WO2000079641A2

WO2000079641A2 - Antenna device

Info

Publication number: WO2000079641A2
Application number: PCT/SE2000/001229
Authority: WO
Inventors: Carl Gustaf Blom; Max Landaeus; Henrik Lindkvist
Original assignee: Moteco Ab
Priority date: 1999-06-17
Filing date: 2000-06-14
Publication date: 2000-12-28
Also published as: SE9902314D0; SE514422C2; SE9902314L; CN1359551A; WO2000079641A3; CN1213509C; AU6031800A

Abstract

An antenna device for several frequency bands comprises a radiating element (15) which, in rough outline, is designed as a planar helix. The radiating element (15) is disposed on a carrier (4) of insulating material and radiates in at least two discrete and separate frequency bands. The radiating element (15) further includes a number of substantially straight conductor portions (16, 16', 16', ..., 17, 17', 17', ...). The straight conductor portions (16, 16', 16', ..., 17, 17', 17', ...) are galvanically united with one another by the intermediary of curved or angular conductor portions (18, 18', 18'). Together, the different conductor portions (16, 16', 16', ..., 17, 17', 17', ..., 18, 18', 18') form an angular helix.

Description

ANTENNA DEVICE

TECHNICAL FIELD

The present invention relates to a miniature antenna device for several frequency bands and in rough outline comprises an element formed as a planar helix and radiating in at least two separate, discrete frequency bands, the element being disposed on a carrier of insulating material.

BACKGROUND ART

Antennas are previously known in the art which have been designed as planar helixes of substantially circular configuration. Such antennas may function well in certain situations. However, they are large and have a diameter of a half wave length or more which, in 1800 MHz, implies 8 cm or more. Because of the size, they are not usable in connection with mobile telephones. Further, prior art helical antennas often have two or more arms which are supplied from the centre, which may be a drawback if, for example, they are to be manufactured using circuit card technology.

Antennas are also known in the art which, in the opened-out state, display meandering conductors applied on a foil-formed carrier. The carrier is then rolled or wrapped around a cylindrical, conical or elliptical support member so that the construction thereby becomes compact.

Such a construction suffers from serious drawbacks caused by the fact that the opposing ends of the meandering conductor or conductors, as a result of the wrapping together of the foil, come so close to one another that the conductors, in electric terms, powerfully influence one another. This implies that it must be ensured there is a safe distance remaining after the wrapping operation between the opposing ends of the antenna device. This entails that the area which the antenna device as a whole may take up in the opened-out state will be relatively slight in comparison with the total available area. Hence, the available space is poorly utilised, which entails that the antenna loses in both band width and in efficiency. The concept of etching or producing by other means a pattern of electric conductors, constituting a radiating element, on an insulating plastic foil or other suitable carrier may appear to be attractive. However, the wrapping up of the plastic foil into a cylindrical or conical form of circular, elliptical or, in general terms, round or oval cross section entails problems in that, as was mentioned above, different parts of the radiating element tend to electrically affect one another so that the properties of the antenna are destroyed or at least considerably impaired.

In an antenna of this type, the intention is also to have a radiating element which, in surface, is as large as possible in relation to the outer dimensions of the plastic foil, in order that the resulting antenna will have as large aperture as possible.

A radiating element which is large in relation to the outer dimensions of the plastic foil increases the above-described problems of interaction between different parts of the radiating element on wrapping together.

Hitherto, there has been no solution to the problem of how to form the pattern of electric conductors forming the radiating element in order simultaneously to be able to provide a maximum size of radiating element on a given area and minimise electric interaction between different parts of the radiating element.

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 and the antenna will have a maximum degree of efficiency, as well as extremely good band width in the frequency bands where it is to be employed, with a high degree of miniaturisation. Furthermore, the present invention has for its object to design the antenna according to the present invention such that it may be manufactured at low cost in a rational manner. SOLUTION

The objects forming the basis of the present invention will be attained if the antenna device intimated by way of introduction is characterised in that the radiating element includes a number of substantially straight conductor portions which are galvanically united with one another by the intermediary of markedly curved or angled conductor portions.

