Showing papers on "Pulse repetition frequency published in 1983"

A High-Resolution Radar Detection Strategy

Abstract: A comparison of single range cell detection and integrated contiguous range cell detection for a high range resolution radar is presented. A simulation was used to generate probability of detection curves for the two detection strategies using 10 target models with different target scattering characteristics. The integrated range cell detection strategy was found to be superior in all cases except when the target is composed of a single strong flare point.

Vestibular stimulation method

Abstract: An apparatus and method for treating a patient suffering from motion sickness such as air sickness and the like. The method includes the steps of applying electrodes to the vestibular area of the patient's head and providing current pulses in the current range of 0.5-3.8 mA, the pulses having a frequency in the range of 1-5 pulses per second and a pulse width in the range of 100-200 msec. The apparatus comprises a timing generator for determining pulse frequency, an impulse generator for generating a pulse waveform, an impulse former for controlling pulse shape and a driver stage for developing current pulses to be applied to the electrodes.

A Millimeter-Wavelength Dual-Polarization Doppler Radar for Cloud and Precipitation Studies

Abstract: A pulse Doppler radar system operating at 35 GHz and having full polarization (linear and circular) diversity capability is described. Separate antennas are used for the transmitter and the receiver because this design approach allows better overall radar sensitivity. The transmitter operates in the double-pulse mode to optimize the unambiguous Doppler velocity measurable with the system. A polarizer capable of handling about 200 kW of peak power when pressurized with sulfur hexafluoride (SF6) at 25 psi was developed for the transmitter. The radar system has built-in test sequences for checking the gain and alignment of the transmitter and receiver antennas. The dual-polarization intermediate frequency (IF) receiver has a total of six analog channels. A very flexible data acquisition and processing system has been developed to allow both coherent and incoherent dual-polarization measurements to be performed; the system includes a microprocessor-controlled pulse-pair processor and a minicomputer w...

A new technique for reducing radar response to signals entering antenna sidelobes

Abstract: A new technique for reducing a radar's response to undesired signals entering a radar's sidelobes is described and analyzed theoretically. This technique involves moving a phased array antenna's phase center to Doppler shift sidelobe signals out of the radar receiver's passband.

Altitude determining radar using multipath discrimination

Abstract: A height-determining radar utilizing both direct and multipath signals coising a radar transmitter and receiver and means for measuring the variation of the pulse widths of the received radar signal, the variation being caused by fluctuating multipath contribution to the received signal, and further comprising means for calculating the target height h from the equation h=cRτ B /4e, where c is the speed of light, R is the target range, τ B is the pulse width variation and e is the radar height. The multipath variation may be enhanced by varying the linear polarization of the emitted radar signal.

Vector phase angle change distribution processor

Abstract: A system and technique is disclosed for estimating the real-time spectral width of radar returns to provide an indication of weather turbulence The system includes a Doppler radar to provide the in-phase and quadrature phase signals from successive range returns which are digitized and converted to a phase angle prior to processing Successive angular samples at the pulse repetition frequency are subtracted to provide a phase angle change The phase angle change is filtered to determine an average angular mean which is then subtracted from new angular samples to determine the angular deviation The angular deviation for each sample is in turn compared with a threshold to provide an output which is averaged over time to determine when the standard deviation of the samples exceeds a reference value When the standard deviation of the samples exceeds that reference value, the spectral width is of a magnitude which indicates the presence of turbulence

Observations of the HF‐enhanced plasma line with a 46.8‐MHz Radar and reinterpretation of previous observations with the 430‐MHz radar

Abstract: During 5.1-MHz HF transmissions below the F region penetration frequency by a nearby ionospheric modification facility, radar echoes coming from F region heights at a frequency of 46.8 + 5.1 = 51.9 MHz were received while a VHF radar using the 305 m spherical reflector at Arecibo was transmitting pulses coherently on 46.8 MHz. The bandwidth of the echoes was less than 10 Hz. The so-called decay line due to the parametric decay instability was expected at a frequency lower by about 300 Hz, but it was not observed. Density variations caused by the ponderomotive force resulting from the standing wave pattern at 5.1 MHz are tentatively invoked to explain the observations. Poorly understood aspects of some previous observations with the 430-MHz radar can be similarly explained.

