Showing papers on "Dipole antenna published in 1990"

Analysis for mean effective gain of mobile antennas in land mobile radio environments

Abstract: A method is described for analyzing the mean effective gain (MEG) of antennas moving in a mobile communication environment. The MEG characteristics of a mobile antenna are determined by the mutual relation between the antenna patterns and the statistical distribution of incident waves in an environment. To analyze this relation theoretically, a general expression for the MEG using a statistical model of incident waves is derived, and a novel statistical model, whose distribution is uniform in azimuth and Gaussian in elevation, is proposed. The validity of the statistical model is confirmed through 900-MHz-band measurements carried out in a Tokyo urban area, and the empirical parameters for the statistical distribution are described. The MEG characteristics of a half-wavelength dipole antenna are investigated using the proposed method, and it is shown that the theoretical curves calculated using the empirical parameters are in excellent agreement with experimental results. This analysis is extremely applicable for evaluating the MEG characteristics of arbitrary mobile antennas in various mobile communication environments. >

Characterization of an optoelectronic terahertz beam system

Abstract: The performance of an optoelectronic terahertz (THz) beam system is described. The transmitter operation is based on the repetitive, subpicosecond laser excitation of a Hertzian dipole antenna embedded in a charged coplanar line. With this transmitter electromagnetic beams of 1/2 cycle THz pulses at a repetition rate of 100 MHz are produced. The associated optoelectronic receiver is gated in synchronism with the excitation of the transmitter by subpicosecond pulses from the same laser source. With this receiver, the 10-nW beams of THz pulses were observed with a signal-to-noise ratio greater than 10000:1. Several sources contributing to the noise of the receiver are discussed, together with ways to reduce them. With an integration time of 125 ms, a signal-to-noise ratio of 1 is obtained for a THz beam with an average power of 10/sup -16/ W. The receiver operates in the sampling mode and has a time resolution of 0.5 ps. >

Dielectric resonator antenna using aperture coupling

Abstract: A practical antenna configuration for use at microwave and millimetre wave frequencies is investigated. It consists of a circular cylindrical dielectric resonator fed by a microstrip feedline through a coupling aperture in the ground plane between them. Several elements, with different physical parameters, operating between 14 and 16GHz were constructed and tested. Experimental results confirm the effective and practical performance of the antenna structure.

A study of the quadrifilar helix antenna for Global Positioning System (GPS) applications

Abstract: An analytic model for computing the radiation properties of the quadrifilar helix volute antenna is discussed and various design considerations for GPS applications are presented. The effects of modifying the antenna length and diameter on the antenna amplitude and phase performance are presented, and using the antenna for dual-frequency operation is discussed. The effects of phase imbalances are presented and compared with measured pattern anomalies. >

Practical Antenna Handbook

Abstract: This edition contains BASIC computer programs for antenna design and impedance matching, expanded coverage of long-wire directional antennas and radio-wave propagation theory, and new material on small loop direction-finding antennas. It presents practical projects, providing nuts-and-bolts information on an array of antenna types, including: high frequency dipole, vertically polarized HF, multi-band and tunable wire, hidden and limited-space, directional-phased vertical and directional beam, VHF/UHF transmitting and receiving antennas, antennas for shortwave reception, microwave antennas and mobile, marine and emergency antennas. Also explained are circuits and methods for matching antenna load impedance to an RF source or transmission line, antenna measurement and adjustment methods, antenna measurement and adjustment methods, antenna grounding techniques and how to use the Smith chart as a problem-solving device.

Broad-band gap coupled microstrip antenna

Abstract: A microstrip antenna with large bandwidth is developed using a parasitic technique. Compared to the available wideband antennas, the proposed antenna structure is very compact and gives a less distorted radiation pattern with frequency. An impedance bandwidth eight times that of a conventional patch antenna of the same size is achieved. The concept of coupled microstrip line model is extended for theoretical interpretation of the impedance loci. The experimental procedure and results are described, and a theoretical analysis is presented. >

Highway vehicle identification system with high gain antenna

Abstract: An apparatus for communicating with a transponder (10) carried by a vehicle moving along a multi-laned roadway (101, 103) comprising transmitter means (22) for producing a triggering signal, an antenna system (102) coupled to said transmitter means and being embedded in said multilane roadway, a receiver (18) coupled to said antenna system for monitoring transponder response electrical signals from said antenna system incorporating data related to the identity of the vehicle and correlating means to associate said lane of said multi-laned roadway with each identified vehicle. Said antenna system for mounting in a roadway comprises an electrically lossy material and has a reflector trough shield (123) filled with a solid dielectric (130). Said antenna, preferably comprised of coaxial cable, is positioned in the reflector trough, which prevents electromagnetic waves radiated by the antenna from being lost into the roadway.

