Showing papers on "Interference (wave propagation) published in 1981"
••
TL;DR: In this paper, the authors proposed a method of ambiguity resolution for short-baseline interferometric observations of GPS, which is suitable for observations made with antennas of low directive gain.
Abstract: With the recent launching of several satellites of the global positioning system (GPS), a variety of schemes based on radio interferometry have been proposed for the accurate determination of relative positions of receiving terminals on the ground. Provided that the integer-cycle ambiguities of the interferometric phase observations can be correctly resolved, the baseline vector extending from the antenna of one terminal to that of another should be determinable with uncertainty much smaller than the 19-cm wavelength of the GPS transmissions. We propose a method of ambiguity resolution that is suitable for observations made with antennas of low directive gain. Such antennas are compact, but the feasibility of their use has been questioned because observations with them are susceptible to multipath interference. For short-baseline interferometric observations of GPS our method yields correct ambiguity resolution despite severe multipath interference and significant sky blockage, even when instability of the frequency standards governing the separate receiving terminals limits the time span of coherent integration to five minutes.
218 citations
•
23 Feb 1981TL;DR: In this article, a transmitter, a receiver and techniques for use in a frequency-hopping, multilevel frequency shift keyed (FH-MFSK) radio system are described.
Abstract: The present invention relates to a transmitter, a receiver and techniques for use in a frequency-hopping, multilevel frequency shift keyed (FH-MFSK) radio system which permits the selective concurrent transmission of one or two encoded frequencies per time slot of the transmitted sequence for improving reception at a receiver experiencing interference from the system transmitters above a predetermined interference threshold level. An alternative arrangement permits all transmitters and receivers to communicate with one another by transmitting a separate one of multiple frequencies in a separate one of an equal number of multiple frequency subbands forming the system frequency band during each time slot for providing flexibility in system design. Combinations of the two arrangements can also be employed.
70 citations
••
TL;DR: A laser interferometer which provides absolute distance measurements using tunable lasers by using an active feedback loop system to tune the laser wavelengths.
Abstract: This paper describes a laser interferometer which provides absolute distance measurements using tunable lasers. An active feedback loop system, in which the laser frequency is locked to the optical path length difference of the interferometer, is used to tune the laser wavelengths. If the two wavelengths are very close, electronic frequency counters can be used to measure the beat frequency between the two laser frequencies and thus to determine the optical path difference between the two legs of the interferometer.
59 citations
•
02 Jan 1981TL;DR: In this paper, a receive-transmit steerable null antenna prosor includes incrementally adjustable delay lines and a variable ratio power network (amplitude balance control) for adjusting the relative phase and amplitude in two or more antenna branches to steer a null on an interference source.
Abstract: According to the invention, a receive-transmit steerable null antenna prosor includes incrementally adjustable delay lines and a variable ratio power network (amplitude balance control) for adjusting the relative phase and amplitude in two or more antenna branches to steer a null on an interference source. A digital controller compares a signal which includes a representation of the interference level to a previously sampled value to note improvement or not and adjusts the delay lines and amplitude balance accordingly.
53 citations
••
TL;DR: In this paper, a method for automatically measuring the 3D deformation of a diffuse surface is studied, using a real-time holographic interferometer and a television-computer system.
Abstract: A method for automatically measuring the three-dimensional (3-D) deformations of a diffuse surface is studied, using a real-time holographic interferometer and a television-computer system. The object surface is illuminated from three different directions. The scattered waves are recorded on a thermoplastic hologram. Real-time holographic interference patterns are observed through the hologram in a fixed direction by sequentially applying the three illuminating beams. The three fringe patterns are put into the computer using a television (TV) camera. The relative fringe order numbers are determined over the whole surface. Calculations for obtaining 3-D deformation distributions are performed, and the results are displayed on a cathode-ray tube (CRT) monitor.
33 citations
••
TL;DR: In this article, the effects of the forward and backward-wave interference in a standing-wave resonator on laser output intensity were considered and the results were compared with those obtained when the interference effects are neglected.
Abstract: The effects of the forward- and backward-wave interference in a standing-wave resonator on laser output intensity are considered. In the paraxial- and plane-wave approximation and with boundary conditions appropriate for a Fabry–Perot resonator, the intensity equations are analytically solved. The variation of the output intensity with various parameters, such as the mirror reflection and absorption coefficients, small-signal gain, and atomic detuning, is considered, and the results are compared with those obtained when the interference effects are neglected. Considerable departure from the latter case is found. Our results should find application in choosing optimum parameters in the design of a laser resonator.
