Showing papers on "Antenna (radio) published in 1999"

Space-time block coding for wireless communications: performance results

Abstract: We document the performance of space-time block codes, which provide a new paradigm for transmission over Rayleigh fading channels using multiple transmit antennas. Data is encoded using a space-time block code, and the encoded data is split into n streams which are simultaneously transmitted using n transmit antennas. The received signal at each receive antenna is a linear superposition of the n transmitted signals perturbed by noise. Maximum likelihood decoding is achieved in a simple way through decoupling of the signals transmitted from different antennas rather than joint detection. This uses the orthogonal structure of the space-time block code and gives a maximum likelihood decoding algorithm which is based only on linear processing at the receiver. We review the encoding and decoding algorithms for various codes and provide simulation results demonstrating their performance. It is shown that using multiple transmit antennas and space-time block coding provides remarkable performance at the expense of almost no extra processing.

An empirically based path loss model for wireless channels in suburban environments

Abstract: We present a statistical path loss model derived from 1.9 GHz experimental data collected across the United States in 95 existing macrocells. The model is for suburban areas, and it distinguishes between different terrain categories. Moreover, it applies to distances and base antenna heights not well-covered by existing models. The characterization used is a linear curve fitting the decibel path loss to the decibel-distance, with a Gaussian random variation about that curve due to shadow fading. The slope of the linear curve (corresponding to the path loss exponent, /spl gamma/) is shown to be a random variate from one macrocell to another, as is the standard deviation /spl sigma/ of the shadow fading. These two parameters are statistically modeled, with the dependencies on base antenna height and terrain category made explicit. The resulting path loss model applies to base antenna heights from 10 to 80 m, base-to-terminal distances from 0.1 to 8 km, and three distinct terrain categories.

Aperture-coupled patch antenna on UC-PBG substrate

Abstract: The recently developed uniplanar compact photonic bandgap (UC-PBG) substrate is successfully used to reduce surface-wave losses for an aperture-coupled fed patch antenna on a thick high dielectric-constant substrate. The surface-wave dispersion diagram of the UC-PBG substrate has been numerically computed for two different substrate thickness (25 and 50 mil) and found to have a complete stopband in the frequency range of 10.9-13.5 and 11.4-12.8 GHz, respectively. The thicker substrate is then used to enhance broadside gain of a patch antenna working in the stopband at 12 GHz. Computed results and measured data show that, due to effective surface-wave suppression, the antenna mounted on the UC-PBG substrate has over 3-dB higher gain in the broadside direction than the same antenna etched on a grounded dielectric slab with same thickness and dielectric constant. Cross-polarization level remains 13 dB down the co-polar component level for both E- and H-planes.

Intrabody navigation system for medical applications

Abstract: This invention is a system, a method for tracking the position, and orientation of a probe such as a catheter whose transverse inner dimension may be at most about 2 millimeters. Three planar antennas (26, 28, 30) that at least partly overlap are used to transmit electromagnetic radiation simultaneously, with the radiation transmitted by each antenna (26, 28, 30) having its own spectrum. In the case of single-frequency spectra, the antennas (26, 28, 30) are provided with mechanisms for decoupling them from each other. A receiver (10) inside the probe includes sensors (16a, 16b, 18a, 18b, 20a, 20b) of the three components of the transmitted field, with sensors (16a, 16b, 18a, 18b, 20a, 20b) for at least two of the three components being pairs of sensors (16a, 16b, 18a, 18b, 20a, 20b), such as coils, disposed symmetrically with respect to a common reference point.

Radio frequency identification tag having an article integrated antenna

Abstract: A radio frequency identification tag (14) utilizes an antenna (22) formed in association with, and thus integral to, an article, package, package container, label and/or identification badge (10). In a preferred embodiment, a radio frequency identification tag circuit chip assembly (12) is secured to the article (10) and is electrically coupled to the antenna (22) formed on the article (10). Printing a conductive pattern on the article using conductive ink forms a preferred antenna.

