EP0378838A1 - Method for the reduction of backscattering electromagnetic radiation at cavity structures open at one side - Google Patents

Method for the reduction of backscattering electromagnetic radiation at cavity structures open at one side Download PDF

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Publication number
EP0378838A1
EP0378838A1 EP89123645A EP89123645A EP0378838A1 EP 0378838 A1 EP0378838 A1 EP 0378838A1 EP 89123645 A EP89123645 A EP 89123645A EP 89123645 A EP89123645 A EP 89123645A EP 0378838 A1 EP0378838 A1 EP 0378838A1
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EP
European Patent Office
Prior art keywords
electromagnetic radiation
cavity structure
cavity
reduction
cavity structures
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.)
Withdrawn
Application number
EP89123645A
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German (de)
French (fr)
Inventor
Joachim Bettermann
Manfred Hochmann
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Airbus Defence and Space GmbH
Original Assignee
Deutsche Aerospace AG
Messerschmitt Bolkow Blohm AG
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Filing date
Publication date
Application filed by Deutsche Aerospace AG, Messerschmitt Bolkow Blohm AG filed Critical Deutsche Aerospace AG
Publication of EP0378838A1 publication Critical patent/EP0378838A1/en
Withdrawn legal-status Critical Current

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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

Definitions

  • the invention relates to a method for reducing the backscattering of electromagnetic radiation on cavity structures that are open on one side, such as engine inlets of missiles, aircraft and helicopters. It also relates to a cavity structure that is open on one side.
  • Cavity structures such as the engine inlets of missiles, aircraft or helicopters, caused by multiple reflections of the incident radar energy on the inner walls of the inlets and subsequent reflection at the rear end, for example at the first compressor blade ring, show a high degree of backscattering of the incident radar radiation. This gives for a large aspect angle range and a broad frequency band of the incident electromagnetic radiation. Because of this high Reflection rate, such aircraft can be detected even at a comparatively large distance.
  • the object of the invention is therefore to provide a method by means of which the probability of detection of aircraft equipped with such cavity structures is significantly reduced. Furthermore, the invention is intended to provide a cavity structure which is open on one side and has a significantly reduced radar cross section.
  • the invention solves the problem by a method with the characterizing features of claim 1 and to carry out the method, a cavity structure is formed according to the features of the claim.
  • the method according to the invention leads to a broadband lowering of the radar backscatter cross section of such cavity structures, such as engine inlets, while at the same time requiring little space for any additional structural elements that may be used. Furthermore, the arrangement is characterized by an extremely small restriction of the effective inlet cross-section of the cavity structure while at the same time optimally suppressing the reflection of the incident radar radiation.
  • a largely radar-absorbing design of the inner walls of cavity structures with at least one opening, in particular engine inlets, is therefore provided.
  • These inner walls can be designed as a primary, secondary or non-load-bearing structure.
  • the inner walls of the cavity structure can also be the surfaces of inlet dividers, so-called duct splitters, which are designed according to aerodynamic, structural and / or operational aspects.
  • the cavity structure in the inlet area can be filled with a straight or diagonally arranged mesh which, due to its frequency selectivity, only allows radar energy from certain frequency areas to enter the inlet and reflects radar energy from the other frequency areas.
  • the frequency-dependent absorption profiles of the absorbers on the inner walls in front of and behind the grating are advantageously matched to the reflection characteristics of the grating.
  • the geometric shape of the grille depends on its operationally required filter properties and the aerodynamic and structural boundary conditions.
  • the grid can consist of completely or limited conductive or absorbent material.
  • FIG. 1 The arrangement shown in FIG. 1 is a cross-section through an engine inlet 1, the inlet opening 2 of which is located on the left-hand side of the picture and leads to a first stage (not shown in the figure) of a compressor blade.
  • the inlet opening 2 is inserted in relation to the direction of flow mesh grid 3 which is shown in the left part of Fig. 1 again in plan view.
  • a first absorber 4 is arranged in the form of a thin, approximately 1 millimeter thick layer made of a material that absorbs the electromagnetic radiation.
  • a second absorber 5 is arranged in the area of the greatest curvature of the engine inlet 1 over the entire inner circumference, and finally an inlet divider 6 arranged in the center line of the engine inlet 1 is provided with an absorber layer 7 made of an absorber material.
  • the materials for the three absorbers 4, 5 and 7 mentioned are selected so that their maximum adsorption capacity is in each case at different frequencies of the incident radar radiation, so that due to these mutually offset adsorption profiles, as shown in FIG. 2, in combination with the reflection characteristic of the mesh 3, the broadband suppression of the reflection of the incident radar radiation already described sets.
  • the measures described above are suitable both for newly manufactured engine inlets and for retrofitting existing engines. However, they are not on engine intakes limited, but applicable to all cavity structures on an aircraft that are open on one side and whose radar backscatter cross section is to be reduced.
  • the absorbers 4, 5 and 7 are made of elastomer material, but fiber composite materials or thermoplastics, for example, are also suitable as absorber materials.

