Showing papers on "Phase (waves) published in 1975"

Phase-locked loop circuit

Abstract: A phase locked loop circuit comprises a phase comparator having an operation range with specific limits for phase comparing A voltage-controlled oscillator produces an output at the output of the phase locked loop At the same time, the oscillator output is fed to the phase comparator A detector circuit, supplied with the output of the phase comparator, detects any exceeding of a specific limit of the phase by comparing the operation range of the phase comparator with a phase deviation of the oscillator output signal fed to the phase comparator The detector produces an output correction voltage An adder circuit adds this output correction voltage and an output error voltage of the phase comparator and supplies the resulting added voltage, as a control voltage, to the voltage-controlled oscillator This phase locked loop operates in a state wherein the lock range thereof has been equivalently expanded by the correction voltage

Phase−matched harmonic generation in a laminar structure with wave propagation in the plane of the layers

Abstract: A technique for obtaining phase−matched second harmonic generation using a finely layered structure with the radiation propagating parallel to the layers is analyzed.

A new method of measuring propagation coefficients and characteristic impedance in blood vessels.

Abstract: True propagation coefficients of pulse wave harmonics in an artery can be determined in vivo by measuring pulsatile blood pressure and flow at each of two points along the length of the vessel. These coefficients, which are complex numbers that describe the attenuation and the phase shift imposed on a traveling wave, are independent of the reflected waves in the circulation and thus provide information about the viscoelastic state and other properties of an artery. The equations involved are implicit in standard transmission-line theory, but they have not previously been applied in this particular way to blood vessels. The femoral artery, exposed in situ, was studied in 11 anesthetized dogs. At 1.5 Hz, true attenuation constants averaged 0.0151 nepers/cm, and true phase constants averaged 0.0155 radians/cm. As frequency increased, the apparent phase velocity of flow, in contrast, was relatively low at the first harmonic and rose as frequency increased. True phase velocities lay between the apparent pressure and flow values. Characteristic impedance at 1.5 Hz had an average modulus of 1.76 times 10-4 dyne sec/cm5 and a phase of minus 0.31 radians. The modulus diminished as frequency increased, and the phase became less negative. These results show that true phase constants and characteristic impedances determined by this method are consistent with data reported by others and provide information not previously available about flow wave propagation.

Phase tracking network

Abstract: A phase tracking network comprising a phase correction network for correcting at least some of the phase error of an input signal to provide a phase corrected signal having components in first and second channels and a detector responsive to the phase corrected signal for providing a detected signal having first and second components in the first and second channels. An error calculator provides a phase correction signal back to the phase correction apparatus which responds to the phase correction signal to correct the phase error of the input signal. The phase error signal contains substantially no noise from the first channel at least when the first component of the detected signal is zero and contains substantially no noise from the second channel at least when the second component of the detected signal is zero. This is accomplished by utilizing the error calculator to provide a first control signal which represents a first fixed value, zero, and a second fixed value when the first component of the detected signal is ideally positive and not zero, ideally zero, and ideally negative and not zero, respectively. The error calculator similarly provides a second control signal for the second component of the detected signal.

A new method for the analysis of multi-mode surface-wave dispersion: Application to Love-wave propagation in the east Pacific

Abstract: A new technique is presented for simultaneously measuring the average, regional phase velocity of two or more surface-wave modes, even if they travel with the same group velocity. Many observations are required over paths of varying length with earthquake sources of known focal mechanism. The phase of the signal observed at each station can be predicted if the initial phase of the source and the phase velocity and relative amplitude of each mode is known. The square of the difference between the observed phase and the predicted phase is summed over all paths for a set of trial phase velocities. The trial velocities which give the minimum sum correspond to the average phase velocity of each mode. By applying this technique to Love-wave data from the east Pacific, the dispersion of the first higher Love mode was measured for the first time in an oceanic area. The phase velocity of the fundamental mode was found to increase with increasing age of the sea floor, probably as a result of the cooling of the oceanic lithosphere. The region was found to be anisotropic for Love-wave propagation, with the fastest velocities roughly perpendicular to the ridge. The degree of anisotropy appears to increase with increasing period.

