Showing papers on "Antenna (radio) published in 1996"

A re-examination of the fundamental limits on the radiation Q of electrically small antennas

Abstract: An exact method, which is more straightforward than those previously published, is derived for the calculation of the minimum radiation Q of a general antenna. This expression agrees with the previously published and widely cited approximate expression in the extreme lower limit of electrical size. However, for the upper end of the range of electrical size which is considered electrically small, the exact expression given here is significantly different from the approximate expression. This result has implications on both the bandwidth and efficiency limitations of antennas which fall into this category.

Method and apparatus for controlling and determining the status of electrical devices from remote locations

Abstract: Apparatus for controlling an electrical device by remote control including a control device coupled to the electrical device by a wire connection for providing power to the electrical device, the control device having an actuator for adjusting the status of the electrical device and a radio frequency transmitter/receiver and antenna for adjusting the status of the electrical device in response to control information in a radio frequency signal. The transmitter/receiver receives the radio frequency signal via the antenna and transmits a status radio frequency signal with information regarding the status of the electrical device. A master control unit has at least one actuator and status indicator and a transmitter/receiver for transmitting a radio frequency signal having the control information therein to control the status of the electrical device and for receiving the status information from the control device. The status indicator indicates the status of the electrical device in response to the status information. A repeater receives the radio frequency signal from the master unit and transmits the control information to the control device and receives the status information from the control device and transmits it to the master unit.

A circularly polarized small-size microstrip antenna with a cross slot

Abstract: An antenna with a low profile, small size, and a light weight is required in mobile satellite communications. A new, circularly polarized small-size microstrip antenna using a proximity coupled feed method is proposed. A simple configuration based on a cross slot with unequal slot lengths on a circular patch is adopted to realize a small-size element antenna. The proposed antenna has no 90/spl deg/ hybrid coupler for circular polarization. The measured results verify the circular polarization, and the antenna radius was reduced by about 36% by using the slot lengths which are nearly equal to the diameter of the circular patch antenna. Good impedance and axial ratio characteristics have been obtained.

A study of the handset antenna and human body interaction

Abstract: The antenna radiation pattern and other characteristics are significantly altered by the presence of the human body. This interaction as well as the resultant deposition of microwave power in the body (specific absorption rate-SAR) are of particular interest for cellular telephones and similar communication devices. This paper builds on and extends the previous analyses of parameters that influence the antenna-user interaction. Computer tomography (CT) and magnetic resonance imaging (MRI)-derived, high-resolution models of the human head are used. The numerical analysis is performed with the finite-difference time-domain (FDTD) method. The specific findings are: 1) a box model of a human head provides grossly distorted and unreliable results for the antenna radiation pattern; 2) a spherical model of the human head provides results that are relatively close to those obtained with a relatively simple, but more realistic, head model; 3) the SAR values obtained with spherical or simplified head models, that do not include the ear, are greater than those for a realistic head model that includes the ear; and 4) a hand holding the handset absorbs significant amount of antenna output power, which can be considerably decreased by modifying the geometry of the handset metal box.

A geometrically based model for line-of-sight multipath radio channels

Abstract: This paper provides a geometrically based model for single bounce multipath components in line-of-sight (LOS) microcell radiowave propagation channels. The model characterizes the excess delay, direction-of-arrival, and received power of multipath components and is particular useful for microcell and PCS systems with low transmitter and receiver antenna heights. The model includes analytical expressions for the probability density functions for all critical channel parameters and is thus useful for analytical purposes. The model is also useful for simulating both wideband and narrowband systems and in particular the model has been used extensively in a study of code division multiple access (CDMA) cellular radio systems employing adaptive antennas and switched beam systems at the base station.

