EP1902491A1

EP1902491A1 - Antenna system with second-order diversity and card for wireless communication apparatus which is equipped with one such device

Info

Publication number: EP1902491A1
Application number: EP06794184A
Authority: EP
Inventors: Françoise Le Bolzer; Franck Thudor; Geert Matthys; François BARON
Original assignee: Thomson Licensing SAS
Current assignee: THOMSON LICENSING
Priority date: 2005-07-13
Filing date: 2006-07-13
Publication date: 2008-03-26
Also published as: CN101223672A; WO2007006982A1; KR20080025703A; FR2888675A1; JP2009501468A; US20090073047A1

Abstract

The invention relates to an antenna system with second-order diversity, comprising a metallisation plane (2) and first and second radiating elements (3 and 4) on a single substrate (1), each of said radiating elements comprising an inverted-F-type antenna printed on the side of the metallisation plane. Moreover, the first and second elements are positioned perpendicularly to one another close to the periphery of the substrate and are connected at the ends thereof such as to form a mass (32, 42).

Description

2-D DIVERSITY ANTENNA SYSTEM AND CARD FOR WIRELESS COMMUNICATION APPARATUS PROVIDED WITH SUCH A SYSTEM

The present invention relates to an antenna system with diversity of order 2. It also relates to a wireless communication device card comprising such an antenna system.

In the field of wireless communications, particularly within a room, there are phenomena of multi-projects. These phenomena can be very penalizing for the quality of the signal received. Indeed, phenomena of interference and fading of the signal are observed.

In order to overcome these fluctuation problems in the received signals, it is customary to use diversity techniques. One of the widely used solutions in WIFI-type wireless communication devices is to have two receiving antennas and to switch between one or the other of these antennas in order to choose the best one. To ensure good diversity, it is therefore necessary that the two antennas are completely decorrelated. As a result, the antennas must be sufficiently spaced apart from each other.

Thus, the most commonly used systems in WIFI devices consist of two external antennas dipole type. This solution has the advantage of easy integration since the antennas are then connected to the wireless card by coaxial flexible cables. However, the cost of this solution is relatively high. On the other hand, the antenna being an external element, it is fragile and can be easily destroyed or damaged.

To overcome these drawbacks, we sought to integrate the antenna to the wireless card. Different techniques have been proposed. Thus, in the patent application US 2003/0210191 published November 13, 2003, there is described an electronic card having at its periphery two antennas of PIFA type (Planar Inverted - F-Antenna or Planar Antenna of type F inverted). In this case, the two PIFA type antennas each consist of a radiating plate and two perpendicular tabs, one forming a ground plane and the other forming a feed line. This antenna therefore has a non-negligible thickness. On the other hand, to obtain a good decorrelation of the antennas, the two antennas are spaced apart from each other. As a result, the system described in this patent application remains cumbersome and requires the transfer of 3D metal components onto the card. On the other hand, in the patent application US 2003/022823 published December 4, 2003, describes a dual-band antenna system consists of inverted F-type antennas made in the RF shielding sheet of a portable display . As in the case above, the antennas are distant from each other to obtain good decorrelation of said antennas.

The present invention relates to a very compact second order diversity antenna system, easily integrable on an electronic card for wireless communication apparatus and having significant decorrelating properties.

The present invention thus relates to a system of antenna of diversity of order 2 comprising, on the same substrate, first and second radiating elements positioned on two adjacent sides of the substrate near the periphery of said substrate, characterized in that, the substrate comprising a metallization plane, the first and second radiating elements each consist of an inverted type F antenna printed on the metallization plane of the substrate, the first and second radiating elements being positioned on the substrate at the angle formed by the two adjacent sides and being connected to each other at their end connected to the metallization plane. The invention thus defined has the form of an arrowhead (or "Arrowhead" in English).

Despite the proximity of the two antennas, this solution, which makes it possible to obtain a very compact system, presents a good decorrelation of two antennas. The quality of the decorrelation obtained is far from being implicit to those skilled in the art who tends to move away the two radiating elements or to add mass artifices to ensure this decorrelation as described in the documents of the art. prior.

According to a first embodiment, the inverted type F antenna is etched in the metallization plane.

According to another embodiment and in the case of multilayer substrates, the inverted type F antenna is etched in at least two metallization planes of the substrate, each metal plane of the substrate thus etched and forming the body or strand of the antenna F-inverted being connected to each other via vias or metallized holes.

On the other hand, the inverted type F antenna is constituted by a conductive strand parallel to one side of the substrate, the conductive strand being extended by an end portion connected to the metallization plane of the substrate, the antenna being connected to a feed line adapted perpendicular to the conductive wire.