Fourier-transform holography by pseudo-random phase shifting

Abstract: A phase mask comprised of a rectangular array of phase shifting areas arranged in a pseudo-random pattern is illuminated with a beam of electromagnetic radiation. The array of pseudo-randomly phase shifted beams is focused on a Fourier transform plane on which the power spectrum of the beams distributes in two orthogonal directions from its center maxima. The phase shifting areas are arranged in such a manner that there is an approximately equal number of phase shifts for each of the different phase shifting areas with a constant phase relation between orthogonally adjacent phase shifting areas. The center maxima of the spectrum is confined to a rectangular-shaped area and uniformly distributed by suitably selecting the number of different phase shifts. Coherent noise on the reconstructed image is effectively eliminated.

Phase sequence detector for three-phase ac power system

Abstract: The phase sequence of the phase currents supplied by a three-phase AC power supply to a phase-sensitive load (such as a three-phase AC motor) is monitored by developing three phase-displaced, rectangular shaped logic signals, respectively representing the three phase currents, and applying these logic signals to respective ones of the J, C and K inputs of a J-K flip-flop. When the load is correctly connected to the power supply, the phase relationship of the three logic signals will be appropriate to trigger the flip-flop to its set operating state. Any other sequence actuates the flip-flop to its reset state which, in turn, disconnects the load from the power supply.

An Optimal Phase Demodulator

Abstract: : The paper presents the results of an investigation on the optimal performance of the phase demodulator using Bucy's non-linear filtering theory. A cyclically optimal non-linear phase estimation technique was developed for modular phase tracking. (Author)

Phase−matched second harmonic generation in a liquid−filled waveguide

Abstract: Phase−matched second harmonic generation in a nitrobenzene−filled waveguide has been accomplished by using a periodic electrode to modulate the nonlinear susceptibility.

Phased array antenna with coarse/fine electronic scanning for ultra-low beam granularity

Abstract: An antenna and scanning means therefor particularly useful in an aircraft landing system operating in the microwave frequency range. The antenna is of the line phased array type which includes digitally controlled phase shifters for each of the radiating elements of the array. The beam formed by the antenna is steered by incrementing the phase shift applied at each of the array radiating elements by an amount of phase which is dependent in part upon the position of the radiating element in the array. Phase increments sufficient to shift the beam position by one coarse step (0.1°) are applied to symmetrically located radiating element pairs, pair by pair, until all elements have been incremented. The beam is thereby caused to move through one coarse step in a number of fine steps equaling the number of pairs of elements in the array. An additional feature of the scanning means is the application of phase increment to the array elements in a pseudo-random sequence.

π-Loop phase bit apparatus

Abstract: The use of electronically variable phase shifters is required in phased array radar systems. Diode phase shifters are particularly well suited for use in phased array radar systems because they have size and weight advantage over other types of phase shifting components such as ferrite devices and traveling wave tubes and, in addition, offer the potential of cost reductions through the application of batch processing techniques. In accordance with the present invention, a phase bit is provided by the appropriate forward or reverse biasing of one series and one shunt diode to switch between a π circuit and a loop transmission line circuit shunting the equivalent capacitance of the series diode when reverse biased.

Method and apparatus for providing a phase compensated optical beam

Abstract: According to one herein disclosed embodiment, an initial uncompensated energy pulse is transmitted towards a remotely located target; a portion of the energy reflected from the target is received, processed so as to be back-scattered from a Brillouin mirror, amplified and then retransmitted along a path coincident with the received path. The backscattered energy from the Brillouin mirror is the complex phase conjugate of the received pulse and consequently the second transmitted pulse is phase encoded such that the effects of phase perturbations encountered along the received path are substantially canceled, and near diffraction-limited convergence of the beam upon the target is obtained.

Linear and nonlinear optical properties of ferroelectric BaMgF4 and BaZnF4

Abstract: These first measurements of the nonlinear optical properties of fluorides (BaMgF4 and BaZnF4) show these air‐stable compounds to be noncritically phase matchable at room temperature for a 1.06‐μ pump. The highly ionic compounds are also quite resistant to optical damage (∼109 W/cm2). The materials should find applications as frequency doublers in cases where spatial power distribution makes crystals with walk off less desirable and/or cases where high pump powers require crystals which are resistent to damage.

