WO2002101876A1

WO2002101876A1 - Antenna device and portable radio communication apparatus

Info

Publication number: WO2002101876A1
Application number: PCT/SE2002/001103
Authority: WO
Inventors: Tomas Rutfors; Laurent Noguer
Original assignee: Amc Centurion Ab
Priority date: 2001-06-08
Filing date: 2002-06-07
Publication date: 2002-12-19
Also published as: SE0102032D0; KR20020095046A

Abstract

An antenna device for use in a portable radio communication apparatus comprises a dielectric substrate (1); a dual-strip antenna pattern (3, 5) adapted to transmit radio waves at a given frequency, the dual-strip antenna pattern being arranged on the dielectric substrate; and a feed connector (7, 9) connected to the dual-strip antenna pattern and connectable to radio frequency circuitry of said portable radio communication apparatus for feeding said dual-strip antenna pattern with radio frequency signals at the given frequency. The two strips (3, 5) of said dual-strip antenna pattern are according to the invention substantially parallel and of different lengths (L1, L2). Further, the feed connector (7, 9) is adapted to feed the dual-strip antenna pattern and/or the radio frequency circuitry with two similar but phase-shifted radio frequency signals, e.g. a balanced feed.

Description

ANTENNA DEVICE AND PORTABLE RADIO COMMUNICATION

APPARATUS

FIELD OF INVENTION

The present invention relates generally to the field of radio communications and particularly to antenna devices for use in portable radio communication apparatus, and to such portable radio communication apparatus.

BACKGROUND OF THE INVENTION AND RELATED ART

A common general antenna type is the wire antenna. It may be provided as a single wire or more conveniently as a two-wire antenna. Two commonly used two-wire antennas are the linear dipole antenna and the flared transmission line, both of which make use of outwardly bent wires. The lengths of the bent portions of the wires may be different to match the antenna to a radio circuit.

Such antennas are, however, not adapted to be used in communication devices such as portable radio communication units, since they require a large volume or area. Further, the feeding of such antennas is performed in a central region of the antenna, which makes the design of the portable radio communication unit even more difficult.

A trend in communication devices of today is that the units are become more and more complex with a plurality of functions, and at the same time they become smaller. Thus, the antennas therein will also have to exhibit improved performance and be smaller. For instance, dual band, or even triple band operation is today common, and such operated units thus need an antenna structure adapted to each band. Further, it is more and more common to separate the transmit and receive branches in the communication units such that duplex filters and switches can be dispensed with.

In such circumstances, the above-described dipole and flare-type antennas are particularly impractical; they occupy large space and the feedings of a plurality of antennas within a communication unit will be difficult. Coupling between the antennas will result in deteriorated performance.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a wire- or strip-based antenna device for use in a portable radio communication device, which occupies a small volume or area.

In this respect there is a particular object of the invention to provide such an antenna device, which can house a plurality of different antenna elements or patterns having low coupling to each other, such that said antenna device can be provided with separate transmit and receive radiation structures and/or provided with dual-band functionality.

A further object of the present invention is to provide such an antenna device, which is easy to tune to a given resonance frequency and to a given input impedance almost independently of each other. Yet a further object of the present invention is to provide such an antenna device, which is easy and inexpensive to manufacture and assemble.

Still a further object of the present invention is to provide such an antenna device, which provides for a balanced feed, or at least a feed with two similar but phase-shifted radio frequency signals.

In this respect there is a particular object of the present invention to provide such an antenna device, which can be used in a portable radio communication apparatus without the need of a balun upstream of a low noise amplifier in the receiver branch of the apparatus for converting a received signal from unbalanced to balanced.

Yet a further object of the present invention is to provide a portable radio communication apparatus , such as e.g. a mobile telephone, comprising an antenna device, which attains the above-said objects.

These objects, among others, are according to the present invention attained by antenna devices and portable radio communication apparatus as defined in the appended patent claims.

By providing an electrically conductive dual-strip or two-wire antenna pattern adapted to transmit and/or receive radio waves at a given frequency, wherein the two strips or wires of the antenna pattern are substantially parallel and of different lengths, an antenna device is obtained, in which the resonance frequency and the input impedance can be tuned, i.e. adjusted, more or less independently of each other.

