Abstract:
A radiating antenna element intended to be used in small-sized radio devices, and a radio device having an antenna element according to the invention. The antenna element is part of the covers of a radio device. The antenna element may be conductive throughout, or it may comprise a dielectric portion and a conductive portion, which constitute a single integral component. The radiating portion of the antenna element is relatively large, e.g. in a foldable phone ( 20 ) the antenna element ( 200 ) may comprise the whole cover of a foldable part ( 21 ) except for the front side. The radiating element is advantageously fed electromagnetically through a feed element. As the radiating element is relatively large and is located on the outer surface of the device, the radiation characteristics of the antenna are good, and the space required by the antenna inside the device is relatively small.

Description:
The invention relates to a radiating antenna element intended to be used in small-sized radio devices in particular. The invention also relates to a radio device having an antenna element according to the invention. 
     BACKGROUND OF THE INVENTION 
     In antenna design, the space available is an important factor. It is relatively easy to make an antenna of good quality if there are no size limitations. In small-sized radio devices, such as mobile phones, an antenna which protrudes outside the covers of the device is tried to be avoided, for convenience. This means that as the devices become smaller and smaller, the space available for the antenna becomes smaller, too, making antenna design even more challenging. 
     Internal antennas in mobile terminals usually have planar structures: The antenna comprises a radiating plane and a ground plane parallel thereto. The electrical characteristics of a planar antenna, such as bandwidth and antenna gain, depend on the distance between said planes, among other things. As mobile terminals become smaller in the direction of thickness, too, this distance inevitably becomes shorter, whereby the electrical characteristics become worse. Particularly this problem concerns foldable mobile phone models, as their folding parts are relatively flat and thin. Therefore, antennas in foldable models are in practice protruding antennas. 
     Available space can be used more efficiently in a radio device by fabricating the radiating element of the antenna within the cover of the device or as part of the cover, which is known as such.  FIG. 1  shows an example of a radiating antenna element known from application FI20012219 which element is intended to be part of a cover of the radio device. Strictly speaking the planar bottom  110  of the antenna element  100  and its curved rim  120  are included in the cover of the device. The rim is found on three sides of the bottom, corresponding to an end of the radio device and the side surfaces at that end. When mounted, the element  100  is a radiating element in a planar inverted F antenna (PIFA), where an antenna feed conductor and short-circuit conductor are connected to the element. Antenna feed point  101  and short-circuit point  102  are marked as broken-line circles on the bottom  110 . When the antenna element  100  is pressed into its place in the radio device the feed and short-circuit conductors make galvanic contact with points  101  and  102 . Starting from the edge of the element  100  there is a slot  105  which makes a rectangular turn such that the element, viewed from the short-circuit point  102 , is divided into two branches of different lengths. The antenna is thus a dual-band antenna. On both sides of the portion of the slot  105  which starts from the edge of the element there is a capacitance plate perpendicular to the bottom. A first capacitance plate  131  is located at the electrically outermost end of the longer branch of the element, and a second capacitance plate  132  at the electrically outermost end of the shorter branch. Both the mutual capacitance of the capacitance plates and their capacitances with the ground plane (not shown) increase the electrical lengths of the radiating branches. This reduces the size of an antenna operating in particular frequency bands. Furthermore, the antenna element  100  includes, protruding from the surface of the bottom  110 , a support leg  141  and a ridge  142  which resembles a wide U and adds to the mechanical strength of the antenna element. For attachment of the antenna element it further comprises locking parts  151  and  152 . All parts may be included in a single extrusion piece. 
     A disadvantage of the element shown in  FIG. 1  is that its parts have to have certain electrical sizes, which limits the design of the element. Moreover, the characteristics of the antenna using the element may be inadequate in flat and thin radio devices. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to reduce said disadvantages associated with the prior art. An antenna element according to the invention is characterized in that which is specified in the independent claim  1 . A radio device according to the invention is characterized in that which is specified in the independent claim  17 . Some preferred embodiments of the invention are specified in the other claims. 
     The basic idea of the invention is as follows: A radiating antenna element is part of the covers of a radio device. The antenna element may be conductive throughout or it may comprise a dielectric portion and conductive portion, which together constitute a single component. The radiating part of the antenna element is relatively large: in a foldable phone, for example, it advantageously comprises the whole cover of one folding part with the exception of the front side. The radiating element is fed electromagnetically through a feed element or galvanically. 
