EP0669674A1 - Device for camouflaging antennas - Google Patents

Device for camouflaging antennas Download PDF

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Publication number
EP0669674A1
EP0669674A1 EP94119638A EP94119638A EP0669674A1 EP 0669674 A1 EP0669674 A1 EP 0669674A1 EP 94119638 A EP94119638 A EP 94119638A EP 94119638 A EP94119638 A EP 94119638A EP 0669674 A1 EP0669674 A1 EP 0669674A1
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EP
European Patent Office
Prior art keywords
antenna
layer
microwaves
magneto
polarizer
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Granted
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EP94119638A
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German (de)
French (fr)
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EP0669674B1 (en
Inventor
Joachim Dr. Kaiser
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Airbus Defence and Space GmbH
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Daimler Benz Aerospace AG
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Publication of EP0669674A1 publication Critical patent/EP0669674A1/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
    • H01Q17/007—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems with means for controlling the absorption
    • 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
    • H01Q15/0006—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices
    • H01Q15/0013—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective
    • 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
    • H01Q15/148—Reflecting surfaces; Equivalent structures with means for varying the reflecting properties
    • 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
    • H01Q15/22—Reflecting surfaces; Equivalent structures functioning also as polarisation filter

Definitions

  • the present invention relates to a device for camouflaging antennas against the location by microwaves.
  • camouflage consists of using only very narrow-band frequency-selective layers to allow only the useful signal frequency of the radio system belonging to the antenna to reach the detector, but to deflect and / or absorb all other frequencies .
  • the main reflector of a parabolic antenna can be constructed from a broadband radar absorber, the outer surface of which has a frequency-selective reflective film which is matched to the radio frequency.
  • the radome can also be constructed in a frequency-selective manner, i.e. be transparent only for the useful frequency and reflective for other frequencies.
  • the present invention has for its object to provide a device for camouflaging antennas against the location by microwaves, which enables considerably better camouflage, especially against impinging microwaves, the frequencies of which differ only slightly from the frequencies of the useful waves of the antenna.
  • the device consist of an electromagnetically non-reciprocal component, which is arranged in front of the antenna as seen in the direction of incidence of the microwaves.
  • the non-reciprocal component has the shape of a radome arranged at a distance in front of the antenna and contains a magneto-optical layer which is surrounded by a ring magnet and which is covered on both sides by a polarizer layer, which is highly transparent have a given linear polarization direction and have a high absorption for the polarization directions perpendicular thereto, the two polarization layers being arranged rotated by 45 to one another.
  • the magneto-optical layer is advantageously a so-called Faraday rotator, which rotates the electromagnetic, linearly polarized waves penetrating it by 45 and which consists of a ferrite and / or garnet.
  • the polarizer layers advantageously consist of thin strips of an absorber arranged parallel to one another.
  • Each polarizer layer can be provided on the surface facing away from the Faraday rotator with a quarter-wavelength layer made of a uniaxially anisotropic material for transforming circularly polarized waves into linearly polarized waves.
  • the magneto-optical layer is applied directly to the surface of the antenna facing the incident microwaves and if the two polarizer layers are rotated by 45 on the one hand on a radome aperture and on the other on the subreflector or exciter or detector are arranged.
  • radio signals in the range of the useful frequency can only penetrate from the outside to the antenna at a certain time or can be radiated from the antenna to the outside.
  • Radio signals of a different frequency can be deflected and / or absorbed in a known manner, with frequency-selective layers and broadband radar absorbers again being able to provide additional support.
  • Another advantage is that the selectivity of a frequency-selective layer for supplementary external frequency camouflage is subject to less stringent requirements; it can be weakened to the range of effectiveness of the non-reciprocal layer; if the effective range of the non-reciprocal layer is sufficient, supplementation by conventional camouflage measures may not be necessary.
  • Non-reciprocal phenomena here are preferably understood to mean magneto-optical effects which are based on the reciprocity law for electromagnetic waves formulated by Helmholtz and which presuppose that an additional magnetic field is present (Bergmann / Schaefer "Textbook of Experimental Physics", Volume 111 Optics (Walter de Gruyter -Verlag, Berlin) Other non-reciprocal effects may also be useful.
  • Fig. 1 denotes an antenna which is connected via a line 2 to a radio system, not shown.
  • the level in the radome aperture is designated by 3, a device according to the invention for camouflaging the antenna 1 against the location by opposing microwaves being arranged in this level.
