Antenna device

Abstract

The invention relates to a timepiece comprising a case formed of a metallic case (40) in which are arranged a metallic dial and a remote communication system provided with a multi-band antenna device (1) arranged above said dial, the communication system comprising a bracelet (49) of said timepiece connected at its ends to said case and comprising a body formed of a plurality of attachment elements having different electrical conductivity properties, the arrangement of said attachment elements in the body of the bracelet (49) being configured to achieve a broadening of the radiation pattern of said antenna device (1).

Description

Technical field of the invention

[0001] The invention relates to an antenna device used in a communication system for a timepiece. Technological background of the invention

[0002] For several years now, watches have been incorporating communication means to connect to different communication networks, such as Bluetooth to connect to a mobile terminal, and geolocation, to connect to different satellite location systems such as GPS, Glonass or Galileo. To achieve this, a watch incorporates one or more antennas.

[0003] It is known that the optimal size of an antenna depends directly on the wavelength of the transmitted / received signal. An antenna of optimal length allows sending / receiving a signal in full and at full power.

[0004] In a watch, since the available space is limited, an antenna must have a suitable design to fit into the case of the watch.

[0005] And if the watch incorporates a means of radio communication that operates on radio frequencies (such as 2.4 GHz or 1.5 GHz), the size of the product becomes critical in relation to the wavelength (120 mm and 200 mm).

[0006] Furthermore, other constraints must also be taken into account: The watch has many metal parts, including its case, and an antenna must be insulated from it. The watch can integrate several communication devices in the same case, as specified above. The watch cannot have a volume exceeding a certain size (diameter of

[0007] 50mm maximum as a general rule). CN 111 029 731 A discloses a smartwatch comprising two antenna radiators, on the bezel and the bracelet. In this way, different frequency bands can be covered or certain frequency bands can be covered simultaneously. WO 2020 / 129352 A1 discloses a smartwatch having a circular substrate intended to be used in a communication system of a timepiece, said substrate comprising an antenna circuit of the NFC or GPS or Bluetooth type.

[0008] In this context, it is understood that there is a need to find a solution, in particular one which does not have the drawbacks of the prior art. Summary of the invention

[0009] Under these conditions, one of the aims of the invention is consequently to have an antenna device intended to be used in a communication system for a timepiece, such as a watch, which integrates at least two antenna circuits each having an optimal length for sending / receiving a signal in full and at full power and being integrated into the caseband of a watch, the reception volume of which is limited.

[0010] For this purpose, the invention relates to a timepiece according to claim 1. Preferred embodiments are defined in dependent claims 2 to 9. Brief description of the figures

[0011] Other features and advantages of the present invention will become more apparent from the following detailed description, taken in conjunction with the appended figures listed below: There figure 1represents a timepiece comprising a bracelet provided with a plurality of attachment elements, here links, each of which can be made of metallic material or dielectric material, according to one embodiment of the invention; The figure 2 represents the antenna device according to the invention; The figure 3 represents, seen in partial section, a timepiece incorporating the antenna device according to the invention; The figure 4 represents a diagram illustrating the gain seen by each frequency band employed in the communication system of the invention, and The Figure 5 represents a diagram illustrating the principle of isolation of the frequency bands permitted by the antenna device of the invention. Detailed description of an embodiment of the invention

[0012] In the remainder of the description, the terms "top", "bottom", "upper", "lower", "above" and "below" are to be considered taking into account a horizontal median plane (P) parallel to the horizontal support plane of the case of the timepiece on a surface.

[0013] The terms "exterior", "external", "interior" and "internal" are to be understood taking into account a median axis (X) oriented perpendicular to said median plane visible on the figure 3

[0014] On the figure 1 , the timepiece 4 comprises a case formed from a middle 40 in which are arranged a metal dial and a remote communication system provided with a multi-band antenna device 1 visible on the figure 2. As we will see later, this timepiece 1 comprises a bracelet 49 provided with a body formed from a plurality of attachment elements 50, here links, having different electrical conduction properties and the arrangement of which in this body contributes to the creation of the configuration of the broadening of the radiation pattern of said antenna device 1.