Object tracking system with non-contact object detection and identification

Abstract: An object tracking system is provided for tracking the removal of objects from a location and the replacement of the objects at the location. The system includes a radio frequency identification (RFID) tag attached to each of the objects to be tracked and each tag has an antenna. When activated, the RFID tag of an object transmits a unique code identifying the object. A storage unit is provided at the location and the storage unit has a plurality of receptacles configured to receive objects replaced at the location. Each receptacle has an associated antenna for activating the RFID tag of an object in the receptacle and receiving the radio frequency transmitted code of the object. The antennae of the system can be capacitive plates for conveying the radio frequency transmissions through capacitive coupling or inductive loops for conveying the transmissions through inductive coupling. A computer-based controller is coupled to the antenna of the receptacles for receiving transmitted codes and determining based thereon the absence or presence and location of objects within the storage unit.

Radio frequency identification tag apparatus and related method

Abstract: A radio frequency identification tag (100) includes a substrate member (110) having an inner surface and an outer surface. Disposed on the inner surface are first (112) and second (114) antenna elements. The antenna elements are electrically isolated from each other and coupled to two separate pads on an integrated circuit (116). Adhesive (118) is applied on the inner surface of the substrate, the antenna elements and the integrated circuit for securing the tag. The tag may employ an interposer (600) to attach integrated circuit (116) to the antenna elements (112, 114). The interposer (600) has a substrate (602) and first and second connecting pads (602, 604) electrically isolated from each other and electrically connected to the connecting pads on the integrated circuit (116). Interposer (600) reduces the amount of the precision required to successfully couple integrated circuit (116) to the antenna elements (112, 114).

Calibration and integrated beam control/conditioning system for phased-array antennas

Abstract: A near-field calibration arrangement for an antenna array determines the phase shifts or attenuation of the elemental control elements of the array. The calibration system includes a probe located in the near field, and a calibration tone generator. The tone generator is coupled to the probe in the case of calibration of a receive antenna, and to the signal port of the array in the case of calibration of a transmit antenna. A code generator generates sets of values, with each set being orthogonal to the others. The codes are applied to the control input port of the array antenna, so that the codes encode the tone passing through the antenna. The encoded tones are applied to a decoder and processor, which processes the signals to determine the phase shift or attenuation associated with each bit of the control signal. A transmit antenna attitude determination or pointing arrangement uses the calibration tone generator in conjunction with a plurality of remote sites.

A parameter study of stripline-fed Vivaldi notch-antenna arrays

Abstract: A parameter study of Vivaldi notch-antenna arrays demonstrates that the wide-band performance of these antennas can be improved systematically. Stripline-fed Vivaldi antennas are comprised of: (1) a stripline-to-slotline transition; (2) a stripline stub and a slotline cavity; and (3) a tapered slot. The impedances of the slotline cavity and the tapered slot radiator combine at the transition to yield an equivalent series impedance on the feedline. The stripline stub can be represented by a series reactance. The resistance and reactance of the antenna impedance yield insights into the effects of various design parameters. In particular, it is found that the minimum operating frequency can be lowered primarily by increasing the antenna resistance through a change of design parameters. However, beyond a limit for each design parameter, the in-band performance begins to deteriorate. Plots of antenna impedance versus frequency for several parameter variations have been obtained by using a full wave method of moments analysis of infinite arrays. These plots provide a means for designers to systematically improve array performance with bandwidths in excess of 6:1 having been achieved.

Optimum beamforming using transmit antenna arrays

Abstract: Transmit beamforming is a powerful means of increasing capacity in systems in which the transmitter is equipped with an antenna array, especially in systems in which receive beamforming is not available, as is typical in the base-to-mobile downlink in a cellular communication system. In this paper, the problem of transmit beamforming is formulated as one of minimizing the power radiated by the base station, subject to satisfying quality of service requirements at the mobiles. For a single cell system, a global minimum is shown to exist, and an iterative algorithm that converges to it is provided. The solution extends to accommodate receive beamforming at the mobiles. It also extends to provide a mechanism for space-time transmit filtering, which exploits the differences between the temporal as well as the spatial channels between the base station and different mobiles. Finally, a system with multiple source-destination pairs (e.g., in an ad hoc network) is considered. An iterative algorithm that outputs a convergent sequence of feasible points with monotonically decreasing costs is provided for this case.

Application for a radio frequency identification system

Abstract: Antenna shelf tape (310) is disclosed for use with items (1-26) having radio frequency identification elements or tags associated with items of interest.

