WO1999026314A1

WO1999026314A1 - An antenna device for dual frequency bands

Info

Publication number: WO1999026314A1
Application number: PCT/SE1998/002031
Authority: WO
Inventors: Carl Gustaf Blom
Original assignee: Moteco Ab
Priority date: 1997-11-14
Filing date: 1998-11-11
Publication date: 1999-05-27
Also published as: SE9704167L; SE513368C2; SE9704167D0

Abstract

The disclosure relates to an antenna device for a radio communications apparatus operating in dual frequency bands and being switchable between a stand-by position and a talk position. In the antenna device, there are included two antenna elements (11, 12) for the stand-by position and two antenna elements (15, 16) for the talk position. The two pairs of antenna elements (11, 12; 15, 16) both include an antenna element for each frequency band. The antenna elements for the stand-by position consist of two helix antennae, where the one is disposed within the other, and the antenna elements for the talk position constitute a rod arrangement (3) which is displaceable through the helix antennae arrangement (4). The helix antennae (11, 12) are galvanically separated from one another. The antenna elements (15, 16) of the rod arrangement (3) are disposed axially in sequence after one another and galvanically discrete from one another.

Description

AN ANTENNA DEVICE FOR DUAL FREQUENCY BANDS

TECHNICAL FIELD

The present invention relates to an antenna device for a radio communications apparatus operating in dual frequency bands, the antenna device being switchable between a state for the stand-by position of the apparatus and a state for its talk position.

BACKGROUND ART

Radio communications apparatuses are common occurrences in many different types and variations for use within several different frequency bands. In daily parlance they are entitled mobile telephones.

The frequency bands which have hitherto occurred commonly are a lower band around 450 MHz, the so-called GSM band around 900 MHz. A new band in higher frequency, the so-called DCS band is growing in topicality and lies in the frequency range of between 1710 and 1880 MHz.

In order for a mobile telephone to be able to operate in the DCS band, there is naturally required an antenna device set for this frequency range. Correspondingly, an antenna device is required which is set for the GSM band if the mobile telephone is to be able to be employed in this frequency range. However, increasingly growing requirements have arisen in the art to be able, in one and the same apparatus, to operate in both frequency bands, for which reason an antenna device must be available which functions well in both bands.

A mobile telephone works in a stand-by position, or paging mode, when it is not employed for talking. On the other hand, during conversation, talk position, a better antenna performance is required than that which is necessary in the paging mode.

In a mobile telephone, there are in addition very strong wishes that the antenna device be physically compact in dimensions and also not place demands on a complicated mechanical switching device for switching between the different states and frequency bands.

PROBLEM STRUCTURE

The present invention has for its object to design the antenna device intimated by way of introduction such that it is capable of operating with a good level of efficiency within two frequency bands, for example the GSM band and the DCS band. In addition, the present invention has for its object to design the antenna device such that, at least in the paging mode, it will be extremely compact, and that it places no requirements on complicated switching devices on switching between frequency bands and on switching between paging mode and talk position. Finally, the present invention has for its object to realise an antenna device which satisfies the requirements of being simple and economical to manufacture.

SOLUTION

The objects forming the basis of the present invention will be attained if the antenna device intimated by way of introduction is characterized in that the antenna device includes two antenna elements for stand-by position, one for each frequency band, and two antenna elements for talk position, one for each frequency band, the antenna elements for stand-by position or paging mode being helix antennae disposed one interiorly in the other, while the two antenna elements for talk position together form a rod arrangement which is displaceable in its longitudinal direction through the helix antennae.

With this design and construction, a dual helix will be realised which, in paging mode, gives an extremely compact and easily-handleable construction with a fully sufficient degree of operational efficiency. By switching of the antenna rod from paging mode to talk position, the necessary improvement of the antenna performance will be obtained, at the same time as the switching operation between stand-by position, or paging mode, and talk position may be made simply as a result of the above- mentioned displacement of the rod antenna arrangement. Further advantages will be attained according to the present invention if this is also given one or more of the characterizing features as set forth in appended Claims 2 to 10.

