WO2002049152A1

WO2002049152A1 - Antenna device

Info

Publication number: WO2002049152A1
Application number: PCT/SE2001/002577
Authority: WO
Inventors: Max Landaeus; Björn Cederberg; Carl Gustav Blom
Original assignee: Moteco Ab
Priority date: 2000-12-12
Filing date: 2001-11-22
Publication date: 2002-06-20
Also published as: AU2002224271A1; CN1479955A; SE0004600L; SE518819C2; SE0004600D0

Abstract

An antenna for a radio communications apparatus, a so-called mobile telephone, operates in two frequency bands and comprises, on the one hand, a helical radiator (11) and, on the other hand, a bar- or rod-shaped radiator (10). The one end (12) of the bar- or rod-shaped radiator (10) is a supply end and its other end (13) is galvanically connected to a first end (14) of the helical radiator (11). The supply end (12) is connected to the circuits of the apparatus. The other end (15) of the helical radiator (11) terminates freely.

Description

ANTENNA DEVICE

TECHNICAL FIELD

The present invention relates to an antenna for a radio communications apparatus, a so-called cell or mobile telephone, operating in two frequency bands and comprising a helical radiator and a bar- or rod-shaped radiator.

BACKGROUND ART

Radio communications apparatuses, in daily parlance cell or mobile telephones, are often designed to be able to operate in two different frequency bands. In such situations, twin antennas are required, or one antenna which has the capability to operate in both frequency bands.

As one example of the latter alternative, mentioned might be made of a so-called helix antenna which, in its lower end i.e. located most proximal the mobile telephone, is of greater pitch than applies to its upper region. As a result, the lower region will operate in the higher frequency band of the mobile telephone, while the whole of the antenna operates in the lower frequency band. An antenna of this type may function satisfactorily in many situations.

However, in certain cases problems arise in the higher frequency band as a result of poor performance. This has its basic cause in the fact that the proportion of the total height of the helix which is utilised in the higher frequency band is relatively slight, for which reason the antenna will be "short" or low.

A "dual helix" of the above-outlined type also involves purely practical problems in manufacture, since, in winding of the helix, it may be difficult to realise precision in the transitional region between the two pitches. Further, assembly problems may be encountered in such a "dual helix". PROBLEM STRUCTURE

The present invention has for its object to design the antenna intimated by way of introduction such that the drawbacks inherent in prior art technology are obviated. In particular, an antenna of greatly improved performance in the upper frequency band is sought for, and in addition an antenna which is easy to manufacture with good precision and which moreover may readily be mounted in a mobile telephone.

SOLUTION

The objects forming the basis of the present invention will be attained if the antenna intimated by way of introduction is characterised in that the bar- or rod-shaped radiator has a first end which is a supply end and which is connected to the circuits of the apparatus, and a second end which is galvanically connected to a first end of the helical radiator which has a second end which terminates freely.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will now be described in greater detail hereinbelow, with reference to the accompanying Drawings. In the accompanying Drawings:

Fig. 1 is a longitudinal, diametric section through an antenna according to the present invention;

Fig. 2 shows, in a vertical side elevation, a radiator element included in the antenna of Fig. 1;

Fig. 3 shows the radiator element of Fig. 2 turned through 90° about its longitudinal direction in relation to Fig. 2; and

Fig. 4 is a view corresponding to that of Fig. 2 of an alternative embodiment of the radiator element. DESCRIPTION OF PREFERRED EMBODIMENT

Fig. 1 shows an antenna designed according to the present invention, and it will be apparent from the Drawing that it has an upper end 1 and a lower end 2 which are located internally in a mobile telephone whose outer contour is intimated at reference numeral 3. The upper end is also that which is located most distal from the mobile telephone proper.

The antenna has a body portion 4 which extends to the interior of the mobile telephone, i.e. in Fig. 1 beneath the outer contour 3. The body portion 4 is manufactured from an electrically insulating and non-magnetic material, for example a suitable plastics. The body portion 4 consists of an elongate, interior cavity 5 in which, to the greater part, is accommodated a radiator element, which will be described in greater detail below.

Outside the body portion 4, there is provided a protective casing 6 which is also produced from an electrically insulating, non-magnetic material, also this part suitably manufactured from plastics. The protective casing is upwardly closed and is secured on the body portion 4 by means of snap catches 7, in the illustrated embodiment an interiorly projecting bead in the protective casing 6 which is accommodated in a corresponding, circumferential groove in the outer circumferential surface of the body portion 4.

