GB2261292A - Radar signal receiving and processing device for countermeasures analyzer - Google Patents

Abstract

The amplitude-frequency spectrum of an input signal can be reproduced as an amplitude-time waveform by mixing (2) the input E with a linear frequency ramp (4) and supplying the difference frequency to a linear dispersive filter 12 whose time-delay/frequency characteristic has a slope matching that of the ramp. To avoid discontinuities at the end of each ramp, the system includes two mixers (2, 3) enabling two multiplications of the input signal to be made in parallel by two linearly frequency modulated frequency ramps, shifted with respect to each other by a duration T. This device also includes, for the processing, means of recognizing the carrier frequency of radar transmissions thus detected, by taking account of the special nature of the output signals of the spectrum analyzer. <IMAGE>

Description

RADAR SIGNAL RECEIVING AND PROCESSING DEVICE FOR COUNTERMEASURES ANALYZER The present invention relates to a radar signal receiving and processing device for countermeasures analyzer.

Such a device, associated with a receiving antenna, has the puroose of intercepting radar signal transmissions and measuring their transmission parameters, such as the carrier frequency, the pulse duration, the spectral width and the spectral level.

The fact that these parameters are divided into HF parameters and video-frequency !oarameters has, up to the present time, led to the envisaging of two types of system.

A first system, called a direct detection system, consists in obtaining the carrier frequency directly from the HF signal, and, in parallel, the video-frequency parameters from the corresponding video signal. 3ecause of the direct detection of the carrier frequency from the HF signal, this system has the advantage of having an interception probability of close to 100X. On the other hand it has the disadvantage of having poor sensitivity and selectivity.

A second system, called the superheterodyne system, consists in obtaining all the parameters from a medium frequency signal obtained from a radar transmission by beating with the signal supplied by a local oscillator.

Unlike the previous system, this system has the disadvantage of having an interception probability of less than 100X. This is due to the fact that, the carrier frequency of radar transmissions to be analyzed being a priori unknown, it is necessary to scan an entire frequency band with the local oscillator before achieving tuning. On the other hand, this system has good sensitivity and good selectivity.

The subject of the present invention is a radar signal receiving and processing device which combines the advantages of the two previously mentioned techniques without having their disadvantages.

The device according to the invention depends upon a third type of system, called the spectral analysis system. Various embodiments of such spectrum analyzers are known, particularly through paper IX.4 by C. LARDAT, entitled "Analyseurs de spectre utilisant des filtres dispersifs à ondes de surface - (Spectrum analyzers using surface wave dispersive filters)", at the 1978 International Colloquium on Radar (pages 303 to 311).

At the end of a time interval T, this system makes an output signal correspond with a time slot T of an input signal having a frequency band B, the output signal's position in time with respect to the start of the spectral analysis representing the band B.

As shown in Figure la, the spectral analysis is obtained by premultiplication, or BLU transposition, in a mixer 1 of the input signal of band B and duration T with a linearly frequency modulated ramp, of band 2B and of duration 2T, then compression in a dispersive filter 2 of band 8 and delay T.

Figure 1b shows the successive transformations by these two operations of an input signal whose representation in the time-frequency domain is in the shape of a parallelogram 3. By multiplication with the frequency ramp, referenced 4 on this diagram, we obtain a parallelogram 5 (the sides marked with arrows respectively corresponding in this transformation). By compression in the dispersive filter 2, the parallelogram 5 is transformed into a rectangle 6, the sides marked with arrows also respectively cor responding.

On this figure it appears that a spectral analysis can only be carried out correctly if the input signal and the frequency ramp are synchronous. Zn fact, if they are asynchronous, which occurs, particularly in the case of application to countermeasures analyzers in which the position of the radar transmissions likely to be intercepted with respect to the frequency ramp is not known in advance, the first transformation can lead to an indetermination which then results in an interception probability of less than 100%.

The present invention aims at solving this problem.

According to the invention, this problem is solved by carrying out in parallel two premultiplications of the input signal by two identical frequency ramps of duration 2T, and time shifted with respect to each other by a duration T, then by summing the signals obtained as a result of these two premultiplications.

We are therefore assured of being able to correctly carry out the first transformation whatever the relative positions in time of the input signaL and the frequency ramps may be.

Although this solution provides a good solution to the problem mentioned, it does however make another problem appear which is an ambiguity in interpretation for the frequencies of the input signal located at the end of the band. In fact, for two successive analysis slots of duration T of the input signal, the resulting rectangles, such as 6, would be strictly joined in such a way that, in the common zone, the decision to attribute a frequency to one rather than the other would be impossible.

