Showing papers on "Phased array published in 1973"

A wide-band square-waveguide array polarizer

Abstract: A stepped-septum polarizer has been designed that is capable of at least 26 dB of isolation over a 20 percent frequency band. The three-port device may be used to excite high purity left or right circular, as well as tilted linear polarizations in a phased array of square waveguides.

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.

Spatial distribution of intermodulation products in active phased array antennas

Abstract: In an active phased array (i.e., an array that has amplifiers in each element) transmitting multiple beams, the intermodulation products generated by the amplifier amplitude nonlinearities form beams that, in general, radiate in directions different from the principal beam directions. In effect, the phased array antenna spatially filters the intermodulation products formed by signals from different beams. In a communications application this effect can be used to reduce the signal-to-intermodulation interference ratio. A description of this phenomenon is given and examples are presented that illustrate the mainbeam directions of beams formed by third- and fifth-order intermodulation products. An experiment that was performed to demonstrate this effect is described. The spatial filtering effect for beams with amplitude modulated signals is also treated, with an improvement in carrier-to-intermodulation ratio theoretically demonstrated.

Phased array sequential switching between short and long distance targets

Abstract: A function generator is connected to an airborne phased array radar antenna for steering a beam between high and low positions. During receiving on the high beam, the generator blanks long range target signals. During the low beam, the generator blanks short range target signals. A receiver is connected to the output of the antenna and a display is connected to the receiver output. By sequentially switching between low and high beams, with the described blanking, short and long range targets are displayed simultaneously, relatively free of ground clutter.

Beam-pointing errors of planar-phased arrays

Abstract: The beam-pointing error of an (M + 1) \times (N + 1) planar phased array is analyzed by the use of both analytical and Monte Carlo techniques. Simple formulas for the rms pointing error are obtained for uniform planar arrays with both uniform and Gaussian uncorrelated phase-error distributions and for any arbitrary scan angle.

Closely spaced orthogonal dipole array

Abstract: A broadband phased array antenna is shown wherein pairs of mutually orthogonal printed radiating elements, each one of such elements having a flared notch formed therein, are adapted to transmit or receive radio frequency energy having any one of a variety of polarizations.

Optically operated microwave phased-array antenna system

Abstract: An optical processing technique is employed to optically generate a set of properly phase-controlled signals that are appropriate to forming and steering, in space, a beam from a two-dimensional phased array antenna

Microstrip phased array antennas

Abstract: High velocity aircraft, missiles, and rockets require conformai, thin antennas. Ideally, an antenna "paper thin" would best suit the aerodynamic and mechanical engineer. This antenna would neither, disturb the aerodynamic flow, nor would it protrude inwardly to disrupt the mechanical structure.

Lens fed antenna array system

Abstract: A circular phased array system is described which utilizes a lens feed to simplify the problem of commutating the RF distribution system through 360* of steering of the antenna beam. The lens feed consists of a circular parallel-plate radial transmission line with a central set of probes and a ring of peripheral probes. The peripheral probes are coupled via switches to an array of radiating elements arranged in a circle. The central set of probes can be energized and phased to produce electromagnetic energy with an amplitude distribution within the parallel-plate line in any given direction. By selective settings of phase and amplitude of the energy coupled to the central set of probes to achieve the proper energy distribution to the peripheral probes and by operating the switches to determine which radiating elements are coupled to the peripheral probes, a desired directive antenna pattern with low side lobes is provided.