The resonance frequency is tuned by the length of the longer strip or wire, and the input impedance is tuned by the length of the shorter strip or wire, or more correctly by the ratio of the two strip or wire lengths (even though it is the shorter length, which is adjusted to achieve a desired input impedance for a given resonance frequency). Optionally, the input impedance may be tuned by the distance between the strips or wires.

Preferably, a feed connector of the antenna device is adapted to feed the antenna pattern and/or receiving radio frequency circuitry with two similar but phase- shifted radio frequency signals. The phase shift between the phase-shifted radio frequency signals may be between about 90° and about 270°, preferably between about 120° and about 240°, more preferably between about 150° and about 210°, and most preferably about 180° to provide for a balanced feed.

Further characteristics of the invention and advantages thereof will be evident from the following detailed description of preferred embodiments of the invention given hereinbelow and the accompanying Figs . 1-5, which are given by way of illustration only, and thus are not limitative of the present invention. BRIEF DESCRIPTION OF DRAWINGS

Figs, la-d illustrate, schematically, four different embodiments of an antenna according to the present invention.

Fig. le illustrate, schematically, a general embodiment of a two-wire antenna according to the present invention.

Figs. 2a-d are diagrams illustrating the electrical properties of the general antenna embodiment of Fig. le for different values of the ratio of the lengths of the two wires .

Figs. 3a-b are diagrams illustrating the electrical properties of the general antenna embodiment of Fig. le for different values of the distance between the two wires .

Figs. 4a-c are diagrams illustrating the electrical properties of the general antenna embodiment of Fig. le for different values of the length of the longer one of the two wires .

Fig. 5 illustrates, schematically, an embodiment of an antenna for dual-band operation in separate transmit and receive branches according to the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Four embodiments of an antenna device according to the present invention are illustrated in Figs. la-d. The antennas are to be used in a portable radio communication device, such as a mobile phone (not illustrated) .

The first of these antennas, illustrated in Fig. la, comprises generally a dielectric substrate 1 having a main surface 2, which preferably is substantially planar.

An electrically conductive dual-strip antenna pattern 3 , 5 adapted to transmit and/or receive radio waves at a given frequency is arranged on main surface 2 of said dielectric substrate; and a feed connector 7, 9 is connected to dual-strip antenna pattern 3, 5 and is connectable to radio frequency circuitry of the portable radio communication apparatus for feeding the dual-strip antenna pattern 3, 5 (transmit mode) and/or the radio frequency circuitry (receive mode) with radio frequency signals at the given frequency. The feed connector 7, 9 is preferably connected galvanically, capacitively, or inductively to the two strips 3, 5 of the dual-strip antenna pattern at an end 3a, 5a thereof.

According to the present invention the two strips 3, 5 of the dual-strip antenna pattern are substantially parallel and of different lengths LI, L2. The antenna device of Fig. la is further distinguished in that the two substantially parallel strips 3, 5 of the dual- strip antenna pattern are each a straight strip.

In Fig. lb is shown an embodiment of the antenna device, wherein the longer one 3 of the two substantially parallel strips of the dual-strip antenna pattern is provided with a capacitive load 11, preferably in the form of a patch, in a far end 3b thereof as seen from the feed connector. Such capacitive load lowers the resonance frequency of the antenna and thus the antenna pattern may be made shorter than without the capacitive load.

Fig. lc illustrates an embodiment of the antenna device wherein the two substantially parallel strips 3, 5 of the dual-strip antenna pattern are each bent to form a U, wherein the shorter U-formed strip 5 is arranged at the inner side of the longer U-formed strip 3.

It shall be appreciated that other forms such as an L- form may be used in the present invention.

Fig. Id, finally, combines the aspects of the Figs, lb-c embodiments. The strips 3, 5 are U-formed, and the longer one 3 is provided with capacitive load 11.

The antenna devices of Figs, la-d are preferably fed with a balanced input at the two strips. At least, each of the antenna devices is fed with two identical or similar but phase-shifted radio frequency signals. The phase shift between the signals may for instance range from about 90° to about 270°, from about 120° to about 240°, from about 150° to about 210°, or from about 170° to about 190°. If a phase shift of 180° or close thereto is provided a balanced feed is obtained.