Closed-loop, RF-coupled implanted medical device

Abstract: The implantable, electrically operated medical device system comprises an implantable radio frequency (RF) receiver and an external RF transmitter. The receiver has a receiving antenna and electronic circuitry coupled to the receiving antenna and includes a microcontroller having an output, a non-volatile memory coupled to the microcontroller and an implanted, electrically and autonomously operated medical device is coupled to the output of the microcontroller. The external RF transmitter has a power source and a transmitting antenna. The receiver further includes circuitry coupled to the microcontroller for regulating the power transmitted by the transmitter, whereby, RF energy can be transmitted by the transmitter and coupled into the receiver and the level of RF energy transmitted by the transmitter is controlled by the circuitry. The transmitter is also used to: a) program into the memory of the implanted device (receiver) its operating values; b) start and stop delivery of medical therapy by the implanted device, c) interrogate the operating values of the implanted device, and d) interrogate physiological parameters which are measured by the implanted device.

Digitally programmable multifunction radio system architecture

Abstract: A system that partitions or divides the functions of a radio into channels and divides the functions of each channel into two major functions: 1) antenna interfce and power amplification; and 2) hardwired mixing, modulation/demodulation and signal processing and further partitions the mixing through signal processing functions into the functions of a) programmable analog mixing and b) programmable digital modulation/demodulation and signal processing. Control and user interface functions, if needed for a particular application can also be functionally partitioned. A typical received signal pathway will encounter an antenna module, an antenna interface and power amplification module, a receiver module partitioned into an analog submodule that performs mixing and down conversion to produce a common intermediate frequency signal and a digital submodule that further down converts the intermediate frequency signal, demodulates the signal and performs the other signal processing necessary to provide a useful information signal. A typical transmitter pathway includes a transmitter module partitioned into a digital submodule that performs signal processing and modulation and an analog submodule that performs upconversion and mixing, followed by a power amplification and interface module and an antenna module. Control and user interface modules can also be provided along with modules that perform additional processing and information security functions.

Fractal multiband antenna based on the Sierpinski gasket

Abstract: Experimental and computed results show a multiband behaviour over five bands for the new fractal Sierpinski antenna. Such a behaviour is based on the self-similarity properties of the antenna's fractal shape, which might open an alternative way for designing new multiband and frequency independent antennas.

Communication system and methods utilizing a reactively controlled directive array

Abstract: A reactively controlled directive antenna array that has a single central monopole or dipole as a radiating element excited directly by a feed system. A plurality of parasitic elements surround the radiating element and through changing the state of the parasitic impedance causing the antenna to be in an omni directional or beam pointing mode according to whether the parasitic elements are open circuited or short circuited. A computer modem and memory including stored programs control the antenna array in an omnidirectional or directive mode to locate, identify and communicate with nodes in a wireless communication network. A stored table is created in the memory indicating the antenna direction for communicating with each node in the network. Using the stored table, the computer initiates a communication sequence with a selected node, the sequence having the advantages of improved signal sensitivity and angular discrimination for wireless communication systems.

Combined GPS positioning system and communications system utilizing shared circuitry

Abstract: A combined GPS and communication system having shared circuitry. The combined system includes an antenna for receiving data representative of GPS signals, a frequency converter coupled to the antenna, a frequency synthesizer coupled to the frequency converter, an analog to digital converter coupled to the frequency converter and a processor coupled to the frequency converter. The processor processes the data representative of GPS signals to determine a pseudorange based on the data representative of GPS signals. The integrated communication receiver includes a shared component which is at least one of the antenna, the frequency converter, the frequency synthesizer and the analog to digital converter. Typically, in certain embodiments the processor also demodulates communication signals received as well as controls the modulation of data to be transmitted as a communication signal through a communication link.

Monopole antennas for microwave catheter ablation

Abstract: We study the characteristics of various monopole antennas for microwave catheter ablation of the endocardium. The investigation is done with a computer model based on the finite-element method in the frequency domain. Three monopole geometries are considered: open-tip, dielectric-tip, and metal-tip. Calculations are made for the magnetic field, the reflection coefficient and the power deposition pattern of the antennas immersed in normal saline. The theoretical results are compared with measurements performed on prototypes and good agreement Is obtained. The antenna characteristics suggest that the metal-tip monopole best fulfils the requirements of catheter ablation. The computer model is then used to compare metal-tip monopoles of different dimensions and to determine design trade-offs.