31 citations
•
22 Jan 1981
TL;DR: In this paper, the regeneration characteristic of the laser oscillation can be determined by a peak in the reflected or transmitted wave produced by the cooperation of the optical interference system and the absorption medium.
Abstract: Radiation at the frequency of a preselected absorbing resonance is produced by use of split and recombined interfering optical paths, arranged to produce near white light interference effects, and a preselected absorption medium disposed in one path of the interfering configuration. By association of this configuration with a laser oscillator, the regeneration characteristic of the laser oscillation can be determined by a peak in the reflected or transmitted wave produced by the cooperation of the optical interference system and the absorption medium. Use with standing wave, ring, and gain-switched transient lasers all can produce radiation essentially confined to the narrow absorption profile of a selected gas. Improved methods of laser chemistry and remote and close range gas detection are made possible by the new system. The system is also useful as an extremely narrow filter for broader band light sources, or as an optical element for other purposes, such as for establishing high Q response for optical resonators of the standing wave or traveling wave, ring type.
31 citations
••
TL;DR: In this paper, both approximate algebraic and numerical calculations have been carried out for the noise due to electrostatic waves incident on a dipole antenna, both for a thermal equilibrium plasma, and one having several components at different temperatures.
Abstract: Calculations, both approximate algebraic and numerical, have been carried out for the noise due to electrostatic waves incident on a dipole antenna. The noise is calculated both for a thermal equilibrium plasma, and one having several components at different temperatures. The results are compared with measurements from the IMP-6 satellite. In various frequency ranges, the noise power is dominated by Langmuir oscillations, by electron acoustic waves and by ion acoustic waves. The measurements are consistent with all of these, although the ion waves are not definitely observed, due to interference from shot noise.
27 citations
•
02 Mar 1981
TL;DR: In this article, a position encoder including a holographically recorded, single-frequency, phase grating is proposed, which acts as a basic common path interferometer and constitutes a highly efficient source of high contrast, stable, interference fringe patterns.
Abstract: A position encoder including a holographically recorded, single-frequency, phase grating. When this phase grating is illuminated by a quasi-monochromatic spatially coherent light source, it acts as a basic common path interferometer and constitutes a highly efficient source of high contrast, stable, interference fringe patterns. In a position encoder application, a carrier moves the grating in a plane that is orthogonal to an axis from the light source. Motion of the carrier is detected as the fringe pattern moves past detecting means thereby to sense motion and provide position information in the form of electrical signals.
27 citations
••
TL;DR: In this paper, the authors investigated a novel device concept for generating CW millimeter waves with output power in the multi-watt range, which involves the utilization of modulated laser radiation to induce in a distributed Schottky-diode structure a traveling-wave current which, in turn, synchronously excites the dominant mode of a waveguide structure to generate millimeter power.
Abstract: We have investigated a novel device concept for generating CW millimeter waves with output power in the multiwatt range. The concept involves the utilization of modulated laser radiation to induce in a distributed Schottky-diode structure a traveling-wave current which, in turn, synchronously excites the dominant mode of a waveguide structure to generate millimeter power. The induced traveling-wave current is directly proportional to the laser modulation generated by the interference of two overlapping laser beams of millimeter beat frequency. Detailed analysis indicates that the device has both high-output and frequency-tunable characteristics.
26 citations
•
30 Mar 1981TL;DR: In this article, an optical track is provided which rotates with the assembly of interference filters to generate pulses from index markings in the optical track, spaced so that one pulse is generated for each angstrom of variation of the center frequency transmitted through an interference filter.
Abstract: In an instrument adapted particularly for analyzing agricultural products, such as grain, interference filters are rotated successively through an infrared wide wavelength band beam of light, which irradiates a sample of the product. Each of the interference filters operates to transmit a narrow wavelength band of light, the center frequency of which is scanned through a range of values as the angle of incidence of the beam of light to the interference filter varies as the filter rotates through the beam of light. An optical track is provided which rotates with the assembly of interference filters to generate pulses from index markings in the optical track. The markings in the optical track are spaced so that one pulse is generated for each angstrom of variation of the center frequency transmitted through an interference filter. The pulses are counted in the counter and the counts in the counter are used to control the selection of intensities reflected from the sample to be used in the analysis of the sample.
•
10 Jul 1981
TL;DR: In this paper, a portable dual-laser-beam interferometer is described that nonintrusively measures skin friction by monitoring the thickness change of an oil film at two locations while said oil film is subjected to shear stress.
