Showing papers on "Antenna (radio) published in 2000"

Fading correlation and its effect on the capacity of multielement antenna systems

Abstract: We investigate the effects of fading correlations in multielement antenna (MEA) communication systems. Pioneering studies showed that if the fades connecting pairs of transmit and receive antenna elements are independently, identically distributed, MEAs offer a large increase in capacity compared to single-antenna systems. An MEA system can be described in terms of spatial eigenmodes, which are single-input single-output subchannels. The channel capacity of an MEA is the sum of capacities of these subchannels. We show that the fading correlation affects the MEA capacity by modifying the distributions of the gains of these subchannels. The fading correlation depends on the physical parameters of MEA and the scatterer characteristics. In this paper, to characterize the fading correlation, we employ an abstract model, which is appropriate for modeling narrow-band Rayleigh fading in fixed wireless systems.

Unitary space-time modulation for multiple-antenna communications in Rayleigh flat fading

Abstract: Motivated by information-theoretic considerations, we propose a signaling scheme, unitary space-time modulation, for multiple-antenna communication links. This modulation is ideally suited for Rayleigh fast-fading environments, since it does not require the receiver to know or learn the propagation coefficients. Unitary space-time modulation uses constellations of T/spl times/M space-time signals (/spl Phi//sub i/, l=1, ..., L), where T represents the coherence interval during which the fading is approximately constant, and M

Differential unitary space-time modulation

Abstract: We present a framework for differential modulation with multiple antennas across a continuously fading channel, where neither the transmitter nor the receiver knows the fading coefficients. The framework can be seen as a natural extension of standard differential phase-shift keying commonly used in single-antenna unknown-channel systems. We show how our differential framework links the unknown-channel system with a known-channel system, and we develop performance design criteria. As a special ease, we introduce a class of diagonal signals where only one antenna is active at any time, and demonstrate how these signals may be used to achieve full transmitter diversity and low probability of error.

Energy-efficient antenna sharing and relaying for wireless networks

Abstract: We develop energy-efficient transmission protocols for wireless networks that exploit spatial diversity created by antenna sharing: coordinated transmission and/or processing by several distributed radios. We focus on single-user transmission and examine several possibilities for the strategy employed by the assisting radio, or relay, including decoding and forwarding as well as amplifying and forwarding. In each case, we develop receivers based upon maximum-likelihood and/or maximum signal-to-noise ratio criteria, relate their structures, and compare their bit-error probability performance by means of analysis and simulations. We cast single-hop and multihop routing into our framework for comparison purposes. All of our antenna sharing protocols offer diversity gains over single-hop and multihop transmission, and our results suggest that low-complexity amplifying and forwarding is energy-efficient in spite of noise amplification at the relay.

Array gain and capacity for known random channels with multiple element arrays at both ends

Abstract: Two arrays with M and N elements are connected via a scattering medium giving uncorrelated antenna signals. The link array gain relative to the case of one element at each end is treated for the situation where the channels are known at the transmitter and receiver. It is shown that the maximum mean gain achieved through adaptive processing at both the transmitter and the receiver is less than the free space gain, and cannot be expressed as a product of separate gains. First, by finding the singular values of the transmission matrix, fundamental limitations concerning the maximum gain and the diversity orders are given, indicating that the gain is upper bounded by (/spl radic/M+/spl radic/N)/sup 2/ and the diversity order is MN. Next an iterative technique for reciprocal channels which maximizes power at each stage transmitting back and forth is described. The capacity or spectral efficiency of the random channel is described, and it is indicated how the capacity is upper bounded by N parallel channels of gain M(N

Microwave and Rf Design of Wireless Systems

Abstract: From the Publisher: This book offers a quantitative and design-oriented presentation of the analog RF aspects of modern wireless telecommunications and data transmission systems from the antenna to the baseband level. It takes an integrated approach to topics such as antennas and proagation, microwave systems and circuits and communication systems.