Microwave ablation catheters having antennas with distal fire capabilities

Abstract: A variety of improved antenna arrangements for ablation catheters and methods for constructing catheter with these antenna arrangements are described. In various apparatus aspects of the invention, the catheter includes an elongated flexible tubular member adapted to be inserted into a vessel in the body of a patient. A transmission line suitable for transmitting electromagnetic energy is received within the tubular member. An antenna is coupled to the transmission line for generating an electric field sufficiently strong to cause tissue ablation. In one embodiment, the antenna takes the form of an antenna coil that is oriented such that its longitudinal axis extends substantially perpendicular to the longitudinal axis of the flexible tubular member. In another embodiment, a plurality of such laterally oriented antenna coils are provided at longitudinally spaced locations relative to the catheter axis. In other embodiments, the antenna coil is spirally wound. A variety of spiral antenna arrangements are contemplated. In some embodiments, the coil is wound in a substantially conical or frusto-conical manner expanding either distally or proximately. In still another embodiment, the antenna coil is wound in a substantially flat coil.

Thin radio frequency transponder with leadframe antenna structure

Abstract: A novel radio frequency transponder (tag) with a minimum of components and connects is thin and flexible because these components and connects can be unsupported by a substrate layer. This is accomplished by using a conducting leadframe structure not only as a connection medium but also as a circuit element, i.e., the transponder antenna. In various preferred embodiments, the leadframe is mechanically positioned and fixably attached to a circuit chip so that the leadframe (antenna) is self supporting. A protective coating can be added where the leadframe is attached to the circuit chip. Further a protective surrounding can envelops the entire leadframe antenna, circuit chip, and, if provided, the protective coating.

Electromagnetic noise detector for implantable medical devices

Abstract: Disclosed are apparatus and method for detecting electromagnetic interference (EMI), or noise, that may disrupt the proper operation of medical devices (10) implantable in patients, such as cardiac stimulators. Circuitry of the detector of the invention is independent of other circuitry of the medical device. EMI is magnetically induced on an antenna (40) that may be within the metal housing (252) of the device (10) in a receiver circuit (40), and the EMI signals are output to the noise detector (66, 68). A variety of alert signals may be provided to the medical device circuitry to warn of the presence of EMI so that appropriate responses may be taken to insure the safety of the patient dependent on the device. The detector may share the telemetry antenna of the medical device, or utilize a separate, dedicated antenna to receive EMI. Alternative antennas external to the metal housing of the medical device include leads from the device to the heart of the patient, and a dedicated antenna (260) in the nonmetal header (254) of the device.

Radar module and antenna device

Abstract: A radar module has an antenna assembly, a plurality of transmitting and receiving assemblies, and a plurality of circulators all mounted on a dielectric substrate. The antenna assembly has a plurality of transmitting and receiving channels including respective planar array antenna elements each composed of a plurality of patches connected to and spaced along a linear distal end portion of a feeder line. The planar array antenna elements are arrayed in a direction substantially perpendicular to the linear distal end portion of the feeder line. The transmitting and receiving assemblies, implemented as monolithic microwave integrated circuits, selectively transmit high-frequency signals to the planar array antenna elements and selectively receive echo signals from the planar array antenna elements. The circulators are associated with the transmitting and receiving channels, respectively, and connect the respective linear distal end portions of the feeder lines to transmission and reception end portions which are connected to the transmitting and receiving assemblies, respectively.

A fully three-dimensional simulation of a ground-penetrating radar: FDTD theory compared with experiment

Abstract: A fully three-dimensional, finite-difference time-domain (FDTD) model of a ground-penetrating radar is described. The FDTD simulation completely models the transmitting and receiving antennas, the antenna feeds, the dispersive Earth, and the buried object. Results of scattering from three different buried cylindrical pipes are compared to previously measured results for a one-third size scale model of an actual radar and are shown to be in good agreement.

