Showing papers on "Pulse repetition frequency published in 1985"

Two Methods of Ambiguity Resolution in Pulse Doppler Weather Radars

Abstract: A comparison is made of the performance of a weather Doppler radar with a staggered pulse repetition time and a radar with a random (but known) phase. As a standard for this comparison, the specifications of the forthcoming next generation weather radar (NEXRAD) are used. A statistical analysis of the spectral moment estimates for the staggered scheme is developed, and a theoretical expression for the signal-to-noise ratio due to recohering-filtering-recohering for the random phase radar is obtained. Algorithms for assignment of correct ranges to pertinent spectral moments for both techniques are presented.

A method for radar mapping an area and a radar equipment to carry out the method.

Abstract: A method for radar mapping an area and a radar equipment for wideband exploration at frequencies below 300 MHz. A large number of frequencies, for instance 1000, are distributed over a frequency band between for instance 12.5 and 200 MHz, and approximately corresponding to terms in a geometrical series but being different harmonics to a certain fundamental frequency. This is accomplished by a synthesis generator (1) coupled to a phase control device (7) and the generated frequencies are each amplified in a separate amplifier (2), the outputs of which are guided in groups to a number of antennas, tuned to different frequency bands and fewer than the number of frequencies. The reception is carried out in a similar way from the antennas with pre-amplifiers and a mixer (3) each and an A/D-converter (4) and a registration device (5). The equipment is meant to use the principle of so called synthetic aperture (SAR).

Medium PRF for the AN/APG-66 radar

Abstract: This paper discusses the medium pulse repetition frequency (PRF) pulse doppler mode of the AN/APG-66, the multimode fire control radar for the F-16A/B aircraft. This radar is currently in production and as of January 1984 over 1700 have been delivered. Included is a discussion of the three PRF types: high, low, and medium PRF, leading to the conclusion that for an airborne, look-down application the medium PRF waveform is the best choice. System tradeoffs between a high peak power and a low peak power transmitter are discussed which show that when only a medium PRF waveform is required, the high peak power transmitter yields better performance. Some system design considerations concerning the PRF selection and sidelobe clutter are also included. Finally, the radar mechanization is presented. The AN/APG-66 radar in general, and its medium PRF mode in particular, have undergone extensive operational evaluation and the results have been excellent. The radar has met or exceeded its performance design specifications and the field reliability has been outstanding. For example, for the year 1983 the MTBF was 102.9 h based on 64 204 operating hours from two operational air bases.

Reliability of Velocity Measurement by MTD Radar

Abstract: For an ATC radar with MTD-type of signal processing, admissible PRF stagger ratios for expanding the unambiguous velocity interval are derived, and formulas and curves for the parameters describing the reliability of velocity information, based on simulation, are presented. In a noise-only environment and for a Swerling 1 target with S/N resulting in Pd = 90 percent, there is a probability of > 50 percent of obtaining velocity information with an expanded unambiguous velocity interval of 832 knots and a standard deviation of < 1 knot. The probability of false measurement is < 10-5.

Optical radar transceiver control apparatus

Abstract: The apparatus is part of an optical radar set and comprises a high poweredO 2 pulsed transmitter laser which is injection controlled to operate at a fixed frequency offset from a lower powered CO 2 local oscillator laser. A portion of the output of the local oscillator laser is applied to an acousto-optic Bragg cell, together with an RF signal equal to the desired intermediate frequency of the radar set. The upshifted first order output of the Bragg cell is injected into the transmitter laser for stabilization purposes. This results in a stable intermediate frequency for the optical radar set.

Composite pulse radar system having means for eliminating interference between pulses

Abstract: A composite pulse radar has a composite pulse generator (7) generating cycles of short and long pulses with varying intervals between the short and iong pulses. The pulses are transmitted through a transmitter (8) coupled between the generator (7) and a radar antenna (9). The respective echo pulses from near and distant targets are coupled from the antenna (9) through a long pulse receiver (11) and a short pulse receiver (10) to processing section (6) which combines the short and long pulse video signals and eliminates asynchronous interference caused by reflection of the short pulses from distant targets. The section (6) includes a correlator (63) which correlates a plurality of the combined signals for a plurality of successive cycles of pulse transmission.