[0015] In reference to the figure 2, the case of a timepiece 4 comprises a receiving volume defined by a caseband 40, generally made of metallic material, forming its side wall around said median axis, made in a single part or in two parts with an upper bezel 41, for example made of ceramic or titanium. The receiving volume of the timepiece 4 is closed from the top by means of a window 42, for example made of sapphire crystal, supported by the caseband 40 and fixed in a sealed manner to the latter by a suitable method. The timepiece also comprises a bottom wall (not visible), for example metallic, located opposite its window 42 relative to the median plane, advantageously isolated from the caseband by a seal, closing the receiving volume from the bottom.

[0016] According to a particular aspect of the invention, the timepiece 4 comprises a communication system which mainly comprises: A communication antenna device 1 and, A duplexer / rejector type filtering circuit 20, known per se to those skilled in the art.

[0017] The antenna device 1 comprises a substrate 10, advantageously produced in the form of a flexible printed circuit (commonly called "flex"). With reference to the figure 2 , the antenna device 1 has the particularity of comprising two separate antenna circuits, to allow the timepiece to connect to two separate networks, more precisely a Bluetooth type communication network and a GNSS (Geolocation and Navigation Satellite System) satellite location network, such as for example GPS (Global Positioning System), Glonass or Galileo.

[0018] Both antenna circuits are made on the same substrate using standard processes used in the field of printed circuits. According to the claimed invention The first antenna circuit 11 has a first strand 110 and a second strand 111 which each have a proximal end and a distal end, and which extend in parallel between their proximal and distal ends, the first and second strands being connected 112 by their proximal ends and separated at their distal ends; The second antenna circuit 12 has a third strand 120 and a fourth strand 121 which each have a proximal end and a distal end, and which extend in parallel between their proximal and distal ends, the third and fourth strands being connected 122 by their distal ends and separated at their proximal ends;

[0019] An electrical connection 13 makes it possible to connect the proximal ends of the first, second and third strands 110, 11, 120. This electrical connection 13 comprises a single connection point 130 to which said filtering circuit 2 is connected. A single connection point 130 will thus make it possible to communicate by selectively using the first and second antenna circuits 11 and 12.

[0020] The two-strand parallel architecture of the first antenna circuit 11 makes it possible to expand the frequency band (100 MHz), necessary for example to communicate on a Bluetooth type communication network (2.4 GHz).

[0021] For the second antenna circuit 12 (for example dedicated to a satellite location circuit), the antenna is powered on a current node and its length is folded, making it possible to improve the impedance matching.

[0022] The single connection point 130 for the two antenna circuits 11, 12 in parallel makes it easier to mechanically integrate the antenna device into the receiving volume of the timepiece 4 as well as to provide design independence between the antenna part and the electronic part. Indeed, it is sufficient to adjust the mechanical integration of the support plate of these antenna circuits in the construction, the pattern of the antenna circuits being subsequently produced by a standard etching process that does not compromise said mechanical integration. The second antenna circuit 12 with two strands connected in series makes it possible to communicate on a narrower frequency band, for example at 1.5 GHz used to communicate on a satellite location network (GPS for example).

[0023] In this configuration, each antenna circuit 11, 12 extends essentially along an arc-shaped trajectory, comprising two strands 110, 111, 120, 121 arranged in parallel on the substrate 10 which follow this trajectory.

[0024] For example, each antenna circuit 11, 12 can be produced over an angular range of between 70 and 80° relative to the angle of the angular sector which defines the arc of a circle formed by this antenna circuit 11, 12, on either side of the central junction link. Their trajectory can follow this arc of a circle produced along a radius of between 16 and 22 mm. The two strands 110, 111, 120, 121 can be spaced apart from each other by a distance of between 1 and 2 mm.

[0025] The substrate 10 is in the form of a first plate having a profile made in an arc of a circle, advantageously in a semicircle. This configuration greatly helps to obtain circular polarization for satellite antennas in particular. This configuration also helps for the implementation of the Bluetooth protocol, due to the propagation of waves in enclosed places such as living rooms. The two antenna circuits are printed on the same face of the plate, its upper face, and each extend on either side of a separation part carrying the electrical connection 13 joining the two antenna circuits 11, 12. This separation part is advantageously median, separating the substrate into two arcs of a circle of substantially equal or even equal or strictly equal dimensions.

