Showing papers on "Dipole antenna published in 1973"

Probe compensated near-field measurements on a cylinder

Abstract: A new method is developed for determining the farfield pattern of an antenna from probe compensated near-field measurements over the surface of a right circular cylinder enclosing the antenna. The method is derived by first expanding both the field radiated by the antenna and the field radiated by the measurement probe, when it is used as a transmitter, into cylindrical wave expansions. The Lorentz reciprocity theorem is then used to solve for the field radiated by the antenna from the probe output voltage. It is shown rigorously that the antenna pattern can be determined independently of the characteristics of the measurement probe provided that certain calibration data are known. A method for determining these data from the measured far field radiated by the probe is described. It is shown that the necessary numerical integration can be performed with the fast Fourier transform algorithm. Experimental results are presented to validate the theory and to demonstrate its practicality from a measurement and computational viewpoint.

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.

Linearly polarized phased antenna array

Abstract: There is disclosed herein a linearly polarized mat-strip phased antenna array wherein the antenna array is phased by incorporating in series relationship one or more mat-strip loaded line type phase shifters in the mat-strip power division distribution network for the mat-strip dipole elements and/or a combined mat-strip dipole element and phase inverter. Two embodiments are illustrated.

Automatic antenna coupler utilizing system for measuring the real part of the complex impedance or admittance presented by an antenna or other network

Abstract: An automatic antenna coupler is described which includes a matching network having adjustable reactive elements. Control for these elements is provided by a system for detecting the real part of the complex impedance presented by the antenna or matching network. A logic and control system for adjusting the reactive elements is operated in accordance with the real part detector output so as to provide the desired impedance match.

The measurement of large antennas with cosmic radio sources

Abstract: Strong cosmic radio sources provide a constant broadband and accurately positioned test transmitter for measurements of large antennas. Some sources have their flux density determined absolutely and can be used to calibrate the antenna gain. This paper presents up-to-date data on the radio sources which are useful for antenna measurements. The measurement of pointing and focusing corrections is discussed. The main part of the paper is concerned with the derivation of major antenna parameters such as aperture and beam efficiency, beam solid angle, sidelobe levels, error pattern characteristics from measurements on radio sources. The effects of a finite angular source size are discussed, and it is shown how measurements on sources of different size increase the information on the derived antenna parameters. The methods to measure very weak sidelobes are treated and the external factors, solar and galactic radiations influence of the earth and atmosphere, which might limit the accuracy of the measurement are described. The paper takes a practical approach to the subject and contains graphs with numerical data.

The insulated dipole antenna in a relatively dense medium

Abstract: The properties of an insulated dipole antenna are derived when the wavenumber of the surrounding infinite, homogeneous, and isotropic medium is large compared with that of the insulation. It is shown that even when the surrounding medium is a perfect dielectric, the distributions of current and charge along the antenna and its driving-point admittance are substantially like those of a section of transmission line with a distributed radiation loss appearing as a part of the series impedance per unit length.

Stripline slotted balun dipole antenna

Abstract: A stripline slotted balun dipole antenna, suitable for use as a single antenna or as an array antenna element, is fabricated from two metal-clad dielectric sheets, from which metal has been removed in predetermined patterns, and then the sheets are sandwiched together to form both the slotted balun dipole antenna and its stripline feed. The metal remaining on the exterior of the laminated structure constitutes a slotted balun dipole and the metal remaining between the dielectric sheets constitutes the center conductor of the stripline feed. The structure obviates the need for metallic connections in the antenna area.

Comments on the design of log-periodic dipole antennas

Abstract: The design procedure of the log-periodic dipole (LPD) antennas is discussed. The results of the calculations carried out by the use of the more recent and accurate methods of the analysis for the arrays of unequal dipoles, are compared with those already available in the literature. The calculations refer to the gain of LPD antenna as a function of Z_{0} , the characteristic impedance of the exciting transmission line, of h/a , the ratio between the half-length and the radius of dipoles, of \tau and \sigma , two parameters which describe the geometry of the LPD antenna. The values of gain are lower than those given by earlier calculations. The degradation of the gain is more consistent, when the values either of Z_{0} or h/a are increased with respect to Z_{0} = 100 \Omega and h/a = 125 , which are parameters often used in the literature. The many diagrams included in this paper for different values of \tau, \sigma, Z_{0} , and h/a can be useful in a more accurate design of an LPD antenna. Confirmation of the computer data has been obtained by the tests performed on various scale models and on a full scale antenna.