In order to solve this problem, the solution adopted consists in extending the band of the spectrum analyzer, increasing from (28, 2T) to (2.18, 2.7T) for the frequency ramp and from (B, T) to (1.18, 1.1T) for the dispersive filter, and in filtering the additional band resulting from this. This filtering is particularly carried out on input by means of a sharp-edged bandpass filter.

The receiving device according to the invention, equipped with a spectrum analyzer having these improvements, has an interception probability of 100%. It also has good sensitivity and good selectivity which are appropriate to any spectrum analyzer. It also offers the possibility of detecting simultaneous transmissions at different frequencies, which the traditional direct detection and superheterodyne techniques do not allow.

According to a preferred variant embodiment, acoustic dispersive lines are used for the ramp generation and for the compression, which provides the widest frequency bands.

Another object of the present invention is a processing device enabling the recognition of the carrier frequency of the radar transmissions thus detected by the receiving device, by taking account of the special nature of the output signals of tne spectrum anaLyzer.

The purposes and haracreristics of the present invention will appear more yearly on reading the following description of an example of embodiment, given with reference to the appended drawings in which: - Figures la and 1b represent a spectrum analyzer according to the prior art and a corresponding functional diagram; - Figure 2 is a block diagram of a receiving device according to the invention; - Figure 3 is a block diagram of a first part of a processing device according to the invention; - Figure 4 is a time diagram representing the signals obtained at various points in Figure 3; - Figure 5 is a block diagram of a second part of a processing device according to the invention; - Figure 6 is a diagram explaining the functioning of the diagram in Figure 5.

The receiving device represented in Figure 2 inc ludes a band-pass fiLter 1 of bandwidth 8, 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 including a dispersive line 5 of bandwidth 0.5258, and with delay 2.1T, which receives at its input a control signal C formed from Di rac pulses repeating at a frequency 2.2T, followed by a times four frequency multiplier, 6. The ramp generator 4 provides a first frequency ramp of width 2.1B and of duration 2.lT.

A second input of the mixer 3 similarly receives the output signal of a second ramp generator 7. This second ramp generator includes a delay line 8 of delay 1.1T, which receives at its input the same control signal C as before, followed by a dispersive line 9 of bandwidth 0.525B and of delay 2.1T, identical with line 5 and itself followed by a times four frequency multiplier, 10. The ramD generator 7 provides 3 second frequency ramp of width 2.18 and of duration 2.1T, sniffed with respect to the first by a duration 1 .1T.

The receiving device also includes an adder 11 to whose inputs are applied the output signals of the mixers 2 and 3, and a dispersive line 12 of bandwidth 1.18 and of delay 1.1T connected to the output of the adder 11.

The receiving device also includes a detector 13, produced for example by means of a diode, connected to the output of the dispersive line 12, and enabling the retention of only the part of this signal that is 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 produced from medium frequency mixers operating at constant level.

The processing device following the receiving device of figure 2 will now be described with reference to Figure 3.

This device includes an analog-digital converter 15 to convert the analog input signal S, i.e. the output signal of the receiving device, into a digital signal.

This converter is a "fLash" converter, including a series of (n+1) comparators 15j which simultaneously compare the input signal S with (n+1) levels i(#V), where AV is the quantization step of the converter and "i" is an index varying from 0 to "n", each comparator 15 providing a signal COMP;.

To give a better understanding of the composition and functioning of this processing device it is first useful to show the appearance of the signals S and COMPi . We refer to Figure 4 for this purpose. According to the principle of spectral analysis, the signal S has the same appearance as the spectrum A(f) of a radar signal (giving the amplitude A as a function of frequency f) and consequently has a main lobe centered on a time t1 such that the duration t1t0 (where t0 reoresents the start time of the spectral analysis giving rise to the considered pulse of the signal S) represents the carrier frequency f of the radar signal (f = K(t1 - t0) where K is a constant).

By way of example we have shown on this same diagram four successive quantization levels of the converter 15: V0 + (2i + 1) L'V, Vg + 2i 'V, Vo + (2i - 1) #v, and Vs + C2i - 2) V, whose respective intersections with the signal S delimit the parts of signals COMP2i+l, COMP2i, COMPZ,1, and COMP2 -2 having a logic level of "1".

One of the purposes of the processing device is to measure the carrier frequency of radar signals intercepted by the receiving device.

