WO2007084051A1

WO2007084051A1 - An antenna arrangement for a plurality of frequency bands

Info

Publication number: WO2007084051A1
Application number: PCT/SE2007/000021
Authority: WO
Inventors: Axel Von Arbin; Alexander Azhari
Original assignee: Laird Technologies Ab
Priority date: 2006-01-23
Filing date: 2007-01-12
Publication date: 2007-07-26

Abstract

The present invention relates to an antenna arrangement comprising a radiating element (2) provided to resonate in a plurality of frequency bands, comprising a low frequency band and a high frequency band separate from said low frequency band, and a printed wiring board (1; 1') provided as a ground plane for the radiating element (2), wherein the radiating element (2) is arranged at a first end of said printed wiring board (1; 1'). The antenna arrangement further comprises a parasitic element (4; 4') connected to a second end of the printed wiring board (1; 1') at a connection point (5) opposite the first end, and the parasitic element (4; 4') extends towards the first end of the printing wiring board (1; 1'), wherein the parasitic element (4; 4') is provided to resonate at another low frequency band near the low frequency band of the plurality of frequency bands.

Description

AN ANTENNA ARRANGEMENT FOR A PLURALITY OF FREQUENCY BANDS

FIELD OF THE INVENTION

The present invention generally relates to antenna arrangements . In particular the present invention relates to an antenna arrangement for a plurality of frequency bands .

BACKGROUND OF THE INVENTION

There is today a demand for mobile phones, and similar portable radio communication devices, that communicate over a plurality of frequency bands, such as GSM850, GSM900, GSM1800, GSM1900 and WCDMA2100. It is also desirable with thin and small sized mobile phones, which puts design restrictions on mobile phone antennas, particularly internal antennas . One known way to provide antenna arrangements having broad frequency bands, possibly covering several operating frequencies, is to increase the distance between a radiating element and its corresponding ground plane. This is however not in line with the desire to provide thin mobile phones .

SUMMARY OF THE INVENTION

An object of the present invention is to provide an antenna arrangement that can resonate in a plurality of frequency bands, wherein the antenna arrangement has a limited size.

Another object of the present invention is to provide a portable radio communication device that can communicate over a plurality of frequency bands, wherein the portable radio communication device has a limited size.

These objects, among others, are according to the present invention attained by an antenna arrangement and a portable radio communication device, respectively, as defined in the appended claims.

By providing an antenna arrangement, comprising a radiating element at a first end of a printed wiring board, provided to resonate at a plurality of frequency bands including a low frequency band and a high frequency band separate from the low frequency band, and a parasitic element connected to an opposite second end of the printed wiring board, wherein the parasitic element extends towards the first end of the printing wiring board, the parasitic element can be provided to resonate at another low frequency band near the low frequency band of the plurality of separate frequency bands. In this way the antenna arrangement can be made to resonate at another low frequency band without increasing the thickness of a portable radio communication device into which the antenna arrangement is to be arranged in.

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 drawings, which are given by way of illustration only, and thus, are not limitative to the present invention, wherein:

Fig. 1 shows a plan view of an antenna arrangement according to a first embodiment of the present invention;

Fig. 2 shows side view of the antenna arrangement shown in Fig. 1; Pig. 3 shows an exploded view of a parasitic element, a printed wiring board, and a back cover of a portable radio communication device according to the antenna arrangement of the first embodiment of the present invention;

Fig. 4 shows mounting of the parasitic element mounted to the back cover of Fig. 3;

Fig. 5 shows a plan view of an antenna arrangement according to a second embodiment of the present invention;

Fig. 6 shows side view of the antenna arrangement shown in Fig. 5;

Fig. 7 shows a side elevation view of a variation of the second embodiment of the present invention shown in Figs. 5 and 6;

Fig. 8 shows a diagram of antenna efficiency for an antenna arrangement comprising a parasitic element according to the present invention and an antenna arrangement without a parasitic element according to the present invention;

Fig. 9 shows a plan view of an antenna arrangement according to a third embodiment of the present invention; and

Fig. 10 shows a plan view of an antenna arrangement according to a fourth 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 arrangement, for a portable radio communication device, according to a first embodiment of the present invention comprises a radiating element 2, a printed wiring board (PWB) 1 provided as a ground plane for the radiating element 2, and a parasitic element 4. The radiating element 2 is positioned at a first end of the PWB 1 and the parasitic element 4 is connected to the PWB 1 at a second end of the PWB 1, opposite the first end. The radiating element 2 is connected to the PWB 1 through feeding 3. The feeding 3 to the radiating element 2 can include, apart from a connection to RF circuitry of the portable radio communication device, also grounding to the PWB 1. The parasitic element 4 is connected to the PWB 1 thorough grounding 5.

