Showing papers on "Antenna (radio) published in 1998"

Smart antennas for wireless systems

Abstract: In this article we discuss current and future antenna technology for wireless systems and the improvement that smart and adaptive antenna arrays can provide. We describe standard cellular antennas, smart antennas using fixed beams, and adaptive antennas for base stations, as well as antenna technologies for handsets. We show the potential improvement that these antennas can provide, including range extension, multipath diversity, interference suppression, capacity increase, and data rate increase. The issues involved in incorporating these antennas into wireless systems using CDMA, GSM, and IS-136 in different environments, such as rural, suburban, and urban areas, as well as indoors, are described. Theoretical, computer simulation, experimental, and field trial results are also discussed that demonstrate the potential of this technology.

Joint optimal power control and beamforming in wireless networks using antenna arrays

Abstract: The interference reduction capability of antenna arrays and the power control algorithms have been considered separately as means to increase the capacity in wireless communication networks. The minimum variance distortionless response beamformer maximizes the signal-to-interference-and-noise ratio (SINR) when it is employed in the receiver of a wireless link. In a system with omnidirectional antennas, power control algorithms are used to maximize the SINR as well. We consider a system with beamforming capabilities in the receiver, and power control. An iterative algorithm is proposed to jointly update the transmission powers and the beamformer weights so that it converges to the jointly optimal beamforming and transmission power vector. The algorithm is distributed and uses only local interference measurements. In an uplink transmission scenario, it is shown how base assignment can be incorporated in addition to beamforming and power control, such that a globally optimum solution is obtained. The network capacity and the saving in mobile power are evaluated through numerical study.

Fading correlation and its effect on the capacity of multi-element antenna systems

Abstract: We investigate the effect of fading correlations in multi-element antenna (MEA) communication systems. The enormous capacity of an MEA system can potentially be reduced by fading correlation. To model the narrowband Rayleigh-fading multipath environment, we propose an abstract model. Using this model, the fading statistics can be determined from the geometrical parameters of the MEA and the multipath environment. This, model allows us to directly observe how the choice of antenna geometry affects capacity. We show that the MEA capacity can be expressed as the sum of the capacities of several subchannels, whose gains are affected by the fading correlation. As the fading correlation becomes higher, the disparity between the gains of these subchannels becomes larger and as a result some of the subchannels do not convey information at any significant rate.

Design and experiments of a high-conversion-efficiency 5.8-GHz rectenna

Abstract: A high-efficiency rectenna element has been designed and tested at 5.8 GHz for applications involving microwave-power transmission. The dipole antenna and filtering circuitry are printed on a thin duroid substrate. A silicon Schottky-barrier mixer diode with a low breakdown voltage is used as the rectifying device. The rectenna element is tested inside a waveguide simulator and achieves an RF-to-DC conversion efficiency of 82% at an input power level of 50 mW and 327 /spl Omega/ load. Closed-form equations are given for the diode efficiency and input impedance as a function of input RF power. Measured and calculated efficiency results are in good agreement. The antenna and circuit design are based on a full-wave electromagnetic simulator. Second harmonic power levels are 21 dB down from the fundamental input power.

Broadband microstrip patch antenna

Abstract: The characteristics of a rectangular microstrip antenna with an L-shaped probe are investigated. A foam layer with a thickness of around 10% of the wavelength is used as the supporting substrate. An impedance bandwidth of 35% and an average gain of 7.5 dBi can be achieved. The radiation pattern is stable across the passband.

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 dB path loss to the dB-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 meters; base-to-terminal distances from 0.1 to 8 km; and three distinct terrain categories.

