GB2517663A - Device for eliminating false radar blips injected from the digital memory of a scrambler - Google Patents
Device for eliminating false radar blips injected from the digital memory of a scrambler Download PDFInfo
- Publication number
- GB2517663A GB2517663A GB9623771.4A GB9623771A GB2517663A GB 2517663 A GB2517663 A GB 2517663A GB 9623771 A GB9623771 A GB 9623771A GB 2517663 A GB2517663 A GB 2517663A
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- GB
- United Kingdom
- Prior art keywords
- blips
- circuit
- scrambler
- radar
- false
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- 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
-
- 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
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/06—Systems determining position data of a target
- G01S13/08—Systems for measuring distance only
- G01S13/10—Systems for measuring distance only using transmission of interrupted, pulse modulated waves
- G01S13/24—Systems for measuring distance only using transmission of interrupted, pulse modulated waves using frequency agility of carrier wave
-
- 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
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/06—Systems determining position data of a target
- G01S13/08—Systems for measuring distance only
- G01S13/10—Systems for measuring distance only using transmission of interrupted, pulse modulated waves
- G01S13/26—Systems for measuring distance only using transmission of interrupted, pulse modulated waves wherein the transmitted pulses use a frequency- or phase-modulated carrier wave
- G01S13/28—Systems for measuring distance only using transmission of interrupted, pulse modulated waves wherein the transmitted pulses use a frequency- or phase-modulated carrier wave with time compression of received pulses
- G01S13/284—Systems for measuring distance only using transmission of interrupted, pulse modulated waves wherein the transmitted pulses use a frequency- or phase-modulated carrier wave with time compression of received pulses using coded pulses
-
- 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
- G01S7/36—Means for anti-jamming, e.g. ECCM, i.e. electronic counter-counter measures
-
- 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
- G01S7/282—Transmitters
-
- 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
Landscapes
- 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)
Abstract
A device for eliminating false radar blips injected from the digital memory of a scrambler comprises apparatus 21 for modulating the radar transmitted power from a recurrence to another and adapted to distinguish between real blips and false blips generated by the scrambler, where real blips and false blips vary to different extents in accordance with the law of transmitted power modulation. It can be applied in particular to radars operating in a scrambled 15 environment, for example surveillance or battlefield radars. The scrambler operates with a digital radio frequency memory to re-transmit a received radar pulse during a succeeding radar period. With the change in transmitted power during that period, the false echo is apparent at the radar. By varying the radar gain 25, 27 in an inverse manner to the change in transmitted power, the time echoes can be made to appear as fixed amplitudes whereas false echoes vary from period to period.
Description
DEVICE FOR ELIMINATING FALSE RADAR BLIPS INJECTED FROM
THE DIGITAL MEMORY OF A SCRAMBLER
The invention relates to a device for eliminating false radar blips injected from the digital memory of a scrambler. It can be applied in particular to radars operating in a scrambled environment, such as surveillance and
battlefield radars.
The digital memories used in some scramblers memorise the radar pulses to be scrambled, which are then retransmitted in a distorted and demultiplied form. Such a digital scrambler memory is generally known as a DRFM, or "Digital Radio Frequency Memory'.
Scrambler DRFMs record the pulses emitted by the radar and reconstitute their contents at the next recurrence by injecting blips which contain the radar signature, that is its phase orfrequency compression law.
It is very difficult for reception systems to overcome these false radar blips injected from the scrambler% digital memory, by simple and cost-effective means.
The aim of the invention is to solve this problem, in particular by modulating the transmitted and/or received power of a radar which is likely to be scrambled.
To this end, the invention COIflPflS9Sa device for eliminating false radar blips injected from a digital scrambler memory, consisting of, in its minimum form, means for modulating the transmitted power of the radar from one recurrence to another and means for distinguishing the real blips from the false blips caused by the scrambler, taking into account the fact that real blips and false blips vary to different extents according to the law of transmitted power modulation.
