Showing papers on "Pulse repetition frequency published in 1988"
TL;DR: The results indicate that the threshold for transient cavitation produced in water by pulsed ultrasound is independent of pulse duration and acoustic frequency for pulses longer than approximately 10 acoustic cycles.
150 citations
TL;DR: The acoustic cavitation threshold of an aqueous solution has been measured at megahertz frequencies as a function of pulse width and pulse repetition frequency for various combinations of these quantities and it was observed that the cavitation thresholds of water under pulse conditions decreases both when the pulse width is fixed and the pulse repetition Frequency is increased.
Abstract: The acoustic cavitation threshold of an aqueous solution has been measured at megahertz frequencies as a function of pulse width and pulse repetition frequency for various combinations of these quantities. The fluid tested was a 0.1M KOH–H3BO3 buffer solution with pH 10.9, which contained luminol, was saturated with argon, and filtered to 25 μ. The presence of cavitation was detected by a photomultiplier tube that required the emission of visible light that was both larger in magnitude and longer in duration than a preset criterion. It was observed that the cavitation threshold of water under pulse conditions decreases both when the pulse width is fixed and the pulse repetition frequency is increased, and when the pulse repetition frequency is fixed and the pulse width is increased. Acoustic cavitation thresholds measured in aqueous solutions are significantly less than those acoustic pressures associated with instruments that are currently in widespread use in medicine.
106 citations
Patent•
01 Feb 1988TL;DR: In this article, a radar transmission, reception and signal processing system generates highesolution synthetic aperture radar ground maps from air or space platforms using waveforms in which frequency is changed pulse-to-pulse.
Abstract: A radar transmission, reception and signal processing system generates highesolution synthetic aperture radar ground maps from air or space platforms using waveforms in which frequency is changed pulse-to-pulse. The transmitted radar signal is comprised of a series N bursts with n pulses per burst wherein each of the pulses is a fixed frequency step, Δf, either above or below one or the other of the n pulses, i.e. the n pulses comprises an ordered set and further, preferably, wherein the set of n pulses is arranged in time as a random permutation of the ordered set. In each of the k sample gates for each burst the n complex samples of reflectivity are inverse Fourier transformed from frequency domain samples of reflectivity to synthetic range domain profiles to result in an array of aligned range profiles in each of k coarse range delay positions. Azimuth or cross-range processing is accomplished by convolving complex range data appearing in each synthetic range cell with a suitable azimuth reference to result in a set of complex numbers that represent complex reflectivity maps of the earth's surface in that coarse range bin. "Zoom" capability is achieved by discrete Fourier transforming the data in each synthetic range cell of the selected delay. "Zoom" is achieved by increasing the target dwell time and simultaneously increasing the radar signal bandwidth. In both the spotlight "zoom" mode and the SAR mode, the processed data is converted from complex numbers to absolute magnitudes before display.
50 citations
Patent•
04 Aug 1988
TL;DR: In this article, a technique for accurately controlling both the pulse repetition interval and pulse width of a pulse signal generator which uses a crystal oscillator to maintain a very accurate time base is presented.
Abstract: A technique for accurately controlling both the pulse repetition interval and pulse width of a pulse signal generator which uses a crystal oscillator to maintain a very accurate time base. Two separate digital counters clock-in the clock pulses. When the desired number of clock pulses are registered by the first counter, a first digital comparator generates a start pulse which resets the first counter and triggers an output flip-flop. The change of state in the flip-flop enables the second counter to begin its count. When the desired number of clock pulses are registered by the second counter, a second digital comparator generates an end pulse which resets the second counter and triggers the flip-flop a second time. The second change of state of the flip-flop disables the second counter until the first comparator generates a new start pulse. The new start pulse toggles the flip-flop and the entire process is repeated continuously to generate at the output of the flip-flop a periodic pulse train having the desired pulse width with the leading edges separated by the desired pulse repetition interval.