System and method of integrating and concealing antennas, antenna subsystems and communications subsystems

Abstract: A system and method of deploying a plurality of aesthetically unobtrusive radio frequency (RF) antenna systems or complying with zoning ordinances and other restrictive covenants, and for providing an array configuration which is intelligently controlled to overcome many of the limitations of conventional RF antenna systems. Antennas and communications systems components including filter-preamplifier, frequency-converter, and beam-selection/manipulation subsystems are concealed by packaging and integrating them within common pole-like objects and panel-like structures. The pole-like objects include utility poles, street lamps, flagpoles, signs, church steeples, columns, railings, and roof balconies. Panel-like structures include advertising billboards and road signs, and building panels. The concealed antennas and related components are then integrated into larger scale antenna subsystems. The antenna subsystems are connected to an intelligent controller to provide enhanced performance, functionality, and service in communications systems.

Telemetry for implantable devices using the body as an antenna

Abstract: A telemetry system and method includes an implantable medical device implanted in a body and an external communication device, e.g., a programmer. The implanted device includes a housing having transmitter/receiver circuitry positioned therein. The external communication device includes transmitter/receiver circuitry connected to an antenna thereof. The transmitter/receiver circuitry of the implanted device is electrically coupled to the body such that the body functions as an antenna for the implanted device to facilitate communication of data between the implanted device and the external communication device.

The diversity gain of transmit diversity in wireless systems with Rayleigh fading

Abstract: In this paper, we study the ability of transmit diversity to provide diversity benefit to a receiver in a Rayleigh fading environment. With transmit diversity, multiple antennas transmit delayed versions of a signal to create frequency-selective fading at a single antenna at the receiver, which uses equalization to obtain diversity gain against fading. We use Monte Carlo simulation to study transmit diversity for the case of independent Rayleigh fading from each transmit antenna to the receive antenna and maximum likelihood sequence estimation for equalization at the receiver. Our results show that transmit diversity with M transmit antennas provides a diversity gain within 0.1 dB of that with M receive antennas for any number of antennas. Thus, we can obtain the same diversity benefit at the remotes and base stations using multiple base-station antennas only.

Design and performance of small printed antennas

Abstract: Electrically small microstrip patches incorporating shorting posts are thoroughly investigated. These antennas are suitable for mobile communications handsets where limited antenna size is a premium. Techniques to enhance the bandwidth of these antennas are presented and performance trends are established. From these trends, valuable insight to the optimum design, namely broad bandwidth, small size, and ease of manufacturing, is given.

Bipolar electrostatic structures in the shock transition region: Evidence of electron phase space holes

Abstract: We present observations of intense, bipolar, electrostatic structures in the transition region of the terrestrial bow shock from the Wind spacecraft. The electric field signatures are on the order of a tenth of a millisecond in duration and greater than 100 mV/m in amplitude. The measured electric field is generally larger on the smaller dipole antenna, indicating a small spatial size. We compare the potential on the two dipole antennas with a model of antenna response to a Gaussian potential profile. This result agrees with a spatial scale determined by convection and gives a characteristic scale size of 2–7 λd. We interpret the observations as small scale convecting unipolar potential structures, consistent with simulations of electron phase space holes and discuss the results in the context of electron thermalization at strong collisionless shocks.

Small but long Koch fractal monopole

Abstract: A small but long wire fractal antenna based on the Koch curve is presented. Experimental and numerical results show that the antenna improves the features of a common linear monopole. The radiation resistance is increased and the Q is reduced at each fractal iteration, approaching the fundamental limit on small antennas.

Experimental study of large rectenna array for microwave energy transmission

Abstract: For a field experiment on microwave power transmission (MPT) which was jointly conducted by the Radio Atmospheric Science Center of Kyoto University, Robe University, and Kansai Electric Power Company from 1994 to 1995, we had developed and tested a new type of rectenna (rectifying antenna) based on a circular microstrip antenna (CMA). A square shape of array with an area of 3.2 m/spl times/3.6 m was then constructed using the developed rectennas for experiment. The whole rectenna array is composed of 256 sub-arrays, each with nine rectenna elements. We place the rectenna sub-array with better RF-DC conversion efficiency in the central area of the whole rectenna array. Such spatial optimization is needed because the power density of the microwave beam used in the experiment has a spatial gradient with a peak at the center of the beam. We then examined dependence of the rectenna array characteristics on the electrical connection of the sub-arrays. The difference of the output DC power of the whole array for five different electrical connections is within 5%. The load characteristics, therefore, suffers little change even if the electrical connection of the rectenna sub-array is changed.

