Showing papers on "Slot antenna published in 1968"

A simple formula of current in dipole antennas

Abstract: A simple and quantitatively accurate representation of the current distribution in a dipole antenna is derived. Numerical data are given and are found to be in good agreement with the experiment when h \geq O.15\lambda .

Holographic antennas

Abstract: Antennas having any mean surface and any prescribed feeder and radiation pattern can be experimentally obtained by the extension of the holographic technique to the microwave field. An experiment is described, based on the simple case of a plane antenna. Different types of microwave holograms, which constitute the synthesized antenna, have been tested.

Theory of conical equiangular-spiral antennas: Part 2--Current distributions and input impedances

Abstract: According to the behavior of the current, an equiangular-spiral antenna may be divided into three distinct regions. Since the positions of these regions are frequency independent, it is possible to obtain a complete description of the current distribution on almost all practical equiangular-spiral antennas by a set of carves, which is given in this paper. It is also found that for rapidly expanding antennas there are, in general, two or more active regions that are characterized by differences in rate of attenuation. Such a phenomenon is interpreted in terms of the Brillouin diagram. A variational formulation of the input impedance of the antenna is also presented. The variation method using the approximate current provided by the set of curves gives a quick, direct means of finding the input impedances.

Transmission line loaded annular slot antenna

Abstract: A probe is connected to the bottom of a cavity, and a spiraled conductor is connected to the top of the probe, where the outer turns of the spiral are spaced from the cavity top edges to form an electrically small slot. This antenna is fed from the cavity bottom near the probe by the extension of the center conductor of a terminated coaxial line.

Numerical solution of dipole radiation in a compressible plasma

Abstract: The electric current and surface electron distributions for a dipole antenna in a compressible plasma are solved numerically. The results also include the input impedance and the upper limit of the driving voltage below which the small signal approximation is valid.

Digital computer analysis of aperture antennas

Abstract: Digital computer predictions of aperture antenna patterns are shown to be far more complete, in terms of information concerning the field vectors over virtually unrestricted angular sectors and even at short distances, when vector rather than scalar diffraction theory is applied.

Far field of large circular loop antennas: Theoretical and experimental results

Abstract: Far field patterns of large circular loop antennas of circumferences up to two and one-half wavelengths were calculated using Storer's theory for the current distribution on the antenna. To verify the theory, radiation pattern measurements were made at 3 GHz; the experimental results are in good qualitative agreement with theory.

Rollable slot antenna

Abstract: An antenna having a rectangular sheet of metal foil with parallel spaced slots formed therein. The slotted sheet serves as a radiator operating in the UHF band. The metal sheet is enclosed between overlying and underlying plastic sheets which are heat sealed to the metal sheet. The composite laminate structure is flexible thus permitting the rolling thereof.

Crescent shaped cavity backed slot antenna

Abstract: The invention comprehends a cavity backed slot antenna having improved RF bandwidth characteristics. The cavity is cylindrical and has a series coaxial transmission line feed which provides radially symmetrical TEM mode cavity field excitation. The slot is substantially crescent shaped. A radially disposed vane member within the cavity is used to generate an internal E field.

A log-periodic cavity-backed slot array

Abstract: This communication describes the element investigation, design, and testing of a backfire log-periodic cavity-backed slot array operating from 2.8 to 5.9 GHz in a frequency-independent fashion. The gain of the antenna is approximately 10 dB, and the VSWR is below 2.5 to 1. The H -plane power patterns are given with nearfield plots along file array. The advantages of the antenna are a simple stripline feeding system and the fact that the structure protrudes a little because shallow cavities are used.

Leaky waveguide continuous slot antenna

Abstract: A continuous slot leaky waveguide antenna for radiating radio frequency sohat the far E-field elevation pattern will closely follow a predicted pattern.

Waveguide-fed log periodic antennas

Abstract: : Almost all log periodic antenna designs incorporate a parallel or tapered-vee transmission line, as the feeding mechanism for the radiating elements. These lines propagate the TEM mode. Techniques whereby log periodic antennas may be fed with waveguides are introduced in this report. In this case the dominant TE sub 10 mode of the waveguide is used in the feeder transmission line application. Methods of coupling energy to the radiating elements of the log periodic structure by probes inserted in the waveguide are presented. It is shown that an array may be fed either on the broad wall or narrow wall of the waveguide. The useful operating frequency range of these antennas is limited to the normal waveguide bandwidth. The waveguide-fed method is primarily useful for monopole arrays although dipole arrays can also be fed in this manner. Results of measurements performed on various antenna models are discussed. It is shown that VSWR responses below 2:1 and absolute radiation pattern gains above 10 db can be achieved. The effects of different design parameters on antenna characteristics are discussed. In addition, a requirement is presented in which either the element lengths or element spacings must be compensated to achieve constant H-plane radiation patterns. (Author)

Improvement of Pattern Circularity of Panel Antennas Mounted on Large Towers

Abstract: Three techniques using partial skew are developed in this paper. They do not lead to the same degree of smoothing of the patterns of circular arrays as the 90 °skew, but they present the advantage of being less sensitive to the presence of the supporting structure. They also provide a large flexibility in the choice of dimensions and feeding systems of such antennas.

Constant-beamwidth antenna development

Abstract: Broad-band microwave receiving and tracking systems generally require medium to high-gain antennas that have a minimum beamwidth requirement dictated by probability of intercept and acquisition time considerations. This paper discusses a technique whereby the secondary pattern beamwidth variation is decreased or eliminated over portions of the frequency band of these antennas. The antennas consist of a parabolic reflector illuminated by a ridge-loaded horn. A brief analysis, based on empirical antenna equations, is presented along with a description of a pencil-beam antenna and a very broad-band conical-scan tracking antenna that were made possible through the use of this technique.

