Showing papers on "Slot antenna published in 1973"

Effects on Correlation Between Two Mobile Radio Base-Station Antennas

Abstract: The correlation between signals received by two mobile radio base-station antennas is investigated to determine spacing requirements for space diversity. Measurements of the fading of UHF signals received by two base-station horn antennas oriented at different angles with respect to the incoming mobile radio signal were made for different antenna spacings. The experimental results are compared with an analytical expression derived in this paper; they agree fairly well. A further experiment was made after removing the possible local scatterers surrounding the base station. Comparing these two experimental results, we find that the following are true. 1) Propagation in the direction of a line connecting the two base-station antennas is the critical case and requires a large separation of 70 wavelengths. As soon as the incoming wave is 10° away from the inline axis, the spacing requirement drops to 30 wavelengths. 2) Local scatterers at the base station tend to decrease the correlation between signals received at the two antennas. We conclude that an upper limit to the spacing of antennas used for diversity can be obtained and that it is within the achievable range.

Electromagnetic propagation between antennas submerged in the ocean

Abstract: Experiments are described for determining the distributions of current, the driving-point impedance, and the electromagnetic fields characteristic of dipole antennas immersed in the sea near the surface. Measured and theoretical results are compared at two frequencies with good agreement.

Impedance properties of a longitudinal slot antenna in the broad face of a rectangular waveguide

Abstract: The impedance properties of a waveguide longitudinal slot antenna of arbitrary length and offset in guide walls of finite thickness are investigated. These properties are obtained by treating the slot discontinuity as an electromagnetic boundary value problem and the resulting pair of coupled integral equations are solved by numerical techniques. Results are given for slots having lengths from 0.35\lambda to 1.7\lambda and are in good agreement with experimental results.

Impedance and radiation pattern of antennas above flat discs

Abstract: Antenna imaging by a perfectly conducting finite flat disc is investigated analytically and numerically as a function of the radius of the disc. A conical monopole of variable length is considered above the screen and the normalized terminal admittance of the antenna is plotted versus the disc radius. The radiation pattern is also plotted and the current distribution above and below the screen is evaluated. The results provide a quantitative measure of the effectiveness of finite screens in imaging antennas and bring to light the persistent distortion of the pattern caused by the finite size of the screen in contrast to the behavior of the impedance.

Equivalent-circuit representation and characteristics of a radiating cylinder driven through a circumferential slot

Abstract: The problem of an infinitely long coaxial cylinder with a single circumferential slot in the sheath is investigated analytically. When the slot width is small compared with the radius of the outer cylinder, an exact integral equation for the aperture field is formulated and subsequently solved by a quasi-static technique. Equivalent circuit representation of the coupling between the outside antenna and the inside coaxial line is obtained in closed form. Due to the highly localized nature of the coupling, the result thus obtained is applicable to finite cylindrical antenna with multiple feed slots.

Cavity backed dipole-slot antenna for circular polarization

Abstract: Aerial for receiving or transmitting circularly polarized electromagnetic radiation includes a dipole mounted substantially within the aperture of a slot and means for coupling the slot to the dipole asymmetrically. It may also include an electromagnetic cavity adjacent the coupled dipole and slot. In one embodiment the dipole is formed on one side of an insulating substrate and a narrow conductor is formed on the other side substantially opposite the dipole, with part of the dipole, the substrate, and the conductor together forming a stripline feed which may have a matching network formed by a further part of the dipole, the substrate, and the conductor.

The performance of transistor fed monopoles in active antennas

Abstract: The performance of radiating elements in the form of monopoles and driven by transistors is examined theoretically and experimentally. A single element comprising a printed monopole over a ground plane and fed at its terminals by a microwave transistor is shown to have superior frequency characteristics compared to the passive element. Using a two-element array configuration, it is verified that the mutual impedance values are suppressed. The improved individual characteristics of the active elements together with their mutual behavior combine to produce a significantly improved frequency performance of the array. The results presented suggest that the transistorized array principle offers a means both of maintaining directivity of a transmitter, and discriminating against interfering sources by a receiver, over a greater frequency band.