  • the device consists of an electromagnetically non-reciprocal component, which has a non-reciprocal layer 4, which is arranged in level 3 of the radome aperture.
  • the non-reciprocal layer 4 is surrounded by a ring magnet 5, which generates the necessary magnetic field in the aperture. Both electric and permanent magnets can be used.
  • Electromagnets offer the advantage of switching between the transparency states of the component.
  • a homogeneous field can be achieved in the area of the non-reciprocal layer 4 of the component.
  • a variation of the magnetic field over the aperture can possibly be used to increase the effective bandwidth or prevents a reduction in the effectiveness of the camouflage when the cross-sectional area of the antenna is smaller than the aperture, since penetrating waves of the locating radar do not hit the antenna at the edge of the aperture and therefore do not be reflected.
  • a so-called Faraday rotator made of ferrites and / or grenades, as they come into question can also be used for directional lines in HF technology.
  • Layer 4 is designed for a rotation by 45 for frequencies in the region of interest here.
  • a polarizer layer 6, 7 is applied to both sides of this non-reciprocal layer 4, each of which has a high transparency for a predetermined polarization direction and a high absorption for the polarization direction perpendicular thereto.
  • the two polarizer layers 6, 7 are arranged rotated relative to one another by 45. 8 also denotes a holder for the ring magnet, the non-reciprocal layer and the two polarizer layers.
  • the direction of the applied magnetic field determines the transparency state of the radome, i.e. the transmission or reception transparency.
  • the polarizer layers 6, 7 can advantageously be constructed from thin strips of an absorber arranged in parallel, the field components being absorbed parallel to the strips, but those being transmitted perpendicularly thereto.
  • the use of non-reciprocal effects for the purpose of camouflaging the antenna means that the backscattering of the opposing electromagnetic waves used for the location is largely avoided.
  • the backscatter cross section can have very large values and thus destroy the camouflage measures used in other places.
  • the transmission of the radome takes very high values in the receiving direction and very low values in the transmitting direction, the incident wave of the locating radar can penetrate to the antenna, but cannot emerge again, in order to provide an echo to the locating radar.
  • the antenna camouflaged in this way can receive incoming signals with only slight attenuation.
  • the antenna If the antenna is also to transmit, the direction of transparency must be reversed, for which the cause of the measures causing the non-reciprocal effects (for the magneto-optical effect the applied magnetic field) must be reversed.
  • the electromagnetic wave of the location radar cannot penetrate the radome.
  • suitable anti-reflective coatings on the radome as are known from optics, the wave penetrates into the radome and is absorbed there.
  • the camouflaged antenna can transmit its signals with only a small amount of attenuation.
  • the radome must be switched to "transmission transparency” in the relatively short transmission phases and to "reception transparency” during the rest of the time.
  • Anti-reflective coatings on the radome are useful not only for the absorption of incident waves in the state of transmission transparency, but also for increasing the radome transparency for the transmitted useful signals and for reducing the reflection in the state of reception transparency.
  • the antenna to be camouflaged is a mirror antenna, for example a parabolic antenna 11, as shown in FIG. 2, a part of the antenna itself can be made non-reciprocal instead of or in combination with it.
  • the non-reciprocal layer 14, ie the Faraday rotator is applied to the antenna surface 19 in the form of the latter.
  • the two polaris twisted by 45 to each other Sator layers 16, 17 can in this case be arranged on the one hand on the radome aperture, the level of which is designated by 13 in FIG. 2, and on the other hand on the subreflector or exciter and / or detector 20.
  • 18 also here again denotes a holder for the radio aperture, 15 a ring magnet surrounding the non-reciprocal layer and 12 a connection to a radio system.
  • the useful signal of the antenna to be camouflaged remains practically undisturbed if it is linearly polarized, the orientation of the polarization layers 6, 7; 16, 17 and the antenna 1 or 11 must be matched to the desired polarization direction.
  • the antenna 1 to be camouflaged is to receive or transmit circularly polarized waves in the exemplary embodiment shown in FIG. 1, this can be done by additionally providing a so-called quarter-wavelength layer 9 on each of the two outer sides of the polarizer layers 6, 7 facing away from the Faraday rotator 4 , 10 is applied from uniaxial anisotropic material.
  • the additional layers 9, 10 transform circularly polarized waves into linearly polarized waves and vice versa.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Aerials With Secondary Devices (AREA)
  • Radar Systems Or Details Thereof (AREA)

Abstract

The cloaking device uses an electromagnetically non-reciprocal component, arranged in the path of the incident microwaves in front of the antenna. The non-reciprocal component has 2 polarisation layers offset relative to one another by 45 degrees. Pref. the non-reciprocal component is provided by a radome at a given spacing from the antenna, having a magneto-optical layer (4) enclosed by an annular magnet (5), with a polarisation layer on each side of the magneto-optical layer, exhibiting a high transparency for a given linear polarisation direction and a high absorption for the perpendicular polarisation direction.

