US3651412A - Receivers for pulsed signals - Google Patents

Receivers for pulsed signals Download PDF

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Publication number
US3651412A
US3651412A US30808A US3651412DA US3651412A US 3651412 A US3651412 A US 3651412A US 30808 A US30808 A US 30808A US 3651412D A US3651412D A US 3651412DA US 3651412 A US3651412 A US 3651412A
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signals
outputs
receiver
signal
inputs
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US30808A
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English (en)
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Henri Poinsard
Marie-Jacques Jullien
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Thales SA
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Thomson CSF SA
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/28—Details of pulse systems
    • G01S7/285—Receivers
    • G01S7/292—Extracting wanted echo-signals
    • G01S7/2923—Extracting wanted echo-signals based on data belonging to a number of consecutive radar periods

Definitions

  • the present invention relates to receivers designed for the detection of pulse-type recurrent radio signals, in particular radar receivers, in which the effective signals are as picked up mixed with noise components and other parasitic signals.
  • the signals are generally integrated that is to say that the signals, supplied by the video circuits at intervals of time spaced by T, T being the periodicity of recurrence of the effective pulse signals, are added up, this with a greater or lesser degree of accuracy.
  • This integrating operation has the effect of reducing the level of the majority of the parasitic signals in relation to that of the effective signals, the former generally not being recurrent or, if they are, generally not having the same recurrence frequency as the effective signals.
  • the threshold should be regulated to the minimum value permissible in order to avoid excessive losses in terms of weak effective signals.
  • the mean amplitude of these false elements of information being an essentially random factor, it is necessary to regulate the threshold constantly or to provide automatic gain control.
  • the invention relates to a radio receiver in which the false alarm incidence is statistically constant whatever the level of the signals picked up.
  • E is a vector representing the sum of the signals S (t) and S (t dt), S(t) and S (t+dt) representing the signals S received respectively at the instants t and t+dt, and d! being of the same order of magnitude as 1',
  • Kis a vector representing the difference between the sigrials S(t) and S(t+dt) and wherej A is a vector deduced from A by rotation through 11/2 in the
  • the signal U being independent of the absolute value of the amplitudes of the signals S(t) and S(t+dt), the bottom clipping threshold can be fixed.
  • the integrated signals corresponding to the random parasitic signals will be weaker in relation to the effective signals, the larger the number of periods of integration.
  • the algebraical sums S(t) S(t-l-dt) and S(t) S(t+dt) can be effected at intermediate frequencies, either directly if f, is a multiple of l/dt, or else after phase shift of one of the signals; the signal U can then be obtained quite simply by applying to the two inputs of an amplitude phase detector, respectively the two sum signals after limitation thereof if the signal U cos is desired, one of the sum signals being in addition phaseshifted by 1r/2 if the signal U sin 45 is desired.
  • the signals 8(2) and S(t+d!) are on the other hand available at video frequency, then it will be possible to respectively remodulate two auxiliary carrier waves of the same frequency and phase, either directly by the signals or by 8+8 and SS'.
  • the signal U can then be obtained in the manner described hereinbefore, using an amplitude phase detector.
  • the signal U sin cancels out for S(!) S(t+d!).
  • the signal S(t) has, as a function of T, a symmetrical envelope with a maximum on the axis of symmetry, for example a substantially triangular envelope
  • the curve illustrating U as a function of t is an odd function of (tt,) cancelling out for t t,,, where t is the instantaneous value of t which defines the axis of symmetry.
  • This curve in the neighborhood of zero, has a shape similar to the error curve of a range tracking system the constant alarm probability receiver in accordance with the invention thus exhibits the interesting additional feature that it is utilizable, without any supplementary arrangements, for the range tracking of targets to this and the output signal from the integrator can be used.
  • FIG. 1 illustrates an example of the shape of the signal detected by a receiver in accordance with the invention.
  • FIG. 2 is an explanatory vector diagram.
  • FIGS. 3 and 4 illustrate examples of signals produced in the receiver in accordance with the invention.
  • FIG. 5 is the general basic diagram of a receiver in accordance with the invention.
  • FIG. 6 is a diagram showing details of FIG. 5, in the context of one application of the invention.
  • FIG. 7 is a diagram showing details of FIG. 5, in the context of another application of the invention.
  • FIG. 8 is an example of application of the invention in an electromagnetic detection receiver.
  • the invention will be described in the context of a receiver for an electromagnetic detection system which transmits substantially rectangular waveform pulses of width 1' at a constant recurrence frequency F,.
  • the receiver must therefore detect from among all the signals received, those which are in fact echoes of the transmitted pulses.
  • the targets returning these echoes are illuminated by the transmitter beam for a predetermined time T, which is a function of the beamwidth and also of the target width if the latter is not negligible.
  • the N T F echos from a target are processed in a filtering device, the internal characteristic of which more or less approaches that of the optimum filter.
  • integration during the time T produces a signal whose power is compared for each range quantum, with an adjustable threshold. An echo is defined as having been received, when this threshold is exceeded.
