Showing papers on "Antenna (radio) published in 1971"

Computation of characteristic modes for conducting bodies

Abstract: A procedure for computing the characteristic modes for conducting bodies of arbitrary shape is developed. The method is applied to conducting bodies of revolution and to wire objects, and general computer programs are discussed. Illustrative examples of the computation of characteristic currents and characteristic fields are given for a cone-sphere, a disk, and a wire arrow. Modal solutions using these modes are computed for representative antenna and scattering problems to illustrate convergence of the solution as the number of modes is increased.

Amplitude modulation using phased-array antennas

Abstract: An antenna system for producing an amplitude modulated signal at a receiver by properly varying the spatial amplitude distribution of the antenna beam. The antenna beam variation is accomplished by varying the relative phase of a phase-array antenna at the desired modulation rate. A variable DC bias signal is applied to each element of the antenna which is used to steer the beam in angle. An AC signal is also applied to each element which will qppear as AM modulation at a distant receiver.

Photon-noise-limited laser transducer for gravitational antenna.

Abstract: We have constructed and tested a laser interferometer transducer for a long, wideband, laser-linked gravitational radiation antenna. Photon-noise-limited performance was achieved using 80 microW from a single mode Spectra-Physics 119 laser in a modified Michelson interferometer on a vibration isolation table in a quiet room. A piezoelectric driver on one of the interferometer mirrors was used to generate subangstrom (3 x 10(-14)-m) vibrations of known amplitude. The measured displacement sensitivity of the system in the kilohertz region was 1.3 x 10(-14)m/Hz(1/2), which compares well with the calculated photon noise limit of 1.06 x 10(-14) m/Hz(1/2). This is the smallest vibrational displacement measured directly with a laser to date.

Omnidirectional loop antenna array

Abstract: An antenna array for use with a system for receiving signals from a radio capsule disposed within a patient''s gastrointestinal tract. The array of antennas comprises three mutually perpendicular loop antennas, two of which are ferrite-core loop antennas disposed near the center of the array, the third being a loop antenna surrounding the two ferrite-core antennas. The antenna array includes means for matching the impedance of the loop antennas to transmission lines to which they are to be connected.

Adjustable aperture antenna employing dielectric and ferrimagnetic material

Abstract: In order to obtain wide aperture and high directivity radiation patterns from the same antenna, the radiating structure is made of a non magnetic dielectric and a dielectric ferrimagnetic material. The magnetic part is associated with magnetizing coils energized from an aperture control current source. When the antenna is of the rod type, the rod is made of the non magnetic dielectric which is covered at least partly with a magnetic coating. When the antenna is of the spherical type, a magnetic material core is surrounded with a non magnetic dielectric shell.

Transmission and reception system for generating and receiving base-band pulse duration pulse signals without distortion for short base-band communication system

Abstract: An electromagnetic signal communication system utilizing short base-band pulse signals of sub-nanosecond duration employs dispersionless, broad band antenna transmission line elements for generating and preserving the character of the short base-band pulses in respective transmitter and receiver sub-systems.

A variable-coverage satellite antenna system

Abstract: A multibeam antenna system and-combiner switch capable of producing a variable-coverage radiation pattern are described. The antenna consists of a waveguide lens illuminated by a 19-element feedhorn array. The combiner switch consists of a corporate arrangement of variable power dividers; the latter is made up of two phase shifters and two conventional hybrid power-dividers. An earth-coverage radiation pattern with less than 2-dB ripple and an antenna gain ≈ 20 dB is obtained by equally exciting all beams of the muItibeam antenna simultaneously. Excitation of a single feedhorn results in a narrow beam with an antenna gain ≈ 30 dB and a near-in sidelobe level less -20 dB. The side|obe level can be reduced appreciably by appropriately exciting the adjacent feedhorns. The frequency bandwidth corresponding to 0.5-dB decrease in antenna gain is 10 percent. A technique for computing the radiation properties of the antenna is described; the agreement with measured data is shown to be excellent.

