Showing papers on "Pulse compression published in 1975"

Dynamic spectroscopy and subpicosecond pulse compression

Abstract: Picosecond pulses from a mode‐locked cw dye laser have been compressed in time to produce pulses as short as a few tenths of a picosecond Dynamic spectroscopic investigations of the laser pulses reveal temporal asymmetry and frequency chirping on a subpicosecond time scale

Frequency spectrum analyzer

Abstract: A frequency spectrum analyzer adapted for use in a real time signal processing radar system is disclosed. In such system a plurality of sets of radar returns, each one of such sets corresponding to radar returns from objects disposed in each one of a like plurality of range cells, is stored in a time compressor section, the radar returns in each one of the sets thereof being stored at the pulse repetition frequency (PRF) of such radar system. After storage of such radar returns, a like plurality of chirp pulses is produced, each one of such pulses having a dispersive time Kτ. Synchronously with each one of the chirp pulses, one of the plurality of sets of stored radar returns is retrieved from the time compressor section, in a time duration equal to Kτ. Each one of the retrieved sets of radar returns is mixed with a corresponding one of the plurality of chirp pulses to produce a series of mixed signals which is coupled to a pulse compressor. Each one of the mixed signals is compressed into a pulse occurring at a time related to the Doppler frequency of any object in the range cell producing such associated radar returns. The time compressor section is used prior to pulse compression to effectively "match" the radar dwell time, generally several milliseconds in duration, to the dispersive time of the chirp pulse, generally several microseconds in duration, thereby enabling the pulse compressor to include a practical surface acoustic wave (SAW) delay line. Further, the "compressive" bandwidth, β, of the pulse compressor is equal to, or greater than, the dispersive bandwidth of the chirp pulses, thereby to maximize the power in the compressed pulses. Means are provided to adjust the dispersive time of the chirp pulse, thereby to correspondingly adjust the effective number of frequency resolution cells of the frequency spectrum analyzer.

Pulse width modulated amplifier

Abstract: A pulse width modulation circuit which comprises a mixer for combining an input audio signal with a feedback signal and for developing a difference signal to feed to an integration circuit. The integration circuit is coupled to a pulse width modulator which has a sawtooth carrier input for modulating the input audio signal. The resulting pulse modulated signal is then fed to a pulse amplifier and a low-pass filter and finally to a load. The output of the low-pass filter is coupled back to the mixer.

A dispersive modulator

Abstract: Amplitude modulation and temporal compression of 10−μ light at a frequency up to 80 MHz were demonstrated using a dispersive molulator—a NH3 vapor cell with a near−resonant time−dependent transition frequency controlled externally via the Stark effect. The peak output intensity was observed to be higher than the input intensity, showing that compression effects due to the time−dependent dispersion are essential in determining the output waveform.

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

Abstract: In a previous letter we proposed a compression scheme which reduces the intensity of a laser pulse in an Nd:glass amplifier chain and thereby allows more efficient energy extraction. In this scheme the nonlinear index of refraction (n 2 ) of the glass in the amplifier impresses a frequency sweep or "chirp" on the pulse. Further analysis is presented here. The stability to amplitude noise is demonstrated. We calculate that impressed periodic amplitude modulation is responsible for the growth of distinct spectral sidebands in the nonlinear host glass, and we find that the compressor converts these sidebands into temporal features which precede and follow the central compressed pulse. When a pulse with 10-percent peak-to-peak impressed periodic modulation passes through a sufficient length of glass so that the peak nonlinear phase is approximately 4π, these precursors are only about 1/20th the intensity of the main compressed pulse. RMS equivalent random noise has a flat sideband spectrum, and the precursors are found to be absent in the compressed pulses. The intensity averaging over possible transverse-mode structures is studied for some axially symmetric spatial mode shapes. This averaging somewhat reduces the compression ratio from the estimates in which the transverse modes were flat-topped. Finally, arguments are presented to explain why it is felt that a grating pair is not likely to be a suitable compressor for such intense nanosecond-duration pulses.

