Hindawi Publishing

Displaying 81-120 of 1771 results

  • White Papers // Oct 2010

    Design, Analysis, andMeasurements of an Antenna Structure for 2.4 GHzWireless Applications

    This paper reports measured results of a multielement antenna implementation, the authors constructed, that performs at 2.4 GHz ISM band. Particular emphasis was given to the scattering parameters and validation characterization of this antenna structure. The constructed multielement antenna that was studied in both azimuth and elevation planes consists of...

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  • White Papers // Sep 2010

    Frequency Invariant Beam Steering for Short-Pulse Systems with a Rotman Lens

    A promising approach for beam steering of high-voltage transient signals for HPEM-systems (High Power Electro Magnetic) is presented. The inherent capability of the Rotman lens to provide true time delays is used to develop a prototype beam steering device for an antielectronics HPEM system in the frequency range from 350MHz...

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  • White Papers // Jul 2010

    Spatial and Temporal Variation of Wideband Indoor Channels

    Extensive studies of the impact of temporal variations induced by people on the characteristics of indoor wideband channels are reported. Singular Value Decomposition Prony algorithm has been used to compute the impulse response from measured channel transfer functions. The high multipath resolution of the algorithm has allowed a detailed assessment...

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  • White Papers // Aug 2010

    Gain Enhancement of Low-Profile

    The present paper describes the gain enhancement of a small and low-profile linear antenna with Capacitive feed (C-feed) using three metallic layers. The antenna has very small leakage current on the outer conductor of the coaxial cable and can easily control the imaginary part of the input impedance. The gain...

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  • White Papers // Jun 2010

    Ultra-Wideband Indoor Channel Modelling Using Ray-Tracing Software for through-the-Wall Imaging Radar

    This paper presents a new software for design of through-the-wall imaging radars. The first part describes the evolution of a ray tracing simulator, originally designed for propagation of narrowband signals, and then for ultra-wideband signals. This simulator allows to obtain temporal channel response to a wide-band emitter (3 GHz to...

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  • White Papers // Jun 2010

    Absorption Efficiency and Physical Bounds on Antennas

    A new set of physical bounds on antennas was introduced. These bounds relate the performance of the antenna to the electro- and magnetostatic polarizability dyadics of a circumscribing geometry. This generalizes the classical bounds by Chu for spherical geometries to geometries of arbitrary shape. The new bounds are valid for...

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  • White Papers // Apr 2010

    Mutual Coupling in Antenna Arrays

    Mutual coupling is an electromagnetic phenomenon which exists in many antenna arrays. In most of the usual cases it is detrimental to the antenna operation, although there are some examples in which its presence can be beneficial. Because of its varying impact, it has attracted a large volume of research...

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  • White Papers // Apr 2010

    Overview on the Phase Conjugation Techniques of the Retrodirective Array

    Retrodirective antenna has the ability of retransmitting a wave to the direction as it is arriving without the prior knowledge of the incoming signals. It has the characteristics of high link gain and low cost which make the retrodirective antenna array useful in many fields, including automatic pointing and tracking,...

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  • White Papers // Apr 2010

    Mutual Coupling Effects on Pattern Diversity Antennas for MIMO Femtocells

    Diversity antennas play an important role in wireless communications. However, mutual coupling between multiple ports of a diversity antenna has significant effects on wireless radio links and channel capacity. In this paper, dual-port pattern diversity antennas for femtocell applications are proposed to cover GSM1800, UMTS, and WLAN frequency bands. The...

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  • White Papers // Apr 2010

    Compact Printed Arrays with Embedded Coupling Mitigation for Energy-Efficient Wireless Sensor Networking

    Wireless sensors emerged as narrowband, resource-constrained devices to provide monitoring services over a wide life span. Future applications of sensor networks are multimedia-driven and include sensor mobility. Thus, sensors must combine small size, large bandwidth, and diversity capabilities. Compact arrays, offering transmit/receive diversity, suffer from strong Mutual Coupling (MC), which...

