Patent Application
20210194142
The invention relates to the technical field of transmitarray antennas. A transmitarray antenna comprises:
Each elementary cell of the transmitarray is capable of introducing a phase shift to the incident wave emitted by the primary source or sources in order to compensate each path difference of the radiation emitted between the primary source or sources and the transmitarray.
More precisely, each elementary cell of the transmitarray comprises at least:
“Planar antenna” is understood to mean an electrically conductive flat surface (normally made of metal) able to emit/receive electromagnetic radiation. One example of a planar antenna is the micro-strip patch.
Other elementary cell architectures may also be used, such as multilayer structures based on the concept of frequency-selective surfaces, or on the concept of Fabry-Perot cavities. Radiating elements such as dipoles, slots etc. may also be used in the elementary cell.
It should be noted that an elementary cell of a transmitarray is able to operate in receive mode or in transmit mode, that is to say that the first antenna of the elementary cell may also be a transmit antenna, while the second antenna of the elementary cell may also be a receive antenna.
The invention is applicable notably for obtaining a reconfigurable antenna. “Reconfigurable” is understood to mean that at least one feature of the antenna may be modified over its service life, after it has been manufactured. The feature or features generally able to be modified are the frequency response (in terms of amplitude and in terms of phase), the radiation pattern (also called beam), and the polarization. Reconfiguring the frequency response covers various functionalities, such as frequency switching, frequency tuning, bandwidth variation, phase shift, frequency filtering etc. Reconfiguring the radiation pattern covers various functionalities, such as angular scanning of the beam pointing direction (also called depointing), the aperture of the beam typically defined at half-power (that is to say the concentration of the radiation in a particular direction), spatial filtering (linked to the aperture and the formation of the beam), beamforming or multi-beamforming (for example a plurality of narrow beams replacing a wide beam) etc. A reconfigurable transmitarray antenna is particularly advantageous from the C band (4-8 GHz) up to the W band (75-110 GHz), or even the D band (110-170 GHz) or up to the 300 GHz band, for the following applications:
A transmitarray antenna known from the prior art, in particular from document WO 2012/085067, comprises:
Such a transmitarray antenna has a thickness, defined by the distance (called “focal length”) between the radiating source and the electromagnetic lens. The various electromagnetic and geometric parameters (for example the typology of the radiating elements of the phase-shifting cells and of the emissive region, the surface of the electromagnetic lens, the focal length, etc.) condition the gain of the antenna and its frequency evolution. For example, at parity of the ratio F/D, where F is the focal length and D is the diameter of the electromagnetic lens, the parameter D—and therefore the parameter F—have to be doubled in order to achieve a gain of 6 dBi (decibels relative to isotropic) and keep the same relative bandwidth at 1 dB or 3 dB. The ratio F/D is typically between 0.3 and 0.7. If it is desired to maintain the ratio F/D, then it is necessary to increase F.
Such an antenna from the prior art is not entirely satisfactory in so far as the search for a high gain for the antenna will therefore lead to an increase in the focal length, and thereby the thickness of the antenna. The search for a high gain, while keeping the same relative frequency behaviour, will therefore require good control of the excitation of the phase-shifting cells over a wide aperture. However, controlling the excitation of the phase-shifting cells over a wide aperture may prove to be a complex task, in particular when the operating frequency of the antenna is of the order of around ten/one hundred GHz or of one THz, specifically because of a need for high precision of the assembly between the emissive region and the electromagnetic lens.
In addition, the control electronics for the switches will have to be positioned with care so as to interfere as little as possible with the radiation transmitted by the phase-shifting cells.
The invention aims to fully or partly rectify the abovementioned drawbacks. To this end, one subject of the invention is a reconfigurable antenna, comprising:
Other elementary cell architectures may also be used, such as multilayer structures based on the concept of frequency-selective surfaces, or on the concept of Fabry-Perot cavities. Radiating elements such as dipoles, slots etc. may also be used in the elementary cell.
Such an antenna according to the invention thus makes it easier to excite the phase-shifting cells over a wide aperture, when a high antenna gain is sought, by virtue of such an electromagnetic coupling region that allows near-field excitation of the phase-shifting cells. The size and shape of the resonant cavity may be adapted in order to optimize the radiation received by the phase-shifting cells, for example to homogenize the amplitude and the phase and to increase the coupling efficiency.
Using electromagnetic coupling then makes it possible notably to obtain an antenna with a reduced thickness in comparison with a slot antenna, to avoid a significant decrease in the electromagnetic field received by the phase-shifting cells located on the edges of the electromagnetic lens, or even to overcome a (frequency) dependence of the electromagnetic radiation received by the phase-shifting cells during beam depointing.