The antenna devices may be used in transmit as well as receive mode, but are particularly advantageous when being used in receive mode. The structure of the antenna device provide for possibilities to tune the antenna elements to obtain strongly phase-shifted signals at the feed connector 7, 9 connected to the two strips 3 , 5.

Thus, a balun, which is found in conventional arrangements for converting a received signal from unbalanced to balanced before being fed to a low noise amplifier at the receive branch (not illustrated), may be omitted provided that the phase shift is large enough. Hereby signal losses, manufacturing costs and the space required by the RF electronics are decreased.

A balanced low noise amplifier is advantageous since it can then be made by Application Specific IC (ASIC) technology, which is preferred. ASIC applications are typically balanced. Further, a downconverter or downmixer (not illustrated) used for downconverting the frequency of the signal as amplified by the low noise amplifier is typically using a differential signal.

Further, the antenna devices are preferably arranged in a respective communication apparatus, which includes an extended ground connector or a ground plane (not illustrated). The antenna devices are then arranged at a certain distance from the ground plane, and preferably parallel thereto such that, during use, the antenna devices can interact with the ground plane to improve the radiation characteristics.

Turning now to Fig. le a general embodiment of the invention is illustrated. An electrically conductive two-wire antenna has two wires 3 , 5 , wherein the two wires are substantially parallel and of different lengths. By wire is here meant any wire-like structure regardless of the cross-sectional form. Thus, the term wire is particularly intended to include strips, e.g. formed by printed circuit technology, and having rectangular or quadratic cross sections, and conventional wires having a circular cross section.

In Fig. le the length of the longer wire is denoted LI; the length of the shorter wire is denoted L2; the distance between the wires is denoted by s, and a cross section width, e.g. diameter, of the wires is denoted by d.

Two main advantages of the antenna device of the present invention are:

1) The antenna pattern occupies very small areas, and it is fed from an end thereof. Thus, the antenna pattern is particularly suitable to be used in a small communication unit, such as a mobile phone.

2 ) The resonance frequency and the input impedance of the antenna device may be adjusted almost independently of each other. The length Ll of the longer one 3 of the two substantially parallel wires 3, 5 of the antenna pattern is adapted or selected according to the given or desired frequency, at which the two-wire antenna pattern is adapted to transmit radio waves. The ratio (L2/L1) of the length of the shorter one 3 to the length of the longer one 5 of the two substantially parallel wires 3, 5 of the antenna is adapted or selected to match a given or desired impedance .

Preferred but not limiting dimensions of the antenna pattern will be given. The dimensions are preferred for an antenna pattern having a resonance frequency of about 1800-1900 MHz.

The length Ll of the longer wire should be about a quarter of a wavelength (λ/4) for the given frequency, at which the dual-wire antenna pattern is adapted to transmit/receive radio waves, i.e. about 75 mm for a frequency of about 1800 MHz.

The length L2 of the shorter wire should be determined to match the input impedance of the antenna device.

The distance s between the two substantially parallel wires 3, 5 may be between 1 and 5 mm, preferably between 2 and 4 mm, and most preferably about 3 mm.

The diameter or width d of the two substantially parallel wires 3, 5 may be between 0.1 and 5 mm, preferably between 0.25 and 3 mm, and most preferably between 0.5-1 mm.

In Figs. 2-4 diagrams of electrical properties of the general antenna embodiment of Fig. le are shown for different wire geometries as simulated. It can be noted that the input impedance is strongly affected by the ratio (L2/L1) (Figs. 2a-c), whereas the resonance frequency is almost unchanged (Fig. 2d). Also, the inter-wire distance affects the input impedance (Figs. 3a-b).

To the contrary, the resonance frequency depends heavily on the length Ll of the longer wire (Fig. 4c), whereas the input impedance is not affected particularly much (Figs. 4a-c) .

With reference next to Fig. 5 a further embodiment of the present invention will be described. The antenna device comprises a dielectric substrate 50 having a main surface 51 divided into a RF circuitry surface 51a and an antenna surface 51b. On the antenna surface 51b there are arranged four different dual-strip antenna patterns 52, 53, 55 and 57, each being an antenna pattern of the present invention. In the illustrated case the patterns are similar to the Fig. Id embodiment.

