WO2004012298A2

WO2004012298A2 - Thin patch antenna

Info

Publication number: WO2004012298A2
Application number: PCT/FR2003/002349
Authority: WO
Inventors: Roland Vincent; Ayoub Annabi; Daniel Leclerc
Original assignee: Amphenol Socapex
Priority date: 2002-07-26
Filing date: 2003-07-25
Publication date: 2004-02-05
Also published as: FR2842951A1; CN1672289A; WO2004012298A3; AU2003269057A8; JP2005534242A; EP1525641A2; AU2003269057A1

Abstract

The invention concerns a thin patch antenna, comprising a radiating element (50), an antenna power supply connected to the radiating element, a conductive surface (66) substantially parallel to said radiating element and spaced away from said element by a distance e, the conductive surface being provided with at least one slot (68) facing said radiating element; and a conductive connection between said conductive surface and said radiating element.

Description

The present invention relates to a thin plate antenna.

Plate antennas of the PIFA or other type are now commonly used in particular for the production of portable radiotelephones. Indeed, these antennas are entirely internal to the housing of the portable telephone and they have relatively reduced dimensions.

In Figure 1 attached, there is shown in vertical section in a simplified manner such an antenna. It consists of a radiant element 10 whose design is adapted to the wavelength or wavelengths in which one wants to work as well as to the desired impedance which is typically 50 Ω. This antenna also includes a ground plane 12 substantially parallel to the radiant element 10. A short circuit 14 is produced between the radiant element 10 and the ground plane 12. Finally, the power supply to the antenna is constituted by more often by a coaxial cable 16 whose central conductor 16a is electrically connected to the radiant element 10 and whose shield 16b is connected to the ground plane. With such antennas, it is necessary to provide a minimum spacing e in order to obtain proper functioning of the antenna. Typically, the minimum spacing e is of the order of 7 to 10 mm when the dielectric between the radiant element and the ground plane is air and the frequency is less than 2 GHz.

If one seeks to reduce the distance e between the radiant element and the ground plane, the antenna obtained has limitations in its operation and in particular limitations as to its bandwidth which are unacceptable. In particular, a distance e of less than 5 mm is difficult to obtain for frequencies below 2 GHz, that is to say for frequency ranges usually used in radiotelephony, in particular in GSM.

However, an evolution of portable radiotelephones takes shape according to which the total thickness of the radiotelephone must become increasingly reduced. It is therefore desirable to be able to have antennas also of reduced thickness and in which, in particular, the distance e is significantly less than 7 mm, for example of the order of 2 to 3 mm. It should also be noted that to save space in the radiotelephone, often metallization on the PCB, shields, etc. constitute the ground plane of the radiotelephone and the assembly formed by the radiant element, the short circuit 14 and the power cable 16 is directly mounted on the printed circuit.

There is therefore a real need to have antennas, the total thickness of which is at most equal to 5 mm while presenting acceptable operating conditions and capable of working in several frequency bands corresponding to those conventionally used in radiotelephones Modems including laptop, PCMCIA card, PDA, etc.

An object of the present invention is therefore to provide a plate antenna of reduced thickness and which nevertheless has a bandwidth in accordance with the standards in force. To achieve this object according to the invention, the thin plate antenna is characterized in that it comprises:

- a radiant element,

- an antenna supply connected to the radiant element,

- a conductive surface substantially parallel to said radiant element and disposed at a distance e from said element, said conductive surface being provided with at least one slot facing said radiant element, said slot being open; and

- a conductive connection between said conductive surface and said radiant element. By slit is meant any recess in the conductive surface regardless of the shape of its outline.

The antenna conforming to the definition given above effectively allows, despite its reduced thickness, for example of the order of 3 mm, to obtain a bandwidth suitable for its use in a portable radiotelephone or other for the frequency bands. commonly used below 2 GHz, especially for GSM. This result is obtained from the fact that in the electric field mainly created by the radiant element, a magnetic field is induced by the existence of the slot made in the conductive surface opposite the radiant element. The composition of these two quadrature fields produces a wave electromagnetic corresponding to that used in an antenna of standard thickness, that is to say of the order of 7 to 10 mm.

By "open slit" is meant a slit which opens into the periphery of the conductive surface. In other words, when the slit is open, the slit is not entirely surrounded by an electrically conductive element. Thanks to the opening of this slot, this slot is prevented from radiating, which allows very efficient operation of the antenna.

Preferably, the open slot has a shape substantially identical to that of the radiant element.

According to an alternative embodiment, the slot has a contour which corresponds substantially to the envelope of said radiant element.

According to a preferred embodiment of the antenna, the conductive surface is constituted by a conductive plate and the antenna further comprises an insulating mechanical structure on which are fixed the radiant element, the conductive plate and the conductive connection.