By providing the planar and, in rough outline, helical radiating element with a number of substantially straight conductor portions, it has proved that the resulting antenna device will have at least two resonance frequencies. Further, it has proved that the wrapping operation does not appreciably affect performance even though the opposite ends of the radiating element come close to one another after the wrapping is completed. Finally, the antenna device may be simply manufactured by an etching process applied on a flexible plastic foil provided with a thin metal layer on one, or possibly both sides.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

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

Fig. 1 is an exploded view of the device according to the present invention seen from one side;

Fig. 2 is a corresponding exploded view of the device according to the present invention seen from approximately the diametrically opposed direction;

Fig. 3 shows a carrier included in the device according to the present invention, with one radiating element;

Fig. 4 is a view corresponding to that of Fig. 3, but of a second embodiment of the device according to the present invention; Fig. 5 is a view corresponding to that of Fig. 3, but of a third embodiment of the device according to the present invention;

Fig. 6 is a view corresponding to that of Fig. 3, but of a fourth embodiment of the device according to the present invention;

Fig. 7 is a view corresponding to that of Fig. 3, but of a fifth embodiment of the device according to the present invention; and

Fig. 8 is a view corresponding to that of Fig. 3, but of a sixth embodiment of the device according to the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

As was intimated above, the device according to the present invention is principally intended for use in a so-called mobile telephone, which should be at least of the dual band type so that it covers the EGSM-band of 880-960 MHz, and at least one of the DCS- and PCS-bands of 1710-1880 MHz, and 1850-1990 MHz, respectively. Preferably, it should naturally be possible to cover all three frequency bands.

In the body of the specification below, an expression "radiating element" will be employed. Naturally, this implies that the element must be able to radiate electromagnetic energy within the above-mentioned frequency bands. However, the term "radiating element" should also be interpreted such that it is capable of receiving electromagnetic energy within the above-mentioned frequency bands.

In Fig. 1, reference numeral 1 relates to a carrier portion of the antenna device, the carrier portion is manufactured from a suitable plastic material with electrically insulating and non-magnetic properties. The carrier portion serves for securement on the casing of the mobile telephone and, to this end, has a guide pin 2 which is designed and placed for accommodation in a corresponding recess or hole in the casing of the mobile telephone. Concerning Figs. 3-8, it should be mentioned that they have been draughted on an approximate scale of 1:1.

The carrier portion 1 has a core or body portion 3 about which a foil-shaped carrier 4 is to be rolled or wrapped. The foil-shaped carrier 4 has a system of electric conductor portions which constitute the radiating element of the antenna device. (The conductor portions are not shown in Figs. 1 and 2.)

The core portion 3 is tubular and is therefore hollow and has a relatively thin material thickness. The cross-sectional configuration of the core portion 3 at right angles to the vertical direction of the antenna is substantially oval or elliptical, but may vary somewhat along the height of the core portion.

In the bottom of the cavity which is formed interiorly in the core portion 3, there is to be disposed a contact device 5 which, in Figs. 1 and 2, is shown lifted to a position above the core portion 3 but beneath the carrier 4. The contact device 5 includes an earth sleeve 6 which is connected to the chassis of the mobile telephone. Above the earth sleeve 6, there is an anchorage portion 7 by means of which the contact device 5 is secured in the carrier portion 1. Above the anchorage portion, there is an insulator 8 and a solder pin 9, the latter serving for electric connection of the radiating element disposed on the carrier 4.

The radiating element is placed, as was mentioned above, about the core portion 3 and is secured thereon. The radiating element has a supply portion (not shown in Figs. 1 and 2) which is passed in through a vertically extending slot 10 in the circumferential surface of the core portion 3 where it is soldered in place to the solder pin 9 in the lower region of the cavity which is formed interiorly in the core portion 3.

Alternatively, the wrapped carrier 4 may be disposed interiorly in the cavity of the core portion 3 and connected to the solder pin 9 as described above. In the assembled state, the carrier 4 is thus wrapped about the core portion 3 and connects tightly to its outer circumferential surface. The antenna device further includes a protective hood 11 which is produced from a suitable plastic material, non-electrically conductive and non-magnetic, and which is snapped onto the carrier portion 1 with the aid of a rib (not shown) which is disposed interiorly in the protective hood 11 and which snaps into a circumferential groove 12 on the carrier portion 1.

