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Antennas
Kinds of Antennas Selected AbstractsReversibly Deformable and Mechanically Tunable Fluidic AntennasADVANCED FUNCTIONAL MATERIALS, Issue 22 2009Ju-Hee So Abstract This paper describes the fabrication and characterization of fluidic dipole antennas that are reconfigurable, reversibly deformable, and mechanically tunable. The antennas consist of a fluid metal alloy injected into microfluidic channels comprising a silicone elastomer. By employing soft lithographic, rapid prototyping methods, the fluidic antennas are easier to fabricate than conventional copper antennas. The fluidic dipole radiates with ,90% efficiency over a broad frequency range (1910,1990,MHz), which is equivalent to the expected efficiency for a similar dipole with solid metallic elements such as copper. The metal, eutectic gallium indium (EGaIn), is a low-viscosity liquid at room temperature and possesses a thin oxide skin that provides mechanical stability to the fluid within the elastomeric channels. Because the conductive element of the antenna is a fluid, the mechanical properties and shape of the antenna are defined by the elastomeric channels, which are composed of polydimethylsiloxane (PDMS). The antennas can withstand mechanical deformation (stretching, bending, rolling, and twisting) and return to their original state after removal of an applied stress. The ability of the fluid metal to flow during deformation of the PDMS ensures electrical continuity. The shape and thus, the function of the antenna, is reconfigurable. The resonant frequency can be tuned mechanically by elongating the antenna via stretching without any hysteresis during strain relaxation, and the measured resonant frequency as a function of strain shows excellent agreement (±0.1,0.3% error) with that predicted by theoretical finite element modeling. The antennas are therefore sensors of strain. The fluid metal also facilitates self-healing in response to sharp cuts through the antenna. [source] Fabrication of Crescent-Shaped Optical Antennas,ADVANCED MATERIALS, Issue 17 2005S. Shumaker-Parry Metal crescent-shaped nanoparticles (see Figure) that are expected to be efficient optical antennas with highly enhanced and localized near-fields are described. The particle-fabrication process combines colloidal templating, metal-film deposition, and ion-beam milling. The crescents exhibit multiple plasmon resonances in the visible and near-infrared that are of the same type as have been proposed for the development of an effective left-handed material. [source] Fluorescent Quantum Dots as Artificial Antennas for Enhanced Light Harvesting and Energy Transfer to Photosynthetic Reaction Centers,ANGEWANDTE CHEMIE, Issue 40 2010Prof. Igor Nabiev Bio-Nano: Quantenpunkte (QDs) können mit photosynthetischen Reaktionszentren (RCs) so markiert werden (siehe Bild), dass der FRET vom QD zum RC eine annähernde Verdreifachung der Geschwindigkeit, in der Excitonen im RC erzeugt werden, zur Folge hat. Es werden sogar noch größere Verstärkungen vorhergesagt, was dafür spricht, dass solche Komplexe die Effizienz der Photosynthese erheblich steigern könnten. [source] Detection efficiency of multiplexed Passive Integrated Transponder antennas is influenced by environmental conditions and fish swimming behaviourECOLOGY OF FRESHWATER FISH, Issue 4 2009J. C. Aymes Abstract,,, The efficiency of a Passive Integrated Transponder (PIT)-tag detection system was tested during a 23-day experiment using a permanent digital video to record the passage of fish through multiplexed antennas. Coupling video to the PIT system allowed the detection of error sources and the correction of erroneous data. The efficiency of the detection system and its variation were investigated according to fish swimming speed, direction of movement and individual fish behaviour. Influence of time and environmental conditions on detection results were also checked. The PIT tag system was 96.7% efficient in detecting fish. Upstream movements were better detected (99.8%) than downstream movements (93.7%). Moreover, results showed that efficiency rate was not stable over the experiment; it was reduced on stormy days. Several sources of errors were identified such as sub-optimal orientation of the PIT tag relative to the antenna plane, the influence of fish swimming speed, individual fish behaviour and influence of environmental conditions. [source] Effects of radio-transmitter antenna length on swimming performance of juvenile rainbow troutECOLOGY OF FRESHWATER FISH, Issue 4 2004K. J. Murchie Abstract,,, Technological advances have lead to the production of micro