A cavity-backed dipole antenna with wide-bandwidth characteristics

Abstract: This communication describes a cavity-backed dipole antenna that has a broad-band VSWR response, unidirectional radiation patterns, and almost constant gain ( 10.5 \pm 1 dB) over an operating bandwidth of 1.8: 1. Measured pertinent electrical characteristics are presented.

Near fields of wire antennas by matrix methods

Abstract: The method of moments [1], [2] is applied to wire antenna near-field problems. Within the general method, two computational procedures are developed. Results of these are compared with those of certain approximate analytical techniques and also with those of other investigators. A treatment for junctions is outlined. Examples are included for a single dipole antenna, for linear arrays of dipoles and also for loop and T -junction radiators.

Microwave detection instrument

Abstract: An instrument for detecting microwave energy and for giving an accurate measurement of the power density thereof, which instrument needs no internal amplifier and is substantially unaffected by polarization or modulation of the electromagnetic waves includes a planar array of parallel-connected diode detectors each having a pair of antenna leads forming a dipole antenna, each of the diode detectors having a pair of output conductors passing through one or more ferrite beads and thence to a meter. The diode array may include groups of diodes having different antenna lead lengths to detect different frequencies of microwave energy, the meter being selectively switched between the outputs of the different groups. The diode array is embedded at the center of a sphere of material transparent to microwaves and the diode antenna leads may be etched on a circuit board.

Interference patterns of a horizontal electric dipole over layered dielectric media.

Abstract: Interference patterns for electromagnetic fields due to a subsurface reflector below a layered lossy dielectric are calculated with the geometrical optics approximation for use in interpreting data to be collected on the moon by Apollo 17 as well as data currently being obtained on terrestrial glaciers. The radiating antenna lies on the surface. All six field components are calculated and studied. For the endfire solutions, the peak of the first reflected wave is found to be different from that of the broadside ones. To facilitate a physical discussion, we plotted the radiation patterns due to the antenna on the surface.

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.

Tunable spiral dipole antenna

Abstract: A tunable dipole antenna including dipole arms formed of a pair of helical coils whose diameter is small compared to the wave length of the frequency to which the dipole antenna is tuned and whose length can be adjustably extended. The coil includes a plurality of turns of flat spring wire. When the coils are extended to a desired length, the turns of flat spring wire can be adjusted such that a number of the turns are expanded while the rest of the turns are contracted near the outer edge. The number of expanded turns can be varied at the given length of the coil to obtain tuning to the desired frequency.

Antenna radiation pattern measurement using time-to-frequency transformation (TFT) techniques

Abstract: A method of inferring microwave antenna radiation patterns over wide bandwidths from a series of subnanosecond pulse measurements is described. Monochromatic patterns can be inferred from the time-domain measurements with simple apparatus. Results are presented which show that the method is inherently insensitive to errors caused by reflections from the environment.

Conformal array beam forming network

Abstract: A beam forming network is disclosed interconnecting one of a plurality of input terminals with a corresponding number or a different number of antenna elements of an antenna array. The beam forming network may be used in conjunction with such an antenna array to receive waves and to provide outputs corresponding thereto, or to radiate waves in response to a selected input signal properly applied. More specifically, each of the plurality of terminals which serve as output ports when receiving and input ports when transmitting, is coupled by a plurality of delay lines to each of the antenna elements. In a radiating system, a signal is applied to one of the input terminals which is coupled to each of the antenna elements through such delay elements that the waves radiated from each of the antenna elements are delayed by specified amounts which cause the direction of the composite wave or beam formed by the waves derived from all antenna elements to be directed along a line disposed at a particular angle with respect to the axis of the antenna array. In one embodiment of this invention, the antenna elements may be disposed in a linear array, which allows selection of beam directions in a plane containing the line of radiating elements, whereas in other embodiments of this invention, the antenna elements may be disposed in two or threedimensional arrays, which allows selection of beam directions representing various combinations of azimuth and elevation angles relative to the array axis.

