WO1999027607A2

WO1999027607A2 - Antenna structure

Info

Publication number: WO1999027607A2
Application number: PCT/FI1998/000924
Authority: WO
Inventors: Anne Isohätälä; Petteri Annamaa
Original assignee: Lk-Products Oy
Priority date: 1997-11-25
Filing date: 1998-11-25
Publication date: 1999-06-03
Also published as: FI974316A0; FI974316A; WO1999027607A3; AU1240099A

Abstract

The invention relates to frame and antenna structures of mobile stations, particularly to an antenna structure inside the cover of a mobile station. In the structure according to the invention the radiator of the antenna structure and the frame structure form an integral body. The radiator is formed already during the frame structure manufacturing step as a projection of the frame structure, or the radiator is partly cut out from the frame structure and bent into the desired final shape. The material and the manufacturing method of the frame structure according to the invention can be selected according to the requirements of the application in question, and the invention is not limited to any particular material or manufacturing method. Preferably the material of the structure according to the invention is a metal or a metal alloy, for instance aluminium or an aluminium alloy. The structure according to the invention can also be made of plastic and other dielectrics, if the radiator is coated with an electrically conducting layer in order to obtain the electrical function. The structure according to the invention can be advantageously formed e.g. by extrusion or casting, or by some other corresponding technique.

Description

Antenna structure

OBJECT OF THE INVENTION

The invention relates to frame and antenna structures of mobile stations, particularly to antenna structures inside the cover of a mobile station.

BACKGROUND OF THE INVENTION

Figure 1 shows a typical prior art PIFA antenna structure (planar inverted-F antenna), which comprises conductive surfaces separated by an air gap or some other dielectric, whereby one of the surfaces acts as the ground plane 18 and the other as the radiating element 8. At one end the radiating element is shorted to the ground plane by a short circuit strip 17 and at the other end it is open. The antenna is fed by a feed line 9, for instance in the manner shown in figure 1. The sum of the height of the antenna and the length of the radiating element 8 is of the order of one quarter wave-length of the resonance frequency, which determines the operating frequency of the antenna. The short circuit means 17 can be realised in many different ways; it may be for instance a strip with the width of the whole side, or only a narrow pin. A narrower short circuit allows the reduction of the resonance frequency without increasing the physical size, but at the same time it reduces the impedance bandwidth of the antenna. The operating frequency of the antenna can also be reduced by making a gap in the radiating element 8, whereby the gap makes the antenna electrically longer. The input impedance of the antenna can be adapted to have a desired value by dimensioning a suitable distance between the feeding point and the short circuit. The distance between the radiator and the ground plane has a strong effect on the radiation characteristics of the antenna. A PIFA antenna is well suited for a multipath environment, because it is sensitive both to vertically and horizontally polarised electromagnetic waves.

The patent application publication WO-9524745 presents a PIFA solution, where a dielectric material coated with an electrically conducting layer is used as the material of the antenna structure in order to obtain mechanical stability. However, the use of a dielectric material results in a reduced impedance bandwidth and a reduced radiation efficiency. Thus a PIFA antenna most preferably is air insulated. Further, the structure presented in the publication is difficult to manufacture, the grounding requires a RF gasket which is inconvenient to install, and coating must be mechanically removed in order to create the conductor patterns. The publication EP-0 484 454 presents an air insulated PIFA antenna solution. However, the solution presented in the publication has a mechanical structure which is not sufficiently durable. Regarding a reliable operation of the antenna it is very important that the air gap between the ground plane and the radiator is kept con- stant. The publication further mentions that the radiator of the antenna is outside the plastic cover of the mobile station, whereby it is very sensitive to changes in the electromagnetic characteristics of the antenna caused by the user's hand or other adjacent subjects.

BRIEF DESCRIPTION OF THE INVENTION

The object of the invention is to realise a frame and antenna structure which is as robust as possible. An object of the invention is also to realise a frame and antenna structure, the manufacture of which is as simple as possible.

The objects are reached by forming the antenna radiator during the manufacture of the frame structure, or by realising the antenna radiator as an integral part of the frame structure. The ground plane and the antenna feed pin can also be realised as a part of the frame structure. The ground plane can also be realised on a separate component, such as a printed circuit board, which is fastened to the frame structure.