  • the mean background noise level varies during the course of operation and accidental noise effects of external origin are frequently superimposed upon it so that the probability of false alarms will vary since the threshold is fixed at least during the time of the recurrence.
  • the output signal from the optimum filter is not directly integrated.
  • An auxiliary signal U is produced which is a function of the relative values of the detected signals at instants differing by a predetermined time interval, but is independent of their absolute values. This is the signal which is integrated over N recurrences. If it stems from random parasitic sources, it is statistically zero (or at least very small): bottom clipping to the level of a fixed threshold is now justified, the mean noise being brought at any instant to a statistically constant level.
  • FIG. 1 illustrates as a function of the time interval t, the signal S(t) at the output of the optimum filter, this in the case where echoes of rectangular wave form pulses, of duration 1', are involved.
  • the signal corresponds to one of the envelopes ABC or ABC of width 2 'r or to the modulated carrier of envelope ABCB'.
  • This signal remains substantially the same for each of the N echos from one and the same target. Its amplitude is a function of that of the input signal to the filter.
  • a noise signal or more generally a parasitic signal can randomly give rise during a recurrence, at the output of the filter, to a similar signal but it will not generally be reproduced during another recurrence.
  • the invention will be explained assuming that the processed signal is at video frequency. It will be shown hereinafter how the invention may equally be applied if the signal is an i.f. signal.
  • S S(t) be the value of the signal at the time t and S S (1+dt) its value at the time 1+ dt, dt being of the same order ofmagnitude as 1-.
  • FIGS. 3 and 4 represent cos 5 and sin (b as a function oftime in the case where dt -r, the signals S(t) having the form shown in FIG. 1.
  • the signal cos is null for r/2.
  • the signal sin 4 is an algebraic signal in all cases, the signal cos only exhibiting two distinct polarities ifS and S do, in other words if two-polarity video working is used;
  • the mean value of the signal sin 5 is zero for the parasitic signals, whatever they may be in other words, S, and S, of S and S for parasitic signal only are by definition identical so that their difference is zero;
  • the mean value of cos 4: is zero for the thermal noise, this noise being en..irely decorrelated at the end of the time 1- however, it may not be zero for certain other parasitic signals.
  • the effective signal will thus be obtained by the integration of the N signals corresponding to N successive recurrences for the echos the same signal will appear N times at the integrator input,-and the signal two-noise ratio is thus improved overall in the ratio V N.
  • the integrated signal will in relation to the parasitic signals have a statistically constant mean value which makes it possible to fix the threshold once and for all.
  • the spectrum width of the parasitic signals is smaller than the passband of the receiver, N, being 5 the number of non-independent samples of parasitic signals (where N, is less than N), the ratio in effective signal to parasitic 7 signal after integration will be in the order of N N oth at the false alarm factor, for the same threshold, will be increased this can be remedied either by increasing the 10 time of illumination of the target in the ratio N/N or by using a transmitter-receiver system of rapidly varying frequency which means that the parasitic signals can be decorrelated from one recurrence to the next.
  • FIG. 5 illustrates the fundamental diagram of a receiver in accordance with the invention.
  • the signals picked up by the antenna A and possibly processed in the manner indicated in an input unit 51 or receiver proper, are applied to a device 52 which at the instant t dt produces at its output 521 the signals received at the instant t, and at its output 522 the signals received at the instant t dt thus, at the outputs 521 and 522 the respective signals S and S are obtained.
  • a device 52 which at the instant t dt produces at its output 521 the signals received at the instant t, and at its output 522 the signals received at the instant t dt thus, at the outputs 521 and 522 the respective signals S and S are obtained.
  • These signals are combined in the operator 53 which produces at two outputs 531 and 532
  • the phase between these latter signals is measured in a phase detector 54 which produces the signal U as a function of this phase.
  • the signals U are integrated, these appearing at the recurrence periodicity of the transmitter of the electromagnetic detection system in question the integrated signal is bottom clipped at 56 and at 57, the effective signal, of statistically constant false alarm factor, is obtained.
  • the receiver unit 51 may produce a video signal in which case the detailed diagram is that of FIG. 6 the unit 52 has two sampling devices 61, 62 which are set in operation a time interval dt one after the other by a clock 63, at the recurrence frequency of the system, and a delay 64, whose characteristic delay is dt, or r in the example described is mounted, in series with one of the sampling devices.
  • the unit 53 has two modulators 65 and 66 coupled to one and the same oscillator 67, the latter operating for, example, at 2 mc./sec., the modulators being followed by a conventional operator 68 comprising a combination of resistors and capaci- 5 tors and forming the sums S (l +j) S (l-j) and S (1j) S
  • the receiver unit may produce an intermediate frequency signal in which case the device 52 may simply comprise, as FIG. 7 shows, a delay device 71 for bringing into time coincidence the signals received at the instants t and t dz, and, if need be, a device 72 for phase control, possibly with a feedback arrangement, the carrier frequency of the signals not generally being a'multiple of l/dt.
  • the device 53 will simply comprise the operator 68, directly supplied with the output signals from the device 52.
  • the diagram of FIG. 7 is a very general diagram.
