FR2685088A1 - DEVICE FOR RECEIVING AND PROCESSING RADAR SIGNALS FOR COUNTERMEASURE ANALYZER. - Google Patents

Abstract

This device comprises, for reception, a spectrum analyzer of the input signal itself comprising two multipliers (2, 3) making it possible to carry out in parallel two multiplications of the input signal respectively by two frequency ramps modulated linearly in frequency, of band 2B (B being the frequency band of the input signal) and of duration 2T, shifted with respect to each other by a duration T, an adder (11) for adding the output signals of these two multipliers, and a dispersive filter (12) of band B and delay T, arranged at the output of the adder. This device also comprises, for processing, means for recognizing the carrier frequency of the radar emissions thus intercepted, taking into account the particular nature of the output signals from the spectrum analyzer. Application: countermeasures.

Description

DEVICE FOR RECEIVING AND PROCESSING

  RADAR SIGNALS FOR COUNTERMEASURE ANALYZER

  The present invention relates to a device for receiving and

  radar signal processing for countermeasure analyzer.

  Such a device, associated with a reception antenna, aims to intercept radar signal transmissions and to measure their transmission parameters, such as the carrier frequency, the duration

  pulse, the spectral width and the spectral level.

  The fact that these parameters are divided into HF parameters and video-frequency parameters has led up to now to

consider two types of montages.

  A first assembly, called direct detection, consists in obtaining the carrier frequency directly from the RF signal, and, in parallel, the video frequency parameters from the corresponding video signal. Because of the direct detection of the carrier frequency from the RF signal, this arrangement has the advantage of having a probability of interception close to 100%.

  the disadvantage of having a low sensitivity and selectivity.

  A second assembly, called superheterodyne, consists in obtaining all the parameters from a signal in medium frequency obtained from a radar emission by beat with the signal

  provided by a local oscillator Unlike the pre-

  However, this arrangement has the disadvantage of having an interception probability of less than 100%. This is due to the fact that the carrier frequency of the radar emissions to be analyzed is a priori

  unknown, it is necessary to sweep a wide range of

  quences with the local oscillator before achieving the agreement In return, this arrangement has a good sensitivity and a

good selectivity.

  The present invention relates to a device for receiving and processing radar signals which combines the advantages of both

  aforementioned techniques without presenting the disadvantages.

  The device according to the invention relates to a third type of assembly, called spectral analysis Different embodiments of

  such spectrum analyzers are known, in particular by the communi-

  C-LARDAT, Annex IX, entitled "Spectrum Analyzers Using Dispersive Surface Wave Filters", at the International Radar Symposium 1978 (pages 303 to 311). At a time slot of duration T of an input signal having a frequency band B, this arrangement corresponds, at the end of a time interval T, to an output signal whose position in time, relative to at the start of the spectral analysis, is representative of the band B. As shown in FIG. 1a, the spectral analysis is obtained by premultiplication, or BLU transposition, in a mixer 1, of the band B input signal and duration T with a frequency ramp modulated linearly in frequency, band 2 B and duration 2 T, then compression in a dispersive filter 2 of band B and delay T.

  FIG. 1b shows the successive transformations

  these two operations, an input signal whose repre-

  in a time-frequency domain in the form of a parallele-

  gram 3 By multiplication with the frequency ramp, referenced

  referenced 4 in this drawing, we obtain a parallelogram 5 (the sides

  arrows corresponding respectively by this transformation).

  By compression in the dispersive filter 2, the parallelogram 5 is transformed into a rectangle 6, the corresponding arrow sides

also respectively.

  It appears in this figure that a spectral analysis can be carried out only if the input signal and the frequency ramp are synchronous. Indeed, if they are asynchronous, what happens

  particularly in the case of the application to counter analyzers

  measures where the position is not known in advance of the

  frequency ramp of radar emissions likely to be

  cepted, the first transformation can lead to an indetermi-

  nation, which then translates into a probability of interception

less than 100%.

