Showing papers on "Antenna (radio) published in 1994"

The impact of antenna diversity on the capacity of wireless communication systems

Abstract: For a broad class of interference-dominated wireless systems including mobile, personal communications, and wireless PBX/LAN networks, the authors show that a significant increase in system capacity can be achieved by the use of spatial diversity (multiple antennas), and optimum combining. This is explained by the following observation: for independent flat-Rayleigh fading wireless systems with N mutually interfering users, they demonstrate that with K+N antennas, N-1 interferers can be nulled out and K+1 path diversity improvement can be achieved by each of the N users. Monte Carlo evaluations show that these results also hold with frequency-selective fading when optimum equalization is used at the receiver. Thus an N-fold increase in user capacity can be achieved, allowing for modular growth and improved performance by increasing the number of antennas. The interferers can also be users in other cells, users in other radio systems, or even other types of radiating devices, and thus interference cancellation also allows radio systems to operate in high interference environments. As an example of the potential system gain, the authors show that with 2 or 3 antennas the capacity of the mobile radio system IS-54 can be doubled, and with 5 antennas a 7-fold capacity increase (frequency reuse in every cell) can be achieved. >

Synthetic aperture radar

Abstract: PURPOSE: To enhance the resolution without sacrificing the image quality by additionally providing a plurality of sub-apertures, hybrid synthetic units and phase shifters and providing two systems of transmitter, receiver and A/D converter. CONSTITUTION: An antenna is divided into four sub-apertures 1-4, each of which is provided with a different phase thus producing two transmission/receiving beams. In other words, four sets of hybrid synthetic units 5, 6, 9, 10 are combined with a 90° phase shifter 78 to produce two beams. At the time of transmission, power is fed from transmitters 13, 15 through circulators 11, 12 to the sub-apertures 1-4. At the time of receiving, analog output signals from receivers 14, 16 are converted through A/D converters 17, 18 into digital data which are then subjected through a signal processing circuit 19 to range compression and frequency synthesis before being imaged through synthetic aperture processing. In other words, two beams are employed in the observation in order to widen the observation band or enhance the resolution per one look thus obtaining a high resolution image. COPYRIGHT: (C)1996,JPO

Effect of fading correlation on adaptive arrays in digital mobile radio

Abstract: In this paper, we investigate the effect of correlations among the fading signals at the antenna elements of an adaptive array in a digital wireless communication system. With an adaptive array, the signals received by multiple antennas are optimally weighted and combined to suppress interference and combat desired signal fading. Previous results for flat and frequency-selective fading assumed independent fading at each antenna. Here, we present a model of local scattering around a mobile where the received multipath signals arrive at the base station within a given beamwidth, and derive a closed-form expression for the correlation as a function of antenna spacing. Results show that the degradation in performance with correlation in an adaptive array that combats fading and suppresses interference is only slightly larger than that for combating fading alone, i.e., with maximal ratio combining. This degradation is small even with correlation as high as 0.5. >

Two signaling schemes for improving the error performance of frequency division duplex (FDD) transmission systems using transmitter antenna diversity

Abstract: We propose two signaling schemes that exploit the availability of multiple (N) antennas at the transmitter to provide diversity benefit to the receiver. This is typical of cellular radio systems where a mobile is equipped with only one antenna while the base station is equipped with multiple antennas. We further assume that the mobile-to-base and base-to-mobile channel variations are statistically independent and that the base station has no knowledge of the base-to-mobile channel characteristics. In the first scheme, a channel code of lengthN and minimum Hamming distanced min≤N is used to encode a group ofK information bits. Channel code symbolc i is transmitted with thei th antenna. At the receiver, a maximum likelihood decoder for the channel code provides a diversity ofd min as long as each transmitted code symbol is subjected to independent fading. This can be achieved by spacing the transmit antennas several wavelengths apart. The second scheme introduces deliberate resolvable multipath distortion by transmitting the data-bearing signal with antenna 1, andN−1 delayed versions of it with antennas 2 throughN. The delays are unique to each antenna and are chosen to be multiples of the symbol interval. At the receiver, a maximum likelihood sequence estimator resolves the multipath in an optimal manner to realize a diversity benefit ofN. Both schemes can suppress co-channel interference. We provide code constructions and simulation results for scheme 1 to demonstrate its merit. We derive the receiver structure and provide a bound on the error probability for scheme 2 which we show to be tight, by means of simulations, for the nontrivial and perhaps the most interesting caseN=2 antennas. The second scheme is backward-compatible with two of the proposed digital cellular system standards, viz., GSM for Europe and IS-54 for North America.

