TECHNICAL FIELD

The present invention relates to an antenna arrangement for a portable radio communication device. The present invention relates more specifically to an antenna arrangement for a portable radio communication device with low external coupling.

BACKGROUND OF THE INVENTION

A portable radio communication device, such as a mobile phone, PDA, portable computer or similar device, generally couples to external tissues or external devices due to use of radio frequency communication. Lately, demands in e.g. US, requires a limited coupling to e.g. hearing aids, which is formulated in the Hearing Aid Compatibility (HAC) requirement given by the FCC in the US . The HAC requirement is today defined as an E-field and H-field limitation around and above the speaker of a mobile phone, which requirement is illustrated in Fig. 1. A 3x3 grid 1 is positioned centred 15 mm over a speaker 2 of a mobile phone 3, wherein each grid is 50x50 mm. The E-field and H-field limitation needs to be fulfilled for each grid apart from the three worst connected grids, since listening adjustment of the mobile phone position relative a hearing aid should provide low enough coupling thereto. The amount of allowed coupling is defined in a number of categories (M1-M4 and T1-T4), and FCC regulations now state that at least an M3 rating for 50 percent of handset models that is offered to consumers on the US market, must be fulfilled.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an antenna arrangement for a portable radio communication device with low external coupling, particularly regarding coupling to a hearing aid.

One major source of hearing aid interference is power emitted by the antenna element of a mobile phone. As the antenna element advantageously is located in one end of the mobile phone and the speaker in the other, the interference is mainly coupled from the antenna element to the hearing aid through the chassis of the mobile phone. This is particularly true for slider type phones, where the antenna and speaker are on separate PCBs (where the slider and/or a flex-film provide the PCB-to-PCB connection). Therefore, the problem of achieving a high HAC rating is generally translated into the problem of reducing the coupling between an antenna element and as chassis of a portable radio communication device at a frequency band of interest.

This object, among others, is according to one aspect of the present invention, attained by an antenna arrangement and a portable radio communication device, respectively, as defined by the appended claims.

By providing an antenna arrangement for a portable radio communication device, comprising a radiating element, a ground plane means and a decoupling means, wherein the radiating element is provided at a first end of the ground plane means, the radiating element is configured to provide radio frequency operation for at least a first radio frequency band, and the decoupling means is provided on the ground plane means to decouple a second end of the ground plane means, opposite the first end, from the first radio frequency band, currents on the ground plane means, close to the position of a speaker of the portable radio communication device, can be reduced enough to meet e.g. the HAC requirements of the FCC regulations in US.

The present invention is particularly advantageous for radiating elements which generate currents on a ground plane means, such as monopoles, IFAs and parasites.

The decoupling means preferably comprises a first conductor electrically connected to a decoupling position on the ground plane means and extend in a general direction towards the first end of the ground plane means, which provides for short circuiting for a specific frequency.

Advantageously the first conductor is a quarter of the wavelength of the first radio frequency band, which preferably is GSM1900 Tx, which has the toughest HAC requirements .

Preferably, the decoupling means also comprises a second conductor electrically connected to the decoupling position and extend in a general direction towards the first end of the ground plane means, wherein the first and second conductors are located on opposite sides of ground plane means, which efficiently decouples the second end of the ground plane means from a desired frequency of the radiating element.

A simple configuration is of the conductors are obtained by means of a conductive wiring, or alternatively of a flex film comprising conductive portions. A preferred configuration of the conductors are provided by an L-shaped cut-out in the ground plane means, which would not require additional space of the portable radio communication device.

By providing a decoupling position 75 mm from the center of the speaker, i.e. the outer rim of the HAC grid, the E- and H-field requirements are easily achievable for all but the three connected lowest grids, in line with the HAC requirement.

By providing a portable radio communication device comprising a radiating element, a ground plane means and a decoupling means, wherein said radiating element is provided at a first end of said ground plane means, said decoupling means is provided on said ground plane means to decouple a second end of said ground plane means, opposite said first end, from said radiating element, preferably having a speaker provided at said second end, the decoupling means is possible to configure to pass M3 HAC requirements.

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

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description of embodiments given below and the accompanying figures, which are given by way of illustration only, and thus, are not limitative of the present invention, wherein:

Fig. 1 schematically illustrates how HAC requirements are defined.

Fig. 2a is a schematic top view of a first embodiment of the present invention. Fig. 2b is a schematic side view of the first embodiment of the present invention shown in Fig. 2a.

Fig. 3a is a schematic top view of a second embodiment of the present invention.

Fig. 3b is a schematic side view of the second embodiment of the present invention shown in Fig. 3a.

