FR2778499A1 - Miniaturized antenna contained within portable telephone handset - Google Patents

Abstract

The aerial structure is reduced in size, yet retains dual frequency capability. The aerial comprises a body (10) made of dielectric material and a conductive wafer (24) covering the upper surface of this dielectric. A conductive patch board (28) covers the side surfaces (18) of the dielectric. The patch board is electrically connected along its upper edge to the wafer. The conductive patch board is electrically connected to an earth plane (26) which is arranged along the dielectric lower surface. The other three sides of the dielectric are not metal coated. A connection (30,32) passes through the dielectric body for connecting an aerial hot spot to the wafer. A capacitance is formed between the wafer and the earth plane.

Description

The present invention relates to plate type antennas

  in particular but not exclusively usable in portable radiotelephones.

  We know that portable telephones are experiencing very significant development in many countries. One of the objectives sought by the designers of radiotelephones is to miniaturize them as much as possible in order to make them of use more and more easy. One of the elements that raises a problem with regard to this miniaturization is the radiotelephone antenna. In the vast majority of known radiotelephones, the antenna is external and therefore increases

the size of the device.

  Another problem related to the design of radiotelephones lies in the fact that currently two frequency bands are used in portable radiotelephone networks. On the one hand, there is the so-called GSM band which corresponds to a frequency band ranging from 890 MHz to 960 MHz and the frequency band called DCS 1800 whose frequency band goes from 1,710 MHz to

1,880 MHz.

  It would therefore be interesting to have radiotelephones which can operate in one and the other of the frequency bands depending on the network used. It is relatively easy to provide electronic circuits in the radiotelephone capable of processing, in transmission and reception, signals corresponding to two frequency bands typically different from those which have been mentioned above. On the other hand, the problem of the antenna corresponding to

two bands is more delicate.

  A plate type antenna has already been proposed in a radiotelephone. This antenna can be placed inside the radiotelephone itself and this therefore considerably reduces the space requirement. However, in this known solution, the plate antenna can only work for one

frequency band.

  There is therefore a real need to have a plate type antenna which can be used in particular for portable telephones and which makes it possible to work in two distinct frequency bands in particular for the bands.

  above mentioned frequencies.

  An object of the present invention is therefore to provide an antenna element or a complete antenna of the plate type which can operate in a

  portable device for two separate frequency bands.

  To achieve this object, according to the invention, the internal antenna element for a portable device of the plate type is characterized in that it comprises: a body of dielectric material having a lower face, an upper face and four lateral faces , - a conductive plate covering said upper face, - a conductive plate covering one of the lateral faces, electrically connected along its upper edge to an edge of said plate and provided with electrical connection means extending along a second edge parallel to the first edge and intended to connect said conductive plate to a ground plane intended to be arranged along the underside of said electrical body, the other three lateral faces being free of metallization, - means passing through said dielectric body between its underside and its face upper, intended to electrically connect the hot spot of an antenna conductor to the adite wafer, and - means forming a capacitor to produce a capacitor between said wafer and said ground plane when said antenna element is mounted on the ground plane, arranged near the lateral face of the dielectric body opposite to that which is covered by said conductive plate, whereby the side face opposite to that which is provided with said plate forms a radiating slot corresponding to a first frequency band and the two other opposite lateral faces not covered with metallization form radiating slots for a

second frequency band.

  It is understood that thanks to the presence on the one hand of the radiating slot corresponding to the short circuit and on the other hand thanks to the other two radiating slot faces, it is possible effectively to use the antenna for two distinct frequency bands which as understood, correspond respectively to the half wavelength, to the quarter wavelength and to the half wavelength. We also understand that thanks to the presence of the capacity we

  obtains a good agreement between the probe or the antenna conductor and the antenna itself

  even for the two frequency bands in which the antenna can work.

  The invention also relates to an internal antenna of the plate type for a portable device which is characterized in that it comprises an antenna element of the type defined above, a conductive plate constituting the ground plane and a power supply whose hot point is connected to said plate and the mass of the power supply of which is connected to the conductive plate forming the plane of

mass of the antenna.

  We understand that thus from the antenna element, it is easy to

  create the complete antenna by adding a ground plane.