The protective casing 6 and the body portion 4 are dimensioned so that, together, they wholly enclose the radiator element, an upper end portion of the radiator element extending over or outside the cavity 5 and being accommodated in a continuation of this cavity provided in the protective casing 6.

In its lower region, i.e. that region which is located inside the outer contour 3, the body portion 4 has an aperture 8 in its wall through which a bent contact portion 9 of the radiator element extends out. This bend portion is spring pre-tensioned in a direction out from the centre of the body portion 4 and may thereby be depressed against the spring pre-tensioning at least partly in through the aperture 8. The bent, projecting contact portion 9 serves for contacting with a corresponding contact in the circuits of the mobile telephone, e.g. a so-called pad on the circuit card of the apparatus.

While not being apparent from Fig. 1, the body portion 4 has a snap catch by means of which it is held fixed in the mobile telephone in a position where reliable contact is obtained between the bent contact portion 9 and the corresponding contact.

Figs. 2 and 3 show the radiator element which, in the mounted state, is located in the antenna according to Fig. 1. It will be apparent from both of these Figures that the radiator element comprises a bar- or rod-shaped radiator element 10 and a helical radiator 11. The bar- or rod-shaped radiator element 10 has a first, lower end 12 which is galvanically connected to the circuits of the mobile telephone via the above- mentioned bent contact portion 9. Further, it has a second or upper end 13 which is galvanically connected to a first end 14 of the helical radiator 11. Finally, it has a second or lower end 15 which terminates blind in the region of the lower end 12 of the bar- or rod-shaped radiator 10.

It will be apparent from Fig. 2 that the helical radiator 11 has a centre axis 16 which is intimated by a broken line. It will further be apparent that the bar- or rod-shaped radiator 10 diverges away from the centre axis in a direction from its second towards its lower end 13 and 12, respectively. Since the entire radiator is produced from a resilient material, it will be realised that the first end of the bar- or rod-shaped radiator may be pressed in against spring pre-tensioning a greater or lesser distance towards the helical radiator 11.

It will be apparent from Fig. 3 that the bar- or rod-shaped radiator 10 is seen to cross the centre line 16 of the helical radiator 11 if the radiator element is viewed in a direction from the bar- or rod-shaped radiator 10 towards the helical radiator. A spring pre-tensioning also applies here, which implies that the radiator element seen according to Fig. 3 can be deformed against spring action so that the bar- or rod- shaped radiator 10 may be bent more or less into a parallel state with the centre line 16. Fig. 4 shows a modified embodiment of the radiator element and, in a comparison between Fig. 2 and Fig. 4, it will be apparent that the bar- or rod-shaped radiator 10 is, in this embodiment seen in the same manner as in Fig. 2, approximately parallel with the centre axis 16 to the helical radiator 11. The oblique inclination of the bar- or rod-shaped radiator 10 seen as in Fig. 3 is as great as or greater than that shown in Fig. 3.

In electric terms, the bar- or rod-shaped radiator 10 will function in the higher frequency band while the whole of the antenna will function in the lower frequency band. Further, the bar- or rod-shaped radiator will have a height which is equal to the height of the helical radiator 11. The bar- or rod-shaped radiator thereby utilises all of the height space which is made available by the cavity 5 and the casing 6.

Determination of the two radiators' resonance frequencies is affected by a whole series of different parameters. Thus, the resonance frequency for the two radiators is reduced with increased material length of the helical radiator 11. However, the low band in the frequency fades more quickly than the high band. The resonance frequency for both bands further falls with increased coupling degree between the helix and the bar- or rod-shaped radiator, the coupling degree being affected by the distance between the helix 11 and the bar- or rod-shaped radiator 10. The pitch in the helix 11 also has a certain importance. As opposed to that which applies concerning the material length, resonance frequency falls for the higher band more quickly in frequency with increasing coupling degree between the radiators.

For an antenna of a given height and total diameter, the most important control parameters concerning the resonance frequencies for the two radiators will be the pitch of the helix 11, the diameter of the helix and its length.