30 citations
Patent•
29 Aug 1988TL;DR: In this article, a method of operating a pulse Doppler radar to increase the probability of detection of an airborne target is presented, which consists of transmitting interrogating pulses with a high pulse repetition frequency and processing received signals using any conventional pulse doppler technique for echo signals.
Abstract: A method of operating a pulse Doppler radar to increase the probability of detection of an airborne target is shown to consist of transmitting interrogating pulses with a high pulse repetition frequency and processing received signals using any conventional pulse Doppler technique for echo signals having a Doppler shift frequency outside the spectrum of Doppler shift frequencies of clutter and using a DPCA technique at a submultiple of the pulse repetition frequency for echo signals having a Doppler shift frequency within the spectrum of Doppler shift frequencies of clutter.
27 citations
Patent•
29 Feb 1988
TL;DR: In this paper, a radar warning receiver is provided having a police radar signal band discrimination circuit which generates evaluation signals, the state of which indicates the voltage level relative a threshold voltage of a discriminator output as the local oscillator is swept through the radar bands.
Abstract: A radar warning receiver is provided having a police radar signal band discrimination circuit which generates evaluation signals, the state of which indicates the voltage level relative a threshold voltage of a discriminator output as the local oscillator is swept through the radar bands. The times during which the evaluation signals are in one state or the other are utilized to identify in which band the received signal is operating (e.g., X-band or K-band).
27 citations
Patent•
13 Jun 1988TL;DR: In this article, a pulsed dye laser with a resonator cell having a passageway through which dye solution is circulated and a pump laser for optically pumping the resonator is described.
Abstract: Laser apparatus is disclosed which comprises a compact pulsed dye laser for high pulse repetition frequency operation. The pulsed dye laser includes a resonator cell having a passageway through which dye solution is circulated and a pump laser for optically pumping the resonator. In order to provide laser apparatus which is capable of very high performance, the dye solution is circulated through a narrow passageway at high flow rate and the pump laser is operated at a high pulse repetition frequency.
22 citations
Patent•
12 Sep 1988
TL;DR: In this paper, a broad band antenna is provided, together with a mixer and a plurality of local oscillators, which are mixed one at a time with signals from the antenna, there being one local oscillator signal for each radar frequency or pair of frequencies of interest which may be received by the antenna.
Abstract: The invention concerns radar detection devices sensitive to signals from various different frequency bands. A broad band antenna is provided, together with a mixer and a plurality of local oscillators. Signals from the local oscillators are mixed one at a time with signals from the antenna, there being one local oscillator signal for each radar frequency or pair of frequencies of interest which may be received by the antenna. Each local oscillator signal is chosen so that when it is mixed with the respective radar frequency signal, an intermediate signal is produced which is the same for all mixtures. This intermediate signal is further down converted and fed to signal processing circuitry to produce an alarm when radar frequencies of interest are detected.
20 citations
Patent•
05 May 1988TL;DR: In this article, a bipolar supply current in the form of pulses was used to operate a high pressure discharge lamp with a mean sodium-vapour pressure of more than 300 mbar, and the duty ratio was between 0.2 and 0.6.
Abstract: In the case of a method for operating a high-pressure sodium-vapour discharge lamp having a mean sodium-vapour pressure of more than 300 mbar, by means of a bipolar supply current in the form of pulses, the pulse repetition frequency (prf) of the supply current is between 60 and 500 Hz, especially between 100 and 400 Hz, and the duty ratio is between 0.2 and 0.6.
19 citations
TL;DR: In this paper, a modification of self-Q-switching in a laser with an isotypic saturable absorber is suggested and implemented in a multisegmented injection laser.
