EP1315052A1 - Structure of a PIFA antenna and a shielding case for a portable electronic apparatus - Google Patents

Abstract

The structure has an antenna (10) with radiating section (20) arranged on top portion. The shield container (11) has a cover (14) that includes substantially plane external surface, and an indentation in the peripheral zone. The radiating section extends in the plane external surface and the bottom surface of the indentation, and forms ground plane of the antenna.

Description

The present invention relates to a structure forming an antenna and a shielding unit capable of containing electronic circuits in a device portable, in particular a watch, the case comprising a cover and a wall lateral, the antenna comprising an elongated radiant element disposed opposite a plane mass which is part of the housing, the radiant element having one end connected to the ground plane by a short-circuit connection and a free opposite end.

The invention also relates to a portable electronic device comprising a such an antenna structure, in particular a wristwatch. This invention applies in particular to devices capable of transmitting and / or receiving signals high frequency electromagnetic and allowing for example to ensure a radio communication with other devices on a mobile phone network or in a Bluetooth type data transfer network.

A PIFA antenna structure of this kind and its incorporation into a portable device of small volume such as a timepiece are described in the Patent application EP 1 093 098 from the same applicant, which is incorporated here by reference. In particular, the reader will find in the above-mentioned document a description of the prior art and principles of the structure of a PIFA antenna (Planar Inverted-F Antenna). Other PIFA antenna structures for devices small are described for example in patent publications US 6,025,805, US 6,130,650, WO 97/44856, WO 01/08257 and EP 1,096,602.

In order to incorporate such an antenna into a portable unit of low volume, like a watch, solutions should be found which advantageously combine a small footprint and nevertheless performance to ensure a radio communication in the best conditions.

The structure described in patent application EP 1 093 098 preferably has a generally cylindrical shape of low height, to be housed in the box of a wristwatch. The radiant element of the PIFA antenna is arranged laterally, at a constant distance from the side wall of the housing. It can either protrude by relative to the generally cylindrical outline of the shielding box, either follow this contour while the housing laterally has a deep recess constant in the area covered by the radiant element.

The antenna proposed in this document has the advantage of being able to be fully integrated into a low-volume structure that combines compactness, rigidity and aesthetic, the radiant element forming an integral part of a housing forming the plane of mass of the antenna. The dimensioning as well as the agreement and adaptation of characteristics of this antenna (frequency, bandwidth, impedance, etc.) are relatively easy.

The housing constituting the ground plane of the antenna advantageously allows to house all or part of the electronics of the portable communication unit inside the antenna structure, this box thus forming a shielded box to inside which the electronics are protected and does not affect performance of the antenna. The proposed antenna can thus advantageously be supplied from the interior of the housing thus formed.

The proposed structure elegantly combines the ground plane of the antenna and a case to accommodate not only the electronics of the portable unit, but also other components that may be present in this unit. This structure can thus advantageously constitute a housing making it possible to accommodate in besides the movement of a timepiece. The structure can also be surrounded or encased in an external plastic element. This external element can thus take various forms, for example the middle of a watch case.

The radiant element of the antenna is electrically small, but the influence of the complete structure (including the housing) determines the radiation properties of the antenna. Associated with low losses due to the absence of a dielectric between the radiant element and the ground plane, or more exactly the presence of a dielectric formed only of air, this leads to gain and efficiency remarkable antenna.

However, as the antenna structure according to the aforementioned document EP 1 093 098 has a generally flattened shape and therefore usually extends in the general plan of the portable device, the functioning of the antenna is somewhat degraded when the device is placed against a body whose presence may disturb the surrounding electric field, for example a metallic body or the human body. This is precisely the case with the lateral arrangement of the antenna in a wristwatch, the antenna being so close to the wearer's arm that the latter absorbs a part of the antenna radiation.

The present invention aims to improve such an antenna structure of so as to remedy the aforementioned drawback, while retaining most of the advantages of the structure described in the aforementioned document.

For this purpose, provision is made for a structure of the kind indicated in the preamble, characterized in that the cover of the housing has an outer surface substantially flat and a recess disposed in a peripheral zone of the cover and set back from the plane of said outer surface, and in that the radiant element extends substantially in said plane above said recess, a bottom surface of which forms the ground plane with respect to the radiant element.

We thus keep all the advantages of the structure of the structure according to art anterior, even maximizing the area available inside the housing, while the antenna part is entirely in the part superior of the structure, therefore as far as possible from a body on which the face lower part of the appliance is installed. In the case of a wristwatch, the distance between the antenna and the arm is thus much larger than in the case of the document supra. In addition, as the area of the housing cover is usually much more larger than that of the side wall, the radiant element can be wider and therefore more efficient.

