EP0995234A1

EP0995234A1 - Patch antenna

Info

Publication number: EP0995234A1
Application number: EP99916981A
Authority: EP
Inventors: Frédéric DIXIMUS; Daniel Leclerc; Roland Vincent
Original assignee: Amphenol Socapex SA
Current assignee: Amphenol Socapex SA
Priority date: 1998-05-05
Filing date: 1999-05-04
Publication date: 2000-04-26
Also published as: TW424350B; KR20010014344A; WO1999057785A1; CN1266542A; FR2778500A1; FR2778500B1; US6326919B1; CN1129200C; JP2002509681A

Abstract

The invention concerns a portable apparatus internal patch antenna element, comprising: a body in dielectric material (10); a conductive wafer (24) covering the dielectric upper surface; a conductive patch board (28) covering the dielectric side surfaces (18), electrically connected along its upper edge to said wafer and provided with electrical connecting means for connecting said conductive patch board to a ground plane (26) designed to be arranged along the dielectric lower surface (14), the other three side surfaces being not metal-coated, means (30, 32) passing through the dielectric body, for electrically connecting an antenna hotspot conductor to said wafer, and means forming capacitance (34) to produce a capacitor between the wafer and the ground plane when the antenna element is mounted on the ground plane, arranged in the proximity of the dielectric body side surface (16) opposite the one which is covered with said conductive patch board.

Description

PLATE ANTENNA

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 going 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 operate for a single 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 frequency bands mentioned above.

It is therefore an object of the present invention to provide an antenna element or a complete antenna of the plate type which can operate in a portable device for two distinct 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 devoid of metallization,

- means passing through said dielectric body between its lower face and its upper face, intended to electrically connect the hot spot of an antenna conductor to said plate, and - means forming a capacitor for producing a capacitor between said plate and said plane ground when said antenna element is mounted on the ground plane, disposed near the side 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.

It is also understood that thanks to the presence of the capacitance, a good agreement is obtained between the probe or the antenna conductor and the antenna itself 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 wafer and whose ground of the power supply is connected to the conductive plate forming the ground plane of the antenna.

It is understood that thus from the antenna element, it is easy to produce the complete antenna by adding a ground plane. According to an alternative embodiment of the antenna, the conductive plate and the conductive plate covering one of the lateral faces of the dielectric belong to the antenna element as well as the conductive plate constituting the ground plane consist of the same folded metal sheet and fixed to the body of dielectric material. According to a preferred embodiment of this variant, the portion of said metal sheet forming the ground plane comprises a first opening surrounded by an electrical connection flange protruding from said sheet and constituting an extension of said sheet, and the hot spot consists of a conductive element passing through the body of dielectric material and a first end of which is electrically connected to said wafer and the second end of which projects into the face of the dielectric material inside said flange.

It is understood that, according to this embodiment, the collar and the second end of the conductive element forming antenna connection elements directly capable of cooperating with a base provided on the printed circuit of the portable device equipped with this antenna.

In many cases, the portable device which is equipped with its internal plate antenna must be able to operate with an external antenna, for example, that of a motor vehicle. The internal antenna must then be disconnected from the antenna circuits of the portable device and the external antenna must be connected to the antenna circuits of this device.

To solve this problem, according to an embodiment which can be combined with the previous embodiment, the antenna is characterized in that the portion of said metal sheet forming said wafer has a second opening opposite said first opening, in that the first end of said conductive element protrudes from the upper face of said body of dielectric material and in that said body has a recess surrounding said conductive element, in that said sheet has a second elastically deformable extension surrounding said second opening, the end of which free protrudes into said recess and is applied elastically against said conductive element. It is understood that the second elastically deformable extension constitutes an electrical switching member. At rest, corresponding to the operation of the device with the internal antenna, the conductive element is electrically connected to the conductive plate forming the radiating plate of the plate antenna via the switching element. On the contrary, when the external antenna connector is connected, this connector discards the second extension of the conductive element forming the switching element, which therefore disconnects the internal antenna.

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 a 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 the appended figures in which: FIG. 1 is a perspective view showing the principle of embodiment of the plate antenna; Figure 2 is a detail view showing a first embodiment of the antenna capacity;

Figure 2a shows an alternative embodiment of the capacity; Figure 3 is a perspective view showing a method of mounting the antenna element on the ground plane; Figure 4 is a schematic view in vertical section of a plate antenna equipped with an antenna connector; Figure 5 is a schematic vertical sectional view of a plate antenna fitted with an antenna connector and an external antenna switch; Figures 6a and 6b show a preferred embodiment of the antenna schematically shown in Figure 5; Figure 7 is a schematic view showing the installation of an 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 feed 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 capacitor 34 is disposed near the side face 20 and the side face 16. In other words, it can be said that the capacitor 34 is diagonally opposite to the antenna feed 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 we call L 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 of which a quarter of the wavelength is substantially equal to 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 must also be added so that the antenna that has just been described is tuned to operate in these two frequency bands that it is necessary to provide the capacity 34 performing the tuning. Preferably, the dielectric material constituting the block 10 has a relative permittivity εr = 6 and a loss angle whose tangent is equal to 10 ⁻⁴ . 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 ′ may be equal to 3 cm. The height h of the radiating slot 16 is equal to 5 mm and the height h 'of the short circuit is equal to 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 produced on these faces. The ground plane 26 is constituted by a conductive plate.

