Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
  • H01Q3/44—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the electric or magnetic characteristics of reflecting, refracting, or diffracting devices associated with the radiating element
  • H01Q3/46—Active lenses or reflecting arrays
• • 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
  • H01Q15/18—Reflecting surfaces; Equivalent structures comprising plurality of mutually inclined plane surfaces, e.g. corner reflector

Definitions

• the field of the invention is that of dihedral devices comprising two plates.
• the invention relates to a technique for adapting (maximizing or minimizing) the radar equivalent surface in a single-static configuration (SER) of a device in the form of flattened dihedron, that is to say a dihedron whose two plates form between them an angle of ⁇ -2 ⁇ , with 0 ⁇ ⁇ / 4.
• SER single-static configuration
• a maximization of the SER it is sought to make an object very easily detectable by a monostatic radar.
• the present invention may for example be used on a bicycle, in order to facilitate its detection by an automobile collision avoidance radar.
• Equivalent applications are possible for the detection of ships (especially light vessels such as sailboats) by coastal radars or radars on board other ships. Again, collision avoidance can be targeted by using a space-saving system.
• all applications requiring a system to respond to an incident wave regardless of its orientation are concerned by this invention when it is used to maximize SER: radio frequency identification, tracking system, SER agility, etc.
• the invention makes it possible to address stealth applications. We try to make an object difficult to detect by a radar.
• ⁇ 0 in Figure 1A and ⁇ ⁇ 0 in Figure 1B.
• the incident wave is reflected in the direction from which it is derived, thanks to a double reflection on each of the metal surfaces 2, 3 of the metal dihedral. It is this double specular reflection which, by virtue of Descartes' law of reflection, makes it possible to maximize the SER of the object (metal dihedral).
• the behavior is similar to that of a reflex reflector in optics. The principle remains the same for a large variation of the angle of incidence ⁇ (approximately ⁇ 15 ° for the main lobe).
• the interesting property of a metal dihedral is to present a quasi-constant SER (with a variation of 3 dB relative to the maximum SER) for a variation of the angle of incidence ⁇ of approximately ⁇ 20 ° with respect to the direction of incidence of the zero incidence pattern.
• Van Atta network is a unique and flat printed network.
• such a network requires printed lines of interconnection between the different elements of the network. These lines are sources of losses, spurious radiation and complexity in the design.
• a third known solution consists in using heterodyne retrodirective network structures that use the principle of phase conjugation for the re-transmitted signal. These structures are more difficult to implement since they are based on an active structure (multiplication with a local oscillator oscillating at the frequency twice the frequency of the received signal). 2.2 Minimization of SER
• a first family of methods amounts to modifying the surface impedance of the faces of a dihedron, for example, by depositing an absorbent material on the faces of the dihedron.
• the reflection mechanisms are attenuated by the presence of this absorbent material.
• RAM Radar Absorbent Materials
• Another method similar to the attenuation of the wave by the material amounts to "trapping" the electromagnetic wave incident in the material through a particular geometry. This geometry is described via a ground plane and a given material thickness (Salisbury screen).
• an objective is to provide a technique for adapting (maximizing or minimizing) the radar equivalent surface (SER) of a device in the form of a flattened dihedron (c '). that is to say a dihedron whose two plates form between them an angle of ⁇ -2 ⁇ , with 0 ⁇ ⁇ / 4), whose size is smaller than a conventional metal dihedral whose two plates form between they an angle of ⁇ / 2.
• SER radar equivalent surface
• At least one embodiment of the invention also aims to provide such a technique that does not require (unlike Van Atta network) printed lines interconnection between different network elements.
• Another objective of at least one embodiment of the invention is to provide such a technique using a fully passive structure (in contrast to the heterodyne retrodirective networks), which makes it much simpler, less expensive and entirely self-sufficient. energy point of view.
• Yet another object of at least one embodiment of the invention is to provide such a technique that allows multi-frequency operation (that is to say operation possible at several operating frequencies, possibly discarded).
• Yet another object of at least one embodiment of the invention is to provide such a technique which is simple to implement and inexpensive.