• la figure 1 est une vue en perspective schématique d'une structure à antenne PIFA selon l'invention, susceptible d'être incorporée à un appareil électronique portable telle qu'une montre;
• la figure 2 est une vue en plan de l'objet de la figure 1;
• la figure 3 est une vue en coupe suivant la ligne III-III de la figure 2, et
• la figure 4 est une vue en perspective schématique d'une montre-bracelet comportant la structure à antenne PIFA illustrée par les figures 1 à 3.

Other characteristics and advantages will appear in the following description of a preferred embodiment, presented by way of nonlimiting example with reference to the appended drawings, in which:

• Figure 1 is a schematic perspective view of a PIFA antenna structure according to the invention, capable of being incorporated into a portable electronic device such as a watch;
• Figure 2 is a plan view of the object of Figure 1;
• FIG. 3 is a sectional view along line III-III of FIG. 2, and
• FIG. 4 is a schematic perspective view of a wristwatch comprising the PIFA antenna structure illustrated in FIGS. 1 to 3.

The structure described below with reference to Figures 1 to 3 constitutes a preferred embodiment of an antenna structure which can be advantageously incorporated into a timepiece provided with a transceiver radio, for example in the 2.45 GHz band usual in technology Bluetooth.

The structure shown forms on the one hand an antenna, indicated overall by the reference 10 in Figure 1, and on the other hand a shielding box electromagnetic indicated by the reference 11 and formed for example of two parts as seen in Figure 3, namely an upper part 12 and a bottom 13. The upper part 12 comprises a cover 14, the outer surface 14a of which extends substantially in a plane 15, and a side wall 16 generally perpendicular to this plane. In the present case, the structure 1 has a generally cylindrical shape of low height compared to its diameter, its side wall 16 is cylindrical and its bottom 13 is flat.

In a peripheral zone of the structure 1, the cover 14 has a recess 17 of generally arched shape, the depth and width of which are substantially constant. This reinforcement is limited downwards by a surface horizontal plane 18 of the housing, which is parallel to plane 15, and laterally by a vertical surface 19 connecting to the side wall 16 of the housing. Above recess 17, the cover 14 is extended by a horizontal blade extending the along the plane 15 and constituting the radiant element 20 of the antenna 10. This element located at a distance D from the bottom surface 18, which constitutes the ground plane of the antenna. The distance D is constant over the entire extent of the radiant element in the this example, but it is not necessary in all cases. Element 20 has a elongated shape in an arc, preferably of constant width and less than that of the recess 17, so that it is separated from the wall 19 by a slot 21 of constant width. One end 20a of the element 20 is mechanically connected and electrically to the cover 14, so that it is connected to the ground plane 18 by a short circuit link. Its other end 20b is free. At a distance determined from its short-circuited end 20a, the radiant element carries a point of connection 23 whose usefulness will be indicated later.

Note that the structure 1 described above has a configuration cylindrical exterior devoid of any protuberance, which facilitates its incorporation in a generally circular watch case. However this configuration could be different according to the needs, in particular for incorporation into a rectangular device. In the example shown, the two parts 12 and 13 are entirely metallic, for example brass. The bottom 13 in this case has an inner rim 24 which can be threaded externally to screw into a corresponding thread on the side wall 16, thereby ensuring good electrical connection between the two parts of the shielding box. We can however provide for a different assembly, for example with bayonet, by hunting or by welding.

Preferably, the cover 14 and the radiant element 20 are made in one part, formed by a flat plate. In a metal version, this plate can be welded to the walls 16, 18 and 19 to form the upper part 12 of the housing. This allows easy fabrication and good dimensional accuracy of the antenna.

In another embodiment, the two parts 12 and 13 could be formed by molded dielectric parts and provided with a coating metallic suitable for performing the electrical functions of the antenna and shielding.

As is known, the length of the radiant element 20 is chosen according to of the wavelength λ of the radiation to be emitted or received and corresponds to preferably around λ / 4, which is around 32 mm for the frequency of 2.45 GHz. Thus, if the structure 1 has an outside diameter of the order of 35 mm to be able to be incorporated in a watch, the recess 19 and the radiant element 20 extend on much less than half of the perimeter of the structure and therefore do not occupy than a small fraction of the area of the case.

