EP1093098B1 - Antenna structure with a casing including electronic components - Google Patents

Description

The present invention generally relates to the field of antennas intended for the emission and reception of an electromagnetic signal. More in particular, the present invention relates to a low volume structure forming antenna derived from a structure known under the name PIFA or "Planar Inverted-F Antenna" intended to be incorporated in a unit portable small volume, like a timepiece. The structure forming antenna according to the present invention is in particular intended for the transmission and reception of high frequency electromagnetic signals allowing by example of ensuring radio telephone communication over a network of mobile telephony. The antenna structure according to the present invention can nevertheless be applied in other systems requiring a wireless communication between a portable unit and a station remote transmitter / receiver.

The present invention also relates to a timepiece, such a watch, suitable for transmitting and receiving signals high frequency electromagnetic incorporating structure forming above-mentioned antenna and for example ensuring radio telephone communication with other users on a network of mobile telephony.

The continuous expansion of radio frequency communication systems, including mobile phone systems, leads to demand growing portable communication equipment more and more compact and light. Along with the technological advances that have allowed the development of electronic circuits and radio circuits low frequency and development of energy sources high-performance antennas have already been proposed to be mounted on portable communication units such as cell phones. Such a structure is known by the name Anglo-Saxon "Planar Inverted-F Antenna" or PIFA.

Figure 1 illustrates an example of a PIFA structure, shown globally by reference numeral 1, as it is typically known in the state of the art. This PIFA 1 structure includes a mass 2, a radiant element 6 of rectangular shape whose length is approximately equal to λ / 4, where λ is the wavelength transmit / receive antenna, arranged substantially parallel to the plane earth 2, as well as a short circuit plate 4 connecting the element radiant 6 to ground plane 2 and now this radiant element 6 to a distance determined from the ground plane 2.

This antenna 1 is supplied by a transmission line, such as a coaxial line 8, from behind the ground plane 2. This coaxial line 8, arranged at a determined distance from the short-circuit plate 4, comprises an internal conductor 8a crossing the ground plane 2 to connect the radiant element 6, and an external conductor 8b connected to the ground plane 2 and distant from the internal conductor 8a by a distance Δd.

A detailed analysis of the PIFA structure illustrated in Figure 1 can be found in the document "Analysis, Design and Measurement of Small and Low-Profile Antennas ", Artech House, Norwood, MA, 1992, Ch. 5, pages 161-180, Kazuhiro Hirasawa and Misao Haneishi, which is incorporated here by reference.

Due to its low profile, this PIFA structure is thus perfectly adapted to be mounted on a portable communication unit, such as a cell phone. This PIFA structure is thus generally mounted on a face of the conductive body of the cell phone which also forms the ground plane of the antenna. Note that the characteristics of the antenna (resonant frequency, bandwidth, etc.) not only depend dimensions of the radiant element and its distance from the ground plane, but also dimensions of the conductive body forming the ground plane of the antenna. The shape and dimensions of this body are not overly restrictive elements in a cell phone because it remains nevertheless a relatively large object compared, for example, to a portable unit such as a timepiece which is characterized by a significantly lower volume.

In order to incorporate such an antenna in a portable unit of low volume, like a watch, it is therefore necessary to find solutions that combine advantageously a small footprint and nevertheless performance allowing radio communication in the best conditions.

An object of the present invention is thus to propose an antenna can easily be arranged and mounted inside a portable unit low volume communication, such as, for example, a timepiece.

Another object of the present invention is to provide an antenna meeting the above definition and the structure of which is of realization as easy as possible to limit manufacturing costs.

To this end, the present invention relates to a structure forming antenna for a small volume portable unit, such as a room watchmaking, the characteristics of which are set out in claim 1.

Advantageous embodiments of the present invention provide the subject of the dependent claims.

The present invention also relates to a timepiece incorporating the above-mentioned antenna structure.

