Showing papers on "Dipole antenna published in 1978"

Reactively controlled directive arrays

Abstract: The radiation characteristics of an N -port antenna system can be controlled by impedance loading the ports and feeding only one or several of the ports. Reactive loads can be used to resonate a real port current to give a radiation pattern of high directivity. The theory of resonance is extended to include complex port currents and impedance loads. The initial design of an array is obtained by resonating a desired port current vector, which is then improved by an optimum seeking univariate search method. The direction of maximum gain can be controlled by varying the load reactances. Several numerical examples are given for a circular array of seven dipole elements.

A New Travelling Wave Antenna in Microstrip

Abstract: The radiation characteristics of the first higher order mode of microstrip lines are investigated. As a result, a simple travelling wave antenna element is scribed, having a larger bandwidth compared with resonator antennas. A method to excite the first higher order mode is shown. A single antenna element is treated theoretically and experimentally, and an array of four antenna elements is demonstrated.

Basic theory of probe-compensated near-field measurements

Abstract: The general problem concerning the interaction of a probe antenna with the near field of an arbitrary antenna is considered. The application of the Lorentz reciprocity theorem to the problem of determining antenna characteristics, including the far-field pattern, is presented. The data required to correct for the directional effects of the probe, the effect of probe correction on the measured data, and the attendant mathematical computations in rectangular systems are described. Extensions to cylindrical and spherical systems are discussed.

A theoretical investigation of the rectangular microstrip antenna element

Abstract: A theoretical treatment of the rectangular microstrip radiating element has been performed. The element has been modeled as a line resonator with radiation taking place at the open-circuited ends. This has been verified by using a liquid crystal visual detector. With the simplified model, the input impedance and the far fields have been calculated for different resonant modes. The interaction between the radiating ends will effect the input impedance, and this has been considered by defining a mutual conductance. Also, a mutual conductance between microstrip elements has been expressed in far-field quantities and plotted as a function of spacing along the E - and H - planes. The directivity of an isolated element has been calculated as the directivity of one radiating end times the contribution due to the array factor.

The ISEE-1 and ISEE-2 Plasma Wave Investigation

Abstract: The ISEE-1 and ISEE-2 plasma wave investigation is designed to provide basic information on wave-particle interactions in the earth's magnetosphere and in the solar wind. The ISEE-1 plasma wave instrument uses three electric dipole antennas with lengths of 215, 73.5, and 0.61 m for electric-field measurements, and a triaxial search coil antenna for magnetic-field measurements. The ISEE-2 plasma wave instrument uses two electric dipoles with lengths of 30 and 0.61 m for electric-field measurements, and a single-axis search coil antenna for magnetic-field measurements. The ISEE-1 plasma wave instrumentation provides a comprehensive determination of wave characteristics over a broad frequency range, including high-frequency resolution spectrum scans, simultaneous high-time resolution electric- and magnetic-frequency-spectrum measurements, wave normal and Poynting flux measurements, and wide-band waveform measurements. The basic frequency range of the ISEE-1 measurements is 5.62 Hz-311 kHz, although wide-band waveform measurements can be made in selected frequency ranges up to 2.0 MHz using a special long baseline interferometer mode of operation. The ISEE-2 plasma wave instrumentation consists of a 16-channel spectrum analyzer covering the frequency range from 5.62 Hz to 31.1 kHz and a wide-band waveform receiver with the capability of making waveform measurements in selected frequency ranges up to 2.0 MHz.

