Showing papers on "Pulse repetition frequency published in 1980"

Radar altimeter mean return waveforms from near-normal-incidence ocean surface scattering

Abstract: Under assumptions common in radar altimetry, the mean backscattered return power for a short-pulse radar and near-normal-incidence scattering from a rough ocean surface is given by the convolution of several terms. For a nearly Gaussian transmitted pulse shape scattered from a nearly Gaussian distributed sea surface, a small-argument series expansion of one of the terms within the convolution leads to a several-term power series expansion for the mean return waveform. Specific expressions are given for the first four terms. These results, which require much less computer time than would the otherwise necessary numerical convolution, are useful for data analysis from current or past radar altimeters and for design studies of future systems. Several representative results are presented for an idealized SEASAT radar altimeter.

Electrothermal model of switching in amorphous silicon films

Abstract: The pulse repetition frequency dependence of the delay time, td, in amorphous silicon films produced by electron‐beam evaporation in a Ti–Si–Ti sandwich structure has been found to give two opposite trends. Below about 1 kHz, td increases as the frequency is increased but is independent of the pulse duration. Above 1 kHz, td decreases with frequency and is also reduced in magnitude by increasing the pulse width. In this paper, an electrothermal mechanism of switching has been used to explain the above phenomenon satisfactorily. The predictions of the model as regards td decreasing with increasing over‐voltage and increasing film thickness, the threshold voltage exhibiting a half‐power law relationship with thickness and its temperature dependence, and the effect of space–charge injection around the electrodes are confirmed by experiments. Finally, a view of switching combining both thermal and electronic elements is presented.

Multitarget interleaved tracking for phased-array radar

Abstract: Use of multiple active devices in phased-array radars to generate r.f. power is becoming more interesting, owing to the technical advantages of solid-state components. Because the solid-state components have peak-power limitations instead of the mean-power limitations of traditional components, it is more cost effective to transmit signals with a high duty factor. Furthermore, one of the most important features of phased-array radars is the capability of performing simultaneous tracking on several targets. A method of interleaving pulse sequences for the multitarget tracking function, thus using a high duty factor, is reported. In particular, a technique of selecting the pulse repetition frequency (p.r.f.) and the transmission frequency is described, depending on the estimated radial velocity of each target, its accuracy, clutter spectral characteristics, and the interleaving algorithm efficiency. A simulation has been performed to evaluate the packing efficiency as a function of the pulse length, the duty factor of the transmitter, the number of targets and their range distribution. Consequently, a typical partitioning of the radar frame time among the different functions (tracking, search, confirmation etc.) has been determined for fixed and rotating phased-array antennas. Finally, an evaluation of computer loading to implement multitarget tracking is given.

Method of reducing side lobes of complementary coded pulses in a coherent pulse compression doppler radar receiving system

Abstract: A method of processing doppler signal data to provide time and frequency (therefore phase) coincidence for complementary code pairs of a coherent, pulse compression radar using a weighting of every other echo pulse of a particular range cell to guarantee pulse compression sidelobe cancellation in accordance with complementary code theory.

Synthetic aperture radar range - Azimuth ambiguity design and constraints

Abstract: Problems concerning the design of a system for mapping a planetary surface with a synthetic aperture radar (SAR) are considered. Given an ambiguity level, resolution, and swath width, the problems are related to the determination of optimum antenna apertures and the most suitable pulse repetition frequency (PRF). From the set of normalized azimuth ambiguity ratio curves, the designer can arrive at the azimuth antenna length, and from the sets of normalized range ambiguity ratio curves, he can arrive at the range aperture length or pulse repetition frequency. A procedure based on this design method is shown in an example. The normalized curves provide results for a SAR using a uniformly or cosine weighted rectangular antenna aperture.

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.

A method in a tracking radar to attain a large unambiguous range for detected targets by means of radar pulses with high repetition frequency

Abstract: The invention relates to a method for a tracking radar which transmits radar pulses towards a certain target whose target range from the beginning is known. The carrier frequency of the transmitted radar pulses are during the target tracking varied from one pulse to the next following, so that a pulse series including a certain number M of carrier frequencies is treated. The number M is chosen with reference to the continuously measured target range and as long as this range is less than a certain value. If the target range exceeds this value the number M of carrier frequencies is changed and a new pulse series including this new number is transmitted. The unambiguous range to the followed target becomes dependent on the frequency repetition frequency in the transmitted pulse series instead of the PRF of the radar.