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 shows an antenna device according to the present invention in talk position;

Fig. 2 shows the antenna device of Fig. 1 in stand-by position, or paging mode;

Fig. 3 is a cross section through an upper portion of the antenna device in the position according to Fig. 2;

Fig. 4 is a view of a lower end portion of the rod arrangement of the antenna device in a first embodiment;

Fig. 5 is a view corresponding to that of Fig. 4 of a second embodiment of the rod arrangement;

Fig. 6 is a cross section through the rod arrangement included in the device according to the present invention; and

Fig. 7 is a magnified sectional view through a lower end portion of the rod arrangement according to Figs. 4 and 6.

DESCRIPTION OF PREFERRED EMBODIMENT

Taken from Figs. 1 and 2 together, the antenna device includes a first antenna unit 1 which is designed as a rod arrangement 3, and a second antenna unit 2 which is designed as a helix arrangement 4. The helix arrangement 4 is secured in the radio communications apparatus, in daily parlance a mobile telephone, which the antenna arrangement is intended to serve.

The first antenna unit 1 is designed to be dual-banded in order to be able to operate within both frequency bands for which the mobile telephone is operative. Correspondingly, the second antenna unit 2 is also of dual band design for the same frequency bands as the first antenna unit. The first antenna unit is intended for the talk position of the mobile telephone, while the second antenna unit 2 is intended for the stand-by position, or paging mode, of the mobile telephone. Switching between the talk position and the stand-by position is realised by the displacement of the first antenna unit 1 in its longitudinal direction through the second antenna unit 2 between both states, as shown in Figs. 1 and 2. It should here be observed that, in the state for stand-by position (Fig. 2), it is only the second antenna unit 2 which is visible on the outside of the outer casing of the mobile telephone.

The antenna device includes means for electric switching between stand-by position and talk position, and the switching between these positions is realised by means of the above-mentioned displacement of the first antenna unit 1.

The means for switching between talk position and stand-by position may include either an electric switching device or a device for bringing either of the antenna units to a resonance position which is located a safe distance outside the selected frequency bands when the relevant antenna unit is not to be used.

The antenna device further includes means for switching both of the antenna units 1 and 2 between the relevant frequency bands. Such means are designed in a such a manner that no mechanical switching device is included therein. Instead, the switching between the frequency bands is realised in that radiating antenna elements included in the antenna units are capacitatively or inductively engaged and disengaged, respectively. Fig. 3 shows a section through the helix arrangement 4 and an upper portion of the rod arrangement 3 extending therethrough. It will be apparent from the Figure that the antenna device is built-up around a bushing portion 5 which is produced from mental and which is intended for securement of the antenna device in a casing (not shown) for the mobile telephone. The bushing portion 5 has a central, through-going channel for accommodating the rod arrangement 3, and further an upper, substantially cylindrical portion 6 on which a tubular carrier portion 7 produced from electrically insulating material is disposed. The carrier portion 7 is secured on the upper, cylindrical portion 6 in that this is provided with circumferential barbs, ridges or threads which engage in the material of the carrier portion 7 which suitably is a plastic material possessing a certain resilience or is a semi-hard plastic. The cylindrical bushing portion 5 further has a lower portion 8 with a thread 9 which serves for securing the antenna device in the mobile telephone.

The carrier portion 7 has a central, substantially cylindrical channel 10 which is open in the upper end of the carrier portion. Interiorly in the channel 10 of the carrier portion 7, there is disposed a first antenna element 11 which is designed as a helix. The first antenna element is set for the lower frequency band for the antenna device and is galvanically connected to the electric circuits of the mobile telephone.

The helix is produced from resilient material and is loosely disposed in the channel 10 so that it is compressible in the axial direction. The upper end of the helix rests against an abutment in the upper end of the channel 10, while its lower end rests on a metal washer 26 which in turn rests on and is in galvanic contact with the upper cylindrical portion 6 of the bushing portion 5.