radio-transmitters capable of being implanted in fish as small as c. 5 g. Although the actual tags are small, transmitters are equipped with long antennas that can increase drag and tangle in debris. We examined the effects of radio-transmitter antenna length on the swimming performance of juvenile rainbow trout, Oncorhynchus mykiss, (N = 156, mean mass = 34 g, mean fork length = 148 mm). Although we tested a variety of different antenna lengths up to a maximum of 300 mm, only the longest antenna significantly impaired swimming performance relative to control fish (P < 0.001). There was no difference in swimming performance between the sham (surgery, but no transmitter) and the control fish (handled, but no surgery), suggesting that the surgical procedure itself did not negatively affect the fish. Regression analysis, however, indicated that there was a significant decrease in swimming performance associated with increased antenna length (R2 = 0.11, P < 0.001). In addition, when held in laboratory tanks, fish with the three longest antennas (150, 225 and 300 mm) frequently became entangled with the standpipe. We suggest that researchers, under the guidance of the tag manufacturer, trim antennas to the shortest possible length required to detect fish in their specific study area. Antenna length is clearly an important issue for small fish, especially for species that inhabit complex habitats where antennas may become entangled, and where fish must attain speeds near limits of their swimming capacity. Resumen 1. Los avances tecnológicos han llevado a producir micro radio-trasmisores capaces de ser implantados en peces de muy pequeño tamaño (,5 g). Aunque las marcas actuales son pequeñas, los trasmisores están equipados con antenas largas que pueden llegar a enredarse en los restos de vegetación. Examinamos los efectos de la longitud de la antena sobre la rutina natatoria de juveniles de Oncorhynchus mykiss (n = 156, peso medio = 34 g, longitud furcal media = 148 mm). 2. Aunque analizamos varias longitudes de antena, hasta 300 mm, solamente las de mayor longitud alteraron la rutina natatoria en relación a los peces control (P < 0.001). No hubo diferencia en la rutina natatoria entre individuos bajo cirugía pero sin trasmisores respecto de los individuos control (manipulados pero sin cirugía) lo que sugiere que los procedimientos de cirugía no afectaron negativamente a los peces. Sin embargo, análisis de regresión indicaron un declive significativo en la rutina natatoria asociado a la longitud de la antena (R2 = 0.11, P < 0.001). Además, al ser mantenidos en tanques, los individuos con las tres antenas mas largas (150, 225, y 300 mm) frecuentemente se enredaron con las tuberías. 3. Sugerimos a los investigadores que, bajo la dirección de los productores de marcas y antenas, consideren el uso de las antenas más pequeñas que permitan detectar a los peces en sus respectivas áreas de estudio. La longitud de la antena es una cuestión importante para los pequeños peces, especialmente para especies en hábitats complejos donde las antenas pueden llegar a enredarse y donde los peces pueden alcanzar velocidades casi al limite de su capacidad natatoria. [source] Dual Luminescent Dinuclear Gold(I) Complexes of Terpyridyl-Functionalized Alkyne Ligands and Their Efficient Sensitization of EuIII and YbIII LuminescenceEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2010Xiu-Ling Li Abstract Reaction of (tpyC6H4C,CAu)n {tpyC6H4C,CH = 4,-(4-ethynylphenyl)-2,2,:6,,2,-terpyridine} with diphosphane ligands Ph2P(CH2)xPPh2 (x = 2 dppe, 3 dppp, 4 dppb, 5 dpppen, 6 dpph) in CH2Cl2 afforded the corresponding dual luminescent binuclear gold(I) complexes [(tpyC6H4C,CAu)2(,-dppe)] (1), [(tpyC6H4C,CAu)2(, - dppp)] (2), [(tpyC6H4C,CAu)2(,-dppb)] (3), [(tpyC6H4C,CAu)2(,-dpppen)] (4), [(tpyC6H4C,CAu)2(,-dpph)] (5). Crystal structural analysis of complexes 1·2CH2Cl2 and 2·2CH2Cl2 show that the terpyridine moieties are free of coordination in these gold(I)-acetylide-phosphane complexes. Spectrophotometric titration between complex 1 and [Eu(tta)3] (Htta = 2-thenoyltrifluoroacetone) or [Yb(hfac)3(H2O)2] (Hhfac = hexafluoroacetylacetone) gave a 2:1 ratio between Ln(,-diketonate)3 (Ln = Eu, Yb) units and the complex 1 moiety, indicating the formation of Au2Ln2 complexes. Both the luminescence titrations and the luminescence quantum yields of Au2Ln2 (Ln = Eu, Yb) solutions show that the energy transfer occurs efficiently from the binuclear gold(I) antennas 1,5 to EuIII and YbIII centers, and all complexes 1,5 are good energy donors for sensitization of visible and NIR luminescence of EuIII and YbIII ions. [source] Fixed relaying with adaptive antenna