Showing papers on "Antenna (radio) published in 1969"

Quality factor of general ideal antennas

Abstract: An expression for the quality factor of an ideal antenna with both TE and TM modes excited is derived and applied to several special cases.

Scanned cylindrical array monopulse antenna

Abstract: A cylindrical antenna array system having two cylindrical subarrays flush mounted on a conducting cylinder, each consisting of a plurality of linear phased arrays fed through a pair of feed rings on the conducting cylinder that has a diode switch for each linear phased array coupled through a switching network to switch one-quarter to one-third of the linear phased arrays ON in a rotating manner to scan throughout 360* around the cylinder axis, and each linear phased array having a pair of rotatable dielectric slabs behind the waveguide slots thereof with all dielectric slabs mechanically coupled to rotate in synchronism to phase the radio waves for angular direction with respect to the cylinder axis, the received signals being coupled through a magic-T junction to provide sum and difference monopulse signals of targets in sight of the antenna

Resonance cones in the field pattern of a short antenna in an anisotropic plasma

Abstract: We report experimental observation of resonance cones in the angular distribution of the radio-frequency electric field of a short antenna in a plasma in a static magnetic field. The cone angle is observed to vary with incident frequency, cyclotron frequency, and plasma frequency in agreement with simple plasma dielectric theory. We discuss the relationship of these cones to the limiting phase- and group-velocity cones which appear in the theory of plane wave propagation.

Compact range techniques and measurements

Abstract: Compact range techniques for measuring the gain patterns of full-size microwave antennas and for making radar reflectivity measurements are described. The basic principle of this technique is the use of a large collimating device to generate a uniform plane wave across the aperture of a target or antenna without requiring the normal far-field separation. Two different collimating devices were used in the investigation, a paraboloid with a point-source feed and a parabolic cylinder with a line-source feed generated by a large hoghorn. Pattern and gain measurements were made on both compact ranges using a 30-inch paraboloidal test antenna, and the measurements were compared with similar ones made on conventional outdoor ranges. Radar cross-section patterns as a function of aspect angle were measured for various size standard targets and compared with theoretically calculable radar cross-section patterns. The results which have been achieved are very encouraging. They demonstrate that the performance of compact ranges at the X -band is comparable to that of outdoor ranges.

Backlobe reduction in reflector-type antennas

Abstract: The axial backlobe of a circular parabolic antenna dish is greatly reduced by providing variation of the phase of radiation diffracted at successive portions of the edge. The phase is varied by providing an edge configuration in which successive portions of the edge are at differing distances from the feed. A dual-polarized antenna employs a polygonal rim surrounding the round reflector. A large increase in front-to-back ratio is obtained. The theory of operation is described to enable use in other structures.

Temperature controlled surface wave feeder lines

Abstract: The invention consists of a surface wave antenna feeder in the form of a conductive tubing coated with a dielectric to produce on the outside of the coated conductor a field carrying substantially the entire electromagnetic wave energy from the transmitter to the antenna, and providing inside the tubing a circulating fluid so controlled as to maintain the line at a constant temperature substantially to exclude longitudinal expansion, regardless of the power level of the surface wave and the temperatures surrounding the line.

Annular slot antenna with stripline feed

Abstract: A stripline antenna having a radiating aperture in the form of an annular slot provided in one of its conducting plates and a pair of orthogonal narrow strip conductor feeds disposed between its two conducting plates and terminating under the central disk formed by the annular slot. Adjustment of the relative phase and amplitude of the electromagnetic energy applied to the strip conductor feeds permits radiation from the annular slot of circular, elliptical or orthogonal linear polarizations into space or into a waveguide.

Analysis of yagi-uda-type antennas

Abstract: A method of analyzing Yagi-Uda-type antennas is presented. Since the Yagi-Uda array is a fairly well-known antenna, it is used as an example to demonstrate the application and accuracy of the method. However, the method of solution is not limited to a planar array, such as the Yagi, but can be applied to arrays of nonplanar linear elements. The approach taken in analyzing Yagi-Uda antennas is based on rigorous equations for the electric field radiated by the elements in the array. All interactions are taken into account. Calculated results are presented for the Yagi-Uda array that show excellent agreement with experimental results reported in the literature. In addition, the dependence of the far-field patterns on the phase velocity is shown. It is also demonstrated that the phase velocity is generally nonuniform along the array.

