The invention relates to the technical field of compact antenna devices. The antenna device may form a directional antenna with beam offsetting, or else form a reconfigurable antenna.
“Compact” is understood to mean that the maximum characteristic dimension of the antenna device is less than or equal to λ/2, where λ is the operating wavelength of the device.
“Directional” is understood to mean the capability of an antenna to concentrate the radiated energy within a solid angle or in a specific direction. This capability, expressed in dBi (decibels relative to isotropic), is defined as being the maximum value of the ratio between the power radiated per solid angle unit and the average radiated power over all directions in space.
“Super-directional” is understood to mean that the antenna has a directivity that exceeds a reference limit, such as the maximum theoretical Harrington limit.
“Beam offsetting” is understood to mean that the radiation pattern of the antenna (also called beam) is able to be directed in any pointing direction with angular scanning, for example over 360° in an azimuthal plane. The azimuth is the angle in the horizontal plane between the direction of the beam and a reference direction.
“Reconfigurable” is understood to mean that at least one feature of the antenna is able to be modified during its lifetime, after it is 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, and the polarization of the electromagnetic field.
The invention is applied notably in the Internet of Things (IoT in acronym form), the spatialization of wireless communications, radiofrequency identification (RFID) readers, electromagnetic compatibility (EMC) devices, radars, etc.
An antenna device known from the prior art, notably from the document H. Kawakami et al., “Electrically steerable passive array radiator (ESPAR) antennas”, IEEE Antennas and Propagation Magazine, vol. 47, no. 2, 43-50, 2005, (hereinafter D1) has:
Such a device from the prior art is compact. Specifically, the monopoles have a height of λ/4 and the ground plane, which is circular, has a diameter of λ/2. The spatial finiteness of the ground plane (i.e. of finite dimension) exhibits a drawback with regard to the radiation pattern of the antenna. Specifically, the ground plane generates an offset of the radiation pattern of the antenna of a certain elevation angle (83° mentioned in D1). Therefore, the gain of the antenna is not maximum in the azimuthal plane. It is for this reason that D1 introduced a skirt, having a height of λ/4, in the extension of the ground plane in order to reduce the elevation angle (by 20°) and thereby to increase the gain (by 1.6 dB) in the azimuthal plane.
However, such a device from the prior art is not completely satisfactory in that introducing the skirt considerably increased the size of the antenna (by a factor of 2 for the thickness).
The invention aims to fully or partly rectify the abovementioned drawbacks. To this end, one subject of the invention is an antenna device, having:
Such a device according to the invention is thus able to remain compact while at the same time keeping maximum gain in the azimuthal plane (i.e. the plane defined by the ground plane), and to do so by virtue of the first and second strands of the or each dipole antenna, which extend on either side of the ground plane. Specifically, such a geometrical configuration of the strands makes it possible to limit the disturbance of the radiation pattern of the corresponding dipole antenna by the ground plane, and to do so in spite of the spatial finiteness of the ground plane.
Furthermore, arranging the control circuit on the ground plane makes it possible to limit the disturbance of the radiation pattern by the components of the circuit (and the metallizations—tracks and connection lands), and thus to allow super-directivity of the device according to the invention in the presence of a network of dipole antennas.
The device according to the invention may have one or more of the following features.
According to one feature of the invention, the first and second strands of the or each dipole antenna extend along the normal to the ground plane.
One advantage that is provided is thus that of overcoming the disturbance of the radiation pattern of the or each dipole antenna by the ground plane.
According to one feature of the invention, the first and second strands of the or each dipole antenna extend on either side of the ground plane with planar symmetry.
“Planar symmetry” is understood to mean that the ground plane forms a plane of symmetry for the first and second strands of the or each dipole antenna.
One advantage that is provided is thus that of reducing cross polarization.
According to one feature of the invention, the first and second strands of the or each dipole antenna respectively have first and second distal ends respectively provided with first and second capacitive roofs, the first and second capacitive roofs being short-circuited.
“Distal end” is understood to mean the end furthest from the ground plane.
One advantage that is provided by such capacitive roofs is thus the possibility of reducing the size of the first and second strands of the or each dipole antenna.