The Koch monopole: a small fractal antenna

Abstract: Fractal objects have some unique geometrical properties. One of them is the possibility to enclose in a finite area an infinitely long curve. The resulting curve is highly convoluted being nowhere differentiable. One such curve is the Koch curve. In this paper, the behavior the Koch monopole is numerically and experimentally analyzed. The results show that as the number of iterations on the small fractal Koch monopole are increased, the Q of the antenna approaches the fundamental limit for small antennas.

Method and apparatus combining a tracking system and a wireless communication system

Abstract: System for tracking mobile tags. Cell controllers with multiple antenna modules generate a carrier signal which is received by the tags. Tags shift the frequency of the carrier signal, modulate an identification code onto it, and transmit the resulting tag signal at randomized intervals. The antennas receive and process the response, and determine the presence of the tags by proximity and triangulation. The recursive-least squares (RLS) technique is used in filtering received signals. Distance of a tag from an antenna is calculated by measuring the round trip signal time. The cell controllers send data from the antenna to a host computer. The host computer collects the data and resolves them into positional estimates. A combined infrastructure including a wireless communication system and the local positioning system is also disclosed.

Experimental study of a microstrip patch antenna with an L-shaped probe

Abstract: The L-shaped probe is shown to be an attractive feed for the thick microstrip antenna (thickness around 10% of the operating wavelength). A parametric study on the rectangular patch antenna is presented. It is found that the antenna attains 36% impedance bandwidth (SWR/spl les/2) as well as gain bandwidth and about 7-dBi average gain. A two-element array fed by L-probes is also proposed. Experiments show that the array design can substantially suppress the cross polarization of the proposed antenna. Both the antennas have stable radiation patterns across the passband. Moreover, the measured resonant frequencies of the proposed antenna agree well with an existing formula and the L-probe does not have much effect on the resonant frequency.

A new quasi-Yagi antenna for planar active antenna arrays

Abstract: In this paper, a novel broadband planar antenna based on the classic Yagi-Uda dipole antenna is presented, and its usefulness as an array antenna is explored. This "quasi-Yagi" antenna is realized on a high dielectric-constant substrate, and is completely compatible with microstrip circuitry and solid-state devices. This antenna achieves a measured 48% frequency bandwidth for voltage standing-wave ratio <2, better than a 12-dB front-to-back ratio, smaller than -15 dB cross polarization, and 3-5-dBi absolute gain. Mutual coupling of the antenna in an array environment is investigated. Finally, three simple arrays are presented, demonstrating the usefulness of the antenna as an array element. This novel antenna should find wide application in wireless communication systems, power combining, phased arrays, and active arrays, as well as millimeter-wave imaging arrays.

MIMO wireless channels: capacity and performance prediction

Abstract: We present a new model for multiple-input multiple-output (MIMO) outdoor wireless fading channels which is more general and realistic than the usual i.i.d. model. We investigate the channel capacity as a function of parameters such as the local scattering radius at the transmitter and the receiver, the distance between the transmit (TX) and receive (RX) arrays, and the antenna beamwidths and spacing. We point out the existence of "pin-hole" channels which exhibit low fading correlation between antennas but still have poor rank properties and hence low capacity. Finally we show that even at long ranges high channel rank can easily be obtained under mild scattering conditions.

Telemetry system for implantable medical devices

Abstract: A device for use in communication with an implantable medical device. The device is provided with a spatial diversity antenna array mounted to a housing and an RF transceiver operating at defined frequency, coupled to the antenna array. The antenna array comprises two antennas spaced a fraction of the wavelength of the defined frequency from one another, each antenna including two antenna elements mounted to the housing and located orthogonal to one another. Selection of which of the antennas is employed is accomplished by a device controller, responsive to the quality of the signals received by the antennas.

Effect of antenna separation on the capacity of BLAST in correlated channels

Abstract: As the base station is usually placed above local clutter, the angular spectrum incident on the base is narrow, inducing correlation among base antenna signals, which reduces the capacity of a multiple transmit and receive antenna systems. In this work the general expression for link capacity is derived, when there is correlation among receive antennas and among transmit antennas. It is found that an antenna separation of 4 wavelengths between nearest neighbors in a linear base array of dually polarized antennas allows one to achieve 80% of the capacity attainable in the uncorrelated antenna case.