An advantage of the present invention lies in the fact that the proposed structure is fully integrated into a weak structure volume that combines compactness, rigidity and aesthetics, the radiant element making integral part of a case forming the ground plane of the antenna. The dimensioning as well as the agreement and adaptation of the characteristics of this antenna (frequency, bandwidth, impedance, etc.) are also very wealthy.

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

The proposed structure elegantly combines the ground plane of the antenna and a case to accommodate not only the electronics of the unit portable but also any other components that may be present in this unit. The structure according to the present invention can thus advantageously constitute a watch case to accommodate in besides a movement of a timepiece.

If aesthetic criteria so require, the structure can also be easily surrounded or coated with an external plastic element. This external element can thus take various forms such as, for example, the shape 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 properties of radiation from the antenna. Associated with low losses due to the absence of a dielectric between the radiant element and the ground plane, or more exactly at the presence of a dielectric formed only of air, this leads to a gain and remarkable efficiency of the antenna.

• la figure 1, déjà présentée, illustre une structure PIFA connue;
• les figures 2a et 2b présentent respectivement une vue de face et une vue en perspective éclatée d'un mode de réalisation préféré d'une structure formant antenne selon la présente invention;
• les figures 3a et 3b présentent respectivement une vue de face et une vue en perspective éclatée d'un autre mode de réalisation d'une structure formant antenne selon la présente invention; et
• la figure 4 présente une vue en perspective schématique d'une pièce d'horlogerie incorporant la structure formant antenne illustrée dans les figures 2a et 2b.

Other characteristics and advantages of the invention will appear more clearly on reading the detailed description which follows, given with reference to the appended drawings given by way of nonlimiting examples and in which:

• FIG. 1, already presented, illustrates a known PIFA structure;
• Figures 2a and 2b show respectively a front view and an exploded perspective view of a preferred embodiment of an antenna structure according to the present invention;
• Figures 3a and 3b respectively show a front view and an exploded perspective view of another embodiment of an antenna structure according to the present invention; and
• Figure 4 shows a schematic perspective view of a timepiece incorporating the antenna structure illustrated in Figures 2a and 2b.

The present invention will now be described with reference to various embodiments. Note however that the skilled person will perfectly capable of modifying and adapting the structures presented to take them in various forms depending on the type of application and the design constraints imposed, without however departing from the framework of the invention defined by the appended claims.

The structure which will be described in the rest of this description in reference to FIGS. 2a and 2b constitutes a preferred embodiment of a antenna structure which can advantageously be incorporated into a timepiece provided with a radio telephone function. In reference in FIG. 4, a schematic example of a timepiece incorporating the structure illustrated in Figures 2a and 2b.

FIGS. 2a and 2b thus respectively show a front view and an exploded perspective view of an antenna forming structure constituting a preferred embodiment of the present invention. This structure forming an antenna, generally indicated by the reference numeral 10, is made of a conductive material and has essentially the appearance, in this example, of a portion of cylinder delimited by a contour which is substantially cylindrical A, and first and second planes B and C substantially perpendicular to the axis of symmetry of the cylinder, perpendicular to the plane of the Figure 2a and shown in broken lines in Figure 2b.

According to the present invention, this antenna-forming structure 10 comprises a radiant element 20, of substantially shape or surface rectangular, integral with a housing 11 forming an integral part of the plane of mass of the antenna. As can be seen from the figures, the housing 11 is preferably made in two parts 12 and 13, one 12 essentially forming a cover of the housing 11, and the other 13 forming essentially a body of the housing 11 and also supporting the element radiant 20. The body 13 of the housing 11 has a bottom 14 and a set of side walls 13a to 13d, and thus defines, with the cover 12, a housing shielded capable of receiving various components, such as electronics necessary for the operation of the antenna. In particular, we will have in this case 11, the radio frequency electronics necessary for the transmission and the reception of electromagnetic signals and any electronics that could potentially influence or be influenced by the emission or reception of these electromagnetic signals. If the size allows or requires it, everything other electronic or non-electronic component may be arranged to the interior of this case, such, for example, the movement of a part clock and / or a power source from the portable unit.

