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Antennas and Propagation for Wireless Communications, 1998. 1998 IEEE-APS Conference on

Date 1-4 Nov. 1998

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Displaying Results 1 - 25 of 47
  • 1998 IEEE-APS Conference on Antennas and Propagation for Wireless Communications (Cat. No.98EX184)

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    Freely Available from IEEE
  • Author index

    Page(s): 181 - 184
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    Freely Available from IEEE
  • Improved feed system design for a wideband dipole array

    Page(s): 97 - 100
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    A high power, wideband HF phased array is being constructed as part of the High Frequency Active Auroral Research Program (HAARP) in Galkona, Alaska. Extensive testing of a demonstration prototype (DP) version of the array discovered undesirable feed resonance effects at discrete frequencies and excessive tower currents under simulated scanned conditions. Analyses and subsequent measurements pointed to even mode excitations of the dipole as the cause of these difficulties. To solve this problem the feed system was modified with the goal of controlling both the even and odd mode excitations. A novel wideband high efficiency hybrid-balun and balanced AMU (antenna matching unit) was designed and tested confirming the superiority of the new feed arrangement. A low-band version is being incorporated into the DP testbed and extends the low-band performance by 20%, with lower loss and reduced tower currents. The feed design is further evaluated by calculating the average efficiency of the array system, which is within 0.25 to 1.5 dB of its theoretical maximum, depending on frequency View full abstract»

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  • A field/polarization diversity antenna for portable phones

    Page(s): 125 - 128
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    The design of a two-element field/polarization diversity antenna for portable phones is considered. The antenna consists of a dipole terminated with a parallel loop capacitor combination. The antenna has a single feed at a point on the loop opposite the junction, and does not require external combining circuitry. The capacitor creates a phase shift between the dipole and loop currents, thereby greatly reducing the probability of deep nulls when the antenna is deployed in the vicinity of a fixed reflector, where standing wave patterns occur. Theoretical and simulation studies based on multiple incident plane wave fields are used to quantify antenna diversity gain in the presence of a fixed reflector. Simulation results are presented for three antenna types: a dipole antenna, a loop-dipole antenna without a capacitor, and the loop-dipole antenna with capacitor. The simulation results are verified by field measurements on an automated outdoor test range, where the incidence angle and distance from the reflector are varied. Both the simulation and field test results show that the loop-dipole-capacitor design provides a substantial diversity gain over the standard dipole antenna and over the loop-dipole antenna without the capacitor View full abstract»

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  • Indoor ISM band multipath fading: frequency and antenna diversity

    Page(s): 9 - 12
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    The frequency fading characterization of the indoor ISM (902-928 MHz) channel are presented. This includes plots of the frequency-dependence of the fading and calculations of the correlation bandwidth. Finally, the measured diversity performance of three novel dual antenna configurations proposed for an ISM band wireless transceiver handset are presented. The diversity performance of these antenna geometries is assessed by measuring the power correlation coefficient of the signal received over each of the two antennas located on the handset. To evaluate the functionality of the measuring apparatus used in these experiments, the correlations of the received signal from two dipole antennas with various separations are measured, for which theoretically computed and previously measured envelope correlation coefficient data is available. Considerable effort is also directed at extraction of the fast fading information from the observed signal level, and its effect is detailed View full abstract»

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  • A new GPS hexafilar slot antenna

    Page(s): 137 - 140
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    This paper presents a new GPS slot antenna consisting of six quarter-wavelength resonant slots. Each of the six resonant slots is rolled a half-turn around the cylindrical laminate and maintains constant phase relation to each other to form a right-hand circular polarization to receive GPS satellite signals. The printed cylindrical slot antenna presented is useful in applications where low-profile installation is required on a highly dynamic aircraft. This new printed GPS antenna provides compact size, low cost, ease of mass production, near-hemispherical radiation coverage and circular polarization properties. Experimental results show that the new hexafilar antennas have a 3 dB beamwidth of more than 120° and a front-back ratio of more than 15 dB View full abstract»