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  • White Papers // Mar 2010

    Optimization of Training Signal Transmission for Estimating MIMO Channel under Antenna Mutual Coupling Conditions

    This paper reports investigations on the effect of antenna mutual coupling on performance of training-based Multiple-Input Multiple-Output (MIMO) channel estimation. The influence of mutual coupling is assessed for two training-based channel estimation methods, Scaled Least Square (SLS) and Minimum Mean Square Error (MMSE). It is shown that the accuracy of...

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  • White Papers // Mar 2010

    Bandwidth Enhancement of Antenna Arrays Utilizing Mutual Coupling between Antenna Elements

    Antenna arrays are widely used in many practical systems to enhance gain or provide beam scanning capability. Mutual coupling between antenna elements is an important issue in designing antenna arrays. It modifies radiation pattern, beamwidth, and directivity of an array, and even degrades the performance of adaptive arrays. However, Ludwig...

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  • White Papers // Mar 2010

    Design and Realization of a Wide-Band EBG Antenna Based on FSS and Operating in the Ku-Band

    EBG antennas are used for directive, omnidirectional, and sectoral applications. Nevertheless, the domain of use of these antennas can be extended to other applications where the authors can take advantage of their interesting performances notably in terms of directivity and compactness. One of these applications can be the broadband application...

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  • White Papers // Apr 2010

    A Transient UWB Antenna Array Used with Complex Impedance Surfaces

    The conception of a novel Ultra-WideBand (UWB) antenna array, designed especially for transient radar applications through the frequency band (300 MHz-3GHz), is proposed in this paper. For these applications, the elementary antenna must be compact and nondispersive, and the array must be able to steer in two dimensions. The geometry...

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  • White Papers // Apr 2010

    The Effect of Mutual Coupling on a High Altitude Platform Diversity System Using Compact Antenna Arrays

    The authors analyze the destructive effects of mutual coupling and spatial correlation between the separate antenna elements on a combined diversity system consisting of multiple HAPs (High-Altitude Platforms) employing various compact MIMO (Multiple-Input Multiple-Output) antenna array configurations, in order to enhance the mutual information in HAP communication links. In addition,...

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  • White Papers // Feb 2010

    An Open-Source Code for the Calculation of the Effects of Mutual Coupling in Arrays of Wires and for the ASM-MBF Method

    Mutual coupling in arrays has been a subject of intense research for several decades. Regular arrays received important attention for radar design purposes, and the subject received more attention recently for civilian applications, like MIMO communication systems and observational systems; among the latter phased arrays devoted to radio astronomy, ground-penetrating...

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  • White Papers // Feb 2010

    Antenna Evaluation for Ultra-Wideband Microwave Imaging

    Microwave techniques for breast imaging have recently generated a great deal of interest. One group of approaches is termed radar-based imaging. This technique involves illuminating the breast with short-time, low-power pulses of microwave energy. Reflections from the breast are collected at the same or multiple antenna locations and are processed...

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  • White Papers // Jan 2010

    Effect of Antenna Mutual Coupling on MIMO Channel Estimation and Capacity

    This paper describes investigations into the antenna Mutual Coupling (MC) effect on channel estimation and capacity of a Multiple-Input Multiple-Output (MIMO) wireless communication system. The presented investigations close the gap existing in the previous works which assessed the effect of mutual coupling on MIMO capacity under the assumption of availability...

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  • White Papers // Jan 2010

    Mutual Coupling Compensation for Direction-of-Arrival Estimations Using the Receiving-Mutual-Impedance Method

    A short review of the Receiving-Mutual-Impedance Method (RMIM) for mutual coupling compensation in direction finding applications using linear array is conducted. The differences between the Conventional-Mutual-Impedance Method (CMIM) and RMIM, as well as the three different determination methods for Receiving Mutual Impedance (RMI), will be discussed in details. As an...

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  • White Papers // Aug 2011

    Burst-Switched Optical Networks Supporting Legacy and Future Service Types

    Focusing on the principles and the paradigm of OBS an overview addressing expectable performance and application issues is presented. Proposals on OBS were published over a decade and the presented techniques spread into many directions. The paper comprises discussions of several challenges that OBS meets, in order to compile the...