The invention has the main advantages of being simple to implement, cost-effective and easy to adapt to a stealth embodiment and to existing radars.
Other characteristics and advantages of the invention will appear more clearly in the description which follows and which refers to the appended figures which show: -figure 1, a diagram of the principle of the invention: -figure 2, a possible embodiment of means for modulating the transmitted power and the received signal: -figure 3, a possible embodiment of a circuit for preventing the display of false blips.
Figure 1 illustrates by means of a chronogram the operating principle of the invention. The transmitted power of the radar is increased by XdB, while the received wave is significantly reduced by the same number X of dB.
Figure 1 shows a chronogram relating to four successive recurrences N, N+1, N+2 and N+3 of transmission E of a radar. This chronogran, illustrates the representation of real and false targets given by blips 1, 2 and 3. A first blip 1 corresponds, for example, to a real target, while blips 2 and 3 are false blips.
In first recurrence N, the transmitted power is increased and the received signal is reduced by the same proportion.
In second recurrence N+1, the transmitted power is nominal, and is not increased. The received signal is not modified, that is it is not significantly reduced.
In third recurrence 14÷2, as in first recurrence N, the transmitted power is increased and the received signal is reduced by the same proportion.
In fourth recurrence 14+3, as in second recurrence 14÷1, the transmitted power is nominal and the received signal is not modified.
For the recurrences which follow the same law of transmitted power and received signal modulation is applied as in the first four recurrences N, 14+1, N+2 and 14÷3.
By operation of the invention,instead of being increased, the transmitted power can be reduced. In this case, the received signal is, for example, increased by approximately the same proportion.
Real blip 1 is, for example, not modified from one recurrence to another and remains approximately constant, while false blips 2 and 3 follow the law of modulation of the received signal. They are significantly greater at recyrrences N and N+1 in the context of a modulation law as illustrated in figure 1.
By the invention, the modulation of the transmitted power and of the received signal, in approximately equal proportions, enables a distinction to be made between real and false blips, as the real blips remain approximately unaffected by the signal modulation. The false blips, due notably to the scramblers, approximately follow the law of transmitted power and received signal modulation, that is they register an increase or decrease according to the modulation law implemented.
According to other laws of modulation, the false blips may remain constant and the real blips may vary.
It would be possible to increase or decrease the transmitted signal and the received signal by different proportions.
This would still enable the discrimination of real and false blips.
The embodiment can consist notably in increasing the power without creating attenuation in the radar receive chain. The real blips are thus is increased and the false blips remain at a constant level from one recurrence to another.
One advantage of the invention which relates to the power modulation, lies in the fact that it can be used with a stealth mode in which the radar transmits at as low a level as possible.
Furthermore, a DRFM cannot adapt transmitted power to received power in real time. It is therefore not able to generate blips before the carder on which it is located, for example an aeroplane or a target attempting to scramble the radar, and cannot guard against the effects of the modulation according to the invention.
By carrying out pseudo-random or random variations of power and frequency, and comparing the relative power levels of the blips with the pulses by which they have been generated, it becomes clear that only real blips have an invariable amplitude, or that only false blips are invariable if the received signal has not been modulated. The false blips generated by the scramblers fluctuate with the power variations of the transmitter, since the fluctuation of the received signal follows this variation. Amplitude correlation can then be used to distinguish between the real andhlse blips.
By combining the use of code changes from pulse to pulse, noise transmission by an auxiliary antenna to cover the side lobes and diffuse lobes of the main antenna, power modulation as described previously and amphtude correlation of the received targets it should be possible to eliminate the false blips generated by a DRFM satisfactorily.
There are two scenarios in particular which should be envisaged.
In the first case, the scrambler is lodated in the axis of the main beam of the radar antenna. If the DREM cén adapt to the received power, which is not the aim of scramblers which are designed to transmit as much as possible, it can only generate blips after the carrier on which it is installed.
This is much less disruptive than receiving blips before the carrier.
