Showing papers on "Chirp published in 1980"

The theory, design, and applications of surface acoustic wave Fourier-transform processors

Abstract: This paper addresses the theory, design, and applications of surface acoustic wave (SAW) Fourier-transform processors. These analog processors are shown to perform several sophisticated real-time signal-processing functions at wide bandwidth (tens of megahertz) making them attractive for use in radar, sonar, and communication equipments. Theoretical results show how specific arrangements of physically realizable SAW chirp filters permit Fourier transformation of both baseband and IF input signals. The operation of SAW Fourier-transform processors, with separate real- and imaginary-baseband inputs, highlights their use as wide-band "FFT-type" processors. The application of individual SAW-based processors to spectrum analysis, network analysis, beamforming, and frequency-hopped wave-form synthesis is discussed and demonstrated. Finally, the use of combinations of two or more SAW Fourier-transform processors for cepstrum analysis and programmable correlation is described.

Tracking characteristics of the LMS adaptive line enhancer-response to a linear chirp signal in noise

Abstract: The transient behavior of the LMS adaptive filter is studied when configured as an adaptive line enhancer operating in the presence of a fixed or variable complex frequency sine-wave signal buried in white noise. For a fixed frequency signal, the mean weights are shown to respond to signal more rapidly than to noise alone. For a chirped signal, a fixed parameter matrix first-order difference equation is derived for the mean weights and a closed-form steady-state solution obtained. The transient response is obtained as a function of the eigenvectors and eigenvalues of the input covariance matrix. Sufficient conditions for the stability of the transient response are derived and an upper bound on the eigenvalues obtained. Finally, the mean-square error is evaluated when responding to a chirped signal. A gain coefficient of the LMS algorithm is determined which minimizes the mean-square error for chirped signals as a function of chirp rate and signal and noise powers.

Time compression multiplexing of video signals

Abstract: Frequency and time division multiplexing arrangements are common for efficiently utilizing bandwidth in a communication system. Still another, lesser known arrangement is called time compression multiplexing. In time compression multiplexing, a signal from each input channel is stored for a short period of time. The signals from all channels are then read from the store, compressed in time and transmitted over a communication path to a receiver. Unfortunately, the art appears to be remiss in the time compression multiplexing of video signals. The subject signal processor includes a plurality of input terminals (111, . . . , 11N), each input terminal being adapted to receive a video signal, each video signal including a plurality of scan lines, each scan line having a time duration T seconds. The signal processor also includes an arrangement for compressing a video signal by a factor M (illustratively M=N). More specifically, the signal processor compressing arrangement includes apparatus (120, 131, . . . , 13N) for modulating each input video signal with a chirp signal. A first, predetermined delay (142, . . . , 14N) is introduced to the modulated signals, which may be added (150 ). The compressing arrangement also includes apparatus (160) for introducing a second, variable delay to the modulated video signals, e.g., with a dispersive filter (160). The resultant time compressed signal is extracted from the dispersive filter output by an envelope detector (170) and extended over a communication path (300) to a receiver (200) where the time compressed signal is expanded through a receiver modulator (230), distributing apparatus (240), dispersive filter (261, . . . , 26N) and envelope detector (271, . . . , 27N) for extension to a plurality of output terminals (281, . . . , 28N).

Generation of stable frequency radiation at an optical frequency

Abstract: Stable-frequency optical radiation is generated by use of an electro-optical modulator to produce from radiation of a power laser that has inherent frequency fluctuations, an optical side band of the radiation that has the stable frequency. A modulating signal is applied to the modulator (12), the signal based upon a difference-frequency signal that represents the difference in frequencies between the output of the power laser (10) and an optical signal obtained from a highly stable reference source (20). The reference radiation shown is the direct output radiation of a stable reference laser. In one embodiment the pulses of a high power CO u TEA laser operating on a single mode are synchronized with a pulsed broad band amplifier (22) which amplifies the difference-frequency signal to produce the modulating signal, and an optical delay (30) in the power laser output path, preceding the modulator, corrects for the delay provided by the amplifier and other sources of delay The invention provides chirp free pulsed lasers, and lasers having stable frequency from pulse to pulse. Improved doppler lidar and other lidar systems are provided that utilize the stabilized output as the probing radiation.