Low-loss antenna system with counterpoise insulated from earth

Abstract: An improved antenna system for transmitting and/or receiving electromagnetic waves, having a counterpoise insulated from the earth and in which the counterpoise is connected to one terminal of a transmitter or receiver through an inductance. The inductance is tuned in conjunction with the tuning of a conventional loading inductance coil so as to maximize the field strength radiated by the antenna into the far field. The power lost in the earth or other antenna supporting surface is unusually small, so that radiated power is large.

Receiving antenna for miniature radio receiver

Abstract: Receiving antenna for miniature radio receiver formed by conducting U-shaped member having substantially parallel elongated arms which form sides of the housing of the receiver and a connecting portion which forms one end of the housing. When the receiver is in the normal position for use, the arms are positioned vertically with the connecting portion at the top, and the U-shaped member acts as an inductive loop antenna to detect the H-field of the electro-magnetic wave. A reactance network, which is capacitive in the frequency range of interest, is connected to the open ends of the arms. The reactance network can be adjustable to tune the antenna for various frequencies, the antenna having been found suitable for use in the frequency range from 148 to 173 megacycles.

Constrained optimization of the performance indices of arbitrary array antennas

Abstract: The solution to the optimization of performance indices of array antennas such as directive gain, efficiency index, and signal-to-noise ratio, do not provide information regarding the sidelobe region of the radiation pattern. It is shown that, with proper constraints on the sidelobes, a given performance index can be optimized to give a radiation pattern with desired sidelobe levels. As most of the performance indices of an array antenna can be expressed as a ratio of two Hermitian quadratic forms, an eigenvalue method is used for the constrained optimization. This method gives explicit expressions for the excitation vector and constrained values of the performance indices. An iterative technique is used to ensure that the specified field values occur at the sidelobe peak positions. The element excitations obtained by this technique for maximum gain and uniform sidelobe level are similar to these obtained by the Dolph-Chebyshev technique.

Subsurface traveling wave antenna

Abstract: A subsurface traveling wave antenna for generating and receiving primarily surface waves in either the vertical or horizontal position below the surface. The antenna comprises an insulated linear radiating element terminated with a matched load for coupling a portion of the surface wave component. Impedance elements interconnecting portions of the radiating element at periodic intervals along its extent provide speed matching between the phase velocity of the wave propagating down the radiating element and the surface wave component.

An investigation of the array of circular-loop antennas

Abstract: A circular-loop antenna composed of N elements with arbitrary circumference arranged parallel in a row is analyzed by Fourier series expansion with emphasis on the existence of finite gaps at the driving points. The integral equations at the beginning are reduced to a series of linear simultaneous equations which contain only the Fourier coefficients of the electric currents of the same order. By appraising the current coefficients, the self-admittance is obtained as a sum of two parts: the finite series truncated at the number determined by the ratio of the circular-loop radius to the wire radius and the gap capacitance, and the mutual admittance is obtained as a finite series of fewer terms. Several computed curves concerning a parasitic endfire array of two elements are given, in which the computed values of the input admittance are substantiated by experiments, and radiation characteristics are examined to obtain a desirable configuration.

Physically small combined loop and dipole all channel television antenna system

Abstract: A low cost, physically small, all channel television antenna system is provided for reception in high signal strength areas. The antenna is characterized by a loop having a pair of separated gaps, one of which is a feed gap and the other an impedance termination gap for operating as a directional reception antenna at the low and high VHF television frequency bands. Inboard the loop is placed a television band UHF dipole antenna. The input terminals of the dipole antenna and the feed terminal of the loop antenna are each coupled to a combiner with a single output from the combiner.

Base-band radiation and reception system

Abstract: A base-band transmitter and receiver antenna system for operation in subnanosecond pulse radio systems of the type detecting the presence or range of near-by reflecting objects utilizes directive, dispersionless, broad band traveling wave transmission line radiator and receiver antenna elements arranged cooperatively to limit the effect of base-band energy directly coupled from the transmitter to the receiver.

System for resolving the sizes and centroid locations of buried objects

Abstract: A broadband, radar-type system for resolving the sizes and centroid locations of objects buried at a maximum depth in the order of 6 to 10 feet is disclosed. The system uses a carrier frequency which is high enough so that an instantaneous bandwidth of about 25 percent provides resolution in the order of 1 foot. The system antenna includes impedance matching and focusing means. Polarization diversity of the transmitted beam may be accomplished to distinguish between elongated and generally round objects.