  The present invention aims to solve this problem.

  According to the invention, this problem is solved by simultaneously performing two premultiplications of the input signal by two identical frequency ramps of duration 2 T, and offset in time with respect to each other by a duration T and then doing the

  sum of the signals obtained at the end of these two premultiplications.

  We are thus assured of being able to carry out the first transfer irrespective of the relative position in the signal time.

  input and frequency ramps.

  If this solution makes it possible to solve the problem mentioned, it does however reveal another problem which is an ambiguity of interpretation for the frequencies of the input signal located at the end of the band. Indeed, for two successive analysis slices of duration T of the input signal, the resulting rectangles, such as 6, would be strictly contiguous so that in the common area, the decision to assign a frequency to one rather

than the other would be impossible.

  To solve this problem, the solution adopted is to extend the band of the spectrum analyzer, going from (2 B, 2 T) to (2.1 B, 2.1 T) for the frequency ramp and ( B, T) to (l IB, 1.1 T) for the dispersive filter, and to filter the resulting excess band This filtering is performed in particular by an input filter

bandpass with steep edges.

  The reception device according to the invention, equipped with a spectrum analyzer provided with these improvements, has an intercept probability equal to 100% It also has good sensitivity and good selectivity, specific to any spectrum analyzer It offers the possibility of detecting

  simultaneous broadcasts at different frequencies, which

  do not put the classical techniques of direct detection and superheterodyne. According to a preferred variant embodiment, dispersive acoustic lines are used for ramp generation and for compression, which makes it possible to obtain the widest frequency bands. The subject of the present invention is also a processing device making it possible to recognize the carrier frequency of the radar emissions thus detected by the reception device, taking into account the particular nature of the output signals of

the spectrum analyzer.

  The objects and features of the present invention appear

  more clearly on reading the following description of a

  Embodiment of the invention, with reference to the accompanying drawings in which: Figures 1a and 1b show a spectrum analyzer

  according to the prior art and a corresponding operating diagram.

  laying; Figure 2 is a diagram of a receiving device according to the invention; Figure 3 is a diagram of a first part of a processing device according to the invention; Figure 4 is a timing chart showing the signals obtained at different points in Figure 3; Figure 5 is a diagram of a second part of a processing device according to the invention; Figure 6 is a diagram explaining the operation

of the diagram of Figure 5.

  The receiving device shown in FIG. 2 comprises a band-pass type I filter of width B, which receives an input signal E. The output signal of the filter 1 is applied to a

  first input of two mixers 2 and 3.

  A second input of the mixer 2 receives the output signal of a first ramp generator 4 having a dispersive line 5 of band 0.525 B, and delay 2, IT, which receives on its input a control signal C consisting of pulses Dirac repeats at a frequency 2, 2 T, followed by a frequency multiplier by four, 6 The ramp generator 4 provides a first frequency ramp 2.1 B wide and duration 2.1 T. A second The input of the mixer 3 likewise receives the output signal of a second ramp generator 7. This latter comprises a delay line 8 with a delay of 1,1 T, which receives on its input the same

  control signal C as before, followed by a disper-

  sive 9 of band 0.525 B and delay 2.1 T, identical to line 5 and itself followed by a frequency multiplier by four, 10 ramp generator 7 provides a second frequency ramp of width 2.1 B and of duration 2.1 T, offset with respect to the first of a duration 1, 1 T The receiving device also comprises an adder 1 i on the inputs of which are applied the output signals of the mixers 2 and 3, and a dispersive line 12 of tape

  1.1 B and delay l, 1 T, disposed at the output of the adder 11.

  The receiving device also comprises a detector 13, made for example by means of a diode, disposed at the output of the dispersive line 12, and making it possible to retain only the portion of this signal situated above a certain threshold The output signal S of the

  receiving device is obtained at the output of a filter 14.