Wide-band loop antenna with outer and inner loop conductors

Abstract: A wide-band loop antenna consists of a main loop antenna conductor and a sub-loop antenna conductor. The main loop antenna conductor is provided on a dielectric plate to extend from one terminal of a pair of feed terminals to another one of the terminals so as to form a one-turn open loop. The loop antenna conductor is provided on the dielectric plate so as to extend along the main antenna conductor to provide a one-turn open loop and is connected to the pair of feed terminals to constitute a synthesized antenna together with the main antenna conductor. Short-circuting conductors are provided to connect the main antenna conductor with the sub-antenna conductor for shifting a resonance frequency of the synthesized antenna outside the operating band to obtain a wide-band frequency characteristic. In a modification, the sub-antenna conductor forms a closed loop serving as a parasitic antenna which improves an impedance characteristic of the main antenna conductor.

Superconducting antennas

Abstract: It is noted that the advent of high-T/sub c/ superconducting materials has prompted a reexamination of the opportunities for improving antenna performance. Areas where superconductors have potential are considered, including superdirective arrays; large millimeter wavelength arrays; electrically small antennas; matching of electrically small antennas, including large transmitting antennas, and of superdirective arrays; switched line or single line phasers for electronic scanning of arrays; and traveling wave arrays where the transmission line phase velocity controls the beam angle. It is concluded that arrays above 5 GHz will benefit from low conduction, and probably also from low dielectric losses. Matching of electrically short antennas, both small (high-frequency) and large (low-frequency), and of arrays of moderate superdirectivity, will allow significant efficiency improvement. >

Electronic animal control system with lightning arrester

Abstract: An animal control system with a lightning arrester is provided for controlling the movement of an animal relative to a predetermined outdoor area A signal transmitter produces an output signal of predetermined frequency A wire loop transmitting antenna is electrically connected with the transmitter and is positioned at the predetermined outdoor area to transmit the output signal from the transmitter A portable receiver responsive to the signal from the antenna is carried by the animal The portable receiver produces an animal control output in the form of an annoying tone or an electrical shock to the animal when the animal moves into a selected vicinity of the antenna A lightning arrester is electrically connected between the transmitter and the antenna The lightning arrester includes a pair of choke coils respectively connected from the transmitter to opposite sides of the antenna Zener diode are respectively used to ground the transmitter side of the choke coils whenever a voltage in excess of the breakdown voltage appears across one of both of of the Zener diodes Gas tubes respectively ground the antenna side of the choke coils whenever a voltage in excess of the sparkover voltage appears across one or both of the gas tubes In addition, a gas tube is connected across the antenna on the antenna side of the choke coils

Effect of an image plane on printed circuit board radiation

Abstract: It is shown that the predominant radiation from a PCB (printed circuit board) with or without an attached cable is the result of common-mode current. For the PCB investigated here, the common-mode current was caused primarily by a source proportional to the signal voltage driving the traces and the cable as an asymmetric dipole antenna. Moreover, the PCB was an effective common-mode antenna even without the cable. The concept of partial inductance was used to calculate the inductance of the ground-return trace. The effect of placing an image plane beneath and close to a PCB was shown. The image plane dramatically reduced the radiated emissions from a PCB even though the plane was not electrically connected to the PCB. The image plane also dramatically reduced the emissions from a PCB with an attached cable when the image plane was correctly connected to the PCB. >

A multiradius, reciprocal implementation of the thin-wire moment method

Abstract: An implementation of the moment method, entitled the multiradius bridge-current (MBC) moment method, for electromagnetic analysis of multiradius thin-wire structures (including multiwire, multiradius junctions) is presented. It is extension of the authors' uniradius bridge-current reformulation (see ibid., vol.37, p.1224-34, Oct. 1989) of Richmond's uniradius thin-wire theory (1974). The method features an exactly symmetric mutual impedance matrix ensuring reciprocity between sources, it is unconstrained with respect to both the length ratio and the radius ratio of adjoining segments (provided that the wires are electrically thin), and it permits the self-consistent inclusion of coaxial cable sections in the configurations under analysis. The method is validated through comparison with transmission-line theory for a two-wire line and a coaxial cable, and through comparison with measurements on a sleeve monopole antenna and a log-periodic dipole antenna. The MBC moment method program is shown to surpass the Numerical Electromagnetics Code (NEC) in terms of reciprocity and convergence for both an AM broadcast tower detuning stub problem and a bent two-wire transmission-line problem. >