In the second case, the scrambler is located in the side lobes or diffuse lobes of the antenna. The power fluctuations are naturally very great in the diffuse lobes. The DRFM can therefore not adapt correctly to the transmitted power level.
One problem with the invention may be caused by the instantaneous power variation which affects the stability of the transmission, as the mean operating level of the transmitter is disrupted. This produces a residual instability. The operating mode according to the invention can therefore only be used when the assumption that false blips are present is well-founded. It is possible, however, to implement a solution to overcome this instability. This solution consists in switching the transmitted signal amplifier on a charge. In this way the transmitter transmits on a permanent basis and consequently does not cool down, thereby eliminating the instability almost completely.
Figure 2 shows a possible embodiment of the part of a device according to the invention which is applied to the transmit/receive chain of a radar. This part includes means for modulating the output power of the transmitter 22. The output of the modulation means 21 is, for example, connected to the input of a duplexer, 23, of which one output is connected to the antenna 24 of the radar and the other is connected to the receive chain.
The means of modulating the received signal are, for example, integrated into the receive chain. These moculation means consist of, for example, a variable gain amplifier 25 connected between the mixer 23 and the receiver 26. Amplifier 25 is, for example, controlled in such a way as to reduce the received signal by approximately the same proportion as the transmitted signal is increased.
Means 21 for modulating the transmitted power consist of a division circuit, for example, at the input of a first amplifier 212 connected to a first output of division circuit 211 and operating on a permanent basis, of a second amplifier 213 connected to the other output of division circuit 211 and a summing circuit 214 whose inputs are connected to the outputs of amplifiers 212 and 213, and whose output is connected to summing circuit 23. The power modulation is carried out, for example, by second amplifier 213. This operates, for example, in "all or nothing" mode. To avoid the aforementioned transmission instability problem, second amplifier 213 can, for example, be switched on a hyperirequency charge when it is not in use, to increase the transmitted signal.
The circuit 27 which controls the means 25 of modulating the amplitude of the received wave is connected, when these mean are used, to the control circuit of second amplifier 213 so that, if this latter increases the power at a recurrence N, received wave modulation means 25 reduce this wave at the same recurrence N. Control circuit 25 is, for example, the gain control circuit of a variable gain amplifier.
Figure 3 shows a possible embodiment of the means of distinguishing between real signals and those caused by the scrambler, as well as means of inhibiting the display of the corresponding false blips.
These means use, for example, an amplitude correlation circuit.
This circuit is illustrated in figure 3.
The embodiment in figure 3 has a pulse compression circuit 31 at input, followed by filters 32 then a circuit 33 to calculate the moduli of the received signals. The output of circuit 33 is connected on the one hand to a modulus mernorisation circuit 34, and on the other to an extraction circuit 35.
Memorisation circuit 34 memorises at least the moduli of two successive recurrences N and N+1. Its output is connected to a subtraction circuit 36 which calculates, for example, the absolute value of the difference between two moduli corresponding to two successive recurrences.
If value A corresponds, for example, to the modulus of the received signal at recurrence N, and value B is the modulus of the received signal at the following recurrence N+1, and if IA-B I > S. where S is a given threshold, then the blip which corresponds to these two successive signals is a false blip, particularly in the case where the received signals are reduced by approximately the same proportion as the transmitted signal is increased.
If only the transmitted signal is modulated, a false blip then corresponds to I A-SI <S.
The output of subtraction circuit 36 is, for example, connected to the input of a comparator 37, the other input of which is connected to a threshold which is predefined or dependent on the attenuation value 371.
The output of comparator 37 is connected to the input of a message or blip forming circuit 38, the other input of which is connected to the output of extraction circuit 35. If the comparator detects, for example, that the output of subtracting circuit 36 is greater than threshold 371, the signals output by the extraction circuit are generated by scramblers. In this case the comparator sends a signal to message forming circuit 38 to inhibit the formation of messages, and therefore prevent the display of a false blip which corresponds to scrambler signals.