Radiation From a Short Electric Dipole in a Hot Uniaxial Plasma

Abstract: The effects of electron temperature on the radiation fields and the resistance of a short electric dipole antenna embedded in a uniaxial plasma have been studied. The radiation condition for solving Maxwell's equations is discussed, and the phase and group velocities for propagation are given. It is found that for ω ωρ the antenna excites two separate modes of radiation. One of the modes is the electromagnetic mode, while the other mode is of hot plasma origin. A characteristic interference structure is noted in the angular distribution of the field. The input and the radiation resistances are calculated and are shown to remain finite for nonzero electron thermal velocities. The effect of Landau damping and the antenna length on the input and the radiation resistances has been considered.

Transmitter combiner having coupled tuned circuits

Abstract: A hybrid coupler for coupling a plurality of transmitters to a single antenna. Inductive coupling through use of variable length transmission line stubs affords tuning over a wide transmission frequency range.

Multi-beam array antenna

Abstract: A multi-beam array antenna assembly is disclosed, such assembly being adapted to form a plurality of simultaneously existing beams of radio frequency energy, each one of such beams having the gain of the entire antenna aperture and a different scan angle. The preferred embodiment of the contemplated assembly is fabricated, using printed circuit techniques and matching sections on a dielectric substrate, to form an array of antenna elements and constrained electrical paths for radio frequency energy between each one of the antenna elements and a number of feed ports. The electrical length of each one of such paths is adjusted so as to focus radio frequency energy in each one of the desired beams at a different feed port. The preferred embodiment also illustrates a multi-beam array antenna assembly having antenna elements spaced to increase the scan angle of each desired beam.

The theory of top-loaded antennas: Integral equations for the currents

Abstract: The general problem involving the distribution of current and the driving-point impedance of a top-loaded antenna is formulated. Consideration is given to an idealized structure having one or more cylindrical top-loading elements. For the practically important case involving conductors of small radius, the axial currents are obtained as the solution to a pair of coupled integral equations. Approximate solutions obtained by numerical methods for the inverted L -, T -, and four-element top-loaded antennas are compared with measured driving-point impedances. Satisfactory agreement indicates the possibility of utilizing the theory in the analysis of practical configurations involving many top-loading elements.

Possibilities of dimensioning doubly curved reflectors for azimuth-search radar antennas

Abstract: To produce directional antenna patterns having a shaped beam in one plane such as is required, for instance, in the case of rotating-search radar antennas having a vertical radiation pattern of cosecant-squared shape, doubly curved reflectors are used as a rule. Besides the well-known composition of such reflectors from a stack of strips of parabolic shape, the paper delineates possibilities of an assembly from strips of elliptic shape that are also segments of parabolic dishes. With reflectors assembled in this way certain antenna characteristics such as directivity, sidelobe suppression, etc., can be modified and improved, depending on the type of strip configuration proposed. Experimental results gained with two different reflectors (width 12.5\lambda , height 5.6\lambda ) assembled from strips of elliptic shape are discussed. One of the strip configurations devised turns out particularly favorable for small reflectors.

Determining distance to lightning strokes from a single station

Abstract: Apparatus for determining the distance to lightning strokes from a single station. The apparatus includes a first loop antenna system for sensing the magnetic field produced by the lightning which signal is filtered, square rooted, and fed into a peak voltage holding circuit. A second antenna is provided for sensing the electric field produced by the lightning which is fed into a filter, an absolute value meter, and to a peak voltage holding circuit. A multivibrator gates the magnetic and electric signals through the peak holding circuits to a ratio meter which produces a signal corresponding to the ratio between the magnetic component and the electric component. The amplitude of this signal is proportional to the distance from the apparatus to the lightning stroke.

Windshield antenna for automobile

Abstract: A glass antenna for automobiles which comprises a first antenna element set so as to be adapted for an FM broadcast band and a second antenna element. These antenna elements cooperate to receive an AM broadcast electric wave. The feeding points of the antenna elements are connected to each other through means for effecting reactance. The antenna elements are provided in relation to the window glass of the car.