Abstract: A modification of a method for self-Q-switching in a laser with an isotypic saturable absorber is suggested and implemented in a multisegmented injection laser. The method consists of the transportation of most parts of the excited absorber population to the amplifier. The carrier transport time must be less than the spontaneous recombination time in the absorber. In a three-section AlGaAs/GaAs double-heterostructure laser with modified Q-switching, optical pulses of 5 ps in duration with a repetition rate as high as 18.5 GHz and peak power above 10 W have been obtained. The latter value is the largest ever reported for a picosecond injection laser. Unique temporal and spectral features exhibited by these lasers have been observed, including the stepped variation of pulse repetition frequency, its dependence on the pump current, large emission spectral width (on the order of kT), spectral chaos and bistability. >
19 citations
Patent•
30 Mar 1988
TL;DR: In this article, a frequency-agile pulsed doppler radar with high pulse repetition frequency (HPRF) in the unambiguous velocity region is used to measure the range of a target, where the complex time signal derived from the echo signals of a coherent processing interval (CPI) is transformed into the frequency domain, the transformed spectrum is multiplied by a bandpass function with a mean frequency coinciding with the dopple frequency of the target, and the product is transformed back into a time signal.
Abstract: With a frequency-agile pulsed doppler radar with high pulse repetition frequency (HPRF) in the unambiguous velocity region, in order to measure the range of a target the complex time signal derived from the echo signals of a coherent processing interval (CPI) is transformed into the frequency domain, the transformed spectrum is multiplied by a bandpass function with a mean frequency coinciding with the doppler frequency of the target, and the product is transformed back into a time signal The real envelope of this re-transformed time signal displays a definite leading edge and a steady state region, from which the echo travel time can be estimated Particular advantages may be derived for the pulsed doppler radar set from a plurality of frequency agile transmitter/receivers operated at the same time at different frequencies, and whose frequency switching times are time-staggered
TL;DR: In this paper, an average output power of 3.9 W at a pulse repetition frequency of 29 kHz was obtained using a water-cooled laser tube 33 cm long and 1 cm in diameter.
Abstract: The maximum attainable average output power of an Sr–He recombination laser (λ = 430.5 nm) was ~ 14 W/m limited by overheating of the active medium. An average output power of 3.9 W at a pulse repetition frequency of 29 kHz was obtained using a water-cooled laser tube 33-cm long and 1 cm in diameter.
TL;DR: In this paper, a laser was constructed using an yttrium scandium gallium garnet containing chromium and erbium, and the threshold of this laser did not exceed 2 J. This made it possible to achieve an average output power of 0.7 W at a pulse repetition frequency of 100 Hz.
Abstract: A laser emitting at the wavelength of 2.79 μm was constructed using an yttrium scandium gallium garnet containing chromium and erbium, and the threshold of this laser did not exceed 2 J. This made it possible to achieve an average output power of 0.7 W at a pulse repetition frequency of 100 Hz.
TL;DR: In this article, the gain characteristics of a 1.5 μm split contact nonlinear laser amplifier are reported with an input power of −51 dBm or greater, with a nonlinear transfer function was observed with a maximum gain of 26 dB.
Abstract: The gain characteristics of a 1.5 μm split contact nonlinear laser amplifier are reported. With an input power of −51 dBm or greater, a nonlinear transfer function was observed with a maximum gain of 26 dB. The maximum pulse repetition frequency for nonlinear gain was 700 MHz.
Patent•
26 Feb 1988
TL;DR: In this paper, a coherent pulse radar is activated successively according to at least two pulse repetition frequencies, such that the received signal is ambiguous both with regard to distance and with respect to velocity, and their ratio is reducible to the quotient of two integers which are preferably adjacent and have no common factors.
Abstract: A coherent pulse radar is activated successively according to at least two pulse repetition frequencies. These frequencies are of values such that (a) the received signal is ambiguous both with regard to distance and with regard to velocity, and (b) their ratio is reducible to the quotient of two integers which are preferably adjacent and have no common factors. For the frequency analysis, a number of samples is taken which depends upon the pulse repetition frequency, the numbers of samples associated with the two pulse repetition frequencies being, in relation to one another, in the ratio of the two integers. The distance/velocity resolution cell is then invariant with respect to the pulse repetition frequency; this permits removal of the ambiguity concerning mean information items appertaining to a long integration time.