Landscapes

  • Radar Systems Or Details Thereof (AREA)
  • Aiming, Guidance, Guns With A Light Source, Armor, Camouflage, And Targets (AREA)
  • Aerials With Secondary Devices (AREA)

Abstract

In a method for the reduction of backscattering electromagnetic radiation, especially of radar radiation, on cavity structures which are open on one side, at least partial regions of the inner surface of the cavity structure are provided with a coating which consists of a material which absorbs the electromagnetic radiation. The materials of the individual absorber coatings (4, 5) are in this case selected such that they have different absorption characteristics depending on the frequency of the incident electromagnetic radiation. The cavity structure may consist of an engine intake (1) for missiles, aircraft or helicopters. The inlet opening (2) can additionally be closed by an obliquely arranged wire mesh (3), a flow divider (6), arranged in the interior, can likewise be coated with an absorber layer (7). <IMAGE>

Description

Die Erfindung betrifft ein Verfahren zur Senkung der Rückstreuung elektromagnetischer Strahlung an einseitig offenen Hohlraumstrukturen, wie Triebwerkseinläufen von Flugkörpern, Flugzeugen und Hubschraübern. Ferner be­trifft sie eine einseitig offene Hohlraumstruktur.The invention relates to a method for reducing the backscattering of electromagnetic radiation on cavity structures that are open on one side, such as engine inlets of missiles, aircraft and helicopters. It also relates to a cavity structure that is open on one side.

Hohlraumstrukturen, wie z.B. die Triebwerkseinläufe von Flugkörpern, Flugzeugen oder Hubschraübern weisen her­vorgerufen durch Mehrfachreflexionen der einfallenden Radarenergie an den Innenwänden der Einläufe und an­schließende Reflexion am rückwärtigen Abschluß, bei­spielsweise am ersten Verdichterschaufelkranz, ein ho­hes Maß an Rückstreuung der einfallenden Radarstrahlung auf. Dies gibt für einen großen Aspektwinkelbereich und ein breites Frequenzband der einfallenden elektroma­gnetischen Strahlung. Aufgrund dieser hohen Reflexionsrate ist eine Detektion derartiger Fluggeräte bereits in einer vergleichsweise großen Entfernung möglich.Cavity structures, such as the engine inlets of missiles, aircraft or helicopters, caused by multiple reflections of the incident radar energy on the inner walls of the inlets and subsequent reflection at the rear end, for example at the first compressor blade ring, show a high degree of backscattering of the incident radar radiation. This gives for a large aspect angle range and a broad frequency band of the incident electromagnetic radiation. Because of this high Reflection rate, such aircraft can be detected even at a comparatively large distance.

Aufgabe der Erfindung ist daher, ein Verfahren anzuge­ben, mit dessen Hilfe die Entdeckungswahrscheinlichkeit von mit derartigen Hohlraumstrukturen ausgerüsteten Fluggeräten deutlich herabgesetzt wird. Ferner soll durch die Erfindung eine einseitig offene Hohlraum­struktur mit einem deutlich verminderten Radarquer­schnitt bereitgestellt werden.The object of the invention is therefore to provide a method by means of which the probability of detection of aircraft equipped with such cavity structures is significantly reduced. Furthermore, the invention is intended to provide a cavity structure which is open on one side and has a significantly reduced radar cross section.

