FR2740226A1 - Jamming system for prevention of radar detection and measurement - Google Patents

Abstract

The procedure provides a jamming system for radar capable of coherent suppression of secondary lobes. From a source of jamming signals (SBR) two supply channels are created. These include two transmission amplifiers respectively (AE1, AE2) which supply two transmission aerials (AP1, AP2) operating in different polarisations. One at least of the channels is subject to rapid time variations w.r.t. the other, operating for example with a programmable length line (LLP). The time variation is more rapid than the estimate response time of the detectors or radars which are to be jammed.

Description

Improved jamming process.

  The invention relates to the jamming of electronic detectors.

  magnetic, in particular of radars.

  The implementation of such interference is called

  a "countermeasure". The radar will respond with 'counter

  countermeasures. "These may include implementing

  work of "holes" in the antenna reception diagram -

  radar, as described for example in the Patent Application

Applicant's N 83 16653.

  But advanced interference now uses lobes

side of the radar antenna.

  The appropriate countermeasure is consistent suppression

  secondary lobe rent ("Coherent Side Looking Cancella-

  tion "). It involves an auxiliary antenna at the radar level. The radiation picked up by the latter is used, after treatment, to cancel unwanted responses from the side lobes of the radar antenna. a kind of neutrodynage, which involves enslavement

  between the auxiliary antenna and the main radar antenna.

  The object of the present invention is to seek to

  lack of such countermeasures.

  It is based first of all on the remark that the said subject

  reacts with a certain delay which can be defined

by a time constant.

  It is also based on the remark that an aerial has not

  only normal side lobes, but also a "dif-

  was "due to backscattering of elements close to the year-

  and that the response of the side lobes and especially

  of this "diffuse" is very different from that of the main lobe

  pal, in terms of gain as a function of the polarization of the

incident signal.

  Finally, it is based on the remark that the ability of the radar

  to implement countermeasures is necessary

  quite limited, in terms of the number of jammers treated,

  and / or processing capacity dedicated to this function.

  So, one of the basic ideas of the invention is to

  create an electromagnetic field at the radar aerials

  genetic whose polarization can be varied with a periodicity less than or equal to the response time

of the aforementioned enslavements.

  The two components (of polarization) of the electromagnetic field

  gnetics are not independent, but have a certain correlation, during a time comparable to the response time of the controls. Consequently, it is not

  not possible to discriminate them in the manner of two scrambles-

independent lages.

  Thus, the invention first of all proposes a scrambling process.

  lage of electromagnetic detectors, in particular radars, characterized by the emission of at least two electromagnetic interference signals having different polarizations, and subject to rapid temporal variations

relative to each other.

  Very advantageously, the two signals come from the same interference source. One of the two signals then undergoes

  a time difference or a phase shift variable over time.

  It is very interesting that this variation over time is made faster than the time constant or the estimated response time of the controls used by

  detectors or radars, for the purpose of suppressing or dis-

Criminate the jammers.

  When the method is implemented against radars

  Doppler, possibly pulsed, the emission of scrambled

  ge can be done in impulse form, in particular by alternating the two channels, and of course by preserving a periodicity lower than the integration time of the filters

Radar Doppler.

  The invention also provides a jamming device comprising a source of an electrical jamming signal, such as a noise of selected bandwidth, and means for amplifying and transmitting an electromagnetic signal.

  interference from this source.

  According to the invention, the transmission means comprise two antennas operating at different polarizations, and

  the amplification means have two channels for supplying

  ter these two antennas. At least one of the channels has a variable temporal signal modification device

electrical jamming.

  This temporal modification member can be a line of programmable length. In this case, said modification

  variable temporal consists of a variable temporal offset

  ble between the signals of the two channels.

  The temporal modification organ can also include

  a variable phase shifter. We then obtain a varia-

  ble between two-way signals.

  It is possible to combine the two solutions.

  The temporal variation can be controlled by a variation circuit, in particular random, provided by this effect

  to control the phase shifter and / or the line with pro-

grammable.

  In a particular embodiment, the amplification means

  Fication include, at least at their input, a controlled inverter, followed by a coupler-phase shifter (called "three decibel coupler"). Such a coupler can bring the signal from one of these two inputs (as desired) on the one hand without phase shift on one of its outputs, on the other hand with a phase shift of 90 on the other output. The inverter allows the input considered to be varied at a rapid rate,

  thus completing the effects already obtained according to the invention.

  When looking at Doppler radars,

  with pulses, change-over switches operating at a rate chosen will be provided so that the device according to the invention can provide a pulse emission,

  preferably alternating the two channels, at a higher rate

  less than the integration time of the radar Doppler filter.

