Showing papers on "Antenna array published in 1975"

Interleaved antenna array for use in a multiple input antenna system

Abstract: An interleaved antenna array is disclosed in conjunction with an improved multiple transmitter antenna system for simultaneously generating two independent groups of composite radiation patterns for two separate pluralities of independent radio devices. A first plurality of isolated independent radio transmitters is coupled, without any signal cancellation, to each and every one of a first plurality of independent antenna elements which form a first group of composite radiation patterns for these transmitters. A second plurality of transmitters is likewise coupled to a second plurality of antenna elements which create a second group of composite patterns for these transmitters. The antenna elements of the first and second pluralities are alternately circumferentially disposed about a central axis and each produces a 90° half power beam width radiation pattern which is directed radially away from the central axis. First and second combining networks produce 90° electrical phase shifts between the adjacent radiation patterns produced by the elements in each of the two pluralities, respectively. By providing such an interleaved antenna array for first and second pluralities of independent transmitters, a single multiple input antenna system is provided which has a small size and produces a uniform omnidirectional pattern for each of the transmitters while maintaining isolation between each transmitter.

Conformal radar antenna

Abstract: A conformal electronically scanned antenna array system utilizing an inve Butler matrix in combination with directive antenna elements. The system provides a simple and inexpensive device for scanning an elemental array without the problems of output frequency shift or mutual coupling between antenna elements.

R.F. power distribution network for phased antenna array

Abstract: An r.f. power distribution network or scanner in which a TEM mode and a pair of selectively phase-shifted TE 11 modes are derived and applied to input ports of a cavity resonator to produce a desired r.f. power distribution at a plurality of output ports. The resonator is in the form of a generally cylindrical member in which the output ports are arranged circumferentially about the periphery and axially spaced from the TE 11 mode input ports. The latter are arranged symmetrically about the TEM mode input port.

Dynamically focused thinned array

Abstract: A thinned array real time radar system having an antenna array with receiving elements spaced more than one wavelength apart and having a dynamic means for programming the focus of the array so that it is time sequentially focused to accommodate radar echoes over a range interval from a near range out to infinity to provide an improvement in azimuth resolution, the improvement being substantially large for the near ranges. The system includes a separate mixer for every element of the array for receiving return energy therefrom and with each mixer having a separate local oscillator input. The local oscillator frequency varies as a prescribed first function during each period of processing over the selected range interval and the path length distribution of the feeds between the local oscillator and each individual mixer vaires as a prescribed second function. The first and second functions may be separable functions of an expression approximating the time-space variations of the spherical phase front received by the antenna array. The local oscillator feed is selected so that the distance from the local oscillator to each particular mixer varies as a function of the distance squared from the center of the array or processing point of the array.

Two dimensional array antenna

Abstract: Two dimensional beam steering of an antenna array is effected by feeding alurality of radiating elements from a hybrid matrix that is a beam forming and phasing network in combination with single pole multiple throw switches where switching the various matrix terminals give the elevation beams. Ferrite phase shifters feeding into the single pole multiple switching means provides steering of the antenna beam in the azimuth plane.

Synthesis of a single null response in an otherwise omnidirectional pattern using a circular array

Abstract: The paper discusses a method for designing an antenna array having an omnidirectional pattern in the horizontal plane plus a single steerable null. Such a system has applications in communications when it is required to reject interfering signals from an unwanted source, while maintaining communication coverage in other directions. Parameters such as null width, null depth and the gain ripple in the directions of coverage are defined in order to make sensible comparisons between performance of various null patterns. An efficient and simple method for the synthesis of such a pattern, using a circular array, is presented. It involves the appropriate combination of a beamcophasal pattern with that of an omnidirectional pattern, and it is shown that by choosing a phase-sequence omnidirectional pattern for this purpose, a narrower `single-zero? null may be obtained. The calculated results show that attractive pattern characteristics can be achieved through this method of synthesis.

Method of making an antenna array using printed circuit techniques

Abstract: Radio frequency array antenna structures and methods for fabricating such structures are disclosed wherein a plurality of radio frequency circuits forming the radiating face of an array antenna and a corporate feed are formed on one or more relatively flexible dielectric sheets and then bonded to a suitable core material to form a complete array structure which is light weight, inexpensive and structurally sound.