Airborne switched array radar system

Abstract: An airborne radar system is disclosed utilizing multiple fixed antenna arrays mounted within the periphery of the aircraft to avoid aerodynamic modifications and optimumly placed to achieve 360* surveillance coverage. The arrays preferably include a fore mounted array, an aft mounted array, a port mounted array and a starboard mounted array for respectively firing beams in different azimuth sectors relative to the aircraft. Each array is comprised of dipole elements having phase shifters coupled thereto for steering a beam within the corresponding sector. The radar system may include both primary and secondary radar subsystems with the dipole elements of primary and secondary radar antennas being physically interleaved in the aforementioned antenna arrays. The primary radar antennas time share an exciter, transmitter, receiver and signal processor through switching devices. The secondary radar antennas (typically an IFF/SIF system) similarly time share transmitting and receiving equipment. Time allocation between antennas of each subsystem and between operational modes such as ''''search'''' or ''''track'''' is based on various factors such as mission objectives, current target characteristics and radar purpose. Time allocation is preferably determined by an ''''on line'''' stored program digital computer which generates a radar control command to define the parameters for each beam to be fired. Typically, the control command specifies (1) array (2) beam elevation (3) beam azimuth (4) total number of fill and data pulses (5) number of fill pulses (6) frequency and (7) pulse repetition rate or frequency. For each radar subsystem, this control command is interpreted by a radar control unit which responds by controlling various system elements including the exciter, transmitter, switches, phase shifters and duplexers to cause the defined beam to be fired. Each control command also preferably specifies parameters utilized to interpret the return beam including (8) ground doppler offset (9) threshold (10) range start time and (11) range end time. This latter information is employed by the radar control unit to enable primarily the receiver and signal processor to generate a beam return report which is then communicated by the radar control unit to the digital computer. The beam return report typically includes a header portion specifying the (1) clutter level and (2) jam level for each different frequency. The report also includes a subreport for each return beam which specifies (3) range (4) amplitude (5) doppler filter number and (6) ratio of signal to clutter plus noise. The digital computer then utilizes the beam return report to determine subsequent control commands.

Phased array scanning antenna

Abstract: A landing system antenna in which a plurality of antenna elements arranged in a circular pattern are sequentially energized to project a scanning planar beam with fine scanning control maintained by controlling the phase in a plurality of small steps.

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.

Method and means for operating an airborne switched array radar system

Abstract: An airborne radar system is disclosed utilizing multiple fixed antenna arrays mounted within the periphery of the aircraft to avoid aerodynamic modifications and optimumly placed to achieve 360* surveillance coverage. The arrays preferably include a fore mounted array, an aft mounted array, a port mounted array and a starboard mounted array for respectively firing beams in different azimuth sectors relative to the aircraft. Each array is comprised of dipole elements having phase shifters coupled thereto for steering a beam within the corresponding sector. The primary radar antennas time share an exciter, transmitter, receiver and signal processor through switching devices. Time allocation between antennas and between operational modes such as ''''search'''' or ''''track'''' is based on various factors such as mission objectives, current target characteristics and radar purpose. Time allocation is preferably determined by an ''''on line'''' stored program digital computer which generates a radar control command to define the parameters for each beam to be fired. This procedure involves calculating the priority value of each track and search beam to be fired in accordance with predetermined criteria contained in the stored program. The priority value of each track beam to be fired involves determining the update rate for that target which is calculated based on the characteristics of the target. Priority values are then determined based on a comparison between the elapsed time since the last update and the calculated update rate.

Digitally controlled phase shift network

Abstract: The present invention relates to a digitally controlled phase shift network for use with an individual antenna element, as would form a part of a phased array radar system wherein a directional beam is formed and electrically scanned by control of the phase of each individual antenna element. The phase shift network here described is responsive to a computed digital signal which it converts in an electrically switched resistancecapacitance timing network to a pulse whose duration is an analog quantity stepped in equivalence to the digital input. The variable duration pulse is used to control the volt time area of a source of magnetizing energy to achieve stepped remanent states in the ferrite phase shifters corresponding to stepped angles of phase shift. A direct conversion of a digital signal into an analog phase shift angle is achieved while also providing electronic compensation for nonlinearity in the magnetization characteristics of the ferrite and for temperature drift. The invention herein described was made in the performance of a contract with the Department of the Army.