  The invention also relates to the application of an internal antenna of the plate type for a portable device of the type defined above to the production of a portable radiotelephone which is characterized in that the conductive plate forming the ground plane is constituted by the ground plate of the radiotelephone circuits. In addition, preferably this conductive plate is interposed between the printed circuit of the radiotelephone and the antenna element by which said conductive plate forms a reflective plane for the antenna thus forming a directivity and

  therefore protection against electromagnetic radiation for the user.

  Other characteristics and advantages of the invention will appear better

  on reading the following description of several embodiments of

  the invention given by way of nonlimiting example. The description refers to

  attached figures in which: Figure 1 is a perspective view showing the principle of realization of the plate antenna; Figure 2 is a detail view showing a preferred embodiment of the antenna capacity; Figure 3 is a perspective view showing a method of mounting the antenna element on the ground plane; and Figure 4 is a schematic view showing the layout of a

antenna in a radiotelephone.

  Referring first to Figure 1, we will describe the overall structure of the plate antenna according to the invention. As shown in FIG. 1, the antenna comprises a block 10 of dielectric material which has an upper face 12, a lower face 14 and four parallel side faces two by two respectively the faces 16 and 18 and the faces 20 and 22. In the embodiment shown in FIG. 1, the upper 12 and lower 14 faces form between them a dihedral angle a, this dihedral angle being between 0 and 45 and preferably between 0 and 25. The upper face 12 of the dielectric block 10 is covered by a conductive metallization layer 24 which thus forms a conductive plate and the lower face 14 also rests on a conductive plate 26 forming the ground plane. The face 18 is also covered by a metallization 28 electrically connected to the ground plane 26 and to the conductive plate 24 thus forming a short circuit. On the other hand, the lateral faces 20, 22 and 16 are devoid of metallization. The antenna also includes a probe 30 or supply conductor which comprises a hot spot 32 connected to the conductive plate 24 and a mass connected to the ground plane 26. In the example described, the supply conductor is in the form of a coaxial conductor but other embodiments could be envisaged. Preferably,

  the antenna supply 30 is arranged near the edge 18 provided with the short

  circuit 28 and the side face 22. The antenna also has a capacity symbolically represented by 34 which electrically connects the ground plane 26 and the conductive plate 24. Preferably, this capacity 34 is arranged near the side face 20 and of the side face 16. In other words, we can

  say that the capacity 34 is diagonally opposite to the antenna supply 30.

  The plate antenna thus formed allows operation in two frequency bands which are respectively defined by the radiating slots formed by the side faces 20 and 22 and on the other hand by the side face 16 opposite the short circuit 28. If the 'L is the length of the faces 20 and 22 and L' the length of the face 16 opposite the short-circuit we understand that the radiating slit 16 corresponds to a frequency band whose quarter of the wavelength is substantially equal at L and that the slots 20 and 22 allow operation in a frequency band whose half wavelength is

  substantially equal to the length L '.

  It is also necessary to add so that the antenna which has just been described is tuned to operate in these two frequency bands which it is

  necessary to provide the capacity 34 carrying out the agreement.

  Preferably, the dielectric material constituting the block 10 has a relative permittivity sr = 6 and a loss angle whose tangent is equal to

  104. A usable material is a ceramic.

  In the case where the two frequency bands are those which have been mentioned previously, that is to say the GSM and DCS 1800 bands the lengths L and L ′ can be equal to 3 cm. The height h of the radiating slit

  16 is 5 mm and the height h 'of the short circuit is 2 mm.

  It should be added that the conductive plate 24 and the short-circuit 18 can be produced either effectively by conductive plates fixed on the corresponding faces of the dielectric block 10, or by metallizations carried out

  on these faces. The ground plane 26 is constituted by a conductive plate.

  Referring to Figure 2 we will describe a preferred embodiment of the capacitor 34. This consists of an extension 36 of the conductive plate 24, this extension has a curved portion 38 which is therefore parallel to the face 20 of the dielectric block. The curved end 38 is spaced from the face 20 and stops above the ground plate 26 and ends in a

  portion 39 folded back towards the lateral face of the block 10 of dielectric material.

  It is understood that this embodiment of the capacity is particularly

  rely advantageous since it does not require any particular component. It goes without saying, however, that the capacitor 34 could consist of a conventional capacitor electrically connected to the conductive plate 24 and to the plane of

mass 26.

