FR2522414A1 - RADAR PULSE-DOPPLER - Google Patents

Abstract

RADAR PULSE-DOPPLER. TO ELIMINATE THE SLOW TARGETS, AN NESTING OF THE RAYS OF ACTION BY PERIODIC CHANGE OF THE REPEAT FREQUENCY OF THE PULSES WITHIN EACH TARGET SCAN IS PERIODICALLY USED BY USING SEVERAL COMMON COMPONENTS OF ONE SYSTEM (TRANSMITTER, ANTENNA, ETC.) OF THE RADAR DEVICE, TAKES PLACE OF SUBDIVIDED SIGNAL PROCESSING ACCORDING TO THE CHANGE OF THE REPETITION FREQUENCY OF THE PULSES IN A NEAR ACTION ZONE AND A FAR ACTION ZONE, BY MAKING SO THAT AT THE EMISSION OF RADAR SIGNALS AT HIGH PULSE REPETITION FREQUENCY (PRF1) AND FOR A LOWER LIMIT FREQUENCY OF THE FIXED ECHO FILTER, ONLY THE NEAR AREA OF ACTION IS EVALUATED AND DURING THE EMISSION OF THE LOW PULSE REPETITION RADAR SIGNALS (PRF2) EXCLUSIVELY THE FAR ACTION ZONE IS EVALUATED. APPLICATION TO FIXED ECHO SUPPRESSION RADARS.

Description

Pulsed-Doppler radar.

  The invention relates to a pulsed radar

  Doppler with a fixture for the elimination of fixed echoes and with a variable pulse repetition frequency (PRF).

  With the trend of reducing

  as far as possible the size of the antennas of

  radar, increase the frequency as much as possible

  the radar transmitter, to the extent that this is made possible by atmospheric conditions

  to be expected and by technology.

  The need to operate with as high a transmission frequency as possible is even greater in the case of altitude-determining radar devices, because of the antenna, which in any case is larger. are imposed in the case

  o radar equipment must be used not only

  in a nearby action zone, but also for average ranges of for example 100 km.

  the increase in the range, linked to a decrease in

  the frequency of repetition of pulses (PRF), the degradation of the elimination of

  Doppler frequencies of unwanted signals of

  slowly moving, as a result of the decrease in

  of the lower limit speed.

  of the repetition frequency of the pulses results, for a relatively identical width of the polar width of the assembly of the elimination of the pulses.

  fixed echoes, also a decrease in the frequency-

  absolute lower limit which is decisive for the lower limit velocity. Moreover, an increase in the lower limit frequency which results in a decrease in the width of the filter bandwidth for the suppression of the fixed echoes, is opposed by inadmissible deterioration of blind speed behavior Requirements

  resulting from this, as regards the increase of

  of radar equipment and improved suppression of slowly moving target signals can no longer be satisfied by

compromise.

  But one can however imagine a pulsed-Doppler radar with which one could operate, to discover nearby targets with a high emission frequency and also with a high frequency of repetition of the pulses, and, to grasp

  distant targets, with an emission frequency

  The results of this mode of operation, with a radar apparatus of this kind, are, it is true, good, however, the technical means

  to implement are important.

  The object of the invention is to show, for a

  Pulsed-Doppler radar of the type recalled at the head of the pre-

  memory, a means of obtaining, with reasonable expenses, also in radar devices which operate with a high emission frequency and which

  are designed for medium range, good

  pressure of targets moving with a speed

  weak, without the favor of the appearance of

  residual parasites and the appearance of

overbreadth.

  This problem is solved, according to the invention,

  thanks to the fact that for the elimination of

  The rays of action are imbricated by periodic change of the frequency of repetition of the pulses within each period of time.

  scan of the target, so that by using

  common components of a system (transmitter,

  the aircraft, etc.) of the radar

  subdivided signals according to the change in the repetition frequency of the pulses in a

  immediate or immediate area of action and a zone of

  far, by ensuring that during

  the transmission of radar signals with repetition frequency

  high pulse rate and for a frequency

  low upper filter limit of the fixed echoes, only the near action zone is evaluated and that during the transmission of the low repetition frequency radar signals the pulses exclusively the

  remote action area is assessed.

  The subdivision of the radar coverage into a near zone and a far zone is based on a nesting of the pulses with two repetition frequencies of the pulses, which are very clearly distinguished from each other, being noted that one starts from a

  common transmission frequency The frequency level

  This repetition rate of the pulses is advantageously at least twice as large as the low repetition frequency of the pulses. The high repetition frequency of the pulses can also be

  a larger integer multiple of the repetition frequency

  weak impulses due to the implementation of a high pulse repetition frequency, which means that the range of the device

  radar is limited to a nearby area, the frequency-

  lower limit of the fixed echo filter is such

  In the detection zone, slowly moving targets are suppressed. Slow movements on the ground can be assumed to disappear behind their shadows, in a distance that lies outside the immediate or immediate action zone of this object. additional measures in the area

  near action, are useless for their suppression.