Selecting an optimal set of transmit antennas for a low rank matrix channel

Abstract: Previous work has shown that the use of multiple antennas in a fading environment results in a linear increase in capacity. This paper examines the capacity of a multiple antenna element array (MEA) in a quasi-static flat fading environment with a rank deficient channel. We assume that the channel is known at the receiver and the existence of a feedback path to the transmitter. For a particular channel realization, we show that the judicious use of fewer transmit antennas when the channel matrix is ill-conditioned can increase system capacity. We develop a criterion for selecting an optimum set of transmit antennas. This selection is optimal in the sense that the capacity of the resulting MEA system is greater than that for any other configuration with the same number of transmit antennas chosen from the original set. The resulting channel is full rank.

A broad-band U-slot rectangular patch antenna on a microwave substrate

Abstract: A broad-band U-slot rectangular patch antenna printed on a microwave substrate is investigated. The dielectric constant of the substrate is 2.33. The antenna is fed by a coaxial probe. The characteristics of the U-slot patch antenna are analyzed by the finite-difference time-domain (FDTD) method. Experimental results for the input impedance and radiation patterns are obtained and compared with numerical results. The maximum impedance bandwidth achieved is 27%, centered around 3.1 GHz, with good pattern characteristics.

Microwave devices for medical hyperthermia, thermotherapy and diagnosis

Abstract: To treat and diagnose tissue, a radiating antenna system is positioned within the tissue to radiate electromagnetic energy into a portion of the tissue desired to be heated, and a plurality of antenna elements are positioned for receiving and/or reflecting the radiated electromagnetic energy from the radiating antenna system. In certain applications, one or more of the antennas has an interior volume for receiving a heat exchange fluid to change the temperature of the tissue proximal to the receiving element.

Tamper-resistant wireless article including an antenna

Abstract: A wireless article, such as an identification tag or badge, includes an electronic device mounted on a substrate and connected a loop antenna for receiving and/or transmitting radio frequency signals. Electrically conductive material disposed on the substrate or in holes through the substrate of the wireless article connect the antenna terminals to the electronic device contacts. The structure and materials of the wireless article may be rugged and strong to provide a tamper-resistant article, and/or may include one or more weakened or frangible portions that easily break to provide a tamper-destruct article. The wireless article may be arranged to resist heat, moisture and/or solvents, to function in severe environments such as laundering and industrial processes.

Antenna sharing switching circuitry for multi-transceiver mobile terminal and method therefor

Abstract: Antenna switching circuitry in a multi-transceiver mobile terminal 10 , which features a first switching unit (SW 1 ) which controllably couples a first transceiver port (P 1 ) to either a first antenna port (P A1 ) or a second antenna port (P A2 ); and a second switching unit (SW 2 ) which controllably couples the second antenna port (P A2 ) to either the first transceiver port (P 1 ), through the first switching unit (SW 1 ), or to an input/output port (P I/O ) of a second transceiver ( 12 ). According to this scheme, the second antenna port is coupled to the input/output port of the second transceiver ( 12 ) in a mode in which the second transceiver ( 12 ) is operational, the first transceiver port (P 1 ) being decoupled from the second antenna port at this time, wherein the first transceiver port is coupled to the first antenna port and the input/output port of the second transceiver ( 12 ) is decoupled from the second antenna port, when the first transceiver is in a transmit mode, and wherein the first transceiver port is coupled to either of the first and second antenna ports, when the first transceiver ( 11 ) is in a receiving mode and the input/output port of the second transceiver ( 12 ) is decoupled from the second antenna port.

Identification of time-variant directional mobile radio channels

Abstract: For the identification of the time-variant, directional structure of the mobile radio channel impulse response (CIR), a broadband vector channel sounder is described. The measurement procedure relies on periodic multifrequency excitation signals, correlation processing, and joint delay-azimuth super-resolution based on the two-dimensional (2-D) unitary ESPRIT algorithm. Problems of imperfect receiver and antenna performance as well as antenna array calibration methods are discussed. Correlation analysis of the directional impulse response records is performed in the time-frequency-spatial domain and the corresponding Doppler-delay-angular domain. Results from measurements in the 5.2 GHz frequency range in an industrial environment are presented.