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  • Radial basis function neural network algorithm for adaptive beamforming in cellular communication systems

    Page(s): 53 - 56
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    A smart antenna based on a neural network implementation of the optimum Wiener solution for the problem of adaptive interference nulling using circular arrays is presented. Modem cellular satellite mobile communications systems and GPS systems suffer from different sources of interference which limit system capacity. This paper develops a fast tracking system to constantly track the mobile users, and then adapt the radiation pattern of the antenna to direct multiple narrow beams to desired users and nulls to sources of interference. The computation of the optimum weights is viewed as a mapping problem which can be modeled using a three-layer radial basis function neural network (RBFNN) trained with input/output pairs. The results obtained from this network are in excellent agreement with the Wiener solution. It is found that networks implementing these functions are successful in tracking mobile users as they move across the antenna's field of view View full abstract»

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  • Electromagnetic ground-wave field of vertical antennas

    Page(s): 5 - 8
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    Communication between the shore and a ship and between ships makes use of frequencies from 1 to 30 MHz. The analysis presented provides new simple formulas for the ground wave along the surface of the sea. These include not only the range in which the surface of the sea is well-approximated by a plane but also the range where accurate account must be taken of the curvature of the spherical Earth. Of practical significance is the fact that when f⩾10 MHz, the amplitude of an outgoing wave decreases much more rapidly than when f<10 MHz. This is true in the planar region when ρi<ρ<ρc , and throughout the spherical region ρsc View full abstract»

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  • The circularly polarized cylindrical patch

    Page(s): 145 - 148
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    The paper presents a new type of antenna with a dipole-like radiation pattern and circular polarization. The antenna is a cylindrical patch antenna fed by a coaxial line, with a special geometry which generates the circular polarization. The configuration was optimized so it would generate the minimum axial ratio in the azimuthal plane where the pattern is omnidirectional. The antenna proposed is a simple and inexpensive solution for any wireless communication system where omnidirectional pattern and circular polarization are required View full abstract»

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  • An analysis of radio signal level variations in strong multipath indoor environment

    Page(s): 29 - 32
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    Dipole antenna performance in a strong multipath environment due to multiple reflections is discussed. A method of computing the field distribution inside a room of arbitrary dimensions and electric characteristics of the walls is proposed. Measurements for different transmitter-receiver configurations and polarizations are presented. Based on computer simulation and measurement results some conclusions are made View full abstract»

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  • Dynamics of attenuation in equatorial Brazil: 1-year analysis of three 12 GHz Earth-space links

    Page(s): 21 - 24
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    The dynamic analysis of attenuation is defined as the statistical analysis of time duration and number of events of a given attenuation level being exceeded. The results from the dynamic statistical analysis of one year of radiometric attenuation measurements in three 12 GHz stations located in equatorial Brazil are presented and discussed. Such data and results are very rarely presented in the literature and may provide design information for the implementation of future satellite communication systems which would operate in such remote and inhospitable areas of the planet View full abstract»

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  • EM interactions between handheld antennas and human: anatomical head vs. multi-layered spherical head

    Page(s): 69 - 72
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    It has been widely acknowledged that comprehensive understanding of EM interactions between human and personal communications antennas is essential for modern handheld antenna design. Results using the FDTD method for the spherical head are compared with those using the eigenfunction expansion method. Also, the near- and far-field patterns of a half-wave antenna with the anatomical head are compared with those of the spherical head. We show that the results obtained with the spherical head can provide useful estimates for various antenna design purposes. Finally, we present engineering design data obtained with a six-layered spherical head. We mainly focus on 900 MHz results View full abstract»

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  • A hybrid MoM/FDTD technique for studying human head/antenna interactions