• Yet another object of at least one embodiment of the invention is to provide such a technique that allows to offer a time-varying SER (SER agility).
• a dihedral-shaped device comprising two plates, characterized in that the two plates form between them an angle of ⁇ -2 ⁇ , with 0 ⁇ ⁇ / 4.
• Each plate comprises a ground plane, at least one dielectric layer and an array of radiating elements, an incident wave being reflected by the device through a double reflection on the two plates.
• the array of radiating elements of each plate makes it possible to produce a phase shift, from the outside towards the center of the dihedron in along an axis perpendicular to an intersection axis of the two plates, according to a determined phase law, to add a misalignment with respect to a specular reflection for a given operating frequency.
• this particular embodiment of the invention is based on a completely new and inventive approach of using two networks of radiating elements (one in each dihedral plate), applying the same phase law but not in the same meaning (each network produces a phase shift from the outside to the center of the dihedron).
• Each network provides additional misalignment with respect to specular reflection. It is thus possible to control the re-radiation direction of an incident wave, irrespective of the opening of the ⁇ -2 ⁇ angle between the two plates.
• An originality of the present invention is therefore due to the fact that the structure is almost flat (if not completely flat like the Van Atta network) but does not require any line in addition to the radiating elements of the network (unlike the Van Atta network) .
• Another originality of the present invention is that several particular implementations are possible with different purposes: increase the SER of the device, reduce the SER of the device or obtain a SER variable in time.
• said phase law allows the device to reflect an incident wave in the direction from which it is derived, in order to increase the radar cross section of the device.
• the misalignment with respect to the specular reflection is: ⁇ / 2 - 2a, towards the center of the dihedron.
• the phase law is written:
• said phase law allows the device to reflect an incident wave in a direction different from that from which it originates, in order to reduce the radar equivalent surface of the device.
• the device comprises means for modulating said phase law as a function of time, making it possible to modulate the radar equivalent surface of the device as a function of time.
• the radiating elements are radiating elements each introducing a variable phase shift
• said modulating means comprise, for each array of radiating elements, a plurality of active circuits each controlling the phase shift of one of said radiating elements.
• the radiating elements are radiating elements printed on said at least one dielectric layer.
• the phase difference between two successive radiating elements, from the outside to the center of the dihedral along said axis perpendicular to the intersection axis of the two plates, is obtained by a modifying at least one dimension of the radiating elements.
• the pitch of each array of radiating elements is less than ⁇ / 2, with ⁇ the working wavelength.
• each plate comprises at least one other array of radiating elements, making it possible to add a misalignment with respect to the specular reflection, for another given operating frequency.
• the number of possible operating frequencies (multi-frequency operation) is increased.
• the radiating elements are radiating elements each introducing a fixed phase shift.
• the device is an entirely passive structure (unlike the prior art heterodyne retrodirective networks), which makes it much simpler, less expensive and entirely autonomous from an energy point of view.
• FIGS. 1A and 1B already described in relation to the prior art, illustrate the principle of reflection in a conventional metal dihedron
• Figures 2 and 3 show views, side and perspective respectively, of a dihedral device according to a particular embodiment of the invention
• FIG. 4 illustrates the phase law of a phase-shifter grating, as well as its operation with a plane wave at normal incidence (angle of incidence ⁇ equal to zero);
• FIG. 5 illustrates the operation of the phase-shifting network of FIG. 4, in the case where the incident wave brings a phase delay with respect to the configuration of the wave at normal incidence;
• FIG. 6 illustrates the operation of the phase-shifting network of FIG. 4, in the case where the incident wave brings a phase advance with respect to the configuration of the wave at normal incidence;
• FIG. 7 illustrates the operation of the device of FIG. 2, for a plane wave at normal incidence with respect to the rear equivalent plane of the device
• FIG. 8 illustrates the operation of the device of FIG. 2, in the case where the incident wave brings a phase delay with respect to the configuration of the wave at normal incidence on the plate (panel) of the left of the device
• FIG. 9 illustrates the operation of the device of FIG. 2, in the case where the incident wave brings a phase advance with respect to the configuration of the wave at normal incidence on the plate (panel) of the left of the device
• FIG. 10 illustrates a variant of the device of FIG. 3, in which the device has two possible operating frequencies
• FIG. 11 illustrates another variant of the device of FIG. 3, in which the device comprises means for modulating the phase law as a function of time.