arrays for the downlink of multihop cellular networksEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 2 2010Zaher Dawy Multihop cellular networks are expected to play an important role in the evolution towards 4G. In this work, we propose the use of advanced antenna techniques (adaptive antenna arrays and directional antennas) at fixed relay stations in order to enhance the downlink performance of multihop cellular networks. The performance gains of various adaptive antenna configurations are analytically studied by introducing a new system-level parameter called the interference reduction factor. Moreover, Monte-Carlo simulation results as a function of various design parameters are presented and analysed in order to further highlight the gains of advanced antenna techniques. Based on the presented analysis, we propose the use of a hybrid antenna configuration at relay stations in order to obtain high gains with limited increase in complexity and cost. Copyright © 2010 John Wiley & Sons, Ltd. [source] A universal metric for sequential MIMO detection,EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 8 2007Christian Kuhn Conventionally, detection in multiple-antenna systems is based on a tree-search or a lattice-search with a metric that can be computed by recursively accumulating the corresponding metric increments for a given hypothesis. For that purpose, a multiple-antenna detector traditionally applies a preprocessing to obtain the search-metric in a suitable form. In contrast to that, we present a reformulation of the search-metric that directly allows for an appropriate evaluation of the metric on the underlying structure without the need for a computationally costly preprocessing step. Unlike the traditional approach, the new metric can also be applied when the system has fewer receive than transmit antennas. We present simulation results in which the new metric is applied for turbo detection involving the list-sequential (LISS) detector that was pioneered by Joachim Hagenauer. Copyright © 2007 John Wiley & Sons, Ltd. [source] Gaussian inputs: performance limits over non-coherent SISO and MIMO channelsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2007Rasika R. Perera Performance limits of information transfer over a discrete time memoryless Rayleigh fading channel with neither the receiver nor the transmitter knowing the fading coefficients except its statistics is an important problem in information theory. We derive closed form expressions for the mutual information of single input single output (SISO) and multiple input multiple output (MIMO) Rayleigh fading channels for any antenna number at any signal to noise ratio (SNR). Using these expressions, we show that the maximum mutual information of non-coherent Rayleigh fading MIMO channels is achieved with a single transmitter and multiple receivers when the input distribution is Gaussian. We show that the addition of transmit antennas for a fixed number of receivers result in a reduction of mutual information. Furthermore, we argue that the mutual information is bounded by the SNR in both SISO and MIMO systems showing the sub-optimality of Gaussian signalling in non-coherent Rayleigh fading channels. Copyright © 2006 AEIT [source] Multi-user detection in OFDM systems using CDMA and multiple antennasEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2003Christoph Degen This paper deals with linear multi-user detection in orthogonal frequency division multiplexing (OFDM) systems. The separation of concurrently transmitted signals is based on space division and code division multiple access (SD/CDMA). The examined OFDM schemes are compared against frequency domain equalization for single-carrier transmission schemes (SC/FDE). Both show strong similarities. Therefore in this paper, we focus on a unified treatment of multi-user detection systems based on OFDM or SC/FDE. The trade-off between exploitation of diversity and user separation is analyzed for different spreading techniques and a varying number of receive antennas. The performance is evaluated in terms of both uncoded and coded bit error ratio (BER). Furthermore, a novel time domain spreading technique for OFDM systems is proposed for which the peak-to-average transmitter power ratio (PAPR) is independent of the applied spreading code. Copyright © 2004 AEI [source] Exploiting the short,term and long,term channel properties in space and time: Eigenbeamforming concepts for the BS in WCDMAEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 5 2001Christopher Brunner The deployment of adaptive antennas at base stations considerably increases the spectral efficiency of wireless