The antenna patterns are adapted and connected such that antenna 52 is a transmit antenna for a low- frequency band, e.g. the 900 MHz band; the antenna 53 is a receive antenna for a low-frequency band, e.g. the 900 MHz band; antenna 55 is a transmit antenna for a high-frequency band, e.g. the 1800 MHz band; and the antenna 57 is a receive antenna for a high-frequency band, e.g. the 1800 MHz band. The antennas are connected to RF circuitry, e.g. filters, switches, amplifiers, mixers etc. in any appropriate manner. Preferably, some radio-frequency circuitry, preferably including at least one power amplifier and one low noise amplifier, is arranged on the RF circuitry surface 51a of the dielectric substrate as schematically indicated by dashed line 59.

Preferred embodiments of an antenna device according to the present invention have been described. The person skilled in the art realizes that such embodiments can be varied within the scope of the appended claims.

Claims

1. An antenna device for use in a portable radio communication apparatus, said antenna device comprising:

- a dielectric substrate (1, 50) having a main surface (2, 51);

- an electrically conductive dual-strip antenna pattern ( 3 , 5 ) adapted to transmit and/or receive radio waves at a given frequency, said dual-strip antenna pattern being arranged on the main surface of said dielectric substrate; and

- a feed connector (7, 9) connected to said dual-strip antenna pattern and connectable to radio frequency circuitry of said portable radio communication apparatus for feeding said dual-strip antenna pattern and/or said radio frequency circuitry with radio frequency signals at said given frequency,

characterized in that

- the two strips (3, 5) of said dual-strip antenna pattern are substantially parallel and of different lengths (Ll, L2 ) ; and

- said feed connector (7, 9) is adapted to feed said dual-strip antenna pattern and/or said radio frequency circuitry with two similar but phase-shifted radio frequency signals.

2. The antenna device as claimed in claim 1 wherein said electrically conductive dual-strip antenna pattern ( 3 , 5 ) is adapted to receive radio waves at said given frequency and to supply said feed connector (7, 9) with said two similar but phase-shifted radio frequency signals.

3. The antenna device as claimed in claim 1 or 2 wherein the phase shift between said two similar but phase-shifted radio frequency signals is between about 90° and about 270°, preferably between about 120° and about 240°, more preferably between about 150° and about 210°, and most preferably between about 170° and about 190°.

4. The antenna device as claimed in claim 1 or 2 wherein the phase shift between said two similar but phase-shifted radio frequency signals is about 180° to provide for a balanced feed.

5. The antenna device as claimed in any of claims 1-4 wherein said feed connector is connected to the two strips of said dual-strip antenna pattern at a first end (3a, 5a) thereof.

6. The antenna device as claimed in claim 5 wherein said feed connector is connected to the two strips resistively, capacitively, or inductively.

7. The antenna device as claimed in claim 5 or 6 wherein said feed connector is connectable to the radio frequency circuitry of said portable radio communication apparatus for feeding said dual-strip antenna pattern with balanced radio frequency signals at said given frequency.

8. The antenna device as claimed in claim 7 wherein said antenna device, during use, is adapted to interact with a ground connector or plane of said portable radio communication apparatus .

9. The antenna device as claimed in any of claims 5-8 wherein one of the two substantially parallel strips of said dual-strip antenna pattern is provided with a capacitive load (11), preferably in the form of a patch, in a far end (3b, 5b) thereof as seen from the feed connector.

10. The antenna device as claimed in claim 9 wherein said one of the two substantially parallel strips provided with a capacitive load is the longer one (3) of the two strips.

11. The antenna device as claimed in any of claims 1- 10 wherein the two substantially parallel strips of said dual-strip antenna pattern are each a straight strip.

12. The antenna device as claimed in any of claims 1- 11 wherein the two substantially parallel strips of said dual-strip antenna pattern are each bent to form an L or a U, wherein the shorter L- or U-formed strip is arranged at the inner side of the longer L- or U- formed strip.