The radiant element 20 has a circular arc profile and is arranged on the side of the housing 11, or more specifically on the cylindrical contour A of the structure 10. This radiant element 20 is linked by one 20b of its ends to the body 13 of the housing 11, and is therefore short-circuited, by this same end 20b, to the ground plane of the antenna formed by the housing 11, the opposite end 20a of the radiant element 20 being left free. The length of the radiant element 20 between the free end 20a and the end shorted 20b is approximately equal to a quarter of the length wave λ transmission / reception of the antenna.

A radial recess 18 having the shape of an arc of a circle is present between the radiant element 20 and the housing 11 of the structure. This recess radial 18 defines, on the housing 11, a surface in an arc 18a concentric with the cylindrical contour A of the structure, and two surfaces substantially flat 18b and 18c extending radially between the surface 18a and the cylindrical contour A of the structure. The housing 11 thus comprises two cylindrical side walls 13a and 13b respectively defined by the cylindrical contour A and the surface in a circular arc 18a of the radial recess 18, and two flat side walls 13c and 13d defined by the surfaces planes 18b and 18c.

The radiant element 20 is thus placed on the cylindrical contour A of the structure 10 opposite the cylindrical side wall 13b, the shorted end 20b of this radiant element 20 being connected to the angle formed by the cylindrical side wall 13a and the flat side wall 13c. The free end 20a of the radiant element 20, for its part, points towards the angle formed by the cylindrical side wall 13a and the flat side wall 13d.

In this embodiment, the antenna structure 10 has thus a general cylindrical appearance, the outline of this structure not being interrupted only by the vacuum left between the free end 20a of the element radiant and the angle formed by the cylindrical side wall 13a and the wall lateral plane 13d of the body 13 of the housing 11. The cylindrical outline of the structure can thus advantageously play the role of a nesting circle allowing the structure to be easily inserted into an external element of the unit portable, like the middle of a watch.

The excitation of the antenna can be carried out in a conventional manner by a transmission line, such as a coaxial line, from inside the housing 11. As illustrated for example in FIG. 2a, the excitation antenna can thus be provided by a coaxial line 28 whose internal conductor 28a, isolated from the ground plane, passes through the side wall cylindrical 13b through an orifice 16 formed in the latter for go and contact the radiant element 20 at a determined point 21 distant from the short-circuited end 20b, and the external conductor 28b of which contacts the inner face of the cylindrical side wall 13b.

By playing on the dimensions of the structure, we will act on the characteristics of the antenna. We can notably act on the distance between the radiant element 20 and the surface in a circular arc 18a as well as on the overall dimensions of the housing 11 to modify the bandwidth of the antenna. We can also act on the length and width of the element radiant 20 to modify the resonant frequency.

According to this embodiment of the present invention, it has thus been designed an antenna structure suitable for transmitting and receiving electromagnetic signals at a frequency of 1.8 GHz whose diameter exterior is of the order of 35 mm and the total thickness of approximately 10 mm, these dimensions perfectly allowing the incorporation of the structure in a timepiece. According to this embodiment, the radiant element 20 of the antenna thus extends over the cylindrical contour A of the structure in an arc about 136º and is placed at a distance of the order of 3 mm opposite the cylindrical side wall 13b of the body 13 of the housing 11.

The antenna structure is preferably made in one metallic material, such as brass, but can alternatively also be made of a dielectric material, such as a plastic material, coated with a film electrically conductive. Different manufacturing and machining techniques known to those skilled in the art make it possible to produce this structure, among which molding, stamping or milling for example.

Figures 3a and 3b respectively show a front view and a exploded perspective view of an antenna structure, indicated generally by the reference numeral 100, constituting another mode of realization of the present invention. In this other embodiment, the antenna structure 100 includes a radiant element 120, in the form or substantially rectangular surface, integral with a housing 111 forming integral part of the antenna ground plane. This housing 111 has basically the appearance, in this example, of a portion of cylinder delimited by a substantially cylindrical contour A *, and first and second planes B * and C * substantially perpendicular to the axis of symmetry of the cylinder, perpendicular to the plane of Figure 3a and indicated by lines interrupted in Figure 3b.