Cellular communications system with centralized base stations and distributed antenna units

Abstract: A microcellular communications network includes a plurality of base station units and corresponding antenna units. The base station units are housed in a common location. Each includes either conventional transmitters and receivers or all digital transmitter and receiver equipment, and interface circuitry to a mobile telecommunications switching office. The microcell traffic output is applied to a frame generator/multiplexer. The output of the frame generator/multiplexer is applied to a digitally modulated laser. The laser output is conveyed by fiber to a remote antenna unit, which demultiplexes the microcell traffic signal and applies it to a digital-to-analog converter. The output of the digital-to-analog converter is applied to a power amplifier, which in turn is connected to a main antenna. RF signals from the mobile units are received at both a main and a diversity antenna. The received signals are filtered, digitized, multiplexed together and transmitted over the optical fiber back to the base station. The strongest signal is selected for use.

Dual distributed antenna system

Abstract: A distributed antenna system (30, 35) is utilized in a communication system for providing multipath signals which facilitate signal diversity for enhanced system performance. Each node (200) of the antenna system (30, 35) comprises more than one antenna (196). Each antenna (196) at a common node (200) provides a path having a different delay to the base station (100).

Baseband-pulse-antenna techniques

Abstract: Frequency-domain concepts and terminology are commonly used to describe antennas. These are very satisfactory for a CW or narrowband application. However, their validity is questionable for an instantaneous wideband excitation. Time-domain and/or wideband analyses can provide more insight and more effective terminology. Two approaches for this time-domain analysis have been described. The more complete one uses the transfer function, a function which describes the amplitude and phase of the response over the entire frequency spectrum. While this is useful for evaluating the overall response of a system, it may not be practical when trying to characterize an antenna's performance, and trying to compare it with that of other antennas. A more convenient and descriptive approach uses time-domain parameters, such as efficiency, energy pattern, receiving area, etc., with the constraint that the reference or excitation signal is known. The utility of both approaches, for describing the time-domain performance, was demonstrated for antennas which are both small and large, in comparison to the length of the reference signal. The approaches have also been used for other antennas, such as arrays, where they also could be applied to measure the effects of mutual impedance, for a wide-bandwidth signal. The time-domain ground-plane antenna range, on which these measurements were made, is suitable for symmetric antennas. However, the approach can be readily adapted to asymmetric antennas, without a ground plane, by using suitable reference antennas. >

Performance analysis of antennas for hand-held transceivers using FDTD

Abstract: The design of antennas for hand-held communications devices depends on the implementation of simulation tools that can accurately model general topologies. The paper presents the analysis of small antennas mounted on hand-held transceivers using the finite-difference time-domain (FDTD) method. The key features of the FDTD implementation are discussed, with particular emphasis placed upon modeling of the source region. The technique is used to predict the gain patterns and broadband input impedance behavior of monopole, planar inverted F, and loop antenna elements mounted on the handset. Effects of the conducting handset chassis, the plastic casing around the device, and lumped elements integrated into the antenna design are illustrated. Experimental results are provided to verify the accuracy of the computational methodology. The concept of antenna diversity is discussed, and key assumptions and expressions are provided that characterize the multipath fading fields. Several computational examples demonstrate the diversity performance of two receiving antennas on a single handset. >