A concentric array for low and medium frequencies

Abstract: It is shown that a concentric array of improved directivity Corum elements disposed about a central tower, driven by appropriate source amplitudes, produces a Fourier series approximation to any desired vertically polarized radiation pattern in the plane of the array. The antenna system is of special interest to broadcasters (where protected contours and interference levels are legally constrained) and also to other medium- and low-frequency users who require a vertically polarized directional array. An elementary example of the pattern synthesis technique is presented. >

Interference cancellation system for interference signals received with differing phases

Abstract: An interference cancellation system for cancelling at least two interfering signals received simultaneously and which is adapted to be connected to a radio receiver system having a receiver antenna, a receiver and a receiver transmission line interconnecting the receiver antenna and the receiver includes an auxiliary antenna, a first directional coupler connected to the auxiliary antenna, a second directional coupler connected to the receiver transmission line, a synchronous detector connected to the first and second directional couplers, a signal controller connected the synchronous detector and a subtractor connected to the receiver transmission line and to the signal controller. The auxiliary antenna has a non-zero phase relationship for the two interferring signals relative to the receiver antenna. The auxiliary antenna is spaced apart from the receiver antenna a predetermined distance so that the two interfering signals are received by the two antennas with a phase difference which is equal and opposite to that which is introduced by the auxiliary antenna. As a result, the two interfering signals are received in the interference cancellation system in the same phase relative to the receiver antenna.

Antenna system for portable radio apparatus

Abstract: An antenna for a portable radio apparatus has a first antenna construction connected to the casing of the apparatus and a second antenna construction affixed to a base plate or earth plate which is incorporated in the casing The first antenna construction has a movable joint which allows the first antenna construction to move between a first position where it is regarded as forming a part of the contour of the casing and a second position where it is protruded from the contour and regarded as being located in free space The second antenna construction corrects the matching state of the first antenna construction such that adequate antenna radiation characteristics are set up in the first position Optimal antenna characteristics are, therefore, achievable when the first antenna construction is in any one of the first and second positions

High‐power radiating facility at the HIPAS Observatory

Abstract: UCLA's radio frequency ionospheric heater, 25 miles (40 km) east of Fairbanks, Alaska, is described. The heater consists of eight crossed dipole antennas arranged in a circular pattern to give a gain of 18.4 dB over isotropic at 2.85 MHz (˜ 2nd electron cyclotron harmonic). At 1.2 MW total radiated power the array has a calculated equivalent radiating power of 84 MW. Each antenna is driven by a 150-KW transmitter, originally from the Platteville heater. The eight transmitter antennas are managed by a personal computer which controls power, modulation, and beam steering. Methods of tuning the antennas, to achieve either right (O mode) or left (X mode) circular polarized radiated beams, are described. The heater is powered by two 1500-horsepower diesel electric generators. It can be operated throughout the year over −30°C to 40°C ambient temperature extremes. Future improvements include the construction of an even larger 840 × 840 m (24 × 24 antenna) array with a gain of 37.5 dBi.

Variable frequency magnetic field device employing multiple antennae for measuring the surface impedance of a material

Abstract: A surface impedance measurement device comprises a transmitting antenna producing a magnetic field in the area surrounding a material to be tested and a receiving antenna receiving the magnetic field. An electric voltage wobbled in frequency is applied to the transmitting antenna, and a circuit measures the voltage at the terminals of the second antenna. For the antennae to be applied on the same side of the material to be tested and of which the surface impedance is to be measured, the antennae are superposed by the intermediary of a dielectric wedge in a compact probe. The impedance measurements are then independent of the dimensions and geometry of the material.