Waveform searching system

Abstract: A waveform searching system for a sampling oscilloscope, in which the instantaneous level of a high-speed sawtooth signal generated by a trigger signal synchronized with an input analog signal and the instantaneous level of a properly attenuated or amplified X-axis sweep wave are compared with each other to generate a pulse in a case of coincidence therebetween, thereby to generate sampling pulses sequentially delayed after the trigger signal by a constant time; the input analog signal is sampled by the sampling pulses to produce sampled pulses; and the sampled pulses are displayed by the X-axis sweep signal on a CRT. In accordance with the present invention, there are provided detecting means for detecting a predetermined condition where a waveform formed by respective peak values of the sampled pulses cross in a predetermined direction at a predetermined search level by a predetermined number; and control means for sequentially changing a time base range until the detecting means detects the predetermined condition, whereby the sampled pulses having the predetermined condition are automatically displayed on the CRT.

A frequency stabilized compact high repetition rate TEA-CO 2 laser

Abstract: A compact atmospheric-pressure hybrid CO 2 laser utilizing a transverse double-discharge technique has been constructed and operated at moderate repetition rates. A pulse output energy of 80 mJ has been obtained under single-mode conditions at repetition frequencies of 100 Hz. Using the hybrid technique to obtain single-longitudinal-mode operation, we have been able to reach a 7 kHz long-term relative frequency instability between the TEA laser and a local oscillator. Measurements of the frequency sweeping during the pulse tail (chirp) are also presented along with a direct measurement of the resonant frequency pulling effect associated with the real part of the electric susceptibility of the gas. Limitations on the pulse repetition frequency for this laser configuration are also discussed.

Response of the adaptive line enhancer to chirped and doppler-shifted sinusoids

Abstract: The adaptive line enhancer (ALE) was first described by Widrow et al. as a practical on-line technique for separating the coherent components from the incoherent components of an input signal. Subsequent work has shown this same adaptive filtering structure to be applicable to maximum entropy spectral estimation, predictive deconvolution, and narrow-band interference rejection. While an often cited advantage of adaptive filtering is its tolerance of slowly time-varying input statistics, the existing analyses of the ALE have concentrated on the stationary case. This correspondence extends these results, applying the theory to the case of inputs containing sinuosids whose frequencies slowly vary in time. This is approached by developing a time-varying eigenvalue-eigenvector description of the expected filter impulse response vector. These results are then used to predict the expected impulse response vector for the ALE input of stationary white noise plus a sinusoid with linearly swept frequency. The response of the ALE for this particular input signal provides useful benchmarks for dealing with more complex forms of frequency modulation. The utility of the theoretical results is demonstrated by considering the ALE's response to an input of practical interest to the sonar community, a sinusoid whose apparent frequency is shifted by Doppler effects.

Matched swept-frequency digital modulation for binary signaling in inhomogeneous dispersive media

Abstract: A digital modulation technique which is most suitable for binary signaling through inhomogeneous dispersive media is introduced. Space-time rays are used to synthesize frequency-modulated input pulses that are either compressed in the medium with enhanced output or dispersed in the medium with widely spread output. The synthesized binary signals are shown to be in the form of swept-frequency signals which are matched to the dispersive properties of the medium. For media with quadratic phase functions, or under narrow-band conditions, the matched binary signals are linearly frequency modulated (chirp) with sweep rates that are related to the medium dispersion. The medium response to the matched chirp-modulated signals is investigated in detail. Conditions for the enhancement of the performance of the proposed modulation technique due to the available bandwidth are also discussed.