  • FIG. 8 the receiver of a pulse-type electromagnetic detection system with fixed echo elimination and range channels, has been illustrated.
  • This receiver is assumed to be of the coherent type, i.e., in which the echoes processed either stem from transmitted pulses, obtained by the chopping of one and the same carrier, or are detected using as a reference signal of each of them, a signal which is in phase with the carrier of the transmitted pulse.
  • the receiver thus, in the conventional way, comprises beyond the circuit 51, which in this case produces intermediate or video frequency signals, a number M of parallel range channels the input gates 81.l,81.2,81.M ofwhich are successively opened during adjacent time intervals of duration 1, by opening pulses synchronized by the general synchronizing device of the system, 200.
  • Each of these channels comprises a fixed-echo rejection filter 83.1 83.2.... 83M.
  • the output signals from two successive channels being, offset by 1 the channels of successive outputs are grouped two by two and the output signal from the rejection filter for a channel thus constitutes both the signal S of said channel and the signal S of the next channel (M-l) operators 68, such as the operator 68 of FIG. 7, in other words 68.1, 68.2.. 68 (Ml), have their inputs respectively coupled to the outputs of the filters 83.i and 83 (i+l respectively.
  • Each operator produces at two respectiveoutputs 8, and 9,, the signals A and B hereinbefore defined.
  • the outputs 8, are sequentially coupled by the electronic switch 100, controlled by the device 200, to the limiting amplifier 69 similarly, the outputs 9, are coupled sequentially in synchronism with the outputs 8,, by an electronic switch 101, to the limiting amplifier 620, which is identical to the one already described.
  • the two amplifiers are coupled as before to the amplitude-phase detector 612, one of them through a 1r/2 phase shift element 611 if the function sin (1: has been chosen.
  • each output of the switch 102 is coupled to an integrating device 55, preceded by a memory device 12,.
  • the signal U of each channel will be compared in 56 with the predetermined threshold, a further switch 103 being placed between 56 and the outputs of the integrators 55,.
  • the field of application of the invention is extremely wide since it covers all the cases of reception of recurrent pulse signals which are mixed with parasitic noise components, that is to say in particular it applies to numerous kinds of receivers used in aerial navigation and for space surveillance purposes.
  • the invention at the same time makes it possible to effect acquisition of the target under good conditions since the false alarm ratio is constant and therefore the presence of echo" factor is optimized in order to effect tracking, it is then sufficient, once the presence of an echo has been indicated by a signal at the terminal 57, to process the signal sin 45 picked up at the input to the clipper 56, in the form of an error signal relating to the feedback loop controlling the displacement of the window, the latter being correctly positioned when sin d) 0.
  • the invention is not limited to the embodiments described and illustrated here purely by way of example.
  • the delay dt could be other than 7.
  • a radio receiver for the detection of recurrent pulse signals S of predetermined duration 7, comprising in series receiving means for receiving the recurrent signals, integrating means for integrating the received recurrent signals and clipping means for clipping the integrated signals, said receiver comprising further means, inserted in series between said receiving means and said integrating means, said further means comprising a two input operator, means for applying to said two inputs the signals S S(t) and S' S(t dt), representing the signals received respectively at the instants t and t dt, and a!
  • said receiver comprises detecting. means, said further means comprises two sampling devices for picking pairs of samples of signal S the two samples of a pair being taken at instants which are spaced by said time dt, said sampling devices having respective outputs, means for bringing into time coincidence the two samples of each pair, an auxiliary oscillator, having an output, two modulators having respective oscillation inputs coupled to said oscillator outputs, respective modulation inputs coupled respectively to said outputs of said sampling devices, and respective outputs coupled to the inputs of said operator.
  • a receiver as claimed in claim 1 wherein said further means comprises a direct channel and a delaying channel introducing a delay equal to said time dt said channels having respective inputs coupled to said integrating means and respective outputs respectively coupled to two inputs of the operator.
  • a receiver as claimed in claim 6 for a pulse radar system transmitting recurrent pulses of duration 1' having a substantially rectangular waveform said receiver comprising a filter device which converts the signals of width 1' into signals with a substantially Vhshaped envelope of width 21-1- M (M being an integer greater than 1) range gate channels, numbered 1 to M successively opened during adjacent time intervals equal to -r each channel including a fixed echo rejection filter having an output, said receiver further comprising (M-l) operators, numbered 1 to M-l an operator numbered i having two inputs respectively coupled to the filter outputs of the channels numbered i and i l said operators respectively having first outputs supplying said signal A and second outputs supplying said signal B a first synchronized switch successively coupling said first outputs of said operators to one of said limiting amplifiers, a second switch, operating in synchronism with said first switch for successively coupling said second outputs of said operators to the other limiting amplifier; integrator circuits numbered 1 to M-l the-integrator
  • a receiver as claimed in claim 6, designed to cooperate with a pulse-type electromagnetic detection system comprising a sliding range gate having a control input; said receiver comprising means for elaborating signal U sin #1 and for feeding said signal U to said control input.