• the present invention is the application of a phase shift between different radiating elements of a reflective grating which makes it possible to produce the desired reflection law, for each plate of a device in the form of dihedron.
• the phase shift produced by each plate makes it possible to add a misalignment to the specular reflection.
• phase law allows the device to reflect an incident wave in the direction from which it is derived in order to increase the radar equivalent surface (ERR) of the device is described in greater detail.
• the device 10 comprises two plates 11a, 11b forming between them an angle of ⁇ -2 ⁇ , with 0 ⁇ ⁇ / 4.
• Each plate 11a, 11b comprises a ground plane 12a, 12b, a dielectric layer 13a, 13b and an array of radiating elements 14a, 14b (also called reflector networks).
• the radiating elements are radiating elements printed on the dielectric layer.
• each plate comprises several dielectric layers.
• the radiating elements are distributed on a single layer on the surface of the single dielectric layer. In an alternative embodiment, the radiating elements are distributed over several layers (this is conventional in the reflector network techniques for increasing the bandwidth).
• An incident wave is reflected by the device through a double reflection on the two plates 11a, 11b. It is assumed that the wave vector of the incident wave is contained in a plane simultaneously perpendicular to the two plates of the dihedron 10.
• the array of radiating elements 14a, 14b of each plate 11a, 11b makes it possible to produce a phase shift, from the outside to the center of the dihedral along an axis (referenced 15a for the left plate and 15b for the right plate) perpendicular to an axis 16 of intersection of the two plates, according to a determined phase law, to add a misalignment with respect to a specular reflection for a given operating frequency.
• the phase shift is achieved by a decrease in the size of the radiating elements towards the center of the dihedron (from left to right for the left plate 11a, and from the right to the left for the right plate 11b).
• the phase law corresponds in this case to a negative phase shift increasing toward the center of the dihedron.
• the phase shifts produced by the radiating element arrays 14a, 14b of the two plates are therefore inverted relative to one another.
• the application of a phase shift between the different elements of each of the networks 14a, 14b makes it possible to maximize the SER while avoiding the orthogonality constraint between the two faces (plates 11a, 11b) involved in the double reflection.
• each grating 14a, 14b is produced solely by varying the geometry of the radiating elements, that is to say by modifying at least one dimension of the radiating elements (instead of take radiating elements all identical as is the case in a conventional network).
• the radiating elements of the networks 14a, 14b are rectangular patches. However, there are many other topologies of radiating elements to achieve the desired phase shift (annular patch, circular patch, patch loaded with slots, patch loaded by a stub, ). In all cases, it is the modification of one or more dimension (s) of the radiating elements on the surface of the network 14a, 14b which produces the desired phase shift.
• phase shift ⁇ between two successive elements must be described by the relation:
• FIG. 7 illustrates the operation of the device 10 of FIG. 2, for a plane wave at normal incidence with respect to the rear equivalent plane of the device.
• This figure 7 thus describes the geometry of the so-called “flattened” dihedral problem, when the incident wave is normal to the rear equivalent plane, that is to say that the incident wave makes an angle ⁇ with the normal of the surface. of the phase shifter grating of the left plate 11a (normal of the surface of those 11a of the two plates 11a, 11b which receives the incident wave). This configuration is called "zero incidence configuration”.
• phase shift between two successive elements must correspond to a delay described with a phase law Y;
• This phase law applied by the network 14a, 14b of each of the plates 11a, 11b makes it possible to compensate for the opening of the dihedral, by providing the additional misalignment of the beam with respect to the specular reflection.
• FIG. 8 illustrates the operation of the device of FIG. 2 in the first case, that is to say in the case where the incident wave brings a phase delay with respect to the configuration of the wave at normal incidence on the left plate (panel) 11a of the device 10.