In FIG. 3, various components have been represented diagrammatically likely to be housed inside the shielding box 11, in particular a electronic clock movement 25, a Bluetooth unit 26 comprising a transceiver associated with the antenna 10, and a source of electrical energy 27 comprising for example a rechargeable battery by induction. Box 11 prevents electromagnetic interference between these components and the antenna 10. The unit 26 is connected to the antenna by a coaxial line 28 whose conductor internal 28a, isolated from the ground plane, crosses the surface 18 of the housing through a orifice 29 to go to connect to the connection point 23 of the radiant element 20. The external conductor 28b of the coaxial line is connected to the ground plane formed by the surface 18. A hole 29 in the center of the cover 14 makes it possible to connect members display external to the clockwork movement 25 and, where appropriate, to other bodies housed inside the housing 11.

Although the embodiment described above has a configuration general cylindrical which is typically suitable for horological use, we will understand that the antenna structure according to the present invention can take various shapes depending on the size constraints of the portable unit in which this structure is incorporated. The antenna structure can thus perfectly present a substantially rectangular, elliptical or polygonal outline.

Figure 4 shows in schematic perspective a timepiece is in the form of a wristwatch with analog display which contains the structure 1 illustrated in FIGS. 1 to 3. The structure 1 forming an antenna 10 is thus surrounded and incorporated in an external element made of a non-material conductor, in particular a plastic material, in this case a case middle watch 30. The movement of the timepiece is advantageously arranged entirely inside the structure 1. The planar upper surface of the housing 11 and of the radiant element 20 can serve as a watch face or be covered with a disc of dielectric material forming a conventional dial, as desired.

The antenna 10 is thus located in a region of the wristwatch which is as far away from the wearer's arm as possible, minimizing arm influences on the performance of the antenna, as explained above.

Small diameter orifices can be provided in the housing 11 of the structure 1, without significantly affecting the characteristics of the antenna 10, for allow the passage, if necessary, of components of display elements and / or control, these elements being electrically isolated from the structure 1. In the example of figure 4, axes or canons of hour and minute hands 32 thus pass through the hole 29 provided in the center of the cover of the housing 11. Similarly, rods of various control members penetrate laterally through the wall cylindrical side of the housing 11, these control members comprising in particular a rotary rod secured to a time setting crown 34 and two push-buttons 35 and 36.

The structure 1 is arranged in the middle part of the watch 30 preferably of so that the radiant element 20 of the antenna 10 is located opposite the organs of control 34, 35 and 36, and generally away from any organ penetrating the inside of the structure 1 case.

An antenna structure according to the present invention can thus be designed to be incorporated into a timepiece, such as a watch, and to receive inside the armored box all or part of a transceiver electronics, timepiece electronics and sound movement. However, the applications of the invention more generally extend to any portable electronic device having a function of emission and / or reception in radio frequency.

It will be understood that different modifications or adaptations can be made to the structure described here without departing from the scope defined by the claims attached. In particular, depending on the desired characteristics of the antenna, the element radiant may have a more complex configuration, for example depending on the lessons from patent application EP 1 096 602, and can be short-circuited at ground plane on only part of its end linked to the housing.

Claims (10)

Structure forming an antenna (10) and a shielding box (11) able to contain electronic circuits in a portable device, in particular a watch, the box comprising a cover (14) and a side wall (16), the antenna comprising an elongated radiant element (20) disposed opposite a ground plane which is part of the housing, the radiant element having one end (20a) connected to the ground plane by a short-circuit connection and one end opposite free (20b),
characterized in that the cover (14) of the housing has a substantially planar outer surface (14a) and a recess (17) disposed in a peripheral zone of the cover and recessed from the plane (15) of said outer surface, and in that the radiant element (20) extends substantially in said plane above said recess, a bottom surface (18) of which forms the ground plane with respect to the radiant element. Structure according to claim 1, characterized in that the housing (11) has a curved lateral contour at least in the region of the antenna (10) and in that the radiant element (20) has, in said plane, a curved shape that follows said outline of the housing. Structure according to Claim 1, characterized in that it has a generally cylindrical external shape and in that the said recess (17) and the radiant element (20) have the shape of an arc of a circle. Structure according to claim 1, characterized in that the housing (11) has a closed configuration and has a bottom (13) on its face opposite to the cover (14). Structure according to claim 4, characterized in that the bottom (13) is formed by a separate part from the rest of the housing. Structure according to one of claims 1 to 5, characterized in that it is made of metal. Structure according to one of claims 1 to 5, characterized in that it is made of a dielectric material covered with an electrically conductive layer. Portable electronic device having an antenna structure according to one of the preceding claims. Apparatus according to claim 8, characterized in that an electronic unit (26) comprising a transceiver is housed inside the housing (11). Apparatus according to claim 8 or 9, characterized in that it is formed by a wristwatch and includes a clockwork movement (25) inside the case (11).

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