This assembly can be directly fixed to a printed circuit and suitably connected to the conductive tracks of the printed circuit. 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 examples. The description refers to the drawings in which:

- Figure 1, already described, shows a known antenna of the PiFa type;

- Figure 2A is a top view of the conductive surface of a first embodiment of an antenna according to the invention;

- Figure 2B is a top view of the radiating element corresponding to Figure 2A; - Figure 2C is a vertical sectional view of the antenna incorporating the components of Figures 2A and 2B;

- Figure 3 shows two curves corresponding to a reference antenna and the antenna of Figures 2A to 2C;

- Figure 4 is a vertical sectional view of a first alternative embodiment of the antenna; - Figure 5 is a vertical sectional view of a second alternative embodiment of the antenna; and

- Figure 6 shows in perspective yet another alternative embodiment of the antenna. Referring now to Figures 2A to 2C, we will describe a first embodiment of an antenna according to the invention.

In this embodiment, as shown in FIG. 2B, the radiant element 50 comprises two main parallel parts 52 and 54 joined at one of their ends by a loop 56 and extended at the second end of the rectilinear part 52 by a branch 58. The shape of the radiant element is defined by the operating frequency or frequencies of the antenna and by the independence sought. The branch 58 is extended by two connection lugs 60 and 62 respectively of the antenna and of the short-circuit fixed on a double connector element 64.

In Figure 2A, there is shown a conductive surface 66 with its slot 68 which has a contour close to that of the radiant element 50 but not necessarily identical to it. The slot is formed by the slot portions 52 ', 54', 56 'and 58'. The branch 58 'of the slot is extended by a portion 70 which opens into the periphery 66a of the conductive surface 66 to thereby obtain an open slot within the meaning of the definition given above. The slot portion 70 is disposed between the connection pads 72 and 74 corresponding respectively to the production of an electrical short circuit between the radiant element and the conductive surface 66 and to the antenna supply. The double connector 64 also constitutes a means of mechanical fixing of the radiant element on the conductive surface to maintain the radiant element parallel to the conductive surface at a distance βi from the latter of the order of 2 mm and in any case less than 5 mm. The conductive surface 66 may be constituted by a conductive plate or by a metallization produced on an insulating substrate.

In FIG. 3, there is shown, on the one hand, a curve I which gives the value of the ROS of a reference antenna as a function of the frequency F and, on the other hand, a curve II which shows the value of the ROS (or WSWR) of the antenna of FIGS. 2A to 2C as a function of the frequency. The reference antenna corresponding to curve I is an antenna identical to that shown in FIGS. 2A to 2C with the exception that the conductive surface 66 then forming the ground plane is devoid of the slot 68.

FIG. 3 clearly shows that the reference antenna corresponding to curve I has a much lower bandwidth and with a much weaker amplification than the antenna object of the invention corresponding to curve I

In Figure 6, there is shown another embodiment of the antenna according to the invention. This embodiment is close to that of FIGS. 2A, 2B and 2C.

FIG. 6 shows the conductive surface 140 which is for example constituted by a metallization produced on an insulating substrate 142. The conductive surface 140 and provided with the slot 144 which will be described later in more detail. This figure also shows a radiant element 146 which is arranged in a plane substantially parallel to the conductive surface 140. In the example considered, the radiant element 146 comprises a first branch 148 corresponding to a first frequency band, a second branch 150 corresponding to a second frequency band and a base 152. The second branch 150 is, for example, constituted by a first portion 150a substantially parallel to the first branch 148 and by a second portion 150b folded back relative to the first portion 150a. Finally, it includes a base 152 common to the two branches. The radiant element 146 can be cut from a thin conductive metal sheet. In the example considered, the radiant element 146 is mounted on a double connector 154. This connector makes a first short-circuit connection between the radiant element and the conductive surface 140 and a second connection between the radiant element and a antenna cable 156. The distance e between the radiant element 146 and the conductive surface 140 is equal to 2 mm. The slot 144 has a contour 144a which corresponds substantially to the envelope of the assembly of the radiant element 146. In the example illustrated by FIG. 6, the contour 144a is a rectangle. Preferably, this slot is arranged substantially opposite the radiant element. The actual slot 144 is extended by an extension 158 which opens into the periphery 140a of the conductive surface 140 to form an open slot in the sense that this expression has been defined above. As already indicated, the conductive surface could have several slots in relation to the shape of the radiant element. Preferably, these slots are open or at least one of the slots is open. Referring now to Figure 4, we will describe another alternative embodiment of the antenna according to the invention. In this variant, the structure of the antenna proper is identical to that which has been described previously, but there is added a mechanical structure making it possible to make the antenna modular. The mechanical structure made of an insulating material, preferably a moldable plastic which bears the reference 80 has the general shape of a cover with an upper wall 82 and four side walls such as 84. Preferably, the radiant element shown in a simplified manner at 86 is molded inside the plastic material constituting the upper wall 82. It may have the shape shown in FIG. 2B. Opposite the portion 86a of the radiant element, the upper wall 82 has recesses 88, 90 for connection. In addition, the mechanical structure 80 defines a housing 92 into which a double connection member 94 can be clipped or mounted in any other suitable manner. The function of this member 94 is to provide the antenna connection and the short circuit. For this, the connection member 94 comprises two upper contacts 96 and 98 penetrating into the recesses 88 and 90 and two lower contacts 100 and 102.