CAD of microstrip antennas for wireless applications

Abstract: From the Publisher: The recent explosion in commercial applications involving RF and microwave systems (e.g. mobile telephones) is fueling customer demand for small, low-cost, easy-to-use systems. It's also driving innovations in antenna technology. This "how-to" book explains why microstrip antennas are the ideal low-profile, low-cost solution for these commercial applications and provides the information and tools necessary to design them. Included are: • A brief description of microstrip antennas, pertinent terminology, plus analysis and modeling techniques to sharpen your insight into the operation of various elements and arrays • Step-by-step coverage of the design of various single-element radiators, including rectangular, circular, broadband, and CP patches. Interaction between design parameters and antenna performance is also discussed • An in-depth explanation of simple array design, including performance and calculations, types of array architectures, and specific design aspects • Discussion of advanced feeding techniques that provide increased design flexibility and performance This book comes bundles with an IBM PC-compatible diskette containing 18 stand-alone computer programs and a user-friendly guide showing sample design cases and expected results to assist in the analysis and design of specific microstrip antennas and arrays. The design approaches, techniques, and nearly 280 equations presented here are essential information for design engineers and engineering managers involved in the design of antennas and RF/microwave circuits. This technical reference helps you develop an intuitive understanding of microstrip antenna operations - andmaster the steps necessary to create more effective designs. Product line managers and marketing managers also find this information valuable when assessing the applicability of microstrip antennas in current and future product lines.

Indoor radio communication system

Abstract: A master station master antenna having a high directivity in an upper direction, a slave station and a slave antenna having a high directivity in the high direction are arranged on a floor of a room, and furniture is arranged on the floor between the master antenna and the slave antenna. Also, a master reflecting mirror is arranged on a ceiling of the room placed just above the master antenna, and a slave reflecting mirror is arranged on the ceiling placed just above the slave antenna. When an electric wave having a data signal is radiated from the master station, the electric wave radiated in the upper direction passes through a first transmission route and is reflected by the master reflecting mirror toward a horizontal direction. Thereafter, the electric wave passes through a second transmission route near the ceiling and is again reflected by the slave reflecting mirror toward the lower direction. Thereafter, the electric wave passes through a third transmission route and is received by the slave antenna because the slave antenna has a high directivity to receive the electric wave transmitted from the upper direction. Therefore, the data signal can be reliably detected by the slave station without being interrupted by the furniture.

Communication system including diversity antenna queuing

Abstract: A wireless communications system comprising a first transponder having a plurality of selectable antennas, and having a stack including locations holding data representing antennas, the stack defining an order in which antennas will be used to attempt communication; a second transponder configured to communicate with the first transponder, wherein the first transponder uses an antenna defined by data in one location of the stack for communication with the second transponder, and, if successful communication with the second transponder is not established, the transponder uses an antenna defined by data in another if location of the stack.

Efficient apparatus for simultaneous modulation and digital beamforming for an antenna array

Abstract: A digital beamforming network for transmitting a first number of digital information signal using a second number of antenna array elements is disclosed. Assemblers are used for assembling one information bit selected from each of the information signals into a bit vector. Digital processors have an input for the bit vector and a number of outputs equal to the second number of antenna elements and process the bit vector. Finally, modulation waveform generators coupled to each of the second number of outputs generate a signal for transmission by each antenna element.

A planar dual-frequency array antenna

Abstract: A dual-frequency array antenna having an essentially planar structure with electronic beam steering capability in both a low and high frequency band independently of each other, constructed, in a layered formation, from a top planar array antenna unit operating in the low frequency band and a bottom planar array antenna unit operating in the high frequency band. The top planar array antenna is transparent to frequencies in the high frequency band.

Phased array antenna with temperature compensating capability

Abstract: Generally, a variation of temperature at the installation site causes a phased array antenna radiation pattern to degrade. This paper describes the temperature characteristics of various components of the phased array antenna and degradations of the radiation pattern originating from temperature variations. It is effective to measure the phase distribution on the aperture and correct it, as the occasion demands, to prevent such degradations. Also, we propose a simple and effective algorithm for the measurement of the current distribution on the aperture, and present the evaluation test results of a phased array antenna with temperature compensation obtained by applying the algorithm.

