Showing papers on "Chirp published in 1974"

Ultrashort pulse measurements

Abstract: The generation of intense ultrashort light pulses in mode-locked laser systems has made possible a wide range of new experiments designed to study the interaction of light with matter. For the quantitative interpretation of the results, accurate measurement of the optical pulse structure is essential, and it is the purpose of this paper to review all the diagnostic techniques currently available. The recent rapid development of the electron-optical streak camera is highlighted, while considerable space is devoted to an extensive description of the many second- and higher order correlation measurements (including the popular two-photon fluorescence method). A discussion of ultrafast shutter techniques is also included, together with a section on pulse chirping and dynamic spectroscopy.

Effects of Range-Doppler Coupling on Chirp Radar Tracking Accuracy

Abstract: Attention is called to the phenomenon of ?range-Doppler coupling,? characteristic of linear FM (chirp) waveforms, and the strong effect this coupling may have on tracking accuracy. Numerical results are presented for simple three-state filters and for a realistic reentry vehicle tracking problem.

Chirp communication system

Abstract: A communication system that is difficult to jam has a transmitter transmitting successive chirp signals, which start at different initial frequencies and all have the same frequency - time slope. At the transmitter successive selections are made from among the different available chirp signal frequencies in accordance with a predetermined pseudorandom program that is known at the receiving station. The receiver has a chirp matched filter capable of receiving all of the different chirps but, being a distributed filter, it delays the different received chirps by differing amounts depending upon the initial frequency of each chirp. The output of the chirp filter is envelope-detected, and the resulting pulse signal is passed through a time gate that is gated on at a time that is selected in accordance with the predetermined program. The system has advantages for anti-jam communications, multiple-access communications, frequency diversity radio, and coding using multiple frequencies, as examples. The chirp matched filter is conveniently a surface wave device.

Distance measuring equipment

Abstract: Disclosed is improved distance measuring equipment comprising an airborne FM coded, chirp, interrogator transmitter in combination with a weighted matched receiver in a ground transponder. The airborne transmitter produces a long low power frequency modulated output pulse. Detection in the transponder receiver is accomplished by pulse compression matched filter techniques.

Pulse compression for more efficient operation of solid‐state laser amplifier chains

Abstract: We propose a pulse compression scheme which reduces the peak intensity while increasing the energy density achievable in a Nd:glass amplifier chain. Self‐focusing is the dominant effect responsible for limiting the power of a short‐pulse Nd:glass amplifier chain, and the reduction of the intensity (through this compression scheme) greatly reduces these problems. We recommend injecting a lower‐intensity and longer‐duration pulse into the chain. Under some circumstances, the glass nonlinearity will impress upon the pulse a chirp suitable for efficient subsequent temporal compression, and this may result in higher effective peak power operation. If a 1‐nsec (full 1/e duration) temporally Gaussian pulse with a chain‐averaged peak intensity of 2 GW/cm2 propagates 2 m in a Nd:glass laser chain, we calculate that the pulse could be subsequently compressed (by a series of Gires‐Tournois interferometers) to 125 psec with good stability against input pulse amplitude noise. Such short pulses are of major interest for laser fusion.

Transversal frequency filter

Abstract: A charge-transfer transversal filter and method of use is provided. In one aspect of the invention a handpass filter is provided where the center frequency of the bandpass is variable responsive to the clock rate applied to the charge-transfer devices. In a different aspect of the invention a matched filter for a chirp signal is provided. The filter requires a minimum number of Nyquist samples by including the provision of a clock rate which varies responsive to the frequency sweep of the input chirp signal. A method for detecting a chirp signal is provided which includes the step of selectively varying the clock rate applied to a charge-transfer shift register responsive to the frequency variations of a selected chirp signal.

Electronically focused imaging system and method

Abstract: An improved electronically focused imaging system for focusing transmitted acoustic waves into a focal line and for scanning the focal line for waves either reflected or transmitted from an object of interest. The system includes N transducer elements in a transmitter array and N transducer elements in a receiver array. These 2N elements can resolve N2 locations on the object of interest. In one embodiment the transmitter array is pulsed through a delay line that is activated by two, independent, frequency varying chirp signals. In this embodiment the receiver array is focused to scan the focal line and to develop a rectangular raster so that the output of the system is viewable on an oscilloscope or a television screen. In another embodiment the transmitter array is pulsed by a delay line activated by one chirp signal and a 45° raster is developed.

Apparatus for the generation of a high capacity chirp-Z transform

Abstract: Apparatus for performing a high-capacity two-dimensional, chirp-z transform, suitable for the signal processing of radar and sonar signals, comprising: an N2 plurality of two-dimensional partial chirp-Z transform devices; an acoustic surface-wave demultiplexer and chirp multiplier, whose inputs comprise all the outputs of the partial transform devices; an acoustic surface-wave discrete chirp filter, whose input comprises the output of the demultiplexer and chirp multiplier; and an output multiplier whose two inputs comprise the output of the surface-wave demultiplexer and chirp multiplier and the output of the acoustic surface-wave discrete chirp generator, the output of the output multiplier comprising the terms of a one-dimensional chirp-z transform in a linear congruential scan.