13. The antenna device as claimed in any of claims 1- 12 wherein the distance (s) between the two substantially parallel strips of said dual-strip antenna pattern is between 1 and 5 mm, preferably between 2 and 4 mm, and most preferably about 3 mm.

14. The antenna device as claimed in any of claims 1-

13 wherein the width (d) of the two substantially parallel strips of said dual-strip antenna pattern is between 0.1 and 5 mm, preferably between 0.25 and 3 mm, and most preferably between 0.5-1 mm.

15. The antenna device as claimed in any of claims 1-

14 wherein the length (Ll) of the longer of the two substantially parallel strips of said dual-strip antenna pattern is adapted to the given frequency, at which said dual-strip antenna pattern is adapted to transmit radio waves .

16. The antenna device as claimed in claim 15 wherein the length of the longer of the two substantially parallel strips of said dual-strip antenna pattern is about a quarter of a wavelength (λ/4) for the given frequency, at which said dual-strip antenna pattern is adapted to transmit radio waves .

17. The antenna device as claimed in any of claims 1-

16 wherein the ratio (L2/L1) of the length of the shorter one to the length of the longer one of the two substantially parallel strips of said dual-strip antenna pattern is adapted to match a given impedance.

18. The antenna device as claimed in any of claims 1-

17 comprising:

- at least a second electrically conductive dual-strip antenna pattern (53, 55, 57) adapted to transmit and/or receive radio waves at a second given frequency, the second dual-strip antenna pattern being arranged on the main surface (51) of said dielectric substrate (50) and the two strips of said second dual-strip antenna pattern being substantially parallel and of different lengths; and

- a second feed connector connected to said second dual-strip antenna pattern and connectable to the radio frequency circuitry of said portable radio communication apparatus for feeding said dual-strip antenna pattern and/or said radio frequency circuitry with radio frequency signals at a second given frequency.

19. The antenna device as claimed in claim 18 wherein:

- said first electrically conductive dual-strip antenna pattern (52, 55) is connectable to transmit circuitry of said portable radio communication apparatus;

- said second electrically conductive dual-strip antenna pattern (53, 57) is connectable to receive circuitry of said portable radio communication apparatus ; and

- said first and second given frequencies are transmit and receive frequencies, respectively, in a common frequency band.

20. The antenna device as claimed in claim 18 wherein said first and second given frequencies are in separate frequency bands.

21. The antenna device as claimed in any of claims 1- 20 wherein said main surface of said dielectric substrate is substantially planar.

22. An antenna device for use in a portable radio communication apparatus, said antenna device comprising:

- an electrically conductive two-wire antenna (3, 5) adapted to transmit and/or receive radio waves at a given frequency;

- a feed connector ( 7 , ) connected to said two-wire antenna and connectable to radio frequency circuitry of said portable radio communication apparatus for feeding said two-wire antenna and/or said radio frequency circuitry with radio frequency signals at said given frequency,

characterized in that

- the two wires ( 3 , 5 ) of said two-wire antenna are substantially parallel and of different lengths (Ll,

L2 ) ; and

- said feed connector (7, 9) is adapted to feed said two-wire antenna and/or said radio frequency circuitry with two similar but phase-shifted radio frequency signals.

23. The antenna device as claimed in claim 22 wherein said electrically conductive two-wire antenna (3, 5) is adapted to receive radio waves at said given frequency and to supply said feed connector (7, 9) with said two similar but phase-shifted radio frequency signals.

24. The antenna device as claimed in claim 22 or 23 wherein the phase shift between said two similar but phase-shifted radio frequency signals is between about 90° and about 270°, preferably between about 120° and about 240°, more preferably between about 150° and about 210°, and most preferably between about 170° and about 190°.

25. The antenna device as claimed in claim 22 or 23 wherein the phase shift between said two similar but phase-shifted radio frequency signals is about 180° to provide for a balanced feed.

26. A portable radio communication apparatus comprising the antenna device as claimed in any of claims 1-25.

27. The portable radio communication apparatus as claimed in claim 26 wherein said feed connector (7, 9) is directly connected to a filter of said portable radio communication apparatus, which filter in turn is directly connected to a low noise amplifier of said portable radio communication apparatus .