Method of magnetic resonance imaging and spectroscopic analysis and associated apparatus employing a loopless antenna

Abstract: The invention provides a method for magnetic resonance imaging and spectroscopic analysis of a specimen which includes positioning the specimen within a main magnetic field and introducing an antenna having a loopless antenna portion in close proximity to the specimen. Radio frequency pulses are provided to the region of interest to excite magnetic resonance signals, gradient magnetic pulses are applied to the region of interest with the antenna receiving magnetic resonance signals and emitting responsive output signals. A processor processes the responsive output signals to provide image information for display in a desired manner. The method in a preferred form involves employing a flexible antenna. The method in another preferred form involves employing an impedance matching circuit electrically interposed between the loopless antenna and the processor to enhance radio frequency power transfer and magnetic resonance signal-to-noise ratio from the loopless antenna to the processor. The method may be used on a wide variety of specimens and in a preferred use is introduced into small blood vessels of a patient to facilitate determination of atherosclerotic plaque. Medical intervention procedures, such as plaque removal, may be employed generally simultaneously with the imaging of the present invention. Corresponding apparatus and magnetic resonance antenna assembly are provided.

Characteristics of the SAR distributions in a head exposed to electromagnetic fields radiated by a hand-held portable radio

Abstract: Presents characteristics of the specific absorption rate (SAR) distributions calculated by the finite-difference time-domain (FDTD) method using a heterogeneous and realistic head model and a realistic hand-held portable radio model. The difference between the SAR distributions produced by a 1/4-wavelength monopole antenna and those produced by a 1/2-wavelength dipole antenna is investigated. The dependence of the maximum local SAR on the distance d/sub a/ between the auricle of the head and the antenna of the radio is evaluated. It is shown that the maximum local SAR decreases as the antenna length extends from 1/4 to 1/2 of the wavelength. The maximum local SAR's in a head model with auricles are larger than these in one without auricles. The dependence of the SAR on the electrical inhomogeneity of the tissues in the head model is not significant with regard to the surface distribution and the maximum local SAR when the radio is near the head. It is also shown that the maximum local SAR is not strongly dependent on the position of the hand when the hand does not shade the antenna. Furthermore, the SAR's experimentally measured in a homogeneous head phantom are compared with the calculated SAR's.

Dual band mobile station employing cross-connected transmitter and receiver circuits

Abstract: A multi-mode radiotelephone (10) includes at least one antenna (12) for transmitting and receiving RF signals within at least two frequency bands. The radiotelephone also includes a first receiver (30, 34) having an input coupled to the antenna for amplifying and down-converting RF signals within a first frequency band and a second receiver (30a, 34a) having an input coupled to the antenna for amplifying and down-converting RF signals within a second frequency band. The radiotelephone further includes a first transmitter (44, 46, 48) having an output coupled to the antenna for up-converting and amplifying RF signals within the first frequency band and a second transmitter (44a, 46a, 48a) having an output coupled to the antenna for up-converting and amplifying RF signals within the second frequency band. In accordance with this invention the first receiver and the second transmitter are disposed within a first circuit package (29a), and the second receiver and the first transmitter are disposed within a second circuit package (29b). The first and second circuit packages may be integrated circuits or hybrid (e.g., thick or thin film) circuits.

Analytical antenna model for chiral scatterers: comparison with numerical and experimental data

Abstract: An analytical model for polarizability dyadics of small chiral conductive particles in free space or those embedded in a lossy material is presented and discussed. Chiral particles are modeled by a wire loop connected to two straight wire elements. The electromagnetic analysis is based on the replacement of the particles by two connected antennas representing the wire and loop portions. Analytical expressions for polarizabilities are given. For electrically small particles, a lumped-element equivalent circuit can be constructed and the polarizabilities can be expressed in terms of equivalent circuit parameters. It is shown that the wire-and-loop antenna model for scatterers satisfies the reciprocity condition and other basic physical requirements. Approximate analytical expressions are compared with numerical simulations and with the experimental data on reflection from single chiral particles, and the results are seen to be in good agreement. The model can be used in analytical modeling of chiral and omega composite materials.