Description

Die vorliegende Erfindung betrifft eine Vorrichtung zur Tarnung von Antennen gegen die Ortung durch Mikrowellen.The present invention relates to a device for camouflaging antennas against the location by microwaves.

Bei der Tarnung gegen Radar militärischer Geräte stellen Antennen ein besonderes Problem dar. Die herkömmliche Tarnung besteht darin, unter Ausnutzung sehr schmalbandiger frequenzselektiver Schichten nur die Nutzsignalfrequenz des zur Antenne gehörenden Funksystems zum Detektor gelangen zu lassen, alle anderen Frequenzen jedoch abzulenken und/oder zu absorbieren. Beispielsweise kann der Hauptreflektor einer Parabolantenne aus einem breitbandigen Radarabsorber aufgebaut werden, dessen Außenfläche eine auf die Funkfrequenz abgestimmte frequenzselektive Reflexionsfolie besitzt. Alternativ kann auch das Radom in frequenzselektiver Weise aufgebaut werden, d.h. nur für die Nutzfrequenz transparent und für andere Frequenzen reflektierend sein.Antennas pose a particular problem when camouflaging radar from military devices. Conventional camouflage consists of using only very narrow-band frequency-selective layers to allow only the useful signal frequency of the radio system belonging to the antenna to reach the detector, but to deflect and / or absorb all other frequencies . For example, the main reflector of a parabolic antenna can be constructed from a broadband radar absorber, the outer surface of which has a frequency-selective reflective film which is matched to the radio frequency. Alternatively, the radome can also be constructed in a frequency-selective manner, i.e. be transparent only for the useful frequency and reflective for other frequencies.

Der vorliegenden Erfindung liegt die Aufgabe zugrunde, eine Vorrichtung zur Tarnung von Antennen gegen die Ortung durch Mikrowellen zu schaffen, die eine erheblich bessere Tarnung ermöglicht, insbesondere gegen auftreffende Mikrowellen, deren Frequenzen sich nur geringfügig von den Frequenzen der Nutzwellen der Antenne unterscheiden.The present invention has for its object to provide a device for camouflaging antennas against the location by microwaves, which enables considerably better camouflage, especially against impinging microwaves, the frequencies of which differ only slightly from the frequencies of the useful waves of the antenna.

Zur Lösung dieser Aufgabe wird vorgeschlagen, daß die Vorrichtung aus einem elektromagnetisch nicht-reziproken Bauelement besteht, das in Einfallsrichtung der Mikrowellen gesehen vor der Antenne angeordnet wird.To achieve this object, it is proposed that the device consist of an electromagnetically non-reciprocal component, which is arranged in front of the antenna as seen in the direction of incidence of the microwaves.

Bei einem bevorzugten Ausführungsbeispiel weist das nicht-reziproke Bauelement die Form eines im Abstand vor der Antenne angeordneten Radoms auf und enthält eine magnetooptische Schicht, die von einem Ringmagneten umgeben ist und die auf beiden Seiten von je einer Polarisatorschicht bedeckt ist, welche eine hohe Transparenz für eine gegebene lineare Polarisationsrichtung aufweisen und eine hohe Absorption für die dazu senkrechten Polarisationsrichtungen aufweisen, wobei die beiden Polarisationsschichten um 45 zueinander verdreht angeordnet sind.In a preferred embodiment, the non-reciprocal component has the shape of a radome arranged at a distance in front of the antenna and contains a magneto-optical layer which is surrounded by a ring magnet and which is covered on both sides by a polarizer layer, which is highly transparent have a given linear polarization direction and have a high absorption for the polarization directions perpendicular thereto, the two polarization layers being arranged rotated by 45 to one another.

Vorteilhafterweise ist die magnetooptische Schicht ein sogenannter Faraday-Dreher, der die sie durchsetzenden elektromagnetischen, linear polarisierten Wellen um 45 verdreht und der aus einem Ferrit und/oder Granat besteht.The magneto-optical layer is advantageously a so-called Faraday rotator, which rotates the electromagnetic, linearly polarized waves penetrating it by 45 and which consists of a ferrite and / or garnet.

Die Polarisatorschichten bestehen vorteilhafterweise aus parallel zueinander angeordneten dünnen Streifen eines Absorbers.The polarizer layers advantageously consist of thin strips of an absorber arranged parallel to one another.

Jede Polarisatorschicht kann auf der dem Faraday-Dreher abgewandten Oberfläche mit einer Viertelwellenlängenschicht aus einem einachsig anisotropen Material zur Transformation zirkular polarisierter Wellen in linear polarisierte Wellen versehen sein.Each polarizer layer can be provided on the surface facing away from the Faraday rotator with a quarter-wavelength layer made of a uniaxially anisotropic material for transforming circularly polarized waves into linearly polarized waves.