  In this version, we can predict that the second of the commu-

  tateurs is followed by at least one coupler-phase shifter, arranged

like before.

  Other characteristics and advantages of the invention appear

  will review the detailed description below,

  and appended drawings, in which: - Figure 1 illustrates a first embodiment of the device according to the invention;

  - Figure 2 illustrates an alternative embodiment of the provision

  sitive according to the invention; - Figure 3 illustrates another alternative embodiment of the device according to the invention;

  - Figure 4 illustrates a version of the device according to the

  vention planned against Doppler radars; and - Figure 5 illustrates a variant of the device provided according to the invention against Doppler radars. The accompanying drawings contain elements of a certain character. As a result, they will not only be able to serve

  to make the detailed description below easier to understand,

  but also contribute to the definition of the invention, the

optionally.

  In the drawings, the reference SBR designates a source of a

electrical interference signal.

  The references AP1 and AP2 designate two antennas operating

  according to different polarizations.

  In a first case, the antenna AP1 can be a horizontal polarization antenna while the antenna AP2 is a vertical polarization antenna. These two antennas

  can also have two crossed oblique polarizations.

  They can still have one circular polarization

  the right and the other a left circular polarization.

  The antennas used can be simple antennas, or two independent array antennas transmitting according to crossed polarizations, with the same variants as above.

  Those skilled in the art will understand that it is not necessary to a-

  see antennas with the same phase center.

  When the phase centers are separate, this appears

  an additional phase difference which constitutes a

  other source of offset on delay or phase shift varies

  ble that we will impose according to the invention, between the two

  polarizations of the interference signal.

  In FIGS. 1 and 2, the output of the SBR member is applied

  than a CD coupler-distributor, which has two output channels. One of the channels is connected to a transmission amplifier AE1 followed by the antenna AP1 via a line with programmable length (LLP, figure 1) or a variable phase shifter (DPV, figure 2). The other channel can be connected directly to the transmission amplifier AE2 followed by the antenna AP2. But this second way could also be mounted like the previous one. A CVR quick-change control circuit controls the line to

  programmable length of the phase shifter, as appropriate.

  Those skilled in the art will understand that electromagnetic signals

  that interference from the two antennas AP1 and AP2 are not independent, therefore cannot be considered

  as coming from two separate jammers.

  However, since they have different polarizations and faster relative variations than

  the response time of the counter-counter servos

  measurement of hostile radar, and that the auxiliary antenna (s)

  res of it do not have the same response as the secondary lobes and especially the diffuse of its main antenna,

  it will be very difficult if not impossible for this radar to eliminate

  the effects of such interference in the signals it receives. Figure 3 illustrates a variant that makes the task of the radar

even more difficult.

  In this figure, the CR circuit can be either the line

  with programmable length LLP of figure 1, that is to say the depha-

variable variable DPV of figure 2.

  Instead of the CD coupler-distributor, a com-

  CP mutator, the two outputs of which are connected by two unidirectional transmission lines L1 and L2 to the two inputs of a three-decibel coupler CTD. Depending on whether one or other of the inputs is used, a phase jump of 90 is obtained at each of the two outputs of this coupler. This phase jump of 90 is added

  to the rapid variations provided by the CR circuit.

  The effect of the invention is thus further reinforced.

  We can describe this effect more precisely as follows:

  - To eliminate a normal stationary jammer (different

  rent of those of the invention) having a narrow emission spectrum, it suffices an auxiliary antenna pointed in

  the direction where you want to perform this elimination.

  Even if you use two auxiliary antennas to try to discriminate the two interference signals of different polarization, this will not work because the two auxiliary antennas will see signals which present between them

  a certain correlation, over a time comparable to the cons-

  aunt of the radar countermeasures time control.

  The two auxiliary antennas will therefore in fact have the im-

  pressure to treat a single jammer.

  - When the interference spectrum is wider, the diffi-

  cultivation is further increased, owing to the fact that the ratio of the two signals emitted by the jammer according to the invention can also be variable with the frequency, because one can modify its radiation patterns, or even make it evolve

polarization with frequency.

  It therefore appears that the radar task is seriously

  complicated, in the presence of a jammer according to the invention.

  In practical situations, the speed camera will be in the pre-

  several jammers of this type. The presence of several jammers according to the invention makes

  quickly illusory the form of electronic countermeasure

  tronic of the type coherent suppression of secondary lobes.

