WO2002063715A1

WO2002063715A1 - Patch antenna for bluetooth and wlan

Info

Publication number: WO2002063715A1
Application number: PCT/SE2001/000950
Authority: WO
Inventors: Shaofang Gong; Johan Nilsson
Original assignee: Bluetronics Ab
Priority date: 2001-02-05
Filing date: 2001-05-03
Publication date: 2002-08-15
Also published as: SE0100349L; SE0100349D0; SE518467C2

Abstract

A patch antenna for radio communication in accordance with the Blue Tooth concept and/or the WLAN concept, as well as 3G-GSM and other corresponding communications systems, wherein the antenna is integrated in a transmitter and receiver module, wherein the module has a carrier in the form of a laminated PCB-card (Printed Circuit Board) which includes a number of electrically conductive metal layers (2; 3; 4) and so-called microvias (17), wherein a first side (19) of the card is its antenna side and its other side (20) is its component side, and where vias extend in teh card between different metal layers. The invention is characterised in that the antenna is comprised of two or more metal layers (2; 3; 4); in that the antenna supply point (21) includes a part (22) of a metal layer; in that a gap (23) is present between said part (22) and the rest of the metal layer; in that said part (22) is connected to the component side (20) of said card through the medium of a via (18); and in that the capacitance between said part and said metal layers forming the antenna is so adapted to the inductance that occurs as a result of the via (18) connection to said part (22) that a generally pure resistive impedance is obtained in said supply point (21).

Description

PATCHANTENNAFORBLUETOOTHANDWLAN

The present invention relates to a so-called patch antenna for the so-called Blue Tooth concept and the so-called wireless-LAN concept (WLAN).

The main purpose of the Blue Tooth concept is to replace cables with radio signals where the required range is relatively short. The main purpose of WLAN is to obtain wireless access to the Internet.

Both technologies use the ISM (Industrial, Scientific and Medical) frequency bands. Blue Tooth will operate at 2.4 GHz, whereas WLAN will operate at both 2.4 and 5.7 GHz.

According to the marketing firm Cahners In-Stat Group, two billion modules will be required for these technologies by the year 2005.

WLAN has a much higher data transmission capacity than Blue Tooth.

These devices require antennas that radiate the available energy effectively in all directions, i.e. omnidirectionally, without interfering with the host device with which it communicates, and where it is possible to utilise the host device to improve the communications range. The nominal link distance in Blue Tooth is from 10 centimetres to 10 metres, but can be increased up to 100 metres by increasing transmission power. WLAN also requires a communications distance of 100 metres.

Since the transmission power in Blue Tooth is limited while it is necessary to maintain the communications distance, the design of the antenna is decisive. Every antenna that wastes available output power or that points in the wrong direction can completely destroy a Blue Tooth or WLAN coupling.

Thus, there are required antennas that are omnidirectional, that are small, and that can be integrated in modules in order to keep both size and costs low.

Swedish Patent Specification No. 0001943-0 describes module for this purpose. The aforesaid patent relates to a module for radio communication in accordance with the Blue Tooth concept and/or in accordance with the wireless-LAN concept that includes a transmitter and receiver circuit and an antenna. The module further includes a carrier in the form of a laminated PCB-card (Printed Circuit Board) which has a number of electrically conductive metal layers and so-called microvias, where an integrated antenna is formed in the metal layer on a first side of the card and connected to the remainder of the module. A radio frequency chip is surface-mounted on the other side of the card. The module also includes passive components, such as filters, Baluns, inductors and capacitors, integrated in the PCB-card and connected to various microvias.

The present invention relates to an antenna of particular design for achieving the aforesaid requirements.

The present invention thus relates to a patch antenna for radio communication in accordance with the Blue Tooth concept and/or the WLAN concept, as well as 3G-GSM and other corresponding communications system, said antenna being integrated in a

' transmitter-and-receiver module, wherein the module includes a carrier in the form of a

PCB-card (Printed Circuit Board) that has a plurality of electrically conductive metal layers and so-called microvias, where as first side of the card is its antenna side and its other side is its component side, and where vias extend in the card between different metal layers, and wherein the module is characterised in that the antenna is comprised of two or more metal layers; in that the antenna supply point includes a part of a metal layer; in that a gap is situated between said part and the remainder of the metal layer; in that said part is connected to the component side of the card through the medium of a via and in that the capacitance between said part and the antenna forming metal layers is so adapted to the inductance caused by the connection of the via to said part that an essentially pure resistive impedance is obtained in the supply point.

The invention will now be described in more detail partly with reference to an exemplifying embodiment of the invention illustrated in the accompanying drawings, in which

- Figures 1 and 2 illustrate a first embodiment of an inventive antenna from above and in cross-section respectively; - Figures 3 and 4 illustrate a second embodiment of an inventive antenna from above and in cross-section respectively;

- Figures 5 and 6 illustrate a third embodiment of an inventive antenna from above and in cross-section respectively; and - Figure 7 illustrates a fourth embodiment of an inventive antenna from above.