Im Falle von Parabolantennen ist es besonders vorteilhaft, wenn die magnetooptische Schicht direkt auf der den einfallenden Mikrowellen zugewandten Oberfläche der Antenne aufgebracht ist und wenn die beiden um 45 zueinander verdrehten Polarisatorschichten zum einen auf einer Radomapertur und zum anderen auf dem Subreflektor bzw. Erreger oder Detektor angeordnet sind.In the case of parabolic antennas, it is particularly advantageous if the magneto-optical layer is applied directly to the surface of the antenna facing the incident microwaves and if the two polarizer layers are rotated by 45 on the one hand on a radome aperture and on the other on the subreflector or exciter or detector are arranged.

Durch die erfindungsgemäße Verwendung elektromagnetisch nicht-reziproker Schichten wird der Vorteil erzielt, daß Funksignale im Bereich der Nutzfrequenz zu einer bestimmten Zeit nur entweder von außen bis zur Antenne vordringen oder von der Antenne nach außen abgestrahlt werden können. Funksignale abweichender Frequenz können in bekannter Weise abgelenkt und/oder absorbiert werden, wobei auch hier wieder frequenzselektive Schichten und breitbandige Radarabsorber zusätzlich unterstützend sein können.The use of electromagnetically non-reciprocal layers according to the invention has the advantage that radio signals in the range of the useful frequency can only penetrate from the outside to the antenna at a certain time or can be radiated from the antenna to the outside. Radio signals of a different frequency can be deflected and / or absorbed in a known manner, with frequency-selective layers and broadband radar absorbers again being able to provide additional support.

Gegenüber der konventionellen Tarnung mittels frequenzselektiver Schichten wird auch die Rückstreuung im Bereich der Nutzfrequenz unterbunden. Dies ist besonders vorteilhaft, da sich die Arbeitsfrequenzen der Radarsysteme um typische Frequenzstellen im Mikrowellenspektrum gruppieren.Compared to conventional camouflage using frequency-selective layers, backscattering in the area of the useful frequency is also prevented. This is particularly advantageous since the working frequencies of the radar systems are grouped around typical frequency points in the microwave spectrum.

Ein Ortung durch ein gegnerisches Radarsystem, welches auf der nahezu gleichen Frequenz arbeitet, wie die zu tarnende Antenne, ist somit bei konventioneller Tarnung durchaus möglich, nicht jedoch bei Anwendung der erfindungsgemäßen Vorrichtung.A location by an opposing radar system, which operates at almost the same frequency as the antenna to be camouflaged, is therefore entirely possible with conventional camouflage, but not when using the device according to the invention.

Ein weiterer Vorteil ist darin zu sehen, daß die Trennschärfe einer frequenzselektiven Schicht zur ergänzenden Fremdfrequenz-Tarnung geringeren Anforderungen unterliegt; sie kann auf die Bandbreite der Wirksamkeit der nicht-reziproken Schicht abgeschwächt werden; bei ausreichender wirksamer Bandbreite der nicht-reziproken Schicht erübrigt sich gegebenenfalls die Ergänzung durch konventionelle Tarnmaßnahmen.Another advantage is that the selectivity of a frequency-selective layer for supplementary external frequency camouflage is subject to less stringent requirements; it can be weakened to the range of effectiveness of the non-reciprocal layer; if the effective range of the non-reciprocal layer is sufficient, supplementation by conventional camouflage measures may not be necessary.

Unter nicht-reziproken Erscheinungen werden hier vorzugsweise magnetooptische Effekte verstanden, die auf dem von Helmholtz formulierten Reziprozitätsgesetz für elektromagnetische Wellen beruhen und die voraussetzen, daß ein zusätzliches Magnetfeld vorhanden ist (Bergmann/Schaefer "Lehrbuch der Experimentalphysik", Band 111 Optik (Walter de Gruyter-Verlag, Berlin). Andere nicht-reziproke Effekte könnten eventuell auch nützlich sein.Non-reciprocal phenomena here are preferably understood to mean magneto-optical effects which are based on the reciprocity law for electromagnetic waves formulated by Helmholtz and which presuppose that an additional magnetic field is present (Bergmann / Schaefer "Textbook of Experimental Physics", Volume 111 Optics (Walter de Gruyter -Verlag, Berlin) Other non-reciprocal effects may also be useful.

Eine bekannte Anwendung des nicht-reziproken Effektes im Zusammenhang mit Spiegel für Ringlaser ist beispielsweise in der deutschen Patentanmeldung P 32 33 035 beschrieben.A known application of the non-reciprocal effect in connection with mirrors for ring lasers is described, for example, in German patent application P 32 33 035.