Moreover, such a resonant cavity makes it possible not to lose energy on the lateral parts of the antenna, thereby making it possible to increase the quality of the radiation transmitted by the phase-shifting cells located on the edges of the electromagnetic lens, and to control the illumination law for the electromagnetic lens (apodization or “aperture taper”). Mention may be made for example of the increase in radiation efficiency, by virtue of the reduction in “spillover” (portion of the emitted radiation that does not reach the phase-shifting cells, a phenomenon that is present if the resonant cavity is permissive to electromagnetic waves), the reduction in the levels of the side lobes (SLL for “Side Lobe Level”), etc.
The set of electrically conductive elements, forming a contour of the resonant cavity, allows electromagnetic shielding close to the lateral parts of the transmitarray antenna.
Finally, the fact that the set of electrically conductive elements comprises first tracks electrically connected to the bias lines makes it possible to contemplate moving the control electronics for the switches (for example to under the antenna) so as to interfere as little as possible with the radiation emitted by the radiating source or sources, and the radiation transmitted by the phase-shifting cells.
The antenna according to the invention may include one or more of the following features.
According to one feature of the invention, the resonant cavity has:
According to one feature of the invention, the electromagnetic coupling region extends in a dielectric medium.
One advantage that is afforded is thus that of avoiding electromagnetic interference in the electromagnetic coupling region. The dielectric medium may be air.
According to one feature of the invention, the electromagnetic coupling region comprises a dielectric substrate, comprising interconnect levels; the first tracks being formed on the interconnect levels;
“Dielectric substrate” is understood to mean that the substrate has an electrical conductivity at 300 K of less than 10−8 S/cm.
“Via” is understood to mean a metallized hole for establishing an electrical connection between various interconnect levels.
One advantage that is afforded is thus that of contemplating integrating the resonant cavity within the dielectric substrate.
According to one feature of the invention, the set of electrically conductive elements comprises second tracks electrically connected to the bias lines.
According to one feature of the invention, the second tracks are formed on the interconnect levels;
According to one feature of the invention, the antenna comprises switching means configured so as to switch between the first and second tracks, the non-switched first or second tracks being at floating electrical potential.
“Floating electrical potential” is understood to mean that the non-switched tracks are not subjected to a reference electrical potential at the operating frequency of the antenna.
One advantage that is afforded is thus that of adding a degree of freedom to adjust the electromagnetic behaviour of the resonant cavity. More precisely, there is a first resonant cavity whose contour is formed by the first tracks and the first vias. Likewise, there is a second resonant cavity whose contour is formed by the second tracks and the second vias. The switching means therefore make it possible to switch between the first resonant cavity and the second resonant cavity. By way of non-limiting examples, the first resonant cavity may be configured (in terms of size and shape) so as to widen the bandwidth, while the second resonant cavity may be configured (in terms of size and shape) so as to increase the depointing range.
According to one feature of the invention, the set of electrically conductive elements is arranged such that the contour of the resonant cavity has a cross section that increases from the emissive region towards the electromagnetic lens.
“Cross section” is understood to mean a section perpendicular to an axis corresponding to the normal to a plane defined by the electromagnetic lens.
“Increasing” is understood to mean that the area of the cross section increases from the emissive region towards the electromagnetic lens.
One advantage that is afforded by such a shape of the resonant cavity is thus that of promoting a large gain for the antenna.
According to one feature of the invention, the set of electrically conductive elements is arranged such that the contour of the resonant cavity exhibits axial symmetry.
“Axial symmetry” is understood to mean symmetry about an axis corresponding to the normal to a plane defined by the electromagnetic lens.
One advantage that is afforded by such a shape of the resonant cavity is thus that of promoting the directivity of the antenna, that is to say the ability of the antenna to concentrate the radiated energy in a solid angle or in a specific direction.
According to one feature of the invention, the emissive region is planar.
One advantage that is afforded is thus that of allowing monolithic integration of the emissive region into the resonant cavity when the resonant cavity is formed in a dielectric substrate.
According to one feature of the invention, the electromagnetic lens is planar.
One advantage that is afforded is thus that of monolithically integrating the electromagnetic lens into the resonant cavity when the resonant cavity is formed in a dielectric substrate.
According to one feature of the invention, the emissive region, the electromagnetic coupling region and the electromagnetic lens are monolithic.
“Monolithic” is understood to mean that the emissive region, the electromagnetic coupling region and the electromagnetic lens share one and the same substrate, in the sense that the emissive region, the electromagnetic coupling region and the electromagnetic lens are formed on the same substrate.