Spatial channel characteristics in outdoor environments and their impact on BS antenna system performance

Abstract: This paper present measurement results obtained with a testbed equipped with an array antenna. The investigations focus on the power azimuth spectrum of the channel in urban and rural areas, for various base station antenna heights. The power azimuth spectrum is well modeled with a Laplacian function. The local azimuth spread is found to range from 1/spl deg/ to 25/spl deg/ depending on the environment and antenna height. The azimuth spread significantly increases as the antenna height is reduced. An analytical expression for the spatial correlation function is derived based on the Laplacian model. Finally, the power azimuth spectrums impact on a conventional beamformer ability to suppress interfering users is investigated.

Spatial and temporal communication theory using adaptive antenna array

Abstract: An adaptive antenna array or a smart antenna is named a software antenna because it can form a desired antenna pattern and adaptively control it if an appropriate set of antenna weights is provided and updated in software. It can be a typical tool for realizing a software radio. An adaptive antenna array can be considered an adaptive filter in the space and time domains for radio communications, so communication theory can be generalized from a conventional time domain into both space and time domains. This article introduces a spatial and temporal communication theory based on an adaptive antenna array, such as spatial and temporal channel modeling, equalization, optimum detection for single-user and multi-user CDMA, precoding in a transmitter, and joint optimization of both transmitter and receiver. Such spatial and temporal processing promises significant improvement of performance against multipath fading in mobile radio communications.

Injection- and phase-locking techniques for beam control [antenna arrays]

Abstract: Applications of millimeter-wave radar, imaging, and communication technology requires cost-effective implementation of intelligent scanning antenna systems Injection-locking and phase-locked-loop (PLL) techniques can be used to achieve synchronous operation of a number of antenna array elements, and allow for the manipulation of the phase distribution without additional phase-shifting circuitry, suggesting a potential for low-cost beam-scanning systems This paper describes a number of techniques, with an assessment of some remaining technical challenges for practical implementation

Predictive collision sensing system

Abstract: A relatively narrow beam of either RF or optical electromagnetic radiation is scanned over a relatively wide azimuthal range. The return signal is processed to detect the range and velocity of each point of reflection. Individual targets are identified by clustering analysis (102) and are tracked (106) in a Cartesian coordinate system using a Kalman filter. The threat to the vehicle for a given target is assessed (116) from estimates of the relative distance, velocity, and size of each target, and one or more vehicular devices are controlled (120) responsive to the assessment of threat so as to enhance the safety of the vehicle occupant. In a preferred embodiment, a quantized linear frequency modulated continuous wave RF signal is transmitted from and received by a multi-beam antenna having an azimuthal range of at least +/- 100 degrees and an individual beam width of approximately 10 degrees.

Performance monitor for antenna arrays

Abstract: An antenna monitor collects statistics about the received signal strengths of each antenna in a cooperating antenna array over long periods of time. In cellular telephone base station applications for a base station using an array of antenna elements to obtain spatial diversity, samples of the received signal strength are taken during particular times whenever an active mobile subscriber is operating in the area. Periodically, such samples are averaged and added to a running total that is maintained in a long-term accumulator for each antenna. The accumulated totals are then compared after a statistically sufficient number of samples have been collected and averaged. Faulty antennas, including broken ones and ones with bad connections, will be revealed by those corresponding signal paths having relatively low accumulated totals. Given long enough collection periods, the spatial diversity of the antennas in the array will have only a minimal impact on favoring one antenna over another.