We have seen previously that the measuring of the carrier frequency f of a radar transmission, giving rise to an output from the receiving device of a signal S such as described in Figure 4, is based on the measuring of the duration tl - to, and therefore, the time to being known, on a determination of the time t1 at which the signal S reaches a maximum amplitude S(t1). Now, because of the quantization carried out by the analog-digital converter 15, the time t1 is not accessible; the only times accessible are those such as t2 and t3, or t4 and t5, corresponding respectively in the example shown in Figure 4 with the intersections of Ve (t) with the levels Vg + (AV) and Vg + (2i - 1) ~V.

The sought carrier frequency f is therefore obtained by detecting the times t4 and t51 these times corresponding with two frequencies fmin and fmax on either side of the carrier frequency and verifying the expressions ts - to = Kfmax and t4 - to = Kfmjn. The detection of times t4 and t5 are in fact preferred to the detection of times t2 and t3 in order to ensure, in the case in which the signal S nas a relatively wide and not perfectly flat oeak (which is the case of a modulated radar signal) that a momentary dropback of the signal below the threshold V0 + 2i V is not interpreted as a definitive decrease in this signal.

We shall now describe the components of the processing device determining the times t4 and t5, i.e.

the frequencies fmin and fmax These components comprise circuits 162i and 162i +1 for the storage of the first passing, in the ascending direction, of each even threshold Vg + 2i( \ V) and of each odd threshold Vo + (2i + 1) V, by the signal S as it develops.

Each circuit 16; is for example formed by a D type flip-flop whose D input is at the logic "1" level, whose clock input CK is connected to the output of the comparator 152i and whose reset to zero input CL receives a signal RAZ1 which is the same for all the flip-flops and which is obtained at the output of a counter 17 whose control will be described later.

To the Q output of each of the flip-flops 162;, providing a signal C2i1 is connected a differentiation cell 182i which is formed from a resistor 192i and a capacitor 202i, and which provides a signal A2i. The signal A2 is applied to one of the inputs of an "OR" gate 212i whose other input is at logic "0" level and whose output provides a signal POS25.

The set of signals POSz; is applied to the input of an "OR" gate 22 which provides a signal POS1 where POS1 = POS2;. Similarly the set of signals POS2i+1 is applied to the input of an "OR' gate 23 which provides a signal POS2, where POS2 = POS2i+1 The sought time t4 therefore coincides, except for the pulse width of the signals POS2 and POS2+1 which is however known, with the last falling edge of a POS signal obtained by producing the intersection of the signals POS1 and POS2 by means of an "AND" gate 24.

Figure 4 shows the signals 2, A and POS associated with each of the COMP signals carresponding with the four levels of comparison V0 + (2i + 1) V, V9. + (2i) I, Vg + (2i - 1) V and V0 + C2i - 2) V closest to the maximum S(t1). The same reasoning could of course be used for comparison levels lower than V0 + (2i - 2) V, but, for greater clarity of the drawing, the corresponding signals have not been shown.

For determination of the time t5, a set of "NQR" gates 25j has been provided (where j is any number, odd or even, between 0 and n-l) each of which receives on the one hand the signal COMPj, and on the other hand the signal Cj+1 inverted by means of an inverter 26j, and which each provide a signal NEG.

The sought time t5 therefore coincides with the rising edge of a NEG signal obtained by logically bringing together all the NEGj signals by means of an "OR" gate 27.

The durations t4 - to and t5 - to, representing the frequencies fmin and fmax on either side of the sought carrier frequency f are then obtained by storing the times t4 and t5 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 NEG signal, the content of a counter 32 increased by a clock signal H and regularly reset to zero for each new spectral analysis by a ramp synchronizing signal SY. The reset to zero counter 17 for flip-flops 162i and 162i+1 is itself incremented by the clock signal H and reset to zero by a signal RAZ2 obtained at the output of an "OR" gate 33 which receives on the one hand the signal POS, and on the other hand the signal NEG via an inverter 34. This RAZ2 signal has also been shown in Figure 4b.

The counter 17 is thus reset to zero at each new detection of an increase, followed be a aecrease, in the signal S obtained at the output of the spectrum analyzer, on condition however that the new increase detected takes the signal S to 3 value greater than that to whicn it had been taken by the previous decrease.

As for fLip-flops 162i and 162 +1, these are only reset to zero by the RAZ1 signal when the counter 17 reaches a certain value (that can be determined in advance), without having been reset to zero, which signifies that the signal S has reached its highest maximum, i.e. that the main lobe of this signal has been detected.