The frame structure according to the invention is characterised in what is presented in the characterising clause of the independent claim regarding the frame structure. The invention further relates to a mobile station, which is characterised in what is presented in the characterising clause of the independent claim regarding the mobile station. Further preferred embodiments of the invention are presented in the dependent claims.

In the antenna structure according to the invention the radiator and the frame struc- ture of the device form an integral body. The radiator is formed already during the frame structure manufacturing step as a projection of the frame structure, or the radiator is partly cut out from the frame structure and bent into the desired final shape. The material and the manufacturing method according to the invention can be freely selected according to the requirements of the application in question, and the inven- tion is not limited to any specific material or manufacturing method. The material of the structure according to the invention is preferably a metal or a metal alloy, for instance aluminium or some aluminium alloy. The structure according to the invention can also be formed from plastic or another dielectric material, if the radiator is coated with an electrically conducting layer in order to obtain the electrical function. The structure according to the invention can advantageously be formed for instance by extrusion or by casting, or by any other corresponding technique.

In the solution according to the invention the frame structure and the antenna of the mobile station are formed with the aid of one integral body. A solution of this type provides substantial advantages. It is simpler to manufacture one component than to manufacture and join two separate components. An integral structure has fewer joints and parts than separate components, whereby the failure probability will be lower. The structure is simple, light and mechanically durable. Due to the durability of the structure the air gap will be kept constant, whereby air can be used as the di- electric of the antenna structure, whereby the impedance bandwidth and the radiation efficiency will be better than by using a dielectric substrate. Moreover, an internal antenna in a mobile station is not so sensitive to the effects of adjacent external subjects, such as the user's hand and/or head, as external antenna solutions are.

With the aid of the solution according to the invention the antenna can be realised within the cover of the mobile station. Then the antenna will not hinder the use of the mobile station, it will not get entangled in clothes, and there is no need to take particular care of it. Also, an internal antenna does not impose as high requirements on the mechanical strength as an external one, which often also must act as a shock absorber if the telephone is dropped. In final products sold to consumers the appear- ance is also a very important factor, which must be observed in the design of an external antenna, which again increases the design and manufacturing costs caused by the antenna. The internal antenna solution according to the invention reduces the design and manufacturing costs also in this respect. Further, the antenna structure according to the invention is directional, and when it is suitable positioned in the mobile station it will direct the radiation power away from the user, which reduces unnecessary power loss. This again reduces the power consumption of the mobile station, which extends the operating time of the mobile station with one battery charging operation.

BRIEF DESCRIPTION OF THE FIGURES

Below the invention is described with the aid of some embodiment examples with reference to the enclosed figures, in which

Figure 1 shows a prior art PIFA antenna structure,

Figure 2 shows an antenna and cover structure according to a first preferred em- bodiment of the invention,

Figure 3 shows a cross section of the structure in figure 2,

Figure 4 shows a cross section of a second preferred embodiment of the invention,

Figure 5 illustrates the embodiment of figure 4,

Figure 6 shows a cross section of a third preferred embodiment of the invention,

Figure 7 illustrates the embodiment of figure 6, and

Figure 8 shows a cross section of a fourth preferred embodiment of the invention.

The same reference numerals and markings are used for corresponding parts in the figures.

DESCRIPTION OF SOME PREFERRED EMBODIMENTS OF THE

INVENTION

Figure 2 shows an antenna and frame structure according to a preferred embodiment of the invention. The figure shows the frame 1, the antenna radiator 8 and the device printed circuit board 6 of a mobile station or of another device utilising high fre- quency radio communication. The frame structure 1 and the radiator 8 form a single integral component. The ground plane 18 of the antenna structure is formed on the printed circuit board 6 with the aid of an electrically conducting pattern. The feed line 9 connects the radio frequency signals from the feed conductor 19 on the printed circuit board to the antenna radiator 8. In this embodiment the feed line 9 can be advantageously realised as a projection of the single component formed by the radiator and the frame structure. The feed line can also be realised in other ways, for instance with the aid of a conductor soldered between a separate printed circuit board and the radiator. The cross section of the structure along the line A - B is shown in figure 3.

