Classifications

• • 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
  • H01Q15/006—Selective devices having photonic band gap materials or materials of which the material properties are frequency dependent, e.g. perforated substrates, high-impedance surfaces
• • 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
  • H01Q17/008—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems with a particular shape
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K1/00—Printed circuits
  • H05K1/02—Details
  • H05K1/0213—Electrical arrangements not otherwise provided for
  • H05K1/0216—Reduction of cross-talk, noise or electromagnetic interference
  • H05K1/0236—Electromagnetic band-gap structures

Definitions

• TITLE System for reducing the reflectivity of an electromagnetic wave incident on a surface and device implementing this system
• the present invention relates to a system allowing the reduction of the reflectivity of an electromagnetic wave incident on a surface.
• a system for controlling the reflection of an electromagnetic wave incident on a surface is described below.
• the system is integrated into the surface and is equipped with a checkerboard composed of first facets and second facets, each first facet is composed by the repetition of a first pattern comprising a first dielectric zone and a first electrically conductive zone, said first zones being configured so that the first facet comprises a series equivalent resonant circuit having an impedance Zs.
• the reflection system has one or more of the following characteristics, taken separately or according to all the technically possible combinations:
• the first dielectric zone has a first shape and the first electrically conductive zone has a second shape, furthermore the second dielectric zone has the second shape and the second electrically conductive zone has the first shape.
• the first patterns and the second patterns have the same geometry and the first electrically conductive zones are connected by electrical connection means so as to be short-circuited.
• This has the advantage of having first facets and second self-complementary facets to obtain the cancellation of the backscattered field in the axis of reflection over a wide frequency band.
• a rate of pairs T p of the checkerboard is defined by: min(number of first facets, number of second facets). . . . .
• T p — y — ⁇ — — - — 7 — - - — — - — 7 - - - -, the rate of pairs being greater than max(number of first facets, number of second facets) 1 1 or equal to 0, 95, preferably greater than or equal to 0.98.
• each first facet is not necessarily associated with a second complementary facet. To obtain a satisfactory result, the rate of pairs must be sufficiently high so as to ensure a negligible residue of the backscattered field.
• the description also relates to a device implementing the system for controlling the reflection of an electromagnetic wave incident on a surface comprising a first dielectric layer, a checkerboard, a second dielectric layer and a conductive plane arranged so as to act as a mass and stacked in the following order: the first layer then the checkerboard then the second layer then the conductive plane.
• This arrangement makes it possible in particular to protect the checkerboard from attacks from the external environment, improving for example the resistance to shocks and corrosion.
• the device has one or more of the following characteristics, taken separately or according to all the technically possible combinations:
• an additional grid can also advantageously be placed between the third layer and the first layer to improve the performance of the device at large angles of incidence.
• Figure 1 shows a detail of the reflection system
• Figures 2a and 2b show elementary and complementary patterns in the form of slits and rings.
• Figure 3 shows a checkerboard composed of first and second constituent facets of the invention
• FIG. 4 [Fig. 5][Fig. 5] Figures 4 and 5 show respectively multi-periodic and symmetric and non-periodic and non-symmetric checkerboard embodiments
• Figure 6 shows a graph illustrating measured attenuation performance as a function of frequency.
• FIG. 7a [Fig. 7b] Figures 7a and 7b show a particular embodiment of the so-called self-complementary system.
• Figure 8 is a graph illustrating the variation of the phases obtained for each of the facets as well as their difference calculated on the embodiment of Figure 7 as a function of the frequency.
• Figure 9 shows a longitudinal sectional view of an example of the device implementing the system of the invention.
• Figure 1 shows a checkerboard 1 according to the invention.
• the checkerboard 1 comprises first facets 2 and second facets 3.
• Figure 2a shows a basic pattern of the first facet 2.
• Figure 2b shows a basic pattern of the second facet 3.
• the base pattern of the first facet 2 consists of a first non-conductive zone 4 and a first conductive zone 5 while according to Figure 2b, the base pattern of the second facet 3 consists of a second conductive zone having the shape of the non-conductive zone 4 of the first pattern and a second non-conductive zone having the shape of the conductive zone 5 of the first pattern.
• first and second facets 2, 3 are complementary: the superposition of the conductive zones of the elementary patterns of the first and second facets gives an entirely conductive surface.
