DE4344909B4 - Radar antireflection - Google Patents

Abstract

Radar anti-reflection element (2) for reflection reduction of radar radiation (30) on a multi-pane building glazing (1), which has at least one thin, transparent first electrically conductive layer (14),
wherein the radar anti-reflection element (2) is arranged at a predetermined distance on the side of the incident radar radiation (30) in front of the multi-pane building glazing (1) and a thin, transparent second electrically conductive one applied to a transparent, dielectric substrate (21) Layer (20) and wherein the distance (D) between the first electrically conductive layer (14) of the multi-pane building glazing (1) and the second electrically conductive layer (20) depending on the angle of incidence and polarization state of the radar radiation is dimensioned such that the standing wave field between the conductive layers (20 and 14 or 31) is just adjusted so that the currents induced in the conductive layers dissipate the radar radiation as quantitatively as possible,
characterized,
that the surface resistance of the second electrically conductive layer (20) is dimensioned so that the total admittance of the radar anti-reflection element (2) and the multi-pane building glazing ...

Description

The The invention relates to a radar anti-reflection element which is both metallic building facades as well as a building glazing be set to reduce the reflection of radar radiation can.

Especially in the area of airports There is an increasing problem that the signals of the air traffic control radar often at a short distance from the stationary radars built organization buildings of the airport. These additional reflection signals complicate the interpretation and evaluation of the radar signals considerably. At the facades of buildings In the area of an airport, therefore, measures should be taken to disturbing Reduce radar reflections.

In This connection has already been proposed in the facade elements to introduce dispersed graphite particles containing the radar radiation absorb in the manner of a wave sump. This measure is however, not suitable in the area of the windows of the building, as the Graphite particles not only the radar radiation, but also visible Absorb light.

From the DE 41 01 074 A1 It is known to provide the radar-facing side of a double-glazing with a translucent, slightly electrically conductive layer. An effective reduction of the radar reflection can not be achieved with this measure.

From the DE 40 08 660 A1 It is known to design a double glazing with a radar-absorbing layer on the radar-facing side and a radar-reflecting layer on the side facing away radar. The arrangement works on the principle of interference absorption. The radar-reflecting layer consists of a conductive Rasterbedampfung, which is applied externally on the side facing away from the incident radar disc of double glazing. The disadvantage of the DE 40 08 660 A1 However, the known measure for reducing the reflection of radar radiation is that both the radar absorbing layer and the radar reflecting layer must already be incorporated in the production of the double glazing elements in this. A subsequent retrofitting of an existing building glazing, if emanating from this disturbing radar reflexes, is therefore not possible. Rather, already assembled conventional glazing elements are to be replaced by the radar-absorbing glazing elements, which is very cost-intensive.

On the other hand, z. B. from the DE 38 07 600 A1 Double glazing elements with a heat protection filter known, which has a thin, transparent metal layer for reasons of heat insulation. This thin, transparent metal layer has radar-reflecting properties, so that the use of these provided with a heat-shielded double glazing elements in the catchment area of the air traffic control was previously subjected to difficulties.

From the DE 41 03 458 A1 For example, a transparent glazing element with low reflectance for radar radiation and high reflectance for IR radiation is known. The glazing element consists of a first, the radiation source facing glass with a thickness d between 4 mm and 15 mm and a second, facing away from the radiation source glass. The first glass sheet carries a light-transmitting, electrically conductive layer having a sheet resistance between 100 Ω / cm ² and 600 Ω / cm ^2, and the second glass sheet carries a light-transmitting, electrically highly conductive layer having a sheet resistance of at most 50 Ω / cm ² . The two electrically conductive layers are arranged at a distance that is radar optically equivalent to a glass gap of at least about 30 mm-n _glass- d and at most about 100 mm-n _glass- d.