Inductively coupled wireless system and method

Abstract: A short range inductively coupled wireless communication system employs analog frequency modulation of a high frequency carrier and magnetic coupling between a transmitting antenna and a receiving antenna. A transmitter coupled to the transmitting antenna modulates multiple high-fidelity analog audio signals and digital control messages onto separate high frequency (“HF”) carriers. The electric field portion of the transmitted electromagnetic field is substantially eliminated during transmission, while the magnetic field portion is substantially unaffected. The receiving antenna is coupled to a demodulator which reproduces the audio frequency signals and decodes control messages sent by the transmitter.

Adaptive antenna arrays for OFDM systems with cochannel interference

Abstract: Orthogonal frequency-division multiplexing (OFDM) is one of the promising techniques for future mobile wireless data systems. For OFDM systems with cochannel interference, adaptive antenna arrays can be used for interference suppression. This paper focuses on a key issue for adaptive antenna arrays, that is, parameter estimation for the minimum mean square error (MMSE) diversity combiner (DC). Using the instantaneous correlation estimation approach developed in the paper, an original parameter estimator for the MMSE-DC is derived. Based on the original estimator, we propose an enhanced parameter estimator. Extensive computer simulation demonstrates that the MMSE-DC using the proposed parameter estimators can effectively suppress both synchronous and asynchronous interference in OFDM systems for packet and continuous data transmission.

Eddy current error-reduced AC magnetic position measurement system

Abstract: A device is disclosed for measuring the position (location and orientation) in the six degrees of freedom of a receiving antenna with respect to a transmitting antenna utilizing multiple frequency AC magnetic signals. The transmitting component consists of two or more transmitting antenna of known location and orientation relative to one another. The transmitting antenna are driven simultaneously by an AC excitation, with each antenna occupying one or more unique positions in the frequency spectrum. The receiving antennas measure the transmitted AC magnetic field plus distortions caused by conductive metals. A computer then extracts the distortion component and removes it from the received signals providing the correct position and orientation output to a high degree of accuracy.

Radio frequency identification tag having a printed antenna and method

Abstract: A radio frequency identification tag (14) includes a radio frequency identification tag circuit chip (12) coupled to an antenna (10) including a conductive pattern (22) printed onto a substrate (16). The substrate may form a portion of an article, a package, a package container, a ticket, a waybill, a label and/or an identification badge. The conductive pattern includes a first coupling region (28) and a second coupling region (30) arranged for coupling to the radio frequency identification tag circuit chip. The first coupling region and the second coupling region are precisely located and isolated from one another via an aperture (31) formed in the substrate.

Dual mode tracking 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. Data are archived in a data warehouse, such as an SQL Server. Also disclosed is an article tracking system that supports both active and passive tags with a cell controller able to read both passive and active tag signals.

Multi-signal transmit array with low intermodulation

Abstract: A transmitter is provided for simultaneously transmitting a plurality of signals in a plurality of directive beams to corresponding destination stations, each destination station located in a separate fan within a service area. The transmitter includes a plurality of beamformers, each beamformer receiving one of the signals to be transmitted to an associated fan, each of the beamformers having a plurality of outputs for each different signal to be transmitted. A plurality of Butler matrices each receive one of the plurality of outputs from the plurality of beamformers for each different signal to be transmitted, each Butler matrix having a plurality of outputs in phased relationship to one another, wherein each of the signals to be transmitted is simultaneously provided across the outputs of each Butler matrix in a phased relationship. An antenna is provided with an aperture within which a two-dimensional array of antenna elements are disposed, wherein equal fractions of adjacent antenna elements are connected to the outputs of each Butler matrix, and wherein each of the plurality of signals are simultaneously transmitted by the entire two-dimensional array of antenna elements. Each of the plurality of beamformers receives steering control signals for steering the direction of each beam within its respective fan.

Phased array antenna calibration system and method

Abstract: Apparatus and method for self-contained calibration and failure detection in a phased array antenna having a beamforming network. The beamforming network includes a plurality of array ports and a plurality of beam ports or a space fed system. A plurality of antenna elements and a plurality of transmit/receive modules are included. Each one of the modules is coupled between a corresponding one of the antenna elements and a corresponding one of the array ports. A calibration system is provided having: an RF input port; an RF detector port; an RF detector coupled to the RF detector port; and an antenna element port. A switch section is included for sequentially coupling each one of the antenna elements through the beam forming/space-fed network and the one of the transmit/receive modules coupled thereto selectively to either: (a) the detector port during a receive calibration mode; or, (b) to the RF input port during a transmit calibration mode. The switch section includes a switch for selectively coupling a predetermined one of the antenna elements, i.e., a calibration antenna element, selectively to either: (a) the RF test input of the calibration system during the receive calibration mode through a path isolated from the beamforming network; or, (b) to the detector port during the transmit calibration mode through a path isolated from the beamforming network. In one embodiment, the calibration antenna element is disposed in a peripheral region of the array of antenna elements. In another embodiment, the array of antenna elements is arranged in clusters, each one of the clusters having a calibration antenna element.