• FIG. 9 illustrates the operation of the device of FIG. 2 in the second case, that is to say in the case where the incident wave brings a phase advance with respect to the configuration of the wave at normal incidence on the left plate (panel) 11a of the device 10.
• the incident wave brings a phase advance with respect to the configuration of the wave at normal incidence on the left plate (panel) 11a of the device 10.
• the angle ⁇ in order to preserve the dihedral effect and not to arrive on the reflecting grating in grazing incidence (remembering that this effect is also present with a classical dihedral). It is said that the dihedron is characterized by an opening angle. It is possible to increase this opening angle by creating a network of dihedrons. Thus, it becomes quite appropriate to have dihedres 10 according to the present invention, having a small footprint.
• each reflector array 14a, 14b It is possible to choose among several shapes for the radiating elements (also called “cells") constituting each reflector array 14a, 14b: ring elements, circular elements, rectangular elements, square elements ...
• the choice of a cell shape is essentially based on the total range of phase shift that can be obtained by varying the cell sizes, as well as the frequency behavior of the phase shift law. Through simulations, it is shown that a ring-type cell is a good compromise if one seeks to have the maximum excursion possible for the phase shift with the best possible linearity over the largest possible frequency range.
• each reflector array 14a, 14b is chosen so as to limit as much as possible the rise of secondary lobe levels (in particular the lattice lobes): this step is thus chosen less than ⁇ / 2, with ⁇ the length of working wave.
• this network pitch must not be too small if it is desired to have a large possible variation of phase shift between the cells (variation fixed by the size).
• the choice is therefore based on the comparison of simulations between a network at ⁇ / 2 and a network at ⁇ / 3.
• the result of the simulations shows that the network pitch of ⁇ / 3 is preferable because it induces lower side lobes than for the network pitch of ⁇ / 2.
• each reflector array 14a, 14b (size of each panel 11a, 11b) influences the maximum SER level of the device 10 (dihedral with two reflector gratings). It is thus a question of finding a compromise between size of network and maximum level of SER. It is possible to make a comparison with a metal dihedron of the same size knowing that for this metal dihedral, the SER is maximum.
• the bandwidth is not necessarily a constraint.
• the frequency of use is known and fixed. Broadband is not useful. It is the same for identification type applications.
• each plate 11a, 11b comprises, for example, at least one other array of radiating elements, making it possible to add a misalignment with respect to the specular reflection, for another given operating frequency.
• each plate comprises N reflector gratings, each having a distinct operating frequency, with N greater than or equal to two.
• the first relies on first networks of radiating elements 14a, 14b (identical to those of FIG. 3, with radiating elements which are rectangular patches); and
• the second relies on second networks of radiating elements 14a ', 14b' (with radiating elements which are circular patches).
• the incident wave is sent in a direction different from that of the radar in the case of a single-static configuration. This extension allows to address stealth applications.
• the device comprises means for modulating the phase law as a function of time, thus making it possible to modulate the SER of the device as a function of time (agility of SER).
• the phase shift produced by each element of each grating 14a, 14b is for example controlled by an active circuit (phase shifter circuit) 111.
• the radiating elements are radiating elements each introducing a variable phase shift (and no longer a fixed phase shift as in the example of FIGS. 2, 3 and 7 to 9), and the modulation means comprise, for each array of radiating elements, a plurality of active circuits 111 each controlling the phase shift of one of the radiating elements.
• This plurality of active circuits is itself controlled by a suitable control device (processor for example) 113, receiving as input a setpoint indicating the desired variation of the SER of the device.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Aerials With Secondary Devices (AREA)
• Variable-Direction Aerials And Aerial Arrays (AREA)
• Radar Systems Or Details Thereof (AREA)

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• 2012
  • 2012-11-08 FR FR1260615A patent/FR2997796B1/fr not_active Expired - Fee Related
• 2013
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  • 2013-11-07 WO PCT/EP2013/073306 patent/WO2014072431A1/fr active Application Filing
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