The 3-Dimensional Radio Mapping Experiment (SBH) on ISEE-C

Abstract: The SBH experiment on ISEE-C will provide maps of the large scale structure of the interplanetary magnetic field from ten solar radii altitude to the Earth orbit, in and out of the ecliptic. These data are necessary to improve our understanding of the solar wind flow and of the propagation of solar disturbances to the Earth magnetosphere whose reactions will be simultaneously studied by ISEE-A and -B. The SBH instrument will track type III solar radio bursts at 24 frequencies in the range 30 kHz-2 MHz thus providing the positions of 24 points along the line of force which guides the electrons producing the radio radiation. The antennas are two dipoles: one (90 m long) in the spin plane, the other (15 m long) along the spin axis. The receiver was designed for high sensitivity (0.3 ?V in 3 kHz BW), high intermodulation rejection (80 dB/1 ?V input for order 2 products), large dynamic range (70 dB), high selectivity (-30-dB response 6.5 kHz away from the center frequency of 10.7 MHz for the 3 kHz BW channels), and high reliability (expected orbital life: 3 years).

Energy deposition in simulated human operators of 800-MHz portable transmitters

Abstract: The measured values of energy deposited in simulated human tissue exposed for one minute in the immediate vicinity of 800 MHz portable radio transmitters are presented. The deposited RF energy was evaluated by temperature measurements. The portable radio used in the tests had a 6-W experimental transmitter operating at 840 MHz. Two different antennas were tested for energy deposition: a sleeve dipole and a resonant whip. The two antennas have given substantially different results indicating different field structures near the two radiators. The experiments with flat slabs have shown that the sleeve dipole deposits higher levels of power density than the resonant whip in the near field although the length of the latter radiator is about half the size of the former. The temperature profiles generated by both antennas inside the head of the simulated operator indicate the presence of a "hot spot" about 1 in below the surface of the temporal bone. This phenomenon was not detected previously at lower frequencies. The short antenna exposes the eye of the operator to more intense power deposition than the sleeve dipole. The temperature increases measured during the investigation are so small that no thermal damage to tissue should be caused by normal use of the portable radio.

Electrically short monopole antennas with dielectric or ferrite coatings

Abstract: A comprehensive analysis of the electrically-small material-clad monopole is performed by representing the various fields by discrete and continuous eigenvalue spectrums. The cladding creates a dominant quarter-wavelength resonant-cavity effect whereby the leakage of radiation at the terminal plane is transformed into a low impedance at the annular feed. The mode coupling taking place at both feed and terminal plane is solved by variational methods to yield the antenna radiation pattern, bandwidth, efficiency and input impedance as a function of electrical size and frequency. The agreement between the computed and measured results establishes the usefulness of the analysis, and design curves are presented; other factors that influence the system performance of the antennas in practice are discussed. It is concluded that the optimisation of this type of antenna centres on the choice of suitable low-loss material with comparable relative permeability and permittivity values at the frequency of interest. In general, this calls for research into improved materials, but useful antennas can be made with commercially available materials.

Coaxial phased array antenna

Abstract: Disclosed is a coaxial antenna array for communicating circularly polarized electromagnetic radiation. A pair of open ended antenna cavities is coaxially constructed and operates by excitation of linear radiation elements arranged within each of the cavities. A pair of crossed-dipole radiation devices are centered within the inner cavity and operated by means of a phase-shifting network circuit to transmit as well as receive circularly polarized radiation. Four monopole radiation devices are symmetrically arranged to operate in the outer cavity in phase quadrature by means of the phase-shifting network circuit to also both transmit and receive circularly polarized electromagnetic radiation. Combined operation of the two antenna cavities with a 180° phase differential between the fields related to the two antenna cavities provides a broad beam, relatively wide frequency bandwidth communication capability. Particular embodiments disclosed feature a generally square cavity array as well as a circular cavity array.

Corner fed electric microstrip dipole antenna

Abstract: A corner fed electric microstrip dipole antenna consisting of a thin eleccally conducting, rectangular shaped radiating element formed on one surface of a dielectric substrate, the ground plane being on the opposite surface. The feed point is located at one corner of the antenna element and the input impedance is matched with a matching microstrip transmission feed line connected to the corner of the antenna. The length of the radiating element is greater than the width and determines the resonant frequency along the Y axis (i.e., length dimension) and the width determines the resonant frequency along the Z axis (i.e., width dimension). This antenna is capable of generating linear polarized radiation along the length thereof with minimal cross-polarization when the radiating element width dimension approaches one-quarter waveguide wavelength and less using a single corner fed element and single feed point. Elliptical polarization is also available with the rectangular radiating element.