Inductively stabilized rare‐gas halide minilaser for long‐pulsed operation

Abstract: Inductively stabilized discharges are developed for the rare‐gas halide minilasers. 6.8 mJ per pulse with 40‐ns full width at half‐maximum pulse lengths and 3.7 mJ per pulse with 60‐ns full width at half‐maximum pulse lengths are obtained for KrF. 3.1 mJ per pulse with 40‐ns full width at half‐maximum pulse lengths and 1.7 mJ per pulse with 60‐ns full width at half‐maximum pulse lengths are obtained in XeCl. The discharge dimensions are 2.5‐mm electrode separation by 4 mm wide and 27.6 cm long. Orders of magnitude increases in pulse repetition frequency are obtained in devices that do not utilize gas flow.

Rate discrimination of high-pass-filtered pulse trains.

Abstract: Difference limens for trains of 30‐μs pulses were determined for repetition rates of 50, 100, 200, 400, and 800 pulses per second under conditions of no filtering and high‐pass filtering (115 dB/oct) with corner frequencies of 2.5, 5.0, 7.5, and 10 kHz. Low‐pass‐filtered noise was mixed with the trains of impulses to preclude discrimination on the basis of potential low‐frequency signal components. Measures were obtained from four trained listeners at a signal level of 30 dB SL relative to individually determined thresholds for each filter condition and repetition rate. The data support the hypothesis that resolution of pulse‐train repetition rate involves both temporal‐ and frequency‐based processes—the latter becoming ineffective when frequency resolution of the ear is insufficient to resolve separate harmonics of the signal. Inter‐ and intra‐individual differences are interpreted as reflecting frequency resolution capacity.

A fifty megawatt klystron for the Stanford Linear Collider

Abstract: The proposed Stanford Linear Collider (SLC) has been designed to provide 50 on 50 GeV electron-positron collisions. The performance of the 240 klystrons driving the two-mile long linac must be upgraded to achieve at least 50 Megawatts of peak power output at a pulse width of 5 µsec and a pulse repetition frequency of 180 pulses per second. The operating frequency of the upgraded linac will continue to be 2856 MHz. A klystron amplifier meeting these new requirements has been designed to operate at 315 KV, µk = 2, with a computed efficiency of slightly greater than 50%. Initial tests indicate the achievement of the basic power objectives; however, observed parasitic instabilities make beam focusing, RF drive frequency and drive level extremely critical. High electric fields in the electron gun, output gap and output window are all potential problems. Steps taken in the design to overcome these problems are discussed and test results are presented.

Short pulse generator

Abstract: A baseband generator for pulses of high peak amplitude, rapid rise time, subnanosecond duration, and high pulse repetition frequency is disclosed. A plurality of capacitors are charged in parallel then discharged in series to cause a plurality of avalanche of transistors to fire sequentially. The resulting sum voltage across the capacitors is then applied to a step recovery diode to generate the pulse.

Pulse compressor for doppler tolerant radar

Abstract: A radar system employing Doppler tolerant radar pulses such as linear FM or hyperbolic FM chirps includes a pulse compressor configured as a digital finite impulse response filter. In one embodiment, the radar returns are split into in-phase and quadrature phase components for manipulation in complex form within the filter.

Spread signal spectrum communication circuits and system

Abstract: The present invention provides a covert radar system in which radar signals emitted are capable to search receiver thermal noise and, therefore, are substantially undetectable in the normal radar operating range.

Dual frequency band radar detector

Abstract: A dual frequency band radar detector responds to radar signals occurring within either of a first or a second range of frequencies. The detector comprises one or more antennas for receiving radar signals including radar signals occurring within the first and second ranges of frequencies. At least one pilot signal at a predetermined frequency is produced for modulating the received radar signals. The modulated signals produced in response to received signals in either of said first range of frequencies or said second range of frequencies are isolated. A detector is coupled in circuit for detecting the one pilot signal in these isolated and modulated signals and a control output signal is produced responsive to the detected pilot signal. Accordingly, the presence of a control output signal indicates the reception of radar signals occurring within at least one of the first and second ranges of frequencies.

Waveform design for optimized ambiguity response

Abstract: This is a method of waveform design and range correlator implementation t uses weighting to optimize a radar receiver's ambiguity response in both the temporal and frequency dimensions of the ambiguity function. It is an extension of group-complementary code structure and is based on a multipulse processing technique. The procedure minimizes frequency sidelobes over a selected interval in the spectral domain between dc and the pulse repetition frequency and completely eliminates temporal sidelobes throughout the pulse repetition interval. It minimizes clutter and multitarget interference in an active-sensor target acquisition and tracking application, and still allows weighting of the pulse responses to reduce frequency domain sidelobes.