A practical method for measuring the complex polarization ratio of arbitrary antennas

Abstract: A technique for measuring the complex polarization ratio of an arbitrary antenna is presented. The technique requires the use of two antennas which are not circularly polarized but are otherwise arbitrary. Only reciprocity and linearity are assumed. Six amplitude and phase measurements are performed, two measurements for each pair of antennas. The complex polarization ratio of each antenna is then calculated from the six measurements. The specific details of the measurement technique are described and some measurement results presented.

Antenna - aperture distributions from holographic type of radiation-pattern measurement

Abstract: Two methods are presented for determining antenna aperture distributions from the magnitudes (moduli) of radiation patterns. Antennas under test are measured in the presence of fixed-reference antennas. Invoking the principle of holography, the radiation-pattern measurements are arranged so that all the required information can be obtained without having to make any phase measurements. The methods are illustrated with laboratory experiments, performed with acoustic antennas, for which the aperture distributions are determined to an estimated accuracy of within 5%.

Radiation characteristics of a waveguide excited dielectric sphere backed by a metallic hemisphere

Abstract: The experimental results of the radiation characteristics of waveguide excited dielectric spheres backed by metallic hemispheres are reported. The test antenna consists of a dielectric loaded hemispherical horn excited by a circular waveguide. The test data have shown that such a structure produces a radiation pattern with low sidelobe levels, increased on-axis gain, and reduced 3 dB beamwidth as compared to a waveguide excited dielectric sphere of same diameter and an optimum horn having an aperture of identical cross section area. Also, it presents a low VSWR over the waveguide band.

Measurement of the radiation patterns of full-scale HF and VHF antennas

Abstract: A system has been developed to measure the directivity patterns of full-scale antennas when located in their operational environments. The primary component of this system is an aircraft-towed multifrequency transmitter that is designed to approximate an elementary dipole antenna. An HF and a VHF version of this transmitter provide frequency coverage from 2 to 100 MHz. Techniques have been developed to measure the entire radiation pattern, from the horizon to the zenith, for several antennas simultaneously. Data derived from this system are processed to provide the radiation patterns as contour plots of the measured signal strength on azimuthal equal-area projections. The measurement hardware, data acquisition, and data processing techniques are described, and examples are given of measured and processed data derived from the system.

Radio frequency slot antenna

Abstract: A stripline slotted array antenna is disclosed wherein the radiating efficiency and bandwidth are improved by including in each radiating element a pair of adjacent radiating slots. The antenna includes center conductor circuitry separated from a pair of ground plane elements, one of which is the radiating face of the antenna and one of which is the back plate of the antenna. The pair of slots is formed in the radiating face of the antenna. The pair of radiating slots is disposed adjacent to an end portion of the center conductor circuitry, one being coupled to an electric field existing between the end of such circuitry and the back plate and the other one of such pair of radiating slots being coupled to an electric field existing between the center conductor circuitry and the radiating face of the antenna.

Reception Characteristics of Monopole Antennas for Electron Plasma Waves

Abstract: The radiation patterns of a longitudinal electron plasma wave excited in a warm unbounded plasma by a grid and parallel plane grids and the reception patterns for wire antennas and the grid having a grounded plate were measured experimentally. The results agreed well with theoretically predicted radiation patterns based on a fluid model description for electrons. The dependence of the received amplitude of a gridded parallel plate on the D. C. potential of the antenna was studied. The possibility of estimating the wavelength from measured amplitudes of the wire antenna and the gridded parallel plate is also discussed.

Studies on waveguide-fed slot antenna

Abstract: The paper presents investigations of the effect of stored energy inside a waveguide, near a displaced narrow longitudinal slot, on the immittance properties of the radiating slot. It is shown that internal stored energy accounts for the discrepancy between the theoretical and experimental results of the immittance characteristics observed in earlier studies. The effect of stored energy is to contribute an additional reactive term in the expression for the immittance of the slot. By the addition of this extra reactive term to the theoretical expression for the immittance, it has been possible to predict the point of resonance with better accuracy. Further, an expression is derived for the immittance presented by a slot to the transmission-line representation of the waveguide, as a function of slot length, displacement etc. by the application of the principle of duality to the dipole antenna.