The drawings illustrate a patch antenna for radio communication in accordance with the Blue Tooth concept and/or the WLAN concept, as well as 3G-GSM and other corresponding communications systems. Examples of further systems are HiperLAN2 and HomeRF.

The antenna is integrated in a transmitter and receiver module, where the module has a carrier in the form of a laminated PCB-card 1 (Printed Circuit Board) which includes a number of electrically metal layers 2; 3; 4 and so-called vias. Reference 17 denotes a microvia and reference 18 denotes a through-passing via.

A first side 19 of the card 1 is its antenna side, while the other side 20 is its component side.

According to the invention, the antenna is comprised of two or more of said metal layers 2; 3; 4. The antenna supply point 21 includes a part 22 of a metal layer. A gap 23 is present between said part 22 and the remainder of said metal layer. This part of the metal layer is connected to the component side 20 of the card through the medium of a via 18.

The capacitance between said part 22 and those metal layers that form the antenna is so adapted to the inductance that arises as a result of the connection of the microvia 18 to said part 22 that an essentially pure resistive impedance is obtained in the measuring point 21. The resistive impedance will preferably be about 50 Ω.

In addition to obtaining an omnidirectional antenna in this way, there is also obtained an antenna of considerably improved bandwidth. An antenna which is supplied directly from a via, i.e. an antenna of the kind taught by the aforesaid Swedish patent specification, gives a bandwidth of about 4%. An antenna constructed in accordance with the present invention provides a bandwidth of about 6%, i.e. an enhancement of 50%. The λ sign in the figures identifies the wavelength at which the antenna operates.

According to one preferred embodiment, said part 22 is rectangular in shape, although it may have other shapes.

When said part has a rectangular shape, it is preferred that the metal layers from which the antenna is formed are also rectangular.

In the case of the embodiment illustrated in Figures 5 and 6, the PCB-card has four strata 4 of mutually parallel metal layers. The metal layer 14 is an earth plane. The antenna is formed on said antenna side by two metal layers 5, 6.

In the case of another embodiment, shown in Figures 1 and 2, the PCB-card has six strata of mutually parallel metal layers 2, where three of said layers, 7-9, form the antenna on said antenna side 19. Two metal layers may also form an antenna.

According to another embodiment, shown in Figures 3 and 4, the PCB-card has eight strata 3 of mutually parallel metal layers, of which four, 10-13, of said layers form an antenna on said antenna side 19. Alternatively, the antenna may comprise two or three metal layers.

It will be obvious that the number of metal layers in the PCB-card board can be varied, as can also the number of layers that co-act to form an antenna.

Figure 7 illustrates an example where more than one antenna is used. The configuration shown in Figure 7 can be used for WLAN modules, which require antenna diversity since the antennas have two orthogonal polarisations.

Naturally, two or more antennas can be configured in a number of ways.

The present invention shall not therefore be considered limited to the aforedescribed exemplifying embodiments thereof, since variations can be made within the scope of the accompanying Claims.

Claims

1. A patch antenna for radio communication in accordance with the Blue Tooth concept and/or the WLAN concept, as well as 3G-GSM and other corresponding communications systems, wherein the antenna is integrated in a transmitter and receiver module, wherein the module has a carrier in the form of a laminated PCB-card (Printed Circuit Board) which includes a number of electrically conductive metal layers (2; 3; 4) and so-called microvias (17), wherein a first side (19) of the card is its antenna side and its other side (20) is its component side, and where vias extend in the card between different metal layers, characterised in that the antenna is comprised of two or more metal layers (2; 3; 4); in that the antenna supply point (21) includes a part (22) of a metal layer; in that a gap (23) is present between said part (22) and the rest of the metal layer; in that said part (22) is connected to the component side (20) of said card through the medium of a via (18); and in that the capacitance between said part and said metal layers forming the antenna is so adapted to the inductance that occurs as a result of the via (18) connection to said part (22) that a generally pure resistive impedance is obtained in said supply point (21).

2. A patch antenna according to Claim 1, characterised in that said resistive impedance is about 50 Ω.

3. A patch antenna according to Claim 1 or Claim 2, characterised in that said part (22) is rectangular in shape.

4. A patch antenna according to Claim 3, characterised in that the metal layers forming said antenna are rectangular in shape.

5. A patch antenna according to any one of Claims 1, 2, 3 or 4, characterised in that the PCB-card has four strata (4) of mutually parallel metal layers; and in that the antenna is formed on said antenna side (19) by two (5, 6) of said metal layers.

6. A patch antenna according to any one of Claims 1, 2, 3 or 4, characterised in that the PCB-card has six strata of mutually parallel metal layers (4); and in that the antenna is formed on said antenna side (19) by two or three (7-9) of said metal layers.

7. A patch antenna according to any one of Claims 1, 2, 3 or 4, characterised in that the PCB-card has eight strata (3) of mutually parallel metal layers; and in that the antenna is formed on said antenna side (19) by two, three or four (10-13) of said metal layers.