  The dispersive lines 5, 9 and 12 are produced using acoustic components. The multipliers 6 and 10 are

  from medium frequency mixers operating at constant level.

  With reference to FIG. 3, the device

  treatment device placed downstream of the receiving device of FIG.

  This device comprises an analog-digital converter for converting the input analog signal S, that is to say the

  output signal of the receiving device, in a digital signal.

  This converter is a converter of the "flash" type, comprising a series of (n + 1) comparators 15 i which simultaneously perform the comparison of the input signal S with (n + 1) levels i (AV), where AV is the step quantization of the converter and "i" an index varying from 0 to N, each comparator 15 provides a COMP signal To better understand the constitution and operation

  of this treatment device, it is first necessary to

  For this purpose, see Figure 4 In accordance with the principle of spectral analysis, the signal S has the same appearance as the spectrum A (f) of a radar signal (giving the signal amplitude A as a function of the frequency f) and therefore comprises a main lobe centered on a time t 1 such that the duration tl-t O (o to represents the start time of the spectral analysis giving rise to the considered pulse of the signal S) is representative of the carrier frequency f of the radar signal (f = K (t 1 t 0)

o K is a constant).

  The diagram shows, by way of example, four successive quantization levels of the converter 15: VO + (2 i + 1) AV, VO + 2 i AV, VO + (2 i 1) AV and V 0 + (2 i 2) AV, whose respective intersections with the signal S delimit the portions of the signals COMP 2 i + 1 CO COMP 2, COMP 2 i-1 and COMP 2 i-2

having a logic level at "1 i".

  One of the objects of the processing device is to measure the carrier frequency of the radar signals intercepted by the device

reception.

  It has been seen previously that the measurement of the carrier frequency f of a radar emission, giving rise at the output of the reception device to a signal S such as that of FIG. 4, amounts to a measurement of the duration t 1 -to, therefore, the so-called instant t 0O, at a determination of the instant t 1 o the signal S reaches a maximum amplitude S (tl) Or, because of the quantification effected by the

  analog digital converter 15, the instant t 1 is not acces-

  sible; only the instants such as t 2 and t 3, out 4 and tr, respectively corresponding in the example shown in FIG. 4, are accessible at the intersections of Ve (t) with the levels V O + 2 i (AV) and

V O + (2 i-1) AV.

  The carrier frequency f sought is then obtained by detecting the instants t 4 and t 5, these instants corresponding to two frequencies fmin and fmax framing the carrier frequency, and

  checking relations t 5 t O = Kfmax and t 4 O = Kfmin Detection

  the instants t 4 and t 5 are in fact preferred to those of the instants t 2 and t 3, in order to ensure, in the case where the signal S has a relatively large peak and not perfectly flat (which is the case of a modulated radar signal) that a momentary descent of this signal in

  below the threshold V 0 + 2 i V is interpreted as decreasing

of this signal.

  The elements of the processing device for determining the times t 4 and t 5, that is to say the fmin and fax frequencies, are now described.

mmmax-

  These elements comprise circuits 162 i and 162 i + 1 for storing the first crossing, in the ascending direction, of each even threshold V 0 + 2 i (AV) and each odd threshold.

  V 0 + (2 i + 1) AV, by the signal S as and when it evolves.

  Each circuit 16 is for example constituted by a flip-flop of the type "D" whose input D is at logic level "1", whose clock input CK is connected to the output of the comparator 152 i, and whose reset input CL receives a reset signal 1 which is the same for all flip-flops and which is obtained at the output of a counter 17

  whose order will be described later.

  At the output Q of each of the flip-flops 162 i, supplying a signal C 2 i, is connected a drifting cell 182 i which is formed of a resistor 192 i and a capacitor 202 i, and which supplies a signal A 2 i The signal A 2 i is applied to one of the inputs of an "OR" gate 212 i whose other input is at logic level "O" and whose

output provides a signal PO 52 i.