Im folgenden wird die Erfindung anhand der Zeichnung näher erläutert, in der vorteilhafte Ausführungsbeispiele dargestellt sind. Es zeigen:

  • Fig. 1 einen Schnitt durch ein erstes Ausführungsbeispiel und
  • Fig. 2 einen Schnitt durch ein zweites Ausführungsbeispiel.
The invention is explained in more detail below with reference to the drawing, in which advantageous exemplary embodiments are shown. Show it:
  • Fig. 1 shows a section through a first embodiment and
  • Fig. 2 shows a section through a second embodiment.

In Fig. 1 ist mit 1 eine Antenne bezeichnet, die über eine Leitung 2 mit einem nicht dargestellten Funksystem verbunden ist. Mit 3 ist die Ebene in der Radomapertur bezeichnet, wobei in dieser Ebene eine erfindungsgemäße Vorrichtung zur Tarnung der Antenne 1 gegen die Ortung durch gegnerische Mikrowellen angeordnet ist. Die Vorrichtung besteht aus einem elektromagnetisch nicht-reziproken Bauelement, das eine nicht-reziproke Schicht 4 aufweist, die in der Ebene 3 der Radomapertur angeordnet ist. Die nicht-reziproke Schicht 4 ist von einem Ringmagneten 5 umgeben, der das notwendige Magnetfeld in der Apertur erzeugt. Es können sowohl Elektro- als auch Permanentmagnete verwendet werden. Elektromagnete bieten den Vorteil eines Umschaltens zwischen den Transparenzzuständen des Bauelementes. Durch geeignete Formgebung kann ein homoges Feld im Bereich der nicht-reziproken Schicht 4 des Bauelementes erzielt werden. Andererseits kann eine Variation des Magnetfeldes über der Apertur gegebenenfalls zu einer Erhöhung der wirksamen Bandbreite ausgenutzt werden oder verhindert bei gegenüber der Apertur kleineren Querschnittsfläche der Antenne eine Wirksamkeitsreduzierung der Tarnung, da am Rande der Apertur eindringende Wellen des Ortungsradars nicht auf die Antenne treffen und somit nicht reflektiert werden.In Fig. 1, 1 denotes an antenna which is connected via a line 2 to a radio system, not shown. The level in the radome aperture is designated by 3, a device according to the invention for camouflaging the antenna 1 against the location by opposing microwaves being arranged in this level. The device consists of an electromagnetically non-reciprocal component, which has a non-reciprocal layer 4, which is arranged in level 3 of the radome aperture. The non-reciprocal layer 4 is surrounded by a ring magnet 5, which generates the necessary magnetic field in the aperture. Both electric and permanent magnets can be used. Electromagnets offer the advantage of switching between the transparency states of the component. By means of suitable shaping, a homogeneous field can be achieved in the area of the non-reciprocal layer 4 of the component. On the other hand, a variation of the magnetic field over the aperture can possibly be used to increase the effective bandwidth or prevents a reduction in the effectiveness of the camouflage when the cross-sectional area of the antenna is smaller than the aperture, since penetrating waves of the locating radar do not hit the antenna at the edge of the aperture and therefore do not be reflected.

Als Material für die nicht-reziproke Schicht 4, welches unter dem Einfluß des Magnetfeldes, das durch den Ringmagneten 5 erzeugt wird, die Polarisationsebene elektromagnetischer linear polarisierter Wellen verdreht, kommt ein sogenannter Faraday-Dreher aus Ferriten und/oder Granaten in Frage, wie sie in der HF-Technik auch für Richtungsleitungen verwendet werden. Die Schicht 4 ist ausgelegt für eine Drehung um 45 für Frequenzen im hier interessierenden Bereich.As a material for the non-reciprocal layer 4, which rotates the plane of polarization of electromagnetic linearly polarized waves under the influence of the magnetic field that is generated by the ring magnet 5, a so-called Faraday rotator made of ferrites and / or grenades, as they come into question can also be used for directional lines in HF technology. Layer 4 is designed for a rotation by 45 for frequencies in the region of interest here.

Auf beiden Seiten dieser nicht-reziproken Schicht 4 ist eine Polarisatorschicht 6, 7 aufgebracht, die jeweils eine hohe Transparenz für eine vorgegebene Polarisationsrichtung und eine hohe Absorption für die dazu senkrechte Polarisationsrichtung aufweisen. Die beiden Polarisatorschichten 6, 7 sind um 45 gegeneinander verdreht angeordnet. Mit 8 ist ferner eine Halterung für den Ringmagneten, die nicht-reziproke Schicht und die beiden Polarisatorschichten bezeichnet.A polarizer layer 6, 7 is applied to both sides of this non-reciprocal layer 4, each of which has a high transparency for a predetermined polarization direction and a high absorption for the polarization direction perpendicular thereto. The two polarizer layers 6, 7 are arranged rotated relative to one another by 45. 8 also denotes a holder for the ring magnet, the non-reciprocal layer and the two polarizer layers.