Abstract: A portable dual-laser-beam interferometer is described that nonintrusively measures skin friction by monitoring the thickness change of an oil film at two locations while said oil film is subjected to shear stress. An interferometer flat is utilized to develop the two beams. Light detectors sense the beam reflections from the oil film and the surface thereunder. The signals from the detectors are recorded so that the number of interference fringes produced over a given time span may be counted.
••
TL;DR: The error rate performance of several digital modulation methods in a fading environment and in the presence of one cochannel interference and AWG noise is analyzed and a unique formula emerges for different PSK systems.
Abstract: The error rate performance of several digital modulation methods in a fading environment and in the presence of one cochannel interference and AWG noise is analyzed. A unique formula emerges for different PSK systems. It is shown how this information can be used in determining acceptable degradation caused by cochannel interference in the case of a digital mobile communication system.
••
TL;DR: Using the image waves from two similar objects as, respectively, object wave and reference wave in an electronic speckle pattern interferometer (ESPI) setup, it is possible to obtain interference patterns that indicate the amount of relative displacement between the two objects as discussed by the authors.
Abstract: Using the image waves from two similar objects as, respectively, object wave and reference wave in an electronic speckle pattern interferometer (ESPI) setup, it is possible to obtain interference patterns that indicate the amount of relative displacement between the two objects. Experimental results demonstrating direct interferometric subtraction and addition of vibration patterns are presented. Possible applications of the technique are also discussed.
••
TL;DR: Rapid-double-exposure, diffuse-illumination holography is evaluated analytically and experimentally as a flow visualization method for time-varying shock waves for transonic compressor rotor cases.
Abstract: Rapid-double-exposure, diffuse-illumination holography is evaluated analytically and experimentally as a flow visualization method for time-varying shock waves. Conditions are determined that minimize the distance (localization error) between the surface or curve of interference-fringe localization and the shock surface. Treated specifically are the cases of shock waves in a transonic compressor rotor for which there is laser anemometer data for comparison and shock waves in a flutter cascade.
••
TL;DR: In this article, the analysis and evaluation of bit error probabilities of coherent MPSK nonlinear satellite communication systems were presented, in which there is uplink noise, downlink noise, and CW tone interference with random phase uniformly distributed over the interval [0, 2π].
Abstract: This paper presents the analysis and evaluation of bit error probabilities of coherent MPSK nonlinear satellite communication systems, in which there is uplink noise, downlink noise, and CW tone interference with random phase uniformly distributed over the interval [0, 2π]. The evaluation of bit probabilities also includes intersymbol interference whose statistical distribution is constructed through a two-dimensional moment technique. This moment technique is as effective and accurate as the standard Gauss quadrature formulas (GQF), yet more versatile than GQF for evaluating an expectation over random variables. Some numerical examples for the performance of satellite channels are illustrated.
••
TL;DR: In this article, a novel type of neutron interferometer was constructed and tested employing a split cylindrical zone plate with neutrons of 20 A wavelength, its performance and relative merits are discussed.
Abstract: A novel type of neutron interferometer was constructed and tested employing a split cylindrical zone plate with neutrons of 20 A wavelength Its performance and relative merits are discussed
••
TL;DR: In this paper, interference effects have been observed at the edges of images of cubic MgO crystals oriented so that one {100} face is almost parallel to the electron beam.
••
29 Jul 1981TL;DR: In this article, a high speed optical sampler is proposed that is driven by cw microwaves, which is composed of waveguide interferometers of the type originally proposed by Martin.
Abstract: A high speed optical sampler is proposed that is driven by cw microwaves. The sampler is composed of waveguide interferometers of the type originally proposed by Martin. A voltage applied to one (or both) arms of the interferometer modulates the interference of the optical radiation at the output. Such an interferometer can be driven at high frequencies if synchronism is maintained between the optical radiation and the applied voltage pattern. Spatially periodic exciting structures can serve this purpose. Deviations from synchronism can be compensated (within limits) by adjustment of the peak amplitude of the microwave voltage. A cascade of four interferometers on LiMb03, driven at 10 GHz, at multiples of (appr.) 3V (3, 6, 12, 24) have a predicted sampling-function width of 2 ps at 20 GHz repetition rate. Experiments on single section and double-section interferometers will be reported.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
••
TL;DR: The improvement offered by the proposed demodulator is of such a degree that some of the important restrictions in planning different radio systems could be relaxed.