According to one feature of the invention, the first and second capacitive roofs are provided with slots.
One advantage that is provided by the presence of slots is thus the possibility of reducing the size of the capacitive roofs.
According to one feature of the invention, the first and second strands of the or each dipole antenna are printed on a printed circuit board.
One advantage that is provided is thus ease of manufacture and low cost.
According to one feature of the invention, the device has short-circuit strands arranged so as to short-circuit the first and second capacitive roofs; and the short-circuit strands are printed on the printed circuit board.
One advantage that is provided is thus ease of manufacture and low cost.
According to one feature of the invention, the device has a set of dipole antennas extending through the ground plane, each dipole antenna of the set comprising first and second strands extending on either side of the ground plane.
One advantage that is provided is thus that of being able to form a super-directional network of dipole antennas the beam direction of which is able to vary in the azimuthal plane.
According to one feature of the invention, the device has:
The second dipole antenna forms a stray antenna that makes it possible, by virtue of the electromagnetic coupling to the first dipole antenna and of the introduction of matched load impedances within the control circuit, to achieve a reconfigurable antenna.
According to one feature of the invention, the set of dipole antennas has:
One advantage that is provided by the pair or pairs of peripheral dipole antennas is thus that of defining an aperture angle for the beam. The pair or pairs of peripheral dipole antennas will be distributed over the ground plane, around the central dipole antenna, in the preferred directions depending on the targeted application. Each pair of peripheral dipole antennas, arranged around the central dipole antenna with central symmetry, defines a direction with two possible orientations for the radiation of the antenna. The pair or pairs of peripheral dipole antennas form stray antennas that make it possible, by virtue of the electromagnetic coupling to the central dipole antenna and of the introduction of matched load impedances within the control circuit, to achieve a super-directional antenna.
According to one feature of the invention, the set of dipole antennas has four pairs of peripheral dipole antennas, arranged around the central dipole antenna with central symmetry.
One advantage that is provided is thus that of achieving an aperture angle of 45° for the beam if the four pairs of peripheral dipole antennas are distributed uniformly around the central dipole antenna, and with matched load impedances within the control circuit.
According to one feature of the invention, the dipole antennas of the set are spaced from one another by a distance less than or equal to λ/2, preferably less than or equal to λ/5, where λ is the operating wavelength of the device.
According to one feature of the invention, the device has a single dipole antenna, and the control circuit has matched load impedances in order to form a reconfigurable antenna.
According to one feature of the invention, the device has a maximum characteristic dimension less than or equal to λ/2, where λ is the operating wavelength of the device.
The invention also relates to an object having a device according to the invention.
By way of nonlimiting example, the object may be selected from the group containing an object connected to the Internet, a radiofrequency identification reader, a radar, a sensor or an electromagnetic compatibility device.
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.
It should be noted that, for the sake of readability and ease of understanding, the drawings described above are schematic. The strands 20, 21 of the dipole antenna that are illustrated in
Elements that are identical or provide the same function will carry the same references for the various embodiments, for the sake of simplicity.
One subject of the invention is an antenna device, having:
at least one dipole antenna 2, extending through the ground plane 1, and comprising first and second strands 20, 21 extending on either side of the ground plane 1;
The ground plane 1 may be formed from a metal material, such as copper. The ground plane 1 may be circular in shape, for example with a diameter λ/2, where λ is the operating wavelength of the antenna. However, the diameter of the ground plane 1 may be less than λ/2. By way of nonlimiting example, in the case of an RFID spatial filtering application in the UHF band (around 868 MHz), the diameter of the ground plane 1 is 18 cm.
However, other shapes may be contemplated for the ground plane 1, such as a rectangular or square shape.
The ground plane 1 is at floating potential, that is to say that the ground plane 1 is not subjected to an electrical reference potential at the operating frequencies of the device, for example in the radiofrequency range (between 3 kHz and 300 GHz). The ground plane 1 is thus not “seen” by the device at the operating frequency or frequencies.
Apertures are formed in the ground plane 1, such that the or each dipole antenna 2 is able to extend through the ground plane 1. The or each dipole antenna 2 is arranged such that the first and second strands 20, 21 are situated at a distance from the ground plane 1, so as to avoid any contact with the ground plane 1.