[0026] The antenna device further comprises a connection part 100, in the form of an outgrowth of the plate.

[0027] When integrating the substrate 10 into the caseband 40 of the timepiece 4, the connection part 100 of the substrate 10 is intended to be folded relative to the first plate, around an axis perpendicular to the axis (X) and parallel to the plane (P).

[0028] This connection part 100 comprises one or more conductive connections making it possible to connect the antenna circuits 11, 12 (at the electrical connection 13) to an electronic control circuit 2 carrying the duplexer / rejector type filtering circuit 20. The connection part 100 comprises electromagnetic shielding of these conductive connections to prevent any radiation towards the outside and to prevent the connection part 100 from influencing the impedance of the antenna circuits 11 and 12. For example, the shielding can be achieved by assembling several superimposed layers: a lower shielding layer, an insulating layer, a layer integrating the conductive connections, then a new insulating layer and a new upper shielding layer.

[0029] A control card carrying the electronic control circuit 2 (the control circuit 2 carrying for example one or more RF transmitter / receiver circuits and of design known per se) can be arranged in the bottom of the case of the timepiece 4.

[0030] The antenna device 1 is connected to the control board, by the connection part 100 via the conductive connection(s).

[0031] In reference to the figure 3 , in its receiving volume, the timepiece 4 can integrate a dial 43, advantageously made of metal, located above the back wall. This dial can bear aesthetic indications visible through the glass of the timepiece. It advantageously has a disc shape.

[0032] The timepiece may incorporate a shim 44 arranged on the dial. This shim 44 defines a horizontal support plane and is intended to support the substrate 10 carrying the antenna circuits. This shim may have a circular or semi-circular shape and defines a constant thickness determined above the dial.

[0033] The substrate 10 of the antenna device 1 is arranged to be positioned on the wedge 44, its first plate bearing against the bearing plane formed by the wedge. Its connection part 100 is folded to be positioned vertically, along a plane transverse to the mean plane (P).

[0034] A first wedging element 45, for example made of insulating foam, can be positioned between the substrate and the bezel surmounting the caseband. A second element 46, for example made of insulating plastic, for example of semi-annular shape, comprises an upper part bearing against the upper face of the substrate 10, a vertical part extending downwards, to the dial and a lower part bearing against the dial.

[0035] A touch screen 47, for example of the capacitive type, can be fixed under the glass 42, over a major part of the surface of the glass, separated from said second element 46 by air.

[0036] To fix the bracelet 49, the timepiece has on either side of its case two horns 48 each arranged to fix a separate strand of the bracelet 49.

[0037] The antenna device is multi-band to operate at least two communication circuits, which have different characteristics in terms of frequencies, polarization, gain and impedance.

[0038] For the impedance, the electronic control circuit 2 may include a radio frequency duplexer / rejector filter 20.

[0039] For gain and polarization, it is the pattern of each antenna circuit 11, 12 which allows these parameters to be managed.

[0040] The use of a duplexer / rejector filter makes it possible to isolate the two communication circuits (Bluetooth and GPS for example).

[0041] For example, it should be noted that a Bluetooth communication circuit requires linear polarization while a GPS communication circuit requires circular polarization. The GPS system, in particular, requires so-called left-hand polarization.

[0042] Furthermore, the solution of the invention makes it possible to take into account the fact that the timepiece 4 comprises a caseband 40 made of metallic material.

[0043] According to a particular aspect of the invention, the antenna device 1 is intended to be placed as high as possible in the case of the timepiece, that is to say as close as possible to the glass, while remaining hidden from the user's eyes.

[0044] Furthermore, the arrangement of the antenna device 1 in the case of the timepiece makes it possible to benefit from the metal case 40 of the timepiece, through which the antenna device 1 can emit its radiation. The bezel 41, which can be made of a ceramic-type material, makes it possible, in order not to deteriorate the radiation, in particular laterally, by adding a high-dielectric material, to increase the electrical length of the antenna and thus improve its efficiency relative to its physical size.

[0045] The antenna device 1 being placed above the dial 43 which is also metallic, there is a volume mainly filled with air (thus improving the efficiency of the antenna), above the antenna device. This metallic dial 43 also acts as a screen, making any modification to the construction below this dial partly transparent with respect to the antenna device 1.