Pulse radar method and system

Abstract: A pulse radar system which is designed for installation on a vehicle. A control pulse generating circuit is triggered by the trailing edge of a transmitting pulse to generate a pulse train consisting of 8 time-divided pulses which in turn are supplied to a distributor. Simultaneously, the echo of the transmitted pulse is demodulated and the resulting signal is applied to the distributor so that depending on which one of the 8 divided pulses corresponds to the applied demodulated signal, the distance to the target is displayed on the corresponding indicator.

Hard Limiting in Synthetic Aperture Signal Processing

Abstract: In synthetic aperture radar a large linear phased array is formed from the rapid movement of a single element through each position in the array. Storage and coherent combining of the successive radar echoes are central to the array-forming process. Optical processing is the most common technique because of the efficiency with which Fourier transformation may be accomplished with simple optics. Real-time operation, however, requires all-electronic processing, which is difficult to accomplish because of the huge quantity of data to be manipulated. Dynamic range compression by hard limiting may ease the problem by reducing the number of bits per frame. The effects of hard limiting are analyzed in this paper. It is shown that large targets simultaneously illuminated by the radar antenna will produce image targets or ghosts displaced in angle. Statistically homogeneous clutter will "linearize" the hard-limited receiver and suppress the ghosts without loss in contrast, as does thermal noise if it is larger than the target echoes. Pulse compression reduces the probability of images from prominent targets. Judicious choice of the pulse-compression waveform is a powerful tool for destroying coherent buildup of images from all large targets not in the same range resolution cell. Linear FM, the most common choice, unfortunately does not exhibit this desirable property.

Signal compression system for binary digital signals

Abstract: A signal compression system for efficient transmission of an input binary digital signal, in the form of a binary pulse signal, in which bit polarity reversal is checked after sampling for a predetermined number of bits of the sampled binary pulse signal In a case of detection of any bit polarity reversal, the sampled binary pulse signal is sent out into a converted output pulse signal for the predetermined number of bits In a case of non-detection of any polarity reversal, the number of bits or the number of bit blocks having no polarity reversal is coded as a coded pulse signal and sent out into the converted output pulse signal A coded pulse signal is distinguished, the the converted output pulse signal, from the binary pulse signal by at least one flag bit

Reflective-Array Matched Filter for a 16-Pulse Radar Burst

Abstract: : A new type of matched filter has been designed and fabricated for a doppler-sensitive burst waveform with 16 equally spaced linear-FM subpulses, each of which has a 60MHz bandwidth and is 3 microsec long. The interpulse period is 5 microsec, and the total duration of the waveform is 80 microsec. The filter consists of 16 reflective-array-compressor sections ion-beam etched in the surface of a 15.2-cm-long Y-Z LiNbO sub 3 substrate. The reflective-array section for each subpulse is depth-weighted according to a Hamming function for range-sidelobe suppression, and the peak responses of successive sections have a Hamming weighting for doppler-sidelobe suppression. A reduction of system complexity and an improvement in dynamic range is expected with filters of this type as compared to conventional doppler burst processors. We have fabricated on one substrate a matched filter for an entire burst, thus providing the full correlation gain inherent in the waveform within a single device. This yields a large dynamic range despite a relatively high insertion loss (43 dB CW at center frequency (200 MHz) for the central section). Within a given section, the phase deviations from quadratic are typically 5 deg. r.m.s. and corresponding range sidelobes are more than 30 dB down from the correlation peak. These phase deviations and the errors in delay between sections can be reduced by metal overlay patterns. A filter for the zero-doppler channel was built to operate at a temperature of 60 C. When the temperature is changed by 0.98 C, the peak response of this filter is shifted by an amount equal to the doppler resolution (18 kHz).

Microwave Distance Meter with ± 2.5 mm Resolution

Abstract: A range resolution of ± 2.5 mm has been obtained with a FMCW radar and a sophisticated signal processing. The system operates at X-band with 1.5 GHz frequency sweep. It makes use of the fact, that the total phase length ?? of the IF waveform produced by superposition of the transmitted and reflected FMCW signal is an exact measure of the distance, if reflections of only one target are present. The measurement of the total phase length is performed by counting the zeros of m subsequent IF pulses, while the start phase of each pulse is changed in steps of 2/?m. This procedure results in an accuracy of the ?? measurement ? 2?/m. The signal processing is realized by a combination of a single-sideband mixer and a low frequency modulator followed by digital electronics.