communication systems. To reduce the computational complexity and increase performance of space,time (ST) processing, processing may take place in reduced dimension, i. e., pre,filtering takes place which is related to linear estimation theory based on second order statistics. To this end, long,term and short,term channel estimates are integrated into specific Tx/Rx systems. In this article, we present a new ST rake structure for uplink reception in WCDMA which operates in reduced dimension. Accordingly, our approach combines short,term and long,term spatial and temporal channel properties using an eigenanalysis. By choosing dominant eigenbeams in time and space, the algorithm enhances interference suppression as well as spatial and temporal receive diversity. In contrast to previously introduced well,known receiver structures, the ST eigenrake inherently adapts to different propagation environments and achieves higher spectral efficiency than other receivers. This is illustrated by Monte,Carlo simulations. Then we extend the proposed concept to the downlink. The downlink eigenbeamformer improves closed,loop downlink diversity compared to other proposals in standardization (3GPP) which only exploit short,term channel properties. Even though the short,term feedback rate remains unchanged, additional antenna elements can be included to increase antenna and diversity gain. We also present a tracking solution to the downlink eigenbeamforming in WCDMA. To this end, we propose a distributed implementation of the eigenspace/,beam tracking at the mobile terminal and base station (BS), respectively. Moreover, the specific nature of the deployed tracking scheme offers an advantageous feedback signalling. [source] Silver Surface Iodination for Enhancing the Conductivity of Conductive CompositesADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Cheng Yang Abstract The electrical conductivity of a silver microflake-filled conductive composites is dramatically improved after a filler surface treatment. By a simple iodine solution treatment, nonstoichiometric silver/silver iodide nanoislands form on the silver filler surface. Evidence of the decrease of surface silver oxide species is provided by TOF-SIMS and the redox property of the nanoclusters is studied using cyclic voltammetry and TOF-SIMS depth profile analyses. The redox property of the nanoclusters on silver flakes helps enhance the electrical conductivity of the conductive composites. The electrical resistivity of the improved conductive composites is measured by four-point probe method; the reliability of the printed thin film resistors is evaluated by both the 85 °C/85% relative humidity moisture exposure and the ,40 , 125 °C thermal cycling exposure. The conductive composite printed radio frequency identification (RFID) antennas with 27.5 wt% of the modified silver flake content show comparable performance in the RFID tag read range versus copper foil antennas, and better than those commercial conductive adhesives that require much higher silver content (i.e., 80 wt%). This work suggests that a surface chemistry method can significantly reduce the percolation threshold of the loading level of the silver flakes and improve the electrical conductivity of an important printed electronic passive component. [source] Silver Surface Iodination for Enhancing the Conductivity of Conductive CompositesADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Cheng Yang Abstract The electrical conductivity of a silver microflake-filled conductive composites is dramatically improved after a filler surface treatment. By a simple iodine solution treatment, nonstoichiometric silver/silver iodide nanoislands form on the silver filler surface. Evidence of the decrease of surface silver oxide species is provided by TOF-SIMS and the redox property of the nanoclusters is studied using cyclic voltammetry and TOF-SIMS depth profile analyses. The redox property of the nanoclusters on silver flakes helps enhance the electrical conductivity of the conductive composites. The electrical resistivity of the improved conductive composites is measured by four-point probe method; the reliability of the printed thin film resistors is evaluated by both the 85 °C/85% relative humidity moisture exposure and the ,40 , 125 °C thermal cycling exposure. The conductive composite printed radio frequency identification (RFID) antennas with 27.5 wt% of the modified silver flake content show comparable performance in the RFID tag read range versus copper foil antennas, and better than those commercial conductive adhesives that require much higher silver content (i.e., 80 wt%). This work suggests