• Each facet is formed by the repetition of an elementary pattern so as to form a high impedance surface (SHI).
• the patterns are repeated for example periodically in a facet.
• the elementary patterns are square in shape.
• the conductive zones are made with, for example, a metal such as copper.
• Any other electrically conductive material can be envisaged to produce these conductive areas and in particular conductive inks.
• the non-conductive zones are made by spaces occupied by air, vacuum or a dielectric material, for example a polyurethane resin, filling this space during integration into a complete device.
• a dielectric material for example a polyurethane resin
• phase difference between the reflection coefficients of the two circuits is then equal to 180° whatever the possible losses and the frequency (including at resonance).
• the amplitudes of the backscattered fields are equal to 1 while in the case with losses they are less than 1 but remain equal to each other.
• a cancellation of the backscattered field in the axis is thus obtained, that is to say that the electromagnetic wave incident on the surface of the system is canceled during its reflection, thus making it possible to improve the integration of antennas or other radiating devices by reducing the interference between them by means of separators implementing the system of the invention or reducing the backscattering of the wave emitted by a radar and therefore improving the wearer's stealth.
• the dimensioning therefore consists in using a normalization impedance which is compatible with the known inductances and capacitances of the realizable gates.
• the first and second facets 2 and 3 are associated in pairs to obtain the effect of cancellation of the backscattered field in the axis.
• the reflection system has a pair rate equal to 1 or as close as possible to 1.
• Figure 3 shows an embodiment where the checkerboard 1 has a set of facets 2 and 3 arranged periodically.
• the x and y directions are the transverse directions in the plane of the checkerboard 1 .
• the first and second facets 2 and 3 alternate regularly without the surfaces of the facets varying in any direction.
• Each first facet and each second facet have the same geometry. Their areas are equal.
• Figures 4 and 5 present two embodiments of the invention for which the checkerboard 1 is non-periodic.
• the x and y directions are the transverse directions in the plane of the checkerboard 1 .
• the checkerboard 1 formed is multi-periodic and symmetrical, the first and second facets 2, 3 have different dimensions depending on their location in the network.
• the first and the second facet have a larger dimension along the direction x than along the dimension along y.
• the first and the second facet have a larger dimension along the y direction than along the dimension along x.
• the checkerboard 1 is non-symmetrical, the alternation of the first and second facets is not regular.
• the arrangement begins with three second facets 3 then two first facets 2, followed by a second facet 3, three first facets 2 and finally a second facet 3.
• multi-periodic or non-periodic arrangements make it possible to process the grating lobes, so as to minimize them, or even to eliminate them.
• the type of non-periodic arrangement can be optimized according to the frequencies, incidences and observation zones of the electromagnetic waves considered.
• Figure 6 presents a graph illustrating the reduction of the effective radar surface SER (or RCS radar cross section) according to the frequency.
• the RCS is the ability of the surface to backscatter the incident wave towards a given direction (bistatic) or in particular towards the point of emission (monostatic). The measurement is taken at normal incidence.
• the curve is the result obtained for a device implementing the system of the invention having the following characteristics: non-periodic checkerboard, with dimensions of 244.8 mm ⁇ 244.8 mm.
• the invention therefore allows excellent attenuation as well as attenuation beyond -20 dB over a very wide frequency band.
• Figures 7a and 7b show a particular embodiment of the system of the invention.
• Figure 7a illustrates a square elementary pattern composed of a conductive area 5 and a non-conductive area 4.
• the conductive zone 5 is a square and the non-conductive zone 4 consists of triangles joined to each side of the square of the conductive zone 5.
• Figure 7b shows the checkerboard 1 which comprises a set of first facets 2 and second facets 3 arranged periodically.
• the first facet 2 comprises meshes made up of patterns composed of a conductive zone 5 and a non-conductive zone 4. Four elementary patterns are gathered together for each non-conductive zone 4.
• the conductive zones 5 are electrically connected to each other by electrical connection means 6.
• the conductive zones 5 are therefore short-circuited.
• the second facet 3 has the same arrangement of patterns as the first facet 2.
• the first facet 2 and the second facet 3 therefore have the same geometry.
• the conductive zones 5 of the second facet 3 are not connected to each other. They are open circuit.
• the first facet 2 is equivalent to a series resonant circuit and the second facet 3 is equivalent to a parallel resonant circuit.