Figure 3 illustrates the structure of the embodiment in figure 2, more particularly the cross section of the structure along the line A - B. The figure shows the device's printed circuit board 6, the feed line 9 and the antenna radiator 8 and the frame structure 1 forming the integral body, whereby the frame structure includes partitions 5 supporting the printed circuit board 6. In this embodiment the feed line 9 can be realised as a part of the integral body forming the radiator and the frame structure. Figure 4 illustrates a second preferred embodiment of the invention. In this embodiment the radiator 8 of the antenna structure is in a different plane than the frame structure 1, slightly outside the frame structure. A radiator of this kind can be formed in the frame structure for instance after the manufacture by cutting a groove corresponding to the edges of the radiator and by bending the radiator outside the frame structure. However, the invention is not limited to an embodiment of this kind, but the frame structure formed by the radiator 8 and the frame structure 1 shown in figure 4 can be made also in one manufacturing step, for instance by casting. The figure also shows the device's printed circuit board 6, the feed line 9 and a separating partition 5 of the frame structure supporting the printed circuit board 6.

Figure 5 is a perspective view illustrating the embodiment of figure 4. The figure shows the frame structure 1 and the radiator 8 as a projection of the frame structure. The cross section shown in figure 4 represents the line A - B in figure 5.

Figure 6 illustrates a third preferred embodiment of the invention. In this embodi- ment the radiator 8 is substantially in the same plane as the side of the frame structure 1. The frame structure 1 has a recess at the position of the radiator 8. In this embodiment the ground plane is preferably formed on the printed circuit board 6. The figure also shows the feed line 9 and a partition 5 supporting the printed circuit board 6.

Figure 7 is a perspective view illustrating the embodiment of figure 6. The figure shows the frame structure 1 and the radiator 8 as a projection of the frame structure. The cross section shown in figure 6 represents the line A - B in figure 7.

Figure 8 shows the cross section of a fourth preferred embodiment of the invention. In this embodiment the side of the frame structure 1 acts as the ground plane of the antenna structure. According to the desired material and the manufacturing technique the radiator 8 can be bent for instance into the position shown in figure 8. In this embodiment there is a hole 9' for the feed line 9, so that the feed line can be directed through this hole from the printed circuit board 6 to the radiator 8.

The antenna structure according to the invention is very robust and durable. Further the antenna structure according to the invention is simple to manufacture, whereby the number of required manufacturing steps is lower than in prior art solutions.

The figures of this application show different exemplary frame structure solutions. A mobile station, where the antenna and frame structure solution according to the invention is applied, can have a separate protecting cover in addition to the frame structure 1, whereby the radiator according to the embodiment of figure 8 can be completely within such a protecting cover. In the embodiment of figure 8 the battery of the mobile station can be located for instance on the same side of the frame structure as the radiator 8, whereby the radiator 8 will not form a projection in the appearance of the mobile station which would be visible outside the mobile station.

Although we above described how the antenna and frame structure according to the invention is applied in a mobile station, the invention is not exclusively limited to an embodiment of this type. The antenna and frame structure according to the invention can also find application in other radio equipment, such as radio modems and small- sized, wall-mounted base stations of intercommunicating systems or mobile communication systems, and for instance in wireless data acquisition terminals.

Above the invention was described with reference to its preferred embodiments, but it is obvious that the invention can be modified in many different ways in accor- dance with the inventive idea defined in the enclosed claims.

Claims

1. A frame structure (1), characterised in that it comprises an antenna radiator (8), which forms an integral body with the frame structure.

2. A frame structure according to claim 1, characterised in that it forms the ground plane of the antenna structure.

3. A frame structure according to claim 1, characterised in that it comprises an antenna feed line (9), which is formed by the same integral body as the frame structure (1) and the radiator (8).

4. A frame structure according to claim 1, characterised in that it is manufac- tured of an aluminium alloy.

5. A frame structure according to claim 1, characterised in that it is manufactured of plastic and that at least the radiator (8) is coated with an electrically conducting material.

6. A mobile station having a frame structure (1), characterised in that it com- prises an antenna radiator (8), which forms an integral body with the frame structure.

7. A mobile station according to claim 6, characterised in that the frame structure forms the ground plane of the antenna structure.

8. A mobile station according to claim 6, characterised in that it comprises a feed line (9), which is formed by the same integral body as the frame structure (1) and the radiator (8).