It will be apparent from the foregoing that the antenna device, in the assembled state, will be a compact, outwardly smooth and gently arched device which, on its lower side, has the guide pin 2 and connection or earth sleeve 6 for connection to the mobile telephone.

Figs. 3 and 4 show two variations of the planar, approximately helical radiating element included in the device according to the present invention. This has a supply portion 13 which is inserted through the slot 10 in the core portion 3 and which has a lower end 14 in the Figures which is intended to be electrically connected to the solder pin 9 on the contact device 5.

It will be apparent from Fig. 3 that the supply portion 13 is, in its upper end, connected to an outer, straight and substantially vertical conductor 17 which is galvanically connected to a substantially straight, horizontal portion 16 via a markedly curved or angled conductor portion 18. The horizontal conductor portion 16 is, via a second, angled conductor portion 18', connected to a second approximately vertical conductor portion 17' which, in its turn, is connected in its lower end via a further angled conductor portion 18", to an approximately horizontal conductor portion 16'. An outer "turn" has thereby been described of an angular, planar and approximately square spiral or helix. The helix continues inwards in a manner which is totally analogous with that described above, and has, in the embodiment according to Fig. 3, slightly more than three "turns". The inner end of the spiral or helix terminates blind. The curved or angled conductors portions 18, 18', 18", etc., have an angle of curvature of the order of magnitude of 70-110° which depends upon the configuration of the carrier 4. The angle of curvature may be different for different angled portions in one and the same radiating element. The embodiment according to Fig. 4 follows the same principles but is produced in right-hand turn as opposed to that which applies in Fig. 3. A further difference is that the embodiment according to Fig. 4 is somewhat lower and elongate in the horizontal direction and, as a result, fills out a considerably greater part of the surface of the carrier 4. It may be expected that this larger surface extent imparts to the finished antenna a greater aperture and thereby better radiation capacity.

The above described, angular, helical radiating elements 15 are both supplied from outside at their periphery.

It has proved that radiating elements according to Figs. 3 and 4 have at least two resonance frequencies. The higher resonance frequency is in principle determined by the height of the helix, i.e. in Fig. 3 by the length of the vertical conductor portions 17 and 17'. The shorter these are, the higher will be the resonance frequency, and vice versa. The lower resonance frequency is determined by the total length of all conductor portions 16, 17, 16', 17', etc., i.e. "the total wire length included in the helix". In practice, this implies that, with a given height, the width of the helix, i.e. the length of the horizontal conductor portions 16, determines the lower resonance frequency. Analogous with that described above, it applies that the shorter these are, the higher will be the resonance frequency, and vice versa. In the embodiment according to Fig. 3, the resonance frequencies will be of the order of magnitude of 900 MHz and 1800 MHz, while, in the embodiment according to Fig. 4, it will be of the order of magnitude of 800 MHz and 1900 MHz (the Figures on a scale of 1:1). The higher level of the higher resonance frequency is because the height of the helix in Fig. 4 is slightly less than that which applies in Fig. 3. Further, the resonance frequency will naturally be affected by the plastic material in the carrier 4, but, of course, also by the material in the core portion 3 and the protective hood 11. The influence from these plastic materials entails that the resonance frequencies fall somewhat. In that the radiating element in the embodiment according to Fig. 4 has larger surface area than that which applies in the embodiment according to Fig. 3, a greater degree of efficiency for the embodiment according to Fig. 4 may be expected.

Fig. 5 shows a modified embodiment of the radiating element according to Fig. 3. That which distinguishes the two embodiments is that in the embodiment according to Fig. 5, a short circuit 19 has been added, i.e. a conductor portion which interconnects two closely adjacent conductor portions included in the radiating element with each other.