Preferably, the resonant frequency of the conductive strand is given by the relation:

D1 + H = °,

A.Fres. ^ Ε _eff where c represents the speed of light in a vacuum, ε and _f the effective permittivity of the propagation medium, F _res the resonance frequency, D1 the length of the conducting strand between its free end and the point of connection with the supply line and H the height between the conductive strand and the metallization plane of the substrate.

According to another characteristic of the present invention, to improve the decorrelation between the two radiating elements, a slot is made at their ends connected to the metallization plane. The length of this slot can be chosen so that its resonant frequency corresponds to that of the strands of the antenna. This makes it possible to obtain an enlargement of the operating band of the antenna. The present invention also relates to an electronic card for a wireless communication device provided with an antenna system with diversity of order 2 as described above.

Other characteristics and advantages of the present invention will appear on reading the description of several embodiments, this description being made with reference to the accompanying drawings in which:

Figure 1a is a partial perspective view of a first embodiment of a system according to the present invention and Figure 1b is a very schematic representation of the substrate used.

FIG. 2 represents the various adaptation and isolation curves of the system of FIG. 1.

FIGS. 3 and 4 respectively represent the radiation patterns obtained by exciting one or the other of the antennas of the system of FIG. 1.

Figure 5 is a partial perspective view of another embodiment of a system according to the present invention.

Figure 6 shows the adaptation and isolation curves of the system of Figure 5.

Fig. 7 is a partial perspective view of a third embodiment of the present invention.

FIG. 8 represents the adaptation and isolation curves of the embodiment of FIG. 7.

FIGS. 9 and 10 represent the radiation patterns obtained by exciting one or the other of the antennas of the system represented in FIG. 7.

Fig. 11 shows a partial perspective view of another embodiment of a system according to the present invention.

FIG. 12 represents the various adaptation and isolation curves of the system of FIG. 11. Figures 13 and 14 show the radiation patterns obtained by exciting one or the other of the antennas of the system of Figure 11.

FIG. 15 represents the adaptation and isolation curves of an antenna system according to the embodiment of FIG. 11 in which the width of the slot has been optimized.

Fig. 16 is a partial perspective view of yet another embodiment of an antenna system according to the present invention.

To simplify the description in the figures, the same elements bear the same references.

First, with reference to FIGS. 1, 2, 3 and 4, a first embodiment of a second order diversity antenna system according to the present invention will be described.

As shown in FIG. 1a, on a substrate 1 provided at least on its upper face with a conductive layer forming a metallization plane or ground plane 2, two antennas 3 and 4 of the inverted F type were produced. These antennas 3 and 4 are made by etching the ground plane 2 along the periphery of the substrate 1 so that the antennas 3 and 4 are perpendicular to each other while being connected by their ends forming a mass. In this configuration, the antenna system is in the form of an arrowhead.

More specifically, and as clearly shown in FIG. 1a, the antenna 3 which has a total length L and is positioned along an edge of the substrate 1 comprises a conductive strand having a first portion 30 of length D1 and a second part 31 of length D2. The portion 31 is extended by a portion 32 forming mass which is connected to the ground plane 2. The two parts 30, 31 are fed by a supply line 33 perpendicular to the conductive strand at the junction point of the parts 30, 31. This power line 33 ends with a port 34 and is adapted to 50Ω. Of similarly, the inverted antenna 4 comprises a conductive strand having a first portion 40 extending through a second portion 41 which is extended by a mass portion 42. This portion 42 is connected to the ground portion 32 of the antenna 3 at an outer corner of the substrate. The parts 40, 41 are fed by a power supply line adapted to 50Ω connected to the port 44.

According to the present invention, the resonance frequency of antennas 3 or 4 is obtained by the following equation:

£> 1 + H = ^c - = _≈

4.Fres.Jε _eff in which:

D1 represents the length of the portions 30 or 40 of the conductive strand,

Η represents the height or dimension between the ground plane 2 and the conducting strand, c represents the speed of the light in the vacuum, ε _e ff represents the effective permittivity of the propagation medium and,

F _res represents the resonant frequency of the conductive strands.

In this case, the dimension D2 of the portion 31 or 41 is chosen to play on the input impedance of the resonant portion 30 or 40 of the conductive strand. Thus at constant frequency, that is to say for fixed Η and D1, an increase (respectively a reduction) of D2 will have the effect of reducing (respectively increasing) the input impedance of the resonant strand. The mass portions 32 and 42 are connected to the ground plane. These parts have a length D3 whose value constitutes a degree of freedom to integrate the antenna system to an electronic card. Indeed, this current-free portion can receive fixing studs or other elements, even metal, allowing the integration of the card and the mechanical strength of the assembly.