• first and second facets 2, 3 are self-complementary. This embodiment also makes it possible to obtain the cancellation of the backscattered field in the axis whatever the frequency and any losses.
• the pattern of the second facet 3 is generally obtained by a rotation, a symmetry or a translation of the pattern of the first facet 2.
• the conductive zones 5 are for example metallic, such as copper or conductive ink. Any other electrically conductive material can be envisaged to produce these conductive areas.
• the non-conductive zones 4 are for example made by spaces occupied by air, vacuum or by a dielectric material, for example a polyurethane resin, filling this space during integration into a complete device.
• a dielectric material for example a polyurethane resin
• Figure 8 presents a graph illustrating the phase of the wave reflected by the surface of the system of the embodiment of Figure 7 with respect to the phase of the wave incident as a function of frequency.
• the dashed line represents the phase shift of the wave reflected by the first facets 2, ie the facets in short circuit.
• the dotted line represents the phase shift of the wave reflected by the second facets 3, i.e. the open circuit facets. In both cases, it can be seen that the phase shift applied to the reflected wave evolves continuously as a function of the frequency.
• Figure 9 illustrates a device implementing the system of the invention.
• the device is a stack consisting of the conductive plane 9, the dielectric layer 8, the checkerboard 1, the second layer 7.
• the first and second facets 2, 3 of the checkerboard 1 are visible in the form of long dashes for the first facet 2 and short dashes for the second facet 3.
• the conductive plane 9 is also called the reflector plane or ground plane and makes it possible to reflect the waves incident on the surface of the device.
• the conductive plane 9 is a metal surface for example which comprises copper or a composite such as a ply of carbon fibers.
• the first and second layers 7, 8 comprise dielectric materials, for example resins or composite materials. These resins may or may not include reinforcing fillers to improve the mechanical strength of the device.
• the resins can for example be chosen from the family of polyesters or vinyl esters.
• the first and second layers 7, 8 also make it possible to protect the checkerboard 1 from attacks from the environment in which the device implementing the system of the invention is used.
• the first layer 7 comprises a vinylester resin and woven polyethylene fibers and the second layer 8 comprises a polyester resin and high modulus glass fibers S2.
• first layer 7 having a low dielectric permittivity as well as low losses
• second layer 8 having a stiffness allowing the use of the stack of the device as a structural panel.
• the first layer 7 has a thickness of 4.1 mm and a dielectric permittivity of 2.6.
• the second layer 8 has a thickness of 3.5 mm and a dielectric permittivity of 4.
• the first layer 7 is configured so as to function as an impedance transformer and transform the impedance of the surface of the checkerboard ZT in order to bring its value closer to that of the vacuum impedance Zo by varying in particular the thickness of this layer as a function of the permittivity of said layer.
• the thickness of the second layer 8 is configured so as to optimize the performance of the device over a wide operating band. This thickness is chosen according to the permittivity of the material. The thickness is generally substantially close to a quarter of the wavelength of the central frequency of the frequency band considered.
• the impedance transformer can be supplemented by a third layer, not shown, there is then a stack comprising the third layer then the first layer 7, the checkerboard 1, the second layer 8 and the conductive plane 9.
• the third layer completes the role of impedance transformer and its thickness and dielectric permittivity characteristics are chosen so as to raise the impedance of the surface of the checkerboard ZT towards the impedance of the vacuum Zo.
• the device can be completed by a grid in addition to the third layer.
• the grid can have a regular geometry in the form of a plate pierced with recesses at regular intervals. This grid makes it possible to extend the operation of the device to large angles of incidence by straightening the incident wave.
• the different materials used can be lossless. This means that when the electromagnetic wave passes through them, its amplitude does not change.
• the materials used for the non-conductive and/or conductive patterns are lossy. That is, when the electromagnetic wave passes through them, its amplitude is attenuated.
• some areas of the device implementing the inventive reflection control system include lossless materials while other areas include lossy materials.
• the edges of the device include lossy materials to deal with edge effects and grating lobes.

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Aerials With Secondary Devices (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

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• 2021
  • 2021-01-29 FR FR2100857A patent/FR3119491A1/fr active Pending
• 2022
  • 2022-01-27 WO PCT/EP2022/051864 patent/WO2022162050A1/fr active Application Filing
  • 2022-01-27 EP EP22705027.5A patent/EP4285441A1/de active Pending

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