Localizer antenna array for use with localizer transmitters operating at one carrier frequency

Abstract: A broadband localizer antenna array with an even number of elements is supplied by a backmatched power dividing network comprising two chains of directional couplers and a group of hybrids which divide the power among the elements in accordance with geometrical progessions. The center elements in the array may be spaced 0.6 wavelength apart at the average frequency. Other spacings between the elements are greater than 0.6 wavelength.

Two-frequency instrument landing system with integral monitor

Abstract: A two-frequency capture-effect instrument landing system employs a single localizer antenna array for both course-frequency and clearance-frequency radiation. The composite course and clearance signals are formed by networks that utilize trees of hybrid power dividers to effect unequal power division and distribute the signals to the antenna feeders. Integral monitoring is provided by similar networks, operating backwards in a functional sense, which recombine samples of the RF energy on the antenna elements and separate the same into the basic, frequency-separated course and clearance signal components. Redundant monitoring for antenna fault detection is provided by detecting RF signal levels on unused ports of the monitor circuit power dividers.

Direction-finding method and system

Abstract: High-frequency waves transmitted by a rotating antenna array at a ground tion are intercepted by an airborne receiver for photoelectric evaluation by one or more discs whose light transmissivity, by translumination or reflection, varies periodically according to a sinusoidal law in one diametral direction while being constant in another diametral direction orthogonal thereto. The disc or discs are rotated at a speed corresponding to that of the transmitting antenna array, under the control of periodic synchronizing pulses, and are illuminated by a flux modulated by an electrical signal derived from the incoming wave, this signal containing a phase component dependent on two spatial coordinates such as elevational and azimuthal angles determining the relative position of the ground transmitter and the airborne receiver. The flux optically filtered by any such disc has a peak at a point determined by the spatial coordinates whereby the relative position can be visualized by a display device such as a vidicon camera and an associated oscilloscope screen. Parasitic components due to reflections from moving objects can be suppressed by integration of the optically filtered flux over a limited period.

Image element antenna array for a monopulse tracking system for a missile

Abstract: An image element antenna array comprised of slot radiating elements is used for the antenna system for a monopulse tracking system. The image element antenna includes the radiating source disposed between two parallel reflecting planes, one of which is a total reflector and the other a partially reflecting and partially transmitting reflector. The employment of a partially reflecting plane allows for minimizing the number of radiating elements comprising a given antenna array while providing substantially the same gain and pattern activity. The antenna system may be mounted in a missile or the like for transmitting and receiving monopulse energy for steering the missile. The reduced number of radiating elements required reduces the feed network complexity and number with an attended increase in aperture efficiency.

Beam pattern synthesis for line arrays subject to upper and lower constraining bounds

Abstract: A technique is described for synthesizing the coefficients of an antenna array which satisfy a constrained minimax criterion. Inhibition regions can be formed in the beam pattern and placed advantageously in directions associated with strong sources of interference. Modified Dolph-Chebyshev beam patterns are obtained by imposing upper and lower constraining bounds on the beam pattern over regions of directions in space. Specific examples are presented for line arrays.

Commutated log periodic antenna array for automatic direction finding

Abstract: A plurality of log periodic antennas are arranged in a commutated antenna array to amplitude modulate an RF signal for providing bearing information with respect to the signal direction in an automatic direction finding system.

Nonlinear optimization extends the bandwidth of Yagi antenna

Abstract: A cost function is given for the optimization of the directivity of an antenna array while simultaneously achieving the flat behavior over the wide range of frequencies. The optimization of a six-element Yagi antenna resulted in a virtually flat directivity over the bandwidth of 33 percent. The allowable tolerances on element lengths of the optimized antenna are 0.25 percent or larger.

Antenna array encased in dielectric to reduce size

Abstract: Constructions for radio antennae, whose size is made appreciably less than the size of conventional antennae by using the dielectric properties of a mixture of barium titanate and strontium titanate.

Method of admittance matrix measurement of an antenna array

Abstract: A method is described for measuring the admittance matrix of an antenna array considered as an N-port network. The method utilizes the properties of hybrid junctions to apply at the antenna ports, taken two at a time, with all other ports short-circuited, two pairs of incident voltages of known amplitudes and phases. Measurements are obtained of the reflections coefficients ( \Gamma ) and of the input admittances ( Y_{in} ) at the pair of antenna ports under test for both modes of excitations. The desired admittance parameters are then easily determined from the measured quantities as shown in the formulation given below. The proposed method applies to arbitrary arrays and is gererally easier to implement than those that are now available [1-4].