Quasi-optical transceiver having an antenna with time varying voltage

Abstract: A transceiver for transmitting and receiving high frequency radiation is described. The transceiver includes a first light source that generates radiation at a first frequency and a second light source that generates radiation at a second frequency. The first and the second light source have a difference frequency that is approximately equal to the difference between the first and the second frequencies. The transceiver also includes a transmitter that comprises a first photomixer that is optically coupled to the first and the second light source. A first antenna that radiates a signal at the difference frequency is electrically coupled to the first photomixer. The transceiver also includes a receiver that comprises a second antenna positioned to receive the signal radiated by the first antenna. The second antenna generates a time varying voltage in response to the signal. A second photomixer is electrically coupled to the second antenna and optically coupled to the first and the second light source. The second photomixer generates a current signal in response to the time varying voltage generated by the second antenna.

Phase array calibration by orthogonal phase sequence

Abstract: Methods and systems for calibrating an array antenna are described. The array antenna has a plurality of antenna elements each having a signal with a phase and an amplitude forming an array antenna signal. For calibration, the phase of each element signal is sequentially switched one at a time through four orthogonal phase states. At each orthogonal phase state, the power of the array antenna signal is measured. A phase and an amplitude error for each of the element signals is determined based on the power of the array antenna signal at each of the four orthogonal phase states. The phase and amplitude of each of the element signals is then adjusted by the corresponding phase and amplitude errors.

SAR distribution and temperature increase in an anatomical model of the human eye exposed to the field radiated by the user antenna in a wireless LAN

Abstract: Wireless personal communication is a rapidly expanding sector, particularly in the field of cellular mobile phones and wireless local area networks (WLAN's). In an indoor WLAN system, the user of the mobile terminal can find himself in close proximity to the radiating antenna. It is, therefore, important to consider possible health hazards due to this type of exposure. As the most considered adverse effects of the electromagnetic (EM) fields are of thermal nature, particularly with reference to the eye, in this paper, the authors have evaluated the temperature increase induced in a human eye exposed to WLAN-like fields. In particular, they have considered possible WLAN's operating in the range between 6-30 GHz, so that the incident field can be simulated via a plane wave. As a first step, the authors have computed the specific absorption rate (SAR) distribution in a human-eye anatomical model, developed from the "visible human" data set, by using the finite-difference time-domain (FDTD) numerical technique with a cell resolution of 0.5 mm. Starting from the calculated SAR values, the heating distribution has been derived through the bioheat equation, which has been solved using an explicit finite-difference scheme. Temperature increases of the order of 0.04/spl deg/C have been calculated in the eye lens with an incident power density of 1 mW/cm/sup 2/ at 6 GHz. Lower heating is obtained in the lens when the frequency increases. Finally, considerations about the exposure limits in the considered frequency range are made.

Multi-directional RFID antenna

Abstract: A multi-directional RFID read/write antenna unit is described which provides multi-directional RF communication to a source, such as a RF tag. The antenna comprises a plurality of coils adapted to transmit multi-directional RF signals to a RF tag and receive RF response signals from the RF tag. The RF antenna includes a switch for selecting at least one of the RF antenna coils for transmission of the RF signals and receipt of the RF response signals whereby the RF signals can be directed toward and received from a plurality of different directions from a fixed position.

An improved small antenna radiation-efficiency measurement method

Abstract: An examination of the available literature shows that the accurate measurement of antenna efficiency is a difficult task, and that the available methods have potential for a substantial amount of error. This paper refines a method already presented, and gives detailed results with some newly defined reference antennas. Two methods of determining antenna efficiency are presented. One method may be considered to be a generalization of the "Wheeler cap method." The two methods presented show excellent agreement with each other, and show excellent agreement with the reference antennas. The reflection method appears to give the better results of the two methods, except under special circumstances.

Coherent terahertz radiation detection: Direct comparison between free-space electro-optic sampling and antenna detection

Abstract: We compare the use of free-space electro-optic sampling (FSEOS) with photoconducting antennas to detect terahertz (THz) radiation in the range of 0.1–3 THz. For the same average THz power and low-frequency modulation, signal-to-noise ratio and sensitivity are better with antenna detection at frequencies smaller than 3 THz. When the modulation frequency is increased to more than 1 MHz in FSEOS, both detection schemes have comparable performance. Using a singular-electric-field THz emitter, we demonstrate the feasibility of a THz imaging system using real-time delay scanning in FSEOS and only 20 mW of laser power.