A Closed-Form Analysis of Reflective-Array Gratings

Abstract: A new analysis of oblique-incidence reflective array gratings is presented. Gratings with a constant spatial period and with a linear spatial chirp are considered. lutions are derived for the grating waves that incorporate a1 1 orders of ,nul ti ple reflections and power depletion within the gratings. are obtained using coupling-of-modes theory. solutions shed new light on the operation of such grating devices. In particular they permit a more detailed and exact analysis of the reflective-array compressor (RAC) than was previously possible with complex numerical computer analyses. The implications of the new analysis for RAC design are examined in detail and distortions of the device response, caused by previously ignored effects, are elucidated. For the first time exact soThe solutions These

Rotating optical frequency chirp device

Abstract: A system for generating pulses of laser radiation which vary in frequency with time to achieve a chirp or frequency sweep in which single or multiple laser spectra in the form of mode lines are displaced or shifted in frequency during the generation of the laser pulse. The system provides for the mode line shift through the use of an optical wedge which moves tranversely through one of the optical paths utilized in the optical loop to generate the laser pulse. This provides a linear increase with time in the optical path length so as to perturb the wavelength of oscillation of the laser output, which results in a linear chirp. In a preferred embodiment a number of prisms of optically dense material with a wedge-like profile are mounted on a rotating disc. When the disc with the prisms is interposed in the optical loop of an injection locked laser oscillator, successive prisms traverse the laser's optical loop. In a further embodiment, pairs of identically configured optical elements are located on diametrically opposite sides of the rotating disc so as to remove any beam position jitter introduced by shaft wobble, prism misalignment or refraction angle changes due to input beam angle deviation, with the second prism of the pair cancelling errors introduced by the first prism of the pair. To further reduce errors, all prisms are positioned at the point of minimum deviation.

Low sidelobe linear FM chirp system

Abstract: An improved FM pulse compression system which has low range-time sidelobesnd is doppler tolerant. This system is implemented by using an analog-type linear FM modulated transmission pulse and processing the echo from this pulse by means of baseband sampling at the Nyquist sampling rate and then compressing this sampled signal by means of a discrete phase compression circuit. In brief, the present invention comprises a receiver for receiving the FM echo pulse, a sampling and holding circuit for sampling the echo at baseband at the Nyquist sampling rate and then converting to IF, and a discrete phase compression circuit for compressing the appropriate number of sampled outputs from the sampling and holding circuit. If an echo is properly indexed in the phase compression circuit, then a short pulse with a relatively high amplitude is generated.

A general purpose 1024-stage electronically programmable transversal filter

Abstract: The architecture, design, and performance of a filter implemented in CCD/NMOS technology is described. The device features programmability of the reference signal, the filter length, and weighting coefficient resolution. Off-chip circuitry is minimized by incorporating both analog and digital support circuitry, such as clock logic, drivers, amplifiers, and microprocessor interface circuitry on chip. This results in a monolithic analog signal processing system that has the flexibility to be operated in nine programmable configurations, from 1024 stages by 1 bit, to 128 stages by 8 bits. The versatility of the device makes it suitable for a wide range of applications, from matched filtering with chirp signals and very long binary sequences, to image correlation and chirp signals and very long binary sequences, to image correlation and programmable filtering.

Stabilized sweep frequency generator with adjustable start and stop frequencies

Abstract: The oscillation frequency of a variable frequency oscillator is swept by a sweep signal from a sweep signal generator and the oscillation frequency is compared with a preset sweep start frequency for detecting coincidence therebetween. Upon detecting the coincidence, the sweep operation of the sweep signal generator is stopped and, at the same time, the oscillation frequency of the variable frequency oscillator is made by phase lock loop means to be phase-synchronized with a reference frequency. When the phase synchronization is established, an error signal in the phase synchronization is held and the loop of the phase lock loop means is cut off and then the error signal is applied to the sweep signal generator to re-start the frequency sweep of the variable freqency oscillator. When coincidence is detected between the oscillation frequency of the variable frequency oscillator and a preset sweep stop frequency, the sweep operation is stopped.

Method and apparatus for shaping and aiming narrow beams

Abstract: A method and apparatus for using a linear frequency chirp in a transmitter/receiver (14/16) having a correlator to synthesize a narrow beamwidth pattern from otherwise broadbeam transducers when there is relative velocity between the transmitter/receiver and the target. The chirp is so produced in a generator (20) in bandwidth. B, and time, T, as to produce a time-bandwidth product, TB, that is increased for a narrower angle. A replica of the chirp produced in a generator (26) is time delayed and Doppler shifted for use as a reference in receiver (16) for correlation of received chirps from targets. This reference is Doppler shifted to selecttargets preferentially, thereby to not only synthesize a narrow beam but also aim the beam in azimuth and elevation.