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  • White Papers // Oct 2009

    A Review on Spectrumsensing for Cognitive Radio: Challenges and Solutions

    Cognitive radio is widely expected to be the next Big Bang in wireless communications. Spectrum sensing that is, detecting the presence of the primary users in a licensed spectrum, is a fundamental problem for cognitive radio. As a result, spectrum sensing has reborn as a very active research area in...

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  • White Papers // Jan 2011

    Hierarchical Spread Spectrum Fingerprinting Scheme Based on the CDMA Technique

    Digital fingerprinting is a method to insert user's own ID into digital contents in order to identify illegal users who distribute unauthorized copies. One of the serious problems in a fingerprinting system is the collusion attack such that several users combine their copies of the same content to modify/delete the...

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  • White Papers // Oct 2010

    A Simple Scheme for Constructing Fault-Tolerant Passwords From Biometric Data

    The authors present a simple combinatorial construction for the mapping of the biometric vectors to short strings, called the passwords. A verifier has to decide whether a given vector can be considered as a corrupted version of the original biometric vector whose password is known or not. The evaluations of...

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  • White Papers // Sep 2010

    Secure Arithmetic Coding With Error Detection Capability

    Recently, arithmetic coding has attracted the attention of many scholars because of its high compression capability. Accordingly, this paper proposed a Joint Source-Cryptographic-Channel Coding (JSCC) based on Arithmetic Coding (AC). For this purpose, embedded error detection arithmetic coding, which is known as Continuous Error Detection (CED), is used. In the...

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  • White Papers // Aug 2010

    GUC100 Multisensor Fingerprint Database for In-House (Semipublic) Performance Test

    For evaluation of biometric performance of biometric components and system, the availability of independent databases and desirably independent evaluators is important. Both databases of significant size and independent testing institutions provide the precondition for fair and unbiased benchmarking. In order to show generalization capabilities of the system under test, it...

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  • White Papers // May 2010

    Reversible Watermarking Techniques: An Overview and a Classification

    An overview of reversible watermarking techniques appeared in literature during the last five years approximately is presented in this paper. In addition to this a general classification of algorithms on the basis of their characteristics and of the embedding domain is given in order to provide a structured presentation simply...

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  • White Papers // Jan 2010

    On the Implementation of Spread Spectrum Fingerprinting in Asymmetric Cryptographic Protocol

    Digital fingerprinting of multimedia contents involves the generation of a fingerprint, the embedding operation, and the realization of traceability from redistributed contents. Considering a buyer's right, the asymmetric property in the transaction between a buyer and a seller must be achieved using a cryptographic protocol. In the conventional schemes, the...

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  • White Papers // Sep 2009

    High-Rate Data-Hiding Robust to Linear Filtering for Colored Hosts

    The Discrete Fourier Transform-Rational Dither Modulation (DFT-RDM) has been proposed as a way to provide robustness to Linear-Time-Invariant (LTI) filtering for quantization-based watermarking systems. This scheme has been proven to provide high rates for white Gaussian hosts but those rates considerably decrease for nonwhite hosts. In this paper, the theoretical...

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  • White Papers // Feb 2009

    Active Reflectors: Possible Solutions Based on Reflectarrays and Fresnel Reflectors

    An overview about some of the recent Spanish developments on active reflectors is presented. In the first part, a novel beam-steering active reflectarray is deeply studied. It is based on implementing in each elementary radiator an IQ modulator structure, in which amplitude and phase control of the scattered field is...

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  • White Papers // Nov 2009

    Decoupling of Multifrequency Dipole Antenna Arrays for Microwave Imaging Applications

    The mutual coupling between elements of a multifrequency dipole antenna array is experimentally investigated by S-parameter measurements and planar near-field scanning of the radiated field. A multifrequency array with six dipoles is analyzed. In order to reduce the coupling between dipoles, a planarmeta surface is placed atop the array acting...