  Indeed, because of the risks of pumping out of the control system incorporated into this countermeasure, the implementation of this latter can prove to be much more harmful than useful, and this is precisely the aim sought by the interference

according to the invention.

  An interesting application consists in seeking to facilitate the penetration of an air raid. By equipping the raid's aircraft with jammers operating against the same radar,

  we will soon be able to saturate the processing capacity

  of these radars, in terms of the number of auxiliary channels

  independent res capable of neutralizing each a jam

  their. In addition, the radar processing system will need to do

  in the face of very many amb guitars, when he wants

  guler all the interference sources thus defined by the various aircraft carrying devices according to the invention. If we consider for example three real sources of interference, these will create six phantoms that the radar will have to discriminate before implementing

  these countermeasures. More generally, for n sour-

  these interference according to the invention, the number of ghosts is n (n-l). This number grows very quickly with the number

  sources of interference used.

  The devices which have just been described work

with regard to any type of speed camera.

  When it is only desired to be able to counter Doppler radars or pulse Doppler radars, a single transmitter may suffice in the device according to the invention, if it

  is switched in a shorter time than the integration time

  grating of the Doppler filters between the polarized antennas

cross tion.

  Thus, in Figure 4, we observe that the two amplifications

  emission sensors AE1 and AE2 in FIG. 1 are replaced by a single amplifier AE, surrounded by two inverters

  SB1 and SP controlled by a pulse modulation circuit

We are MI.

  Here we use a power switch SP, which supplies

the two antennas AP1 and AP2.

  In the variant according to FIG. 5, the switching takes place

  at the low level, that is to say on either side of an amplification

  tor AB, in the form of two inverters SBl and SB2.

  It is then possible to put following the switch

  downstream SB2 two unidirectional links Lll and L12, followed

  lives of a CTDl three decibel coupler. The two outings

  in quadrature of it are applied to two amplifications

  AE1 and AE2 transmitters, followed by a second three-decibel CTD2 coupler, the two quadrature outputs

supply the antennas APl and AP2.

  This arrangement not only provides the temporal variations linked to the use of the CR circuit (which is a line with programmable length LLP and / or a variable phase shifter DPV), but also the interesting effect of the sudden phase jumps that

  have already been described in connection with FIG. 3.

  The Applicant has observed that the devices according to the

  vention allow an average gain of ten decibels in the effectiveness of interference penetrating outside the main lobe of the aerial of a radar. This is because,

  generally, the diagrams according to the 2 cross polarizations

  are substantially complementary to each other in

  side lobes and diffuse.

Claims (11)

Claims.   1. A method of jamming electromagnetic detectors, in particular radars, characterized by the emission (AP1, AP2) of at least two electromagnetic interference signals having different polarizations and subject to   rapid time variations from one another.   2. Method according to claim 1, characterized in that 1O the two signals come from the same interference source (SBR), at least one of the two undergoing a time shift   (LLP) or a variable phase shift with time (DPV).   3. Method according to claim 2, characterized in that said variation with time is faster than the estimated response time of the detectors or radars in suppression or discrimination from jammers.   4. Method according to one of the preceding claims, des-   tined to operate against Doppler radars, possibly   pulse, characterized in that the emission of scrambled   ge is impulse, in particular alternating (MT), with a periodicity lower than the integration time of the filters Radar Doppler.   5. Jamming device comprising a source of an electrical jamming signal (SBR), such as a noise of selected bandwidth, and means for amplification (AE) and emission (AP) of a signal electromagnetic interference from this source, characterized in that the transmission means comprise two antennas (AP1, AP2) operating according to   different polarizations, and in that the means of   plification (AE) comprise two channels for supplying these two antennas, at least one of the channels comprising a variable temporal modification member of the electrical signal interference (LLP, DPV).   6. Device according to claim 5, characterized in that the temporal modification member comprises a line programmable length (LLP).   7. Device according to one of claims 5 and 6, charac-   terized in that the temporal modification organ includes a variable phase shifter (DPV).   8. Device according to one of claims 5 to 7, charac-   terized in that the temporal variation is controlled by   a variation circuit, in particular random (CVR).   9. Device according to one of claims 5 to 8, charac-   characterized in that the amplification means comprise, at the input, an inverter (CP) followed by a coupler-phase shifter (CTD).   10. Device according to one of claims 5 to 9, charac-   Terrified in that the amplification means include reversing switches (SB1, SB2) operating at a rate   chosen, for impulse transmission.   11. Device according to claim 11, characterized in that the second (SB2) of the switches is followed by at least a coupler-phase shifter (CTD1).