[0046] As mentioned above, in this timepiece, the bracelet 49 helps to achieve the configuration of the broadening of the radiation pattern of said antenna device 1. In this configuration, the radiation is done by the middle 40 and this bracelet 49 plays a notable role in terms of radiation. It can in fact be partially made with several links 50 made of metallic material to broaden the radiation pattern in the directions that would be attenuated by the wearer's wrist. Furthermore, the electrical looping between the top and bottom of the middle (from horn to horn) via the metal bracelet 49 can be avoided by integrating a non-metallic link 51 into the bracelet 49. The placement of this link is optimized to achieve the expected specifications.

[0047] There figure 4illustrates the performance in terms of gain, seen by each of the frequency bands, the ISM band (Industrial, Scientific and Medical - corresponding to the frequency band used by a network such as Bluetooth) and the GNSS frequency band (Geolocation and Navigation by a Satellite System), in use of the communication system of the invention.

[0048] There Figure 5 represents two curves illustrating the separation of the frequency bands permitted by the use of the antenna device according to the invention. It can be seen that the ISM band is well isolated from the GNSS frequency band.

[0049] Furthermore, such an invention thus contributes to the realization of a unique radiating structure of miniature multiband type which uses the properties of the nearby materials (metal case, sapphire crystal) and in particular the bracelet with its attachment elements. This integration is made possible by a separation between the physical integration (the construction) and the antenna shape, thanks to a printing technique (PCB flex for example). This multiband structure is connected to the electronics by means of a circuitry of the rejector filter type.

Claims

1. A timepiece comprising a case formed of a metal middle part (40) wherein are disposed a metal dial and a remote communication system provided with a multi-band antenna device (1) arranged above said dial, the communication system comprising a bracelet (49) of said timepiece connected at its ends to said middle part and comprising a body formed of a plurality of fastening elements having different electrical conduction properties, the arrangement of said fastening elements in the body of the bracelet (49) being configured to achieve an enlargement of the radiation pattern of said antenna device (1), characterised in that the antenna device (1) includes: - a substrate (10) in the form of a first plate having a circular arc-shaped profile; - a first antenna circuit (11) produced on said substrate and having first and second strands (110, 111) having a proximal end and a distal end, and extending in parallel between their proximal and distal ends, the first and second strands being connected by their proximal ends and separated at their distal ends; - a second antenna circuit (12) produced on said substrate (10) and having third and fourth strands (120, 121) having a proximal end and a distal end, and extending in parallel between their proximal and distal ends, the third and fourth strands being connected by their distal ends and separated at their proximal ends; - an electrical junction link (13) joining the proximal ends of the first and third strands; - a connection part (100) configured to be bent relative to the first plate, around an axis perpendicular to the axis (X) and parallel to the plane (P), and including a conductive connection connected to the electrical junction link (13) and including an electromagnetic shielding of said conductive connection.

2. The timepiece according to the preceding claim, characterised in that the fastening elements comprise links which can each be made of metallic material or of dielectric material.

3. The timepiece according to the preceding claim, characterised in that the dielectric material link is comprised in the body of the bracelet (49) at one of its two ends, intended to be connected to the middle part.

4. The timepiece according to any one of claims 2 to 3, characterised in that the number of metallic material links constituting the body of the bracelet (49) contributes to achieving the configuration of the enlargement of the radiation pattern of said antenna device (1).

5. The timepiece according to any one of the preceding claims, characterised in that said strands (110, 111, 120, 121) are curved.

6. The timepiece according to any one of claims 4 to 5, characterised in that the first and second antenna circuits (11, 12) are disposed on either side of said electrical junction link (13).

7. The timepiece according to any one of the preceding claims, characterised in that the remote communication system comprises: - the antenna device (1), and - a duplexer / notch circuit (20) connected to said electrical junction link via the conductive connection of the connection part (100).

8. The timepiece according to the preceding claim, characterised in that said duplexer / notch circuit (20) includes a first communication circuit configured to communicate according to a Bluetooth type protocol and a second communication circuit configured to communicate on a satellite positioning network via the first and second antenna circuits respectively.

9. The timepiece according to any one of the preceding claims, characterised in that it is a connected watch.

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