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  • White Papers // Dec 2009

    Triband Compact Antenna for Multistandard Terminals and User's Hand Effect

    A novel compact wideband triband antenna for mobile terminals based on PIFA element is proposed. The antenna operates at the following frequency bands: Wireless-LAN 802.11 b, g, a and WiMAX 3.5 GHz. The antenna was studied by means of numerical simulations as well as the ground plane dimensions and user's...

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  • White Papers // Dec 2009

    Efficient Time-Domain Ray-Tracing Technique for the Analysis of Ultra-Wideband Indoor Environments Including Lossy Materials and Multiple Effects

    This paper presents an efficient application of the Time-Domain Uniform Theory of Diffraction (TD-UTD) for the analysis of Ultra-WideBand (UWB) mobile communications for indoor environments. The classical TD-UTD formulation is modified to include the contribution of lossy materials and multiple-ray interactions with the environment. The electromagnetic analysis is combined with...

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  • White Papers // Oct 2009

    Far-Field Reconstruction from Transient Near-Field Measurement Using Cylindrical Modal Development

    The aim of this paper is to get far field radiation patterns for any radiating source from transient acquisition, in a large frequency range. An outdoor transient Ultra-Wideband near-field measurement base will be installed, a single time pulse radiated by the source will cover the desired spectrum, and the accurate...

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  • White Papers // Jul 2009

    Performance of Narrowband Signal Detection under Correlated Rayleigh Fading Based on Synthetic Array

    The performance of a single moving antenna receiver in detecting a narrowband signal under correlated Rayleigh fading is considered. The spatial motion of the antenna during signal capture provides a realization of a synthetic antenna array. As shown, there is a net processing gain obtained by using a synthetic antenna...

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  • White Papers // Jul 2009

    Rigorous Solution to Plane Wave Scattering by an Arbitrary-Shaped Particle Embedded into a Cylindrical Cell of Similar Material

    An infinite cylinder of arbitrary shape is embedded into a circular one, and the whole structure is illuminated by a plane wave. The electromagnetic scattering problem is solved rigorously under the condition that the materials of the two cylinders possess similar characteristics. The solution is based on a linear Taylor...

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  • White Papers // Jun 2009

    Low-Profile Array of Wire Patch Antennas

    A low-profile antenna over a ground plane that radiates a directive lobe in the end fire direction is described in this paper. An array of 16 Wire Patch Antenna (WPA) fed by an integrated 16 ways power divider has been designed. Owing to its low height, low cost, high robustness,...

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  • White Papers // Jun 2009

    Synthesis of Phased Cylindrical Arc Antenna Arrays

    This paper describes a new approach to synthesize cylindrical antenna arrays controlled by the phase excitation, to synthesize directive lobe and multilobe patterns with steered zero. The proposed method is based on iterative minimization of a function that incorporates constraints imposed in each direction. An 8-element cylindrical antenna has been...

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  • White Papers // May 2009

    The Effect of Fabrication Method on Passive UHF RFID Tag Performance

    In passive Radio Frequency IDentification (RFID), transponders or tags are used to label objects to be identified. In this study passive tag antennas were produced using etching, screen-printing, and gravure printing methods. The threshold and backscattered signal strengths of the tags were measured to determine the effect of different manufacturing...

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  • White Papers // May 2009

    Design of a Dual-Band Sectoral Antenna for Hiperlan2 Application Using Double Layers of Metallic Electromagnetic Band Gap (M-EBG) Materials as a Superstrate

    A novel design of a sectoral antenna that utilizes a double layer Metallic Electromagnetic Band Gap (M-EBG) as a superstrate for dual band directivity enhancement is presented in this paper. The authors obtain the different operating frequencies by adjusting the distance of the lower M-EBG layer from printed patch antenna...

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  • White Papers // Mar 2009

    Low Profile EBG Resonator Antennas

    An Electromagnetic Band Gap (EBG) antenna is a planar structure which is composed of a cavity and an EBG material. In most applications, the height of the EBG antenna is half wavelength. The authors present in this paper the conditions to reduce the profile of an EBG antenna to subwavelength...

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