Mechanism for aural pulse compression in mammals

Abstract: The pulse compression phenomenon is examined in terms of nonlinear phase functions in the frequency domain. The concepts of neural inhibition and critical bandwidth filtering are then employed to show that a logarithmic spectral phase function can be easily synthesized in the mammalian auditory system. Pulse compression of linear period−modulated signals, such as those used by some bats, can therefore be simply implemented at a peripheral level of the aural processor.Subject Classification: 65.35, 65.42.

BGO Reflective-Array Compressor (RAC) with 125 micro seconds of Dispersion

Abstract: : Linear FM pulse expanders and compressors in the reflective-array configuration have been fabricated on bismuth germanium oxide substrates. The low surface-wave velocity on this material and the folded RAC configuration allow 125 microseconds of dispersion over the 2.5-MHz bandwidth to be obtained in a compact device. The reflective arrays were depth weighted to provide a flat frequency response in the down-chirp expansion lines and a Hamming frequency response in the up-chirp compression lines. Maximum amplitude deviation from ideal was 0.5 dB. Midband (60 MHz) insertion loss was approximately 33 dB in both types of devices. Reflective arrays ion-beam etched with 500-eV argon ions showed no evidence of surface alteration or anomalous acoutic propagation loss. Phase compensation with Au-on-Cr films yielded a typical residual phase error of 2.0 degree and sidelobes below 33 dB were obtained in a subsystem comprising an expander, compressor, and assoicated electronics. Successful development of the devices depended on solving problems of angular accuracy of the reflective arrays and temperature sensitivity. These problems are especially severe in devices with small fractional bandwidth and large dispersion. (author)

Method and apparatus for acousto-optic pulse compression

Abstract: There is disclosed a pulse processing method and apparatus for compressing or changing the time scale of signal information represented by the modulation of a pulse of carrier energy which method and apparatus utilizes a crystal through which both a pulse of radio frequency acoustic energy and a pulse of polarized optical energy are simultaneously and colinearly transmitted to scatter energy in the optical pulse from one polarization state into the orthogonal polarization state. The crystal output is thus comprised of two optical pulses. One is the pulse having the original state of polarization and the other is the pulse resulting from the energy scattered to the orthogonal polarization state. The optical energy of rotated polarization is modulated in a fashion reproducing the modulation of the ultrasonic wave by which it is scattered. Furthermore, a short optical pulse can pass through the ultrasonic wave in a time short compared to the duration or length of the ultrasonic wave in the crystalline device. In so doing it reads the modulation of the acoustic pulse and transfers it to a time compressed pulse scale on the scattered optical output pulse. It is shown that the compression ratio is equal to the ratio of the velocity of light divided by the product of the velocity of sound in the crystal times the absolute value of birefringence of the crystal. If both the optical and acoustic pulses are passed through the crystal colinearly and in the same direction, the device takes a time function represented by the acoustic pulse, reverses it in time and compresses it by the ratio of light velocity to sound velocity thus producing a compressed inverse function. If the acoustic pulse and the light pulses are transmitted through the crystal colinearly but in opposite directions, the device takes a time function and without reversing it, compresses it in substantially the same ratio. The device may be applied, for example as a means of improving the signal-to-noise ratio, detection ratio and range resolution in radar systems or the like.

Multilevel aperiodic Huffman sequences

Abstract: Certain sequences that have zero aperiodic autocorrelation except for zero and the maximum shifts are described They are useful in radar pulse compression

Optimal Resolution of Rectangular Pulses in Noise

Abstract: Optimal detection of rectangular pulses in noise is considered, subject to a sidelobe constraint which ensures adequate resolution capabilities, and a new sidelobe reduction filter is derived. Tests in the laboratory and on a Westinghouse AN/TPS-27 search radar system em indicate that use of the new filter substantially improves both resolution and clutter performance over such standard techniques as fast time constant (FTC), delay line differentiator (DLD), and pulse length discriminator (PLD).