From the DE 39 16 416 A1 is a radar-absorbing outer facade known. The outer facade has an inner shell and an outer shell of a material with low permeability and low dielectric constant, wherein a resonance absorber with a resistive layer and at a distance λ / 4 a wavelength λ to the resistive layer an electrically conductive reflection layer is provided. Between the outer shell and the inner shell, an intermediate layer with a layer structure may be present, wherein the layer structure comprises a resistance layer and a carrier layer, wherein the carrier layer consists of an insulating material and the layers are arranged alternately successively.

In the document DE magazine "ntz", volume 41 (1988) Issue 5, pages 280-283 various types of absorber are described in which to avoid reflections on the surface of the absorber the impedance of the absorber adapted to the wave resistance of the free space of 377 Ω becomes. Here, in particular, the Jaumann absorber is described, in which the parallel connection of all the transformed resistance values of the Slides on the surface of the absorber assume the characteristic impedance of the free space. It flows here but not the resistance of the reflective surface, the is called of the metal, in the calculation of the total admittance.

Of the The invention is therefore based on the object to avoid the radar reflection on multi-pane building glazings, especially for reasons the heat insulation a thin, have transparent conductive layer, as well as for the reduction Radar reflection on metal building facades a suitable Radar anti-reflection element to be applied to existing building facades retrofitted in a simple manner is.

These The task is with respect to the building glazing by the features of claim 1 and with regard to the metal building facades the features of claim 10 solved.

According to the invention Multi-pane glazing buildings or the metal building facade element at a suitable distance from a dielectric substrate and a thin, transparent, electrically conductive layer existing radar anti-reflection element purposed.

Of the The invention is based on the finding that this is the case resulting system of two plane-parallel conductive layers as Fabry-Perot system works and the reflection of radar radiation through Resonant absorption largely suppressed. Therefore, according to the invention the distance between the conductive layer of the multi-pane building facade or between the surface the metal building facade and the provided in the radar anti-reflection element electrically conductive layer to be dimensioned such that the standing wave field between the leading layers are just so adjusted that the in The conductive layers induced currents radar radiation as quantitatively as possible dissipate. The distance D must be according to the expected angle of incidence and polarization state (s or p polarization) of the radar radiation differently be measured.

in this connection is the sheet resistance the second electrically conductive layer dimensioned so that the total admittance the radar anti-reflection element, the multi-pane building glazing or the entire arrangement in the frequency range of the radar radiation about 1 / (377 Ω) is.

such Radar anti-reflective elements can on an existing building facade in case of occurrence of unwanted Radar reflexes can be retrofitted in a simple manner.

The claims 2 to 9 and 11 to 15 relate to advantageous developments of Invention.

The Dielectric layer of the radar anti-reflection element can either according to claim 2 or 11 by a glass pane or according to claim 3 or 12 formed by a plastic layer, in particular polymer glass become.

With the specified in the claims 4 to 5 and 13 parameters of the design of the surface resistances of the radar reflecting layers or the total admittance can be particularly high reflections reductions of more than 20 db reach. According to claims 6 and 7, the infrared radiation reflecting heat protection coatings already existing electrically conductive layer can be exploited for the Radarentspiegelung. When using the materials Ag, SnO ₂ or indium tin oxide (ITO) can be achieved at the same time a good thermal insulation and a more effective Radarentspiegelung in cooperation with the Radarentspiegelungselement.

Of the between the Radarentspiegelungselement and the building facade resulting gap can according to claims 8 and 9 or 14 and 15 can be used to improve heat insulation, by this hermetically sealed and if necessary. with a reduced pressure charged and / or fallen with a suitable filling gas.

In The drawings are embodiments of Invention exemplified. Show it:

1 a first embodiment of the invention for the reflection reduction of radar radiation on building glazings;

2 A second embodiment of the invention for the reflection reduction of radar radiation on building glazings;

3 an embodiment for reflection reduction of radar radiation to metal building glazing elements.

In the in 1 illustrated embodiment of the invention is above the double glazing element 1 the radar anti-reflective element 2 arranged. The double glazing element 1 has two spaced transparent substrates 10 and 11 on. For the transparent substrates 10 . 11 As a rule, these are glass panes, especially flow glass panes. However, the use of polymer plastic glasses, especially of acrylic glass is conceivable.