On the outside of the carrier portion 7, possibly countersunk in its outer casing surface but possibly also wholly outside this casing surface, there is disposed a second antenna element 12, also this being designed as a helix, and designed for the higher frequency band. The second antenna element 12, i.e. the helix, is galvanically discrete partly from the first antenna element 11 and partly from the electric circuits of the mobile telephone, but is supplied inductively/capacitatively from the first antenna element 11. Suitably, the two helices 11 and 12 are of approximately the same axial length, whereby the capacitative/inductive coupling between them will be improved.

Regardless of where the second antenna element 12 is located in the radial direction, i.e. regardless of whether it is wholly or partly countersunk in the casing surface of the carrier portion 7, there is disposed about the carrier portion 7 and the second antenna element 12 a hood 13 of electrically insulating, non-magnetic material. In its upper end (facing away from the bushing portion 5), the hood 123 has an opening 14 to allow the passage and longitudinal displacement of the rod arrangement 3.

Electrically, the helix arrangement 4 functions as follows. The first antenna element 11 , i.e. the helix disposed interiorly in the carrier portion 7, is galvanically connected to the circuits of the mobile telephone via the washer 26 and the bushing portion 5. When the antenna element 11 is supplied with or receives electromagnetic radiation within the lower frequency band, this radiation will pass through the second antenna element 12 without being affected to any appreciable degree thereby, since it has a resonance frequency a safe distance from the resonance frequency of the first antenna element 11 and further because it is so "scant" that it has no appreciable screening effect. The second antenna element, i.e. the outer helix, is set to the higher frequency band, for which reason it must have a considerably fewer number of turns and greater pitch than is the case with the first antenna element. For this reason, the second antenna element 12, seen from the first antenna element 11, will - as was intimated above - be considered as transparent. If transmission takes place within the higher frequency band, the second antenna element 12, i.e. the outer helix, will function as radiating element, which is capacitatively/inductively coupled to the inner helix 11. Correspondingly, on receiving within the higher frequency band, a capacitative/inductive coupling will be found between the two antenna elements 12 and 11 so that received energy is transmitted between them.

If the placing of the two antenna elements 11 and 12 were the reverse compared with that shown on the Drawing, so that the antenna element for the lower frequency band were placed outermost, the device would not function since the outer helix adapted for the lower frequency band would, in this case, function as an effective screen for the helix lying inside which is set for the higher frequency band.

It will be apparent from the foregoing that the antenna device according to the present invention, in the stand-by position, paging mode, of the mobile telephone, functions without the employment of any mechanical switching arrangement between the two antenna elements 11 and 12. Further, the antenna element for the lower frequency band may be permanent and galvanically connected to the circuits of the mobile telephone.

The antenna device according to the present invention comprises, in addition to the helix arrangement 4, also a rod arrangement 3. This is shown in cross section in Fig. 6, it being presupposed that the upper end of the right-hand part figure is united with the lower end of the left-hand part figure, as is intimated by broken lines. Further, the rod arrangement is apparent from Figs. 1 and 2.

In Fig. 1 , it is intimated that the rod arrangement 3 has an upper portion 17 which is produced from electrically insulating, non-magnetic material. The longitudinal extent of this upper portion 17 is such that, when the antenna device is located in the position according to Fig. 2, the upper portion 17 will, in the longitudinal direction, fill out at least the helix arrangement 4 and its lower mounting and connection parts and fittings. The reason for this is that, in the stand-by position, paging mode, in Fig. 2 (where the helix arrangement is in operation), there cannot be any electrically conductive or magnetic material interiorly in the helix arrangement 4 without greatly disrupting its function.

The rod arrangement 3 is further provided with a third antenna element 15 intended for the lower frequency band and a fourth antenna element 16 intended for the higher frequency band.