    Page(s): 81 - 84
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    As advances in numerical methods for solutions to Maxwell's equations accelerate, larger and more complex electromagnetic problems are becoming tractable at an astounding rate. The science of computational electromagnetics (CEM) gains inertia with each passing day. The maturing field of CEM research has sprouted various branches of research. The finite-difference time-domain (FDTD) method, introduced in 1966 by Yee (1966), and pioneered by Taflove (1995), among others, since 1975, provides a simple and robust method for simulating the propagation of electromagnetic radiation through complex media, e.g., human tissue. Although the FDTD method performs superbly for such propagation simulations, it is not very well suited for modeling complex metallic structures, e.g., antennas. Conversely, a distinct branch of CEM research, the method of moments (MoM), is superior for modeling complex metallic structures and is not very well suited for propagation through complex media, such as human tissue. In this paper, a hybrid MoM/FDTD method for simulating the interaction of antennas with the human head is presented View full abstract»

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  • A physical-statistical time-series model for the mobile-satellite channel

    Page(s): 1 - 4
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    The present work describes a time series propagation model which considers three-dimensional urban path profiles where the buildings can have unequal heights, widths and spacings. Based on the Fresnel-Kirchhoff theory, it is mainly applicable to mobile satellite propagation channels where the final building face, just before the mobile user, is the most dominant source of diffraction phenomena. Although the model is considered to adopt a deterministic type of process, the outcome of the proposed work is achieved by considering only statistical distributions for the building path profile View full abstract»

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  • Adaptive base station antennas for mobile communication systems

    Page(s): 49 - 52
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    There has been a rapid increase in the number of mobile communication users, resulting in an equally rapid need for increased capacity in the networks. Extensive research and development work on advanced base station antennas for mobile communication is in progress at Ericsson. This includes both active and adaptive antenna systems. With the introduction of active antenna products, it is now possible to use small-size base stations, with high levels of equivalent radiated power (ERP) and low power consumption. Array designs and measured results from the work on adaptive base station antennas are presented View full abstract»

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  • Pattern nulling synthesis based on adaptive array theory

    Page(s): 65 - 68
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    A novel algorithm for adaptive pattern null synthesis which is based on the Gram-Schmidt orthogonalization is proposed. It uses the element nulling vector method which not only maintains all the advantages of pattern null synthesis but also has a small increase in the pattern sidelobe level for suppressing the wideband clutter and setting up a wide notch. Compared with the original algorithms, when setting up the same null notch, the sidelobe level decreases by about 3~5 dB. Numerical result comparisons between this algorithm and the original ones are given View full abstract»

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  • Circularly polarized single-fed microstrip patch for wireless communications

    Page(s): 167 - 170
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    For more than 25 years the circularly polarized single-fed microstrip patch have been considered to be extremely narrow-band. The performances reported are almost exclusively related to single patches printed on a dielectric substrate, which partially explains the frequency characteristics. The antenna proposed is a variation of the `almost-square' patch and exhibits a theoretical axial ratio of less than 2.5 dB over a 10% bandwidth. The antenna was designed for PCN and PCS applications View full abstract»

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  • Multimode rectangular microstrip antenna for GPS applications

    Page(s): 149 - 151
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    Hand-held GPS receivers have revolutionized navigation for the dismounted soldier. This paper presents the experimental development of a single-element, multimode rectangular microstrip antenna capable of forming a spatial null. Using fundamental and higher order modes within a single microstrip patch radiator, a relatively simple, low-cost adaptive antenna capable of forming a null in the vicinity of the horizon is demonstrated. Numerical and experimental results are presented View full abstract»

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  • Aperture-coupled microstrip antennas using reflector elements for wireless communications

    Page(s): 163 - 166
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    The design advantages provided by aperture-coupled microstrip patches can be very useful in wireless communications applications. A way to improve the front-to-back ratio is to place a microstrip antenna element behind the aperture as a reflector. Proximity coupling between the feed line and the reflecting element is negligible due to the thick foam substrate used, allowing use of the reciprocity method of analysis. Also, the directive patch elements are shielded from the reflector by the ground plane. Therefore, only interactions between the reflector and the aperture need to be modeled, resulting in a simple analysis. For aperture-coupled patch designs with a front-to-back ratio of 10 dB or greater, the introduction of a reflecting element has a negligible effect on the input impedance of the antenna. Therefore, a reflector element can readily be incorporated into existing designs View full abstract»