Radio frequency tag

Abstract: Disclosed is a radio frequency identification (FR ID) tag (20) which is adapted for use in identifying electronic and/or electrical systems which incorporate electronic components mounted on a printed circuit board (40) (PCB). The RF ID tag comprises semiconductor circuitry contained within an electronic package, which package is mounted onto the PCB. In addition to the various components and circuitry of the tagged system, the PCB includes the RF antenna (30) portion of the tag defined either in or on the PCB. The package is connected to the antenna via pads (32) on the PCB.

Smart antenna arrays for CDMA systems

Abstract: There are a diverse range of products and services currently on the market, but cellular or personal communications services (PCS) radio networks probably have the highest public profile. These services provide highly mobile, widely accessible two-way voice and data communications links. In general, the most complex and expensive part of the radio path for these systems is the base station. As a result, manufacturers have been designing networks that have high efficiency in terms of the bandwidth occupied and the number of users per base station. Base station antenna arrays are a promising method for providing large capacity increases in cellular mobile radio systems. This article considers channel-modeling issues, receiver structures, and algorithms, and looks at the potential capacity gains that can be achieved. It considers antenna arrays for the mobile-to-base-station or reverse link of a CDMA cellular system. It begins with an introduction to CDMA communications systems and also addresses the general topic of antenna array receivers.

High gain antenna systems for cellular use

Abstract: In a cellular type communication system a sector antenna (12) provides coverage of a sector with a relatively low receive gain. A multi-beam antenna (20) covers the same sector with a plurality of narrower beams (21', 22', 23' and 24') providing higher gain. A multi-beam antenna system (10) provides higher gain operation by selecting the one of the narrower beams (21', 22', 23' or 24') currently providing best reception of a signal transmitted by a user and coupling that selected beam to a system receiver (18). Beam selection is accomplished by sequentially coupling each narrow beam to a microprocessor based control unit (40) and storing samples of user signals as received in each narrow beam on a continuing repetitive basis. The stored samples are then analyzed in order to select the beam currently providing best reception. If, based on analysis of subsequent samples, a different one of beams (21', 22', 23' or 24') provides best reception (because of user movement or changing transmission conditions) that different beam is coupled to the system receiver (18). Spaced diversity reception is achieved by providing a second multi-beam antenna (20a) and enabling the system receiver (18) to choose either of two, or both, inputs. Fail/safe operation is provided by coupling the sector antenna (12) to the system receiver (18) in the absence of coupling of a superior narrow beam signal. Systems using multiple sector antennas (12 and 12a), transmitters (16 and 16a) and receiver systems (18 and 18a) are described, as are arrangements enabling narrow beam signal transmission. Methods of operation of such a multi-beam receiving arrangement, including methods for beam selection during initial random access user contacts, are also described.

Plural frequency antenna feed

Abstract: Apparatus and method for providing an antenna feed (10) operative at different microwave frequency bands employ a circular waveguide (14) interconnecting an orthomode transducer (20) to a feed horn (16) thereby providing a feed (10) suitable for illuminating the reflector (54) of an antenna (12). The orthomode transducer provides for a coupling of waves in the first frequency band with both vertical and horizontally polarized waves. Included within the feed is a coupler assembly (26) of waves of the second frequency band operative via a sidewall of the circular waveguide. The coupler assembly includes plural identical coupling sections (28) each having a rectangular waveguide section contiguous and parallel to the circular waveguide with a row of apertures for coupling power into and out of the circular waveguide. Pairs of the coupling sections are disposed in orthogonal planes so as to introduce two linearly polarized waves which are perpendicular to each other. A slab (48) of dielectric material is placed in each of the coupling sections to match the phase velocity of waves in the coupling sections to waves in the circular waveguide at the second frequency band while mismatching the phase velocities at the first frequency band. The dispersion of the waveguides provides for interaction with electromagnetic waves in the second frequency band while inhibiting such interaction at the first frequency band.