Wire Dipole Research Articles

The Resonance Structure of the Bistatic Radar Scattering Cross Section of Randomly Oriented Dipoles

A definitive method for the calculation of the bistatic radar scattering cross section of a cloud of randomly oriented conducting wire dipoles has been developed by Dedrick et al. [6]. It is based on a Stokes parameter formalism, thus containing complete information regarding transmitter and receiver polarizations. Since the single-wire cross section exhibits strong resonance effects, it is of interest to investigate to what extent these resonance phenomena are affected by the orientation average in a cloud of randomly oriented wires. To study this question, we present comprehensive three-dimensional graphs of the relevant bistatic cross sections plotted versus scattering angle and frequency, as well as of the various polarization functions, using the Einarsson wire cross section. The results indicate the degree to which the resonance features persist in both cross section and polarizations after orientation averaging.

On quasi‐static source models for wire dipole antennas

AbstractThe moment method computation of the input impedance of dipole antennas, obtained using numerically generated source models which are more closely related to the actual physical shape of the antenna feed region, are discussed.

Theoretical increase in radiation efficiency of a small dipole antenna made with a high temperature superconductor

An electrically small wire dipole antenna with a shunted stub matching network has been analyzed to determine the improvement in radiation efficiency that can be achieved by making the metallic components from high-temperature superconducting (high T/sub c/ or HTS) material. The analysis shows that significantly higher radiation efficiencies can be obtained with HTS material only if the dielectric losses are kept to very low values. A loss tangent of less than 10/sup -4/ is necessary for any dielectric materials in the transmission lines and support structures for the antenna; a loss tangent of at least 10/sup -5/ is desirable, particularly if the dipole length is 0.1 wavelength or less.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Thin wire dipoles—a finite-difference time-domain approach

The computation of thin wire dipole radiation patterns using the finite-difference time-domain method is discussed.

Electrostatic noise in non‐Maxwellian plasmas: “Flat‐top” distribution function

We calculate the electrostatic noise spectrum that should be measured by an antenna immersed in a plasma with a “flat‐top” electron velocity distribution function, for frequencies of the order of the plasma frequency fp. We find that the main part of the spectrum is nearly the same as the thermal noise in a Maxwellian plasma with the same density and equivalent temperature, while the peak near fp depends on the high‐energy tail of the distribution. We consider both wire dipole and double‐sphere antennae, and deduce some practical consequences for plasma wave measurements in the Earth magnetosheath.

Tool kit for antennae and thermal noise near the plasma frequency

This paper provides the essential tools for deriving quickly the quasi‐thermal noise spectrum or the impedance of a given electric antenna near the plasma frequency, for calibration or diagnosis in space plasmas. We give simple analytical expressions and numerical results for either wire or sphere dipoles in an isotropic plasma with one or two Maxwellian electron populations. We include the contribution of the particles collected and/or emitted by the antenna surface. We also indicate some modifications brought about by using more complicated antenna geometries, and a drifting or a magnetized plasma. Finally, we give some conclusions for antenna design or data interpretation in plasma wave experiments.

Electromagnetic direction finding from an antenna array configured near an elliptic cylinder

In this paper, an effort is made to attack the problem of electromagnetic direction finding (DF) by an antenna array configured near a perfectly conducting elliptic cylinder. Over the range of interest, the cylinder has an axial ratio that varies from 1:1 to 1:30. Results for the array with three wire dipoles show the practicality of such an array.

Confocal Fabry-Perot microwave resonator at 48 GHz for high-resolution spectroscopy

A high-Q confocal Fabry-Perot microwave resonator for precision spectroscopy of atoms, ions and molecules is described, giving convenient access to the overlap region of interacting species, microwave field and light. Microwave power is coupled with almost 100% efficiency into the interferometer by means of a small copper wire dipole antenna. The concept of an uncomplicated and inexpensive frequency stabilisation of microwave sources through coupling to a Fabry-Perot reference resonator is discussed.

The Llanherne VHF Radio Telescope

The Llanherne telescope is a meridian transit instrument with an instantaneous bandwidth of two octaves in the range 35 to 150 MHz, and was constructed primarily for studying the low frequency properties of pulsars. The antenna is a 78 × 156 metre filled aperture phased array comprising 4096 wire dipole elements arranged in a 64 × 64 matrix. Uniform illumination of the elements produces a single pencil beam response which is scanned electronically along the meridian from Declination -90° to +30°. The beamwidth at 100 MHz is 1 degree in right ascension and two degrees sec(Dec.) in declination and varies proportionally with wavelength, giving a transit time of 4 sec(Dec) × 100/f(MHz) minutes between half power points.

Microwave Probes for Electric Fields Near Metal Surfaces

An experimental study was made to isolate the types of probe errors made in measuring electrical boundary conditions and nearfield waves over the surfaces of metal diffracting objects and antennas. Because their patterns could be calculated for comparison with measurements, thin metal disks were employed ranging in diameters from 0.1 to 10 wavelengths. The microwave wavelengths ranged from 2 to 80 cm and the probe sizes ranged from 0.50 to 0.01 wavelength long. The probes consisted of wire dipoles with the microwave circuits confined to the detector capsule at the centers of the dipoles. Three types of probe errors were studied: 1) multiple reradiation between probe and surface of object when the axis of the probe is parallel to the surface, 2) bringing the tip of the probe closer than a hundredth of a wavelength from the surface of the object when the fields between the tip and the surface are shaped like electrostatic fields and found to be grossly affected by changes in the spacing, and 3) lengths of probes large compared to the radius of curvature of the lines of force, a limiting case in the measurement of fields near the edges of metal sheets.

Some measurements of aerial impedance in the ionosphere

The admittance of a wire dipole of overall length 20 m was measured at a height of approximately 125 km in the night-time ionosphere. Measurements were obtained at 60 kHz and at a frequency swept over the range 1.4 MHz to 1.8 MHz so as to include the gyro frequency. The results are interpreted in terms of a theory due to Kaiser, and fair agreement is obtained. The electron density and collision frequency in the plasma surrounding the aerial are estimated.

A new method for the measurement of the average dielectric constant of the underground medium on site

An electromagnetic interference pattern in the far-distance condition is utilized to determine the average dielectric constant of the underground propagational medium. The method depends upon the determination of the surface wave velocity by means of measuring the first self-resonance frequency of a dipole wire laid on the earth's surface.