Im Falle eines Elektromagneten bestimmt die Richtung des angelegten Magnetfeldes (nach innen oder nach außen gerichtet) den Transparenzzustand des Radoms, d.h. die Sende- oder Empfangstransparenz.In the case of an electromagnet, the direction of the applied magnetic field (inward or outward) determines the transparency state of the radome, i.e. the transmission or reception transparency.

Die Polarisatorschichten 6, 7 können vorteilhafterweise aus parallel angeordneten dünnen Streifen eines Absorbers aufgebaut werden, wobei die Feldanteile parallel zu den Streifen absorbiert werden, solche senkrecht dazu hingegen transmittiert werden.The polarizer layers 6, 7 can advantageously be constructed from thin strips of an absorber arranged in parallel, the field components being absorbed parallel to the strips, but those being transmitted perpendicularly thereto.

Wie aus der Beschreibung dieses Ausführungsbeispiels deutlich geworden ist, fuhrt die Verwendung nicht-reziproker Effekte zum Zwecke der Tarnung der Antenne dazu, daß die Rückstreuung der zur Ortung eingesetzten gegnerischen elektromagnetischen Wellen weitgehend vermieden wird. Bei ungetarnten Antennen kann der Rückstreuquerschnitt sehr große Werte annehmen und so die an anderen Stellen angewandten Tarnmaßnahmen zunichte machen. Wenn jedoch die Transmission des Radoms in der Empfangsrichtung sehr hohe Werte und in der Senderichtung sehr niedrige Werte annimmt, so kann die einfallende Welle des Ortungsradars zwar zur Antenne vordringen, nicht jedoch wieder austreten, um so dem Ortungsradar ein Echo zu liefern. Andererseits kann die so getarnte Antenne einfallende Signale mit nur geringer Dämpfung empfangen.As has become clear from the description of this exemplary embodiment, the use of non-reciprocal effects for the purpose of camouflaging the antenna means that the backscattering of the opposing electromagnetic waves used for the location is largely avoided. With non-camouflaged antennas, the backscatter cross section can have very large values and thus destroy the camouflage measures used in other places. However, if the transmission of the radome takes very high values in the receiving direction and very low values in the transmitting direction, the incident wave of the locating radar can penetrate to the antenna, but cannot emerge again, in order to provide an echo to the locating radar. On the other hand, the antenna camouflaged in this way can receive incoming signals with only slight attenuation.

Soll die Antenne auch senden, so muß die Transparenzrichtung umgekehrt werden, wofür die Ursache der die nicht-reziproken Effekte hervorrufenden Maßnahmen (beim magnetooptischen Effekt das angelegte Magnetfeld) umgekehrt werden müssen. In diesem Zustand kann die elektromagnetische Welle des Ortungsradars das Radom nicht durchdringen. Bei geeigneten Entspiegelungsschichten auf dem Radom, wie sie aus der Optik bekannt sind, dringt die Welle in das Radom ein und wird dort absorbiert. Die getarnte Antenne kann dagegen ihre Signale mit nur geringer Dampfung aussenden.If the antenna is also to transmit, the direction of transparency must be reversed, for which the cause of the measures causing the non-reciprocal effects (for the magneto-optical effect the applied magnetic field) must be reversed. In this state, the electromagnetic wave of the location radar cannot penetrate the radome. With suitable anti-reflective coatings on the radome, as are known from optics, the wave penetrates into the radome and is absorbed there. The camouflaged antenna, on the other hand, can transmit its signals with only a small amount of attenuation.

Soll eine Bordradar-Antenne auf diese Weise getarnt werden, so muß in den relativ kurzen Sendephasen das Radom auf "Sendetransparenz" und in der übrigen Zeit auf "Empfangstransparenz" geschaltet werden.If an on-board radar antenna is to be camouflaged in this way, the radome must be switched to "transmission transparency" in the relatively short transmission phases and to "reception transparency" during the rest of the time.

Entspiegelungsschichten auf dem Radom sind außer für die Absorption einfallender Wellen im Zustand der Sendetransparenz auch nützlich für die Erhöhung der Radomtransparenz für die jeweils durchgelassenen Nutzsignale, sowie die Reflexionsminderung im Zustand der Empfangstransparenz.Anti-reflective coatings on the radome are useful not only for the absorption of incident waves in the state of transmission transparency, but also for increasing the radome transparency for the transmitted useful signals and for reducing the reflection in the state of reception transparency.