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Radar Systems Or Details Thereof (AREA)
US30808A 1969-04-28 1970-04-22 Receivers for pulsed signals Expired - Lifetime US3651412A (en)

Applications Claiming Priority (1)

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FR6913415A FR2041508A5 (de) 1969-04-28 1969-04-28

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US3651412A true US3651412A (en) 1972-03-21

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US30808A Expired - Lifetime US3651412A (en) 1969-04-28 1970-04-22 Receivers for pulsed signals

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US (1) US3651412A (de)
CH (1) CH529484A (de)
DE (1) DE2020775C3 (de)
FR (1) FR2041508A5 (de)
GB (1) GB1272177A (de)
NL (1) NL173891C (de)
NO (1) NO131481C (de)
SE (1) SE352745B (de)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1389068A (fr) * 1964-02-06 1965-02-12 Int Standard Electric Corp Système de transmission, notamment système de modulation pour transmission à large bande
US3177489A (en) * 1960-01-11 1965-04-06 Thompson Ramo Wooldridge Inc Interference suppression systems
US3423682A (en) * 1962-05-02 1969-01-21 Csf Receiver systems with constant false alarm rate

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3177489A (en) * 1960-01-11 1965-04-06 Thompson Ramo Wooldridge Inc Interference suppression systems
US3423682A (en) * 1962-05-02 1969-01-21 Csf Receiver systems with constant false alarm rate
FR1389068A (fr) * 1964-02-06 1965-02-12 Int Standard Electric Corp Système de transmission, notamment système de modulation pour transmission à large bande

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NO131481B (de) 1975-02-24
DE2020775A1 (de) 1970-11-12
NO131481C (de) 1975-06-04
FR2041508A5 (de) 1971-01-29
DE2020775B2 (de) 1973-11-08
GB1272177A (en) 1972-04-26
NL173891B (nl) 1983-10-17
DE2020775C3 (de) 1974-06-06
CH529484A (fr) 1972-10-15
NL7006169A (de) 1970-10-30
SE352745B (de) 1973-01-08
NL173891C (nl) 1984-03-16

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