisotropic magnetoresistance (AMR) of a single rectangle. The rectangles have a lateral aspect ratio of 2 : 1 and are lined up with the long axis oriented side by side varying the interelement distance down to $60\phantom{\rule{0.3em}{0ex}}\mathrm{n}\mathrm{m}$. The energy density of the Landau state is determined from the hard-axis magnetization reversal for a field applied along the chain direction. As a second approach identical energy densities are deduced from the switching field (Landau to quasisingle domain state) like in the case of a Stoner-Wohlfarth particle. The results show that the impact of the magnetostatic interaction on the energy density of the Landau state in remanence is negligibly small $(&lt;1\phantom{\rule{0.3em}{0ex}}\mathrm{k}$$\mathrm{J}$$/$$\mathrm{m}$${}^{3}$$)$. The magnetostatic interaction between field-distorted Landau states, however, is the same as for rectangles in a single domain state and is therefore governed by the compensation of surface charges at the rim. By studying rectangles with only one neighbor, the important role of symmetry on the magnetostatic interaction is shown.

Design of a Practical and Compact mm-Wave MIMO System with Optimized Capacity and Phased Arrays

In this paper we evaluate the feasibility of short range outdoor mm-wave MIMO links in the 70 GHz portion of the E-band (71–76 GHz). We use phased arrays in order to strongly reduce the impact of the multipath components, thus making the channel mainly line-of-sight (LOS). We design the array using a simple patch as a single element and simulate the performances for a 200 m link and a MIMO system with equal element spacing at the transmitter and the receiver. Each node of the MIMO system consists of a uniform rectangular array (URA) where the single element is a patch antenna, in order to achieve higher gains and narrow beams. Such configuration is much more compact compared to the antennas currently employed for the same bandwidth. We optimize the interelement distances at the transmitter and the receiver and evaluate the capacity achievable with different array sizes. The results show that, for the proposed link budget, capacity up to 29 bit/s/Hz is achievable at a range of 200 m, with practical dimensions. We also show that the beamforming capabilities make the design much more flexible than the single reflector antenna systems. In the last part of the paper, we verify that our antenna can also operate in rainy conditions and longer ranges.