Relation of radar range resolution and signal-to-noise ratio to phased-array bandwidth

Abstract: Phased-array radar systems using wide-band linear-FM pulses suffer from array dispersion. This causes a loss in signal-to-noise (S/N) ratio and in radar range resolution (a broadening of the compressed-pulse width). Depending on the choice of the receiver matched filter (MF) and weighting filter (WF) one or the other of these effects may be minimized. The effects of dispersion in a square planar array with either a parallel feed or a center-fed series feed are studied. Loss in S/N ratio and in range resolution are determined for typical cases, and general curves are given for arrays with arbitrary size, scan range, and signal bandwidth. It is shown that there is an optimum or maximum-useful signal bandwidth for each array, for which the minimum S/N-loss MF-WF design is the same as the ideal-compressed-pulse-shape MF-WF design. For pulses having greater signal bandwidths, time delay steering should be used in the array.

Chirp Waveform Generation Using Digital Samples

Abstract: This paper describes two methods of generating an analog frequency-modulated waveform by the use of a small number of digital samples of the ?chirp? waveform. The number of digital samples required is a function of the time-bandwidth product. For certain values of time-bandwidth product, this type of signal generation becomes extremely efficient. Several proofs are offered which show how to select ?optimum? values of time-bandwidth products. Two hardware implementations are suggested. One is based on the use of modulo arithmetic and a small stored memory table. The second method utilizes the inherent signal symmetries available if ?optimum? time-bandwidth products are selected. The symmetrical signal patterns are stored in recirculating reversible shift registers which can be read out at high speeds.

Apparatus for transforming electronics signals between the time and frequency domains utilizing acoustic waves

Abstract: Apparatus for transforming electronic signals between the time domain and frequency domain in real time which comprises means for mixing the signal to be transformed with a predetermined chirp (variable frequency signal) in an acoustic wave convolver.

Charge coupled device signal processing apparatus using chirp-Z-transform techniques

Abstract: Signal processing wherein signals are processed using chirp-Z-transform (CZT) techniques and charge transfer device (CTD) transversal filters. The chirp weighting signal may be amplitude modulated to achieve signal apodization and may be generated by impulsing a CTD complex filter having an appropriate impulse response. Signal premultiplication using a one-bit quantized chirp signal is described. Application of these techniques to doppler range processing apparatus wherein radar returns are premultiplied to provide up-chirp multiplied time samples prior to being inputted into a CTD range buffer. Each bit of the CTD has an associated CTD chirp-Z-transform complex filter the outputs from each of which are summed and squared. The range bins and the associated complex filters are provided on a common semiconductor chip together with peripheral circuitry.

A Two Dimensional Electronically Focused Imaging System

Abstract: : A two dimensional acoustic imaging device, with electronic focusing and scanning in both directions was constructed. The device is designed to work with 2.25 MHz acoustic waves. It employs M piezoelectric elements in a transmitting transducer, which produce a beam focused and scanned in the y direction. An N element receiving transducer is used to focus and scan in the x direction. This makes it possible to obtain M by N resolvable spots with only M plus N elements, a considerable saving in complexity. The phase reference for the transmitter and receiver are supplied by frequency modulated chirp signals sent along acoustic surface wave delay lines. One of the novel features of this device is the ability to obtain an arbitrary scan velocity, even a stationary focus, with the transmitter.

The Effect of Acoustic Signals on the Chirp Rhythm in the Bush Cricket Pholidoptera Griseoaptera

Abstract: The effect of acoustic signals on the control of chirp production has been investigated using the insect9s own chirp to trigger artificial sound signals (100 msec, 70dB, 12 or 15 kHz) at predetermined phases of the chirp cycle. The signals appear to reset the phase of the chirp rhythm generator, and signals given late in the cycle are followed by the greatest phase shifts. The signals may also have excitatory after-effects which are usually small, but can summate to give a slow, longer lasting increase in chirp rate. This appears to happen during alternation with a natural or artificial partner.

Differential phase-shift keying applied to chirp data signals

Abstract: Chirp communication systems have been constructed that use signals having ascending and descending linear frequency sweeps to define mark and space data states, respectively. Such signal states are approximately orthogonal, and are generally detected noncoherently. The paper describes preliminary investigations into a method of differential phase modulation applied to chirp data signals. This improves the chirp-system performance in white noise and single carrier interference, and essentially retains the inherent protection that chirp signals have in multipath conditions. Also, improved bandwidth utilisation may be achieved with multiphase operation.