Watthour test circuitry

Abstract: The present invention accepts accurately generated pulses, having a frequency of K pulses per second, from a suitable source of such pulses, and uses those pulses to phase correct the operation of a phase lock loop voltage controlled oscillator, which is designed to run at a frequency of N times K pulses per second. The output pulses from the voltage controlled oscillator are passed along a bifurcated path. Along one leg of said bifurcated path, the pulses are directed to a counter where they are divided down to provide an output signal at the rate of NK/P pulses per second and in the preferred embodiment, P equals N. The pulses from the counter are fed at the NK/P rate back to a phase comparator which provides an error voltage at the voltage controlled oscillator for each pulse. The present invention further includes logic circuitry which is connected to the second of said bifurcated path legs to receive the pulses which are at the NK pulse per second rate and this logic circuitry is further connected to the output of the counter to receive pulses therefrom at the NK/P pulse per second rate. The logic circuitry is designed to be able to provide pulses at either the NK rate, or at the NK/P rate depending upon how the pulses are to be employed.

Synthetic aperture radar

Abstract: PURPOSE:To improve measurement precision by generating a control signal by a signal received by an antenna for a right under point and a transmit pulse timing signal, and performing the gain control and pulse timing setting of the receiver of an antenna for observation. CONSTITUTION:A transmitter 2 is connected to the antenna 7 for the right under point through a transmitting/receiving branching filter 3 and a changover switch 8 right before synthetic aperture radar is put in operation. A radio wave is radiated toward a right under point at a pulse repetition frequency determined according to a forecasted track and a reflected wave from the ground surface is led to the receiver through the antenna 7, changeover switch 8, and transmitting/ receiving branching filter 3. Further, it is led to a logical circuit 12 and compared with the timing signal generated by a pulse timing signal generator 5 to calculate.

Method for sea surface high frequency radar cross-section estimation using Dopler spectral properties

Abstract: A method for estimating the high frequency radar cross-section of the sea surface. A Doppler spectrum of the sea surface is obtained by correlating returns from high frequency radar signals. Approach and recede Bragg spectral lines and a zero Doppler frequency continuum level are identified in the Doppler spectrum. The amplitude ratio ρ between the Bragg spectral lines and an amplitude ratio ζM between the maximum amplitude Bragg spectral line and the zero Doppler frequency continuum are measured from the Doppler spectrum. The radar cross-section is then determined from the ratios ρ and ζM. In a further method embodiment, the estimated radar cross-section is used to estimate the radar cross-sections of targets appearing in the Doppler spectrum.

Improvements to a pulse compression radar matched filter

Abstract: A modification to the matched filter is developed that enables a pulse compression radar system with inherently low sidelobes to be achieved. The system is illustrated using a signal with a truncated Gaussian spectrum with TB = 1000 giving sidelobes of ?46 dB, mis-match loss of 0.002 dB and moderate tolerance to Doppler shift.

Laser prf considerations in differential absorption lidar applications.

Abstract: Laser pulse repetition frequency (prf) is a major factor in determining the performance of differential absorption lidar (DIAL) systems. The effects of laser prf on concentration measurement accuracy and maximum usable range are quantified. Heterodyne-detection (coherent) and direct-detection (noncoherent) as well as path-averaged and range-resolved DIAL systems are analyzed.

Fast photoconductive GaAs detectors made by laser stimulated MOCVD

Abstract: Photoconductive detectors with rise times less than 10 ps have been made from GaAs grown by laser-stimulated MOCVD. The growth temperature was 450°C, and laser pulse energy and pulse repetition frequency were 120 mJ and 10 Hz, respectively.