Electromagnetic scattering by slots on a sphere

Abstract: The scattered field when a plane wave is incident on a slotted perfectly conducting sphere is obtained by superposition of the scattered field from an unslotted sphere and the radiation field from the slot on the sphere. The slot is a finite, thin circumferential slot backed by a cavity which is characterised by an admittance. The induced voltage is represented by a sinusoidal distribution. The amplitude of the induced voltage is then related, in the combined problem, to the incident field by expressing it in terms of the radiating and load admittance of the slot. Expressions for the radiation admittance and the scattered fields are derived. Positions of slots with respect to the orientation of the incident plane wave which give rise to maximum or minimum scattering are discussed. Various special cases, such as the half-circumferential slot and the full-circumferential slot, are also derived.

A Method of Obtaining a Smooth Pattern on Circular Arrays of Large Diameters with cos n Φ Elements

Abstract: There are many applications on which one would want to obtain an omnidirectional pattern by mounting many directional antennas around a large structure. If the structure is many wave-lengths in size and if the directional antennas are mounted pointing radially out, then the resulting pattern will usually present very rapid excursions in amplitude with very deep nulls. If one assumes that the directional antennas are of the type cosn ϕ(-π/2⩽ϕ⩽π/2 and zero elsewhere), which are closely approximated by many practical anteunas, then it is possible to smooth out considerably the resulting pattern by pointing the directional antennas tangentially to a circle circumscribing the structure and by properly choosing the radius of the circle. The number of antennas to be uesd determines the value of n.

Aperture coupling in cylindrical dielectric-rod antennas

Abstract: Computed and measured data show that mutual coupling between the launcher and rod-end apertures of a uniform cylindrical dielectric-rod antenna is responsible for certain second-order effects in the radiation pattern. The synthesis of a smooth tapered dielectric antenna by a stepped profile and complications arising from interstep coupling are also discussed.

Investigations on Waveguide-fed Slot Antenna: Equivalent Network Representation

Abstract: The paper presents investigations on equivalent network representation of displaced narrow longitudinal slot as the length of the slot is varied over the range 0·44–1·5 λ. It is shown that the scattering coefficients (symmetrical, antisymmetrical and unsymmetrical) as also the discontinuities in terminal voltages and currents corresponding to the equivalent network depend upon the nature of the field distribution (odd, even or general) in the slot. The equivalent network is realizable in the form of a T or a π. The T and π-networks may be approximated by shunt and series elements respectively. From the elements of the T and π-equivalent networks, the important parameters such as scattering coefficients and scattering metrix and hence the effect of the slot on the wave propagating down the waveguide have been found. Further, a knowledge of the above parameters provides information regarding the change in the nature of field distribution in the slot with change in its length.

The insulated cylindrical antenna in a cold plasma with a longitudinal magnetic field

Abstract: The tangential electric field excited on the conducting surface of a transmitting antenna is calculated by modifying a variational impedance formulation. For an antenna in a magnetoionic medium, the boundary condition requiring that the tangential electric field vanish on the surface is satisfied to approximately the same degree as for dielectric coated antennas, where the variational solution can be verified by comparisons with experimental and other theoretical studies.

An experimental study of simulated plasma-covered slots on cylinders and cones

Abstract: The effect of a plasma on the radiation characteristics of slot and gap apertures located on cylinders and cones has been studied by means of a plasma simulation technique. The relative index of refraction of less than unity between the plasma and free space was maintained for the model by an analog tank in which free space was represented by a high dielectric constant liquid and plasma by a lower dielectric material. The antenna pattern of an axial slot on a cylinder with a simulated plasma covering had good agreement with theory for radiation in the equatorial plane, as did the antenna pattern for a simulated plasma-covered, center-fed, cylindrical antenna. The experimental pattern of a cavity-fed circumferential slot on a cone-hemisphere covered with simulated plasma is also presented.

Enhanced radiation from a plasma-imbedded antenna

Abstract: The radiation of a monopole antenna imbedded in a finite volume of plasma can be enhanced if the antenna is operated at a frequency much lower than the plasma frequency and the antenna dimensions are properly chosen. Experimental observations are reported.

Admittance of an annular slot in a magnetoplasma

Abstract: The admittance of an annular slot situated on a perfectly conducting, infinite plane screen covered with an unbounded, uniform magnetoplasma is investigated for the case when an external static magnetic field is perpendicular to the plane of the screen. The slot is assumed to be driven by a coaxial line which in turn is excited in its dominant TEM mode, and the field in the slot is approximated by that incident on it. A generalized plane wave representation for the fields is developed using Bessel transforms, and integral expressions are derived for the admittance of the slot. Extensive numerical results and a detailed discussion of the dependence of the admittance on the strength of the static magnetic field, the complete range of operating frequencies, and the radius and the width of the slot are also included.

Microwave diagnostics of the plasma sheath produced by slot antenna breakdown

Abstract: The plasma sheath caused by pulsed RF breakdown in helium outside the aperture of a waveguide radiator has been probed. The highest measurable phase shifts and attenuation changes caused by the plasma were compared with those calculated on the basis of a slab model. The results are consistent with an effective thickness of the plasma sheath of about 1 cm, and electron densities in the active sheath being considerably in excess of the critical value.