Filtering without Phase Shift

Abstract: The influences of phase shifts are extremely important in the determination of filtered waveforms and therefore in the interpretation of many biosignals. Low frequency shifts from high pass filtering, for example, are significant because large time displacements result from small phase deviations in the vicinity of the corner frequency. If a filter with a symmetric time response is employed, no phase shift will ensue. The time symmetry in this example is achieved with a tape recorder, first recording a high pass filtered signal and then playing back with time reversal to a second recorder through the high pass filter again. Real time processing is not achievable.

Low‐frequency phase distortion of speech recordings

Abstract: Low‐frequency phase distortion introduced by good quality audio tape recorders causes large errors in the reproduced waveform. It is advocated that a low‐frequency rectangular wave should always precede the speech on recordings intended for wide distribution, so that the correct phase relationships of spectrum components can be identified. Examples of phase correction by backwards filtering with a sampled‐data filter are given. In the absence of a calibration signal, one example used knowledge of typical glottal pulse shapes as a guide for phase correction.Subject Classification: XX.XX.

Segregated phase comparison system

Abstract: This disclosure relates to phase comparison relaying systems for a three phase power transmission line in which the current is measured at each end of each phase conductor. The phasor difference of the currents in a selected two of the phase conductors is determined at each end of the selected conductors and is phase compared to determine the location of phase-to-phase faults whether or not a ground fault is involved while the phasor sum of the current in all three of the phase conductors is determined at each end of the phase conductors and is phase compared to determine the location of phase-to-ground faults.

Phase-controlled voltage regulator

Abstract: A method and apparatus for regulating the RMS voltage applied to a load from an AC source having a peak-to-peak amplitude which varies within a predefined range. The apparatus comprises a waveform generator for producing a predefined periodic waveform, a comparator circuit for comparing such waveform with the sinusoidal waveform of the source whereby a signal is produced each time the algebraic difference between the instantaneous values of the compared waveforms changes sign, and a switching circuit responsive to the comparator circuit output for interrupting the voltage applied to the load at the start of each cycle or half-cycle. The shape of the waveform produced by the waveform generator is such that the desired RMS voltage appearing at the output terminals is produced.

Speckle noise reduction by random phase shifters.

Abstract: Experimental results are given that show that a random phase shifter (RPS) is effective in reducing speckle noise caused by optical defects in coherent imaging systems, including holographic imaging systems. Here the RPS is composed of many tiny transparent blocks, each of which gives a definite phase shift such as O or π to the transmitting light; and the distribution of the phase shift is two-dimensionally random. The optical defects are scattering centers such as scratches or dust on lenses or on the hologram medium in the case of holographic imaging systems.

Spectrometer means employing linear synthesized RF excitation

Abstract: Broadband RF excitation for a Fourier transform spectrometer is obtained by synthesizing the time domain excitation from the desired frequency spectrum of RF excitation. Means are provided to Fourier transform the desired spectral data from the frequency domain into the time domain to obtain a modulation output for modulating an RF carrier signal to generate the desired sideband of RF excitation. In a preferred embodiment, the desired frequency domain data, as tabled in the computer, has a pseudorandom phase shift added to each component for scrambling the phases of the RF excitation. The excited RF resonance signals in the time domain are detected, time-averaged, Fourier transformed to the frequency domain and, in the case of phase scrambling, unscrambled by the pseudorandom phase angle sequence, and displayed.

Phase and/or frequency comparators

Abstract: A phase comparator indicating a phase difference range of n × 360°, between two input signals, comprising edge triggered shift registers, for dividing the input signals by n, means for modulating the width of the resulting output pulses in proportion to the phase difference of the input signals, and integrating means to combine the modulated pulses into a time-averaged signal which is indicative of the phase difference.

