EP1629566A1

EP1629566A1 - Contact arrangement for a planar antenna

Info

Publication number: EP1629566A1
Application number: EP04735249A
Authority: EP
Inventors: Matti Niemi; Jarmo Soinsaari
Original assignee: Pulse Finland Oy; LK Products Oy
Current assignee: Pulse Finland Oy
Priority date: 2003-06-04
Filing date: 2004-05-28
Publication date: 2006-03-01
Also published as: WO2004109847A1; FI20030834A0; FI115870B; FI20030834A; CN1799166A

Abstract

An arrangement for coupling separate spring contacts to the radiating plane of the antenna of a radio device. As a radiator (320) of the antenna is used a conductor foil, which is fastened on the upper surface of the dielectric frame (350) of the antenna. The feed and short-circuit of the radiator are preferably arranged by means of pogo pins (330), which are pushed down into the holes in the frame before the fastening of the radiator. Each hole is shaped, regarding its height and inner surface such that the pin remains steadily in the hole with its upper end towards the radiator. The reliability of the galvanic contact is improved by a dielectric assuring element (360), which is pressed against the radiator from above. The assuring element is mechanically locked in place. The frame with the attached parts is installed in place above the circuit board of the radio device, whereupon the lower ends of the pogo pins are coupled by spring force galvanically against the contact surfaces on the circuit board.

Description

Contact arrangement for a planar antenna

The invention relates to an arrangement intended especially for internal planar antennas of small-sized radio devices for connecting separate spring contacts to the radiating plane of the antenna. The invention also relates to a radio device with an antenna arrangement according to the invention.

The internal antennas of small-sized portable radio devices, such as mobile stations, are most often planar antennas of the PIFA type (Planar Inverted F- antenna), because they provide good electric properties in view of the size. A PIFA comprises a radiating plane and a ground plane superimposed, and feed and short-circuit conductors connected to the radiating plane. These conductors generally function as contacts at one end, i.e. they press by spring force against a conductor surface that functions as a counter-contact. In mass products, such as mobile stations, it is essentially important to keep the production costs as low as possible. With respect to mechanical parts, including antennas, this means aiming towards a simple structure, which does not require a large number of manufacturing steps and an expensive production line.

One simple solution in the manufacture of a PIFA is to make the radiating plane and the feed and short-circuit conductors of a conductor plate as one monolithic piece. The feed and short-circuit conductors comprise a part that functions as a spring and runs in the direction of the radiating plane, and a shank part that runs downward from it towards the ground plane. The actual contact is at the lower end. The conducting plate must be made of sheet metal with sufficient rigidity to provide the pressing force required for a reliable touch at the contacts. This solution has the drawback that it requires a production line for sheet metal handling, which is relatively expensive.

The radiator can also be manufactured of metal foil, which offers saving of material and easier workability as compared to sheet metal. However, for the reason mentioned above, in that case the feed and short-circuit conductors cannot be on a monolithic piece with the radiator, but they must be separate. In practice, they can be so-called pogo pins. A pogo pin is a small, two-part telescopic pipe with a contact surface at both ends and a coil spring inside. When a pogo pin is compressed in the direction of its axis, it exerts an opposite force that pushes its parts away from each other. Fig. 1 shows an example of a known antenna that uses a foil radiator and pogo pin type feed and short-circuit conductors. In the cross-section figure is seen a circuit board 101 of a radio device, wherein the conducting layer on its upper surface functions as a ground plane 110 of the antenna. Above the ground plane there is a foil-like radiating plane 120, which is fastened on the upper surface of the dielectric frame 150 of the antenna by glueing, for example. The frame includes side walls that abut the circuit board at their lower edges, and a "roof". The pogo pin 130 that functions as the feed conductor of the antenna is fastened to the circuit board 101 with a bearing flange 105. The upper end of the pin 130 is in the loose hole in the roof of the frame 150, and presses by spring force against the radiating plane at its feed point FD. The short-circuit conductor between the radiating plane and the ground plane is implemented with a similar pogo pin. This is not shown in Fig. 1.