Antenna pattern synthesis and shaping

Abstract: An antenna utilizes components of spatial harmonics to synthesis and shape radiation patterns. A counterpoise mounts a monopole radiator as well as a plurality of arrays of parasitic antenna elements excitable by the monopole radiator in a manner to produce the selected harmonics and consequently the desired radiation pattern. The parasitic antenna elements are compensated and are provided with switching to cause their activation. A cone radiator cooperates in exciting the parasitic antenna elements.

Method for determining antenna near-fields from measurements on a spherical surface

Abstract: A method for determining antenna near-fields from measurements on a spherical surface. Phase and intensity values are measured by scanning a probe antenna over a spherical surface. The method applies both to planar or conformal antennas. The spherical surface may be in the Fresnel or Fraunhofer regions. The field at the antenna is computed utilizing the complex conjugate of the measured field. As a result, the source antenna at the point at which the antenna radiating field is evaluated is inside the measurement surface. Far-field patterns can be computed from the near-fields reconstructed from the spherical hologram surface.

Input impedance of a monopole antenna at the center of a finite ground plane

Abstract: A technique for computing the input impedance of a monopole on a finite ground plane is provided. The case of an infinite ground plane is first examined, and then the concept of using a magnetic edge current as an equivalent source of diffraction on the limited size ground plane is introduced. The technique used is serf-consistent in that the circular ground plane considered is the limit of a polygonal ground plane as the number of sides tends to infinity. Good agreement has been demonstrated when the nearest edge of the ground plane is at least 0.3 wavelength from the base of the monopole.

Antenna system for electronic security installations

Abstract: An antenna system for an electronic security installation comprising a pair of substantially identical planar multiple loop antennas respectively connected to the transmitter and receiver of the security system and providing an electromagnetic field of high intensity only in the interrogation region of the system while also discriminating against interferring signals originating outside of the interrogation region. Each planar antenna includes two or more loops lying in a common plane with each loop being twisted 180° with respect to each adjacent loop to be in phase opposition. The transmitting antenna and receiving antenna are substantially identical in size and configuration, and each antenna has a total loop area of one phase equal to the total loop area of opposite phase.

Antenna system with multiple frequency inputs

Abstract: An improved antenna system is disclosed in which a single antenna array is simultaneously used in conjunction with several independent radio devices. Isolated and independent radio transmitters are coupled, without any signal cancellation, to each and every one of a plurality of isolated independent antenna elements by a combining network which maintains the isolation between each of the radio transmitters and each of the antenna elements. The combining network comprises an array of hybrid networks and creates a predetermined electrical phase difference between each signal received by an individual antenna element. The antenna elements form a single antenna array consisting of circularly disposed corner reflector antennas. Each reflector independently creates an individual radiation pattern and these patterns combine to form a single desired composite radiation pattern. By maintaining isolation between each of a number of radio transmitters, a plurality of these transmitters may be used simultaneously in conjunction with a single antenna array.

Electromagnetically Coupled Microstrip Dipole Antenna Elements

Abstract: An electromagnetically Coupled (EMC) member of the microstrip dipole antenna family is described. Several configurations differing in the dipole location and in the amounts of electric and magnetic coupling to the micro-strip line yield different bandwidths, efficiencies and construction simplicity. The transformer action inherent in EM coupling allows a wide variation in matching conditions. Radiation characteristics of the element and examples of arrays constructed with the element are described.

Antenna apparatus for bearing angle determination

Abstract: Antenna apparatus for representing a bearing angle includes an antenna array of N antenna elements equispaced around the arc of a circle of at least 90°, and preferably greater than 180° in a plane for receiving microwave energy, microwave power dividing and phase transforming matrix having N input ports respectively connected to the antenna elements and a set of output ports connected to a utilization device for indicating the bearing angle of the incoming microwave energy, and a utilization device including means for measuring the phase difference between signals at pairs of the output ports for representing the bearing angle.

