WO2006088422A1

WO2006088422A1 - Antenna device for a portable radio communication device

Info

Publication number: WO2006088422A1
Application number: PCT/SE2006/000216
Authority: WO
Inventors: Axel Von Arbin; Dan Bremberg
Original assignee: Amc Centurion Ab
Priority date: 2005-02-17
Filing date: 2006-02-17
Publication date: 2006-08-24
Also published as: SE528105C2; SE0500373L

Abstract

The present invention relates to an antenna device, and a radio communication device, such as a mobile phone, comprising one antenna element arranged to operate in two frequency bands: RFID and FM radio.

Description

ANTENNA DEVICE FOR A PORTABLE RADIO COMMUNICATION DEVICE.

FIELD OP INVENTION

The present invention relates generally to an antenna device for a portable radio communication device. Particularly the present invention relates to an antenna device, for a portable radio communication device, comprising an antenna element arranged to operate in two frequency bands .

BACKGROUND

Portable radio communication devices, such as mobile phones, are presently utilized a lot. As users most of their time carry a portable radio communication device with them it is desirable to have as may functions as possible gathered in such a device. However, the size of a portable radio communication device, to be really portable, should be kept as small as possible. This is many times contrary to the desire of gathering as many functions as possible in such a device.

One desired function, and sometimes used function, in a mobile phone, or the like, is a radio receiver. A radio receiver for the FM band is generally arranged to cover carrier frequencies between 76 and 108 MHz.

A previously used function in a mobile phone, or the like, is a bar code reader. An improved function based on this concept is RFID. This is another desired function in a mobile phone, or the like. RFID is a contactless, short distance communication between a reader/writer part and a tag part, or between two reader/writer parts, preferably using a carrier frequency of 13.56 MHz. Other frequencies for RFID are mainly: Low Frequency (125-134 kHz) and Ultra- High Frequency, UHF, (860-960 MHz). Each of the frequency bands for RFID has its advantages and disadvantages .for operation. The lower frequencies usually have less range and slower data transfer rate than the higher frequencies, which have more regulatory controls and differ from country to country. The lower frequency bands, 125-134 kHz and 13.56 MHz, use inductive coupling and have a reading range of about 1 m. The upper frequency band, 860-960 MHz, uses propagation coupling, has a reading range up to 10 m and has more complex components than the lower frequency bands .

RFID can also use even higher frequency bands, 2.45 GHz and 5.8 GHz, characterized by long read range, high reading speed, line of sight requirement and high cost. Applications for such frequencies include rail trolley identification, road toll management, electronic road pricing systems (ERP) in Singapore and Hong Kong, vehicle tracking and logistics real-time location systems (RTLS).

An advantage with RFID is that a tag part can be provided without an internal energy source. Instead an RFID tag uses energy received by RF transmissions from a reader/writer to generate a response transmission.

Possible areas of use for RFID is to exchange information, bi-directionally, between units, e.g. for payment (removes the need for a code), entry card, and stock keeping. RFID may be used as an automatic way to collect information or data on products, places, times, transactions and sensor readings. RFID may be used as identification performed in milliseconds: no line of sight required; contactless work in a harsh environment; and multiple tags read simultaneously. RFID may use ID tags that can: store unique ID information; read and write data to the tag; and serve as a portable data carrier. SUMMARY OF THE INVENTION

Thus, two functions that are desired in a portable radio communication device, such as a mobile phone, a cordless phone, a PDA, an MP3-player, a wristwatch, a laptop computer, or other electronic devices, are the possibility to listen to a radio broadcast and the possibility to exchange information with other devices without having to manually register such information.

An object of the present invention is to provide the functions of FM radio and RFID in a portable radio communication device occupying as little space as possible in the device .

This object is attained by an antenna device and a portable radio communication device, respectively, according to the appended claims.

By providing an FM radio antenna and an RFID antenna in one antenna element space may be saved in a portable radio communication device, such as a mobile phone.

Further features and advantages of the present invention will be evident from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described below in the detailed description of embodiments given in connection with the accompanying figures, which are given by way of illustration only and are thus not limitative of the present invention, wherein:

Fig. 1 schematically illustrates a loop antenna according to a first embodiment of the present invention; Pig. 2 schematically illustrates an alternative design of the loop antenna shown in Fig. 1;

Fig. 3 schematically illustrates a matching network for the antenna device according to the first embodiment of the present invention;

Fig. 4 schematically illustrates an alternative design of the matching network shown in Fig. 3;

Fig. 5 schematically illustrates a loop antenna according to a second embodiment of the present invention; and

Fig. 6 schematically illustrates a matching network for an antenna device according to a third embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description, for purpose of explanation and not limitation, specific details are set forth, such as particular techniques and applications in order to provide a thorough understanding of the present invention. However, it will be apparent for a person skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed description of well-known methods and apparatuses are omitted so as not to obscure the description of the present invention with unnecessary details.

A first embodiment of the present invention will now be described with reference to Figs. 1-4.

An antenna device for a portable radio communication device, such as a mobile phone or other electronic device, comprises one single antenna element to provide FM radio and RFID for the portable radio communication device. The antenna element is preferably a loop antenna element, as -illustrated in Fig. 1. The antenna device also includes a passive or an active matching network between the antenna element and the RFID and FM functions. The portable radio communication device may of course include other antenna elements to provide other functions, such as mobile telephony.