The processing device situated after the spectral analysis device includes, in addition to the circuit shown in Figure 3, a circuit taking account of successive spectral analyses for the purpose of reconstituting as faithfully as possible the parameters (particularly the carrier frequency) of the received radar pulses.

The processing of the signal obtained at the output of a single spectral analysis such as described up to now with reference to Figure 3, would not in fact be sufficient to reconstitute these parameters because, on the one hand, the received radar pulses can be frequency modulated and, on the other hand, several independent radar pulses can be received and analyzed simultaneously. Also, the duration of the radar pulse would not be provided.

This circuit for the taking into account of successive spectral analyses is shown in Figure 5. It can, by way of example, take account of the successive spectral analyses relating to a maximum number of four independent radar pulses simultaneously received.

For each of these simultaneously received independent radar pulses, this circuit includes the following elements: two comparators 40 and 41 to compare the frequencies fmin and max (or fm and f;q) result ing from the spectral analysis in progress, with the currant F min and F max (or Fm and F) frequencies respectively stored in a memory *2 and obtained, during t first spectral analysis by identification sith the frequencies Fmjn and fmax resulting from that analysis, and during the following analyses by updating or not updating this memory according to the results of tne comparisons made by the comparators 40 and 41 respectively, these results being combined in a "NOR" gate 43.

Depending on the various possible results of the comparisons, shown diagrammatically in Figure 6, we have the following different cases: The intervals (fm,f) and (Fm,FM) can first of all be totally disjoined, either because the condition M < Fm is produced (which is the case of Figure 6a), or because the condition FM < is produced (which is the case of Figure 6b). In this case no updating is carried out and the previous values (Fm, FM) are retained.

In the two cases that have just been described we say that there is no identification of the current frequencies with the frequencies resulting from the spectral analysis in progress. This signifies that the frequencies fm and fM resulting from the spectral analysis in progress relate to another simultaneously received radar pulse and it is therefore necessary, as will be seen later, to initialize another memory with these values.

The interval (f,,fy) can also be included in the interval (Fm,FM); this is the case of Figure 6c. In this case no updating is carried out and the previous values (Fm, FM) are retained.

The interval (Fm,F.l) can also be included in the interval (fm,fi), m'Mwnich is the case of Figure 6d. In this case the following updates are carried out: Fm = fm and F = fM- The intervals (f :M) and (Fm,F) can finally over lao, and this can occur in two possible ways.

If tn condition Fm < fM < F9 is produced (the case of Figure 6e), then the update Fm = f is carried out, tne previous FM value being retained.

On the other hand if the condition m < +, < FA < f@ is produced (tne case of Figure 6f), then the update = = f.1 is carried out, the previous Fm value being retained. In the four cases that have just been described, we say that there is identification of the current frequencies with the frequencies resulting from the spectral analysis in progress.

Identification (or non identification) is indicated by an IDENT signal obtained at the output of a logical "NOR" gate 43 connected to the outputs of comparators 40 and 41.

The circuit for the taking into account of successive spectral analyses ralating to a same radar pulse thus described is reproduced as many times as it is possible to process simultaneously received different pulses (four in the example considered).

In addition an initialization circuit 44i is provided for each of the memories 42j (where 1 s i s 4) enabling these memories to be initialized when conditions of non-identification of the frequencies being processed with the current frequencies stored in the memories 421 to 42i-1 are produced.

The initialization control signal INITi for each memory 42j is obtained at the output of an "AND" gate 45i which receives on one of its inputs a signal OCCj indicating non-occupation of memory 42j, on (i-1) other inputs the signals OCC1 to OCCj-1 indicating occupation of memories 421 to 42i-1, and on another input a signal REC to indicate that no identification has been detected between the pair of frequencies (fm,fM) resulting from the spectral analysis in progress and each of the current pairs of frequencies (Fmj,FMj). The signal REC is obtained at the output of a logical "NOR" gate 46 which receives all the INDENT signals (wnere 1 < i #4).

Each signal OCCj is obtained at the output of a memory 471 whose input is itself connected to the output of the logic gate 45;. The signal OCCi is obtained by nverting the signal OCCj by means of an inverter 48i.

For the writing of each memory 42j resulting either from an initialization or from an update, the signals IDENT and INIT are both applied to the input of an "OR" logic gate 50 whose output signal is applied to the write control input of the memory 42i.