Abstract: As a result of investigation of interference into FM systems, a new algorithm for the process of demodulation is proposed. When compared to the method using the conventional limiter-discriminator, it offers better immunity against the baseband interference noise. Desired signal processing is performed by the functional devices added to the conventional limiter-discriminator in such a way that this new demodulator can be optimized in the sense of the minimum baseband interference noise. The statistics of the wanted and interfering signals must be known. Several examples involving interference problems in FDM-FM radio-relay systems carrying multichannel telephone signals are elaborated to illustrate the performances of the proposed demodulator. FDM-FM, PSK, or FSK systems are considered the cause of the interference. The noise power ratio (NPR) at the output of the conventional limiter-discriminator and the improvement factor offered by the new demodulator, obtained on digital computer, are presented versus baseband frequency in the form of diagrams. Different IF filters in FDM-FM receiver and transmit filters in the interfering systems are taken into account. The improvement offered by the proposed demodulator is of such a degree that some of the important restrictions in planning different radio systems could be relaxed.
••
TL;DR: In this paper, a transducer is used to propagate acoustic waves along the three dimensions (X, Y, Z) of a rectangular cross section of a chamber of rectangular cross-section.
Abstract: A system is described for use with acoustically levitated objects, which enables close control of rotation of the object. One system includes transducers (18, 20, 22) that propagate acoustic waves along the three dimensions (X, Y, Z) of a chamber (16) of rectangular cross section. Each transducer generates a first wave which is resonant to a corresponding chamber dimension to acoustically levitate an object, and additional higher frequency resonant wavelengths for controlling rotation of the object. The three chamber dimensions and the corresponding three levitation modes (resonant wavelengths) are all different, to avoid degeneracy, or interference, of waves with one another, that could have an effect on object rotation. Only the higher frequencies, with pairs of them (e.g. 50, 52) having the same wavelength, are utilized to control rotation, so that rotation is controlled independently of levitation and about any arbitrarily chosen axis.
••
TL;DR: Some aspects of a new computerized method for automatic generation of frequency plans for radio communication systems are presented where the frequency planning problem is recast as a set partitioning problem and the objective is minimization of total system interference.
•
10 Jan 1981
TL;DR: In this paper, the interference fringes are formed by the interference of the phase subtracted waves having been removed of the phases of N number (N is integer) of spherical waves and the spherical waves are recorded on a recording medium, whereby a hologram is obtained.
Abstract: PURPOSE:To obtain the beam scanner of large scanning angles, small aberrations and large scanning magnifications by using the hologram formed from the interference fringes obtained by causing the phase subtracted waves having been subtracted of a plurality of spherical waves and the spherical waves to interfere with each other. CONSTITUTION:The interference fringes are formed by the interference of the phase subtracted waves having been removed of the phases of N number (N is integer) of spherical waves and the spherical waves and the interference fringes thus obtained are recorded on a recording medium, whereby a hologram is obtained. The phase distribution phi of the interference fringes may be expressed by formula 1. The light beam scanner using this hologram causes the light beam generated from a laser 23 to be focused by a lens 24 to be made into the divergent spherical waves which then radiate the hologram 25. The primary diffracted light from the hologram 25 focuses on a scanning plane 26 and is scanned in the direction perpendicular to the plane of the paper by a hologram moving mechanism. By using the hologram having been recorded with the interference fringes of high approximate degrees, the scanner of large scanning angles, small aberrations and large scanning magnifications may be obtained.
••
TL;DR: The effects of cochannel interference on the bit error rate of a QPSK satellite system are analyzed and the non-Gaussian nature of the interference and the small-signal suppression which may occur for uplink interferers are investigated.
Abstract: Increased frequency reuse in satellite systems will result in increased levels of cochannel interference. Such interference can in fact become the limiting factor affecting system performance. In this paper, the effects of cochannel interference on the bit error rate (BER) of a QPSK satellite system are analyzed. A nonlinear satellite transponder having a specified AM-AM and AM-PM transfer characteristic is assumed. An arbitrary number of up- and downlink interferers is considered. The theoretical results are compared with results obtained from time-domain computer simulations. Two facets of the cochannel interference problem which are of particular interest are investigated: the non-Gaussian nature of the interference and the small-signal suppression which may occur for uplink interferers.
••
TL;DR: In this paper, short laser pulses carry temporally and spatially coherent radiation which generally exhibits a broad spectrum of monochromatic plane waves and are suitable for experiments of temporally coherent optics: temporal diffraction, interference, filtering and frequency modulation, etc.
Abstract: Short laser pulses carry temporally and spatially coherent radiation which generally exhibits a broad spectrum of monochromatic plane waves. Pulses with narrow temporal frequency spectrum may be involved in operations of spatially coherent optics. On the contrary, pulses with narrow spatial frequency spectrum are suitable to experiments of temporally coherent optics: temporal diffraction, interference, filtering and frequency modulation, etc.