  A sufficiently high limit frequency of the filter of the fixed echoes is obtained by the implementation of

  dual radiation suppressors.

  According to an advantageous development of the invention

  During the scanning time of the target (TOT), the nesting time is

  least one group of unexpanded pulses from the frequency

  high repetition rate of pulses in the expanded pulses of the low repetition frequency of the pulses The width of the high repetition frequency radar pulses of the pulses without compression of the pulses and that of the low repetition frequency pulse pulses of the pulses with pulse compression , are maintained at the

  same value In the processing branch of the

  radar transmitter for low frequency pulses

  repetition of impulses, it is necessary to

  give way to a corresponding compression of the pulses.

  An overlapping, in time, of the two

  pulse trains of different repetition frequency

  It is possible, for example, to replace a pulse of the low repetition frequency of the pulses by a group of repetition frequency pulses.

  high impulses, or to occupy all the in-

  frequency pulses of the repetition frequency

  low pulse, respectively by a

  pulse group of the high repetition frequency

  The pulses can also be used to fill a portion of the intervals, in a periodic series, with pulses of the high repetition frequency of the pulses. Another possibility is to code, possibly differently, one or both of them.

  impulse trains Instabilities that are provoked

  in the signal flow of the low pulse repetition pulse train, by

  insertion of high repetition frequency pulses

  pulses, can be eliminated with known measures for suppressing individual pulses. By way of example, an exemplary embodiment has been described below and shown in the attached drawing.

of the subject of the invention.

  FIG. 1 shows the schematic subdivision of the entire range of distances of a radar apparatus by a nesting of the staves, FIG. 2 represents the schematic diagram of the transmitter part of a radar apparatus, FIG. in principle of the reception part of a radar apparatus, FIG. 4 is a pulse diagram which shows a possibility of the nesting of the two

  pulse repetition rates.

  The total area of distances, represented

  in Figure 1, which can be entered with an appa-

  radar and be represented on an aircraft device.

  is indicated by two concentric circles which limit between them an immediate or immediate action zone B with the maximum distance R 2 and a far-action zone A with the maximum range RI La

  capture of targets in the immediate or immediate action zone

  diate B takes place with the highest repetition frequency of PRF pulses 1 and in the action zone

  distant A with the lower repetition rate

  The ratio PRF 2 / PRF 1 of the pulse repetition frequencies is at least substantially in the ratio 1: 2, and it is from this

  significantly higher than the change in the frequency

  frequency of repetition of pulses which is usually used to suppress zones of blind velocity As a result of the subdivision into two zones of

  distance, one can operate in the far zone with.

  a lowering of the amplification of weaker dyna-

  to a setting of the noise suppression or setting of the low-time-constant coupling The representation of targets that pass from the far-action zone A in the near-action zone B or vice versa is not disturbed sure

the screen of the radar device.

  In the transmitting part of the radar apparatus (FIG. 2), a high frequency generator 4 produces

  an emission frequency which is applied to the antenna

  radar 1, through the stages of manipulation

  5 and 6, an electronic switch 3 and a power stage (final transmission stage). The transmission frequency has a value independent of the manipulation. During each transit time on the target, which depends on the rotation speed of

  the antenna and the opening angle of the lobe of the

  Finally, the transmission frequency is manipulated, in the two handling stages 5 and 6, alternately with the repetition frequency of the PRF 2 and PRF pulses. The electronic switch 3 connects the stage.

  transmitter 2 and the radar antenna 1 respectively.

  With the corresponding handling stage 5 or 6, the handling frequency FT 1 for producing a repetition frequency of the pulses PRF 1 is

  produced directly in a generator 7

  intermediate of a frequency divider stage 8 a second frequency of manipulation FT 2 is obtained

  with which one modulates, in the handling stage

  6, the transmit frequency to produce the low repetition frequency of the PRF pulses 2 A

  control circuit, consisting of a frequency divider

  quence 9 and by a circuit 10 to determine the

  cyclic port, determines the switching function

  of the electronic switch 3 and, consequently,

  quence, the time and duration of each of the pulse trains to be applied to the antenna 1 The frequency divider 9 receives a pulse train,

  which corresponds to the pulse repetition frequency

  PRF 2, from the frequency divider 8 for the repetition frequency The duty cycle of the switch function of the electronic switch

  3 can be fixedly set in stage 10.

  Using the pulse diagram representing

  in Figure 4, it will be made explicit, in the form of

  simplest, the nesting of repetition frequencies

  impulses in connection with the function of the

  electronic switch 3 In line a of the fi

  Figure 4 shows a train of frequency pulses

  low repetition rate of the PRF 2 pulses for the far-field and in the line b the pulse train for the repetition frequency

  higher PRF 1 impulses for the area of

  near or immediate distance from the radar apparatus.

  mode of operation of the radar apparatus, in the-

  that, during a time of passage on the target, a pulse of the PRF pulse repetition frequency 2 is replaced by a series of pulses of the repetition frequency of the pulses PRF 1, it is necessary to sample, by a release pulse

  represented in line c, a pulse of frequency

  repetition of the PRF pulses 2, as is schematically indicated in the line a, with the repetition frequency of the pulses PRF 2 at pulse interval corresponding to the time on the target At the same time, it is necessary to release, by a second release pulse shown in line c, for the duration of a period of the frequency

  repetition of PRF 2 pulses, a train of impulse

  of the high repetition frequency of

  PRF pulses 1, as shown in the

  line b The electronic switch is

  this time in position 3b (Figure 2) In

  the last line a + b in Figure 4, we have

  felt the nested pulse train that is emitted by

the antenna 1.