Claims (11)
- CLAIMSl.A device for eliminating false radar blips injected from the digital memory of a scrambler, which consists of means for modulating the radar transmitted power from one recurrence to another and means of distinguishing real blips from false blips caused by the scrambler, where real blips and false blips vary to different extezis according to the law of transmitted power modulation.
- 2. A device according to claim 1, which includes means for modulating the signals by the radar, such that if the transmitted signal is increased at a recurrence, the received signal is reduced at the following recurrence.
- 3. A device according to claim 2, wherein the rec- eived signal is reduced by the same proportion as the trans-mitted signal is increased.
- 4. A device according to any oneof the preceding claims wherein the means for distinguishing between real blips and false blips consist of at least one modulus mem-orisation circuit for the received signals, a subtracting circuit and a comparator, and wherein said at least one memorisation circuit memorises at least the signals received from two successive recurrences, said subtracting circuit produces the absolute value of the difference between the two aforementioned signals and said comparator compares this difference with a given threshold, and wherein the result of the comparison indicates the presence of a signal generated by the scrambler in accordance with the laws of modulation of transmitted and received signals.
- 5. A device according to claim 4 wherein if the transmitted signal is increased and the received signal is reduced, a signal generated by a scrambler is present if the output of said subtracting circuit is greater than threshold value.
- 6. A device according to claim 4, wherein if the transmitted signal alone is modulated, a signal generated by the scrambler is present if the output of said subtracting circuit is less than said threshold.B
- 7. A device according to any one of claims 4 to 6, wherein the output of said comparator is connected to a blip forming circuit, whose outputs are connected to an extraction circuit for received signals, and wherein the production of blips is inhibited when the result of the comparator ind-icates the presence of a received signal generated by the scrambler.
- 8. A device according to any one of the previous claims wherein said means for transmitted power modulation include at least one division circuit at an input, two amp-lifiers, and a summing circuit at an output, and wherein the input of a first of the amplifier is connected to a first output of a division circuit, and an input of the second amplifier is connected to a second output of the division circuit, and the output *of the amplifiers is con- nected to the inputs of the sununing circuit, and power mod-ulation is carried out by the second amplifier.
- 9. A device according to claim 8 wherein the sec-ond amplifier operates in "all or nothing" mode.
- 10. A device according to claim 9, wherein the second amplifier does not increase the transmitted power and its output is switched on a hyperfrequency charge.
- 11. A device for eliminating false radar blips injected from the digital memory of a scrambler, sub-stantially as deEcribed hereinbefore with reference to the accompanying diawings and as illustrated in either Figure 2 or Figure 3 or in Figures 2 and 3 of those drawings.Amendments to the claims have been filed as followsCLAIMSl.A device f or eliminating false radar blits injected from the digital memory of a scrambler, which comprises means for modulating the radar transmitted power from one recurrence to another and means of distinguishing real blips from false blips caused by the scrambler, where real blips and false blips vary to different exter according to the law of transmitted power modulation.2. A device accordina to claim 1, which. includes means for modulating the signals received by the radar, such that if the transmitted signal is increased at a recurrence, the received signal is reduced at the same recurrence.3. A device according to claim 2, wherein the rec- eived signal is reduced by the same proportion as the trans-mitted sional is increased.4. A device according to claim 1, which includes means for modulating the signals received by the radar, the two modulating means being operable such that: in a first recurrence N, the transmitted power is increased and the received signal is reduced by the same proportion; in a second recurrence N+1. the transmitted power is nominal, and is not increased and further, the received signal is not modified; in a third recurrence N+2, as in first recurrence N, the transmitted power is increased and the received signal is reduced by the same proportion; and in-a fourth recurrence N÷3, as in second recurrence Ni-i, the transmitted jower is nominal and the received signal is not modified, the same law of transmitted power and received signal modulation being