Apparatus for regenerating signals within a frequency band

Abstract: Apparatus for generating signals to interfere with or jam signals detected as unfriendly in a given input frequency band comprises a spectrum analyzer circuit using surface acoustic wave (SAW) chirp filters to provide a transformation of input frequency signals to a series of time displaced signals in a linear frequency-to-time relationship. The analyzer circuit uses the SAW devices to perform multiply-convolve functions that separate the different frequency signals in time and the analyzer is repetitively triggered to perform a spectrum analysis. The time series signals are selectively applied to a frequency synthesizer having a time-to-frequency relationship that matches the analyzer characteristic so as to regenerate signals at the input frequencies. The synthesizer uses two matched chirp filters one activated by a fixed time signal and the other by the time series to generate swept frequencies that are mixed to provide the required frequency outputs. The time series is processed to inhibit those signals corresponding to frequencies identified as friendly. In an alternative synthesizer the time series signals are converted to frequency-representing digital codes which are applied to a programmable frequency generator. Signal processing to protect friendly frequencies is performed on the digital codes.

Doppler signal processing apparatus

Abstract: A doppler type speed sensor produces a doppler signal having a spectrum of frequencies including a frequency of peak amplitude corresponding to the actual speed of an object. The frequencies are supplied to a narrowband voltage tunable filter, the frequency bandwidth of which is continuously adjusted by a periodically reoccurring sweep signal applied thereto. The output of the filter is coupled to a peak detecting circuit which produces a pulse when the maximum amplitude signal is received thereat. The sweep signal and pulse are applied to the inputs of a sample-and-hold circuit to cause the sample-and-hold circuit to hold and produce a signal corresponding to the value of the peak frequency and therefore the speed of the object.

Ccd driven integrated optical modulator array

Abstract: A CCD driven integrated optical modulator array including an array of chirp grating optical lenses implemented on the surface of an electro-optical crystal such as LiNbO3 or LiTaO3, a plurality of channel waveguides and a thin metal film pattern on the surface of the waveguides for modulating the optical waveform in each channel. The thin metal film form planar capacitors, each of the capacitors being electrically connected to the output circuit of a corresponding semiconductor device, such as a CCD array. The CCD array is implemented on a semiconductor wafer bonded to the electro-optical crystal. Signals in each optical channel in the electro-optical crystal are thereby modulated by corresponding circuit elements associated with corresponding CCD channels implemented on the major surface of the semiconductor wafer.

Analysis of mode-locked and intracavity frequency-doubled Nd:YAG laser

Abstract: We present analytical and computer studies of the CW mode-locked and intracavity frequency-doubled Nd:YAG laser which provide new insight into the operation, including the detuning behavior, of this type of laser. Computer solutions show that the steady-state pulse shape for this laser is much closer to a truncated cosine than to a Gaussian; there is little spectral broadening for on-resonance operation; and the chirp is negligible. This leads to a simplified analytical model carried out entirely in the time domain, with atomic linewidth effects ignored. Simple analytical results for on-resonance pulse shape, pulse width, signal intensity, and harmonic conversion efficiency in terms of basic laser parameters are derived from this model. A simplified physical description of the detuning behavior is also developed. Agreement is found with experimental studies showing that the pulsewidth decreases as the modulation frequency is detuned off resonance; the harmonic power output initially increases and then decreases; and the pulse shape develops a sharp-edged asymmetry of opposite sense for opposite signs of detuning.