Method and system for automated optimization of antenna positioning in 3-d

Abstract: A method for engineering management and planning for the design of a wireless communications network in three-dimensions (3-D) combines computerized organization, database fusion, and radio frequency (RF) site-specific planning models. The method enables a designer to keep track of wireless system performance throughout the process of pre-bid design, installation and maintenance of a wireless system. Using a database of information that defines the desired environment (1002), predictions (1001) of antenna coverage, system coverage and interference, and other wireless system performance criteria, such as frame error rate and network throughput, can be made. Watch points (1004) are created to ensure, in real time, that any modifications (1006) to the design of the wireless system do not degrade the performance of the system with respect to the watch point locations.

Low cost long distance rfid reading

Abstract: In the production radio frequency (RF) sensable objects, it is possible to produce a package, envelope, or like container which has enhanced read distance, producable by a simple method. Large areas are printed on the envelope or package in conductive ink which are separated by a non-conductive portion of the package or envelope and function as an RF antenna. Then by placing an otherwise conventional label with an RFID chip associated with it so that it bridges the conductive ink portions of the RF antenna, a much easier to sense or read product is produced. The conductive ink can be applied in a pattern, logo, and letters or character indicia. The label may have conductive pressure sensitive adhesive on one face, which actually connects the antenna sections to the RFID chip to form the operable structure that can be sensed by an RF receiver at a distance of three meters or more.

IC module and smart card

Abstract: A smart card comprises an IC module and an antenna for non-contact transmission. The IC module has both a contact-type function and a non-contact-type function. In the contact-type function, power reception and signal transmission/reception is effected via an electrical contact. In the non-contact-type function, power reception and signal transmission/reception is effected in a non-contact state by an electromagnetic coupling system without providing the IC card with an electrical contact. The IC module and the antenna comprise first and second coupler coils, respectively, which are disposed to be closely coupled to each other, and the IC module and the antenna are coupled in a non-contact state by transformer coupling. An antenna coil is disposed so as not to overlap an engagement portion for the IC module, which is a region of an external terminal electrode serving as a contact-type electrode, an embossing region, or a magnetic stripe region.

Antenna array calibration

Abstract: A method and a system for calibrating the reception and transmission of an antenna array for use in a cellular communication system is disclosed. The calibration of the reception of the antenna array is performed by injecting a single calibration signal into each of a number of receiving antenna sections, in parallel. The signals are collected after having passed receiving components that might have distorted the phase and amplitude. Correction factors are generated and applied to received signals. The calibration of the transmission of the antenna array is performed in a similar way. A single calibration signal is generated and injected into each of a number of transmitting antenna sections, one at a time. The signals are collected, one at a time, after having passed transmitting components that might have distorted the phase and amplitude. Correction factors are generated and applied to signals that are to be transmitted.

Close-proximity radiation detection device for determining radiation shielding device effectiveness and a method therefor

Abstract: A radiation detection device for locally detecting radiation of RF energy emissions from close proximity direct line-of-sight electromagnetic fields emitted by a wireless transmit/receive electronic equipment antenna 22 or body 21 such as a cellular telephone, in miniature/planar design form with suitable embedding form-factoring fashioned arrangement capability joined with radiation shielding devices. Said radiation detection device operates without prerequisite need for a battery or external power source, operationally self-powered by the embodiments of this invention when exposed to electromagnetic field radiation of predetermined thresholding energy level setting for the user's own personal alerting verification and assessment means of suitable predetermined radiation detection measurement tester coupling to radiation shielding devices to encompass an overall shield effectiveness system solution in real-time monitoring response fashion operation.

Synthesis of antenna arrays using genetic algorithms

Abstract: In this article, two particular methods for the synthesis of the complex radiation pattern of a linear and a planar array, based on genetic algorithms (GAs), are discussed. First, we present a combination of Schelkunoff's method and GAs for linear arrays with arbitrary radiation patterns; then, we consider the synthesis of planar arrays with rectangular cells. The results show the flexibility of GAs to solve complex problems related to antenna synthesis, subject to many restrictions which are difficult to treat by classical optimization techniques. There is good agreement between the desired and calculated radiation patterns.