It will be apparent from the foregoing that both the dimensioning and the mutual positioning of the two radiators 10 and 11 affect the setting frequencies. As was mentioned above, the body portion 4 has a cavity 5 in which the radiator element is accommodated. In a comparison between Figs. 1 and 2, it will be apparent that, in the mounted state interiorly in the body portion 4, the bar- or rod-shaped radiator 10 is depressed in a direction towards the helical radiator. In such instance, the depression degree is determined by the dimensioning of the body portion 4 but also by the spring pre-tensioning which the bar- or rod-shaped radiator 10 displays. In Fig. 1, it will be perceived that the lower end 12 of the bar- or rod-shaped radiator 10 abuts with spring force against a guide surface 17 on the inner defining surface of the cavity 5 of the body portion 4. This spring force naturally also strives to displace the entire helical radiator 11 in the opposite direction, i.e. to the right in Fig. 1. From this follows that the helix 11 will be held positionally fixed against the inside 18 of the body portion 4 along at least the greater part of the length of the helix 11. In that both of the radiators are in this manner positionally fixed under spring pre-tensioning interiorly in the cavity, their mutual positions will be accurately established.

The oblique inclination of the bar- or rod-shaped radiator 10 which is illustrated in Fig. 3 is also straightened out for the greater part when the radiator element is in its mounted state as shown in Fig. 1. In the mounted state, the longitudinal direction of the bar- or rod-shaped radiator 10 is thus more or less parallel with the centre axis 16 of the helix 11.

As was mentioned above, the bent contact portion 9 is in abutment under spring pre- tensioning against a corresponding contact fixedly disposed in the mobile telephone. For such spring pre-tensioning to occur, the bent contact portion 9 must be depressed somewhat in a direction to the left in Fig. I in comparison with that which is shown in this Figure. This depression realises a torque against the entire radiator element in a clockwise direction about the guide surface 17 so that there will thereby be realised an additional surety that the helix 11 abuts against the inner defining surface of the cavity 5 to the right in Fig. 1.

On mounting of the radiator element in the body portion 4, this is quite simply shifted in its longitudinal direction down in the cavity 5. In such instance, the defining walls of the cavity, while this is not apparent from the Drawings, display guide surfaces which lead in both of the radiators and the bent contact portion 9 to the correct position whereafter the radiator element is snapped in place and sits positionally fixed in the cavity 5 int. al. as a result of the projection of the bent contact portion 9 through the aperture 8, but also in that the upper end of the helix 11 abuts against the inside of the casing 6.

Claims

WHAT IS CLAIMED IS:

1. An antenna for a radio communications apparatus, a so-called cell or mobile telephone, operating in two frequency bands and comprising a helical radiator (11) and a bar- or rod-shaped radiator (10), characterised in that the bar- or rod-shaped radiator (10) has a first end (12) which is a supply end and which is connected to the circuits of the apparatus, and a second end (13) which is galvanically connected to a first end (14) of the helical radiator (11) which has a second end (15) which terminates freely.

2. The antenna as claimed in Claim 1, characterised in that the second end (15) of the helical radiator (11) is located in the region of the first end (12) of the bar- or rod-shaped radiator (10).

3. The antenna as claimed in Claim 1 or 2, characterised in that the bar- or rod-shaped radiator )10) extends outside and along the helical radiator (11) and a distance therefrom.

4. The antenna as claimed in any of Claims 1 to 3, characterised in that the bar- or rod-shaped radiator (10) and the helical radiator (11) are both at least partly accommodated in an elongate cavity (5) in a body portion (4) of electrically insulating and non-magnetic material; and that the radiators are positionally fixed in relation to one another and the wall of the cavity by spring pre-tensioning in one of or both of the radiators.

5. The antenna as claimed in Claim 4, characterised in that the bar- or rod- shaped radiator (10), prior to insertion in the cavity (5), diverges away from a centre axis (16) of the helical radiator (11), counting from the second end (13) of the bar-or rod-shaped radiator (10) towards its first end (12).

6. The antenna as claimed in Claim 4, characterised in that, seen in the direction from the bar- or rod-shaped radiator (10) and towards the helical radiator (11) and approximately at right angles to the centre axis (16) thereof, the bar- or rod- shaped radiator is seen to cross the centre axis of the helical radiator.

7. The antenna as claimed in any of Claims 1 to 6, characterised in that the bar- or rod-shaped radiator (10) has, in the region of its first end (12), a bend (9) projecting laterally, transversely of its longitudinal direction, and which is disposed under spring pre-tensioning to abut against and realise galvanic contact with a corresponding contact in the mobile telephone.

8. The antenna as claimed in Claim 7, characterised in that the bend (9) is of N- or U-configuration and extends out through an aperture (8) in a side wall of the body portion (4) with an elongate cavity (5) wherein the bar- or rod-shaped radiator (10) and the helical radiator (11) are accommodated for the greater part.