Antenna system using antenna base impedance transforming means

Abstract: An antenna system is disclosed for plural band radio receivers having a common antenna. The system is especially adapted for AM/FM automobile broadcast receivers and may be used with a CB transceiver with a tri-band antenna. An impedance transforming means is provided at the base of the antenna and a single transmission line or lead-in cable extends from the impedance transforming means to the AM/FM receiver. The impedance transforming means has a high input impedance for the AM and FM bands and a relatively low output impedance to minimize the signal loss in transmission from the antenna to the receiver. The impedance transforming means includes a field effect transistor in a common source configuration and means are provided to produce substantially 100% voltage degeneration for both AM and FM signals. The impedance transforming means is also useful for automobile AM broadcast receivers to avoid the need for alignment of the antenna trimmer after installation of the antenna and lead-in cable on the automobile.

Conformal spiral antenna

Abstract: An electrically small, microstrip radiator designed for small-diameter mile applications. The preferred embodiment comprises a cylindrical tube of epoxy fiberglass dielectric having a spiral conducting strip formed thereon. The tubular construction permits the antenna to be conformally mounted to the surface of the missile. RF input coupling may be achieved by an inductive post, and high radiation efficiency is obtained by strongly coupling RF currents to the body of the missile and exciting the dipolar mode of radiation. The design includes means for mechanically tuning the antenna over a narrow frequency range. The resultant spiral-slot antenna produces an axially polarized radiation field and a dipole radiation pattern with isotropic gain in a low cost and rugged construction.

Design of a Miniature Directional Antenna for Geophysical Probing from Boreholes

Abstract: In this report we describe a design for a miniaturized directional antenna for use in geophysical exploration from boreholes Mathematical results are given which indicate the antenna characteristics The concept we use involves an antenna eccentrically located within a high dielectric constant or high permeability sheath

Ground and/or feedline independent resonant feed device for coupling antennas and the like

Abstract: A feed device is tuned to resonance at a selected frequency, to provide essentially infinite impedance between, for example, a system being fed and the power source. The feed device allows passage of feedline currents, which are equal in magnitude and opposite in phase, but prevents passage of any other, unbalanced currents, e.g., common mode currents, antenna radiation currents, etc. This is due to the fact that the infinite impedance of the feed device defines extremely high attenuation to currents other than feedline currents, at the selected frequency. Thus the resonant feed device acts as an isolating circuit for transmitting and receiving antenna systems and the like, since any unbalance in the antenna elements is isolated from the feedlines, and vice versa, whereby the antenna is truly ground and/or feedline independent. When the antenna is located far from a conducting ground two of the resonant devices are required, however only one resonant device is required when the antenna is located in close proximity to a conducting ground.

Flexible dipole antenna for hand-held two-way radio

Abstract: A completely flexible dipole antenna is formed from coaxial cable having a braided wire core with skirt also formed of shielding over a flexible sleeve. A coil spring which is not electrically active supports the antenna above the connector. A non-wearing female connector utilizes a flexible conductive elastomer contact contained within an insulating body.

Parameters of a spherical random antenna array

Abstract: The shape of the beam of a spherical random antenna array is discussed and the main parameters, such as bandwidth, beamwidth and hyperfocal distance are determined.

Heat Potential Distribution in an Inhomogeneous Spherical Model of a Cranial Structure Exposed to Microwaves Due to Loop or Dipole Antennas

Abstract: An inhomogeneous spherical model of a 3.3-cm radius cranial structure is assumed to be placed symmetically in the near field of a small loop antenna or an electrical dipole antenna at 3 GHz. The transitions between the layers are taken to be sharp but sinusoidal. Calculations of the heat potential are performed using a spherical wave expansion technique in which linear differential equations are solved for the unknown multipole coefficients. The results are also compared with the plane-wave excitations. It is seen that a more uniform distribution of the heat potential occurs for the dipole antenna excitation which is also similar to the E-plane distribution in the case of plane-wave excitation. For the loop excitation, a significant hot spot occurs near the center of the structure.