Radio Loss of Lateral Waves in Forest Environments

Abstract: The radio loss between two small dipoles located in a forest is examined in the frequency range of 2–200 MHz by characterizing the forest in terms of a dissipative slab backed by an imperfectly conducting ground. A careful derivation of the total radio loss L shows that it consists of four distinct constituents: (1) a basic loss L0 associated with the forest-air interface, (2) a separation loss L8 due to the vegetation above the antenna, (3) a wave-interference loss Li due to field reflections at the ground plane, and (4) an antenna input resistance loss Lr produced by the ground proximity. The functional variation of these losses is consistent with previously obtained results that viewed the field in terms of a lateral wave, which now affords a simple physical interpretation for each of the separate factors enumerated above. By choosing parameters describing typical forests, we show that the variation of the four constituents leads to a total loss whose behavior agrees with available experimental data and with previous theoretical considerations pertinent to high antennas. In contrast to these, the present investigation predicts, for low antennas, that vertical polarization is preferable to the horizontal one and that communication conditions may be further improved if the operating frequency is increased rather than decreased. The antenna height gain effect is also examined in detail, and it is shown to be strongly affected by the ground proximity in a manner that had not been recognized hitherto.

Radiation resistance of a short dipole immersed in a cold magnetoionic medium.

Abstract: Radiation resistance of short dipole immersed in cold magnetoionic medium, using polarized wave modes

A shallow-cavity UHF crossed-slot antenna

Abstract: The shallow-cavity crossed-slot antenna is a UHF radiator designed primarily for use on a high-speed aircraft operating as the airborne terminal in a satellite-to-air communications link. The requirements, design analysis, and performance characteristics are described. The antenna's shallow profile makes it attractive either as a paste-on- or flush-mounted-type radiator. Near-hemispherical radiation coverage is provided.

Automobile windshield antenna

Abstract: A nondirectional automobile receiver antenna which may be utilized on either the low frequency broadcast band or the very high frequency, frequency-modulated (FM) band, and which is adapted to be adhesively attached to or embedded within the windshield of an automobile.

Combined dipole and waveguide radiator for phased antenna array

Abstract: An antenna includes a waveguide slot aperture radiator and a dipole radiator centrally located therein and located longitudedly with respect to the waveguide a quarter wavelength from the aperture. Each radiator is separately excited.

Active reflection coefficient and element efficiency in arbitrary antenna arrays

Abstract: Relations among the active reflection coefficients, reflected power, element efficiency, and mutual coupling (scattering) coefficients for arbitrary, finite or infinite, regular or nonuniform arrays of possibly dissimilar radiating elements are developed. The excitation which may be employed to define the active reflection magnitudes is not unique; suitable excitations may be chosen from any complete orthogonal set.

Scattering properties and mutual coupling of antennas with prescribed radiation pattern

Abstract: An analysis is presented of the interrelations among the radiative, scattering, and coupling properties of arbitrary lossless antennas. The analysis is based on a well-known scattering representation of antennas in terms of spherical modes in free space. This scattering representation is given a network interpretation which brings into focus the degree of interdependence between scattering and radiation characteristics. The scattering matrix of a reciprocal antenna with one port and a prescribed radiation pattern is represented in a canonical form which exhibits explicitly the permissible range of adjustments in the antenna scattering characteristics. The significance of the canonical form is examined from several points of view, noting in particular its connection with the concept of resonant modes of a scatterer. The network interpretation also facilitates the evaluation of mutual coupling, and the mutual impedance between two antennas is expressed explicitly in terms of the radiative and scattering parameters of each antenna. It is shown that, generally, the mutual impedance may be expressed as a sum of two terms: a zeroth-order term, dependent exclusively on the radiation pattern, and a second term involving the scattering properties as well as the radiation patterns. Under certain conditions the mutual impedance may be approximated by the zeroth-order term alone. It is also shown that a similar zeroth-order approximation of the active impedance in an infinite planar phased array leads to a grating lobe series type of representation.