The structure shown in Fig. 1 has the drawback that fastening the pogo pins to the circuit board of the radio device causes considerable costs in production. In addition, the reliability of the contact between the radiating plane and the pogo pins leaves to be desired.

The purpose of the invention is to reduce the above mentioned drawbacks of the prior art. The contact arrangement according to the invention is characterized in what is set forth in the independent claim 1. The radio device according to the invention is characterized in what is set forth in the independent claim 12. Some preferred embodiments of the invention are set forth in the dependent claims.

The basic idea of the invention is the following: As a radiator of the antenna is used a conductor foil, which is fastened on the upper surface of the dielectric frame of the antenna. The feed and short-circuit of the radiator are preferably arranged by means of pogo pins, which are pushed down to the holes in the frame from above before the fastening of the radiator. Each hole is shaped, regarding its height and inner surface, such that the pin remains steadily in the hole with its upper end against the radiator. The reliability of the galvanic contact is improved by a dielectric assuring element, which is pressed against the radiator from above. The assuring element is locked in place e.g. by means of mechanic shaping implemented in the assuring element and in the frame. The frame with the attached parts is installed above the circuit board of the radio device, whereupon the lower ends of the pogo pins are coupled by spring force galvanically against the contact surfaces on the circuit board. The invention has the advantage that the assembly of an antenna component that comprises a radiator and feed and short-circuit conductors does not require a production line for sheet metal handling and is otherwise simple as well. The assembly can even be carried out manually. In addition, the invention has the advantage that the coupling of the feed and short-circuit conductors to the radiator is more reliable than in corresponding, known antennas. Furthermore, the invention has the advantage that the radiating plane can also be worked after the assembly of the antenna component for tuning the antenna or for separating a parasitic element from it, for example.

In the following, the invention will be described in more detail. Reference will be made to the accompanying drawings, in which

Figure 1 shows an example of a prior art contact arrangement for a planar antenna,

Figure 2 shows the principle of the contact arrangement of a planar antenna according to the invention,

Figure 3 shows an example of a contact arrangement according to the invention,

Figures 4a, bshow another example of a contact arrangement according to the invention,

Figures 5a, bshow an example of an antenna component according to the invention, and

Figure 6 shows an example of a radio device according to the invention.

Figure 1 was already dealt with above in connection with the description of the prior art.

In Fig. 2, the antenna structure according to Fig. 1 has been changed so that from it appears the principle of the invention. The structure comprises a circuit board 201 of a radio device, a ground plane 210, a dielectric frame 250 of the antenna with a foil-like radiator 220 on its upper surface, like in Fig. 1. The pogo pin 230 that functions as the feed conductor of the antenna is now fastened to the frame of the antenna instead of the circuit board. For this purpose, a thickened part 251 has been formed in the frame, with . a hole shaped so that the pin placed in the hole stays steadily in place. The upper end of the pin 230 presses against the lower surface of the radiator at the designed feeding point of the antenna. In order to improve the reliability of the feed point coupling, pressure is exerted to the radiator from above the feed point by means of a assuring element that belongs to the structure. This element is not shown in Fig. 2. The lower end of the pin 230 presses by spring force against the circuit board 201. On the circuit board there is a conductor pad that functions as a counter-contact, from which the connection continues to the antenna port AP of the radio device. The short-circuit conductor between the radiator and the ground plane is also implemented with a similar arrangement.

Fig. 3 shows an example of the implementation of an arrangement according to the invention in more detail. The drawing is a cross-section of the antenna component at one pogo pin 330. It shows a part of the dielectric frame 350 of the antenna. The pin 330 has a lower part 331 and an upper part 332 within each other and axially movable in relation to one another. The lower part is a cylinder with its lower end slightly rounded. In this example, the upper part 332 includes a cylindrical middle part of the pin, which has a larger diameter than the lower part, and above the middle part second cylindrical part, which has a larger diameter than the middle part. The frame 350 includes a thickened part 351 with a vertical hole for the pin 330. The shape of the hole corresponds to the shape of the pin so that when the pin is pushed with its lower end first to the hole from above, only the upper surface of said second cylindrical part, i.e. the upper surface of the whole pin remains above the upper surface of the frame. The frame, which is narrowed downwards, stops the pin at that point, thus preventing it from falling through the hole. The height of the thickening 351 is smaller than the height of the pin, and hence the lower part 331 of the pin is partly protruding from the hole of the frame.