Path loss, delay spread, and outage models as functions of antenna height for microcellular system design

Abstract: This paper presents results of wide-band path loss and delay spread measurements for five representative microcellular environments in the San Francisco Bay area at 1900 MHz. Measurements were made with a wide-band channel sounder using a 100-ns probing pulse. Base station antenna heights of 3.7 m, 8.5 m, and 13.3 m were tested with a mobile receiver antenna height of 1.7 m to emulate a typical microcellular scenario. The results presented in this paper provide insight into the statistical distributions of measured path loss by showing the validity of a double regression model with a break point at a distance that has first Fresnel zone clearance for line-of-sight topographies. The variation of delay spread as a function of path loss is also investigated, and a simple exponential overbound model is developed. The path loss and delay spread models are then applied to communication system design allowing outage probabilities, based on path loss or delay spread, to be estimated for a given microcell size. >

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

Abstract: Studies 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. The author uses 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. Ther 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, one can obtain the same diversity benefit at the remotes and base stations using multiple base station antennas only. >

Antenna pattern synthesis: a new general approach

Abstract: The antenna pattern synthesis problem is of the utmost importance in almost every kind of antenna applications. Therefore, a very large number of contributions have appeared on this subject. But virtually all of them deal with simplified versions of the complete synthesis problem, wherein the degrees of freedom available in principle are strongly reduced, and/or idealized design criteria or requirements are considered. In this paper we present a formulation which allows us to overcome this fragmentation of the synthesis problem. A clear and direct description of the performance actually required by the antenna and a representation of the radiating properties of the antenna as a system allows us to formulate the synthesis problem as an intersections finding problem, i.e., to find a common element between a number of sets, each one containing elements fulfilling part of the requirements. This allows a completely general and flexible formulation of the problem, independent of the actual structure of the antenna. Then the practical implementation of this formulation is widely discussed, showing how an efficient solution procedure can be devised. The implications of the well-known ill-conditioning of the synthesis problem are also discussed. In order to show how the approach works and to assess its flexibility and power, a couple of significant examples are included, namely, a phase-only reconfigurable array and a shaped reflector synthesis. These examples are unconventional since no a priori choice of the intensity distribution (for the array case) or of the feed cluster (for the reflector case) is required. The method presented is able to exploit all the available degrees of freedom in order to fulfill the design requirements. >

Antennas for use in portable communications devices

Abstract: Antenna arrangements for use with portable communications devices are described. In one embodiment, an antenna (50) has four equally spaced monopole elements (52-58) mounted in a regular array on the outer surface of a solid cylinder structure (60). The cylindre (60) has a high dielectric constant, and extends from a conductive ground plane (62). The monopole elements (52-58) can be switched by switching elements (64-70, 76) so that one or more is active, with the others acting as parasitic directors/reflectors being connected commonly to ground or left in an open circuit condition to be effectively transparent. A shielded single monopole antenna (10) is also described.

Adaptive transmitting antenna arrays with feedback

Abstract: We address the problem of transmitting multiple cochannel signals from an antenna array to several receivers so that each receiver gets its intended signal with minimum crosstalk from the remaining signals. In addition to the usual "information" mode, we propose a "probing" mode during which probing signals received at the mobiles are fed back to the transmitter. These probing signals are used to identify an unknown propagation environment, enabling the transmitter to form the necessary transmission beampatterns. >

Ultra-wideband receiver

Abstract: An ultrawide (UWB) receiver utilizes a strobed input line (14) with a sampler (10) connected to an amplifier (18). In a differential configuration (18), +UWB inputs (14a) are connected to separate antennas or to two halves of a dipole antenna. The two input lines (14) include samplers (10) which are commonly strobed (12) by a gating pulse with a very low duty cycle. In a single ended configuration, only a single strobe input line and sampler is utilized. The samples integrate, or average, up to 10,000 pulses to achieve high sensitivity and good rejection of uncorrelated signals.