••
TL;DR: It has been found that among the different quadrature-carrier modulation systems studied, sinusoidal frequency-shift keying seems to exhibit the best overall performance in a cochannel and intersymbol interference environment.
Abstract: A method is presented for determining the performance of a quadrature-carrier modulation system in terms of probability of error in the presence of additive white Gaussian noise, intersymbol interference, and cochannel interference. This method has been applied to determine the error rate of several quadrature-carrier modulation systems using Butterworth receiving filters of different orders. It has been foand that among the different quadrature-carrier modulation systems studied, sinusoidal frequency-shift keying seems to exhibit the best overall performance in a cochannel and intersymbol interference environment. These results are shown through a number of performance curves that provide useful data for the systems designer.
•
IBM1
TL;DR: In this article, a bus-oriented, operated according to the frequency division multiplexing, optical communications system pluggable coupling elements and color encoder and decoder are proposed, which are designed as selbstkollimierende optical elements.
Abstract: To build a bus-oriented, operated according to the frequency division multiplexing, optical communications system pluggable coupling elements and color encoder and decoder are proposed, which are designed as selbstkollimierende optical elements. The coupling elements consist of a built into the manifold selbstkollimierenden part (22a) and an attachable thereon counterpart (22b). Without counterpart coupling element reflects the light exiting the manifold light virtually lossless back into the manifold back, for example by total internal reflection. The patch counterpart contains frequency-selective agents (for example, an interference filter 25) and coupled, for example by interference of total reflection, the desired wavelength band from the manifold from. The frequency encoder and decoder are also made of selbstkollimierenden components which are either connected via coupling elements, or can be incorporated directly into the manifold. The coders prefer to use reflection grating as dispersive element; a color encoder which is incorporated in the manifold consists of two halves with interlocking reflection gratings in which the reflected light is split in frequency, the transmitted light, however, does not undergo decomposition.
••
TL;DR: In this article, a formulation combining three sources of cross polarization in multipath propagation is given, which relates to finite antenna isolation, which becomes worse for off-axis multipath reception.
Abstract: A formulation combining three sources of cross polarization in multipath propagation is given. The first relates to finite antenna isolation which becomes worse for off-axis multipath reception. Antenna amplitude and phase patterns are most important. The second, associated with atmospheric refractive index variations, requires asymmetric gradients for both linear and circular polarization. This by itself is the least signifiant source of depolarization but these rays cause variable interference between themselves and with other rays. The third is due to rays reflected once or twice from the ground. For linear polarization, inclined ground reflectors are required, but for circular polarization, polarization-dependent reflection coefficients are sufficient to give cross-polarization.
•
23 Jul 1981
TL;DR: In this article, a demultiplexer was used to eliminate a plurality of interference waves by using a D/A converter and keeping an optimum state of a lot of notch filters with one converter.
Abstract: PURPOSE:To eliminate a plurality of interference waves, by using a demultiplexer and keeping an optimum state of a lot of notch filters with one D/A converter. CONSTITUTION:Notch filter 2-4 are connected in series and interference waves included in the filters 2-4 are selected at a tuning circuit 12 and detected at a detection circuit 15. A digital voltage is supplied to a D/A converter 19 from a processor 17 and the converter 19 selectively supplies a DC voltage to the filters 2-4 through a demultiplexer 18. Further, the converter 19 and the demultiplexer 18 are controlled with the device 17 including a microcomputer so that the frequency of a wave eliminated interference is made coincident with the frequency of the interference wave at a selected notch filter.
•
04 Dec 1981
TL;DR: In this paper, a frequency selective memory with a storage material for storing frequency holes in at least two spatial dimensions and a frequency dimension was proposed. But the memory was not designed to store holographic interference patterns.
Abstract: The apparatus includes a frequency selective memory having a storage material for storing frequency holes in at least two spatial dimensions and a frequency dimension. Interference patterns are stored in the memory such that each complete interference pattern is found in the spatial dimensions while the series of interference patterns is in the frequency dimension. A laser beam is directed onto the surface of the memory to read the memory. By changing the electric field across the storage material, subsequent interference patterns are shifted in the frequency dimension into resonance with the laser beam thereby changing the interference pattern detected. The interference patterns may be a series of holographic interference patterns which would provide as an output a series of three dimensional images, or they may be a series of gratings which would provide a laser beam which scans in a spatial dimension as an output.