As can be seen from the figures, the housing 111 is made in two parts 112 and 113, one 112 essentially forming a cover for the housing 111, and the other 113 essentially forming a body of housing 111 and also supporting the radiant element 120. The body 113 of the housing 111 has a bottom 114 and a cylindrical side wall 113a, and thus defines, with cover 112, an armored box capable of receiving, so analogous to the previous embodiment, various components of the unit portable in which it is incorporated.

Unlike the previous embodiment, the radiant element 120 is arranged on a concentric circle with a cylindrical outline A * beyond the cylindrical side wall 113a of the body 113 of the housing. Element 115 extending substantially radially between the cylindrical side wall 113a and one end 120b of the radiant element 120 short-circuits this last to the ground plane formed by the housing. The other end 120a of the radiant element 120 is left free.

The excitation of the antenna can be carried out in a similar way to the embodiment illustrated in FIGS. 2a and 2b via a coaxial line, the internal conductor, isolated from the ground plane, passes through the side wall cylindrical 113 through an orifice 116 formed in the latter for go and contact the radiant element 120 at a determined point 121 distant from the short-circuited end 120b, and the external conductor of which contacts the inner face of the cylindrical side wall 113 of the housing 111.

Although the embodiments which have just been illustrated show a generally cylindrical appearance which is typically adapted to a horological use, it will be understood that the antenna-forming structure according to the present invention can take various forms depending on the constraints dimensions 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 a schematic perspective view of a room watchmaking in the form of a wristwatch with display analog illustrating a possibility of incorporating the structure forming antenna 10 illustrated in FIGS. 2a and 2b. The structure 10 is thus surrounded and incorporated into an external element made of a non-conductive material like a plastic material and having the shape of a watch middle, identified by the reference numeral 30 in the figure. The movement, no shown, the timepiece is advantageously disposed entirely inside the antenna structure 10.

Small diameter holes can be perfectly arranged in the housing 11 of the antenna structure 10, without substantially affect the characteristics of the latter, so as to allow the passage, where appropriate, of components of display members and / or control elements, these elements being necessarily isolated from the structure 10. In the example of FIG. 4, axes or canons of hour and hour hands minutes 32 thus pass through the center of the cover 12 of the case 11 of the structure. Likewise, rods from various control members penetrate laterally through the cylindrical side wall (side wall cylindrical 13a in Figures 2a and 2b) of the body 13 of the housing of the structure 10, these control members comprising in particular a rod rotary integral with a time setting crown 34 and two buttons buttons 35 and 36.

It will of course be understood that the antenna-forming structure 10 is preferably arranged in the middle of the watch 30 so that the radiant element 20 is oriented opposite the control members 34, 35 and 36, or, in general, opposite any organ penetrating the interior of the antenna structure 10.

According to the present invention, an antenna structure can thus be made so as to be incorporated into a timepiece, such as a watch, and to receive, inside the armored case, all or part of radio frequency electronics, timepiece electronics and its movement.

It will be understood that different modifications and / or adaptations can be brought to the antenna structure without leaving the frame of the present invention defined by the appended claims. In particular, depending on the desired characteristics of the antenna, the radiant element can thus or not extend over the entire thickness of the structure and may or may not be shorted to the ground plane over the entire length of its end linked to the housing.