Detectionnindication system for scanning sonar

Abstract: PURPOSE:To improve the detection capability of a sonar by furnishing the sonar with an ability to indicate information on a shoal of fish in terms of direction and distance in connection therewith on one of two divisions of an indication surface of an indicator cathode-ray tube, and information on the shoal of fish in terms of position thereof in a perpendicular section of the sea-water on the other division of the mentioned indication surface. CONSTITUTION:Two pulses are generated every one spiral sweep by utilizing as a synchronizing signal an output from a sweep signal generating circuit 2. A pulse P9 is generated from these pulses, and a gate circuit 20 is opened by the time width of the pulse P9 to generate a pulse P10, which is then applied to a cathode-ray tube 13 through an image signal change-over circuit 14. A signal from a hold circuit 17 instead of a reception detection signal P6 from an amplifier circuit 11 is applied from the image signal change-over circuit 14 to the cathode-ray tube 13. As a result, a bright line, the length of which represents the intensity of an echo from a shoal of fish appears on a line indicating an angle of depression. Thus, the position of the shoal of fish in a perpendicular section of the sea-water is displayed.

Analysis of Nonperiodic SAW Transducers Using a Circuit Model

Abstract: [22] B. Weichbrodt, “Signature analysis unit,” General Electric Res, [ 231 S. Braun, “Signal analysis for rotating machinery vibrations,” Pattern Recognition, vol. 7, pp. 81-86, 1975. [24] -, “The extraction of periodic waveforms by time domain averaging,” Acustica, vol. 32, pp. 69-77, 1975. [ 251 S. Braun and P. F. Scott, “Analysis of semi periodic signatures by a combination of averaged and variance functions,” General Electric Res. Devel. Center, Rep. 71-C-136, 1970. [ 261 S. Braun and B. Seth, “The analysis of repetitive mechanical signatures,” submitted to ASME Trans. Dynamics Meas. Contr. [ 271 D. Dyer and R. M. Stewart, “Detection of rolling element bearing damage by statistical vibration analysis,” ASME Paper 77-DET83, 1977.

The Behavior Of A Pulsed Millimeter Wave (70 Ghz) Impatt Diode Oscillator During Laser Illumination

Abstract: The effect of photon injection on a 70-GHz pulsed IMPATT diode was investigated. With the diode mounted in a waveguide oscillator, two useful modes of operation, the "enhancement" mode and the "inhibition" mode, were observed. The enhancement mode permits fast on and off switching (and modulation) of the IMPATT diode oscillator. The inhibition mode permits pulse width control and reduction of undesired intrapulse frequency shift (chirp) .

Synchronizing system in optical apparatus

Abstract: PURPOSE:To readily perform phase correction of high accuracy by applying electrical phase correction to the chopper signal generated at every scanning. CONSTITUTION:An inverter 30, AND circuit 31 and differentiating circuit 32 are connected between the monostable multivibrator 22 connected to input terminal 21 and flip-flop 33, and an AND circuit 23, binary counter 24, binary-decimal conversion circuit 25, bus buffers 26-1-26-4 and presettable counter 29 are connected. As a result of this, when the bus buffers 26-1-26-4 applied with the pulse number of the clock signal corresponding to the phase deviation of the scanning signal and chopper signal as fixed data through the buses 27-1-27-4 are applied with the signal from the binary-decimal conversion circuit, the fixed data are read into the presettable counter 29 and the flip-flop 33 outputs the signal having been removed of the phase deviation at its trailing edge to trigger the sweep signal. thereby removing the jitter of the scanning signal at the image plane.

A 1 GHz Bandwidth SAW Compressive Receiver

Abstract: Modern radar ESM systems require the ability to analyse large bandwidths containing time coincident signals of differing spectral content. The Surface Acoustic Wave compressive receiver offers wide bandwidths with moderate time and frequency resolutions. The choice of transform parameters is a compromise between time and frequency resolution and must take into account the nature of the input signal, and the problem of high output data rates resulting from the chirp implementation of the Fourier transform of wideband signals. A SAW compressive receiver to analyse a 1 GHz bandwidth with 4 MHz resolution has been developed to include specially designed digital output circuits.

Optical signal processing device

Abstract: An optical system including a radio frequency signal input; a chirp signal input; a source for emitting a beam of radiation; a first acousto-optical modulator disposed in the path of the beam and functioning to modulate the beam with the radio frequency signal to produce a first modulated beam; a second acousto-optical modulator disposed in the path of the first modulated beam to modulate the beam with the chirp signal to produce a third modulated beam; and a single detector disposed in the path of the third modulated beam.