One advantage that is afforded is thus that of simplifying the manufacture of the antenna with monolithic technology, for example a PCB (“Printed Circuit Board”) or LTCC (“Low Temperature Co-fired Ceramic”) technology. These technologies allow monolithic implementations, with substrate thicknesses conventionally between 100 μm and 10 mm, and are very particularly suitable when the operating frequency of the antenna is between 1 GHz and 1 THz, small substrate thicknesses being suitable for frequencies of the order of one GHz, while large substrate thicknesses are suitable for frequencies of the order of one THz.
According to one feature of the invention, the resonant cavity has a thickness between λ and 10λ, where λ is the wavelength of the electromagnetic waves.
One advantage that is afforded is thus that of obtaining a compact cavity.
Another subject of the invention is a passive antenna, comprising:
“Passive antenna” is understood to mean that the phase-shifting cells do not have any active electronic components for introducing a phase shift to the electromagnetic waves. The phase shift may be obtained for example through different geometric configurations of the receive and transmit antennas of the phase-shifting cell.
“Ground plane” is understood to mean an electrically conductive surface, preferably made of metal, forming an electrical ground plane so as to define a reference potential for the electromagnetic waves.
Such an antenna according to the invention thus makes it easier to excite the phase-shifting cells over a wide aperture, when a high antenna gain is sought, by virtue of such an electromagnetic coupling region that allows near-field excitation of the phase-shifting cells. The size and shape of the resonant cavity may be adapted in order to optimize the radiation received by the phase-shifting cells, for example to homogenize the amplitude and the phase and to increase the coupling efficiency.
Moreover, such a resonant cavity makes it possible not to lose energy on the lateral parts of the antenna, thereby making it possible to increase the quality of the radiation transmitted by the phase-shifting cells located on the edges of the electromagnetic lens, and to control the illumination law for the electromagnetic lens (apodization or “aperture taper”). Mention may be made for example of the increase in radiation efficiency, by virtue of the reduction in “spillover” (portion of the emitted radiation that does not reach the phase-shifting cells, a phenomenon that is present if the resonant cavity is permissive to electromagnetic waves), the reduction in the levels of the side lobes (SLL for “Side Lobe Level”), etc.
The set of electrically conductive elements, forming a contour of the resonant cavity, allows electromagnetic shielding close to the lateral parts of the transmitarray antenna.
Other features and advantages will become apparent in the detailed description of various embodiments of the invention, the description being accompanied by examples and references to the appended drawings.
The figures are not shown to scale for the sake of legibility and to simplify understanding thereof.
For the sake of simplicity, elements that are identical or that perform the same function in the various embodiments will bear the same references.
One subject of the invention is a reconfigurable antenna 1, comprising:
The emissive region ZE is advantageously planar, such that each radiating source S is located equidistant from the electromagnetic lens 2.
The or each radiating source S is advantageously configured so as to operate at a frequency between 1 GHz and 1 THz, preferably between 10 GHz and 300 GHz.
The emissive region ZE is advantageously electrically connected to a transceiver, located at the rear of the antenna 1 or under the antenna 1.
The electromagnetic lens 2 is advantageously planar.
Each phase-shifting cell 20 may comprise:
The first planar antenna and the second planar antenna Tx are advantageously arranged on either side of a ground plane (not illustrated, except in
The second planar antenna Tx advantageously has first and second radiating surfaces, separate in the sense that they are separated from one another by a separating region so as to be electrically isolated from one another. To this end, a slot is advantageously formed in the second planar antenna Tx in order to electrically isolate the separate first and second radiating surfaces. The slot defines the separating region. The slot is preferably annular, with a rectangular cross section. Of course, other shapes may be contemplated for the slot, such as an elliptical or circular shape. According to one variant implementation, the first and second radiating surfaces of the second planar antenna may be electrically isolated by a dielectric material.
Each phase-shifting cell 20 advantageously comprises a phase shift circuit comprising first and second switches 200 respectively alternately having an on state and an off state, the on or off states corresponding to a respectively authorized or blocked flow of a current between the separate first and second radiating surfaces of the second planar antenna Tx. “Alternately” is understood to mean that the first switch 200 alternates between the on state and the off state, while, simultaneously, the second switch 200 alternates between the off state and the on state. In other words, at all times, the first and second switches 200 belonging to the same phase shift circuit have two opposing states, either on/off or off/on. On/on or off/off states are not authorized.
By way of non-limiting examples, the switches 200 of the phase-shifting cells 20 may be PIN diodes, MEMS (“Micro Electro-Mechanical Systems”), NEMS (“Nano Electro-Mechanical Systems”). PIN diodes may be made from AlGaAs. Other implementation forms may be contemplated for the switches 200. By way of non-limiting examples, radiofrequency switches such as diodes, transistors, photodiodes and phototransistors are possible. The choice of a device for controlling the switches 200 depends on the technology that is chosen. By way of examples, the following devices may be used:
The bias lines BL are electrically conductive tracks, forming control means for controlling the switches 200 of the phase-shifting cells 20. The bias lines BL are preferably made from a metal material, more preferably copper. The bias lines BL may be electrically connected to the set of electrically conductive elements, and to the second planar antenna Tx, by way of transmission lines LT.