The fourth antenna element 16, i.e. the antenna element of the rod arrangement 3 for the high frequency band, includes an elongate, metallic conductor 18 which serves the function of a rod antenna which is set to the higher frequency band. Around the rod antenna 18, the rod arrangement has an insulating tube 19, and outside this a spacer 20 designed as an insulating tube, which is surrounded by a surface coating 21 of insulating material. In its lower end, the straight rod antenna 18 is galvanically connected to a metal washer 22 via which the rod arrangement 3 is supplied.

The third antenna element 15, which is designed for employment in the lower frequency band in talk position of the antenna device, is designed as a helix antenna 23 which is disposed on the outside of the insulating tube 19 of the rod arrangement. Within the longitudinal extent of the helix 23, the spacer 20 is absent, since the helix 23 takes up its space. Possibly however, parts of the spacer 20 may be found between the winding turn in the helix 23. The helix 23 is set for use in the lower frequency band and is, in terms of power, capacitatively coupled to the metallic conductor 18 which, on operation in the lower frequency band, functions as an extension of the supply conductor to the rod arrangement 3. The capacitative coupling is realised in that the helix 23 longitudinally overlaps the metallic conductor 18 within the region which is marked at 24 in the Fig. 6. It will be apparent that the helix 23 terminates with its lower end at the lower end of the region 24, and that the metallic conductor 18 terminates with its upper end at the upper end of the region 24. Within the overlap zone, there is naturally the insulating tube 19 between the helix 23 and the conductor 18.

While not being apparent from Fig. 6, the rod arrangement 3 has, over the helix 23 the upper portion 17 which is electrically insulating. Within this region, the rod arrangement includes the insulating tube 19, the spacer 20 and the surface coating 21.

When in operation, the rod arrangement 3 functions as follows.

On operation in the higher frequency band, the conductor 18 functions as a quarter wave rod antenna, while the helix 23 constitutes a capacitatively coupled top load to the rod antenna. The presence of this top load implies that the rod antenna may be made physically shorter than its electric length. On operation in the lower frequency band, the metallic conductor 18 functions only as a coupling conductor between the connection of the antenna device to the circuits of the mobile telephone and the capacitative coupling zone 24 between the conductor 18 and the helix 23.

In the foregoing, both the rod arrangement 3 and the helix arrangement 4 have been separately described both electrically and mechanically. With reference to Fig. 3, it will be disclosed how the cooperation between them is put into effect.

As was mentioned above, the bushing portion 5 has a through-going channel through which the rod arrangement 3 is displaceable in its longitudinal direction. In order to prevent play and give the desired electric contact, metallic spring elements are disposed interiorly in the bushing portion 5 which slide along the surface coating 21 of the rod arrangement 3 when the rod arrangement is displaced. In the protracted position of the rod arrangement, in the talk position which is shown in Fig. 1 , the bushing portion 5 with its spring elements 25 realises electric contact with the lower contact sleeve 22 of the rod arrangement, whereby the rod arrangement becomes directly galvanically coupled to the circuits of the mobile telephone.

In the position of the rod arrangement according to Fig. 2, i.e. in the stand-by position or paging mode, the lower end of the inner helix 11 rests on an electrically conductive washer 26 which in turn rests on the upper side of the cylindrical upper portion 6 of the bushing portion 5. Hereby, an electric, galvanic connection prevails between the bushing portion and the lower end of the inner helix 11.

On protraction of the rod arrangement from the position illustrated in Fig. 2 to the position illustrated in Fig. 1 , the rod arrangement will slide through the helix arrangement 4 until such time as its projecting edge region 27 (Figs. 4 and 7) on the upper end of the metal sleeve 22 comes into abutment against the lower side of the washer 26. On continued lifting, the washer 26 will accompany the rod arrangement 3 in its upwardly directed movement, whereby the inner helix 11 is compressed in the axial direction. Granted, the helix 11 is still galvanically coupled to the electric circuits of the mobile telephone, but will, as a result of this axial compression, first have a misadaptation as regards frequency and will thereafter wholly cease to exist as a radiating antenna element. Hereby, the outer helix 12 is naturally also electrically disconnected.