Method of controlling the pulse frequency of a pulse operated electrostatic precipitator

Abstract: A method of controlling the pulse frequency of an electrostatic precipitator energized by a pulse superimposed direct voltage, is disclosed in which, for a given direct and/or pulse voltage, the pulse repetition frequency, at intervals which are preset or determined by one or more precipitator or operational parameters, is lowered and then increased stepwise according to a predetermined scale. At each value of the pulse repetition frequency the average current being measured and the transmitted charge per pulse (defined as the average current divided by the pulse repetition frequency) calculated. The stepwise increase of the pulse frequency is stopped when either the transmitted charge per pulse for a given direct and pulse voltage maintained in two successive frequency steps remains constant or increases or, where the charge per pulse is kept constant by regulating the direct and/or pulse voltage, when the numerical value of the controlled voltage in the last one or two successive frequency steps remains constant or drops. The limiting pulse repetition frequency is controlled to assume the frequency in the step where the stepwise frequency increase is stopped, until the next search procedure.

Injection controlled laser transmitter with twin local oscillators

Abstract: A heterodyne CO 2 optical Doppler radar comprising a ring type of traitter laser and twin local oscillator lasers which are automatically controlled to operate at a difference frequency equal to the intermediate frequency of the radar, which may be in the VHF band. The output of one of the twin lasers is injected into the transmitter laser for stabilization purposes and the output of the other of the twin lasers is heterodyned with the received target return signals to form the radar's intermediate frequency signal.

Mechanism limiting the optimal output pulse repetition frequency of metal vapor self-terminating lasers

Abstract: Comparative investigations were made by the method of double-pulse excitation of a lead vapor laser (lambda = 0.723 nm) with electron-beam and gas-discharge pumping. The time tau at which lasing in the second pulse begins to weaken in the case of electron-beam pumping is determined by the deexcitation rate of the metastable level and is roughly equal to 1 ..mu..sec. In the gas discharge laser the reduction in the output power starts at tauapprox. =0.1 msec and is determined by the plasma recombination rate. The specific output energy of the electron-beam laser is double that of the discharge laser, the physical efficiency is an order of magnitude higher, and the optimal pulse repetition frequency is two orders of magnitude higher. The average output power of the electron-beam laser can reach 400 W/m. In copper and manganese vapor discharge lasers the optimal pulse repetition frequency is also determined by the plasma recombination rate.

Process for adapting the post integration in a switched pulse repetition frequency radar and a circuit implementing this process

Abstract: The invention relates to a process for adapting the post integration in a switched pulse repetition frequency radar and a circuit implementing this process. For that, the post integration of the detected signals is effected as a function of the signal received from the Doppler filter. For that, switches are used controlled by comparator circuits. The invention is useful in frequency ambiguous coherent Doppler radars using recurrence frequency switching by blocks.

Channelized receiver continuous wave radar system

Abstract: A continuous wave radar system arrangement for improving the dynamic range of the radar receiver. The transmitted carrier signal is frequency modulated by a periodic sawtooth waveform causing a predetermined peak frequency shift. The radar receiver includes a plurality of separate receiving channels each selective to a small portion of the transmitted bandwidth. As the sawtooth modulation causes the carrier signal to sweep in frequency, the received leakage and clutter signals in the selective receiving channels are blocked momentarily and individually in each channel. The outputs of the separate receiving channels are combined to form a composite signal of the echo returns. Gaussian filters with quadratic phase compensation are used to provide the selectivity of the receiving channels.

Range ambiguity in pulsed Doppler ultrasound: the ambiguity clarified?

Abstract: Pulsed Doppler ultrasound (PW) can be used to determine the location of frequency shifts within the cardiac chambers or great vessels. However, it is possible to record similar frequency shifts at sample volume locations distal to their original site; this is referred to as range ambiguity (RA). Eleven patients were studied with combined Doppler and two-dimensional echocardiography (2-D) to determine the circumstances in which RA occurs. Mapping of various flow patterns with PW was performed in each of four 2-D views beginning at 2 cm distances from the transducer and at subsequent 1-cm intervals until the maximal range of the PW was achieved. Range ambiguity was demonstrated only in the four-chamber view in patients with enlarged cardiac chambers or if an abnormal flow pattern was present. The site of origin of the ambiguous signals was dependent on the pulse repetition frequency (PRF) employed. Range ambiguity occurs more often when a relatively high PRF is used. Range ambiguity may be used for mapping of abnormal flow beyond the range of PW or for recording of high velocities at sample volumes far from the transducer without frequency aliasing.