Die Erfindung löst die Aufgabe durch ein Verfahren mit den kennzeichnenden Merkmalen des Patentanspruches 1 und zur Durchführung des Verfahrens ist ein Hohl­raumstruktur nach den Merkmalen des Anspruches ausgebildet.The invention solves the problem by a method with the characterizing features of claim 1 and to carry out the method, a cavity structure is formed according to the features of the claim.

Das erfindungsgemäße Verfahren führt dabei zu einer breitbandigen Absenkung des Radarrückstreuquerschnittes derartiger Hohlraumstrukturen, wie Triebwerkseinläufen, bei gleichzeitig geringem Raumbedarf für die gegebe­nenfalls zusätzlich eingesetzten Konstruktionselemente. Weiterhin zeichnet sich die Anordnung durch eine äu­ßerst geringe Einschränkung des wirksamen Einlaßquer­schnittes der Hohlraumstruktur bei zugleich optimaler Reflexionsunterdrückung der einfallenden Radarstrahlung aus.The method according to the invention leads to a broadband lowering of the radar backscatter cross section of such cavity structures, such as engine inlets, while at the same time requiring little space for any additional structural elements that may be used. Furthermore, the arrangement is characterized by an extremely small restriction of the effective inlet cross-section of the cavity structure while at the same time optimally suppressing the reflection of the incident radar radiation.

Es ist daher eine weitgehende radarabsorbierende Aus­bildung der Innenwände von Hohlraumstrukturen mit we­nigstens einer Öffnung, insbesondere Triebwerkseinläu­fen, vorgesehen. Diese Innenwände können dabei als Primär-, Sekundär- oder aber als nichttragende Struktur ausgebildet sein. Indem erfindungsgemäß vorgesehen ist, daß unterschiedliche, relativ dünne schmalbandige Ma­terialien mit in der Frequenz verschiedenenA largely radar-absorbing design of the inner walls of cavity structures with at least one opening, in particular engine inlets, is therefore provided. These inner walls can be designed as a primary, secondary or non-load-bearing structure. By providing according to the invention that different, relatively thin narrow-band materials with different frequencies

Absorptionsverläufen an unterschiedlichen Stellen der Struktur eingesetzt werden, wird insgesamt eine extrem breitbandige Unterdrückung der Reflexion der einfal­lenden Radarenergie erzielt. Die Innenwände der Hohl­raumstruktur können dabei, im Falle eines Triebwerks­einlaufes, auch die Oberflächen von Einlaufteilern, sogenannten Duct-Splittern, sein, die gemäß aerodyna­mischen, strukturellen und/oder operationellen Gesichtpunkten ausgelegt sind. Zusätzlich kann die Hohlraumstruktur im Einlaßbereich mit einem gerade oder schräg stehend angeordneten Maschengitter ausgefüllt sein, das durch seine Frequenzselektivität lediglich Radarenergie aus bestimmten Frequenzbereichen in den Einlauf eindringen läßt und Radarenergie der übrigen Frequenzbereiche wegreflektiert. Die frequenzabhängigen Absorptionsverläufe der Absorber an den Innenwänden vor und hinter dem Gitter sind dabei in vorteilhafter Weise auf die Reflexionscharakteristik des Gitters abge­stimmt. Die geometrische Form des Gitters richtet sich nach dessen operationell geforderten Filtereigenschaften und den aerodynamischen und strukturellen Randbedingungen. Das Gitter kann aus vollständig oder begrenzt leitfähigem bzw. absorbierendem Material bestehen.If absorption curves are used at different points in the structure, overall an extremely broadband suppression of the reflection of the incident radar energy is achieved. In the case of an engine inlet, the inner walls of the cavity structure can also be the surfaces of inlet dividers, so-called duct splitters, which are designed according to aerodynamic, structural and / or operational aspects. In addition, the cavity structure in the inlet area can be filled with a straight or diagonally arranged mesh which, due to its frequency selectivity, only allows radar energy from certain frequency areas to enter the inlet and reflects radar energy from the other frequency areas. The frequency-dependent absorption profiles of the absorbers on the inner walls in front of and behind the grating are advantageously matched to the reflection characteristics of the grating. The geometric shape of the grille depends on its operationally required filter properties and the aerodynamic and structural boundary conditions. The grid can consist of completely or limited conductive or absorbent material.