The radiating element 2 is provided to resonate at a plurality of frequency bands, namely a low frequency band covering GSM850, and a high frequency band covering GSM1800, GSM1900 and WCDMA2100. The radiating element 2 is preferably a PIFA, but could be any kind of antenna utilizing a PWB 1 as a ground plane.

The parasitic element 4 extends from the second end of the

PWB 1 towards the first end thereof, and is provided to resonate at another low frequency band of the antenna arrangement near GSM850, namely GSM900. The parasitic element 4 is preferably straight and has an electrical length corresponding to the following formula:

^L~ 360

wherein L is the electrical length of the parasitic element in m, λ₈₅₀ is the wavelength for GSM850 in m, φ₉₀₀ is the phase of the current for GSM900 in degrees at the connection point 5 to the PWB 1 for the parasitic element 4, and φ₈₅₀ is the phase of the current for GSM850 in degrees at the connection point 5 to the PWB 1 for the parasitic element 4.

If a parasitic element instead is connected to a PWB near a connection for a radiating element to the PWB, another low frequency band near a low frequency band of the radiating element can be provided by a parasitic element having an electrical length of λ_goo/4 independent of the phases of the currents on the PWB.

The parasitic element 4 is as mentioned preferably a straight element, but could alternatively be e.g. meandering.

The distance d2 between the parasitic element 4 and the PWB 1 is preferably equal to the distance dl between the radiating element 2 and the PWB 1. The distance d2 can be longer or shorter than dl, but if d2 is longer than dl the portable radio communication device will be thicker than necessary and if d2 is shorter than dl the antenna arrangement will not utilize the possible full bandwidth provided by the parasitic element 4.

The parasitic element 4 is in Figs. 1 and 2 schematically shown as an element that support itself, but the parasitic element 4 is preferably a flex film attached to a dielectric carrier 6, which is illustrated in Figs. 3 and 4, but could alternatively be attached directly to the PWB 1. The parasitic element 4 and its dielectric carrier 6 are preferably attached to a back cover 7 of a portable radio communication device, in which the antenna arrangement is to be mounted, to be connected to the PWB 1 when the portable radio communication device is assembled. The portable radio communication device can e.g. be a mobile phone, a portable computer, or similar.

A second embodiment of the present invention will now be described with reference to Figs. 5-7. This second embodiment of the present invention is identical to the first embodiment described above, apart from the following.

The PWB 1' comprises a slot 8, preferably L-shaped to form the parasitic element 4 ' to extend from the second end to the first end of the PWB 1'. In Figs. 5 and 6 the slot is shown as a slot through both the conductive part as well as the dielectric part of the PWB 1 ' . It is however only necessary for the slot 8 to be a slot through the conductive part of the PWB 1' and not through the dielectric part of the PWB 1', which is shown in Fig. 7. Further, the slot 8 can also be a slot through the conductive part of the PWB 1', and through only a part of the dielectric part of the PWB 1' (not illustrated).

The total antenna efficiency for the antenna arrangement described in connection with Figs. 5 and 6 is shown in Fig. 8 together with the total antenna efficiency for an antenna arrangement without the slot 8, i.e. the total antenna efficiency for an antenna arrangement with and without a parasitic element according to the present invention. A third embodiment of an antenna arrangement according to the invention will now be described with reference to Fig. 9, illustrating a plan view thereof. In this embodiment, which in most aspects is identical to the embodiment described above with reference to Figs. 1-4, a matching element in the form of a stub termination 4a has been added to the parasitic element 4. This stub matching is in the form of two extensions directed perpendicularly to the general extension of the parasitic element.