R.F. system

Abstract: A bearing indicating R.F. system comprising two spaced, broad-beam antennas supplying signals via power dividers to amplitude comparison means and phase comparison means, both operating without down-conversion to I.F. The main lobes of the radiation patterns of the antennas are inclined towards one another so that for non-normal incidence there is a difference between the amplitudes of signals received by the antennas. The amplitude comparison means comprises detector diodes, logarithmic amplifiers, and a first subtractor, the magnitude of the output signal (sensed with a threshold detector indicating which side of normal the radiation is incident. The phase comparison means comprises a hybrid ring having "sum" and "difference" output ports connected to an instantaneous frequency measuring apparatus and a detector diode, and further comprising logarithmic amplifiers and a second subtractor, the outputs of detector diodes in IFM being summed to provide a signal output connected to one amplifier. The output of the second subtractor is an accurate but ambiguous representation of the bearing angle with respect to normal (being an even function; the ambiguity can be resolved by reference to the output signal of the first subtractor which may also be used as an approximate representation of the bearing angle. Using broad-band R.F. components, the system may be operable over a broad bandwidth, e.g. an octave. A data comparator and a pulse repetition frequency filter control gates inhibiting the provision of bearing data except for pulsed incident radiation having desired frequency and PRF.

Radar signal correction system

Abstract: A radar correcting system has features for providing a corrected radar receiver reflection to a Doppler process unit. The corrected receiver pulse accounts for variances in phase, amplitude and frequency of the transmit pulses. The system has a phase detector that detects the phase difference between a stable oscillator and the transmit signal, providing a complex video or real and imaginary outputs. An operator that will normalize the transmit pulse is determined. The operator is applied to the reflections received by the receiver antenna to remove from the reflections any vagaries due to varieties in the transmit pulses. The data proceeding to the processor deals only with the objects causing the radar reflection.

Inductively stabilized, long pulse duration transverse discharge apparatus

Abstract: An inductively stabilized, long pulse duration transverse discharge apparatus. The use of a segmented electrode where each segment is attached to an inductive element permits high energy, high efficiency, long-pulsed laser outputs to be obtained. The present apparatus has been demonstrated with rare-gas halide lasing media. Orders of magnitude increase in pulse repetition frequency are obtained in lasing devices that do not utilize gas flow.

Radar fuze system

Abstract: A radar fuzing system for use in a guided missile wherein the system is tuned in accordance with the estimated intercept closing velocity to permit the use of narrower bandpass filters and thereby reduce the probability of detecting pulse repetition frequency lines and very low Doppler returns from chaff bundles.

Copper vapor laser with stabilized output parameters

Abstract: The possibility was demonstrated of regulating the emission characteristics of a laser utilizing self-terminating transitions by controlled variation of the concentrations of the normal and excited particles in the active medium, and of the electron temperature and density, by applying one or several additional electric pulses. In the case of a copper vapor laser the output pulse energy was stabilized as the pulse repetition frequency was varied over a wide range, as was the average laser output power at one of the selected frequencies. A prototype pulsed copper vapor laser was made which maintained a constant (to an accuracy of 1–3%) laser output pulse energy when the pulse repetition frequency was varied in the range 0.25–6.5 kHz.

Pulsed YAG:Nd3+ laser with a passive Q switch in the form of an LiF crystal containing centers

Abstract: An investigation was made of the energy characteristics of a YAG:Nd3+ laser subjected to pulse-periodic pumping and to passive Q switching of a resonator by an LiF crystal containing color centers. A comparison was made of the energy of giant laser pulses obtained using passive and electrooptic switches when the pump pulse repetition frequency was up to 50 Hz. The use of a passive switch made of an LiF: crystal under optimal lasing conditions did not reduce the energy of the output pulses of the laser compared with that attainable using an electrooptic Q switch.

Pulse-periodic neodymium laser with wavefront reversal in a stimulated-Brillouin-scattering mirror and with frequency doubling

Abstract: A determination was made of the characteristics of a YAG:Nd3+ laser with wavefront reversal and with frequency doubling in a DKDP crystal. The energy carried by each of the second harmonic pulses was 20 mJ and the divergence was close to the diffraction limit when the pulse repetition frequency was up to 50 Hz.

Adaptive radar signal processor

Abstract: An adaptive radar signal processor is operable to effectively suppress clutters and extract a target signal with a high degree of accuracy and includes a memory storing two-dimensional radar data corresponding to range and azimuthal directions, multipliers multiplying each of data of the same range but different azimuthal direction read out from the memory, an adder generating the added data of the multipliers as an estimated data, and a weighting coefficient determinater which determines the optimum weighting coefficients based upon the stored radar data so that the difference between the radar data and the estimated data at an observing position is minimized, and produces the difference data as a clutter-suppressed radar data.