Radar clutter simulator

Abstract: The simulation of clutter echo return signals for a radar system is accomplished using two sets of diode noise sources, a frequency synthesizer for bandwidth control, multiplexing control, two D/A converters and mixers, a 90-degree sower splitter, and a summer; the output of the summer being the simulated clutter. The two sets of noise sources each produce a digital encoded controlled bandwidth Gaussian noise signal which is strobed by the multiplexing control unit firstly to the pulse repetition interval of the radar system and secondly to the data rate of the radar system. The two strobed D/A converters convert the two digital noise signals into their analog equivalents. The two separate video channels are required to obtain the Rayleigh noise distribution characteristic of clutter. This distribution results when the analog signals from the D/A converters are multiplied with in-phase and quadrature RF reference frequencies in the two mixers, then summed in the summer.

Identification of ships

Abstract: Apparatus for determining ship's identity provides a radar "finger print" for a ship. A number of radar receiver channels with closely spaced overlapping intermediate frequencies fL01, fL0Z... classify the ship radar r.f. frequency into one of a number of groups. The summed integrated video outputs are threshold detected and entered into a shift register, the contents of which are analysed to determine the pulse repetition frequency of the ship's radar. The individual receiver outputs are also digitised and analysed to determine the ship radar antenna rotation rate. Sufficient differences exist between different makes and models, also between nominally identical radars, to enable a large number of unique combinations of characteristics to be distinguished and allocated to known ship identities. Thereafter a ship can be identified simply by observing its radar 'finger print'.

Pulsed operation of a segmented longitudinal discharge CO2 laser without ballast impedance

Abstract: It is shown that a longitudinal CO2 laser with two discharge tubes electrically coupled in parallel can be operated in pulsed mode without ballast impedance. This scheme not only yields much higher efficiency (up to 13% at the maximum output energy) and eliminates component failure at high pulse repetition frequency (prf) but also facilitates short pulse availability. In the absence of ballast, current and laser pulse width decrease on increasing the voltage applied to the discharge tubes but these quantities remain unaffected on varying the value of the energy storage capacitor. This enables an independent control of the laser pulse duration and energy. Threshold energy for the onset of nonuniformities in the glow discharge reduces almost exponentially on increasing the discharge current pulse duration but rises on decreasing the operating value of E/N, the electric field to neutral gas density ratio. The maximum output laser energy of about 1 J/pulse, adjustable pulse duration from 30 μs to about 2 ms, ...

Monopulse Radar Angle Tracking Accuracy with Sum Channel Limiting

Abstract: The variance of angle tracking error is found for an amplitude-comparison form of monopulse radar when the sum channel contains a limiter prior to the angle error detector The error expression is valid for any shape of transmitted pulse and any duration of range tracking gate but does assume matched filters in signal processing channels The procedures used are rigorous and an example of results is worked out for the special case of a rectangular transmitted pulse envelope It is shown, for rectangular pulses, that achievable angle tracking error variance with sum channel limiting is not more than 222 dB larger than the theoretical minimum for any processor and not more than 129 dB larger than a similar signal processor that uses a "linear" angle error detector Results apply for large single-pulse signal-to-noise ratio