The gap 12 between the two transparent substrates 10 and 11 is by a peripheral circumferential only schematically illustrated spacers 13 hermetically sealed gas-tight. The space between the transparent substrates 10 and 11 be subjected to a negative pressure and / or filled with a filling gas. The use of filling gases which have a low tendency to convection is advantageous.

On the incident radar radiation 30 remote substrate 10 a coating of an electrically conductive material is provided. Without effect on the operation of the invention, the layer 14 but also on the radar radiation facing substrate or in the space 12 be provided. As a material for this electrically conductive layer 14 is particularly suitable silver (Ag), tin oxide (SnO ₂ ), indium tin oxide (ITO) or various semiconductor materials. The coating may be applied by a sputtering method, vapor deposition method, pyrolytic method or the like. The sheet resistance of the electrically conductive layer 14 is advantageously in the range of 2 to 15 ohms / □. Instead of a double glazing element 1 In the context of the invention, a three-pane or multi-pane glazing element can also be used. The glazing element 1 may also have a plurality of electrically conductive layers.

According to the invention is at a predetermined distance above the double glazing element 1 a radar anti-reflective element 2 arranged. The radar anti-reflective element 2 consists of a stable, optically transparent substrate 21 and an electrically conductive layer applied thereto 20 , The electrically conductive layer may also be in the substrate 21 be introduced, for. B. in a two-pane laminated glass. As materials for the electrically conductive layer 20 are already coming for the shift 14 named materials and semiconductor materials, as well as other transition metals or stainless steel alloys into consideration. The application of the electrically conductive layer 20 may also be effected by a sputtering method, vapor deposition method, pyrolytic method or the like.

The sheet resistance of the layer 20 However, in an advantageous embodiment, to be sized higher than that of the layer 14 , While the shift 14 the incident radar radiation 30 almost completely reflected, the top layer acts 20 as a beam splitter and absorber.

Essential to the invention is the dimensioning of the distance D between the two electrically conductive layers 14 and 20 , The dimensioning of the distance D is done in such a way that in front of the poorly conductive layer 20 on the side facing away from the radar builds up a field, which is the almost complete dissipation of radar radiation in the layer 20 ensured (resonance absorption). The phase difference of the wave field between the layers 14 and 20 is about π / 2 (90 °) or an odd multiple thereof, ie an odd multiple of 1/4 of the wavelength of the incident radar radiation 30 , However, the ideal phase difference depends on the thicknesses and phase velocities of the dielectric layers 21 . 11 and 10 as well as the gas gaps. It must be in the space 12 the phase velocity is taken into account as a function of the type of filling gas and of the filling pressure.

It should be emphasized that the layers 14 and 20 in the frequency range of the radar radiation, ie, for example, has a range between 1 to 10 GHz reflective properties. In the selection of materials for the electrically conductive layers 14 and 20 and when dimensioning their thickness, care must be taken that the absorption in the visible spectral range is as low as possible.

2 shows a second embodiment of the inventive Radarentspiegelung a double glazing element 1 , The structure of the double glazing element 1 is essentially consistent with that of 1 described structure match. However, the electrically conductive layer 14 between two dielectric layers 15 and 16 arranged. Such an arrangement is a heat protection or solar control glazing, as z. B. from the DE 38 07 600 A1 is known. It is also possible to arrange a plurality of electrically conductive layers, in particular metal layers, and intervening dielectric layers alternately one above the other. Like from the DE 38 07 600 A1 known, this results in an advantageous filter effect in the infrared spectral range. In connection with the present invention is essential that such a known arrangement can be advantageously used for the development of the invention. The already provided for thermal protection reasons layer 14 can simultaneously in cooperation with the electrically conductive layer 20 of the radar anti-reflective element 2 used for the radar reflectance. The function of the heat protection glass is retained. The dielectric layers 15 and 16 do not affect the inventive effect of the radar specular reflection when they are thin compared to the radar wavelength.