On the upper surface of the frame, there is a metal foil 320, which functions as the radiator, like in Figures 1 and 2. The radiator 320 is disposed and fastened when the pin 330 is in place in the hole of the frame. Thus the radiator reaches over the pin and contacts the upper surface of the pin. The upper surface is slightly convex to improve the contact. Actually, the reliability of the contact is improved by the assuring element 360. In this example, the locking element is fastened to the frame 350 with a snap coupling. For this purpose, there is an upward protruding plug 352 beside the pin hole, with a cylindrical neck part and a wider part above it, shaped like a truncated cone. The assuring element has an hole 361 , which is narrower at its lower end so that the flange-like edge formed in that way fits exactly around the neck part. When the assuring element has been pressed in place by using sufficient force, the widening of the plug 352 shaped like a truncated cone prevents the assuring element from rising upwards again. In other parts the assuring element is shaped so that it presses the radiator 320 against the upper surface of the pin 330.

Naturally, there can be a lot of variation in the shape and fastening means of the locking element. Figures 4a and 4b present an alternative solution. In Fig. 4a the structure is shown in cross-section and in Fig. 4b from above. The upper surface of the dielectric body 450 of the antenna has two extensions in the form of straight slide bars 452 and 453, on both sides of the contact to be secured. There are grooves on the sides of the slide bars on the side of the space between them, designed to receive the projecting parts on two sides of the assuring element 460, the projecting parts having the same length as said sides of the assuring element. In that case, when the assuring element is pushed with its end first to the space between the slide bars, it is fastened in place mechanically. The pieces are dimensioned so that the assuring element 460 presses the radiator 420 on the upper surface of the frame 450 against the upper surface of the pogo pin 430. The radiator must go round the slide bars 452 and 453, and therefore it forms a fly between the slide bars.

Other ways of fastening the locking element are e.g. glueing and working of the material by clenching or ultrasound.

Figures 5a and 5b show an example of a complete antenna component according to the invention. In Fig. 5a, the parts of the antenna component 500 are apart from each other and upside down compared to Fig. 5b. The foil-like radiator 520 has been cut to the shape of the area reserved for it on the surface of the dielectric frame 550. The antenna component is intended to be a part of a PIFA, and therefore it has a feed conductor 530 and a short-circuit conductor 540, which are implemented by pogo pins. There is a shared assuring element 560 for these pins. The holes for the feed and short-circuit conductors are seen in the frame of the antenna, as well as the fastening plug 552 of the assuring element on the opposite side of the frame.

Fig. 5b shows the complete antenna component 500. Its assembling is simple. The pogo pins are placed in their holes, and the radiator is fastened by means of an adhesive coating in the metal foil, for example. At first, the adhesive material must be removed from the areas that remain under the assuring elements. Then the assuring element is snapped in place, and after that a single-band component would be ready. In this example, the component has been designed for a dual- band antenna, which has an operating band in the frequency ranges of 0.9 GHz and 1.8-1.9 GHz. For this purpose, two non-conductive slots have been machined in the radiator by laser, for example, so as to form, as seen from the point of the short-circuit conductor 540, a first conductor branch 521 , a second, shorter conductor branch 522 and a separate parasitic element 523. The lower operating band is implemented by the first conductor branch and the upper operating band by the second conductor branch and the parasitic element. For the short-circuit of the parasitic element 523, the structure further comprises a third pogo pin 582 shown in Fig. 5a and a second assuring element 581 for the coupling of pin 582.