Im folgenden wird die Erfindung anhand eines in der Zeichnung dargestellten Ausführungsbeispieles näher erläutert werden. Es zeigen:

  • Fig. 1 einen Querschnitt durch eine Hohlraumstruktur und
  • Fig. 2 eine Darstellung des Verlaufes des Rückstreuquerschnittes für elektromagnetische Strahlung in Abhängigkeit von der Frequenz der einfallenden Strahlung
The invention will be explained in more detail below on the basis of an exemplary embodiment shown in the drawing. Show it:
  • Fig. 1 shows a cross section through a cavity structure and
  • 2 shows the course of the backscatter cross section for electromagnetic radiation as a function of the frequency of the incident radiation

Bei der in Fig. 1 dargestellten Anordnung handelt es sich um einen Querschnitt durch einen Triebwerkseinlauf 1 dessen Einlaßöffnung 2 sich auf der linken Bildseite befindet in der zu einer in der Figur nicht darge­stellten ersten Stufe einer Verdichterschaufel führt. In die Einlaßöffnung 2 ist ein in bezug auf die Strö­mungsrichtung schrägstehend angeordnetes Maschengitter 3 eingesetzt, das im linken Teil von Fig. 1 nochmals in der Draufsicht dargestellt ist.The arrangement shown in FIG. 1 is a cross-section through an engine inlet 1, the inlet opening 2 of which is located on the left-hand side of the picture and leads to a first stage (not shown in the figure) of a compressor blade. In the inlet opening 2 is inserted in relation to the direction of flow mesh grid 3 which is shown in the left part of Fig. 1 again in plan view.

Im Bereich vor dem Maschengitter 3 ist ein erster Absorber 4 in Form einer dünnen etwa 1 Millimeter starken Schicht aus einem die elektromagnetische Strahlung absorbierenden Werkstoff angeordnet. Ein zweiter Absorber 5 ist im Bereich der stärksten Krümmung des Triebwerkseinlaufes 1 über den gesamten inneren Umfang angeordnet, und schließlich ist auch ein in der Mittellinie des Triebwerkseinlaufes 1 angeordneter Einlaufteiler 6 mit einer Absorberschicht 7 aus einem Absorbermaterial versehen.In the area in front of the mesh 3, a first absorber 4 is arranged in the form of a thin, approximately 1 millimeter thick layer made of a material that absorbs the electromagnetic radiation. A second absorber 5 is arranged in the area of the greatest curvature of the engine inlet 1 over the entire inner circumference, and finally an inlet divider 6 arranged in the center line of the engine inlet 1 is provided with an absorber layer 7 made of an absorber material.

Die Werkstoffe für die drei genannten Absorber 4,5 und 7 sind dabei so ausgewählt, daß ihr maximales Adsorp­tionsvermögen jeweils bei unterschiedlichen Frequenzen der einfallenden Radarstrahlung liegt, so daß sich aufgrund dieser gegeneinander versetzten Adsorptions­verläufe, wie sie in Fig. 2 dargestellt sind in Kombi­nation mit der Reflexionscharakteristik des Maschen­gitters 3, die schon beschriebene breitbandige Unter­drückung der Reflexion der einfallenden Radarstrahlung einstellt.The materials for the three absorbers 4, 5 and 7 mentioned are selected so that their maximum adsorption capacity is in each case at different frequencies of the incident radar radiation, so that due to these mutually offset adsorption profiles, as shown in FIG. 2, in combination with the reflection characteristic of the mesh 3, the broadband suppression of the reflection of the incident radar radiation already described sets.