Parabolic and log periodic antennas combined for compact high-gain broadband antenna system

Abstract: The disclosed antenna system includes a non-conductive parabolic dish, a first antenna array rigidly positioned in front of the dish, and a second antenna array extending through the dish and having radiating elements on either side thereof. In one embodiment, a plurality of conductive strips are disposed on the dish in a polarization selective pattern; the first antenna array generates linearly polarized electric fields that are reflected by the strips; and the second antenna array generates linearly polarized electric fields that pass through the strips. In another embodiment of the invention a plurality of conductive areas are disposed on the dish in a checkerboard frequency selective pattern; the first antenna array generates electric fields in a frequency band that are reflected by the pattern; and the second antenna array generates electric fields in a frequency band that are passed by the pattern.

Coupling an outer antenna with a radio receiver having a bar antenna

Abstract: Coupling an outer antenna with a radio receiver having a bar antenna is achieved by connecting the outer antenna to a coupling coil which is able to be removably mounted on a bar core of the bar antenna and by mounting the coupling coil on the bar core with such an orientation of the coupling coil that the signal received at the outer antenna does not cancel the signal received at the bar antenna. The connection between the outer antenna and the coupling coil may be made by the use of a coaxial cable with the outer conductor of the cable being not grounded to function as a ground plane. A series circuit of a switch and a resistor may be connected in parallel with the coupling coil to selectively reduce the quality factor Q of the bar antenna.

Portable dipole antenna with end loading

Abstract: A portable antenna construction is provided for high frequency radio transmission and reception. A physically and electrically shortened center-fed dipole, the antenna includes a driven element assembly 62, a center insulator assembly 60, a center loading coil assembly 74, two end loading coil assemblies 70 and 72, two capacity hat assemblies 64 and 68, and a mast assembly 63, each such assembly constructed from parts allowing for easy assembly and disassembly. The antenna further includes a carrying case 78 of sufficient size to hold all disassembled parts, so that such disassembled parts can be easily transported. Center loading coil assembly 74 includes a center loading coil 76 having multiple tap points 77 for transmission line connection, thereby permitted impedance match at any frequency to which the antenna is tuned. End loading coil assemblies 70 and 72 include end loading coils 71 and 73 respectively, each having multiple tap points, permit the antenna to be specifically tuned to resonate at the desired frequency. This linearly polarized antenna, requiring no ground and is easily pivoted between horizontal and vertical modes of polarization. When utilized in the vertical mode, the lower dipole half acts as an image counterpoise so that no ground plane is necessary. Large center 76 and end loading coils 71 and 73 provide high Q for maximum radiation at the tuned frequency.

Antenna for cross polarized waves

Abstract: An antenna comprising a metal panel on which are mounted two parallel collinear dipole arrays spaced on the order of a half-wavelength from each other. Each dipole array is of the order of 9 wavelengths long and is fed at its center. Half way between the two collinear arrays is mounted a zigzag antenna with its center located half way between the centers of the collinear arrays which may be staggered with respect to each other. The two collinear arrays are fed in the same relative phase with each other. The zigzag antenna and the dipole array may be fed from different sources operating at different frequencies or they may be fed from the same source and phased to radiate circularly polarized waves. A plurality of the panel antennas may be mounted around a metal cylinder to serve as an omnidirectional antenna. A square tower may serve as the metal cylinder. Several levels of one to four antennas may be mounted on a square tower depending on the shape of the area to be served.

Flexible dipole antenna

Abstract: A flexible strap-like antenna which may be supported on the outside surface of an aerostat includes a first substrate member having conductors thereon in a pattern which includes a center conductor and dipole antennas on either side of the center conductor. A ground conductor is disposed over the center conductor and is electrically insulated from it by an insulating strip sandwiched between them. A second or covering substrate seals the layered arrangement. To achieve broad band operation, an array of antennas is provided with the width of the center conductor being varied for certain different sections thereof.