Handelt es sich bei der zu tarnenden Antenne um eine Spiegelantenne, z.B. eine Parabolantenne 11, wie sie in Fig. 2 dargestellt ist, so kann anstelle des Radoms oder in Kombination mit ihm ein Teil der Antenne selbst nicht-reziprok ausgeführt werden. Zu diesem Zweck wird die nicht-reziproke Schicht 14, d.h. der Faraday-Dreher, in der Form der Antennenoberfläche 19 auf diese aufgebracht. Die beiden um 45 zueinander verdrehten Polarisatorschichten 16, 17 können in diesem Fall zum einen auf der Radomapertur, deren Ebene in Fig. 2 mit 13 bezeichnet ist, und zum anderen auf dem Subreflektor bzw. Erreger und/oder Detektor 20 angeordnet werden. Mit 18 ist auch hier wieder eine Halterung für die Radomapertur, mit 15 ein die nicht-reziproke Schicht umgebender Ringmagnet und mit 12 eine Verbindung zu einem Funksystem bezeichnet.If the antenna to be camouflaged is a mirror antenna, for example a parabolic antenna 11, as shown in FIG. 2, a part of the antenna itself can be made non-reciprocal instead of or in combination with it. For this purpose, the non-reciprocal layer 14, ie the Faraday rotator, is applied to the antenna surface 19 in the form of the latter. The two polaris twisted by 45 to each other Sator layers 16, 17 can in this case be arranged on the one hand on the radome aperture, the level of which is designated by 13 in FIG. 2, and on the other hand on the subreflector or exciter and / or detector 20. 18 also here again denotes a holder for the radio aperture, 15 a ring magnet surrounding the non-reciprocal layer and 12 a connection to a radio system.

Mit der erfindungsgemäßen Vorrichtung bleibt das Nutzsignal der zu tarnenden Antenne praktisch ungestört, wenn es linear polarisiert ist, wobei die Orientierung der Polarisationsschichten 6, 7; 16, 17 und der Antenne 1 bzw. 11 auf die gewünschte Polarisationsrichtung abgestimmt werden muß.With the device according to the invention, the useful signal of the antenna to be camouflaged remains practically undisturbed if it is linearly polarized, the orientation of the polarization layers 6, 7; 16, 17 and the antenna 1 or 11 must be matched to the desired polarization direction.

Soll bei dem in Fig. 1 dargestellten Ausführungsbeispiel die zu tarnende Antenne 1 zirkular polarisierte Wellen empfangen oder senden, so kann dies dadurch erfolgen, daß zusätzlich auf den beiden, dem Faraday-Dreher 4 abgewandten Außenseiten der Polarisatorschichten 6, 7 je eine sogenannte Viertelwellenlängenschicht 9, 10 aus einachsig anisotropem Material aufgebracht wird. Die Zusatzschichten 9, 10 transformieren zirkular polarisierte Wellen in linear polarisierte Wellen und umgekehrt.If the antenna 1 to be camouflaged is to receive or transmit circularly polarized waves in the exemplary embodiment shown in FIG. 1, this can be done by additionally providing a so-called quarter-wavelength layer 9 on each of the two outer sides of the polarizer layers 6, 7 facing away from the Faraday rotator 4 , 10 is applied from uniaxial anisotropic material. The additional layers 9, 10 transform circularly polarized waves into linearly polarized waves and vice versa.

Claims (6)