Technical guidance and analytic services in support of SEASAT-A

Abstract: The design of a high resolution radar for altimetry and ocean wave height estimation was studied. From basic principles, it is shown that a short pulse wide beam radar is the most appropriate and recommended technique for measuring both altitude and ocean wave height. To achieve a topographic resolution of + or - 10 cm RMS at 5.0 meter RMS wave heights, as required for SEASAT-A, it is recommended that the altimeter design include an onboard adaptive processor. The resulting design, which assumes a maximum likelihood estimation (MLE) processor, is shown to satisfy all performance requirements. A design summary is given for the recommended radar altimeter, which includes a full deramp STRETCH pulse compression technique followed by an analog filter bank to separate range returns as well as the assumed MLE processor. The feedback loop implementation of the MLE on a digital computer was examined in detail, and computer size, estimation accuracies, and bias due to range sidelobes are given for the MLE with typical SEASAT-A parameters. The standard deviation of the altitude estimate was developed and evaluated for several adaptive and nonadaptive split-gate trackers. Split-gate tracker biases due to range sidelobes and transmitter noise are examined. An approximate closed form solution for the altimeter power return is derived and evaluated. The feasibility of utilizing the basic radar altimeter design for the measurement of ocean wave spectra was examined.

Modified Barker Code Approximating Huffman's Impulse-Equivalent Sequence

Abstract: It is shown by use of D.A. Huffman's polynomial representation for a finite sequence of contiguous pulses in a pulse train that Barker's binary-coded sequences can be modified, by a weighting of pulse amplitudes, to a condition where time sidelobes in the pulse compressed signal are substantially reduced. In such a pulse amplitude modification there is a sacrifice in pulse train energy since each pulse does not have maximum energy. Results here are provided for Barker's sequence of length 13 only.

Ratio computing circuit

Abstract: A ratio computer serially accepts a reference signal pulse and two condition indicating signal pulses from a detector. The computer selects the reference pulse, which is then integrated. The resulting voltage represents the energy in the reference signal pulse. The two condition indicating signal pulses are divided by the integral of the reference signal pulse to obtain the desired ratios.

Envelope Threshold Detection in a Class of Non-Gaussian Interference

Abstract: This paper considers the detection of a sinusoidal or chirp signal imbedded in wideband FM interference (as might be generated by some types of active jamming), such that after pulse compression or other integration, the interference can be approximated by a sum of sinusoids of independent phase. The detection probability in such non-Gaussian noise is compared to that for Gaussian noise, with the Gaussian result approached, as required, in the limit that the number of sinusoids in the sum increases without bound. For detection using a comparison of the envelope with a threshold which yields a given false-alarm probability (CFAR detection), the detection probability is improved over the case of Gaussian noise, so that the usual approach basing the design on Gaussian noise would be conservative. Using a threshold determined from the envelope mean, the FM interference yields a lower false-alarm probability than for Gaussian noise, with detection probability only slightly degraded.

The magnetic delay line processor-a new device

Abstract: A new technique of transversal filtering is introduced for real-time matched filtering, pulse compression, decoding and correlation analysis of electrical signals where the data rates are less than several hundred kilohertz. It uses a series of transverse wires in contact with a moving magnetic medium to detect local values of a recorded signal. The number, width, position, length and interconnection of these wires define the processing function. Experimental results confirm the theory and illustrate the application with bandpass filters.

Guide to mode locking

Abstract: A conceptual, nonmathematical explanation of the phenomenon of mode locking is presented History, loss modulation, phase modulation, saturable absorbers, other mode locking methods, frequency shifting and pulse compression, pulse selection, direct measurements, and indirect measurement are discussed (IAA(

The development of surface wave dispersive filters for use in a multichannel pulse compression system

Abstract: : The technology and understanding of acoustic surface wave devices has progressed to the point where they can be used to implement sophisticated processing schemes such as a parallel channel pulse compression filter. The report discusses the design, development and experimental verification of the surface wave dispersive networks necessary to build a 7-channel pulse compression filter with 700 MHz bandwidth and a TW product of 4900. These individual channel filters must be time contiguous with identical linear FM dispersive characteristics. A division synthesis technique is developed for the realization of these filters. The technique is specifically tailored for an acoustic surface wave implementation consisting of one apodized and one unapodized transducer. The resulting filters were quite reproducible and their general characteristics (spectrum shape, bandwidth, and dispersive delay) were essentially as desired.