In their lower part, the side walls 84 of the cover 80 includes extra thicknesses 104 for fixing the periphery of a conductive plate 106 which constitutes the conductive surface. The open slit or open slits 108 made in the plate 106 have been shown in a simplified manner. In addition, the plate 106 has a flexible contact 110 which penetrates into the housing 92 to ensure an electrical connection with the short-circuit contact 102. , and therefore a connection with the radiant element.

FIG. 4 also shows a portion of printed circuit 112 with conductive tracks 114 constituting, on the one hand, an electrical ground and, on the other hand, the antenna conductor. These conductive tracks 114 are connected to the electrical contact 100 and 102 of the connection element 94. It is understood that the assembly formed by the cover 80 with its connection element 94 can be fixed directly to the surface of the printed circuit 112 in order to make the electrical connections already mentioned and the mechanical fixing of this cover on the printed circuit. Of course, in this embodiment, the distance ei between the radiant element 86 and the conductive plate 106 is of the order of 2 mm.

In Figure 5, there is shown a second alternative embodiment of the antenna according to the invention. This is carried out in printed circuit 120. In this figure, the insulating substrate 122 of the printed circuit is shown, the thickness e _{2 of which} is of the order of 2 mm. On a first face 122a of the insulating substrate 122, a first metallization 124 is produced which defines the radiant element, the shape of which can be, for example, that shown in FIG. 2B or in FIG. 6. On the second face 122B of the substrate insulator 122, a second metallization 126 is produced which constitutes the conductive surface of the antenna. This conductive surface is of course provided with one or more open slots 128 facing the radiant element 124 and having a contour substantially identical to that of the radiant element or corresponding to the envelope thereof. The short circuit is produced by a first metallized hole 130 passing through the insulating substrate 122 and connected to the metallization 126. On the face 122B of the insulating substrate 122, another metallization 130 is also made, constituting the antenna conductor. The antenna conductor 130 is connected to the radiant element 124 by a second metallized hole 134. An antenna is thus obtained which has exactly the same characteristics as those which have been described previously, with the difference that the dielectric interposed between the radiant element 124 and the conductive surface 126 is no longer air but the material from which the insulating substrate 122 of the printed circuit is made.

Claims

1. A thin plate antenna, characterized in that it comprises: - a radiant element,

- an antenna supply connected to the radiant element,

- a conductive surface substantially parallel to said radiant element and disposed at a distance e from said element, said conductive surface being provided with at least one slot open substantially opposite said radiant element; and

- a conductive connection between said conductive surface and said radiant element.

2. Antenna according to claim 1, characterized in that said radiant element has a specific shape and in that said slot or said slots have a shape substantially identical to said specific shape of the radiant element.

3. Antenna according to claim 1, characterized in that the contour of said slot corresponds to the envelope of the radiant element.

4. An antenna according to any one of claims 1 to 3, characterized in that said conductive surface is constituted by a conductive plate.

5. An antenna according to claim 4, characterized in that it further comprises an insulating mechanical structure on which are fixed said radiant element, said conductive plate and said conductive connection.

6. Antenna according to claim 5, characterized in that said mechanical structure is made of a moldable material, in that it comprises an upper portion in which said radiant element is molded.

7. Antenna according to any one of claims 5 and 6, characterized in that it further comprises a connection component mounted on said mechanical structure to electrically connect said radiant element to the antenna supply and to form a short -circuit between said radiant element and a mass.

8. Antenna according to claim 7, characterized in that said mechanical structure comprises at least two side walls on which is fixed said conductive plate parallel to said radiant element.

9. An antenna according to any one of claims 1 to 4, characterized in that it comprises a printed circuit insulating substrate, a first metallization produced on a first face of said substrate to form said radiant element, a second metallization produced on the second face of said insulating substrate to form said conductive surface, and two electrical connections passing through said substrate to form said electrical connection and said antenna supply.

10. Antenna according to any one of claims 1 to 9, characterized in that the operating frequency of the antenna is less than 2 GH _Z.