A 3D simulation was performed using a commercial electromagnetic simulator based on the finite element method known as HFSS Ansoft. This simulation was made using a multilayer FR4 substrate having a total thickness of 1.6 mm and a permittivity εr of 4.4. As represented in FIG. 1B, the stack of the substrate consists of a 4-layer FR4 substrate comprising 2 outer layers of a material known under the name Prepreg of 254 μm in thickness and an inner layer of FR4 of 889 μm. thick. The interface between the 3 substrate layers consists of 2 copper inner layers of 35μm thick. The 2 outer conductive layers or metallization plane are made with copper of 17.5 .mu.m.

The feed line is defined on the upper layers 1 for the signal and ground plane 2 for the mass. For the simulation, the Arrowhead is metallized over the entire thickness of the substrate, as well as for the ground plane.

The antenna system of the F-inverted type as represented in FIG. 1 has the following dimensions:

D1 = 14.4 mm

D2 = 12 mm

D3 = 18 mm

H = 6 mm

W = 2 mm

L = 45.5 mm.

A system of this type operates in the 2.4 GHz to 2.5 GHz frequency band.

In the case of this embodiment, the two F-inverted antennas are identical. However, it is obvious that in the context of the present invention, the two antennas 3 and 4 may be of different length, so as to operate on different frequency bands.

The results of the simulation give the adaptation and insulation curves S11, S22 and S21 shown in FIG. S22 of Figure 2 show an adaptation greater than -15dB on the two ports 32 and 42 over the entire band concerned, namely 2.4 - 2.5 GHz. On the other hand, the insulation given by curve S21 is -14 dB.

As shown in FIGS. 3 and 4 which respectively show in FIG. 3, the radiation of the antenna 3 and in FIG. 4, the radiation of the antenna 4, the two radiation patterns show a good decorrelation with respect to FIG. axis of symmetry defined by the direction of the arrowhead (Arrowhead) in the diagrams, this direction corresponding to Phi = -45 °.

Thus, with a structure of very compact 2-order diversity antennas, the two antennas being very close to each other and made using a printed technology, we obtain in a non-implicit way for the man of the art a good decorrelation of the two antennas.

A variant embodiment of an antenna system in accordance with the present invention will now be described with reference to FIGS. 5 and 6.

In this case, two antennas of the F-inverted type 3 ', 4' are produced by etching the metallization of a substrate 1 provided with a ground plane 2. To further reduce the bulk, the antenna system represented by FIG. FIG. 5 shows, for each antenna 3 'and 4', a ground portion 32 ', 42' whose length D3 has been reduced. A structure of this type has been simulated, as mentioned above, taking for D3 a value of 10 mm.

The results of the simulation are given by the curves of FIG. 6. In this case, we obtain adaptation curves S11 and S22 showing an adaptation greater than -15 dB in the frequency band 2.4 GHz to 2.5 GHz and a curve of S21 insulation amounting to -12dB, the mass return points being closer because of a lower value D3.

Reference will now be made to FIGS. 7 to 10, another embodiment of an antenna system according to the present invention. invention. In this case, the antennas 3 and 4 of the F-inverted type are identical to the antennas of FIG. 1. However, as represented in FIG. 7, only a part of the ground plane 2 'deposited on the whole of the substrate 1 has been hollowed out. A system of this type has been simulated using a device as mentioned above.

The dimensions simulated in the embodiment of Figure 7 are as follows.

D1 = 12.4 mm

D2 = 12 mm

D3 = 18 mm

H = 6 mm

W = 2 mm

L ≈ 43.5 mm.

The distance e between the ends of the strands and the ground plane 2 'is 7 mm.

As shown on the adaptation curves S11, S22 and isolation S21 of FIG. 8, it is noted that the adaptation remains very good for the frequency band around 2.5 GHz whereas the insulation represented by the curve S21 is -12dB.

Similarly to the embodiment shown in FIG. 1, the diversity of the diagrams is maintained, as can be seen in the diagrams of FIGS. 9 and 10 respectively representing the radiation of antenna 3, FIG. 9 and the radiation of FIG. antenna 4, FIG.

A variant embodiment of an antenna system in accordance with the present invention will now be described with reference to FIGS. 11 to 15. In this case, on a substrate 1 provided with a ground plane 2, the two F-inverted antennas were made as in the embodiment of FIG. 1.

However, to improve the decorrelation between the F-inverted type antennas 3 and 4, an etching of the ground plane at mass forming parts 32 and 42. This etching forms a slot 6, as shown in FIG. 11. This etching makes it possible to increase the insulation between the two F-inverted type antennas 3 and 4.