Patent•
14 Nov 1988TL;DR: In this article, the position of the nonpulse interval within the radar pulse can be modulated by inserting at least one short non-Pulse interval into the radar signal.
Abstract: A radar system, such as a tracking radar installation or other radar installation which is of the pulse compression type, transmits data during transmission of the radar signal. The data is transmitted by inserting, into the radar signal, at least one short nonpulse interval. The position of the nonpulse interval within the radar pulse can be modulated.
21 Mar 1988
TL;DR: The author documents typical constraints placed on a pulse-Doppler search-mode PRF set and sets forth an efficient approach for selecting a near-optimum set.
Abstract: The principles of medium PRF (pulse-repetition-frequency) radar and the specific requirements of a radar system place restrictions on the choice of these PRFs. The author documents typical constraints placed on a pulse-Doppler search-mode PRF set. He sets forth an efficient approach for selecting a near-optimum set. Finally, as an example, a PRF set is documented that was selected using the described method. >
15 Mar 1988
TL;DR: In this paper, the authors describe techniques for predicting the obscuration as a function of PRF, and details the criteria which shall be used by the TDWR system to automatically and adaptively select an optimal PRF in order to minimize these obscuration effects.
Abstract: : The Terminal Doppler Weather Radar (TDWR) system shall provide high quality Doppler radar data on weather phenomena near high traffic airports. These data shall be used in real time by automated TDWR algorithms to detect weather situations which may be hazardous to the safe operation of aircraft within the vicinity of the airport. One of the major factors which could cause the degradation of the quality of these TDWR data is obscuration by 'distant' storm cells. This obscuration is caused by storms located beyond the range interval being sampled by the radar, yet whose radar echo ambiguously folds within the range interval of interest. These range aliased echoes could trigger false detections by the algorithms, and/or cause actual hazardous situations near the airport to remain undetected. By carefully selecting the pulse repetition frequency (PRF) of the radar, range obscuration from distant storms can be minimized over specified airport regions. This document describes techniques for predicting the obscuration as a function of PRF, and details the criteria which shall be used by the TDWR system to automatically and adaptively select an optimal PRF in order to minimize these obscuration effects.
01 Jun 1988
TL;DR: FM and AM signal-to-noise measurements were made to determine the performance capability of the 10-GHz modulated fiber-optic links for radar applications.
Abstract: Novel applications of fiber-optic delay lines to improve the capability and performance of radar repeater and phase noise test sets are described. Using a 2.25-km-long fiber-optic link, the generation of an ideal target for a radar repeater test set and the measurement of phase noise within 100 Hz of a 9.6-GHz radar carrier signal is demonstrated using a delay line discriminator phase noise test set. FM and AM signal-to-noise measurements were made to determine the performance capability of the 10-GHz modulated fiber-optic links for radar applications. >
Patent•
23 Mar 1988
TL;DR: In this paper, a pulse repetition frequency calculating circuit was used to increase the number of targets which can be tracked by providing a radar device with the pulse repetition frequencies calculating circuit, which calculates a pulse frequency at any time based on a Doppler frequency and supplies it to a PFR generating circuit.
Abstract: PURPOSE:To increase the number of targets which can be tracked by providing a pulse repetition frequency calculating circuit which calculates a pulse repetition frequency at any time based on a Doppler frequency and supplies it to a pulse repetition frequency generating circuit. CONSTITUTION:This radar device is provided with the pulse repetition frequency calculating circuit. Then a target Doppler frequency is calculated from the distance variation rate calculated at the time of the target tracking calculation and the pulse repetition frequency which generates a blind speed is calculated and selected based on the target Doppler frequency to track a target at any speed with the single pulse repetition frequency while removing clutters, thereby increasing the number of targets which can be tracked and shortening a search frame time.