Radar signal detector

Abstract: A sensitive radar signal detector is provided which is operative to reliably detect low level radar radiation characteristic of scattered radiation of very short duration and unknown frequency. Received radar signals which are mixed with a swept frequency signal are passed through to a narrow band FM descriminator, the output of which is amplified by a unidirectional amplifier. The output of the amplifier, present when a signal is received, is utilized to momentarily slow the frequency swept local oscillator resulting in a time expansion of the characteristic S-shaped descriminator output signal. This results in the generation of a negative-going error signal between the two time expanded halves of the S-shaped descriminator response. The error signal when amplified produces a significant voltage spike which ensures reliable detection, to permit the detection of a single radar pulse with a reduced false alarm rate.

Radar radiometer and its use

Abstract: A radar radiometer apparatus including a superheterodyne amplifier, a synonous demodulator, and logic circuitry to provide for the interruption of a local oscillator for a portion of each pulse of a radio frequency repetition cycle in order to isolate radar receiver/transmitter coupling and permit simultaneous radiometer use.

PRF Stabilized surface acoustic wave oscillator

Abstract: Mode locked surface acoustic wave oscillators, configured as comb spectrum generators, are stabilized by means of a variable phase in the closed, oscillation loop, the phase being controlled in response to deviations of the low, pulse repetition frequency from a design reference PRF The variable phase may be provided by a variable phase device inserted in the oscillatory loop, such as varactor-tuned lumped element delay lines or 90° hybrids, or other devices Or, the variable phase may be provided by a voltage tunable surface acoustic wave device used as the basic oscillator SAW delay line

High Resolution in Azimuth for Radar Targets Moving on a Straight Line

Abstract: Target classification is sometimes desired together with airspace surveillance. To some extent this is possible by observing the flight track resulting from typical radar plots. A possibility for measuring the lateral variation of the radar cross section for single targets is described in the following. This method assumes a straight unaccelerated flight path, at least for a few seconds, with tangential components. This restriction is mitigated by prevailing straight flight paths and by observation of targets with radar nets, so there is always a tangential component. This method is especially suitable for electronic steerable radar application.

Mti-filter in a tracking radar receiver

Abstract: An MTI-filter included in the receiver part of a tracking radar for suppressing clutter when receiving echo pulses from a certain target. The transmitting pulses of the tracking radar are transmitted in series where the carrier frequency is varied from pulse to pulse and is repeated from series to series. The MTI-filter (F) contains a number of delay links (DL1-DLN), for example digital shift registers which are stepped forward timely with the radar PRF. The input of the filter and the output of the shift register M(Alpha)N are connected to a differentiator (SK) where M = the number of carrier frequencies in a pulse series.

Energy characteristics of a transverse-discharge copper vapor laser

Abstract: A study was made of the basic energy characteristics of a transverse-discharge copper vapor laser. The average laser output power in the yellow and green lasing components was determined as a function of the amplitude and repetition frequency of the excitation pulses, temperature of the discharge tube walls, and buffer gas pressure. The current-voltage characteristics of the discharge were investigated. An average laser output power of 75 W was obtained, at a pulse repetition frequency of 3 kHz.

Arrangement for detecting the field strength of a field generator by means of a Hall generator

Abstract: In order to detect relatively weak field strengths, it is proposed to provide pulse-shaped signals for the actuation of the Hall generator (5). With a constant field said signals can have any desired pulse repetition frequency, with a changing field they have at least double frequency of the frequency occurring in the traffic signal. The pulse duty factor of the pulses is also selected in such a way that the pulse energy content of a pulse is identical with or smaller than the effective control power of the initial Hall generator (5). With the proposed arrangement, the sensitivity of Hall generators can be increased by a multiple. The arrangement can be used wherever weak field strengths are to be measured. A preferred application is in electrognathography.