A reflection reduction of more than 20 db could be achieved by the sheet resistance of the electrically conductive layer 14 was selected in the range between 2 to 15 ohms / □ and at the same time the distance D and the thickness of the electrically conductive layer 20 have been optimized so that the total admittance of the layer system at the present radar frequency reaches a value of about 1 / (377 ohms).

As in 3 shown, the inventive radar anti-reflection element 2 also for radar reflections of metal Fassadenberei find use. The radar anti-reflection element according to the invention 2 is at a given distance D above the surface 33 of the metal building facade element 31 to be arranged so that at the electrically conductive layers 20 and the surface 33 The building facade results in resonant absorption. A possibly. the building facade covering plastic layer 34 is for the operation of the invention without influence. The refractive index of the plastic layer must, however, if necessary. be taken into account in the calculation of the phase difference of the two partial waves.

Advantageously, the gap between the radar anti-reflection element 2 and the building facade 31 in 3 or between the radar anti-reflection element 2 and the glazing element 1 in the 1 and 2 be used to further improve the thermal insulation of the building. The gap 32 For this purpose, it can be hermetically sealed on all sides and, furthermore, it can be charged with a reduced filling pressure compared to the external pressure and / or it can be a suitable filling gas. Suitable filling gases are, in particular, those with low heat conduction and a low tendency to convection.

In addition, it is possible in the 1 and 2 illustrated double glazing 1 and the radar anti-reflective element 2 to summarize a triple glazing when the radar anti-reflection element 2 not retrofitted, but already with the if necessary. also partial re-glazing of a building should be installed.

The operation of the invention is based on the fact that the radar anti-reflection element 2 with the electrically conductive layer 14 a glazing element or an electrically conductive building facade 31 forms a reflection Fabry-Perot resonator which is dimensioned to show resonance of the absorption for the radar frequency. Its reflectivity is then minimal. To minimize the reflection of the system, the distance D between the conductive layers and the thickness of the conductive layer must be 20 of the anti-reflection element 2 be optimized. Opitmal adjustment is achieved when at the radar frequency the total system response is 1 / (377 ohms). At oblique incidence of radar radiation 30 must be the distance D and the thickness of the conductive layer 20 depending on the angle of incidence and polarization state (s or p polarization) of the incident radar radiation can be optimally adjusted. However, since the ATC works with fixed radar sources, the angle of incidence and the state of polarization of the radar radiation with respect to a certain building surface are usually fixed, so that the thicknesses can be suitably adjusted.

With The present invention thus provides a simple, inexpensive and retrofittable Arrangement for radar-anti-reflection of buildings.

Claims (15)