GPS Antenna Calibration at the National Geodetic Survey

Abstract: The precise point whose position is being measured when a GPS baseline is determined is generally assumed to be the phase center of the GPS antenna. However, the phase center of a GPS antenna is neither a physical point nor a stable point. For any given GPS antenna, the phase center will change with the changing direction of the signal from a satellite. Ideally, most of this phase center variation depends on satellite elevation. Azimuthal effects are only introduced by the local environment around each individual antenna site. These phase center variations affect the antenna offsets that are needed to connect GPS measurements to physical monuments. Ignoring these phase center variations can lead to serious (up to 10 cm) vertical errors. This article will describe the procedure by which the National Geodetic Survey is calibrating GPS antennas and how this information may be obtained and used to avoid problems from these antenna variations. © 1999 John Wiley & Sons, Inc.

Near-field to near/far-field transformation for arbitrary near-field geometry utilizing an equivalent electric current and MoM

Abstract: Presented here is a method for computing near- and far-field patterns of an antenna from its near-field measurements taken over an arbitrarily shaped geometry. This method utilizes near-field data to determine an equivalent electric current source over a fictitious surface which encompasses the antenna. This electric current, once determined, can be used to ascertain the near and the far field. This method demonstrates the concept of analytic continuity, i.e., once the value of the electric field is known for one region in space, from a theoretical perspective, its value for any other region can be extrapolated. It is shown that the equivalent electric current produces the correct fields in the regions in front of the antenna regardless of the geometry over which the near-field measurements are made. In this approach, the measured data need not satisfy the Nyquist sampling criteria. An electric field integral equation is developed to relate the near field to the equivalent electric current. A moment method procedure is employed to solve the integral equation by transforming it into a matrix equation. A least-squares solution via singular value decomposition is used to solve the matrix equation. Computations with both synthetic and experimental data, where the near field of several antenna configurations are measured over various geometrical surfaces, illustrate the accuracy of this method.

Switched parasitic elements for antenna diversity

Abstract: Switched parasitic elements provide a useful implementation of antenna pattern diversity. The basic principle is presented with some examples of wire antennas computed using the method of moments. The modeled diversity gain available from selection combining of uncorrelated signals is used to quantify the expected improvement relative to nondiversity antennas. The advantage of the switched parasitic concept is that it is a relatively simple system, which can give the adaptive antenna performance of many branch selection or switched diversity.

Genetic algorithms and method of moments (GA/MOM) for the design of integrated antennas

Abstract: This paper introduces a novel technique for efficiently combining genetic algorithms (GAs) with method of moments (MoM) for integrated antenna design and explores a two example applications of the GA/MoM approach. Integral to efficient GA/MoM integration is the use of direct Z-matrix manipulation (DMM). In DMM a "mother" structure is selected and its corresponding impedance or Z-matrix is filled only once prior to beginning the GA optimization process. The GA optimizer then optimizes the design by creating substructures of the mother structure as represented by the corresponding subsets of the original mother Z-matrix. Application of DMM with GA/MoM significantly reduces the total optimization time by eliminating multiple Z-matrix fill operations. DMM also facilitates the use of matrix partitioning and presolving to further reduce the optimization time in many practical cases. The design of a broad-band patch antenna with greater than 20% bandwidth and a dual-band patch antenna are presented as examples of the utility of GA/MoM with DMM. Measured results for the dual-band antenna are compared to numerical results. Excellent agreement between numerical and measured results is observed.