Pulse doppler radar

Abstract: PURPOSE:To enhance detection probability at receival of small signals by changing to different frequencies both pulse repetition frequency of transmission signal and its carrier frequency at the same time in pulse doppler radar in which relative speed and relative distance of the target is detected by discrete power spectrum. CONSTITUTION:Pulse repetition frequency Fi of transmission pulse and its carrier frequency fi are changed to different frequencies at the same time, so that the relation fi/Fi=k (constant) can be always maintained. In this case, pulse train of target with velocity v to DPS converter is expressed by the equation in which [Xn] is dependent only on phase phii and is independent of other i, ¦Xp¦ does not change with phase (phii) of [Xn], so [¦Xp¦ ] does not change with i. Therefore, if both pulse if both pulse repetition frequency Fi and carrier frequency fi, while maintaining proportional relationship, are changed to different frequencies, then when multiple PRT are used, discrete power spectrum [¦Xp¦ ] always holds the same response to relative velocity (v).

Ground radar detection of meteoroids in space

Abstract: A special test to lower the detection threshold for satellite fragments potentially dangerous to spacecraft was carried out by NORAD for NASA, using modified radar software. The Perimeter Acquisition Radar Attack Characterization System, a large, planar face, phased radar, operates at a nominal 430 MHz and produces 120 pulses per second, 45 of which were dedicated to search. In a time period of 8.4 hours of observations over three days, over 6000 objects were detected and tracked of which 37 were determined to have velocities greater than escape velocity. Six of these were larger objects with radar cross sections greater than 0.1 sq m and were probably orbiting satellites. A table gives the flux of both observed groups.

Synthetic-Aperture Radar Based on Nonsinusoidal Functions: VII-Thumbtack Ambiguity Functions

Abstract: In the sixth paper of this series, an approximation was used for certain correlation functions, but its justification was postponed. These correlation functions are investigated in more detail in the present paper. The theory of pulse-position and pulse-shape coding of radio signals is further advanced toward correlation and ambiguity functions with low or no sidelobes, and block diagrams of receivers are derived. It is shown how signals can be constructed that have a large average-to-peak power ratio of the radiated wave, and avoid at the same time large antenna currents. A class of signals and their receivers is derived whose ambiguity functions have theoretically no sidelobe in a selectable section of the range-Doppler domain. Such signals are ideal for the detection of low-flying aircraft and cruise missiles by means of an all-weather, look-down radar, the discrimination of radar decoys from an ICBM, and other uses calling for extreme resolution under any weather conditions.

Method and apparatus for preventing the response of a radar beacon to receive radar pulses originating from the side lobes of a transmitter and an arrangement

Abstract: A method for preventing a radar beacon's response to received pulses from a vessel which originate from the side lobes of the vessel antenna. The carrier frequency of the radar signal pulses to and received by the beacon is measured and a value of this frequency is stored when the amplitudes of the signal pulses exceed a certain high threshold level (Th). If signals after that are received which exceed a low threshold level (Tl) (but not the high) the carrier frequency of such signals is measured and a corresponding value is stored. Measuring two subsequent and equal carrier frequencies is considered as a criterion that a response signal from the beacon responding to the second received signal should not be transmitted. An arrangement to carry out the method is described.

Radar Emitter Recognition Using Pulse Repetition Interval

Abstract: : A method for estimating radar emitter pulse repetition interval parameters for intercepted emissions is presented. Adaptive parameter estimates based on certain measurements are derived. The measurements are obtained by a readily implementable observation procedure. The approach can deal with emitters with variable pulse repetition interval in a dense environment. Computer simulation results for the techniques are included.

Generation of nanosecond high-voltage pulses with high repetition rate

Abstract: The letter presents a circuit for the generation of 50 V pulses with 1.2 ns rise time, 2.5 ns duration and a variable pulse repetition frequency up to 3 MHz based on the effect of avalanche multiplication. The use of standard epitaxial silicon planar transistors instead of selected avalanche types permits safe operation with low sensitivity to temperature variations.