The position of the short circuit 19 in the radiating element 15 does not appreciably influence the higher resonance frequency but may be employed for finely tuning the resonance frequency in the lower frequency band. The further out in the helix the short circuit is placed, i.e. in electric terms the closer to the supply portion 13 it is located, the higher will be the resonance frequency in the lower frequency band compared with if the short circuit 19 did not exist. Conversely, the resonance frequency will be lower in the lower frequency band the further in towards the centre of the radiating element 15 the short circuit 19 is placed. In the extreme case, with the short circuit 19 displaced to a maximum inwards, the difference in resonance frequency will be close to zero compared with an identical radiating element without short circuit. If, thus, a radiating element according to Fig. 3 is dimensioned for the nominal frequency bands, the element will probably come into resonance at too low frequencies after assembly of the core portion 3 has taken place and the protective hood 11 applied. It is then possible to place a short circuit 19 in such a manner along the helix that the above-mentioned reduction of resonance frequency is compensated for.

Another argument in favour of employing a short circuit 19 resides in the fact that the outer dimensions of the antenna determine its aperture. This implies that, with large outer dimensions, i.e. large total "wire length" in the angular helix, its lower resonance frequency has a tendency to be too low. By employing the short circuit 19, the lower resonance frequency may be moved up to the correct value maintaining the same outer dimensions, and thereby maintaining the aperture. In one embodiment with a short circuit 19 in the helix, the portion of the helix located inside the short circuit may be considered as a top load for the portion of the spiral located outside the short circuit.

The embodiment according to Fig. 5 also differs from the embodiment according to Fig. 3 by the presence of a blind conductor portion 20. This conductor portion 20 is placed in the end of the outermost vertical conduction portion 17 in the radiating element 15 facing away from the supply portion 13 and is approximately at right angles to the first, vertical conductor portion 17 and may thereby be seen as an extension of the first horizontal conductor portion 18. The effect of the blind and projecting conductor portion 20 is that an optimisation takes place of the resonance in the higher frequency band so that this resonance is amplified at the same time as the band width is increased, even so far that both the DCS- and PCS-bands can be covered. The presence of the blind conductor portion 20 does not appreciably affect the resonance in the lower frequency band.

Possibly, the outermost, vertical conductor portion 17 between the supply portion 13 and the blind conductor portion 20 may be considered as a separate radiating element in the higher frequency band. In this case, the blind conductor portion 20 (possibly together with the helix proper) constitutes a top load to the radiating element in the higher frequency band.

Possibly, the first, vertical conductor portion 17 and the projecting conductor portion 20 may alternatively be considered as an angular, planar helix of less than one turn, in Fig. 5 approximately a half turn.

The embodiment according to Fig. 6 differs from the embodiment according to Fig. 4 principally in that the helix is slightly taller and narrower than is the case in Fig. 4. Further, there is a counterpart to a short circuit 19 as applies according to Fig. 5.

An outer conductor portion 16 included in the radiator element 15 is connected to both the supply portion 13 and to a blind conductor portion 21. In this embodiment, the blind conductor portion 21 has been given the form of a "square, planar helix" of somewhat less than one turn. Theoretically, this may correspond to a "helical antenna" which is set to the higher frequency band. Possibly, it is also conceivable that the blind conductor portion 21 is analogous with the above-described blind conductor portion 20.

The embodiment according to Fig. 7 differs from the embodiment according to Fig. 4 by the presence of both a short circuit 19 and a blind conductor portion 20. However, in this Figure, the short circuit unites three conductor portions with each other.

In the embodiment according to Fig. 8, the blind conductor portion 21 is connected to the angular helix a half a turn in on it, i.e. after the second straight conductor portion 16 which, in this case, is the first horizontal conductor portion. The blind conductor portion 21 is L-shaped and connects to the periphery of the helix so that it extends along the first horizontal conductor portion 16, round the corner 18 between this and the first vertical conductor portion 17 and at least partly along it.

Also in this embodiment, there is a short circuit 19 which is placed a maximum distance in towards the centre of the helix.

DESCRIPTION OF ALTERNATIVE EMBODIMENTS

In the foregoing, it has been assumed that the short circuit 19 is placed on the same side of the carrier 4 as all other conductor portions, and that it consists of the same metal layer as the conductor portions. However, it is possible, instead of a galvanic short circuit, to employ a capacitative short circuit which, in such an event, is placed on the opposite side of the carrier 4.