  In synchronism with the electronic switch

  3 of Figure 2, must be ordered, in the

  radar receiver, a corresponding switch 13.

  In the schematic diagram of the radar receiver according to FIG. 3, reference 1 is used to designate the antenna which is used in common for the transmitter part and the receiver part. The echo signals which are received by the antenna 1 are amplified. , converted and rectified in the receiver portion 12, transmitted as video signals to a signal evaluation circuit

  and finally displayed using a device to

  The signal evaluation device is subdivided into a branch 16 for processing the echo signals from the action zone.

  near or immediate PRF 1 and in the branch of

  15 for the distant action zone with the frequency

  repetition of PRF pulses 2

  electronic transmitter 13 applies the video signals from the output of the reception part 12, alternatively to

  the processing branch 15, with the evaluation circuit

  for the low repetition frequency of

  PRF 2 and with a next recovery, or the second evaluation branch 16 for the echo signals from the far-field For the representation of the target echo signals the output of each of the branches of evaluation 15 or 16 is connected, through an OR gate, 17,

to a display device 14.

  In the described embodiment of the

  transmission and reception part, a

  notable feature of the radar device can be used in common A separate signal processing for both near and far action areas

  only in the two branches of evaluation.

  15 and 16 of the radar receiver, while the antenna,

  transmitter, the receiving part does not require any

  except for the compression of the

  or optimal filter and representation

targets.

Claims (9)

  1 Pulsed-Doppler radar for operation with pulse repetition frequency (PRF) and fixed-echo cancellation arrangement, characterized by the fact that for the elimination of slow targets the action radii are interleaved by periodically changing the repetition frequency of the pulses within each   scan time of the target, so that in use   reading several common components of a system (transmitter, antenna, etc.) of the radar apparatus, the signal processing is subdivided according to the   change in the frequency of repetition of   in a near or far action zone and a distant action zone, by ensuring that during the transmission of high frequency repetition frequency (PRF 1) radar signals and for a high lower limit frequency of filter fixed echoes, only the near action zone (B) is evaluated and during the emission of the low repetition rate radar signals (PRF 2) exclusively the far-action zone (A) be evaluated.   2 Pulsed-Doppler radar according to the claim   1, characterized in that the high repetition frequency of the pulses (PRF 1) is a 4)   integer multiple of the lowest repetition frequency pulses (PRF 2).   3 Pulsed-Doppler radar according to the claim   1, characterized in that the evaluation of the radar signals with the lower repetition frequency of the pulses (PRF 2) takes place with the implementation of   of a compression of the pulses.   4 Pulsed-Doppler radar according to any one of   Claims 1 to 3, characterized in that   the width of the repetition frequency radar pulses   high pulse rate (PRFI) without compression   pulses and radar pulses with frequency   this lower repetition of pulses (PRF 2)   with pulse compression, has the same value.   5 Pulsed-Doppler radar according to any one of   Claims 1 to 4, characterized in that   the emission of the two repetition frequencies; pulses (PRF 1, PRF 2) take place with the same transmission frequency. 6 Pulsed-Doppler radar according to any one of   Claims 1 to 5, characterized in that   during each of the scanning times of the target at least one pulse group of the high pulse repetition frequency (PRF 1) is interleaved in time, in the pulse frequency pulses.   low repetition of pulses (PRF 2).   7 Pulsed-Doppler radar according to any one of   Claims 1 to 6, characterized in that   that at least one pulse of the repetition frequency   pulses (PRF 2) is replaced by a group of pulses with a high repetition rate pulses (PRF 1).   8 Pulsed-Doppler radar according to any one of   Claims 1 to 7, characterized in that   one or both pulse trains (PRF 1, PRF 2)   are also coded differently.   9 Pulsed-Doppler radar according to any one of   Claims 1 to 6 and 8, characterized by   that between all the pulses of the low repetition frequency of the pulses (PRF 2) is inserted a group of repetition frequency pulses high pulses (PRF 1).   Pulsed-Doppler radar according to the claim   9, characterized in that in part of the intervals between the pulses of low repetition frequency (PRF 2), the insertion takes place in a periodic series with the frequency of   pulse repetition (PRF 1).   11 Pulsed-Doppler radar according to any   that claims 1 to 10, characterized by the   that in the remote action zone (A or B), one operates with a lower dynamic amplification lower compared to a setting of the suppression of the   interference (Sensitivity Time Control) for the total area.