A pulse radar system

Abstract: It has previously been known to construct a radar system so that it transmits long pulses and short pulses. The long pulses, which may be subject to pulse compression, are used, because of their high energy, to detect objects at long range whilst the short pulses, because of their good resolution, are used to detect objects at short range. This known technique suffers from the disadvantage of requiring an exceedingly expensive transmitting and receiving system. A transmitter (13) is controlled by unit (14) to produce pulses at T. The frequency of each pulse is changed so as to divide it into two consecutive signals of different frequencies. These consecutive signals are of different duration and are used, as before, for long range and short range detection respectively. The receiver (19) has a local oscillator (18) whose frequency is also changed so as to make the receiver respons ve to the long and short signals when radar returns are expected from long and short ranges. In an alternative embodiment two separate receivers are used.

Method of eliminating the influence of remanence in receiving systems and device for carrying out the method

Abstract: The invention relates to a method and a device for eliminating Remanenzerscheinungen in receiving systems in which for detecting a fire caused by a field generator field flux or a Feldflusanderung one or more Flusaufnehmer with ferromagnetic properties, preferably provided with antennas Hall generators are provided. According to the invention the Flusaufnehmern (I to VIII) Zug leads magnetizing pulses in a periodic sequence whose pulse height and - are wide chosen so that so that the saturation field strength of the Flusaufnehmer is achieved. The Flusaufnehmer (I to VIII) are preferably controlled by means of pulse-shaped signals, the magnetization pulses are supplied in the pulse interval of these signals in synchronism with the pulse repetition frequency. The method is applied in particular in the Gnathographie for recording the mandible movement of a human.

Conopulse Radar Angle Tracking Accuracy

Abstract: An analysis is given of the tracking accuracy of a conopulse radar that angle-tracks on target echo pulses. The analysis includes effects of noises in both sum and difference channels, the effect of the tracking range gate's duration, and applies to any shape of radio frequency (RF) pulse envelope. For large single-pulse signalto-noise ratio and any shape of RF pulse envelope, accuracy approaches the theoretical accuracy of a conopulse system when a short-duration range gate is used. The inportant case of rectangular RF pulses is solved in detail.

Reflected Bragg Imaging Studies and Preliminary Results for Improved Optical Design

Abstract: Because of the right angle geometry between the sound field and the interrogating light wedge, Bragg imaging is ideally suited for the study of reflected images. In order to improve the intensity and the clarity of these reflected images, a pulsed dye laser has been developed and tested. The laser has a variable pulse repetition frequency to a maximum of about 15 pps and operates at a wavelength of 590 nanometers with a maximum power of 5mW. The dye laser is fired through an SCR circuit using a delayed trigger from the transducer generator. Image photographs of various test objects will be presented and system resolution limitations will be discussed.

Pulse transmitting radar apparatus

Abstract: In a radar system utilizing same, a segmented chirp waveform is built up by frequency hopping trains of simple chirp .pulses. Each chirp pulse in a train is identical and is transmitted on one of a set of discrete carrier frequencies. The carrier frequencies are uniformly spaced in a predetermined bandwidth and are used in linear sequence. After transmitting on the last carrier frequency, the entire pattern is repeated, starting again at the first carrier frequency. The returns from the individual pulses are digitized and stored and the history thereof is then assembled by a digital signal processor into a high resolution image.

Quick method for estimating the laser duty cycles

Abstract: Laser diodes with a GaAs--Al/sub x/Ga/sub 1-x/As double heterostructure were tested for longevity at a pulse repetition frequency corresponding to a decrease of the lasing power by 10 and 20%. On the basis of the results obtained, a method is developed for determining the duty cycle of heterolasers. A fast method is proposed for discarding laser diodes which is based on measuring the dependence of the lasing power on the pulse repetition frequency.

Frequency-Stabilized Hybrid CO 2 Laser

Abstract: A compact atmospheric-pressure hybrid CO2 laser utilizing a transverse double-discharge technique has been constructed and operated at moderate repetition rates. A pulse output energy of 80 nil 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 laser. 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.

WELTI Waveforms for High Resolution Radar

Abstract: The problem of detecting and tracking a small target in a m ultipath environment is addressed in terms o f high-resolution radar utilizing carrier-free signals to discriminate the target from its image in range. A class o f carrier-free waveforms which we shall refer to as Welti waveforms is constructed from quaternary codes due to Welti.1 It is shown tha t such wave­ forms offer extremely high resolution in range and doppler. A t the same tim e, large pulse compression ratios can be obtained.