     An advantage of the invention is that a cover element of a radio device, which is required in any case, can be used as a radiator. Another advantage of the invention is that as the radiating element is relatively large and is located on the outer surface of the device, the radiation characteristics of the antenna are better than those of a radiator located more internally in the device. A further advantage of the invention is that the space reserved by the antenna within the device is smaller than in corresponding prior-art antennas. A further advantage of the invention is that it reduces the production costs of the radio device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be now described in detail. Reference will be made to the accompanying drawings in which 
         FIG. 1  shows an example of an antenna element according to the prior art, 
         FIGS. 2   a,b  show an example of an antenna element according to the invention, 
         FIGS. 3   a,b  show a second example of an antenna element according to the invention, 
         FIGS. 4   a,b  show a third example of an antenna element according to the invention; 
         FIGS. 5   a,b  show a fourth example of an antenna element according to the invention, 
         FIG. 6  shows a fifth example of an antenna element according to the invention, 
         FIG. 7  shows a sixth example of an antenna element according to the invention and an example of its feed, 
         FIG. 8  shows a seventh example of an antenna element according to the invention, 
         FIG. 9  shows a second example of the feed of an antenna element according to the invention, 
         FIG. 10  shows a third example of the feed of an antenna element according to the invention, 
         FIG. 11  shows an example of the conductive pattern of an antenna element according to the invention, 
         FIG. 12  shows a second example of the conductive pattern of an antenna element according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 2   a  and  2   b  show an example of a radiating antenna element according to the invention. The antenna element  200  belongs to a radio device depicted in  FIG. 2   a  which in this example is a foldable communication device  20 . The communication device has a first part  21  and a second part  22  which can be turned with respect to one another around a hinge located between them.  FIG. 2   b  shows just the antenna element  200 . This is a single conductive piece constituting the back side and relatively narrow lateral sides and the upper end side of the cover of the first part  21 . It may be made of aluminum by extruding, for example. The size of the antenna element is not bound to the wavelength corresponding to an operating frequency. The element is large compared to a quarter of the wavelength, enabling good radiation and receive characteristics. The location of the radiator on the outer surface of the radio device has the same effect. In the end product, the antenna element  200  as well as the antenna elements of  FIGS. 3 to 7  and  9  to  10  are naturally coated with a thin protective layer. 
       FIGS. 3   a  and  3   b  show a second example of a radiating antenna element according to the invention. The antenna element  300  belongs to a radio device  30  which in this example is an ordinary non-foldable mobile communication device. In  FIG. 3   a  the communication device is seen from behind and in  FIG. 3   b  from a side. The antenna element  300  is a single conductive piece forming about one half of the back side of the cover of the communication device  30 , extending to the lateral sides and end side, too. The element  300  connects to the rest  35  of the cover of the radio device without any discontinuity of the outer surface. 
       FIGS. 4   a  and  4   b  show a third example of a radiating antenna element according to the invention. An antenna element  400  belongs to a radio device  40  which in this case, too, is an ordinary non-foldable mobile communication device. In  FIG. 4   a  the communication device is seen from behind and in  FIG. 4   b  from a side. The antenna element  400  is a single conductive piece forming the whole of the back side of the cover of the communication device  40 , extending to the lateral sides and end side, too. The radiator is thus in this example particularly large. It connects to the rest  45  of the cover of the radio device without any discontinuity of the outer surface. 
       FIGS. 5   a  and  5   b  show a fourth example of a radiating antenna element according to the invention. An antenna element  500  belongs to a radio device  50  which in this case, too, is an ordinary non-foldable mobile communication device. In  FIG. 5   a  the communication device is seen from behind and in  FIG. 5   b  there is shown just the antenna element  500 . This is a single cuplike conductive piece forming the upper portion of the cover of the communication device  50 . Thus the radiator  500  will be overlapped only a little when held in hand in the normal manner. The antenna element connects to the rest  55  of the cover of the radio device without any discontinuity of the outer surface. 
       FIG. 6  shows a sixth example of a radiating antenna element according to the invention. An antenna element  600  is now a single trough-like conductive piece constituting an intermediate part of the back side of the cover of a radio device. 
       FIG. 7  shows in cross section a sixth example of an antenna element according to the invention. An antenna element  700  consists now of a dielectric portion  710  in the cover of a radio device, a radiating conductive layer  720  on the outer surface thereof, and a conductive layer on the inner surface thereof, i.e. a feed element  730 . The antenna element is fabricated using e.g. IMF (In Mould Foil), IMD (In Mould Decoration) or IML (In Mould Label) technology, so that it is a solid single component. 