Multiple-beam antenna for domestic communication satellites

Abstract: This communication describes the design method of and experimental results obtained from a new multiple-beam antenna for domestic communication satellites. A seven-beam model antenna 1.98 m in diameter has been fabricated and evaluated in the 50-GHz frequency band, and the measurement data are reported here.

Reentry vehicle stripline slot antenna

Abstract: A reentry vehicle antenna which is comprised of a stripline slot antenna with the antenna element including a stripline circuit board with a radiating aperture fed by a conventional strip transmission line. A feedback circuit is provided to control the input impedance of the antenna while operating into an RF transparent window as the window depth varies due to erosion upon reentry.

Slot antenna with flare

Abstract: A slot antenna with a flare having flare member having integrally formed therewith a first half section of antenna member and a second half section of antenna member having formed therein slots, in which the second half section of antenna member is mechanically assembled with the first half section of antenna member to provide a slot antenna member.

Offset-reflector antennas with offset feeds

Abstract: The development of a simple mathematical model for the vector radiation fields from offset-parabolic-reflector antennas is outlined. The model permits the primary feed to be offset from the reflector geometric focus, and thus allows the study of multiple-beam antennas. Predicted results are shown and correlated with measurements made on a 30 GHz antenna system.

Spiral top-loaded antenna: Characteristics and design

Abstract: Characteristics of spiral top-loaded antenna (STLA) have been derived by the self-consistent field method, and a general design procedure has been systematized. The results of the analysis suggest that the STLA has desirable characteristics among very low frequency antennas because of its relatively small size, low feed voltage, and absence of tuning inductor.

Unambiguous phase interferometer antenna

Abstract: An ambiguity free phase interferometer antenna system, having arbitrarily high gain characteristics and fine resolution, is provided by a pair of separately fed, forward-looking antennas, each having an amplitude distribution across its aperture of substantially A(y) Ae y. The antenna system may comprise a pair of isolated surface wave antennas, a pair of tilted leaky wave antennas, a pair of specially designed, exponential aperture horn antennas, or an array of a large number of closely spaced individual radiating elements having a suitable composite radiation pattern.

Electromagnetic radiation from a slot antenna surrounded by a moving magnetoplasma sheath

Abstract: Radiation from a slot antenna surrounded by a plasma sheath moving parallel to an external magnetostatic field is considered. It is shown that the radiation pattern is inclined in the direction of the sheath motion as the velocity is increased except for the case where the condition of upper hybrid resonance is satisfied in the rest frame of the plasma. When such a relativistic upper hybrid resonance caused by the sheath motion arises for certain values of normalized plasma and cyclotron frequencies and the velocity parameter, a deep null and a rapid oscillation appear in the radiation pattern, and as a result the shape of the pattern is extremely deformed.

The transition field on the surface of a slot-excited conical antenna

Abstract: A previous derivation of the transition field on the surface of a slot-excited conical antenna is corrected, and the new result as well as the tip-diffraction coefficient are checked by a calculation involving only the exact normal-mode series.

Influence of horn length on radiation pattern of oblique-flare-angle corrugated horn

Abstract: The influence of horn length on the radiation pattern of an oblique-flare-angle corrugated horn is described Two experiments with a 110° horn are reported These show that a horn with three slots has a radiation pattern which is essentially the same as that of a horn with five slots It is also demonstrated that the innermost slot has a dominant effect on the pattern

Multiport multimode slot antenna

Abstract: A slot antenna apparatus for exciting higher order modes to obtain beam scanning and pattern control with a relatively small aperture.

Optimised slot reradiation to modify foreground reflection into an array

Abstract: The reduction of foreground reflection into a vertically polarised 1000 MHz u.h.f. low delta aerial using a half-wave resonant slot in a one-quarter-wavelength-wide conducting flange is examined. The impedance, radiation efficiency and polar-diagram characteristics of a slot in limited conducting planes are presented. Procedures to optimise a slot to complement the Yagi-type array of vertical monopoles are described, and the application of such a slot to a 21.840 MHz h.f. aerial in Townsville, Australia, is discussed.