Tunable microwave ablation catheter system and method

Abstract: A tunable microwave ablation catheter system (20) is disclosed which matches the impedance of its power supply with the transmission line to minimize reflected power and optimize energy delivery to targeted tissue. The tuner (30) itself may be located in the power supply (22), the transmission line or the antenna (53). Tuner mechanisms at these locations can change the antenna configurations, move material relative to the antenna (53), or alter the waveguide (50). A controller (35) monitors the catheter system operation. A method of medical treatment is disclosed where the impedances of the components of the systems are adjusted during use to compensate for impedance variations.

A Practical Approach to the Reduction of Pseudorange Multipath Errors in a Ll GPS Receiver

Abstract: The reduction of multipath biases on GPS measurements has traditionally been achieved through innovative antenna design, such as choke ring ground planes, and careful antenna site selection. These methods, although effective, are not always practical, especially in a kinematic environment. The implementation of Narrow Correlator mspacing design in GPS receiver code tracking loops has greatly reduced the multipath bias and the measurement noise on C/A code pseudorange measurements. Even with these advancements the bias due to multipath is still dominant in GPS position calculations. This paper introduces a new tracking loop which takes full advantage of the Narrow CorrelatorT5t spacing design, but in addition, is much more resistant to multipath effects on the correlation function and thereby reduces the multipath bias on the pseudorange measurements. The theory behind this new tracking loop design is presented along with its implementation into existing receiver hardware. Test results from a prototype receiver are presented. They show a 25 to 50 percent reduction of multipath error effects in the DGPS position solution as compared to a standard narrow correlator receiver.

Helical antenna having a solid dielectric core

Abstract: An antenna for use at UHF and upwards has a cylindrical ceramic core with a relative dielectric constant of at least 5. A three-dimensional radiating element structure, consisting of helical antenna elements on the cylindrical surface of the core and connecting radial elements on a distal end face of the core, is formed by conductor tracks plated directly on the core surfaces. At the distal end face the elements are connected to an axially located feed structure in a plated axial passage of the core. The antenna elements are grounded on a plated sleeve covering a proximal part of the core which, in conjunction with the feeder structure, forms an integral balun for matching to an unbalanced feeder.

Ground‐penetrating radar simulation in engineering and archaeology

Abstract: Forward modeling of ground penetration radar is developed using exact ray-tracing techniques. Structural boundaries for a ground model are incorporated via a discrete grid with interfaces described by splines, polynomials, and in the case of special structures such as circular objects, the boundaries are given in terms of their functional formula. In the synthetic radargram method, the waveform contributions of many different wave types are computed. Using a finely digitized antenna directional response function, the radar cross-section of buried targets and the effective area of the receiving antenna can be statistically modeled. Attenuation along the raypaths is also monitored. The forward models are used: (1) as a learning tool to avoid pitfalls in radargram interpretation, (2) to understand radar signatures measured across various engineering structures, and (3) to predict the response of cultural structures buried beneath important archaeological sites in Japan.

Device for measuring position and orientation using non-dipole magnet IC fields

Abstract: Position and orientation of receiving antennae with respect to magnetic field transmitting antennae are determined. The transmitter consists of two or more antenna whose dimensions are large compared to the distance to the receiver. The receiver consists of two or more antenna that are sensitive to the type of signal transmitted. A computer is used to control the transmitting and receiving elements and to convert the received signals into position and orientation.

Single loop transponder system and method

Abstract: An apparatus including an object 10 associated with a contactless, electronic identifier is disclosed herein. In one example, the object 10 is a trash bin. This object 10 is formed from a non-conductive material. A single-loop antenna 14 is disposed adjacent the object 10. An impedance transformer 18 which is matched to the single-loop antenna 14 is used to generate a desired inductance. A transponder 12 is also disposed near to and associated with the object 10. The transponder 12 is coupled to the antenna 14 through the impedance transformer 18.