An Improved Single Flight Technique for Radar Stereo

Abstract: An improved technique for obtaining stereo radar image pairs is described. The technique uses a unique combination of two different radar beam pattern characteristics. The resulting stereo radar images are illuminated from very nearly the same aircraft position which results in radar shadow and backscatter characteristics which are very similar and in improved image registration possibilities. The reduction in illumination angle and aircraft position differences is shown to be nearly an order of magnitude or more when compared with a previously proposed single flight technique which used two vertical fan beam patterns at different azimuth angles. As a related sidelight it is shown that this previous technique requlres the two fan beam patterns to generate parallax on the images and thus can not be implemented with synthetic arrays squinted at two different squint angles.

Antenna element for circular or linear polarization

Abstract: An antenna element for use in a phased array antenna is disclosed. Such antenna element is a reciprocal device adapted selectively to radiate radio frequency energy of either circular or linear polarization. Such antenna element includes waveguide means for passing radio frequency energy and for radiating such energy; and means adapted to transform the polarization of the radio frequency energy as such passes through the waveguide means to radiate such radio frequency energy selectively with either linear or circular polarization. In a preferred embodiment the just-mentioned means includes a first and a second nonreciprocal quarter-wave plate having field orientations effectively 45° with respect to each other. Such nonreciprocal quarter-wave plates flank a third nonreciprocal quarter-wave plate switchable so that its field orientation is either aligned with the field orientation of the first nonreciprocal quarter-wave plate or, while still aligned as before, turned 180°. Further, the third quarter-wave plate may be switched into a nonenergized state. A reciprocal quarter-wave plate is disposed between the radiating end of the waveguide means and the second nonreciprocal quarter-wave plate. A phase shifter section is disposed between the third nonreciprocal quarter-wave plate and the first nonreciprocal quarter-wave plate. When the field orientations of the first and the third quarter-wave plate are aligned, vertically polarized radio frequency energy introduced into the waveguide means is changed to radiate as horizontally polarized radio frequency energy. When the field orientation of the third quarter-wave plate is reversed by 180°, vertically polarized radio frequency energy introduced into the waveguide means is radiated as vertically polarized radio frequency energy. When the third quarter-wave plate is unenergized, vertically polarized radio frequency energy introduced into the waveguide means is changed to radiate as circularly polarized radio frequency energy. The phase shifter section, whatever the polarization of the radio frequency energy passing through, is operative to change, in accordance with a beam steering control signal, the phase of such energy.

Corporate feed system for cylindrical antenna array

Abstract: A reciprocal corporate microwave feed network A matrix is connected between a selector switch and an antenna ring array The matrix divides microwave energy from sender apparatus and produces a tapered phase distribution to a selectively predetermined sector of the array The active or energized array sector forms a highly directive beam which is normal to the array sector The matrix is circularly symmetric and can feed any sector of the array as selected by an input switch The beam is step scanned over 360*, with the number of steps being determined by switching and matrix circuitry

Planar phased array fan beam scanning system

Abstract: Array element phase commands used to scan the beam of a planar phased array are conventionally obtained by adding to the beam shaping phases, phases obtained by sampling a linear (planar) function of position on the array surface. When this technique is applied to phase shaped fan beams, the beam acquires an increasingly curled or warped shape as the scan angle is increased. To offset this tendency, the scanning phase commands are obtained by sampling a function which becomes increasingly nonlinear (warped) as scan angle is increased.

Review of Ferrite Phase Shifter Technology

Abstract: Ferrite phase shifter technology is reviewed. Particular emphasis is placed on discussion of nonreciprocal, toroidal waveguide phasers and dual mode reciprocal phasers for use in phased array antennas.