Die vorstehend beschriebenen Maßnahmen eignen sich da­bei sowohl für neu herzustellende Triebwerkseinläufe als auch zur Nachrüstung bereits vorhandener Trieb­werke. Sie sind indessen nicht auf Triebwerkseinläufe beschränkt, sondern für alle an einem Fluggerät be­findlichen, einseitig offenen Hohlraumstrukturen an­wendbar, deren Radarrückstreuquerschnitt verringert werden soll. Die Absorber 4,5 bzw. 7 bestehen im Fall des hier beschriebenen Ausführungsbeispieles aus Elastomermaterial es sind aber als Absorber­materialien beispielsweise auch Faserverbundwerkstoffe oder Thermoplaste geeignet.The measures described above are suitable both for newly manufactured engine inlets and for retrofitting existing engines. However, they are not on engine intakes limited, but applicable to all cavity structures on an aircraft that are open on one side and whose radar backscatter cross section is to be reduced. In the case of the exemplary embodiment described here, the absorbers 4, 5 and 7 are made of elastomer material, but fiber composite materials or thermoplastics, for example, are also suitable as absorber materials.

Claims (8)

1. Verfahren zur Senkung der Rückstreuung elektroma­gnetischer Strahlung an einseitig offenen Hohlraum­strukturen, wie Triebwerkseinläufen von Flugkör­pern, Flugzeugen und Hubschraübern, dadurch gekenn­zeichnet, daß zumindest Teilbereiche der inneren Oberfläche der Hohlraumstruktur (1) mit einem Belag (4,5,7) aus einem elektromagnetische Strahlung absorbierenden Werkstoff versehen werden.1. A method for reducing the backscattering of electromagnetic radiation at cavity structures open on one side, such as engine inlets of missiles, aircraft and helicopters, characterized in that at least partial areas of the inner surface of the cavity structure (1) with a coating (4, 5, 7) made of an electromagnetic Radiation absorbing material can be provided. 2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Beläge (4,5,7) in bezug auf die Frequenz der einfallenden elektromagnetischen Strahlen un­terschiedliche Absorptionsverläufe aufweisen.2. The method according to claim 1, characterized in that the coatings (4,5,7) have different absorption profiles with respect to the frequency of the incident electromagnetic rays. 3. Verfahren nach Anspruch 1 oder 2, dadurch gekenn­zeichnet, daß die Öffnung (2) der Hohlraum­struktur(1) durch ein Maschengitter (3) ver­schlossen wird.3. The method according to claim 1 or 2, characterized in that the opening (2) of the cavity structure (1) is closed by a mesh (3). 4. Hohlraumstruktur, insbesondere Triebwerkseinlauf zur Durchführung des Verfahrens, dadurch gekenn­zeichnet, daß zumindest Teilbereiche der inneren Oberfläche mit einem Belag (4,5,7) aus einem die elektromagnetische Strahlung absorbierenden Werk­stoff versehen ist.4. Cavity structure, in particular engine inlet for carrying out the method, characterized in that at least partial areas of the inner surface are provided with a covering (4, 5, 7) made of a material which absorbs the electromagnetic radiation. 5. Hohlraumstruktur nach Anspruch 4, dadurch gekenn­zeichnet, daß die in einzelnen Bereichen angeord­neten Beläge (4,5,7) in bezug auf die Frequenz der einfallenden elektromagnetischen Strahlung unter­schiedliche Absorptionsverläufe aufweisen.5. cavity structure according to claim 4, characterized in that the arranged in individual areas coverings (4,5,7) with respect to the frequency of the incident electromagnetic radiation have different absorption profiles. 6. Hohlraumstruktur nach Anspruch 4 oder 5, dadurch gekennzeichnet, daß die Eintrittsöffnung (2) durch ein Maschengitter (3) verschlossen ist.6. cavity structure according to claim 4 or 5, characterized in that the inlet opening (2) is closed by a mesh (3). 7. Hohlraumstruktur nach Anspruch 6, dadurch gekenn­zeichnet, daß das Maschengitter (3) schrägstehend angeordnet ist.7. cavity structure according to claim 6, characterized in that the mesh (3) is arranged obliquely. 8. Hohlraumstruktur nach einem der Ansprüche 4 bis 7 in Form eines mit einem Strahlteiler ausgestalteten Triebwerkseinlaufes, dadurch gekennzeichnet, daß der Strahlteiler (6) mit einer Schicht (7) aus Absorbermaterial versehen ist.8. Cavity structure according to one of claims 4 to 7 in the form of an engine inlet configured with a beam splitter, characterized in that the beam splitter (6) is provided with a layer (7) made of absorber material.
EP89123645A 1989-01-14 1989-12-21 Method for the reduction of backscattering electromagnetic radiation at cavity structures open at one side Withdrawn EP0378838A1 (en)