Satellite distributed television

Abstract: A television signal distribution system, comprising an antenna for receiving a composite microwave satellite signal having a plurality of television channel signals combined with a modulation and/or encoding format; and a network for distributing the composite satellite signal received by the antenna to each of a plurality of television receivers, such composite satellite signal being distributed as an optical frequency signal having the plurality of television signal channels combined with said modulation and/or encoding format prior to being fed to the television receivers.

Printed multi-band patch antenna

Abstract: The present invention provides a miniature, built-in multi-band antenna which is suitable for use in future compact mobile terminals. According to exemplary embodiments, a built-in patch antenna is provided which includes patch elements of different sizes and capable of being tuned to different frequency bands. On each patch element is formed a slot which divides the patch element into sub-parts. Each sub-part of a patch element is structured so as to be resonant at a frequency in the same frequency band to which the patch element is tuned. As a result, a high efficiency, broad band, multi-band, and surface mountable low profile antenna can be realized.

Array antenna system of wireless base station

Abstract: An array antenna system of a wireless base station in CDMA mobile communications combines signals, which have been received by a plurality of antenna elements of an array antenna, upon subjecting the signals to amplitude and phase-rotation control, and despreads the combined signal. A searcher has matched filters which apply correlation operations to output signals from respective antenna elements to thereby calculate correlation signals that are correlated with a signal transmitted from a mobile station of interest. An adaptive weight calculating unit calculates adaptive weights for obtaining in-phase correlation signals from the respective antenna outputs. A beam former multiplies, by the adaptive weights, output signals from the corresponding antenna elements and combines the resulting products to output a combined signal. The combined signal is found for each path of multipaths and is input to a Rake receiver, which proceeds to identify data.

Novel architectures for high-efficiency amplifiers for wireless applications

Abstract: This paper presents three novel architectures for high-efficiency amplifiers relying on new harmonic-tuning techniques. These methods yield high-efficiency power amplifiers and reduce unwanted harmonic radiation from the transmitter front end. The first method uses the active integrated-antenna approach to perform harmonic tuning. The second method uses a nontraditional periodic microstrip filter, which allows broadband harmonic tuning. Finally, the third method combines the previous two approaches. Each technique is illustrated by a design example of a power amplifier integrated with an antenna. Guidelines for choosing the appropriate antenna structure and for designing the periodic structures are also presented. Another design issue is inclusion of the antenna and/or periodic structures into the amplifier simulation. To do this, a hybrid approach combining the finite-difference time-domain (FDTD) analysis and harmonic-balance simulation is employed.

Stand-alone device for transmitting a wireless signal containing data from a memory or a sensor

Abstract: A stand-alone device includes an integrated circuit (IC) die (optionally free of conventional IC packaging and bond pads) that responds to a signal by (1) storing energy retrieved from the signal, and (2) using the stored energy to generate another signal that is encoded with information provided by a data source (such as a memory or a sensor depending on the implementation) that is included in the device. The IC die includes a power supply, a signal transmitter, and optionally includes an antenna. During operation of one embodiment, the power supply receives from the antenna electrical energy extracted from a portion of a radio frequency signal incident on the IC die. The power supply stores the energy in an energy store over a period of time, and thereafter supplies at least a portion of the stored energy to the signal transmitter. The signal transmitter uses the energy to generate an electrical signal carrying the information from the data source, and on receipt of the electrical signal the antenna transmits another radio frequency signal containing the information. All parts of the IC die are coupled to each other by electrical conductors formed within the IC die. The device is used as a stand-alone component, i.e. free of connections to other electronic components. In one such case the IC die includes the antenna, and all interactions with the device are performed by wireless signals.