Determination of both polarisation and power gain of antennas by a generalised 3-antenna measurement method

Abstract: A method enabling determination of polarisation and power gain of three unknown antennas, requiring no prior quantitative knowledge of polarisation, is developed. An application of the method using a new near-zone extrapolation technique (introduced by Wacker and Bowman), which permits accurate antenna measurements at reduced distances in spite of proximity effects, is described.

The logarithmic spiral in a single-aperture multimode antenna system

Abstract: The n -arm logarithmic spiral antenna having n distinct terminals may be considered as an ( n-1 )-port antenna. It may be operated simultaneously in ( n-1 )independent balanced modes. By varying the relative excitation of these modes it is possible to produce a variety of patterns that have applications to direction finding, tracking, and homing over a broad range of frequencies. It is particularly easy to obtain useful results in this manner because of some unique properties of the logarithmic spiral. The basic relations between mode excitation and the related fields of these multiarm antennas are reviewed together with some properties that are characteristic of the log-spiral geometry. Multimode single-aperture systems, such as those using a relatively simple hybrid matrix to synthesize multiple beams tilted from the axis of the antenna, are discussed. These tilted beams can be conically scanned about the axis of the antenna by a simple phase shift within the excitation matrix.

Null pattern technique for reduction of an undesirable interfering signal

Abstract: A null pattern technique for reducing the effect of an undesired interfering signal in a data link channel, using an accepted monopulse tracking arrangement in a novel mode, such that the source of such interfering signal can be caused to be placed at the null of the antenna pattern used, thus greatly increasing the desired-signal-to-interfering-signal ratio without necessitating a physically large antenna.

Vehicle antenna for vehicular communication system using leaky coaxial cable

Abstract: A vehicle wireless communication system utilizing a leaky coaxial cable installed along the vehicle track and having an array of slots in its outer conductor. A coaxial type antenna is mounted aboard a vehicle traveling on the track. The outer conductor of the coaxial type antenna is provided with an array of slots in the axial direction which substantially coincides with the array of slots in the leaky coaxial cable with respect to slot structure and cycle of slot arrangement. A dielectric material is interposed between the inner and outer conductors of the antenna and is adjustable to equalize the wavelength contraction ratio of the antenna to that of the leaky coaxial cable.

Microstrip to microstrip transition

Abstract: A coupling arrangement for microstrip systems, each system characterized by a dielectric with a ground plane contacting one side thereof and a conductive strip fastened to the other side. A small coupling hole in the ground plane immediately underlies the strip conductor at a current maximum for signal along the line. Two such microstrip systems are placed in back-to-back relation with their ground planes in physical contact and their coupling holes in registry to transfer signal being propagated in a transverse electromagnetic mode via one of the strip conductors to the other of the strip conductors and ultimately to a desired point or points of utilization. In a specific application of the invention, the coupled microstrip systems are used to transfer signal energy from a feed network to a phased array of antenna elements.

Dual polarized diplexer

Abstract: A microwave diplexer employs a section of circular waveguide having a transmit port coupled to two transmitters, an antenna port coupled to an antenna, and a receiver port including four openings symmetrically located around the periphery of the circular waveguide. Coupled to each receiver opening is a filter operative to improve the isolation between the receiver port and the transmit port for signals coming from the direction of the transmitter port. Two orthogonally related signals introduced at the transmit port are conducted along the circular waveguide to the antenna and are isolated from the receiver port by the impedance characteristics of the filters. Signals received via the antenna are isolated from the transmit port by a section of wave guide having a cutoff frequency above that of the received signal.

Current sheet antenna

Abstract: An antenna comprises a conductive ground surface element and at least one conductive radiator element in the form of an extended two dimensional sheet. The conductive radiator element is mounted parallel to the ground surface element and no more than onefifteenth of an operating free-space wavelength from it. Signals are fed to at least two points on the radiator element wherein the signals at the points excite the radiator element symmetrically to cause current to flow across the outer surface of the conductive radiator element in the lowest mode of excitation.