Claims (15)

1. Antenna structure (10; 100) intended for a portable unit of small volume, such as a timepiece, and including a radiating element (20; 120) of substantially rectangular surface arranged at a determined distance from a ground plane and short-circuited with this ground plane by one (20b; 120b) of its ends (20a, 20b; 120a, 120b), the opposite end (20a; 120a) of said radiating element (20; 120) being left free, characterised in that said structure (10; 100) includes a case (11; 111) forming an integral part of said ground plane and including at least a cover (12; 112), a bottom (14; 114), and a lateral wall (13a,13b; 113a), said radiating element (20, 120) being arranged laterally with respect to said case (11; 111) in-between said cover (12; 112) and said bottom (14; 114), the surface of said radiating element facing said lateral wall, said case (11; 111) forming a shielded housing able to accommodate all or part of an electronic circuit and/or other components of the portable unit.
2. Antenna structure (10; 100) according to claim 1, characterised in that said antenna structure essentially has the shape of a cylinder portion delimited by a substantially cylindrical contour (A; A*) defining a cylindrical lateral wall (13a; 113a) of said case (111), and by first and second planes (B, C; B*, C*) respectively defining said cover (12; 112) and said bottom (14; 114) of the case (111), and in that said radiating element (20; 120) substantially has a profile of an arc of a circle concentric to said cylindrical contour (A; A*) and is arranged in the vicinity of the latter in-between said first and second planes (B, C; B*, C*).
3. Antenna structure (10) according to claim 2, characterised in that a radial recess (18) having the shape of an arc of a circle concentric to said cylindrical contour (A) separates said radiating element (20) from said case (11), this radial element (18) defining, on said case (11), another cylindrical lateral wall (13b) concentric to and of smaller radius than said cylindrical contour (A), and two planar lateral walls (13c, 13d) extending substantially radially between the two cylindrical lateral walls (13a, 13b) of the case (11), said radiating element (20) being arranged on said cylindrical contour (A) facing and at a determined distance from said other cylindrical lateral wall (13b), the short-circuited end (20b) of this radiating element (20) being connected to the angle formed by the cylindrical lateral wall (13a) and one of said planar lateral walls (13c, 13d).
4. Antenna structure (100) according to claim 2, characterised in that said radiating element (120) is arranged beyond said cylindrical contour (A*) facing and at a determined distance from said cylindrical lateral wall (113a) of said case (111), the short-circuited end (120b) of the radiating element (120) being connected to an element (115) extending substantially radially from said cylindrical lateral wall (113a) of said case (111).
5. Antenna structure (10; 100) according to any one of the preceding claims, characterised in that excitation of the antenna is assured by a transmission line, such as a coaxial line (28), from the interior of said case (11; 111), this coaxial line (28) including an internal conductor (28a) insulated from the ground plane and contacting said radiating element (20; 120) at a determined point (21; 121) distant from the short-circuited end (20b; 120b), and an external conductor (28b) contacting the ground plane.
6. Antenna structure (10; 100) according to any one of claims 1 to 5, characterised in that said antenna structure is made of a metallic material.
7. Antenna structure (10; 100) according to any one of claims 1 to 5, characterised in that said antenna structure is made of a dielectric material coated with an electrically conductive layer.
8. Antenna structure (10; 100) according to any one of the preceding claims, characterised in that the lateral wall of the case (11; 111) forms a casing ring of a timepiece.
9. Antenna structure (10; 100) according to any one of the preceding claims, characterised in that the radiating element (20; 120) forms an integral part of said case (11; 111).
10. Timepiece including an antenna structure according to any one of the preceding claims.
11. Timepiece according to claim 10, characterised in that the case (11; 111) of the antenna structure is incorporated into an external element (30) made of a non conductive material, such as a plastic material, and which has the form of a watch middle part.
12. Timepiece according to claim 10 or 11, characterised in that a movement of the timepiece is located entirely inside said antenna structure (10; 100).
13. Timepiece according to any one of claims 10 to 12, characterised in that shafts or pipes of hours and minutes hands (32) pass through the cover (12; 112) of the case (11; 111) of the antenna structure (10, 100).
14. Timepiece according to any one of claims 10 to 13, characterised in that control elements (34, 35, 36) penetrate laterally through the lateral wall (13a; 113a) of the case (11; 111) of the antenna structure (10; 100).
15. Timepiece according to claim 14, characterised in that the radiating element (20; 120) of the antenna structure is oriented opposite said control elements (34, 35, 36).

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