There is thus an antenna element constituted by the dielectric body and its metallizations 24 and 28 and its capacitance 34 which forms an autonomous component. Just attach it to the base plate to form a plate antenna.

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 towards the side face of the block 10 of dielectric material.

It is understood that this embodiment of the capacity is particularly 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 ground plane 26.

FIG. 2a illustrates another embodiment of the capacity 34 which, in this case, is adjustable. The capacitor consists of a piece of coaxial cable 35 comprising an axial conductor 37 and a cylindrical conductor 39. The cylindrical conductor 39 is electrically connected to the plate 24, while the end of the axial conductor 37 is connected to the ground plane 26 by a conductive wire 41. By modifying the length of the cable 35 by successive cuts, it is possible to precisely adapt the value of the capacity 24.

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 itself will result from the union of an antenna element 50 shown in FIG. 3 fixed on a ground conductive 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 advantageous to provide on the lower edge 28a of the short circuit 28 a compressible conductive seal 54 which will ensure electrical contact when fixing the antenna element on the plate 52.

Figure 7 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 earphone 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 50 shown in the Figure 3. It is understood that the arrangement of the antenna element 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 arranged relative to the conductive plate 70 so that the latter constitutes a reflective plane for the antenna which thus ensures the directivity of the ray electromagnetic radiation emitted by the antenna and thus protects the user of the antenna.

Referring now to Figure 4, we will describe a first embodiment of the antenna in the case where it is equipped with its own antenna connector. The antenna 80 comprises a body of dielectric material 81 of the same kind as that which is represented in FIGS. 1 to 3, a radiating upper plate 82, a ground plane 84 and a short-circuit plate 86 connecting the plate 82 and the plate 84. The short-circuit plate 86 as already explained occupies only one of the four lateral faces of the body of dielectric material 81. In addition, the antenna has a capacitance 34 not shown as already mentioned Explain. In this embodiment, the radiating plate 82, the base plate 84 and the short circuit 86 are constituted by the same conductive sheet 88 which is folded and fixed on the corresponding faces of the body of dielectric material 81. The portion of the sheet constituting the base plate 84 is machined to define an opening 90 and an extension forming an electrical connection flange 92. In addition, the axial antenna conductor 94 is constituted by a conductive rod, a first of which end 94a is electrically connected to the plate 82 and the second end of which 94b projects from the underside of the body 81 inside the volume defined by the flange 92. In this figure, the printed circuit 96 is also shown. the portable device equipped with the antenna 80. In this figure, the base 98 for connection between the internal antenna 80 and the circuits of the portable device has been shown. It is understood that, to mount the antenna and connect it, it suffices to engage the base 98 inside the flange 92 in order to ensure the connection of the antenna and the printed circuit 96.

The extension 92 may be formed by a part of the deformed metal sheet or be formed by an insert welded to the metal sheet 88 around the opening 90.

Referring now to Figures 5 and 6, we will describe a second embodiment of the antenna in which there is not only an internal antenna connector but also an external antenna connection switch.

Figure 5 shows the block diagram of this antenna. We find the body of dielectric material 81 and the metal sheet 88 which constitutes the radiating upper plate 82, the short-circuit plate 86 and the ground plane 84. We also find the flange 92 forming the internal antenna connection as well as the conductive rod 94 ′ equivalent to the rod 94 whose end 94 ′ b protrudes inside the flange 92. In this embodiment, preferably, a recess 100 surrounds part of the conductive rod 94 ′ and this protrudes by its second end 94'a from the upper face of the dielectric body 81. Machining is carried out in the upper plate 82 to form a second opening 102 in which protrudes the end 94'a of the rod and to form folded elastic tabs 104, the free end 104a of which is pressed against the rod 94 ". In addition, a second conductive flange 106 is fixed to the plate head 82 and protrudes from it to define an electrical connection flange for an external antenna 108. As can be seen in FIG. 5, the end 94'a of the rod 94 'protrudes inside the second flange 106.

When the portable device must operate with the internal antenna, which corresponds to FIG. 5, the conductive tongues 104 are applied against the rod 94 ′ and the end 94 ′ a of this is therefore connected to the radiating plate. 82. The same electrical configuration is thus reconstituted as that shown in FIG. 4. On the other hand, when the external antenna connector 108 is engaged, the insulating part 110 of the latter separates the elastic conducting tabs 104 thus interrupting the electrical connection between the wafer 82 and the rod 94 '. However, the ground of the antenna is connected to the ground of the printed circuit via the flanges 106 and 92 and the axial conductor of the antenna 108 is connected to the rod 94 '.