Multiple-element driven array antenna and phasing method

Abstract: An antenna array for direction-agile applications, such as r.f. packet mesh networks, employs a plurality of quarter-wave radiators disposed normally to a ground plane on a dielectric backing and switching elements for selecting a desired receiving direction and transmission direction and minimizing interference from signals in opposing directions. A control system selects and switches direction rapidly enough to receive and transmit digipeating signals in selected different directions using the phasing and switching elements. A specific embodiment employs eight radiators of 0.2625 electrical wavelengths (quarter wave plus 5%) disposed equidistant along a circle within a circular ground plane in a pattern which is 1/4 wavelength from the outer boundary of the ground plane, each radiator being disposed at least 0.15 wavelengths to about 0.25 wavelengths from adjacent radiators in a circular pattern. The antenna is characterized by eight electronically switchable radiating directions (at 45° intervals) with at least 20 dB front to back ratio and a 3 dB beamwidth of 64°. Pairs of radiators form parasitic elements, driven elements and reflectors with spacing selected as a modest compromise from the ideal spacing to allow electronically selectable directionality using identically-spaced elements acting as driven elements, parasitic elements and reflector elements. The driven elements are slightly reactively fed.

CDMA communications and geolocation system and method

Abstract: A spread-spectrum CDMA communications system for locating remote units, and for communicating message data between a plurality of remote units and a base station. The spread-spectrum CDMA communications system includes a plurality of base stations and a plurality of remote units. A base station has a spread-spectrum modulator for spread-spectrum processing the message data, and a transmitter for transmitting the spread-spectrum processed-message data, combined with a generic-chip-code signal, from the base station to a remote unit. The base station also has an antenna, and spread-spectrum detectors for recovering message-data communicated from the remote-units. A remote-unit has an antenna, and a detector coupled to the antenna for recovering data communicated from the base station. The detector includes a spread spectrum demodulator. Also, the remote unit has a device for converting the format of the data into a form suitable for communicating over radio waves, a spread spectrum modulator and a transmitter. The base station has a range circuit, which comparers the generic-chip-code signal generated at the base station with the generic-chip-code signal received from the remote unit, for determining a range between the remote unit and the base station.

Analytical results for capacity improvements in CDMA

Abstract: Examines the performance enhancements that can be achieved by employing spatial filtering in code division multiple access (CDMA) cellular radio systems. The goal is to estimate what improvements are possible using narrow-beam adaptive antenna techniques, assuming that adaptive algorithms and the associated hardware to implement these systems can be realized. Simulations and analytical results are presented which demonstrate that steerable direction antennas at the base station can dramatically improve the reverse channel performance of multicell mobile radio systems, and new analytical techniques for characterizing mobile radio systems which employ frequency reuse are described using the wedge-cell geometry of Rappaport and Milstein (1992). The authors also discuss the effects of using directional antennas at the portable unit. Throughout the paper the authors use phased arrays and steerable, fixed pattern antennas to approximate the performance of adaptive antennas in multipath-free environments. >

Antenna array having two dimensional beam steering

Abstract: An array antenna includes a ferrite substrate having a two-dimensional planar array of antenna elements disposed over a first surface thereof and means for applying an external magnetic field having a magnitude and direction which can be varied at least in a plane in which the antenna elements lie. The amplitude and direction of the external magnetic biasing field is varied to control the relative phases between each of the plurality of antenna elements and to steer the direction of a main antenna beam in two dimensions.