that a surface chemistry method can significantly reduce the percolation threshold of the loading level of the silver flakes and improve the electrical conductivity of an important printed electronic passive component. [source] Reversibly Deformable and Mechanically Tunable Fluidic AntennasADVANCED FUNCTIONAL MATERIALS, Issue 22 2009Ju-Hee So Abstract This paper describes the fabrication and characterization of fluidic dipole antennas that are reconfigurable, reversibly deformable, and mechanically tunable. The antennas consist of a fluid metal alloy injected into microfluidic channels comprising a silicone elastomer. By employing soft lithographic, rapid prototyping methods, the fluidic antennas are easier to fabricate than conventional copper antennas. The fluidic dipole radiates with ,90% efficiency over a broad frequency range (1910,1990,MHz), which is equivalent to the expected efficiency for a similar dipole with solid metallic elements such as copper. The metal, eutectic gallium indium (EGaIn), is a low-viscosity liquid at room temperature and possesses a thin oxide skin that provides mechanical stability to the fluid within the elastomeric channels. Because the conductive element of the antenna is a fluid, the mechanical properties and shape of the antenna are defined by the elastomeric channels, which are composed of polydimethylsiloxane (PDMS). The antennas can withstand mechanical deformation (stretching, bending, rolling, and twisting) and return to their original state after removal of an applied stress. The ability of the fluid metal to flow during deformation of the PDMS ensures electrical continuity. The shape and thus, the function of the antenna, is reconfigurable. The resonant frequency can be tuned mechanically by elongating the antenna via stretching without any hysteresis during strain relaxation, and the measured resonant frequency as a function of strain shows excellent agreement (±0.1,0.3% error) with that predicted by theoretical finite element modeling. The antennas are therefore sensors of strain. The fluid metal also facilitates self-healing in response to sharp cuts through the antenna. [source] Surface deformation induced by present-day ice melting in SvalbardGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2009H. P. Kierulf SUMMARY The vertical movement of the Earth's surface is the result of a number of internal processes in the solid Earth, tidal forces and mass redistribution in the atmosphere, oceans, terrestrial hydrosphere and cryosphere. Close to ice sheets and glaciers, the changes in the ice loads can induce large vertical motions at intraseasonal to secular timescales. The Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI) antennas in Ny-Ålesund, Svalbard that started observations in 1991 and 1995, respectively, observe vertical uplift rates on the order of 8 ± 2 mm yr,1, which are considerably larger than those predicted by postglacial rebound (PGR) models (order 2 mm yr,1). The observations also indicate increased uplift rates starting some time in 2000. A local GPS campaign network that has been reoccupied annually since 1998, reveals a tilting away from the neighbouring glaciers. The Svalbard glaciers have been undergoing melting and retreat during the last century, with increased melting since about 2000. We compared the observed vertical motion to the motion predicted by loading models using a detailed ice model with annual time resolution as forcing. The model predictions correlate well with the observations both with respect to the interannual variations and the spatial pattern of long-term trends. The regression coefficients for predicted and observed interannual variations in height is 1.08 ± 0.38, whereas the regression coefficient for the predicted and observed spatial pattern turns out to be 1.26 ± 0.42. Estimates of the predicted secular trend in height due to PGR and present-day melting are on the order of 4.8 ± 0.3 mm yr,1 and thus smaller than the observed secular trend in height. This discrepancy between predictions and observations is likely caused by the sum of errors in the secular rates determined from observations (due to technique-dependent large-scale offsets) and incomplete or erroneous models (unaccounted tectonic vertical motion, errors in the ice load history, scale errors in the viscoelastic PGR models and the elastic models for present-day melting). [source] New structures of four-phase oscillators obtained by strongly interweaving mono-phase limit-cycle oscillatorsINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 4 2008D. Yardeny Abstract The present work is a part of our effort of developing multiphase oscillators. The