It is understood that the elastic conductive tabs 104 constitute an electrical switch which, at rest, allows the operation of the portable device with the internal antenna 80 'and which, when the external antenna connector is engaged, ensures the connection between the external antenna and circuits 96 of the portable device.

In order to further improve the functioning of the antenna, in particular the functioning of the external antenna when the latter is connected to the plate antenna, it is preferable for the recess 100 to pass through the dielectric body than right through in such a way that when the antenna connector 108 is mounted, the external conductor of the latter is electrically connected to the external base conductor 98. Thus, the cylindrical electric conductor which surrounds the axial conductor 94 eliminates or considerably reduces the risks the plate antenna is not excited by the external antenna while in operation.

Indeed, such a coupling has the effect of reducing the energy available on the external antenna.

Referring now to FIGS. 6a and 6b, a preferred embodiment of the antenna shown schematically in FIG. 5 will be described in more detail.

In this embodiment, the body of dielectric material 81 has a recess 100 'which passes right through it between the plate 82 and the ground plane 84. The ground plane 84 has an extension 92 in the form of a collar which constitutes the external connection for the base 98 fixed to the printed circuit 96. The base 98 is constituted by an axial conductor 110 which passes through the recess 100 'and which projects from the plate 82, and by an external conductor 112.

The plate 82 in line with the recess 100 'has an elastically deformable extension 114 of generally frustoconical shape. At rest, that is to say when the external antenna is not connected, the free edge 116 of the extension 114 is in electrical contact with the end 110a of the axial conductor 110. An electrical connection is thus established between the antenna plate 82 and the printed circuit 96. 10

When one wants to connect the external antenna via its antenna connector 120, this is introduced into the recess 100 '. The central conductor 122 is then connected to the axial conductor 110. Its external conductor 124 deforms the extension 114 which is then in electrical connection with the external conductor 124 of the antenna connector 120. In addition, the end 124a of the external conductor 124 of the antenna connector 120 comes into electrical contact with the end 112a of the external conductor 112 of the base 98. An electrically conductive cylinder is thus produced which passes through the dielectric 81 and surrounds the axial conductors 110 and 122. Thus , when the external antenna is in operation, there is no coupling with the internal antenna constituted by the plate 82 and the ground plane 84.

Claims

11 CLAIMS

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,

means passing through said dielectric body between its lower face and its upper face, intended to electrically connect the hot spot of an antenna conductor to said wafer, and

- means forming a capacitor for producing a capacitor between said plate 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 plate conductive, 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 other two 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 lateral face covered by the conductive plate having a height at most equal to that from 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. 12

5. antenna element according to any one of claims 1 and 4, characterized in that said capacitance means and said means for connection to the power supply are arranged near two nonadjacent 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 side faces of the dielectric body and of which the length is less than that of the part opposite the lateral face.

7. antenna element according to any one of claims 1 to 5, characterized in that said capacity means comprise a coaxial cable element whose conductive elements are electrically connected to said wafer and connectable to the ground plane.

8. antenna element according to any one of claims 1 to 7, characterized in that said plate and said conductive plate consist of metallizations arranged on the faces of said dielectric body.

9. antenna element according to any one of claims 1 to 8, characterized in that said electrical connection means of the conductive plate comprise a strip of compressible conductive material.

10. 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 to 7.

- a conductive plate constituting the ground plane; and - a power supply whose hot spot is connected to said wafer and whose mass of the power supply is connected to the conductive plate forming the ground plane of the antenna.

11. Antenna according to claim 10, characterized in that the conductive plate and the conductive plate covering one of the lateral faces of the dielectric belonging to the antenna element as well as the conductive plate constituting the ground plane are formed by the same sheet metal bent and fixed on the body of dielectric material.

12. Antenna according to claim 11, characterized in that the portion of said metallic sheet forming the ground plane comprises a first opening surrounded by an electrical connection flange protruding from said sheet and constituting an extension of said sheet and the point hot is 13

consisting of a conductive element passing through the body of dielectric material and a first end of which is electrically connected to said plate and the second end of which protrudes into the face of the dielectric material inside said flange.

13. An antenna according to claim 12, characterized in that the portion of said metal sheet forming said wafer has a second opening opposite said first opening, in that the first end of said conductive element projects out of the upper face of said body of dielectric material and in that said body of dielectric material has a recess surrounding said conductive element, in that said sheet has a second elastically deformable extension surrounding said second opening, the free end of which protrudes into said recess and is applied elastically against said conductive element.

14. Antenna according to claim 13, characterized in that said recess passes right through said body of dielectric material and in that said recess is capable of receiving the connector of an external antenna.

15. An antenna according to claim 14, characterized in that said conductive element is an integral part of a base on which is engaged said elastic collar.

16. Application of an internal antenna of the plate type for a portable device according to claim 10, 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 circuits of the radiotelephone.

17. Application of an internal antenna of the plate type according to claim 10, characterized in that the ground plate of the antenna is arranged in said radiotelephone to form a reflective plane for the antenna thus achieving directivity of the antenna and therefore protection against electromagnetic radiation for the user.