1. Vorrichtung zur Tarnung von Antennen gegen die Ortung durch Mikrowellen, insbesondere durch Mikrowellen, deren Frequenzen sich nur geringfügig von den Frequenzen der Nutzwellen der zu tarnenden Antennen unterscheiden, dadurch gekennzeichnet, daß sie aus einem elektromagnetisch nicht reziproken Bauelement besteht, das in Einfallsrichtung der Mikrowellen gesehen, vor der Antenne angeordnet ist und das zwei um 45 zueinander verdrehte Polarisatorschichten aufweist.1. Device for camouflaging antennas against the location by microwaves, in particular by microwaves, the frequencies of which differ only slightly from the frequencies of the useful waves of the antennas to be camouflaged, characterized in that it consists of an electromagnetically non-reciprocal component which is in the direction of incidence of the Seen microwaves, is arranged in front of the antenna and has two polarizer layers rotated by 45 to one another. 2. Vorrichtung nach Anspruch 1, dadurch gekennzeichnet, daß das nicht-reziproke Bauelement die Form eines im Abstand vor der Antenne angeordneten Radoms aufweist und eine magnetooptische Schicht (4) enthalt, die von einem Ringmagneten (5) umgeben ist und die auf beiden Seiten von je einer Polarisatorschicht (6, 7) bedeckt ist, welche eine hohe Transparenz für eine gegebene lineare Polarisationsrichtung aufweist und eine hohe Absorption für die dazu senkrechte Polarisationsrichtung aufweist und daß die beiden Polarisatorschichten (6, 7) um 45 ° zueinander verdreht angeordnet sind.2. Device according to claim 1, characterized in that the non-reciprocal component has the shape of a radome arranged at a distance in front of the antenna and contains a magneto-optical layer (4) which is surrounded by a ring magnet (5) and on both sides is each covered by a polarizer layer (6, 7) which has a high transparency for a given linear polarization direction and a high absorption for the polarization direction perpendicular thereto and that the two polarizer layers (6, 7) are arranged rotated by 45 ° to one another. 3. Vorrichtung nach Ansprüchen 1 und 2, dadurch gekennzeichnet, daß die magnetooptische Schicht ein sogenannter Faraday-Dreher ist, der die sie durchsetzenden elektromagnetischen, linear polarisierten Wellen um 45 verdreht und daß er aus einem Ferrit und/oder Granat besteht.3. Device according to claims 1 and 2, characterized in that the magneto-optical layer is a so-called Faraday rotator, which rotates the penetrating electromagnetic, linearly polarized waves by 45 and that it consists of a ferrite and / or garnet. 4. Vorrichtung nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß die Polarisatorschichten (6, 7) aus parallel zueinander angeordneten dünnen Streifen eines Absorbers bestehen.4. Device according to one of claims 1 to 3, characterized in that the polarizer layers (6, 7) consist of mutually parallel thin strips of an absorber. 5. Vorrichtung nach Ansprüchen 1 bis 4, dadurch gekennzeichnet, daß jede Polarisatorschicht (6, 7) auf der dem Faraday-Dreher (4) abgewandten Oberflache mit einer Viertelwellenlängenschicht (9,10) aus einem einachsig anisotropen Material zur Transformation zirkular polarisierter Wellen in linear polarisierte Wellen versehen ist.5. Device according to claims 1 to 4, characterized in that each polarizer layer (6, 7) on the surface facing away from the Faraday rotator (4) with a quarter-wavelength layer (9, 10) made of a uniaxial anisotropic material for transforming circularly polarized waves into linearly polarized waves is provided. 6. Vorrichtung nach Anspruch 1, dadurch gekennzeichnet, daß im Falle von Parabolantennen die magnetooptische Schicht (14) direkt auf der den einfallenden Mikrowellen zugewandten Oberfläche (19) der Antenne (11) aufgebracht ist und daß die beiden um 45 zueinander verdrehten Polarisatorschichten (16, 17) zum einen auf der Radomapertur und zum anderen auf dem Subreflektor bzw. Erreger oder Detektor (20) angeordnet sind.6. The device according to claim 1, characterized in that in the case of parabolic antennas, the magneto-optical layer (14) is applied directly to the incident microwaves facing surface (19) of the antenna (11) and that the two polarizer layers rotated by 45 to each other (16 , 17) are arranged on the one hand on the radome aperture and on the other hand on the subreflector or exciter or detector (20).
EP94119638A 1994-02-24 1994-12-13 Device for camouflaging antennas Expired - Lifetime EP0669674B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE4405996 1994-02-24
DE4405996A DE4405996C2 (en) 1994-02-24 1994-02-24 Antenna camouflage device

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EP0669674A1 true EP0669674A1 (en) 1995-08-30
EP0669674B1 EP0669674B1 (en) 1999-02-24

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR3003700A1 (en) * 2013-03-19 2014-09-26 Thales Sa ANTENNA RADAR SIGNATURE REDUCTION DEVICE AND ASSOCIATED ANTENNA SYSTEM

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WO1990010958A1 (en) * 1989-03-15 1990-09-20 Cambridge Computer Limited Improvements in antenna polarizers
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EP0568511A1 (en) * 1992-04-30 1993-11-03 NobelTech Electronics AB Screen device

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Publication number Priority date Publication date Assignee Title
US3309704A (en) * 1965-09-07 1967-03-14 North American Aviation Inc Tunable absorber
GB1416343A (en) * 1972-02-16 1975-12-03 Secr Defence Radomes
EP0517976A1 (en) * 1983-10-31 1992-12-16 Raytheon Company Pulse radar
WO1990010958A1 (en) * 1989-03-15 1990-09-20 Cambridge Computer Limited Improvements in antenna polarizers
EP0568511A1 (en) * 1992-04-30 1993-11-03 NobelTech Electronics AB Screen device

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR3003700A1 (en) * 2013-03-19 2014-09-26 Thales Sa ANTENNA RADAR SIGNATURE REDUCTION DEVICE AND ASSOCIATED ANTENNA SYSTEM

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DE4405996C2 (en) 1996-01-11
DE59407846D1 (en) 1999-04-01
EP0669674B1 (en) 1999-02-24
DE4405996A1 (en) 1995-08-31

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