Radar anti-reflection element ( 2 ) for the reflection reduction of radar radiation ( 30 ) on a multi-pane building glazing ( 1 ) comprising at least one thin, transparent first electrically conductive layer ( 14 ), wherein the radar anti-reflection element ( 2 ) at a predetermined distance on the side of the incident radar radiation ( 30 ) in front of the multi-pane building glazing ( 1 ) and one on a transparent, dielectric substrate ( 21 ) applied, thin, transparent second electrically conductive layer ( 20 ) and wherein the distance (D) between the first electrically conductive layer ( 14 ) of the multi-pane building glazing ( 1 ) and the second electrically conductive layer ( 20 ) is dimensioned in dependence on the angle of incidence and polarization state of the radar radiation such that the standing wave field between the conductive layers ( 20 and 14 , respectively. 31 ) is set in such a way that the currents induced in the conductive layers dissipate the radar radiation as quantitatively as possible, characterized in that the sheet resistance of the second electrically conductive layer ( 20 ) is dimensioned so that the total admittance of the radar anti-reflection element ( 2 ) and the multi-pane building glazing ( 1 ) in the frequency range of the radar radiation ( 30 ) is about 1 / (377 ohms). Radar anti-reflection element ( 2 ) according to claim 1, characterized in that the dielectric substrate ( 21 ) is a glass sheet. Radar anti-reflection element ( 2 ) according to claim 1, characterized in that the dielectric substrate ( 21 ) consists of a transparent plastic material, in particular a polymer glass. Radar anti-reflection element ( 2 ) according to one of claims 1 to 3, characterized in that the sheet resistance of the second electrically conductive layer ( 20 ) is in the range between 350 to 450 ohms / □. Radar anti-reflection element ( 2 ) for reflection reduction against radar radiation ( 30 ) on a multi-pane building glazing ( 1 ) according to one of claims 1 to 4, characterized in that the surface resistance of the first electrically conduct the layer ( 14 ) is in the range between 2 to 15 ohms / □. Radar anti-reflection element ( 2 ) for reflection reduction against radar radiation ( 30 ) on a multi-pane building glazing ( 1 ) according to one of claims 1 to 5, characterized in that the first electrically conductive layer ( 14 ) Component of an infrared radiation-reflecting thermal protection coating ( 14 - 16 ). Radar anti-reflection element ( 2 ) for the reflection reduction of radar radiation ( 30 ) on a multi-pane building glazing ( 1 ) according to claim 6, characterized in that the thermal insulation coating ( 14 - 16 ) of a plurality of dielectric layers ( 15 . 16 ) and one or more electrically conductive layers ( 14 ), in particular of Ag, SnO ₂ or indium tin oxide (ITO). Radar anti-reflection element ( 2 ) for the reflection reduction of radar radiation ( 30 ) on a multi-pane building glazing ( 1 ) according to one of claims 1 to 7, characterized in that the intermediate space ( 32 ) between the radar anti-reflection element ( 2 ) and the building glazing ( 1 ) is hermetically sealed. Radar anti-reflection element ( 2 ) for the reflection reduction of radar radiation ( 30 ) on a multi-pane building glazing ( 1 ) according to claim 8, characterized in that the hermetically sealed gap ( 32 ) between the radar anti-reflection element ( 2 ) and the building glazing ( 1 ) is applied to further improve the heat insulation with a relation to the external pressure reduced filling pressure and / or filled with a filling gas with a low tendency to convection. Radar anti-reflection element ( 2 ) for the reflection reduction of radar radiation ( 30 ) on a metal building facade element ( 31 ) in front of the building façade element ( 31 ) is arranged at a predetermined distance and one on a dielectric substrate ( 21 ) applied thin electrically conductive layer ( 20 ), wherein the distance (D) between the surface ( 33 ) of the building facade element ( 31 ) and the thin, electrically conductive layer ( 20 ) is dimensioned in dependence on the angle of incidence and polarization state of the radar radiation such that the standing wave field between the building facade ( 31 ) and the conductive layer ( 20 ) just so happens that in the leading layers ( 20 and 31 ) induced currents radiate the radiation as quantitatively as possible, characterized in that the sheet resistance of the electrically conductive layer ( 20 ) such that the total admittance of the device is approximately 1 / (377 ohms). Radar anti-reflection element ( 2 ) according to claim 10, characterized in that the dielectric substrate ( 21 ) is a glass sheet. Radar anti-reflection element ( 2 ) according to claim 10, characterized in that the dielectric substrate ( 21 ) consists of a plastic material, in particular a polymer glass. Radar anti-reflection element according to one of Claims 10 to 12, characterized in that the sheet resistance of the electrically conductive layer ( 20 ) is in the range between 350 to 450 ohms / □. Radar anti-reflection element ( 2 ) for the reflection reduction of radar radiation ( 30 ) on a metal building facade element ( 31 ) according to one of claims 10 to 13, characterized in that the intermediate space ( 32 ) between the radar anti-reflection element ( 2 ) and the metal building facade element ( 31 ) is hermetically sealed. Radar anti-reflection element ( 2 ) for the reflection reduction of radar radiation ( 30 ) on a metal building facade element ( 31 ) according to claim 14, characterized in that the hermetically sealed space ( 32 ) between the radar anti-reflection element ( 2 ) and the building facade element ( 31 ) is applied to further improve the heat insulation with respect to the outer space reduced filling pressure and / or filled with a filling gas with a low tendency to convection.