Self-Aligning Bilateral Chirp-Transform System

Abstract: A SAW chirp-Fourier-tr ansform system is described which employs the bilateral property of dispersive delay devices to perform 100% duty-cycle Fourier transformtion using only two SAW devices. It is then shown how alignment of the complex Fourier outputs of a high-performance bilateral processor can be maintained with a digital system using a third SAW device, error-correction circui try and active cl osed-1 oop control to correct for errors at the output arising when device characteristics change due to temperature shifts and device aging. Three major adjustments, the timing of the i nput window over which the transform is taken, the timing of the output samples relative to the transform, and the phase used for in-phase (I) and quadrature (Q) demodulation are required. The input window and the output sample timing are aligned by independently controlling the timing of post and premultiplying chirps, r espectively. I and Q phase are adjusted by digitally controlling the phase of the impulse RF source. Adjustments are made under active closed-loop control utilizing algorithms that derive error corrections from special test signals. These techniques have been implemented in a system which accepts digital data at a continuous 10-Mword/s rate, D/A converts these data and delivers its 256-point Fourier transform to A/D converters. The system processes complex words consisting of 8 bits real and imaginary and maintains accuracy to 1%.

Self scanned optical Fourier transform arrangement

Abstract: An optical system including a radio frequency signal input; a chirp signal input; a source for emitting a beam of radiation; an acousto-optical modulator disposed in the path of the beam and functioning to modulate the beam with the radio frequency signal and the chirp signal to produce a modulated beam; and a single detector disposed in the path of the third modulated beam. The inventor further provides electronic alignment and focusing by changing the chirp frequency.

Analog Encoded Chirp Transmission System Using Surface Acoustic Wave Filters

Abstract: Linear frequency modulation is implemented in encoding analog signals. Using surface acoustic wave (SAW) dispersive delay lines, the transmission system described operates with overlapping chirps that are position-modulated according to the sampled data. Demodulation in the receiver requires pulse compression in a matched fdter. The principle of analog encoding and decoding is explained. Ex- perimental results are provided on the performance of a modem de- signed for handling baseband signals with a spectral range from 300 Hz to 400 kHz. SAW linear FM filters, operating at a center frequency of 60 MHz with a time-bandwidth product of 180, are employed. The system shows good amplitude and phase characteristics and a dynamic range greater than 40 dB. tude of the sampled information signal. Investigating the basic types of simple analog pulse modulation (6) , pulse-amplitude modulation (PAM), is normally excluded in spread spectrum communications. Because of its easy demodulation, it tends to be at cross purposes with the intent of these systems. Vari- ation of the LFM, pulse-duration modulation (PDM), thus varying the bandwidth at the same time, would cause ampli- tude and duration modulation of the compressed pulse in the receiver and a compressive gain depending on the modulating signal. A possible but more complicated approach is the varia- tion of the center frequency of each chirp according to the instantaneous sampled signal amplitude. Here the receiver re- quires a high time bandwidth product in its compression filter, yielding pulses whose time separation corresponds to signal amplitude value. These considerations and the narrow correla- tion peak of the LFM waveform suggest the use of pulse- position modulation (PPM) with its significant simplicity. In the following section of the paper, encoding and decoding in a system transmitting overlapping PPM-chirps is explained. Section 111 provides experimental results on the performance of the SAW filters and the overall system.

Sweep signal generation system

Abstract: A sweep signal generation system for producing an output sweep signal of very high frequency includes a circuit for generating an input sweep signal, and a phase locked loop which includes a phase detector, a voltage controlled oscillator and a harmonic frequency mixer. The output sweep signal is applied to the harmonic mixer together with a local oscillator signal of fixed frequency, the output from the harmonic frequency mixer being applied to the phase detector together with the input sweep signal. The output from the phase detector is applied to the voltage controlled oscillator to cause the frequency of the output thereof to be swept in accordance with variation of the input sweep signal.