The frequencies f, m and fM resulting from the spectral analysis in progress being applied to all the comparators 40 and 41j (where 1 < i # 4), the comparison operations such as described in Figure 6 are in fact more complex, as they involve situating the interval (fm,fM) not only with respect to one interval (Fm, FM) alone, but with respect to four separate intervals (Fmi,FMi) (where 1 % < s # 4), the principLe remaining the same each time.

Claims (11)

1. Radar signal receiving and processing device for countermeasures analyzer, characterized in that it includes, for receotion, an input signal spectrum analyzer, itself including two multipliers (2, 3) enabling two multiplications of the input signal to be made in parallel by two linearly frequency modulated frequency ramps respectively, of band 2B (8 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) to add the output signals of these two multipliers, and a dispersive filter '12) of band 3 and of delay T, connected to the output of the adder.

2. Device according to claim 1, characterized in that the frequency ramos have a bandwidth 2.19 and d duration 2.1T, tne dispersive filter, a bandwidth 1.18 and a duration 1.1T, and in that this device therefore includes ) bandpass filter (1) capable of filtering the excess bandwidth implied by this choice of values.

3. Device according to either of claims 1 and 2, characterized in that the ramp generators (4, 7) are produced by means of a dispersive filter (5, 9) to which is applied a signal of Di rac pulses.

4. Device according to claims 1 and 3, characterized in that the dispersive filters (5, 9) forming the ramp generators (4, 7) have as a bandwidth a fraction of the band a and are followed by frequency multipliers (6, 10).

5. Device according to claims 2 and 3, characterized in that the dispersive filters (5, 9) forming the ramp generators (4, 7) have as a bandwidth 0.5258 and are followed by times four frequency multipliers (6, 10).

6. Device according to one of claims 1 to 5, characterized in that it includes, for the processing, means of measuring the carrier frequency of radar signals by detecting the highest maximum of the output pulse of the spectrum analyzer each time a spectraL analysis is started.

7. Device according to claim 6, characterized in that it includes an analog-digital converter (15) simultaneously making a comparison of the output pulse of the spectrum analyzer with (n + 1) levels Vo + i( V)(O C i # n) and means of detecting the highest maximum of the output pulse of the spectrum analyzer by detecting the intersections of this pulse with the VO + (2i - 1) AV levels in the increasing and decreasing directions respectively, (VO + 2i (V) and Vg + (2i + 1) V being the levels on either side of this highest maximum and corresponding to two frequencies fmin and fmax)

8.Device according to claim 7, characterized in that the means of detecting the freuency min include a circuit (16, 18, 19, 20, 21) 2i for detecting the first increase in the output pulse of the spectrum analyzer with respect to each even level Vg + 2i (#V), a circuit (16, 18, 19, 20, 21, 2 i + 2) for detecting the first increase with respect to each odd level V0 + (Zi + 1)~V, and a Logic circuit (22, 23, 24) for combining the signals obtained as a result of these-detections with each other.

9. Device according to one of claims 7 and 8, characterized in that the means of detection of the frequency fmax include a circuit (16j) for detecting a decrease in the output pulse of the spectrum analyzer with respect to each level V0 + j(CV), this detection taking place after the detection of a first increase in this pulse with respect to this same level, and a logic circuit (25, 26, 27) to combine the signals obtained as a result of these decrease detections with each other.

10. Device according to one of claims 6 to 9, characterized in that it includes means of taking into account the results of measuring the carrier frequency relating to a same radar signal over several successive spectral analyses.

11. A radar signal receiving and processing device substantially as hereinbefore described with reference to and as illustrated in Figures 2 - 6 of the accompanying drawings.

11. Device according to claims 7 and 10, characterized in that the means of taking into account the successive measuring results include means (40, 41, 43) of comparing the frequencies (fmin, fmax) res- ulting from the spectral analysis in progress with the current frequencies (Fmin, Fmax) obtained, during the first spectral analysis, by storing the frequencies (fmin, fmax)z and during the following spectral analyses by updating these values from the values (fmin fmax) in the case in which the interval (Fmin, FMax) is included in the interval mi n' fMax) or in the case in wnicn the intervals (fmin, , fMax) and (Fmin, FMax) overlap.

12. Device according to claim 11, characterized in tnat it includes nears for taking into account the successive resits of the measuring of the carrier frequency relating to several simultaneously received radar signals, the recognition of 3 radar signal not yet identified taking place when, as a result of the comparisons of the frequencies fmin and fMax with the current frequencies Fmin nand F9ax relating to all the already identified radar signals, the intervals (fmin, fMax) and (Fm1n FMax) are disjointed.

