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
  • G01S7/38—Jamming means, e.g. producing false echoes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
  • H01Q15/14—Reflecting surfaces; Equivalent structures
  • H01Q15/18—Reflecting surfaces; Equivalent structures comprising plurality of mutually inclined plane surfaces, e.g. corner reflector
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
  • H01Q15/14—Reflecting surfaces; Equivalent structures
  • H01Q15/18—Reflecting surfaces; Equivalent structures comprising plurality of mutually inclined plane surfaces, e.g. corner reflector
  • H01Q15/20—Collapsible reflectors

Definitions

• the present invention relates to a decoy for deceiving Doppler radar systems.
• Decoys in all forms have constituted and still constitute an important component for deceiving the many sensor systems of war, anything from the eyes of the individual soldier to the ground or air-borne radar system.
• Chaff (bundles of strips) has previously been used as decoy for deceiving radar. If the metallised strips are of a length which is suitably adapted to the radar frequency of the radar that is to be misled, a strong resonance is obtained. The strips that are dispersed from aircraft in bundles then cause echoes that can mislead the radar or conceal the aircraft.
• a pulsed Doppler radar uses the Doppler effect (phase variation from pulse to pulse in the radar echo) to distinguish reflecting objects moving fast in relation to the radar station and stationary objects.
• Doppler radar systems for rejecting ground echoes therefore renders the capability of the bundle of strips of effective misleading impossible.
• Modern decoy solutions often consist of active jamming transmitters which are launched from the aircraft or hauled thereby.
• a pure amplification and transmission of the radar pulse cannot be carried out with isotropic transmitting and receiving antennae owing to insufficient insulation (results in so-called feedback).
• Other active solutions using e.g. microwave memory and delayed transmission result in distortion of the pulse shape.
• Narrow band jamming as well as wide band jamming are known.
• Equipment for jamming by narrow band noise is sensitive to a frequency change of the radar and requires equipment for searching over the frequency band for the new frequency. Wide band noise requires high power output. All in all, active decoys will necessarily be relatively expensive and complicated equipment.
• the present new passive decoy solution eliminates all the restrictions that are connected with traditional passive and active decoys.
• a decoy in the form of a modulated corner reflector has a combination of properties which is new in the context and which comprises:
• Fig. 1 illustrates a corner reflector where one of the three surface planes constitutes a modulatable plane of reflection
• Fig. 2 shows the composition of the modulatable plane of reflection in the form of a wire structure which in the crossing points is connected by a diode structure
• Fig. 3 shows an activated decoy for air-borne application with protective casing and box for support electronics and battery.
• the decoy consists of a radar-cross-section-modulated corner reflector according to Fig. 1 , where two surfaces 2 are metallised and thus fully reflective.
• the reflection of the third surface 1 may be varied, which implies that the total decoy surface is modu- lated.
• the radar-cross-section-modulation will be seen in all directions of incidence except in parallel incidence with the modulated surface.
• Such a radar-cross-section-modulation involves an amplitude modulation of the pulse train of the radar, which generates symmetric Doppler sidebands on both sides of the base frequency.
• the base frequency is the Doppler-shifted radar frequency.
• the sidebands are separated with modulation frequency.
• the decoy After launching, the decoy will quickly assume wind velocity, and therefore the Doppler frequency will be low compared with aircraft. Since the modulation is carried out as a square wave variation, this implies for all pulsed Doppler radar systems (LPD, MPD and HPD systems) that a plurality of modulation tones, above as well as below ground returns, are to be found in the passband active for the radar. Besides, if the modulation frequency is varied (swept), said tones will migrate in a natural fashion in the field of analysis of the radar.
• a launching situation which is suitable for an aircraft is when turning through the O-Doppler (transverse course relative to lobe direction), since a Doppler radar will then be forced to reject also the target, and the probability of relocking on the decoy is great.
• the modulation frequency should suitably be swept in the typical Doppler area close to the 90-degrees-sector position, for instance from 0 to 9 kHz on X-band.