  The set of signals PO 52 i is applied to the input of an "OR" gate 22 which supplies a signal PO 51 with PO 51 = PO 52 i Of 1 2 i even the set of signals PO 52 i + is applied at the input of an "OR" gate 23 which supplies a signal PO 52 with PO 52 = PO 2 i + 2 2 PO 52 i + 1 'The instant t 4 sought then coincides with the pulse width of the signals PO 52 i and PO 52 i + 1 near, which is otherwise known, with

  the last falling edge of a POS signal obtained by

  section of the signals PO 51 and PO 52, by means of an "AND" gate 24.

  FIG. 4 shows the signals Q, A and POS associated with each of the signals COMP corresponding to the four comparison levels V 0 + (2 i + 1) AV, VO + (2 i) LV, VO + (2 i 1) AV

  and V 0 + (2 i-2) AV nearest the maximum S (t 1) The same reason-

  could of course be held for comparison levels below VO + (2 i 2) AV, but, for greater clarity of

  drawing the corresponding signals were not represented.

  For the determination of the instant t 5, there is provided a set of "NOR" gates 25 (with any j, even or odd, between 0 and N 1) which each receive on the one hand the signal COMP, on the other hand, the inverted signal Cj + 1 by means of an inverter 26 j, each of which provides a signal NEG. The desired instant t 5 then coincides with the rising edge of a signal NEG obtained by making the logical union of all the

  NEG signals by means of an "OR" gate 27.

  The times t 4 t 0 and t 5 are representative of the frequencies fmin and f framing the carrier frequency f sought are then obtained by storing at times t 4 and t 5, by means of two memories 30 and 31 respectively activated by the falling edge of the POS signal and by the rising edge of the signal NEG, the contents of a counter 32 incremented by a clock signal H and regularly reset at each new spectral analysis by a signal SY ramp synchronization The counter 17 17 zero of the flip-flops 162 i and 162 i + 1 is in turn incremented by the clock signal H and reset by a signal RAZ 2 obtained at the output of an "OR" gate 33 which receives, on the one hand, the signal POS, on the other hand the inverted NEG signal by means of an inverter 34 Ce

  RAZ signal 2 has also been shown in Figure 4b.

  The counter 17 is thus reset to zero at each new detection of a growth, followed by a decrease, of the signal S obtained at the output of the spectrum analyzer, provided, however, that the new detected growth carries the signal S to a value greater than that at which it was carried by the decay

former.

  The flip-flops 162 i and 162 i + 1 are reset by the signal RAZ 1 only when the counter 17 reaches a certain value (which can be determined in advance), without being reset to zero, which means that the signal S has reached its maximum maximorum, that is to say that the main lobe of this signal has been detected. The processing device located downstream of the spectral analysis device comprises, in addition to the circuit shown in FIG. 3, a circuit for taking into account successive spectral analyzes, with a view to

  to reconstruct as closely as possible the parameters (particularly

  the carrier frequency) received radar pulses.

  of the signal obtained after a single spectral analysis as described so far in connection with Figure 3, would not be sufficient to reconstruct these parameters because, on the one hand received radar pulses can be modulated in frequency and on the other hand, several independent radar pulses can be received and analyzed simultaneously In addition the radar pulse duration does not

would not be provided.

  This circuit for taking into account successive spectral analyzes is represented in FIG. 5. It can, by way of example, take into account successive spectral analyzes relating to a maximum number of independent radar pulses received simultaneously.

equal to 4.

  For each of these independent radar pulses received simultaneously, this circuit comprises the following elements: two comparators 40 and 41 for comparing the frequencies f min and f max

  (ie fm and f M) resulting from the spectral analysis in progress, respec-

  with current frequencies F min and F max (ie F and FM) stored in a memory 42 and obtained, during the first spectral analysis by identification with the frequencies fmin and fmax resulting from this analysis, and during subsequent analyzes by setting whether or not this memory

  results of the comparisons made respectively by the

  40 and 41, these results being combined in one

"NO-OR" 43.