Retractable aircraft antenna with streamlined radome for scanning

Abstract: A rotatable antenna selectively positionable to an operative location beneath the underside of the fuselage of an aircraft; the antenna being capable of being of a greater longitudinal length than the diameter of the aircraft fuselage, and being selectively retractable, vertically, to a stored position entirely within the aircraft fuselage.

Noise Spectrum Received by an Antenna in a Plasma

Abstract: Antenna noise spectrum in collisionless isotropic plasma, considering plasma fluctuation theory and reciprocity theorem

Folded integrated antenna and amplifier

Abstract: An integrated antenna system comprising a ground plane, at least one vertical element substantially perpendicular to the ground plane, a helically shaped element having horizontal polarization and a solid state circuit located at the junction of the horizontal and vertical elements. The described antenna system facilitates control of the characteristics of the antenna without varying the physical dimensions thereof. Consequently, antenna size may be reduced, related equipment simplified and the overall characteristics of the antenna system improved.

Improved radiation from a spherical antenna by overdose plasma coating

Abstract: It is shown that the radiation from a plasma-coated spherical antenna can be enhanced if the antenna is operated at a frequency much lower than the plasma frequency, and if the dimensions of the antenna and the plasma layer are appropriately chosen. This phenomenon may prove useful for overcoming the blackout problem suffered by a reentry vehicle or may offer a novel method of low-loss tuning of a small antenna.

An improved circuit theory of a multielement antenna

Abstract: An integral equation for a multielement antenna having finite gaps at the driving points is derived. An approximation of this equation is calculated on the assumption that the gap capacities are negligible as is the case with ordinary antennas, and it is used to explain the stationary property of the input impedance. If the electric current distribution is expressed by the sum of a number of trial functions, the equation for determining the coefficients of the functions is found from this condition for the stationary properties. This equation is an improvement of the circuit equation for antennas written in terms of self- and mutual impedances defined by the EMF method. The mutual impedance is affected by all antenna elements. The trial functions for the electric current distribution must be smooth near the driving points and must be approximately constant within the gap. Numerical calculations on a circular array consisting of five full-wavelength cylindrical antenna elements are shown to verify the usefulness of the improved theory.

Experimental investigation of the input-impedance characteristics of an antenna in a rectangular waveguide

Abstract: The input impedance of a monopole antenna in a rectangular waveguide is investigated experimentally. It is found that theoretical results based on the assumption of a sinusoidal current distribution are in good agreement for monopole lengths up to about 0.6 of the guide height and about 1/4 λ0. For longer monopoles, a more accurate theory should be sought.

Dipole radio antennae

Abstract: Dipole whip antenna arrangements are disclosed which are capable of operating over a wide frequency band without the use of continual manual or automatic tuning. This is achieved by connecting the dipole whip antenna to the ground plane through a reactance network which is specially designed so as to match the impedance at the feed point of the dipole arrangement to a desired value over the desired frequency band. For this purpose, the reactance network is an active network, and operates by effectively cancelling out the reactance of the antenna.

Asymptotic formulas for coupling between two antennas in the Fresnel region

Abstract: The coefficient of coupling \eta , or the ratio of power transfer between two antennas closely spaced, is defined. A two-term asymptotic approximation for \eta , valid for arbitrary aperture antennas, is derived. The asymptotic approximation is the leading part of an asymptotic series involving powers of 1/Kd , where Kd is the separation distance between transmitter and receiver measured in wavelengths. The first term of the asymptotic approximation for \eta is the usual Friis formula for power transfer between antennas spaced far apart. The second term in the approximation represents a correction term due to effects associated with the finite spacing between antennas. For test cases the on-axis Fresnel region fields of several aperture antennas are computed using the asymptotic approximation. In turn, the gain reduction factor \gamma which is the ratio of Fresnel region gain to far-field gain of an aperture, is computed for each example. These results are compared with exact expressions previously presented in the literature, and close agreement is noted. Also, a means of measuring the far field of a large-aperture antenna with a probe in its Fresnel region is suggested.