The antenna frame 550 of Figures 5a, 5b is designed to be part of the rear part of a mobile phone cover, and therefore its outer surface is slightly curved and rounded on the edges. First of all, the frame has recesses for the assuring elements according to the invention so that their outer surfaces are disposed level with the outer surface of the frame without any protrusions. In the final product, the component can then be covered with a thin and even protective layer.

Fig. 6 shows an example of a radio device according to the invention. The radio device is shown from the back side. The upper part 650 of its back cover is the antenna frame that belongs to the arrangement according to the invention.

In this description and the claims, the qualifiers "upper", "lower" and "vertical" refer to the positions of the antenna and its parts shown in Figures 1 , 2, 3, 4a and 5b, and they have nothing to do with the position in which the device is used.

Examples of a contact arrangement according to the invention have been described above. The invention is not limited to them alone; the spring contact can also be a suitably cut and bent conductor strip instead of a pogo pin. The structure according to the invention can be implemented in different ways within the limits set by Claim 1.

Claims

1. An arrangement for coupling separate spring contacts to a planar radiator of an antenna of a radio device for the feed and matching of the antenna, the antenna having a dielectric frame and the radiator being a conductor foil fastened to the upper surface of the frame, characterized in that the spring contacts (230; 330; 430; 530, 540) are supported to holes in the frame (250; 350; 450; 550) in a fixed position in relation to the frame so that their upper ends touch the radiator (220; 320; 420; 520), and above the radiator there is a dielectric assuring element (360; 460; 560) pressing the radiator towards an end of at least one spring contact to improve the reliability of the galvanic coupling between the radiator and the contact.

2. An arrangement according to Claim 1 , characterized in that said spring contacts are pogo pins.

3. An arrangement according to Claim 2, characterized in that the area of cross-section of said pogo pins decreases from upper end towards lower end of the pin (330; 530; 540), and the area of cross-section of said holes decreases in the same way from the upper end towards the lower end of the holes in order to keep the pin disposed in the hole firmly in place.

4. An arrangement according to Claim 3, characterized in that there is a thickening in the frame of the antenna for said holes, the height of the thickening being less than the height of said pins, in order to make the lower end of the pin visible for connections to be made against the contact surfaces in the radio device.

5. An arrangement according to Claim 1 , characterized in that said assuring element (360; 560) is fastened in place by means of mechanical shapings (352;

552) of the element and the frame.

6. An arrangement according to Claim 5, characterized in that said mechanical shapings comprise a snap coupling.

7. An arrangement according to Claim 1 , characterized in that the frame of the antenna comprises a part intended for machining in order to fasten said assuring element in place.

8. An arrangement according to Claim 1 , characterized in that there is a recess in the frame (550) of the antenna for said assuring element (560) so that outer surface of the locking element installed in place is level with the outer surface of the frame.

9. An arrangement according to Claim 8, characterized in that the frame of the antenna is part of the cover of the radio device.

10. An arrangement according to Claim 1 , characterized in that said assuring element (560) presses the radiator against the head of both the spring contact functioning as a feed conductor (530) and the spring contact functioning as a short-circuit conductor (540).

11. An arrangement according to Claim 1 , characterized in that a part of the radiator (520) is separated as a parasitic radiation element (523), and the arrangement further comprises a third spring contact (582) for the short circuit of the parasitic radiation element, and a second locking element (581) for improving the reliability of the galvanic coupling between the parasitic radiation element and the third spring contact.

12. A radio device (RD), an antenna of which has an arrangement for coupling separate spring contacts to a planar radiator of the antenna for the feed and matching of the antenna, the antenna having a dielectric frame (650) and the radiator being a conductor foil fastened on the upper surface of the frame of the antenna, characterized in that the spring contacts are supported to holes in the frame in a fixed position in relation to the frame so that their upper ends touch the radiator, and above the radiator there is a dielectric assuring element pressing the radiator towards an end of at least one spring contact to improve the reliability of the galvanic coupling between the radiator and the contact.