Antenna problems in RFID systems

Abstract: As the frequency of choice for RFID devices rises into the microwave region, the problem of designing antennas to match the devices on the protected object becomes more acute. The objective of any such antenna must be to maximise the transfer of power into and out of the device on the protected object. This requires careful design to match the antenna to free space and to the following ASIC. The frequency bands considered in this paper are 435 MHz, 2.45 GHz and 5.8 GHz and the usage is for retail goods only. The major considerations in choosing an antenna are: the type of antenna; its impedance; RF performance when applied to the object; and RF performance when the object has other structures around it. Antennas which are omnidirectional should be avoided and, wherever possible, directional antennas should be used because they have the advantage of less disturbance to the radiation pattern and to the return loss. (5 pages)

Radio frequency identification transponder having a high gain antenna configuration

Abstract: A radio frequency identification transponder has a high gain antenna for increased range. In an embodiment, the radio frequency transponder has a reflector to increase its operative range. A system of one or more reflectors is operatively associated with a transponder and may be formed out of any sort of radio frequency reflective material. The reflector system can enhance reception or transmission of radio waves by or from the transponder. The reflector system may also be used to provide for selective coupling of the radio frequency transponder with a base station, user- or vehicle-supported reader, or the like based on relative orientation. In addition, the reflector system may be used to selectively reflect particular radio waves. In another embodiment, the radio frequency transponder has a horn antenna providing increased gain and directivity. In yet another embodiment, the radio frequency transponder has a patch antenna providing increased gain and circular polarization. The patch antenna may further comprise a patch antenna array, a multi-layer patch or a dipole comprised of patch elements.

Beam scanning antennas with plurality of antenna elements for scanning beam direction

Abstract: An array antenna is formed of a plurality of antenna elements, each of which scans a beam in the direction of an angle θ to a boresight of the antenna and electrically varies the direction of a rotation angle φ of the beam. The antenna elements are disposed so that the optical path difference of radio waves transmitted or received by two adjacent antenna elements in the directions of a plurality of direction angles φ on the plane tilted for an angle θ to the boresight of the antenna is nearly a multiple of the wave length of the radio waves.

Dual-window high-power conical horn antenna

Abstract: A high power TM 01 mode radio frequency antenna. The inventive antenna comprises a conical horn for receiving an electromagnetic input signal and radiating an output signal in response thereto. An inner window is disposed within the conical horn. An outer window is mounted at an output aperture of the conical horn in alignment with the inner window. The antenna has a gradual taper from a waveguide input to the aperture over a cone angle of 45 degrees. The outer window is mounted at the aperture in concentric alignment with the inner window. For an optimal compact design, the inner and outer windows are of polycarbonate construction.

Signal coupling methods and arrangements

Abstract: Signal coupling arrangements are described in which the effect of unwanted signals transferred between two antennas is compensated for. In one arrangement a microstrip edge coupler is used as a compensation network to provide a cross-coupling path for the transfer of a compensating signal between two antenna signal paths. In another arrangement, an antenna assembly includes cross-slots which, in association with a conductive ring, provide two mutually orthogonally polarised radiation signals and connections to the conductive ring have closely spaced portions which provide compensation for and minimise the effect of unwanted mutual coupling.

Harmonic control by photonic bandgap on microstrip patch antenna

Abstract: In this work, the single microstrip patch antenna having two-dimensional photonic bandgap (PBG) in the ground has been demonstrated experimentally, and the effectiveness of the PBG structure is discussed for the suppression of the resonance at the harmonic frequencies of the antenna. Experimental results indicate that the radiation patterns at the harmonic frequencies can be drastically diminished comparing with the normal microstrip patch antenna without the PBG structure. For instance, the radiation to the forward of the PBG antenna is suppressed at more than 15 dB at the third harmonic frequency.

Antenna for mobile radiocommunications equipment

Abstract: A new category of antennas for mobile communications devices specifically designed for reducing the emitted power dissipated within biological tissues of the user of the device. The antenna, operating in a single or a multiple band of frequencies, is constituted by an array of radiating elements fed with relative powers and phases specifically chosen to yield, through superposition effects, a small electric field in a region close to the antenna and normally occupied by biological tissues of the user of the device and thus reducing the SAR within said region.

Card for interaction with a computer

Abstract: A smart card (40) comprising: a memory (46) for storing information; at least one transmitting or receiving antenna (42); and a low frequency circuit (44), for handling information associated with said antenna and said memory, which information is modulated at a frequency of between 5 kHz and 100 kHz. Preferably the antenna is an acoustic antenna.