particular system dealt with here is that of strongly nonlinearly coupled four oscillators that form a multiphase source. Such sources possess potential applications in power electronics, in phased-array antennas, and in modern methods of modulation and especially in demodulating multi-phased modulated signals. The present system can be interpreted as embracing four two-phase oscillators. Nevertheless, as a result of the strong coupling, the second state equation of each oscillator merges with the first equation of the following oscillator. The resulted four-phase source is, therefore, represented by merely four state equations. The applications related to communications (especially those related to receivers) may be susceptible to the noise performance of the source. We believe that the presently suggested system, which relies on strong coupling of oscillators, is advantageous in its noise performance in comparison to more straightforward recently described multiphase sources, which incorporate loosely coupled oscillators. Copyright © 2007 John Wiley & Sons, Ltd. [source] Achievable sum-rate analysis of correlated two-antenna MIMO uplink channelsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 8 2009Jin-Woo Lee Abstract This paper analyzes the achievable sum-rate of correlated two-antenna multiple-input multiple-output (MIMO) uplink channels. Most of previous works have considered the case when a single user has multiple transmit antennas (i.e. multi-antenna single-user scenario). This paper considers the case when two-antenna MIMO uplink channels comprise two users with a single transmit antenna (i.e. single-antenna two-user scenario). The analytic and simulation results show that the achievable sum-rate of correlated single-antenna two-user MIMO uplink channels highly depends on the angle difference between the receive correlation coefficients of two users. It is also shown that the achievable sum-rate of correlated single-antenna two-user MIMO uplink channels is larger than that of correlated two-antenna single-user MIMO uplink channels and can even be larger than that of independent and identically distributed Rayleigh two-antenna MIMO uplink channels. Copyright © 2009 John Wiley & Sons, Ltd. [source] QPSK differential space time coding on different unitary matrices sets and initializationsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 9 2006Jia Hou Abstract This paper investigates a distinct set of complex unitary matrices for differential space time coding by using QPSK modulation. The numerical results show that the proper selection of the initial transmission matrix and the set of unitary matrices can efficiently improve the bit error rate performance, especially for the antennas correlated fading channel. The computer simulations are evaluated over slow and fast Rayleigh fading channels. Copyright © 2005 John Wiley & Sons, Ltd. [source] On the performance of recursive space,frequency codes and iterative decoding in wideband OFDM-MIMO systems: simulated and measured resultsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 8 2004Paul N. Fletcher Abstract In this paper, we study the performance of a bandwidth efficient space,frequency turbo encoding scheme over wideband channels. Results are presented for simulated wideband MIMO channels consisting of two transmit antennas and up to two receive antennas. In addition, wideband channel measurements undertaken with practical multi-element antenna structures at both the access point (AP) and mobile terminal (MT) are presented. Analysis is in terms of channel capacity, 10% channel outage capacity and space,frequency iterative decoding for an lEEE802.11a physical layer complaint modem. It is shown when operating with a spectral efficiency of 1.2 bits/s/Hz, the iterative decoded space,time codes comes within approximately 4.7 dB of 10% outage capacity over Rayleigh fading wideband channels with two transmit and two receive antennas. Over measured channels the iterative decoding scheme performs within 7.7 dB 10% of outage capacity. Losses due to channel state information estimation are also investigated. Copyright © 2004 John Wiley & Sons, Ltd. [source] Fabrication of Crescent-Shaped Optical Antennas,ADVANCED MATERIALS, Issue 17 2005S. Shumaker-Parry Metal crescent-shaped nanoparticles (see Figure) that are expected to be efficient optical antennas with highly enhanced and localized near-fields are described. The particle-fabrication process combines colloidal templating, metal-film deposition, and ion-beam milling. The crescents exhibit multiple plasmon resonances in the visible and near-infrared that are of the same type as have been proposed