  According to the different possible results of the comparisons, represented diagrammatically in FIG. 6, there are the following different scenarios: The intervals (fm f M) and (Fm, FM) can first of all be totally disjoint, either because the condition f M <Fm is performed (this is the case of Figure 6 a), or because the condition FM <f is performed (this is the case of Figure 6 b) In this case no update n is performed, and the previous values (Fme

FM) are preserved.

  In the two cases just described, it is said that there is no identification of the frequencies common to the frequencies resulting from the current spectral analysis. This means that the frequencies fm and f M resulting from the spectral analysis in course relate to another received radar pulse simultaneously and it is then necessary, as will be seen later, to initialize another memory with

these values.

  The interval (f m f M) can also be included in the inter-

  valle (Fm, FM): this is the case of Figure 6 c In this case no update is performed, and the previous values (Fm, FM) are retained. The interval (Fm, FM) can also be included in the interval (fm f M) as in Figure 6 d In this case the following updates are made: Fm = fm and FM = f MI

  The intervals (fm f M) and (FM, FM) can finally be

  in two possible ways If the condition: Fm <f M <FM is realized (case of figure 6 e), then the setting

  day: Fm = fm is performed, the previous value FM being con-

  On the other hand, if the condition: F <f <FM <f is

  read (case of Figure 6 f), then the update: FM = f M is performed, the previous value F is retained In the four cases just described, it says that there is frequency identification current at frequencies resulting from spectral analysis

In progress.

  The identification (or non-identification) is indicated by a

  IDENT signal obtained at the output of a logic gate 43 of the type "NON-

  OR "connected at the output of the comparators 40 and 41.

  The circuit for taking into account successive spectral analyzes relating to the same radar pulse thus described is reproduced as many times as it is possible to process different pulses.

  received simultaneously (four in the example).

  There is further provided an initialization circuit 44 i of each of the memories 42 i (with I <i <4) making it possible to initialize the latter when the conditions of non-identification of the frequencies being processed at the current frequencies stored in memories

42 to 42 are made.

  The INI signal Ti of the initialization command of each memory 42 is obtained at the output of an "AND" gate 45 i which receives on one of its inputs an OCCC indication signal of nonoccupancy of the memory 42 j, on (it) other inputs of the OC signals Cc to OCC i 1 occupation indication of the memories 421 to 42 i 1-i and on another input a REC signal intended to indicate that no identification has been detected between the pair of frequencies (fm f M) resulting from the current spectral analysis and each of the common frequency pairs (Fmjy F Mj) The signal REC is obtained at the output of a logic gate 46 of the "NON-OR" type which receives all the IDENT signals (with 1 ii <4) Each OCCC signal is obtained at the output of a memory 47 whose input is itself connected at the output of the logic gate 45 The OCCC signal is obtained by inverting the OCCC signal by means of an inverter 48

  The writing of each memory 42 resulting from an initialization

  In the case of an update, the IDEN signals Ti and INI Ti are both applied to the input of a logic gate 50 of the "OR" type whose output signal is applied to the control input. The frequencies fm and f M resulting from the current spectral analysis being applied to all the comparators 40 i and 41 i (with 1 <i <4), the comparison operations as described are described in FIG. in Figure 6 are actually more complex, because they return to situate the interval (fm f M) not with respect to a single interval (Fmy FM) but with respect to four distinct intervals (Fmi,

  F Mi) (with 1 i <4), the principle remaining the same each time.