With this stub impedance matching, there is a complex interaction of wave reflections and refractions occurring between the antenna line and the stub line, which are not separate from one another. It has been found that the wave reflections created at the stub termination do not cancel the wave reflections created at the end of the parasitic element. Rather, the multiple reflections from the parasitic element and the stub termination 4a combine to cancel the initial reflected wave created at the connection point, resulting in improved overall impedance matching. Thus, stub matching enables the desired performance with shorter extension and improves the matching of the antenna comprising the main antenna 2.

In a fourth embodiment of an antenna arrangement according to the invention illustrated in Fig. 4 a further PWB 9 has been added to the third embodiment described above with reference to Fig. 3. This configuration with two PWBs can appear in so-called fold phones, for example, i.e., in radio communication devices comprising two parts which are interconnected via a hinge or fold line. In this embodiment, the stub matching can be particularly advantageous since the added PWB can create mismatching of the antenna arrangement. 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. One such variation is that specific frequency bands have been mentioned, but the only important feature is that the parasitic element is provided to resonate at a low frequency band of the antenna arrangement.

The impedance matching element 4a has been described in an antenna arrangement similar to that of Fig. 1. It will be appreciated that it can be comprised also in the parasitic element 4' illustrated in Fig. 2.

It is also appreciated that the additional PWB illustrated in Fig. 10 also can be provided in the embodiments illustrated in Figs. 1-8.

Claims

1. An antenna arrangement comprising a radiating element (2) provided to resonate in a plurality of frequency bands, comprising a low frequency band and a high frequency band separate from said low frequency band, and a printed wiring board (1; 1') provided as a ground plane for said radiating element (2), wherein said radiating element (2) is arranged at a first end of said printed wiring board ( 1 ; 1 ' ) , characterized in that said antenna arrangement comprises a parasitic element (4; 4') connected to a second end of said printed wiring board (1; 1') at a connection point (5) opposite said first end, and said parasitic element (4; 4') extends towards said first end of said printing wiring board (1; 1'), wherein said parasitic element (4; 4') is provided to resonate at another low frequency band near said low frequency band of said plurality of frequency bands.

2. The antenna arrangement as claimed in claim 1, wherein said extension of said parasitic element (4; 4') has an electrical length according to the following formula:

360

wherein L is the electrical length of the parasitic element (4; 4'), λ₈₅₀ is the wavelength for said low frequency band of said plurality of frequency bands, φ₉₀₀ is the phase of the current for said another low frequency band at the connection point (5) to the printed wiring board (1; 1') for the parasitic element (4; 4'), and the phase (φ₈₅₀) of the current for said low frequency band of said plurality of frequency bands at the connection point (5) to the printed wiring board (1; 1') for the parasitic element (4; 4').

3. The antenna arrangement as claimed in claim 1 or 2, wherein a slot (8) is provided in said printed wiring board (1') to form said parasitic element (4') out of said printed wiring board ( 1 ' ) .

4. The antenna arrangement as claimed in claim 3, wherein said slot (8) is L-shaped.

5. The antenna arrangement as claimed in any of claims 1-4, wherein a distance (d2) between the parasitic element (4; 4') and the printed wiring board (1; 1') is equal to or less than a distance (dl) between the radiating element (2) and the printed wiring board (1; 1').

6. The antenna arrangement as claimed in claim 5, wherein said distance (d2) between the parasitic element (4; 4') and the printed wiring board (1; 1') is equal said distance (dl) between the radiating element (2) and the printed wiring board ( 1 ; 1 ' ) .

7. The antenna arrangement as claimed in any of claims 1-6, wherein said low frequency band is GSM850 and said another low frequency band is GSM900.

8. The antenna arrangement as claimed in any of claims 1-7, wherein said high frequency band includes one or more of the following: GSM1800, GSM1900 and WCDMA2100.

9 The antenna arrangement according to any of claims 1-8, wherein the parasitic element (4) comprises an impedance matching element (4a).

10. The antenna arrangement according to claim 9, wherein the impedance matching element (4a) is a stub matching element .

11. The antenna element according to any of claims 1-10, comprising an additional printed wiring board (9) provided adjacent to the second end of the printed wiring board (1).

12. A portable radio communication device, characterized in that it comprises an antenna arrangement as claimed in any previous claim.

13. The portable radio communication device as claimed in claim 12, comprising a back cover (7), wherein said parasitic element (4) is mounted to said back cover (7).