Multi-mode broadband patch antenna

Abstract: A multi-mode broad band patch antenna is provided that allows for the same aperture to be used at independent frequencies such as reception at 19 GHz and transmission at 29 GHz. Furthermore, the multi-mode broadband patch antenna provides a ferroelectric film that allows for tuning capability of the multi-mode broadband patch antenna over a relatively large tuning range. The alternative use of a semiconductor substrate permits reduced control voltages since the semiconductor functions as a counter electrode.

ESPRIT-based 2-D direction finding with a sparse uniform array of electromagnetic vector sensors

Abstract: Aperture extension (interferometry baseline extension) is achieved in this novel ESPRIT-based two-dimensional (2-D) arrival angle estimation scheme using a sparse (a.k.a., thin or thinned) uniform rectangular array of electromagnetic vector sensors spaced much farther apart than a half-wavelength. An electromagnetic vector sensor is composed of six spatially co-located, orthogonally oriented, diversely polarized antennas, distinctly measuring all six electromagnetic-field components of an incident multisource wavefield. Each incident source's direction of arrival (DOA) is estimated from the source's electromagnetic-field vector component and serves as a coarse reference to disambiguate the cyclic phase ambiguities in ESPRIT's eigenvalues when the intervector sensor spacing exceeds a half wavelength. Simulations demonstrate the significant performance gain realizable by this method for radar and wireless mobile fading-channel communications.

Radio frequency identification tags and labels

Abstract: Radio frequency identification elements (15), including linerless or lined labels (56), are produced with enhanced effectiveness. The antenna (18) is printed with conductive ink or toner, and cross-over may be provided by spot printing a non-conductive material (21) over a portion of the antenna and then printing a conductive cross-over element (25) on the non-conductive material (21). Typically the antenna (18) is printed on one face (22) of a web (10), and the radio frequency identification chip (30) is moved into contact with the opposite face (27) of the web (10) so that the contacts (31) penetrate the web and engage the antenna so that the web material acts as a dielectric. Alternatively part of the antenna on the first face may be over-printed with a non-conductive material (40) and the chip attached to the first face passing through openings (41) in, or penetrating, the non-conductive material (40) to engage the antenna. A protective substrate (45, 46) or coating is provided on at least one of the chip and antenna, for example by heating heat expandable microspheres, or applying a substrate having hot melt adhesive. The antenna may be printed with a printing media comprising a carrier including resin and wax and containing conductive material in it, and by heating the carrier so that it becomes fluid and is applied as a thick film on the substrate, and by allowing the carrier to cool so as to provide a conductive antenna. The printing may be accomplished at a speed of about 500 feet per minute or more.

Microwave ablation instrument with a directional radiation pattern

Abstract: A medical instrument is disclosed The medical instrument includes a transmission line suitable for the transmission of electromagnetic energy and an antenna coupled to the transmission line The antenna is configured for generating an electromagnetic field sufficiently strong to cause tissue ablation The medical instrument further includes a reflector arranged to be electrically coupled to the transmission line The reflector is positioned laterally to a first side of the antenna and configured for redirecting a portion of the electromagnetic field to a second side of the antenna opposite the reflector, wherein a majority of the electromagnetic field is directed away from the second side of the antenna

Tunable dual-band ferroelectric antenna

Abstract: A multilayer tunable ferroelectric antenna assembly that includes two superimposed substrate layers. A first substrate layer consists of a low dielectric material carrying on one face an electrically ground plane, and on its opposite face an electrically conductive patch serving as an active feeder-resonator. A second substrate includes a ferroelectric material having one face positioned on top of the feeder-resonator and carrying on the opposite face an electrically conductive patch acting as a director. The upper director patch is fed through capacitve coupling of energy from the feeder-resonator. Application of bias voltage between the director and the feeder-resonator changes the permittivity of the ferroelectric substrate, thereby causing a shift in resonance frequency. A radiation null, corresponding to energy absorption, could be tuned into the resonance frequency at which the antenna is previously exhibiting a radiation characteristic. This provides the antenna a means to behave either as a radiator or an absorber at particular frequency.