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.

Multipurpose antenna system for a submarine

Abstract: There is disclosed herein a multipurpose antenna system for a submarine having a hollow mast capable of movement into and out of a submarine hull. A first antenna system is mounted at the top of the mast with this first antenna system being capable of transmitting and receiving in a time shared relation a radar signal and a satellite communication signal. A second antenna system is disposed in the mast below the first antenna system. This second antenna system is capable of receiving an electronic countermeasure signal. The second antenna system includes a plurality of different antennas disposed in spaced relation with respect to each other about the circumference of a transverse cross-section of the mast. The plurality of different antennas are flush mounted with respect to the outer surface of the mast. Each of the plurality of different antennas of the second antenna system employs two printed circuit spiral antennas stacked in the same plane one above the other with one of the spiral antennas being responsive to right-hand circular polarization and the other spiral antenna being responsive to left-hand circular polarization. A switching arrangement is coupled to each of the spiral antennas to appropriately cause the plurality of spiral antennas to scan 360* in both left-hand and right-hand circular polarization.

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.

Coaxial horn antenna

Abstract: A wide band, multi-mode antenna having a plurality of coaxial, independently fed, radiating horns. Each horn has multiple feeds which can be energized in various phase relationships to control polarization. The antenna can be used as a direct radiator, or to illuminate a reflector, has transmit or receive capabilities, and is adaptable to monopulse operation. The antenna is a compact rigid unit of very simple construction.

A comparison of time- and frequency-domain measurement techniques in antenna theory

Abstract: Although the impulse response and complex spectral frequency response are mathematically equivalent, their measurement for wide-band antennas and probes is quite different in the equipment required, calibration and experimental procedure, and in the character of experimental errors. The subject of this communication is an automated facility for measurement of both time- and frequency-domain antenna response data, and a comparison of the results obtained by the two techniques.

Analysis and design of circular antenna arrays by matrix methods

Abstract: The antenna arrays considered in this paper consist of identical parallel dipoles equally spaced around and perpendicular to a circle. Application of the "method of moments" to the analysis problem yields a matrix description of the array. Economies of computation are achieved by exploiting the array symmetries. The matrix description of the array leads to a network description for feed design and a relationship between principal H -plane pattern synthesis and pattern synthesis for an array of point sources. Some classes of pattern synthesis problems are considered and calculated examples presented.

Efficiency as a measure of size of a phased-array antenna

Abstract: This communication addresses the problem of estimating the minimum size a phased-array antenna must have in order that analyses based on simple infinite-array models yield meaningful results. The measure of array size proposed herein is an efficiency parameter defined for an infinite array with truncated excitations. Numerical results are presented for arrays of slots and dipoles, showing the rate of convergence of the efficiency parameter for various spacings and scan angles. The conclusions deduced from this analysis as to the minimum array size are in substantial agreement with exact computations dealing with finite arrays published in the literature.

Measurement techniques for antennas in dissipative media

Abstract: Methods used to simulate dissipative media environments for antennas are reported and special techniques developed to determine the electrical properties of antennas in such media are discussed Tank systems for simulating infinite homogeneous isotropic media characterized by ratios of \alpha/\beta in the range 0 are described along with the apparatus for determining the constitutive parameters \sigma and \epsilon of the media A new device for measuring antenna input admittance is presented which permits a simple measurement of admittance over a broad frequency range where conventional methods are cumbersome in field use Apparatus for measuring antenna current and charge distributions is described together with a discussion of the associated probing errors Measured admittances and current and charge distributions are compared with current theories for thin wire linear and loop antennas in the dissipative media and are found to be in good agreement

A theoretical and experimental study of the insulated loop antenna in a dissipative medium