Absorbed power deposition for various insertion depths for 915 MHZ interstitial dipole antenna arrays: Experiment versus theory

Abstract: Dipole antennas are commonly used in interstitial clinical hyperthermia treatments because of their compatibility with brachytherapy techniques and their good power deposition patterns when used in arrays. For accurate treatment planning, however, there must be a comprehensive knowledge base to predict the power deposition patterns when insertion depth is a non-resonant length. This is especially true for insertion depths that result in significant power deposition outside of the antenna junction plane and presumably outside of the tumor volume. A computer controlled measurement system was used with a muscle equivalent phantom to make measurements of specific absorption rate (SAR) or absorbed power per unit mass of tissue at 598 points in a plane. The diagonal plane was the measurement plane of choice because it characterized the SAR profiles at the array center as well as areas in the proximity of the antennas. Dartmouth dipole antennas were used (0.9 mm O.D.) in brachytherapy catheters with inner catheters (2.2 mm O.D./1.2 mm I.D). The resonant half-wavelength of this dipole antenna/catheter combination is 7.8 cm. A choke modification of the dipole was also investigated. Four antennas were used in a boxlike configuration with 2.0 cm separation. Insertion depths of 5.9, 7.8, 9.8, 12.7, 15.6 and 17.6 cm were used. The h A subsection (junction to tip) was held constant at 3.9 cm. Plots were made of the experimental SAR data normalized to the maximum SAR measured in the plane. Theoretical plots were calculated in the same plane for each of the insertion depths. SAR comparisons were also made longitudinally along the central axis of the array and through the antenna junctions in the diiagonal plane for resonant half-wavelength insertion depth. Experimental results verified theoretical predictions of the existence of a secondary hot-spot in the center of the array, but outside of the antenna junction plane and approximately a quarter-wavelength from the insertion point. This secondary hot-spot appears for all insertion depths greater than 10 cm. At longer insertion depths approaching a full wavelength, however, this secondary peak is not dominant. Choke antennas demonstrated a solution to the problem of shifting SAR patterns with varying insertion depths by restricting the active length of the antenna.

Pulse-receiving characteristics of resistively loaded dipole antennas

Abstract: The pulse-receiving characteristics of resistively loaded dipoles are analyzed using a time-domain numerical technique. The Wu-King nonreflecting dipole and several other dipoles with higher and lower distributed resistances are considered. The time-domain responses of these dipoles to Gaussian electromagnetic pulses (incident in boresite direction) are calculated. Frequency-domain receiving transfer functions are obtained using the fast Fourier transform (FFT) technique. Dipoles terminated with high resistance loads are also considered. The effect of the distributed resistance and terminal resistance on the pulse response and bandwidth is discussed. >

Dual polarization dipole array antenna

Abstract: A dual polarized dipole array antenna for high efficiency power reception or transmission of electromagnetic waves comprises an array of dipole antenna elements and connecting transmission lines, all highly symmetrically arranged each other on a dielectric layer. Rectifiers and wave filters are added to the transmission lines to produce rectified outputs of each dipole antenna element.

A New Class of Scannable Millimeter-Wave Antennas

Abstract: The complexity usually associated with scanning arrays at millimeter wavelengths produces fabrication difficulties, so that alternative methods are needed that employ simpler structures. This paper describes such an alternative scanning approach, and presents a group of new and simpler radiating structures suitable for millimeter-wave applications. Additional significant advantages are that the radiation has negligible cross polarization, no blind spots and no grating lobes. The theoretical analyses for all of the antenna structures are accurate and yield dispersion relations in closed form for most of them; the array analyses take all mutual coupling effects into account. For two of the antennas, measurements have also been taken that show very good agreement with the theory.

Broadband directional antenna having binary feed network with microstrip transmission line

Abstract: A broadband antenna array, formed of pairs of horizontally-spaced dipoles that are balun-fed, uses an air dielectric microstrip binary-feed network to optimize antenna bandwidth. Each dipole is fed by a three-wire balun which maintains the proper current distribution on the dipoles over the operating bandwidth. The binary-feed network feeds each dipole individually to further optimize the antenna's pattern bandwidth. The binary-feed network is formed using a conductive ground plane with spaced conductors to utilize an air dielectric, thereby minimizing antenna losses in the feed network. The feed network impedances are chosen to give a broadband impedance match to the dipoles, and the entire assembly of binary-feed network and dipoles is mounted in a reflector box, the dimensions of which are chosen to control the antenna beamwidth. Vertically stacked pairs are used to compress the vertical radiation pattern for greater antenna gain.