Fig. 4 is a schematic top view of the second embodiment of the present invention shown in Fig. 3a combined with HAC requirements .

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.

An antenna device for a portable radio communication device according to a first embodiment of the present invention will now be described with reference to Figs. 2a-2b.

A ground plane means 201 is provided in a portable radio communication device 202, such as a mobile phone, PDA, or similar device. The ground plane means 201 is most often provided as a part of a printed wiring board (not shown), but may also be provided by other means . As can be seen in figures 2a and 2b the ground plane means 201 has a substantially plane, rectangular shape with a radiating element 203 provided at a first end 201b of the ground plane means 201. The radiating element 203 is configured to provide the portable radio communication device with an operating frequency band, such as at least GSM1900, and typically also GSM850, GSM900 and GSM1800. The radiating element may be provided completely over, partially over or at the side of the ground plane means 201. Furthermore, the radiating element may be a PIFA, IFA, L- antenna, half-loop, monopole, non-resonant or any other antenna means which induces radiating currents in the ground plane.

At a second end 201a opposite to the first end 201b a speaker 205 is provided.

A decoupling means 204 is provided on the ground plane means 201. The decoupling means 204 comprises a first and second conductive wire 204a and 204b provided on opposite sides of the ground plane means 201. The conductive wires 204a and 204b extends a short bit out from, or orthogonally to the ground plane means 201, is bent 90 degrees and extends further, at the side of the ground plane means 201, in the direction towards the first end 201b. The length of the conductive wires 204a and 204b are approximately a quarter of the wavelength for GSM1900 Tx (1850 MHz). If the space between the conductive wires and the ground plane is filled with a dielectric the length may be shortened. This may affect the electrical impedance, but then again this may be corrected by adjusting the spacing between the conductive wires and the ground plane.

The conductive wires 204a and 204b may conveniently be provided in the housing of the mobile device or at any other convenient place. The space between the conductive wires 204a and 204b and the ground plane means 201 may be filled with a suitable dielectric material for further tuning of the bandwidth. The conductive wires 204a and 204b could alternatively be exchanged with a flex film comprising conductive portions.

Although the decoupling means has been described having two conductive wires on opposite sides of the ground plane means it is possible to only provide one conductive wire on one side of the ground plane means, but the decoupling effect will be significantly reduced.

A second embodiment of the present invention will now be described with reference to Figs. 3-4.

Figure 3a is a schematic top view of a variant of the present invention showing a ground plane means 301. Figure

3b is a schematic side view of the arrangement according to figure 3a. A radiating element 303 is provided at a first end 301b of the ground plane means 301. The radiating element 303 is configured to provide the portable radio communication device with an operating frequency band, such as at least GSM1900, and typically also GSM850, GSM900 and

GSM1800. The radiating element may be provided completely over, partially over or at the side of the ground plane means 301. Furthermore, the radiating element may be a PIFA, IFA, L-antenna, half-loop, monopole, non-resonant or any other antenna means which induces radiating currents in the ground plane.

At a second end 301a opposite to the first end 301b a speaker 305 is provided.

A decoupling means 304 is provided on the ground plane means 301. The decoupling means 304 comprises first and second conducting means 304a and 304b provided on opposite sides of the ground plane means 301. The conducting means 304a and 304b, respectively, are provided by a cut-out in the ground plane means 301. The cut-out is L shaped as is seen in figure 3a. The length of the conductive means 304a and 304b are approximately a quarter of the wavelength for GSM1900 Tx (1850 MHz). If the space between the conductive wires and the ground plane is filled with a dielectric the length may be shortened. This may affect the electrical impedance, but then again this may be corrected by adjusting the spacing between the conductive wires and the ground plane.

The positioning of the decoupling means 304, i.e. the decoupling position 306, at the side of the ground plane means 301, is preferably at the rim of the HAC grid. The part of the ground plane means beyond the decoupling position, relative the radiating element 303 at the first end of the ground plane means, is decoupled for GSM1900 Tx frequencies. Depending on the specific design of the radiating structure, the design of the ground plane means, circuitry located in the PCB, the design of the handset etc, the decoupling could be positioned closer to the speaker and still fulfill M3 HAC requirements.

The discussion of the decoupling position in connection with the second embodiment of the present invention is valid also for the first embodiment of the present invention described above .

It should be mentioned that currents will still flow in the ground plane means in the decoupled portion. There will be a current minimum at the open ends of the conductive means and a current maximum at the connection between the conductive means and the ground plane means. The currents in the ground plane in the decoupled portion will however not be significant for e.g. HAC requirements.

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 as 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.