Performance assurance apparatus for phased antenna array drives

Abstract: A circuit for monitoring the accuracy of the phase shift produced in an r.f. power distribution network in which the phase shift network includes diodes, means for sensing the conductive state of the terminating diodes, and structure for comparing the state of the diodes against a desired condition to provide a warning indication in the event the diodes are not in the proper condition to provide the desired phase shift.

S-band antenna phased array communications system

Abstract: The development of an S-band antenna phased array for spacecraft to spacecraft communication is discussed. The system requirements, antenna array subsystem design, and hardware implementation are examined. It is stated that the phased array approach offers the greatest simplicity and lowest cost. The objectives of the development contract are defined as: (1) design of a medium gain active phased array S-band communications antenna, (2) development and test of a model of a seven element planar array of radiating elements mounted in the appropriate cavity matrix, and (3) development and test of a breadboard transmit/receive microelectronics module.

Light-weight low-cost antenna element

Abstract: An antenna array comprising a plurality of antenna elements formed from ml-clad boards and conductive pins. Two metal-clad boards are placed together to form a sandwich, the metal-clad surfaces of the boards forming the top and bottom walls of a waveguide. Pins are placed perpendicular to the clad surfaces to form the sidewalls. The signal is introduced by a coaxial probe in the broad wall of the waveguide in a conventional manner. A row of pins defines the backwall of the waveguide.

Phase-controlled linearly-polarised strip-line antenna array - has impedance transformers and phase shifters and commutating diode switches

Abstract: The phase-controlled, linearly-polarised, strip-line antenna array has N dipole elemental radiators formed on an integrated circuit board using strip-line techniques and bearing a given spacial relationship to one another. The dipoles are linearly polarised and each is coupled to the supply line over a strip-line impedance transformer with phase shifter. The main supply line is divided into four branches and each branch has a diode switch. The four diode switches are normally non-conducting and act as the array's commutator.

DAASM Project-High Latitude Aircraft HF Propagation Experiment

Abstract: : The purpose of the DAASM project is to investigate the effects and limitations caused by the auroral and polar ionosphere on over-the-horizon HF propagation using a backscatter sounding system. The technique measures and records the complex amplitude of incoming, forward or backscatter signals, including noise, at each of the 12 elements of a broadside antenna array. The data is subsequently processed using sophisticated software on a CDC-6600 computer at AFCRL. This process, using Fourier analysis techniques, provides output in the form of Doppler frequency vs arrival-angle maps as well as coherence maps.

Adaptive Array Control.

Abstract: : Radar targets such as slow, low flying aircraft and moving ground vehicles may be detected by employing an adaptively controlled antenna array with an AMTI radar set, conformally mounted in a high performance jet aircraft. Clutter cancellation is achieved through moving the active subaperture of the phased array to the rear of the aircraft with the transmission and reception of each pulse. The adaptive control unit which forms these subapertures employs a Guided Accelerated Random Search algorithm to maximize the clutter cancellation ratio of a coherent two-pulse canceller. The test results demonstrated that the adaptive array control circuitry can achieve a +8.5 dB output target-to-clutter power ratio for moving targets as much as 34 dB below the input clutter power. It took approximately one hundred iterations of the control algorithm to reach the minimum normalized cancelled clutter power level, and less than fifty iterations to achieve 30 dB of clutter cancellations.

Photography at Radiowavelengths.

Abstract: : The report contains the description of the concept and the instrumentation developed for imaging radiowave object fields. The electromagnetic field in the plane of an antenna array is specified by the waves arriving from different directions. The complex electromagnetic field may be sampled by the antennas in the array, faithfully amplified through those many identical receivers, to energize an equivalent array of ultrasonic emitters. The Fraunhofer image formed by the ultrasonic array may then be converted to yield a visible image. The imaging system developed is a one-dimensional version. It consists of a row of 20 antennas (equiangular spirals), 20 identical, high gain receivers and a linear array of ultrasonic emitters. The one-dimensional ultrasonic image is then detected by an array of 'pinducers', amplified and made to proportionately illuminate a row of L.E.D. light bulbs. The L.E.D. row is then photographed by means of a continuous run, 16 mm camera.

An optical processor for radio pulses from an antenna array

Abstract: A coherent optical method of processing pulsed radio signals received by a planar antenna array is described. The output is the two-dimensional optical image of the brightness distribution of the radio sky. Experimental results for a 4 × 4 array are presented.