  When the antenna is mounted in a radiotelephone, it may be advantageous to use the ground plate of the electronic circuits of the radiotelephone as the ground plane of the antenna. In this case, the antenna proper will result from the union of an antenna element 50 represented in FIG. 3 fixed on a conductive ground plate 52. In this case, the antenna element 50 comprises the dielectric block 10 already described, the conductive plate 24 and the short circuit 28. To ensure electrical continuity when the antenna element 50 is mounted

  on the plate 52 it is interesting to provide on the lower edge 28a of the short

  circuit 28 a compressible conductive joint 54 which will ensure electrical contact

  when fixing the antenna element on the plate 52.

  Figure 4 schematically illustrates the mounting of an antenna in a radiotelephone 60. In this figure, there is shown in a simplified manner, the housing 62 with its microphone 64 and its earpiece 66. There is also shown the keyboard 68 of the radiotelephone , as well as its display 69. Inside the housing 62, the ground plate 70 of the electronic circuits 72 of the radiotelephone and the battery 74 has been made visible. On this plate 70 is mounted the antenna element

shown in figure 3.

  It is understood that the arrangement of the antenna element is particularly

  This is particularly advantageous since it is of reduced size, that it can use the ground plate of the radiotelephone circuit as the antenna ground plane and that, moreover, the antenna 50 which includes the ground plane 70 is placed with respect to the conductive plate 70 so that it constitutes a reflective plane for the antenna which thus ensures the directivity of the electromagnetic radiation

  emitted by the antenna and thus protects the user of the antenna.

Claims (11)

CLAIM   1. Internal antenna element for a portable device of the plate type, characterized in that it comprises: - a body of dielectric material having a lower face, an upper face and four lateral faces, - a conductive plate covering said upper face , - a conductive plate covering one of the lateral faces, electrically connected along its upper edge to an edge of said wafer and provided with electrical connection means extending along a second edge parallel to the first edge and intended to connect said conductive plate to a ground plane intended to be arranged along the underside of said electrical body, the other three lateral faces being devoid of metallization, - means passing through said dielectric body between its underside and its upper face, intended to electrically connect the hot spot an antenna conductor to said plate, and - means forming capacity for producing a capacitor between said plate and said ground plane when said antenna element is mounted on the ground plane, disposed near the lateral face of the dielectric body opposite to that which is covered by said conductive plate, whereby the side face opposite to that which is provided with said plate forms a radiating slot corresponding to a first frequency band and the two other opposite lateral faces not covered with metallization form radiating slots for a second frequency band.   2. antenna element according to claim 1, characterized in that said upper and lower faces of the dielectric body form a dihedral angle of between 0 and 45, the side face covered by the conductive plate having   a height at most equal to that of the side face opposite it.   3. antenna element according to claim 2, characterized in that   said dihedral angle is between 0 and 25.   4. antenna element according to any one of claims 1 and 3,   characterized in that the length of the dielectric body in the direction orthogonal to the conductive plate corresponds substantially to a quarter of the wavelength of the first frequency band, and in that the length of said dielectric body corresponds substantially to half the wavelength of the second frequency band.   5. antenna element according to any one of claims 1 and 4,   characterized in that said capacity means and said power connection means are arranged near two non-adjacent edges of the dielectric body.   6. antenna element according to any one of claims 1 and 5,   characterized in that said capacitance means comprise an extension of said conductive plate forming a flat surface extending parallel to one of the lateral faces of the dielectric body and whose length is less than   that of the part opposite the lateral face.   7. antenna element according to any one of claims 1 and 6,   characterized in that said plate and said conductive plate are formed   by metallizations arranged on the faces of said dielectric body.   8. antenna element according to any one of claims 1 and 7,   characterized in that said means for electrical connection of the plate   conductive include a strip of compressible conductive material.   9. Internal antenna of the plate type for a portable device, characterized in that it comprises:   - said antenna element according to any one of claims 1   at 8. - a conductive plate constituting the ground plane; and - a power supply, the hot spot of which is connected to said wafer and the mass of the power supply of which is connected to the conductive plate forming the ground plane of the antenna.   10. Application of an internal antenna of the plate type for a portable device according to claim 9, in the production of a portable radiotelephone, characterized in that the conductive plate forming the ground plane is   constituted by the ground plate of the radiotelephone circuits.   11. Application of an internal antenna of the plate type according to claim 9, characterized in that the earth plate of the antenna is arranged in said radiotelephone to form a reflective plane for the antenna thus achieving a directivity of the antenna and therefore protection against radiation   electromagnetic for the user.