Other phase-shifting cell 20 architectures may also be used, such as multilayer structures based on the concept of frequency-selective surfaces, or on the concept of Fabry-Perot cavities.
The electromagnetic coupling region ZC advantageously extends in a dielectric medium.
The electromagnetic coupling region ZC advantageously comprises a dielectric substrate 4, comprising interconnect levels. By way of non-limiting example, the dielectric substrate 4 may be made of a commercial material such as RT/Duroid® 6002. The dielectric substrate 4 has a thickness typically of between 100 μm and 1500 μm for an operating frequency of the antenna of between 10 GHz and 300 GHz. By way of non-limiting example, the dielectric substrate 4 may have a thickness of the order of 4 mm when the operating frequency is 60 GHz.
The first tracks P1 are advantageously formed on the interconnect levels. The set of electrically conductive elements advantageously comprises first vias V1, designed to electrically connect the first tracks P1 between the interconnect levels.
The set of electrically conductive elements may comprise second tracks P2 electrically connected to the bias lines BL. The second tracks P2 are advantageously formed on the interconnect levels. The set of electrically conductive elements advantageously comprises second vias V2, designed to electrically connect the second tracks P2 between the interconnect levels. The antenna 1 advantageously comprises switching means 5 configured so as to switch between the first and second tracks P1, P2, the non-switched first or second tracks P1, P2 being at floating electrical potential. To this end, additional switching means 5′ may be provided on the bias lines BL such that the non-switched first or second tracks P1, P2 are at floating electrical potential.
The resonant cavity 3 advantageously has:
The resonant cavity 3 is therefore defined by the emissive region ZE, the electromagnetic lens 2 and the set of electrically conductive elements. According to one embodiment, the resonant cavity 3 is defined by the emissive region ZE, the electromagnetic lens 2, the first tracks P1 and the first vias V1. In other words, the first tracks P1 and the first vias V1 form the contour of the lateral part 32 of the resonant cavity 3. According to another embodiment, the resonant cavity 3 is defined by the emissive region ZE, the electromagnetic lens 2, the second tracks P2 and the second vias V2. In other words, the second tracks P2 and the second vias V2 form the contour of the lateral part 32 of the resonant cavity 3.
The resonant cavity 3 advantageously has a thickness between λ and 10λ, where λ is the wavelength of the electromagnetic waves. The size and shape of the resonant cavity 3 are defined by the template of the first and second tracks P1, P2 and of the first and second vias V1, V2. The template is determined by electromagnetic simulations according to the desired properties of the antenna 1.
According to one embodiment, the set of electrically conductive elements is arranged such that the contour of the resonant cavity 3 has a cross section that increases from the emissive region ZE towards the electromagnetic lens 2.
According to one embodiment, the set of electrically conductive elements is arranged such that the contour of the resonant cavity 3 exhibits axial symmetry.
The emissive region ZE, the electromagnetic coupling region ZC and the electromagnetic lens 2 are advantageously monolithic, within the dielectric substrate 4.
The antenna 1 may be manufactured with a planar technology allowing a monolithic implementation, preferably selected from among:
Another subject of the invention is a passive antenna 1, comprising:
The ground plane PM is preferably made of a metal material, more preferably copper. By way of non-limiting example, the ground plane PM may have a thickness of the order of 17 μm when the operating frequency of the transmitarray antenna is 29 GHz.
Each phase-shifting cell 20 may comprise:
Other phase-shifting cell 20 architectures may also be used, such as multilayer structures based on the concept of frequency-selective surfaces, or on the concept of Fabry-Perot cavities.
The first planar antenna and the second planar antenna Tx are arranged on either side of the ground plane PM. The ground plane PM may be electrically connected to the set of electrically conductive elements by way of transmission lines LT.
The electromagnetic coupling region ZC advantageously comprises a dielectric substrate 4, comprising interconnect levels. The tracks P are advantageously formed on the interconnect levels. The set of electrically conductive elements advantageously comprises vias V, designed to electrically connect the tracks P between the interconnect levels.
The resonant cavity 3 advantageously has:
The resonant cavity 3 advantageously has a thickness between λ and 10λ, where λ is the wavelength of the electromagnetic waves.
The invention is not limited to the described embodiments. A person skilled in the art has the ability to consider technically operative combinations thereof and to substitute them for equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 19 14717 | Dec 2019 | FR | national |