• the sweeping velocity should correspond to a typical aircraft operation seen in Doppler frequency, for instance 3 kHz/s on X-band.
• a further convenient launching procedure involves the increasing of the distance uncertainty of the radar by active noise, whereupon the noise jamming is interrupted at the time of launching, and the radar locks on the decoy.
• reflection against the decoy takes place without the pulse form and the wave form otherwise changing. This implies that radar systems having different wave form techniques (for instance, different pulse compression techniques) will receive echo returns which conform with the returns from physical targets. Thus, such echo returns cannot be readily distinguished as false ones.
• the controllable surface may consist of lines in a check pattern according to Fig. 2, where each cross 4 in the check pattern is connected by a switching element.
• the switching element may consist of a diode bridge 5.
• the diodes can be PIN diodes.
• the diode bridge 5 may consist of four diodes, where the diodes are arranged such that, in forward voltage, current is conducted from the upper arm into the three other arms. In this position, both vertical and horizontal lines will thus be conducting and the surface as such will be strongly reflecting. In reverse voltage, all diodes, however, will be operated in reverse voltage and no current flows in the line pattern. The surface will assume a pattern of dipoles which, if they are shorter than half a wavelength of the incident radar frequency, give the surface its low reflection. It should be noted that this special diode constellation means that the entire surface can be operated by a very simple feeding network that does not interfere with the conductor network for radar-cross-section-modulation.
• the decoy can be optimised for various frequency ranges.
• the following dimensioning can be suitable for X-band:
• both the two conductive surfaces and the modulating surface can be made of a flexible, foldable material, e.g. a foil-prepared fabric or a line-etched flexible dielectric.
• the diode bridges have been applied by automatic soldering.
• the surfaces and the support electronics with battery are packed in a box of the size 100 - 200 c ⁇ A
• a gas cartridge is activated, which develops a protective casing 7 (balloon, cf. air bag) which in turn fixes the reflector planes according to Fig. 3.
• the support electronics and the battery 6 constitute a stabilising weight, such that the modulating surface 1 after stabilisation is vertical and thus minimises the risk of situations with radar reflection below a low modulation index.
• the gas cartridge can suitably contain some light inert gas, for example helium, which extends the time of function in the air.
• decoys for ground use can be made considerably simpler with rigid planes of reflection and a simple plastic cover as radome.
• the basic rules for interference action against Doppler radar follow the above description in all essentials.
• Attack and reconnaissance systems which utilise the fact that different ground elements within the main lobe of the antenna get a varying Doppler frequency for Doppler beam sharpening can also be interfered with by the proposed decoy.
• a random frequency control should then suitably be selected to interfere with the Doppler filtration of the radar.
• controllable surface comprises lines in a check pattern.
• An alternative way of producing this surface is to use a conducting surface having a slotted pattern being separated from a second conducting surface via a dielectric. (In a similar way as a printed circuit with a metallised surface on both sides.) Across the respective slot an element with a varying impedance is connected, e.g. a diode. If the diodes are fed by a varying voltage, a varying reflectivity in the surface will be the result. The function will be the same as for the embodiment of the decoy discussed above.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• General Physics & Mathematics (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Radar Systems Or Details Thereof (AREA)

Priority Applications (8)

Applications Claiming Priority (1)

Publications (1)

Family

ID=38723548

Family Applications (1)

Country Status (7)

Cited By (4)

Citations (8)

• 2006
  • 2006-05-19 BR BRPI0621762-1A patent/BRPI0621762A2/pt not_active IP Right Cessation
  • 2006-05-19 WO PCT/SE2006/000589 patent/WO2007136308A1/en active Application Filing
  • 2006-05-19 CA CA002652984A patent/CA2652984A1/en not_active Abandoned
  • 2006-05-19 EP EP06747794A patent/EP2033012A1/en not_active Withdrawn
  • 2006-05-19 AU AU2006344025A patent/AU2006344025A1/en not_active Abandoned
• 2008
  • 2008-11-16 IL IL195322A patent/IL195322A0/en unknown
  • 2008-12-16 NO NO20085260A patent/NO20085260L/no not_active Application Discontinuation

Patent Citations (8)

Non-Patent Citations (1)

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