Composite multi-beam and shaped beam antenna system

Abstract: A composite antenna for use in satellite communication provides both the functions of multiple beams and a shaped beam radiated from a single radiating aperture. The radiating aperture may employ a mirror or a lens. Transmitted radiation from an array of radiators is coupled via a subreflector to the main reflector or lens which constitutes the radiating aperture of the antenna system. During reception of radiant-energy signals, signals received by the main reflector or lens are coupled via a separate subreflector to a separate array of receiving radiators operated at a frequency band different from that of the transmit array. The two subreflectors are combined into a single subreflector assembly employing a metallic concave reflector covered by a layer or coating of frequency selective optical material which allows for propagation of radiation at one frequency to the metal reflector while reflecting radiation in the other frequency band from a surface of the coating. Separate beamformers are employed for receiving and transmitting radiant-energy signals, the beamformers combining signals of clusters of radiators to provide for multiple beams wherein each of a plurality of the beams is formed by a cluster of radiators. Additional connection is provided via diplexers to the beamformers to select radiators to be employed for generation of shaped beams for both reception and transmission. The reflecting surfaces have diameters much larger than the diameters of the radiators to provide for individual beams from each of the radiators.

Input impedance of dielectric resonator antennas excited by a coaxial probe

Abstract: A formulation based upon the method of moments (MoM) is presented for the computation of input impedance of dielectric resonator antennas. The class of antennas modeled by this method consists of axially symmetric dielectric resonators fed by thin wire elements. The formulation is general in that the feed structure may be interior or exterior to the dielectric resonator. To demonstrate the utility of this technique, parametric studies are performed on a cylindrical dielectric resonator antenna (CDRA) operating at frequencies that excite the important HEM/sub 11/ resonator antenna mode. The integrity of this technique is established both experimentally and numerically. >

The spectrum efficiency of a base station antenna array system for spatially selective transmission

Abstract: The goal of this paper is to estimate the gain, in terms of system capacity at a given outage probability, which can be obtained by applying antenna arrays in the base stations of a mobile cellular network. For this purpose a propagation model which incorporates the angular distribution of the rays in the vicinity of the mobile is postulated. Also included in the model is the interference from co-channel cells. With the aid of the model, a weight selection algorithm is derived. The proposed system is simulated with different numbers of mobiles per channel in each cell and different numbers of antenna elements in the arrays. Also varied is the cluster size. This is done to determine the optimal trade-off between reduced cluster size and multiple mobiles per channel in each cell. The results show that it is possible to increase capacity between two and twelve times depending on the number of antennas in the arrays and the spread of the local scattering. >

Antenna support with multi-direction adjustability

Abstract: An antenna support for mounting one or more antenna on a support structure such as a tower. The antenna support includes a framework mountable to the structure, and an antenna mounting support assembly coupled to the framework. The antenna mounting support assembly is configured to mount the antenna in a fashion to be adjustable in a multitude of directions relative to the support structure, such that the mounted antenna may be tuned by an installer by adjustments in these directions.

Low profile dielectric resonator antennas using a very high permittivity material

Abstract: Low profile rectangular dielectric resonator antennas, fabricated out of a very high permittivity material ( epsilon /sub r/=100) are reported. An antenna having a height of approximately 0.026 lambda /sub 0/ and a bandwidth of 3% is demonstrated.< >

Inductor/antenna for a recognition system

Abstract: An improved inductor/antenna (100)improves the selectivity of a recognition system (10) by ensuring that only the transponder (14) closest to the inductor/antenna (100) of an interrogator (12) receives therefrom, and reacts to, an interrogation signal (S1). The improved inductor/antenna (100) also receives the resulting recognition signal (S2) from the transponder (14)for analysis by the interrogator (12). The inductor/antenna (100) includes two or more coils (102,104; 124,126,128,130; 132,134) which may be wound on ferromagnetic cores (108), spaced around a metal mass (46,48) such as a lock cylinder (46) of an ignition switch (24). The shape, number, location and relative winding sense of the coils are selected to shape and locate the energy field (F; 118,122) radiated by the inductor/antenna (100) so that only the transponder (14) in a key (26) which is inserted into or operating the ignition switch (24) responds to the interrogation signal (S1) radiated by the inductor/antenna (100).