Radio frequency system

Abstract: A fairly simple R.F. system for indicating the bearing of the source of incident microwave radiation comprises two spaced, broad-beam antennas (A1, A2) supplying signals via power dividers (PD1, PD2) to amplitude comparison means and phase comparison means, both of which operate without down-conversion to an I.F. The main lobes of the radiation patterns of the antennas (A1, A2) are inclined towards one another so that for non-normal incidence there is a difference between the amplitudes of signals received respectively by the two antennas (A1, A2). The amplitude comparison means comprises detector diodes (D1, D2), logarithmic amplifiers (LA1, LA2), and a first subtractor (SUB1), the magnitude of the output signal from which [sensed for example with a threshold detector (TD)] indicates from which side of normal the radiation is incident. The phase comparison means comprises a hybrid ring (HR) having > and > output ports (3, 4 respectively) connected respectively to an instantaneous frequency measuring apparatus (IFM) and a detector diode (D3), and further comprises logarithmic amplifiers (LA3, LA4) and a second subtractor (SUB2), the outputs of detector diodes in IFM being summed to provide the signal at its output (6) connected to one amplifier (LA3). The output of the second subtractor (SUB2) is an accurate but ambiguous representation of the bearing angle with respect to normal (being an even function thereof); the ambiguity can be resolved by reference to the output signal of the first subtractor (SUB1) which may also be used as an approximate representation of the bearing angle. … Using broad-band R.F. components, the system may readily be operable over a broad bandwidth, e.g. an octave. … A data comparator (DC) and a pulse repetition frequency filter (FLTR) control gates G1-G3) which inhibit the provision of bearing data except with pulsed incident radiation having substantially a desired frequency and PRF.

Improved pulsed plasma process

Abstract: 57 In a pulsed radio frequency plasma deposition process the pulse repetition frequency is matched to the gas exchange rate. This is achieved by using a pulse width of 50 to 500 microseconds and a pulse repetition rate corresponding to the time within which gas is exchanged in the reaction region.

Portable radar simulator with adjustable side lobe generator

Abstract: A scan oscillator and a Pulse Repetition Frequency (PRF) oscillator with associated analog and digital circuits provide drive signals for two different RF PIN diode attenuators. When driven by a portable Gunn Diode Oscillator or other microwave source RF is generated that provides main lobe and adjustable side lobe radar signals to a directional microwave antenna. This output signal has adjustable scan rate, beam width, PRF, pulse width, and side lobe level and is self-contained in a package measuring 83/8×73/8×3 inches. The system allows "on the sail" testing for periscope mounted Direction Finding Systems.

Improved performance of the pulsed copper-vapor-laser. CuCl-vapor-laser with a compact device by applying an AC continuous-glow-discharge

Abstract: An additional continuous-glow-discharge was applied to the aperiodic pulsed CuCl-vapor-laser. The experimental results exhibited an increase of up to 60% the laser-output average power at the maximum point, an increase of 1.5 times the peak power and pulse repetition frequency, and twice the pulse width in the laser oscillation against the laser without the continuous-glow-discharge. Further, the additional technique led the CuCl-vapor-laser to operate in the higher operating-temperature region.

An amplifier for pulse width modulated signals

Abstract: In a pulse width modulated signal amplifier employing a tetrode valve S1, current to the grid G1 and screen G2 is controlled by constant current sources 19 and 24 respectively. Each constant current source comprises a switch S3 a current sensor R1, R2 and an inductor L1, L2. Each switch S3 S4 is switched on and off at a set frequency which, in the illustrated system, is the same as the pulse repetition frequency of the signal to be amplified. Each time the switch S3 or S4 is closed the current in the associated inductor L1, L2 builds up until a set limit, determined by sensor R1, R2 is reached whereupon the sensor opens the switch S3, S4. Thus, the period for which switches S3 and S4 remain closed varies to maintain the currents to G1 and G2 at the desired levels. By employing this technique the inductors L1 and L2 do not need to be as large as would be required using a known technique described in UK Patent Specification 1566095. Stray capacitances and resulting distortion are thus minimised. Also, since the switching frequencies of the switches S3 and S4 are identical the generation of harmonics of these frequencies, resulting in further interference with the signal to be amplified, is also avoided.

Modulation drive circuit for CRT deflection of television and data display termials

Abstract: An LC tank circuit in the collector of a power transistor controls the vertical modulation of the horizontal deflection of a CRT through additional deflection coils properly oriented. The tank circuit is tuned at a frequency nf for the desired modulation, where n is the number of cycles of oscillation of the tank for each drive pulse at a frequency (pulses per second) f, and each drive pulse is adjusted in width to one fourth or less of a cycle of the modulation frequency nf using an adjustable RC differentiating circuit and a threshold device to couple a squarewave signal at frequency f to the base of the power transistor.