     Below the antenna element  700  there is an antenna ground plane GND provided by the conductive upper surface of the circuit board PCB of the radio device. There is only electromagnetic coupling between the feed element  730  and radiator  720  because the dielectric cover  710  isolates them galvanically from each other. Furthermore, the radiator  720  is not galvanically connected to any other conductive part of the radio device. The feed element  730  is galvanically connected to the antenna port of the radio device by a feed conductor FDC and to the ground plane by a short-circuit conductor SHC. In this example the feed and short-circuit conductors are conductive strips attached to the antenna element, which are pressed against the circuit board PCB by a spring force. 
       FIG. 8  shows a seventh example of an antenna element according to the invention. An antenna element  800  consists of a dielectric portion  810  of the cover of a radio device, a radiating conductive layer  820  therein, and a conductive layer on the inner surface, i.e. the feed element  830 . The difference of this antenna element from the antenna element  700  of  FIG. 7  is that the radiator is now within the dielectric cover and not on the outer surface thereof. The antenna element  800  can be fabricated using the same above-mentioned techniques as in fabricating the element  700 . Alternatively, in the examples of  FIGS. 7 and 8 , also the feed element may be embedded within the dielectric portion of the antenna element. 
       FIG. 9  shows a second example of the feed arrangement of an antenna element according to the invention. This figure shows a radiating antenna element  900  which is a single conductive piece. Below the antenna element there is the ground plane GND of the antenna. Between the radiator  900  and ground plane there is a conductive feed element FDE which in this example is galvanically isolated from the radiator by a separate thin dielectric layer DIE. The radiator is not galvanically connected to any conductive part in the radio device. The feed element FDE is galvanically connected to the antenna port of the radio device by a feed conductor FDC and to the ground plane by a short-circuit conductor SHC. Encircled within a broken line there is an example of the shape of the feed element FDE. It is a conductive strip which has two branches of different lengths, viewed from the short-circuit point S, to produce two operating bands for the antenna. The longer branch together with the radiating antenna element and ground plane resonates in the lower operating band area, and the shorter branch together with the radiating antenna element and ground plane resonates in the upper operating band area. 
       FIG. 10  shows in cross section a third example of the feed arrangement of an antenna element according to the invention. In this figure there is shown a radiating antenna element A 00  and, below that, the ground plane GND of the antenna. The radiator A 00  is now galvanically connected to the antenna port of the radio device by a feed conductor FDC and to the ground plane by a short-circuit conductor SHC. The antenna is thus PIFA type. The feed and short circuit conductors are e.g. so-called pogo pins, in which case their internal springs press the upper parts of the conductors against the radiator. A direct feed to the radiating element according to  FIG. 10  requires that, in the element design, not only the desired appearance of the radio device need to be known, but also the electrical dimensions of the element need to be taken into account. 
     The radiating portion of an antenna element according to the invention is advantageously “unbroken”, i.e. its border line will not deviate inwards from the, say, rectangular or roundish outline of the element. This is possible especially when using the feed arrangement according to  FIGS. 7 to 9 . However, in order to enhance the electrical characteristics of the antenna, the radiating portion may be shaped as required.  FIG. 11  shows an example of such an antenna element. The element B 00  includes a dielectric portion B 10  and a radiating portion B 20 . The radiating portion is inside the dielectric portion and therefore drawn in broken line. The radiating portion has ends extending perpendicularly from its middle region so that a pattern is formed which resembles a wide rectangular U. For example, the radiating portion  720  of the element of  FIG. 7  or the radiating portion  820  of the element of  FIG. 8  may be shaped like portion B 20 . 
       FIG. 12  shows a second example of a shaped radiator. The radiating portion C 00  has two non-conductive slots. From the lower edge starts a first slot C 05  shaped like letter L and a straight second slot C 06 . In a complete radio device there is a dielectric protective layer on top of the slots and the whole radiator. 
     The attributes “lower” and “upper” refer in this description and in the claims to the positions of the antenna element presented in  FIGS. 5   a  and  7  to  10  and have nothing to do with the operating positions of the devices. 
     Antenna elements according to the invention were described above. The shape of an antenna element may differ from those presented, and the invention does not limit the fabricating method of the element. The inventional idea can be applied in different ways within the scope defined by the independent claim  1 .