applicable for' following recurrences as in the first four recurrences N, N+1, N+2 and N÷3.5* A device according to any one of the preceding claims wherein the means for distinguishing between real blips and false blipâ consist of at least one modulus mem-orisation circuit for the received signals, a subtracting ci±cuit.and a comparator, and wherein said at least one memorisation circuit memorises at least.the signals received from two successive recurrences, said subtracting circuit produce5 the absolute value of the difference between the two aforementioned signals and said comparator compares this difference with a given threshold, and wherein the result of the comparison indicates the presence of a signal generated by the scrambler in accordance with the laws of modulation of transmitted and received signals.6. A device according to claim 5, wherein if the traismitted signal is increased and the received signal is reduced, a signal generated by a scrambler is present if the output of said subtracting circuit is greater than threshold value.7. A device according to claim 5, wherein if the transmitted signal alone is modulated, a signal generated by the scrambler is present if the output of said subtracting circuit is less than said threshold.8. A device accord-ins to any One of claims 5 to 7, wherein the output of said comparator is connected to a blip forming circuit, and an input of the blip forming circuit is connected to an extraction circuit for received signals,and wherein the production of blips is inhibited when the result Of the comparator ind-icates the presence of a received signal generated by the scrambler.9. A device according to any one of the previous claims wherein said means for transmitted power modulation include at least one division circuit at an input, two amp..liE iers, and a summing circuit at an output, and wherein the input of a first of the amplifier is connected to a first output of a division circuit, and an input of the second amplifier is connected to a second output of the division circuit, and the output of the amplifiers is con- nected to the inputs of the summing circuit, and power mod-ulation is carried out by the second amplifier.10.. A device according to claim 4 wherein the sec-ond amplifier operates in "all or nothing" mode.ii.. A device for eliminating false radar blips injected from the digital memory of a scrambler, sub-stantially as described hereinbefore with reference to the accompanying drawings and as illustrated in either Figure 2 or Figure 3 or in Figures 2 and 3 of thos! drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR9513662 | 1995-11-17 |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9623771D0 GB9623771D0 (en) | 2014-06-04 |
| GB2517663A true GB2517663A (en) | 2015-03-04 |
| GB2517663B GB2517663B (en) | 2016-03-30 |
Family
ID=50928900
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9623771.4A Expired - Fee Related GB2517663B (en) | 1995-11-17 | 1996-11-14 | Device for eliminating false radar blips injected from the digital memory of a scrambler |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2517663B (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105572643A (en) * | 2015-12-22 | 2016-05-11 | 河海大学 | Radar signal emission method for resisting radio frequency storage forwarding interference |
| CN107422311A (en) * | 2017-07-03 | 2017-12-01 | 上海无线电设备研究所 | A kind of anti-distance based on α β filtering tows method |
| EP3339876A1 (en) * | 2016-12-20 | 2018-06-27 | Rheinmetall Air Defence AG | Method for operating a radar system for preventing deception by third parties |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4384292A (en) * | 1970-08-04 | 1983-05-17 | Prime Jr Kermit L | Electronic counter-counter-measure device |
| US4713662A (en) * | 1986-10-17 | 1987-12-15 | Westinghouse Electric Corp. | Modulated digital radio frequency memory |
-
1996
- 1996-11-14 GB GB9623771.4A patent/GB2517663B/en not_active Expired - Fee Related
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4384292A (en) * | 1970-08-04 | 1983-05-17 | Prime Jr Kermit L | Electronic counter-counter-measure device |
| US4713662A (en) * | 1986-10-17 | 1987-12-15 | Westinghouse Electric Corp. | Modulated digital radio frequency memory |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105572643A (en) * | 2015-12-22 | 2016-05-11 | 河海大学 | Radar signal emission method for resisting radio frequency storage forwarding interference |
| EP3339876A1 (en) * | 2016-12-20 | 2018-06-27 | Rheinmetall Air Defence AG | Method for operating a radar system for preventing deception by third parties |
| CN107422311A (en) * | 2017-07-03 | 2017-12-01 | 上海无线电设备研究所 | A kind of anti-distance based on α β filtering tows method |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2517663B (en) | 2016-03-30 |
| GB9623771D0 (en) | 2014-06-04 |
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| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20160630 |