Adaptive doppler filter banks

Abstract: A radar system for cancelling radar clutter with a minimum of equipment comprising an N-point Fast Fourier Transform for dividing the radar's doppler space into N contiguous frequency subbands; a delay line disposed at each frequency output port for the FFT for obtaining a set of M+1 consecutive samples from each subband, with the sampling performed at the radar's pulse repetition rate divided by N; a single M degree-of-freedom adaptive-canceller moving-target indicator; and M+1 commutating switches for consecutively applying different sets of M+1 subband samples to the MTI. This operation permits clutter cancellation in each subband with N different frequency zeros placed in the radar's doppler space for each MTI degree-of-freedom.

Determination of the number of revolutions of electrical machines

Abstract: of EP00682371. A device for producing a signal which corresponds to the actual rate of rotation of an electrical machine, with a pulse generator (4) coupled to the machine (3) to produce a pulse sequence having a pulse repetition frequency proportional to the rate of rotation of the machine, characterized by the following features : (a) means for the production of a signal (i) proportional to the electrical moment of the machine, (b) a correcting circuit which serves to superimpose on the signal (i), proportional to the electrical moment, a correcting signal proportional to the load moment (Le which acts upon the machine, (c) an integrator (51) which produces the rate of rotation actual value (n) by integrating the output signal of the correcting circuit with a time constant (Te ) proportional to the time constant (Te ) of the machine, and (d) a comparator circuit (53-56; 58, 59) which obtains the correcting signal by forming the difference between the pulse repetition frequency and the actual rate of rotation and integrating the difference signal.

A Coherent, Frequency Agile 94 GHZ Radar with Dual Polarisation Capability

Abstract: A coherent, frequency agile 94 GHz radar has been built. This radar includes features like pulse-to-pulse frequency agility within a 400 MHz bandwidth, wide PRF-range from 1-50 kHz with fixed and staggered PRF. The polarisation of the transmitter is switchable from pulse to pulse either from RHC to LHC or from horizontal to vertical depending on the primary feed of the 300 mm cassegrain antenna which is used. Two identical receivers are included for co- and cross-polarized signal reception. A linescanner using a flat mirror has also been built. A rotating speed of 600 rpm gives a scanrate of 20 scans/second using both sides of the mirror.

Arrangement for automatic receiver-end correction of an incorrectly recovered carrier phase

Abstract: The invention is intended to lock quadrature-amplitude modulation receivers for e.g. 16-QAM via a phase-locked loop back onto the reference carrier phase in the event of an incorrectly recovered carrier phase, with no need for differential coding nor a different transmission-end procedure to mark the reference phase. For this purpose, a pulse generator 5 is provided according to the invention which is started up by an alarm signal which is derived from the synchronisation failure of the data receiver 6 and whose pulse voltage is superimposed on the phase-lock voltage at the input of the voltage-controlled oscillator 2 in such a way that locking onto a different carrier phase condition of the voltage-controlled oscillator, which repeats itself until the alarm signal subsides, i.e. until the provided reference carrier phase is attained, shuts off the pulse generator 5. The pulse generator is preferably designed as an astable multivibrator 51, 52, whose pulse repetition frequency f = 1/(2RC.In3) is selected by corresponding dimensioning of its frequency-defining components 53, 54 in such a way that it becomes shorter than the response time of the data receiver 6 (Fig. 1).

Precision Microwave Attenuation Measurement by Time Interval Ratio

Abstract: : A method of measuring microwave attenuation by substitution is described. As attenuation is inserted into the device under test, the pulse repetition frequency of a pulse modulated PIN diode switch in series with the device is changed to maintain a constant mean power output from the circuit. The ratio of the pulse repetition frequencies before and after insertion is shown to be simply related to the attenuation of the device under test. Sources of error are examined in detail and results are quoted showing inaccuracies of less than + or - 0.002 dB over a range of 0 to 20 dB. (Author)

Coherent 95 GHz High Power Radar

Abstract: This paper discusses the design to be used in the development of a high power, wide bandwidth, coherent 95 GHz instrumentation radar. The system design provids for operation of the radar in two separate transmitter modes; a moderate power, 100 Watt peak power mode using a state-of-the-art wideband TWTA with greater than 2 GHz of bandwidth and a high power, 1 kWatt peak power mode using a state-of-the-art EIKA. The radar will be polarzation agile and coherent frequency agile, making it possible to measure the complete polarization scattering matrix as a function of frequency and resolution.