In one alternative embodiment, it is possible to place, on the upper end of the metallic sleeve 22 on the lower end of the rod arrangement 3, a ring 28 of insulating material. On protraction of the rod arrangement 3, the ring 28 will come into abutment against the washer 26 and lift this out of electric contact with the bushing portion 5.

Hereby, the inner helix 11 will be electrically disconnected from the circuits of the mobile telephone as soon as the washer 26 has been lifted out of electric contact with the bushing portion 5.

In one practical embodiment, the outer helix 12 is set to the DCS band. IN this band, the outer helix has approximately 2 turns with a diameter of 8.5 mm and a pitch of approximately 7 mm. Correspondingly, the inner helix 11 is set for the GSM band and has a diameter of approximately 7 mm, a pitch of approximately 4 mm and approximately 5.5 turns.

As regards the rod arrangement, the helix 23 has a length of approximately 40 mm comprising 40-42 turns with a pitch of 0.8 mm. The overlap length 24 amounts to approximately 9 mm. The total length of the entire rod arrangement is approximately 116 mm.

The present invention may be modified without departing from the scope of the appended Claims.

Claims

WHAT IS CLAIMED IS:

1. An antenna device for a radio communications apparatus operating in dual frequency bands, the antenna device being switchable between a state for the stand-by position of the apparatus and a state for its talk position, characterized in that the antenna device includes two antenna elements (11 , 12) for stand-by position, one for each frequency band, and two antenna elements (15, 16) for talk position, one for each frequency band, the antenna elements (11 , 12) for stand-by position or paging mode being helix antennae disposed one interiorly in the other, while the two antenna elements (15, 16) for talk position together form a rod arrangement (3) which is displaceable in its longitudinal direction through the helix antennae (4).

2. The antenna device as claimed in Claim 1 , characterized in that the helix antennae (11, 12) are galvanically discrete from one another.

3. The antenna device as claimed in Claim 1 or 2, characterized in that the helix antenna (11) which is provided for the lower frequency band is disposed interiorly in the helix antenna (12) which is provided for the higher frequency band.

4. The antenna device as claimed in any of Claims 1 to 3, characterized in that both antenna elements (15, 16) for the talk position are disposed axially in sequence after one another in the rod arrangement (3).

5. The antenna device as claimed in any of Claims 1 to 4, characterized in that both of the antenna elements (15, 16) for the talk position are galvanically discrete from one another.

6. The antenna device as claimed in any of Claims 1 to 5, characterized in that out of the two antenna elements (15, 16) for the talk position, the antenna element (15) for the lower frequency band is disposed most proximal the top of the rod arrangement (3) and capacitatively coupled to the circuits of the radio communications apparatus via the antenna element (16) for the higher frequency band, said antenna element (16), in the protracted position of use of the rod arrangement, being galvanically connected to the circuits.

7. The antenna device as claimed in any of Claims 1 to 6, characterized in that out of the antenna elements (15, 16) for the talk position, the antenna element (16) for the higher frequency band is a metal rod (18), while the antenna element (15) for the lower frequency band is a helix (23), said helix, on operation in the higher frequency band, being a capacitatively coupled top load to the antenna element for the higher frequency band.

8. The antenna device as claimed in any of Claims 1 to 7, characterized in that the rod arrangement (3) in a retracted position is electrically discrete from the circuits of the radio communications apparatus, while the helix (11) for the lower frequency range of the stand-by position is galvanically connected to the circuits of the radio communications apparatus.

9. The antenna device as claimed in any of Claims 1 to 8, characterized in that in the protracted position of the rod arrangement (3), i.e. in the talk position, the radially innermost helix (11) of the antenna elements for the stand-by position is electrically discrete from the circuits of the radio communications apparatus.

10. The antenna device as claimed in any of Claims 1 to 8, characterized in that in the protracted position of the rod arrangement (3), i.e. in the talk position, the radially innermost helix (11) of the antenna elements for the stand-by position is axially compressed, whereby it has a resonance frequency outside both of the frequency bands.