A structure as shown in FIG. 11 was simulated using the apparatus mentioned above. In this case, the following dimensions were used for the simulation, namely:

D1 = 15.4 mm

D2 = 12 mm

D3 = 18 mm

H = 6 mm

W = 2 mm

L = 46 mm.

The slot 6 has a width of 2 mm and a length of 23 mm. The slot made in the ground plane is a rectangular slot placed in the axis of symmetry of the structure, as shown in Figure 11, so as to maintain the symmetry of the diagrams.

In FIG. 12 giving the adaptation curves S11, S22 and the isolation curve S21 of the system of FIG. 11, there is an improvement in the insulation between the two ports, this insulation having values up to -22 dB. There is also an adaptation over the entire frequency band around 2.5 GHz.

The presence of the slot 6 thus makes it possible to reinforce the decorrelation between the radiation of the antennas 3 and 4, as can be seen in FIGS. 13 and 14 respectively representing the radiation pattern of the antenna 3 and the radiation pattern of the antenna. antenna 4.

It is possible to size the slot 6 so that its resonance frequency is close to that of the antennas 3 and 4. This gives an enlargement of the operating band of the antenna, as shown in Figure 15.. With respect to the structure without slot, we thus observe the appearance of a second adaptation peak (S11 <-10dB) around 2.1GHz corresponding to the resonance of the slot and which contributes to the adaptation of the complete structure over the entire band from 2GHz to 2.5GHz is a bandwidth of 22% against 16% for the structure without slot.

In Figure 16, there is shown yet another embodiment of an antenna system according to the present invention. In this case, on a substrate 1 comprising at least one upper conductive layer and one lower conductive layer, two antennas of the F-inverted type have been etched by etching a strand 3A on one face and a strand 3B on the other side of the substrate. , likewise for the antenna 4. These strands 3A, 3B or 4A, 4B are connected by vias or metallized holes 3C as shown in FIG. 16. The advantage of this embodiment is the widening of the frequency band of 'a strand. Figure 16 shows an F-inverted type antenna etched on 2 metal layers. However, the invention also applies to antennas etched on several layers connected by metallized holes.

It is obvious to those skilled in the art that the embodiments described above can be modified in many ways. With the invention, an antenna solution is obtained integrating a second order of radiation diversity compatible with the most stringent cost constraints and very easily integrable on a motherboard for a wireless communication device such as a device. type WIFI. The integration of the antenna system described above is possible on any wireless transmission device. The antenna accesses are adapted to 50 ohms and are therefore directly integrable with a SPDT type switch ("Single Port Double Through" in English) or DPDT ("Double Port Double Through" in English) and the overall size of the system is as its use on already existing maps can be considered very easily.

Claims

A first order diversity antenna system comprising, on the same substrate (1), first and second radiating elements (3,4) positioned on two adjacent sides of the substrate, near the periphery of said substrate, characterized in that that, the substrate (1) having a metallization plane (2), the first and second radiating elements each consist of an F-inverted antenna printed on the metallization plane side of the substrate, the first and second elements being positioned on the substrate at the angle formed by the two adjacent sides and being connected to each other at their end connected to the metallization plane.

2 - System according to claim 1, characterized in that each antenna type F-inverted is etched in the metallization plane.

3 - System according to claim 1, characterized in that each F-inverted type antenna is etched in at least two metallization planes of the substrate, the strands thus etched being connected via vias or metallized holes.

4 - System according to one of claims 1 to 3, characterized in that the antenna type F-inverted (3,4) has a parallel conducting strand (30,31; 40,41) to one side of the substrate, the conductive strand being extended by an end portion (32, 42) connected to the metallization plane of the substrate, the antenna being connected to a feed line (33, 43) adapted perpendicular to the conducting strand.

5 - System according to claim 4, characterized in that the antenna has a resonance frequency obtained using the relation: £> i + H =

4.Fresψ _eff where c is the speed of light in vacuum, ε _eff the effective permittivity of the propagation medium, F _re s resonant frequency, the length D1 of the stranded conductor between its free end and the connection point with the supply line and Η the height between the conductive strand and the metallization plane of the substrate.

6 - System according to one of claims 1 to 5, characterized in that the length of the conductive strands of two radiating elements is identical.

7 - System according to one of claims 1 to 5, characterized in that the length of the conductive strands of the two radiating elements is different.

8 - System according to one of claims 1 to 7, characterized in that a slot (6) is formed between the two radiating elements (3,4) at their ends connected to the metallization plane.

9 - System according to claim 8, characterized in that the length of the slot is chosen so that its resonant frequency corresponds to that of at least one antenna (3 or 4).

10 - Electronic card for wireless communication device, characterized in that it is provided with a second order diversity antenna system according to one of claims 1 to 9.