Formulation of normalized site attenuation in terms of antenna impedances (EMI measurement applications)

Abstract: General formulas for normalized site attenuation (NSA) are derived in terms of antenna impedances by using the two-port circuit theory to show the effects of mutual coupling. The investigations focus on the antenna factors and antenna calibration procedures that are appropriate for NSA, and the validity of the NSA concept is discussed on the basis of these theoretical investigations. The NSA measurements are found to be appropriate for site validation when using broadband antennas having constant antenna factors. It is theoretically concluded, however, that the original concept of the NSA may not be applicable to the use of tuned dipole antennas, even after adopting the correction factors specified in the existing ANSI standard. NSA is shown to require different correction factors if the antennas have changeable antenna factors. >

Portable radio communication equipment

Abstract: PURPOSE: To obtain an antenna diversity branch with a small correlation characteristic by providing an antenna to both of two cases turnable at one connection part. CONSTITUTION: Antennas 121, 122 are provided to both of two cases 102, 103 freely-rotatable at one connection part and an antenna is selected based on the reception quality. That is, the 1st antenna 121 and the 2nd antenna 122 are connected to separate printed circuit boards 110, 111 and the printed circuit boards 110, 111 are covered by different chassis 102, 103. Thus, the distribution of a high frequency current flowing to the printed circuit boards 110, 111 or the chassises 102, 103 is different specially when the antennas 121, 122 are energized to acquire a different radiation characteristic. Thus, the portable radio communication equipment provided with plural antenna diversity branches and excellent correlation characteristic is realized. COPYRIGHT: (C)1991,JPO&Japio

Portable transmitter apparatus for inducing alternating current in a buried metallic line

Abstract: A system of apparatus for locating underground metallic lines includes a transmitter apparatus at a first work station above ground for inducing a current in the line and a receiver at a second work station for making field measurements. The transmitter apparatus includes a battery-powered transmitter circuit supported from a portable housing, a ferrite core antenna incorporated within the transmitter circuit, and a separate tank circuit which includes a loop antenna and a capacitor and is tuned to a predetermined operating frequency and is electrically isolated from the ferrite core antenna. The ferrite core antenna transfers energy through a magnetic flux field to the loop antenna, and a magnetic field generated from the loop antenna inductively creates an alternating current in the line which then generates an alternating electromagnetic field about the line at the second work station.

Triangle size effect in spaced antenna wind measurements

Abstract: MF radar ionospheric drift measurements are usually performed by correlating signals from spaced antennas. It has long been noted that the speeds obtained tend to increase to a limiting value when the antenna spacing is increased, and noise was indicated as a likely factor. This paper takes the view that noise is the only significant factor, and, with the help of some simplifying assumptions, shows that elimination of the noise term also eliminates the speed discrepancy on experimental data from two receiving arrays, each with two available spacings.

Superconducting antenna system

Abstract: A superconductive array antenna system provides a substantial improvement of gain, in the range of from about 5 db to over 20 db, at frequencies in excess of 20 gigahertz, and preferably in the range from 40 to 100 gigahertz and beyond. The antenna system includes a phased antenna array, operating at superconductive cryogenic temperatures, with superconductive phasing and switching systems, to permit antenna beam steering and polarization independent of operating frequencies. The invention also permits the elimination of amplifiers and other such elements that have been needed to overcome system losses, and permits further miniaturization of such systems.

Pane antenna having an amplifier

Abstract: An active window pane antenna for use in motor vehicles includes an antenna conductor arranged on the window pane and being connected via a conductor of negligible length to an input terminal of an active four terminal network also arranged on the pane. The output terminals of the network are connected via a first section of a transmission line to an antenna connector whose ground contact is connected for high frequencies to a ground point on the body of the motor vehicle. The impedance of the first section of the transmission line is not negligible for the received frequency bands and the input impedance of the four terminal network is balanced with respect to the first section. A second section of the transmission line extends from the antenna connector to a receiver.

Some potential antenna applications of high-temperature superconductors

Abstract: A review of possible applications of high-temperature superconductors (HTS) to antennas and antenna feed networks is presented. The frequency range of consideration is 1 MHz to 100 GHz. Three antenna application areas seem appropriate for HTS material. (1)Electrically small antennas and their matching networks: An increase in efficiency is possible for electrically short antennas, but at the expense of bandwidth. Substantial radiated power levels (on the order of kilowatts) can be handled by the best HTS material. Substantial improvement may be realized by making only the matching network of HTS material. (2)Feed and matching networks for compact arrays with enhanced directive gain (superdirective arrays): HTS material should permit such arrays to be fabricated that have high efficiency. (3)Feed networks for millimeter-wave arrays: Low-loss feed networks using HTS microstrip transmission lines give many decibels improvement in gain.