TL;DR: In this paper, the influence of the pulse repetition frequency on the radiation divergence was investigated for helium-and neon-containing gas mixtures, and a theoretical interpretation was given of the results of the experiments.
Abstract: Investigations were made of a pulse-periodic electric-discharge XeCl laser with two types of resonator. When an unstable confocal resonator with a magnification of M = 12 was used, the divergence exceeded the diffraction limit by a factor of only 2?3 and there was only a slight ( ? 30%) reduction in the output energy relative to that from a laser with a plane?plane resonator. The influence of the pulse repetition frequency on the radiation divergence was investigated for helium- and neon-containing gas mixtures. A dependence of the divergence on the pulse repetition frequency was discovered. A theoretical interpretation is given of the results of the experiments.
Patent•
31 Oct 1988
TL;DR: In this paper, the authors propose a Doppler-type radar in which all possible sets (p 1, q 1 ) and (p 2, q 2 ) corresponding to echoes at different repetition frequencies are stored in a first memory.
Abstract: A device for removing ambiguities in the range and speed at the output of a Doppler-type radar in which all possible sets (p 1 , q 1 ) and (p 2 , q 2 ) corresponding to echoes at different repetition frequencies are stored in a first memory, p 1 and p 2 representing the number of the range quantum from which an echo signal is received and q 1 and q 2 the number of the filter at the output of which an echo signal is maximum. Pairs of signals are supplied in response to a first clock signal together with radar data in a second memory to two calculating circuits which carry out tests to determine of p 1 and p 2 and q 1 and q 2 respectively come from the same target and calculate the true target distance and true Doppler frequency. If both tests are positive the true distance and frequency are stored in a memory. If either is negative the first clock signal is produced to supply a new pair to the respective calculating circuits.
12 Apr 1988
TL;DR: In this article, an injection-locked, pulsed Doppler lidar for atmospheric wind monitoring is described, which produces up to 50 pulses per second with energies of about 1 J per pulse.
Abstract: An injection-locked, pulsed Doppler lidar for atmospheric wind monitoring is described. The lidar produces up to 50 pulses per second with energies of about 1 J per pulse. Transverse mode suppression is effected with an output coupler whose radial reflectivity is parabolically-tapered. The lidar has been used to measure winds in several unique field experiments.
Patent•
25 May 1988
TL;DR: In this paper, a multi-time-round echo detection system was proposed for radar with the capability of transmitting in frequency agility and, besides the advantages due to this type of technique, further, capable of reading the ambiguity of distance directly by separating in frequency the multiple time-around echoes.
Abstract: Device for radar utilized to detect multiple-time-around echoes with the capability of transmitting in frequency agility and, besides the advantages due to this type of technique, further, capable of reading the ambiguity of distance directly by separating in frequency the multiple-time-around echoes. The device described is applicable to any pulses radar, such as for example, search or tracking, in which it is necessary to detect targets and recognize multiple-time-around echoes. Nevertheless its application is especially suited to a multifunctional radar (with phased-array antenna and monopulse capability).
20 Jun 1988
TL;DR: In this paper, the XTRON-4b crossatron switch has been advanced to 2.5 MW at average current with 1.2 ms pulsewidth and 500 Hz pulse repetition frequency (PRF).
Abstract: The demonstrated average-power-modulating capability of the XTRON-4b crossatron switch has been advanced to 2.5 MW at average current. Tests are described in which the switch was integrated into a simple square-wave, resistive-load modulator circuit consisting of a 10 MW power supply, a capacitor bank, and a water-tank load. The switch operated successfully at 140 A peak current, 32.2 kV open-circuit voltage, and 77.2 A average current with 1.2 ms pulsewidth and 500 Hz pulse repetition frequency (PRF) (60% duty). This advanced performance represents 2.5 MW of high-speed power-modulating capability. At higher voltages, 500 kW was modulated at 50 kV and 1 kHz PRF, and 250 kW was modulated at 75 kV and 100 Hz PRF. >
TL;DR: In this article, a femtosecond continuum was generated in the wavelength range 380-720 nm using a ring rhodamine 6G laser with passive mode locking, with an energy of 5 × 10− 7 J in a specially developed multipass amplifying stage.