Spatial statistics of instrument-limited angular measurement errors in phased array radars

Abstract: The major contributors to the random component of the instrument limited angular measurement errors in electronically scanned phased array radars are reviewed and formulas are developed for statistical modeling of these error sources. The error model employed is applicable to space-fed and certain types of corporate-fed arrays. A comprehensive computer program, embodying this analysis, has been developed for determining these array measurement errors and their spatial correlation statistics, in two angle variables. This program is used to evaluate the statistical behavior of angular errors for some typical situations of interest. The use of angle, frequency, and phase "dithering" for improving the correlation statistics of these arrays is examined. The phase dithering technique is shown to be at least as effective as angle and frequency dithering and has the virtue of being readily implemented in the beam steering computer.

Beamwidth of phased arrays

Abstract: A formula is developed for estimating the far-field beamwidth of an arbitrary narrow-beam phased array of identical isotropic elements at a single frequency. Equations are developed for the effects of errors in the estimated positions of the array elements.

Maritime Communications via Satellites Employing Phased Arrays

Abstract: This paper examines the feasibility of providing maritime mobile telecommunications as a new service via satellites. A global system with a capacity of 10 duplex voice/data channels (plus an interrogation/reply channel) per satellite is described. The capability is achieved with a 0-dB gain UHF antenna in the ship and a UHF phased array in the satellite, which produces 11 steerable beams, each with 30-dB peak gain. The links between satellite and shore are assumed to be at SHF. A dedicated satellite weighs 320 kg, which can be launched with an up-rated Thor-Delta. The prime power requirement of 730 watts is provided by an oriented solar array.

An Investigation of the Accuracy of Far-Field Radiation Patterns Determined from Near-Field Measurements,

Abstract: : The results reported show that far-field antenna patterns determined on the near-field range are as accurate as those determined on a far-field range. The patterns of a single plane, monopulse antenna, operated at 5.45 GHz were measured on a near-field range and two different far-field ranges, and detailed comparisons were made. The results of a computer-aided simulation study to determine the effects of various near-field measurement errors on the far-field patterns are also described. It was found that some near-field parameters are relatively critical; point source reflections are very deleterious. Far-field accuracy was found to be surprisingly insensitive to many near-field parameters. Comparisons of near-field and far-field techniques indicate several additional, non-technical, advantages of the near-field approach. Recommendations are made for future work to demonstrate the near-field technique on phased array antennas, and to improve the data processing procedures so as to increase the resolution of far-field patterns obtained from near-field measurements. (Author)

Microwave frequency amplifier constructed upon a single ferrite substrate

Abstract: A compact high power microwave frequency amplifier is constructed entirely upon a single ferrite substrate Negative resistance diodes, mounted directly in the ferrite substrate using low capacitance techniques, form the amplifying devices A number of similar amplifying stages may be joined onto a single substrate or divided into a number of similar substrates and used to advantage in phased array radar systems and in microwave communication systems because of their superior phase stability characteristics

Ultra-Wideband Phased Arrays

Abstract: : The report describes the activities and accomplishments associated with the two major technical tasks on this project. The first task is the development of a linearly polarized two-dimensional phased array which is well matched simultaneously over a large scan angle range and over an octave bandwidth. The second task is to extend the impedance matching of the linearly polarized element to an arbitrarily polarized element for wide-angle scanning and wide tunable bandwidth.

Phased array antenna with phase shifter cooling

Abstract: A phased array radar antenna including a plurality of individual radar emitters disposed in honeycomb arrangement and supplied through corresponding waveguides from a common source of microwaves to propagate a radar wavefront. The phases of the microwaves in the conduits are shifted to slow the waves and scan the wavefront by changing the magnetization of ferrite toroids in the conduits. Capillary means and a coolant cooperate in the conduits to remove excess heat from the toroids.

Adaptive array retrodirective landing control responser

Abstract: A landing control system normally quiescent but responsive to pulsed interrogation from an aircraft to be given (typically) elevation and azimuth angle information for landing approach The ground responser equipment determines the angle of arrival of the interrogation pulses through an adaptive phased array arrangement and retransmits that information as a coded reply Range information is air derived through the measurement of time delay in receiving the coded responser reply corresponding to each interrogation