Claims (9)

  1 device for receiving and processing radar signals for a countermeasure analyzer, characterized in that it comprises, for receiving a spectrum analyzer of the input signal,   comprising itself two multipliers (2, 3) making it possible   in parallel, perform two multiplications of the input signal respectively by two linearly frequency-modulated frequency ramps, of band 2 B (B being the frequency band of the input signal) and of duration 2 T, shifted relative to one another to the other of a duration T, an adder (11) for adding the output signals of these two multipliers, and a dispersive filter (12) of band B and   delay T, disposed at the output of the adder.   2 Device according to claim 1, characterized in that the frequency ramps have a band 2, IB and a duration 2.1 T, the dispersive filter, a band 1.1 B and a duration 1.1 T, and in that that this device then comprises a band-pass filter (1) able to filter the   extra band involved in the choice of these values.   3 Device according to one of claims 1 and 2, characterized   in that the ramp generators (4, 7) are produced by means of a   dispersive filter (5, 9) attacked by a pulse signal of Dirac.   4 Device according to claims 1 and 3, characterized in that   that the dispersive filters S (5, 9) forming the ramp generators (4, 7) have a bandwidth of a fraction of the band B and are monitored   frequency multipliers (6, 10).   Device according to claims 2 and 3, characterized in that   that the dispersive filters (5, 9) forming the ramp generators (4, 7) have a bandwidth of 0.525 B and are followed by multipliers of frequency by four (6, 10).   Device according to one of Claims 1 to 5, characterized   in that it comprises, for processing, means for measuring the carrier frequency of the radar signals by detecting the maximum maximorum of the output pulse of the spectrum analyzer at each triggering of a spectral analysis. 7 Device according to claim 6, characterized in that it comprises an analog-digital converter (15), performing   simultaneously a comparison of the output pulse of the   spectrum analyzer with (n + 1) levels V 0 + i (AV) (O i i 4 n) and means for detecting the maximum maximorum of the output pulse of the spectrum analyzer by detecting the intersections of this spectrum analyzer impulse respectively with the levels VO + (2 i 1) AV, in the increasing and decreasing directions, (V 0 + 2 i (to V) and   VO + (2 i + 1) AV being the levels surrounding this maximum maximum   morum, and corresponding to two frequencies f min and fmax).   8 Device according to claim 7, characterized in that the frequency detection means f min comprises a circuit (16, 18, 19, 20, 21) 2 i of first growth detection of the output pulse of the spectrum analyzer with respect to each even level V 0 + 2 i (AV), a first growth detection circuit (16, 18, 19, 20, 21, 2 i + 2) with respect to each odd level VO + ( 2 i + 1) AV, and a logic circuit (22, 23, 24) for combining   between them the signals obtained at the end of these detections.   9 Device according to one of claims 7 and 8, characterized   in that the means for detecting the frequency f max comprise a circuit (16) for detecting the decay of the output pulse of the spectrum analyzer with respect to each level V 0 + j (AV),   this detection occurring after the detection of a first growth   said pulse with respect to the same level, and a logic circuit (25, 26, 27) for combining the signals   obtained at the end of these decay detections.   Device according to one of Claims 6 to 9, characterized   in that it comprises means for taking into account the measurement results of the carrier frequency relative to the same   radar signal on several successive spectral analyzes.   11 Device according to claims 7 and 10, characterized in   the means for taking into account successive measurement results comprise means (40, 41, 43) for comparing the frequencies (fmin 'fmax) resulting from the current spectral analysis at current frequencies (Fmin' Fmax) obtained , during the first spectral analysis, by memorizing the frequencies (fmin fmax), and during the following spectral analyzes by updating these values from the values (fmin 'fax) in the case where the interval (Fmin' FM ) is included in the interval (fmin 'f Max) or in the case o   the intervals (fmin 'f Max) and (F min' F Max) overlap.   12 Device according to claim 11, characterized in that it comprises means for taking into account the successive measurement results of the carrier frequency relative to several radar signals received simultaneously, the recognition of a signal   unidentified radar taking place when, at the end of the   reasons of the frequencies f min and f Max at the current frequencies F min and F Max relating to all the radar signals already identified the   intervals (f min 'f Max) and (Fmin' F Max) are disjoint.