Abstract: Light pulses of wavelength of 620 nm, duration of 40 fs, and energy 4 × 10− 11 J, generated in a ring rhodamine 6G laser with passive mode locking, were amplified to an energy of 5 × 10− 7 J in a specially developed multipass amplifying stage pumped by a copper vapor laser. The pump power was less than 1 W when the pulse repetition frequency was 10 kHz. The duration of the amplified pulses was 45 ± 5 fs and the divergence was twice the diffraction limit. A femtosecond continuum was generated in the wavelength range 380–720 nm.
TL;DR: In this article, a narrow synthetic radar beam was generated from square-law detected radar pulses provided the return pulse is incoherent, and the processing would provide the same range resolution as a linear synthetic aperture system, but would reduce the azimuth resolution by the ratio of the transmitted pulse length to the carrier wavelength.
Abstract: A narrow synthetic radar beam may be generated from square-law detected radar pulses provided the return pulse is incoherent. The processing would provide the same range resolution as a linear synthetic aperture system, but would reduce the azimuth resolution by the ratio of the transmitted pulse length to the carrier wavelength. >
TL;DR: In this paper, the effects of target depolarization in measurements made by stationary microwave systems have been extensively investigated and extended to non-stationary (Doppler) systems, where adequate antenna polarization isolation is required to allow high quality polarization measurements to be acquired.
Abstract: The effects of target depolarization in measurements made by stationary microwave systems have been extensively investigated. The use of depolarized measurements can provide information not available in the like-polarized measurement alone. Depolarized measurements acquired by non-Doppler systems were susceptible to errors induced by the measurement antenna. We extend this previous research to non-stationary (Doppler) systems. In both stationary and Doppler systems, adequate antenna polarization isolation is required to allow high quality polarization (especially depolarized) measurements to be acquired. In the synthetic aperture radar (SAR) systems the effect of azimuth ambiguities caused by the pulse repetition frequency (prf) of the system must also be incorporated in the analysis. Normally the effects of PRF can be filtered by the azimuth spectrum processor, however when measuring the weak depolarized cross-section in the presence of the strong like-polarized cross-section the polarization is...
TL;DR: In this article, the design and operational characteristics of a high repetition rate TEA CO2 laser are described, and the performance of optical components at various pulse repetition frequencies is presented.
Abstract: The design and operational characteristics of a high repetition rate TEA CO2 laser are described. The laser operates at variable pulse repetition frequencies up to 100 Hz. Stable operation is obtained in a closed cycle which includes a gas mixture regenerator. Energies of up to 10 J/pulse are obtained in pulses having 25 MW peak powers. Average powers as high as 500 W are reached at the maximum pulse repetition frequency. The performance of optical components at various pulse repetition frequencies is presented.
24 Jun 1988
TL;DR: In this article, the internal gain of APD is modulated in synchronism with a syncpumped cw dye laser, enabling frequency-domain measurements up to about 3000 MHz at multiples of the laser pulse repetition frequency.
Abstract: We report on new approaches to picosecond fluorescence spectroscopy, using commercial silicon avalanche photodiodes (APD's) as opto-electronic cross-correlators. By integrating lock-in techniques, fluorescence radiation can be detected with 0.001 photons per pulse sensitivity. In our method, the internal gain of the APD is modulated in synchronism with a syncpumped cw dye laser. Using pulsed gain-modulation, time-domain measurements with an apparatus response FWHM of 150 ps can be accomplished. In a second mode, sinusoidal gain-modulation is employed, enabling frequency-domain measurements up to about 3000 MHz at multiples of the laser pulse repetition frequency. This mode also allows high-resolution lifetime-selective detection and fluorescence lifetime direct indication.