However, the first and second strands 20, 21 may be in contact with the ground plane 1 when the first and second strands 20, 21 extend on either side of the ground plane with planar symmetry. By way of nonlimiting example, the or each dipole antenna 2 may be joined to the ground plane 1 by way of a spacer (not illustrated in the figures) that is not electrically conductive.
It is possible to equip the ground plane 1 with components, for example a DC current circuit, a radiofrequency (RF) circuit, or else a power supply cell, and to do so without altering the operation of the device.
The first and second strands 20, 21 of the or each dipole antenna 2 advantageously extend along the normal to the ground plane 1. The first and second strands 20, 21 of the or each dipole antenna 2 advantageously extend on either side of the ground plane 1 with planar symmetry.
All of the first and second strands 20, 21 of the or each dipole antenna 2 have for example a height of the order of λ/5. By way of nonlimiting example, in the case of an RFID spatial filtering application in the UHF band (around 868 MHz), the height of all of the first and second strands 20, 21 is 7 cm.
Advantageously, the first and second strands 20, 21 of the or each dipole antenna 2 respectively have first and second distal ends 200, 210 equipped respectively with first and second capacitive roofs 40, 41. Each capacitive roof 40, 41 extends in a direction perpendicular to the direction of the corresponding strand 20, 21. The first and second capacitive roofs 40, 41 are short-circuited, preferably by way of two short-circuit strands 401, for example produced in the form of wires. However, it is possible to use a larger number of short-circuit strands 401, as described in document U.S. Pat. No. 6,750,825 B1. The short-circuit strands 401 may be in contact with the ground plane 1. Each capacitive roof 40, 41 is preferably circular in shape, with a diameter of the order of λ/6. Other shapes may however be contemplated, such as a square, rectangular, elliptical or else a star shape. As illustrated in
The first and second strands 20, 21 of the or each dipole antenna 2 are preferably made from a metal material. As illustrated in
As illustrated in
According to one embodiment (not illustrated), the set of dipole antennas 2 has:
The second dipole antenna 2b forms a stray antenna that makes it possible, by virtue of the electromagnetic coupling to the first dipole antenna 2a and of the introduction of matched load impedances within the control circuit 3, to achieve a reconfigurable antenna.
The set of dipole antennas 2 advantageously has:
It should be noted that the central symmetry makes it possible to simplify the design of the device, but is not essential to solving the technical problem.
The dipole antennas 2 of the set are advantageously spaced from one another by a small enough distance (≤0.5λ, where λ is the operating wavelength of the device) to take advantage of the electromagnetic coupling between them, and to do so in order to form a super-directional beam. By way of example, this distance is 0.15λ in the proposed RFID application. The dipole antennas 2 of the set are advantageously spaced from one another by a distance less than or equal to λ/5, where λ is the operating wavelength of the device, so as to achieve the formation of a super-directional beam.
By way of nonlimiting example illustrated in
By way of nonlimiting example illustrated in
It is possible to increase the number of pairs of peripheral dipole antennas 2b so as to reduce the aperture angle of the beam.
In the case illustrated in
As illustrated in
The central dipole antenna 2a is preferably supplied with power in differential mode, and not in common mode, in the absence of a ground. To this end, by way of nonlimiting example, the control circuit 3 may have two cross-coupled bipolar transistors, as described in document US 2017/0163224. The collectors of each bipolar transistor are connected to the bases of the other transistor, so as to form a feedback loop. A load impedance is arranged in the loop formed by the two bipolar transistors so as to achieve a floating negative impedance between the emitters of the two bipolar transistors. The first and second strands 20, 21 of the central dipole antenna 2a are connected to the emitters of the two bipolar transistors.
As illustrated in
Object Equipped with an Antenna
The invention also relates to an object having a device according to the invention. By way of nonlimiting example, the object may be selected from the group containing an object connected to the Internet, a radiofrequency identification reader, a radar, a sensor or an electromagnetic compatibility device.
The invention is not limited to the described embodiments. A person skilled in the art is capable of considering technically feasible combinations thereof and of substituting them with equivalents.
Number | Date | Country | Kind |
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18 57848 | Aug 2018 | FR | national |