Nonrecursive digital filters for detecting multifrequency code signals

Abstract: It is shown that for nonrecursive digital filters in the first canonic form the hardware requirements are proportional to the output rate. Using a low output rate, a relatively simple receiver for multifrequency-code (MFC) signals can be achieved. Linear phase bandpass pairs with a 90° phase difference are used to eliminate the input signal phase dependence. Narrow linear phase bandpass filters with even and odd symmetric impulse response are compared with filters with no phase constraints. It turns out that linear phase filters are almost as good as filters without phase constraints and that 8 bits are enough for the filter coefficients. Some aspects of the design of a digital receiver for PCM-encoded MFC signals are discussed.

Two-mode RF phase shifter particularly for phase scanner array

Abstract: A space-fed phased-array arrangement in which the plural antenna elements each include first and second (front and rear) individual radiators. Between these input and output radiators, there is a combined controllable phase shifter and controllable electronic switching arrangement. In accordance with external control signals, the amount of phase shift (phase delay) introduced by each element may be controlled, and by appropriate programming of these phase shifts, beam formation and pointing angle may be determined. The electronic switch devices are programmable to convert any or all of the antenna elements to reflector or retro-directing elements whereby a rear-pointing beam may be generated and scanned in substantially the same way as the forward beam is generated and scanned. In the retro-directive (reflective) mode, energy from the primary feed passes bi-directionally through the reciprocal controllable phase shifter sections.

Network-fed phased array antenna system with intrinsic RF phase shift capability

Abstract: An integral element/phase shifter for use in a phase scanned array. A non-resonant waveguide or stripline type transmission line, series force feeds the elements of an array. In the embodiments shown, four RF diodes are arranged in connection within the slots of a symmetrical slot pattern in the outer conductive wall of the transmission line to vary the coupling therefrom through the slots to the aperture of each individual antenna element. Each diode thus controls the contribution of energy from each of the slots (at a corresponding phase) to the individual element aperture and therefore determines the net phase of the said aperture. Three species of the invention are shown, the first and second involving RF diodes in the slots of waveguide broad and narrow walls respectively, and the third having slots through the shield plane of a stripline. The invention facilitates array phase scanning without the need for separate, and relatively more expensive, discrete phase shifters for each antenna element.

The application of iterative techniques to the investigation of strong phase objects in the electron microscope

Abstract: Modifications to iterative procedures for recovering phase information from recorded electron intensity distributions, which are applicable to strong, periodic phase objects are considered. Test calculations involving functions resembling those encountered when studying magnetic thin films in the electron microscope are made, and in particular the success or otherwise in recovering the original phase function, when only imperfectly recorded electron intensities are available, is discussed. For objects with peak-to-peak phase shifts less than 10 radian considerable success is achieved, but only if some a priori knowledge of the nature of the specimen is available have satisfactory results been obtained for stronger phase modulators. Under suitable conditions rapid and accurate results may be obtained for objects with peak-to-peak phase shifts of 30 radian using an appropriate iterative technique.

Phase memory in W.K.B. and phase integral solutions of ionospheric propagation problems

Abstract: In a slowly varying medium the propagation of waves remote from turning points or coupling points can be expressed in terms of W.K.B. solutions. For an isotropic medium a W.K.B. solution includes a factor that is an exponential of a phase integral or eikonal function. This expresses the cumulative change of phase that has occurred in the medium previously traversed, and has been called the 'phase memory'. It depends on the forms of the functions describing the spatial dependence of the medium. The remaining factor of the W.K.B. solution is a function only of the local properties of the medium. For an anisotropic medium such as the ionosphere, however, each W.K.B. solution may contain another factor which is also the exponential of an integral, and which has a memory content because it cannot be absorbed into the local factor. The properties of this new memory term, including its physical explanation, are here examined for radio waves obliquely incident in a horizontally stratified ionosphere. The omission of this extra term from phase integral solutions can some-times lead to serious errors. This is demonstrated by adopting several typical models of the ionosphere and comparing full wave solutions for radio reflexion coefficients with solutions calculated by the phase integral method, with and without the extra memory term. The opportunity is taken to describe also a method in which full wave solutions and the phase integral method are combined.