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  • Effects of element pattern for adaptive array in W-CDMA mobile radio

    Page(s): 45 - 48
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    The next generation of land mobile communication systems must offer high bit data rates for multimedia and high-quality services. Adaptive arrays are considered to be a key technology to satisfy these demands, and applying them to land mobile radio has been investigated extensively. However, those reports mainly focus on structures of adaptive receivers or adaptive algorithms, few reports consider antenna arrays, especially the effect of the pattern of the antenna elements of the array antenna on adaptive array performance. The effects of the antenna element pattern on performance have been reported, but the investigation was of adaptive array characteristics for a TDMA cellular system. Recently, W-CDMA has been investigated extensively as an access technology for the third-generation mobile radio, IMT-2000. Interference environments are so different between the TDMA system and W-CDMA (DS-CDMA) system, that it is unknown whether their study can be applied to W-CDMA adaptive arrays or not. We examine the performance of an adaptive array receiver of a base station for a W-CDMA system by computer simulation from the viewpoint of the element pattern of the array antenna. We then discuss the relationship between 3 dB element beamwidth and service area in satisfying a bit error rate (BER) of <10-3 View full abstract»

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  • Modified quadrifilar helix antennas for mobile satellite communication

    Page(s): 141 - 144
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    Quadrifilar helix antennas have gained attention recently as antennas for satellite telephone handsets. Here a modification procedure is introduced for decreasing the length of the quadrifilar helix antenna. Two modified and two non-modified, quadrifilar antennas are designed and measured. The measurement results are shown View full abstract»

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  • A tissue-equivalent solid phantom for estimation of interaction between human head and handset antenna

    Page(s): 89 - 92
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    In this paper, accurate measurements for the SAR of modeled human heads using the brain equivalent phantom are presented. First, SARs of cubic and spherical phantoms in the vicinity of a dipole antenna are measured and compared with calculation. Secondly, a monopole antenna in a metal box, which simulates a mobile phone, is used. The operating frequency is considered only at 900 MHz. To enhance the accuracy of the experiments, the ingredients for the head model were carefully conditioned complying with COST 244 (1994) View full abstract»

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  • Dielectric resonator antenna technology for wireless applications

    Page(s): 117 - 120
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    This paper features some of the recent advances in dielectric resonator antenna technology at the Communications Research Centre, Ottawa, Canada. Several novel elements are presented offering significant enhancements to parameters such as impedance bandwidth, circular polarization bandwidth, gain, or coupling to feed structures. A variety of linear and planar arrays are also presented to illustrate the performance of these elements in an array environment. Dielectric resonator antenna technology offers a promising alternative to conventional antennas for wireless communication applications View full abstract»

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  • Multiple sources neural network direction finding with arbitrary separations

    Page(s): 57 - 60
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    Interference rejection is very important and often represents an inexpensive way to increase the system capacity of cellular and mobile communication systems. This paper presents a modification to the radial basis function-based direction finding algorithm where the DOA problem is approached as a mapping which can be modeled by training the network with input output pairs with multiple angular separations. The network is then able to track a fixed number of sources with arbitrary angular separations using a linear array. A novel training technique is suggested and the performance of the RBFNN algorithm is compared to ideal data View full abstract»

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  • Identification approach for mapping the propagation losses models

    Page(s): 33 - 36
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    Many models to predict the propagation losses, the signal strength, etc., have been developed, but the vertiginous development of radio networks has prompted an examination of the propagation characteristics along the coverage area. However, the diversity in the available methods make the appropriate selection, for any particular situation, a hard task. We introduce an identification algorithm for mapping the propagation loss models (a feature of great relevance in radio network design) View full abstract»

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