A capacitative short circuit 19 may also be located on the same side of the carrier 4 as the straight conductor portions 16, 16', 16"... 17, 17', 17"... etc., and be realised in that closely adjacent conductor portions in the region of the capacitative short circuit 19 have slight mutual spacing. In the alternatives in the short circuit 19, those portions of the radiating element 15 which are located inside the short circuit may be given a configuration deviating from the helical configuration. The portions of the radiating element located inside the short circuit 19 function, in this context, as a top load for the radiating element in the lower frequency band.

The portion of the angled helix located inside the short circuit 19 may possibly be omitted.

In the foregoing, it has been described how the carrier 4 is rolled or wrapped externally around a core or body portion 3. As an alternative, the carrier 4 may, in the more or less wrapped-up state, be disposed interiorly in a cavity or recess in the core portion. The cavity may be cylindrical, conical etc., and may be of circular, oval, elliptical or otherwise configured cross section.

In yet a further embodiment of the present invention, the carrier 4 is planar as shown on the Drawings. In this alternative, it may be secured on a planar core portion or may even be secured on the inside of the hood with which the mobile telephone is provided.

Claims

WHAT IS CLAIMED IS:

1 . An antenna device for several frequency bands, comprising a radiating element (15) which, in rough outline, is formed as a planar helix and radiating in at least two separate and discrete frequency bands, the element being disposed on a carrier (4) of insulating material, the radiating element (15) including a number of substantially straight conductor portions (16, 16', 16"..., 17, 17', 17"...) which are galvanically united with one another by the intermediary of markedly curved or angular conductor portions (18, 18', 18") whereby they together form an angular helix, characterised in that two adjacent conductor portions are interconnected (19) with one another.

2. The antenna device as claimed in Claim 1, characterised in that the connection (19) between the adjacent conductor portions is galvanic and is located on the same side of the carrier (4) as the conductor portions.

3. The antenna device as claimed in Claim 1, characterised in that the connection (19) between the conductor portions is substantially capacitative and is located on the side of the carrier (4) facing away from the conductor portions.

4. The antenna device as claimed in Claim 1, characterised in that the connection (19) between the conductor portions is substantially capacitative and is realised in that the distance between the conductor portions is slight.

5. The antenna device as claimed in any of Claims 1 to 4, characterised in that a supply portion (13) is connected to an outer, peripheral conductor portion in the radiating element (15).

6. The antenna device as claimed in any of Claims 1 to 5, characterised in that a freely terminating conductor portion (20, 21) and a supply portion (13) are connected to an outer conductor portion in the radiating element (15).

7. The antenna device as claimed in Claim 6, characterised in that the freely terminating conductor portion (20, 21) and the supply portion (13) are connected to the outer conductor portion a distance from one another.

8. The antenna device as claimed in Claim 6, characterised in that the freely terminating conductor portion (21) and the supply portion (13) are connected to the outer conductor portion at the same point.

9. The antenna device as claimed in any of Claims 6 to 8, characterised in that the freely terminating conductor portion (21) is a second radiating element which is substantially set to the highest of the two frequency bands to which the first radiator element (15) is set.

10. The antenna device as claimed in any of Claims 1 to 9, characterised in that the curved or angled portions (18, 18', 18") have an angle of curvature of the order of magnitude of 70-110°.

11. The antenna device as claimed in any of Claims 1 to 10, characterised in that the carrier (4) with the conductor portions (16, 16', 16"..., 17, 17', 17"...) is wrapped or rolled about a core portion (3) of insulating, nonmagnetic material.

12. The antenna device as claimed in any of Claims 1 to 10, characterised in that the carrier (4) with the conductor portions (16, 16', 16"..., 17,17', 17"...) is, in the wholly or partly wrapped-up state, disposed in a correspondingly configured cavity in a carrier of insulating and non-magnetic material.

13. The antenna device as claimed in any of Claims 1 to 10 characterised in that the carrier (4) with the conductor portions (16, 16', 16"..., 17,17',

17"...) is substantially planar.