As RFID comprises a very short distance communication some arrangements may be utilized to improve the communication distance. To minimize transmission loss the antenna element is preferably fed unbalanced, at a feeding point 1 and a grounding point 2. FM and RFID circuits are connected 6 to the feeding point 1 , and a ground means 5 is connected to the grounding point 2. By feeding the antenna element unbalanced, a balun may be omitted. Further, a magnetic material covering one side of the antenna element is preferably provided in the antenna device, to reduce coupling to nearby metallic surfaces, such as a printed wiring board or a battery. The one side should be the side of the antenna element closest to a metallic surface. The magnetic material should have a high real part of permeability and low imaginary part of permeability, at the RFID frequency, preferably 13.56 MHz. An alternative to provide a magnetic material is to provide a plastic spacer, or air, between the antenna element and the metallic surfaces. These two alternatives may of course be combined.

To provide the needed frequency band for FM radio the matching net for the antenna element preferably includes a varactor 4 for tuning the antenna element within the FM frequency band. The varactor 4 may be connected to the feeding point 1, as illustrated in Fig. 3, or to the grounding point 2, as illustrated in Fig. 4, of the antenna element . Further, the loop antenna may comprise more than one turn, as is illustrated by two turns in Fig. 2. More turns provide an increased communication range for RFID, but at the same time more turns consume more power. Tests have shown that six turns for the loop antenna is preferred, as this gives an optimum between increased communication range and power consumption. When several turns are provided the feeding point 1 is inside the turns and the grounding point 2 is outside the turns. This could be vice versa. Although the turns of the loop antenna have been illustrated as square- shaped they may alternatively have other shapes such as polygon, ellipsoid and stacked.

To separate transmissions to or from FM radio and RFID, respectively, a switch may be provided. Alternatively a duplex filter may be used to separate the different transmissions to or from the portable radio communication device. The switch may be user controlled by e.g. a button, or a processor of the portable radio communication device may automatically control the switch.

A second embodiment of the present invention will be described with reference to Fig. 5. This second embodiment is identical to the first embodiment described above, apart from the following.

The antenna element comprises at least two turns. The configuration of the turns is divided into a first portion 7 and a second portion 8. The first portion comprises essentially square-shaped turns of the loop antenna. The second portion 8 comprises a projection from the essentially square-shaped turns, such that a feeding point 1 inside the turns may be positioned outside of the first portion 7. .In this way the feeding point 1 is positioned inside the loop antenna, but outside of the main -radiation. The second portion 8 may further be bend to be positioned 90 degrees to the first portion 7. This facilitates contacting of the antenna element. When the feeding point 1 is positioned inside the turns, the grounding point 2 is positioned outside the turns. Preferably, also the grounding point 2 is positioned in the second portion 8.

A third embodiment of the present invention will next be described with reference to Fig. 6. This third embodiment is identical to the first embodiment described above, apart from the following.

A first 3 and a second 11 feeding point for connection to FM radio 10 and to RFID 9, respectively, are provided, wherein the feeding points 3, 11 are electrically distanced from each other in the antenna element. By providing the first feeding point 3 for FM electrically closer to the grounding point 2, compared to the electric distance between the second feeding point 11 for RFID and the grounding point 2, the matching network may be simplified.

This third embodiment may also be applied to the second embodiment described above. In this case a third portion may be provided to allow also the second feeding point 3 to be positioned outside of the first portion 7.

The antenna element as described above, according to any one of the embodiments, may be provided in several positions in the portable radio communication device. It may e.g. be positioned outside of the battery in a mobile phone, either above the cellular antenna, or away from the cellular antenna. If the antenna element is positioned close to the cellular antenna it may disturb the cellular communication, in which case magnetic material there between preferably is used to reduce such disturbances. Xf the portable radio communication device comprises several parts,- e.g. hinged to each other, the antenna element is preferably positioned in a portion where a cellular antenna is not positioned.

It will be obvious that the present invention may be varied in a plurality of ways . Such variations are not to be regarded as departure from the scope of the present invention as defined by the appended claims. All such variations that would be obvious for a person skilled in the art are intended to be included within the scope of the present invention as defined by the appended claims .

Claims

1. An antenna device -for a portable radio communication device, comprising one antenna element arranged to operate in a first and a second frequency band, characterized in that

- said first frequency band is for FM radio, and

- said second frequency band is for RFID.

2. The antenna device according to claim 1, comprising a matching network, including a varactor (4), connected to the antenna element, wherein the varactor (4) is utilized to tune the antenna device within said first frequency band.

3. The antenna device according to claim 1 or 2, wherein said antenna element is a loop antenna.

4. The antenna device according to claim 3, wherein said loop antenna comprises at least two turns .

5. The antenna device according to claim 3 or 4, wherein said loop antenna comprises a grounding point (2), a first feeding point (3) for FM radio and a second feeding point (11) for RFID.

6. The antenna device according to claim 5, wherein the electric path between said first feeding point (3) and said grounding point (2) is shorter than the electric path between said second feeding point (11) and said grounding point ( 3 ) .

7. The antenna device according to claim 3 or 4, wherein said loop antenna comprises a feeding point (1) for FM radio and RFID and a grounding point ( 2 ) .

8. The antenna device according -to claim ^'7, wherein said loop antenna comprises a first portion ( 7 ) having a square- shaped form, and a second portion ( 8 ) protruding out from said square-shaped form, wherein said feeding point (1) is located inside said loop antenna in said second portion (8) and said grounding portion (2) is located outside of said loop.

9. The antenna device according to any previous claim, comprising a magnetic material covering one side of said antenna element.

10. A portable radio communication device characterized in that it comprises an antenna device according to any previous claim.