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DE19893901010 DE3901010C1 (en) 1989-01-14 1989-01-14
DE3901010 1989-01-14

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2859702A1 (en) * 1994-07-08 2005-03-18 Aerospatiale Air supply system for aircraft e.g. missile, has duct sub-divided into two branches at continuously varying sections between rear and front sections, where walls of branches are partly covered internally with magnetic material
EP2676099B1 (en) * 2011-02-14 2017-04-26 Leonardo S.P.A. Equipment for the reduction of the radar marking for aircrafts
EP2675712B1 (en) * 2011-02-14 2018-07-04 Leonardo S.P.A. Aircraft with improved aerodynamic performance.
CN111005807A (en) * 2019-11-22 2020-04-14 北京机电工程研究所 Cavity structure applying wave-absorbing material
CN112448110A (en) * 2020-11-17 2021-03-05 四川天邑康和通信股份有限公司 Cavity power divider applicable to 5G passive DAS system

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DE4007986C1 (en) * 1990-03-13 1991-09-19 Messerschmitt-Boelkow-Blohm Gmbh, 8012 Ottobrunn, De Aircraft structure with cavities - filled with material absorbing or reflecting radar vanes for camouflage or imaging
DE4121584A1 (en) * 1991-06-29 1993-01-21 Messerschmitt Boelkow Blohm Camouflaging and strong elimination of radar radiation in inlet of drive - includes impinging radar radiation in inlet duct using divergent tube and associated mode converter
DE4216837C2 (en) * 1992-05-21 1995-11-16 Daimler Benz Aerospace Ag Radar camouflage for slow-flying roll-stabilized missiles
DE19528343C2 (en) * 1995-08-02 1997-05-22 Markus Muehleisen Device for low-reflection absorption of microwaves
DE19807556B3 (en) * 1998-02-23 2013-11-28 Friedrich-Ulf Deisenroth Camouflage element for camouflage of e.g. military vehicles utilized for tracking of enemy weapon systems, has outer plate formed with apertures whose size lies in range of light distance between inner plate and outer plate
DE102012023718A1 (en) * 2012-12-05 2014-06-05 Eads Deutschland Gmbh Inlet for an engine of an aircraft
RU2623031C1 (en) * 2016-06-30 2017-06-21 Публичное акционерное общество "Авиационная холдинговая компания "Сухой" Aircraft air intake

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2859702A1 (en) * 1994-07-08 2005-03-18 Aerospatiale Air supply system for aircraft e.g. missile, has duct sub-divided into two branches at continuously varying sections between rear and front sections, where walls of branches are partly covered internally with magnetic material
EP2676099B1 (en) * 2011-02-14 2017-04-26 Leonardo S.P.A. Equipment for the reduction of the radar marking for aircrafts
EP2675712B1 (en) * 2011-02-14 2018-07-04 Leonardo S.P.A. Aircraft with improved aerodynamic performance.
CN111005807A (en) * 2019-11-22 2020-04-14 北京机电工程研究所 Cavity structure applying wave-absorbing material
CN112448110A (en) * 2020-11-17 2021-03-05 四川天邑康和通信股份有限公司 Cavity power divider applicable to 5G passive DAS system

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