for the development of an effective left-handed material. [source] Teletraffic capacity of CDMA cellular mobile networks and adaptive antennasINTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 4 2002Abdulaziz S. Al-Ruwais The teletraffic capacity of a CDMA mobile network with adaptive antennas at the receiver base station is considered and a simplified expression for the system outage probability associated with the teletraffic capacity is obtained. Analytical as well as numerical results show that the outage probability, and consequently the teletraffic capacity of the system, is improved using adaptive antennas at the receiver base station. Copyright © 2002 John Wiley & Sons, Ltd. [source] A three-dimensional mesh refinement algorithm with low boundary reflections for the finite-difference time-domain simulation of metallic structuresINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 3 2010W. H. P. Pernice Abstract We present a method for including areas of high grid density into a general grid for the finite-difference time-domain method in three dimensions. Reflections occurring at the boundaries separating domains of different grid size are reduced significantly by introducing appropriate interpolation methods for missing boundary points. Several levels of refinement can be included into one calculation using a hierarchical refinement architecture. The algorithm is implemented with an auxiliary differential equation technique that allows for the simulation of metallic structures. We illustrate the performance of the algorithm through the simulation of metal nano-particles included in a coarser grid and by investigating gold optical antennas. Copyright © 2009 John Wiley & Sons, Ltd. [source] Shape optimization of multi-band antennas using the coupling between microgenetic algorithms and TLM methodINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 3 2004H. S. Chu Abstract This paper presents a new combination between transmission line matrix method (TLM) and microgenetic algorithm (µGA). This coupling is used to design patch shapes of microstrip and planar inverted,F antennas (PIFA) for broad-band or multi-band applications. Measured results of the µGA/TLM optimized designs show good agreement with TLM simulation. Copyright © 2004 John Wiley & Sons, Ltd. [source] Efficient analysis of wireless communication antennas using an accurate [Z] matrix interpolation techniqueINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 4 2010Yikai Chen Abstract An accurate impedance matrix interpolation technique based on the surface integral equation (SIE) is presented for the analysis of wireless communication antennas over wide frequency bands. The first-order derivative of the impedance matrix at the internal frequency is considered in the cubic polynomial-based interpolation scheme, thus the novel impedance matrix interpolation scheme will provide high accuracy and high efficiency over a frequency band. To demonstrate the efficiency and accuracy of the proposed method, numerical results for planar inverted F antennas (PIFA) and a wideband E-shaped patch antenna are presented. Good agreement among the interpolation results, exact MoM solutions, finite element method (FEM) solutions, and measured data is observed over the bandwidth. Besides, dimensions of the feeding probe are also studied to investigate their effect on the input impedance and radiation patterns. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010. [source] Probe compensated single feed circularly polarized fractal-shaped microstrip antennasINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 6 2009P. Nageswara Rao Abstract A single feed circularly polarized fractal boundary microstrip antenna with improved axial ratio bandwidth is presented. The low-axial ratio bandwidth of single feed circularly polarized microstrip antenna is due to its probe reactance. In this article, the inherent disadvantage of this low-AR bandwidth is overcome by compensating the probe reactance by incorporating capacitance in the form of small patch between the radiating patch and the probe. The perturbation of the patch is done using fractal curve as boundary. The proposed antenna exhibits impedance and axial ratio bandwidths of 9 and 2.2% respectively at 2.4 GHz. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009. [source] A high-gain dual-band directional/omnidirectional reconfigurable antenna for WLAN systemsINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 3 2008Min Ding Abstract A high-gain dual-band antenna for the wireless local area network system is presented in this article. Two symmetrical linear arrays can be dynamically reconfigured that could switch radiation pattern with a switchable feed circuit between direction and omnidirection. The antenna can also be used for a pattern diversity antenna for the multiple-input,multiple-output communication systems. The design process for the antenna system is given, and the parameters and characteristics of the antennas are achieved by the method. Measured return losses, isolation, and radiation patterns are in good agreement with the simulated ones, which illustrates that the method is valid and the antenna system can be integrated with pattern reconfigurable and pattern diversity applications. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008. [source] Reduction of sidelobe levels in interrupted phased array antennas by means of a genetic algorithm,INTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 2 2007David A. Tonn Abstract Interruptions in the regular lattice of a phased array antenna can lead to elevated sidelobe levels in the resulting antenna pattern. A method for reducing the sidelobe level in such an array is presented, based on the use of a genetic algorithm that modifies the element weights in the array. Results are presented for both scanned and unscanned arrays. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007. [source] Probe-fed microstrip antennas loaded with very high-permittivity ceramicsINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 5 2006Y. Hwang Abstract This article reports the feasibility study of miniaturizing probe-fed microstrip patch antennas by dielectric loading. The loading materials are barium tetratitanate ceramics of very high dielectric constant (,r = 38, 80). It is shown that, simply through loading, the antenna sizes are greatly reduced; however, the antenna performances are deteriorated. For instance, the antenna gain becomes lower. Then enhancement of the antenna performances follows. A substrate,superstrate structure is used to recover the gain. Both the experiments and the finite-difference time-domain (FDTD) simulations demonstrate that the gain and impedance bandwidth can be retrieved such that they are comparable to those of conventional microstrip antennas loaded with low permittivity materials (,r < 3). © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006. [source] Two-dimensional beam-scanning using tapered slot antennas and piezoelectric transducersINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 4 2006Sang-Gyu Kim Abstract A wideband phased array is demonstrated using antipodal exponentially-tapered slot-antenna (ATSA) arrays operated by piezoelectric transducer (PET)-controlled phase shifters. A 4 × 4 ATSA array is designed to scan two-dimensionally across the entire X -band. The phase shifters for 2D scanning consist of two sets of multiline phase shifters controlled by the PET for scanning in both planes. The 2D phased array has an antenna gain greater than 8 dBi, including all losses due to the phase shifters and transitions, and shows a wide beam-scanning capability greater than 30° in both the E -plane and the H -plane. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006. [source] Modeling and optimization of cylindrical antennas using the mode-expansion method and genetic algorithmsINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 6 2005Dawei Shen Abstract For monopole antennas with cylindrically symmetric structures, a mode-expansion method is highly time efficient, which is a realistic approach for integrating function-optimization tools, such as genetic algorithms (GAs), in order to extract the best bandwidth property. In this article, a mode-expansion method is used to simulate the impedance characteristics of the cylindrical antennas. As examples, two new types of monopole antennas are presented, one of which possesses a two-step top-hat structure while the other has an annulus around the stem. After the modeling scheme is examined for convergence and data validity, the associated optimization problem, with dimensions as decision variables, structural limitations as linear constraints, and desired bandwidth performance as an objective function, is solved using GAs. The effects of the geometric parameters on the impedance characteristics are investigated in order to demonstrate the optimality of the calculated solutions. Two optimized practical antennas are designed based on our numerical studies. One has a broad bandwidth of 3 GHz while the other shows a dual-band property, which can satisfy the bandwidth requirements for both Bluetooth (2.45-GHz band) and WLAN (5-GHz band) systems. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005. [source] | ||||||||||||||||||||||