Abstract: The performance of a bare antenna as a radiator in a dissipative medium can be significantly altered by placing a dielectric coating around the antenna. For certain antenna types and specific properties of the dissipative medium, the dielectric insulation has been shown to improve the performance of the antenna. In this paper the thin-wire circular-loop antenna centered in an insulating spherical cavity and immersed in an infinite homogeneous isotropic dissipative medium is analyzed. A Fourier series solution for the antenna current distribution is derived. The coefficients of the series are a combination of the coefficients for the loop in an infinite dielectric medium, which were determined previously by Wu [1962], and a second term, which is an infinite sum. The properties of the sum are examined, and expressions for the antenna input admittance, impedance, and electromagnetic field in the dissipative medium are obtained. Numerical results are presented for specific antenna sizes and dissipative media. For the special case of a loop with a uniform current distribution in an electrically small sphere the expression for the input impedance is shown to reduce to a solution previously given by Wait and Spies [1964]. The construction of an experimental model for the antenna is discussed, and antenna input impedances and current distributions measured with the model immersed in various salt-water solutions are compared with theoretical calculations.

Self-phasing array with a time-shared processor

Abstract: A phase alignment system for a self-phasing antenna array is described. A single time-shared processor sequentially phase aligns each array element with a suitable reference signal. This technique is applicable to a self-phasing array in which the random phase of the signal received at each array element is slowly varying (bandlimited). Individual antenna signals are summed and the phase of the signal from a selected one of those antennas is compared to the phase of the sum (reference) and a variable phase shift is introduced into that selected one antenna output to bring that output into closer conformity with the phase of the sum. This process is repeated sequentially for the entire group of antennas and optionally the sequential comparing and adjusting may be interrupted, maintaining the phase-shifts for the several antennas at their most recent value, and the antenna array employed for a transmitter to thereby provide a transmission radiation pattern substantially the same as the reception sensitivity pattern as it existed just prior to the interruption.

Absolute calibration of antennas at extremely low frequencies

Abstract: To calibrate electric-field sensors at extremely low frequency (ELF) the measured terminal voltage V at a receiving antenna is compared with the Analytically predicted V for a precisely known incident field. That incident field is generated by an electrically very short thin linear radiator. Formulas are given for the field in the immediate vicinity of such a radiator above a perfectly conducting ground. Also given is an expression for the integral of this field along a vertical path starting at ground level. The expressions involve the magnitude of the current at the base of the radiator and methods are described for establishing that quantity precisely by measuring the base-to-ground voltage and the very small capacitance (about 20 pF) of the radiator. The methods for small capacitance measurement are also applied to linear and spherical receiving antennas, and experiments are described in which it was possible to predict the terminal voltage at a receiving antenna to within \pm3 percent when the voltage applied to the transmitting radiator, located at a relatively short distance ( \approx 16 to 21 m) was known. Details of measurement circuitry are given including descriptions of an extremely high input impedance ( \approx 5000 M\Omega ) amplifier and a circuit for the compensation of cable capacitance. For a uniform incident field the effective height of both, a vertical linear receiving antenna and of a spherical antenna, is equal to the distance between ground level and the center of the conducting part of the antenna. Typical values for the natural, ambient ELF field in the frequency range 3 to 30 Hz are shown to be in the vicinity of 0.1 mV/m/Hz1/2.

Sensitivity improvement of spaced-loop antenna by capacitive gap loading

Abstract: An improved antenna system having a plurality of loop antennas surrounded coaxial shields which have dual electrostatic shield gaps therein. A shunt capacitance is placed across each of the shield gaps. The shunt capacitances are matched and variable among discrete values. Variation of the capacitances provides increased antenna sensitivity without a change in physical dimensions of the antenna.

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.

Dual-band array antenna

Abstract: A unitary antenna comprising two different arrays. The first is a group of waveguide antenna elements in alternately displaced rows forming a triangular grid structure and the second is another group of waveguide antenna elements forming a triangular grid structure within the first grid structure. The two groups of elements are dielectrically loaded, are polarized to radiate orthogonally to each other, and are designed to radiate at different frquency bands.