Chirped Fourier Spectroscopy. 1:Dynamic Range Improvement and Phase Correction

Abstract: Chirping is the deliberate dispersion of the frequencies in a signal to remove a strong central peak. In a Fourier spectrometer, chirping improves dynamic range. For typical applications, the improvement is equivalent to about 16 dB in SNR. A very large nonlinear phase correction is required, but this is shown to be surprisingly simple to achieve in practice.

Adjustable frequency scanning signal processor

Abstract: A compressive or "microscan" signal processor adapted for the simultaneous measurement of multifrequency signal components which encompass a broad frequency spectrum. In accordance with one embodiment of the invention, the applied signals are processed through a mixer which is driven by a linear frequency versus time waveform sweep signal. The output from the mixer is applied to one input port of a nonlinear correlator, and a second input port of the correlator is supplied with a linear frequency versus time waveform signal whose slope is opposite from that of the sweep signal applied to the mixer. The output signal from the correlator comprises a series of pulses which are displaced in time as a function of the frequency of the corresponding portions of the applied signals, and whose amplitudes are representative of the relative energy distribution of the applied signals.

Use of chirping to compensate for nonlinearities in Fourier spectroscopy

Abstract: Chirping introduced into a Michelson interferometer permits correction for nonlinearities, distortion, and intermodulation in the final spectrum. This is because the false harmonics of each frequency carry the characteristic phase of the original frequency, whereas true spectral components at higher frequencies have their own characteristic phase. In an unchirped interferogram, there is no such distinguishing phase. This paper explains how the distinguishing phase occurs, presents two algorithms for carrying out the distortion correction when the form of the distortion is known, and displays results of correcting selected distorted experimental interferograms. This capability is a new advantage of chirping in Fourier spectroscopy.

Circuit arrangement for synchronizing a television receiver

Abstract: The invention provides a circuit for centrally generating the horizontal and vertical sweep frequencies in a TV receiver. A central oscillator provides a frequency which is divided to obtain the horizontal frequency. A periodic counter with adjustable final counting value divides the central oscillator frequency to establish a vertical sweep signal. Phase comparators and gate circuits are used to gate the oscillator signal to the periodic counter to synchronize the vertical sweep with the transmitted vertical sync signal.

A Time Sidelobe Reduction Technique for Small Time-Bandwidth Chirp

Abstract: A filtering technique is described which permits time sidelobe suppression of small time-bandwidth product shirp. Signal-to-noise loss and time sidelobe level sensitivity to Doppler shift are presented for a filtered chirp waveform whose time-bandwidth product is 10.

Sweep and memory control circuit

Abstract: A control circuit having a digital memory for providing sweep voltages to receivers in a doppler satellite tracking station of proper amplitude and duration to ensure searching in the correct doppler frequency range. An internally generated ramp function voltage is combined with a reference voltage to produce a composite sweep signal for the receiver. The reference voltage level is determined either from a set of digi-switches or from a digital memory circuit which outputs a digital signal that is a function of the frequency of a received doppler signal.

Application of dispersive networks in data-transmission receivers

Abstract: The chirp-signal data-communication system, and the application in communication to civil aircraft via satellite relay, are outlined. A vital part of the receiver is the dispersive network, which processes the chirp signal; the problems encountered in the realisation and utilisation of this network are examined.

Pulse chirping in a Nd:YAG laser

Abstract: The 1.06-μm output of a loss-modulation mode-locked and frequency-doubled Nd:YAG laser was examined using a microwave avalanche photodiode with a rise time of ∼40 ps, and a scanning Fabry-Perot. The pulses were found to be transform limited only in the case where the 0.53-μm output of the laser was suppressed. When conversion efficiency was restored, the spectrum exhibited narrowing, but the pulses were much wider than the transform limit, indicating the presence of chirping.

Variable acoustic surface wave correlator

Abstract: : The report describes an experimental and theoretical study of nonlinear tapped delay lines for use in electronically variable, radar chirp signal correlation The devices consist of a hybrid configuration employing a piezoelectric surface acoustic wave delay line whose P equi-spaced taps are wire bonded to an attached, integrated circuit, semiconductor diode array The device performs as a high speed, real time convolver by use on nonlinear mixing in the diode array The design, fabrication and test of 51 and 300 tap devices are described which use lithium niobate delay lines and silicon-on-sapphire diode arrays These devices operate with signal and reference inputs near 120 and 180 MHz In order to achieve a chirp signal processing bandwidth near 30 MHz, these devices used an unusually small tap spacing, 0005 inch A complete theory for the devices is developed and is compared with experimental results for convolution and chirp signal correlation operation with input signals with up to 30 MHz bandwidth

Electronically Variable Chirp Signal Correlation with the Diode-Correlator

Abstract: The application of the Diode-Correlator to electronically variable chirp signal correlation is described. Theory and experiments for this nonlinear tapped delay line device are presented which show that input chirp signal bandwidth may be arbitrarily variable up to a maximum specified by the tap sampling frequency.