A probabilistic approach to large circular and spherical arrays

Abstract: Antenna arrays with elements distributed at random in a three-dimensional space are studied. Arbitrary excitation and nonisotropic elements are considered. The distribution of the sidelobe level below a certain value for all directions of observation, as well as other probabilistic properties are determined approximately. These general results are then applied to circular and spherical arrays. In particular, for the latter case, conical log-spiral antennas are considered in some detail. It is found that for large arrays with high resolution, the required number of elements can be several orders of magnitude smaller than what is commonly required on the basis of one element per (\lambda/2)^{2} Finally, a few experiments simulated by the Monte Carlo method were conducted and excellent agreements with theory have been found in all cases.

Monopole and conic antennas on spherical vehicles

Abstract: The radiation and impedance characteristics of a spherically capped conic antenna protruding from a spherical vehicle are studied as a function of cone height, cone angle, and diameter of the vehicle. The conic antenna is excited by a gap at the cone base. The excitation is assumed rotationally symmetric. Considered in detail is the thin conical monopole extending from a sphere. The radiation patterns and antenna impedance referred to the base are calculated and compared with that of a cylindrical monopole over an infinite conducting plane.

Cylindrical Antennas Immersed in Arbitrary Homogeneous Isotropic Media

Abstract: The cylindrical antenna is potentially useful as a probe for studying the properties of any material in which it is immersed. Examples of possible media are the earth, plasmas, and organic tissues. Such applications presuppose a knowledge of the detailed behavior of the currents and charges along an antenna in a medium with very general properties. In this paper the integral equation for the current along a highly conducting center‐driven cylinder of length 2h and radius a when immersed in a homogeneous isotropic medium is solved analytically and simple, and quite accurate formulas are obtained for the distribution of current, the distribution of charge, and the admittance. The lengths 2h may range from zero to over a wavelength; the radius a is assumed to satisfy the condition a≪h. The real effective conductivity of the medium may extend from zero to arbitrarily large values, the real effective permittivity from large negative values (as in certain plasmas) to large positive values (as in ordinary dielectrics like water).

Mutual coupling between log-periodic antennas

Abstract: Numerical techniques are used for the analysis of mutual coupling in arrays of log-periodic dipole antennas. The analysis is formulated in terms of impedance and admittance matrices for the dipole and transmission line networks. Approximations are made to allow the solution for moderately sized arrays to be practical with the existing generation of computers. Antenna patterns for the array are expressed in terms of the current incident on each log-periodic antenna. Results are presented for systems of one, two, and three log-periodic antennas.

Modulated impedance feeding system for log-periodic antennas

Abstract: A modulated impedance feeding system for log-periodic antennas including loading elements, a transmission line to couple energy to or from the elements, and impedance-modulating means for matching the image impedances of the transmission line and the loading elements in the regions of local reflections to realize essentially frequency independent performance A log-periodic monopole array and a cavity backed slot array are provided, fed with a modulated impedance meandering line according to the invention A log-periodically scaled directional coupler feed line for antenna arrays is provided, including in one embodiment thereof a coupler fed, log-periodic resonant V array

a Class of Boundary Value Problems-Part II: Waveguide Phased Arrays, Modulated Surfaces, and Diffraction Gratings

Abstract: URRENT applications in radio astronomy and radar have generated great interest in electronically scanned or phased array antennas. One such antenna is the phased array of open-end rectangular waveguides, a segment of which is shown in Fig. 1. An essential consideration in design of such antennas is that of matching the antenna over a wide range of scan angles to maximize power transfer from antenna to the space region. Thus, in the analysis of these arrays, the essential properties to be determined are the aperture fields, from which the radiation pattern may be calculated, and the reflection coefficient in each waveguide as a function of scan angle.