13. A radar signal receiving and processing device substantially as hereinbefore described with reference to and as illustrated in Figures 2 - 6 of the accompanying drawings.

Amendments to the claims have been filed as follows CLAIMS: 1. Radar signal receiving and processing device for countermeasures analyzer comprising, for reception, an input signal spectrum analyzer, itself including two multipliers enabling two multiplications of the input signal to be made in parallel by two linearly frequency modulated frequency ramps respectively, 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 to add the output signals of these two multipliers, and a dispersive filter of band B and of delay T, connected to the output of the adder, and, for the processing, means of measuring the carrier frequency of radar signals by detecting the highest maximum of the output pulse of the spectrum analyzer each time a spectral analysis is started, the device including an analogdigital converter simultaneously making a comparison of the output pulse of the spectrum analyzer with (n + 1) levels VO + i(nV)(Oin) and means of detecting the highest maximum of the output pulse of the spectrum analyzer by detecting the intersections of this pulse with the VO + (2i - I)nV V levels in the increasing and decreasing directions respectively, (VO + 2i(AV) and VO + (2i + I)AV being the levels on either side of this highest maximum and corresponding to two frequencies fmin and fmax 2. ~ Radar signal receiving and processing device for countermeasures analyzer comprising, for reception, an input signal spectrum analyzer, itself including two multipliers enabling two multiplications of the input signal to be made in parallel by two linearly frequency modulated frequency ramps respectively, of band 2.1B (B being the frequency band of the input signal) and of duration 2.IT, shifted with respect to each other by a duration 1.1T, a bandpass filter capable of filtering the excess bandwidth implied by this choice of values, an adder to add the output signals of these two multipliers, and a dispersive filter of band B and of delay T, connected to the output of the adder, and, for the processing, means of measuring the carrier frequency of radar signals by detecting the highest maximum of the output pulse of the spectrum analyzer each time a spectral analysis is started, the device including an analog-digital converter simultaneously making a comparison of the output pulse of the spectrum analyzer with (n + 1) levels VO + i(t V)(O (i (n) and means of detecting the highest maximum of the output pulse of the spectrum analyzer by detecting the intersections of this pulse with the VO + (2i - I)V V levels in the increasing and decreasing directions respectively, (V0 + 2i(bV) and VO + (2i + I)AV being the levels on either side of this highest maximum and corresponding to two frequencies fmin and fmax) 3.Device according to either of claims 1 and 2, in which the ramp generators are produced by means of a dispersive filter to which is applied a signal of pirac pulses.

4. Device according to claims 1 and 3, in which the dispersive filters forming the ramp generators have as a bandwidth a fraction of the band B and are followed by frequency multipliers.

5. Device according to claims 2 and 3, in which the dispersive filters forming the ramp generators have as a bandwidth 0.5253 and are followed by times four frequency multipliers.

6. Device according to any preceding claim, in which the means of detecting the frequency fmin include a circuit for detecting the first increase in the output pulse of the spectrum analyzer with respect to each even level VO + 2i(V), a circuit for detecting the first increase with respect to each odd level VO + (2i + 1)V, and a logic circuit for combining the signals obtained as a result of these detections with each other.

7. Device according to any preceding claim, in which the means of detection of the frequency fmax include a circuit for detecting a decrease in the output pulse of the spectrum analyzer with respect to each level V0 + j( AV), this detection taking place after the detection of a first increase in this pulse with respect to this same level, and a logic circuit to combine the signals obtained as a result of these decrease detections with each other.

8. Device according to any preceding claim, which includes means of taking into account the results of measuring the carrier frequency relating to a same radar signal over several successive spectral analyses.

9. Device according to claim o, in which the means of taking into account the successive measuring results include means of comparing the frequencies fmin max res- ulting from the spectral analysis in progress with the current frequencies mint Fmax obtained, during the first spectral analysis, ny storing the frequencies fmin, fmax t and during the following spectral analyses by updating these values from the values fmin, fmax in the case in which the interval Fmin, FMax is included in the interval fmin, Max @@ in the case in which tie intervals fmin, fMax and Fmin, FMax over@@@.

10. Device according to claims 9* which includes means or taking @@@ account the succes- s i v e r e s u l t s of the measuring of the carrier frequency r e l a t i n g to several simltaneously received radar sia- nals, the recognition of 3 radar signal not yet identified taking Place when, as a result of the com parisons of the frequencies mi n and fMax with the current frequencies Fmin and FMax relating to ail the already identified radar signals, the intervals f ni in' Max and Fmin ax are disjointed.