Patent Publication Number: US-2005128149-A1

Title: Antenna device

Description:
BACKGROUND OF THE INVENTION  
      1. Technical Field  
      The present invention relates to an antenna device for a mobile radio communication apparatus, a so-called cell or mobile telephone, and designed for operation in at least two frequency bands, comprising at least a first antenna element connected to the circuits of the mobile telephone.  
      2. Background Art  
      The downsizing of mobile telephones has proceeded so far that the space available for the antenna of the mobile telephone is extremely limited. Further, among other things for aesthetic reasons, attempts have been made to avoid antennas which project outside the apparatus casing of the mobile telephone. This entails problems in antenna performance, on the one hand because the radiator components of the antenna are physically to the apparatus itself and, on the other hand, because they are also physically close to the head of the user.  
      One method of increasing antenna performance would be to employ telescopic rod antennas, but at least in the lower frequency bands that are employed in mobile telephony, even such a rod antenna designed as a quarter wave antenna would hardly have room interiorly inside the apparatus casing, since, for example, in the GSM band, an antenna length of approx. 80 mm would be required. Complex mechanical solutions would be called for to achieve the integration of such an antenna.  
      Many prior art antennas further have an impedance which greatly deviates from the 50 Ω, which is standard. This implies that matching networks must be employed between the antenna and the circuits of the mobile telephone, which is less desirable both with regard to cost and with regard to antenna performance.  
     SUMMARY OF THE INVENTION  
      The present invention has for its object to design the antenna device intimated by way of introduction such that its performance may be drastically improved without the physical dimensions of the apparatus casing of the mobile telephone of necessity needing to be increased. The present invention further has for its object to realise an antenna device which obviates the drawbacks inherent in prior art technology. Finally, the present invention has for its object to realise an antenna device which is simple and economical in manufacture and which facilitates impedance adaptation to the circuits of the mobile telephone.  
      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 first antenna element has at least a first and a second radiator of a surface extent which is shaped so as to comply with the configuration of an adjacent part of the inside of a casing in which the mobile telephone is accommodated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention will now be described in greater detail hereinbelow, with reference to the accompanying Drawings. In the accompanying Drawings:  
       FIG. 1  is, in perspective, an exploded view of a first embodiment of an upper part of a mobile telephone and a wrist strap or neck strap connectable thereto;  
       FIG. 2  is a perspective view corresponding to that of  FIG. 1  with the components included in the assembled state;  
       FIG. 3  schematically illustrates the co-operation between the inner, permanent antenna of the mobile telephone and the outer antenna in a first embodiment;  
       FIG. 4  is a view corresponding to that of  FIG. 3 , but of a modified embodiment;  
       FIG. 5  is a view corresponding to that of  FIG. 3 , in yet a further modified embodiment;  
       FIG. 6  is a view corresponding to that of  FIG. 3 , but in still a further modified embodiment;  
       FIG. 7  is a perspective view of a second embodiment of an antenna device according to the present invention;  
       FIG. 8  is a second perspective view of the antenna device according to  FIG. 7 ;  
       FIG. 9  shows a first alternative of the interconnection of two radiators included in the antenna device according to  FIGS. 7 and 8 ;  
       FIG. 10  shows a second alternative of the interconnection of two radiators included in the antenna device according to  FIGS. 7 and 8 ; and  
       FIG. 11  shows a third alternative of the interconnection of two radiators included in the antenna device according to  FIGS. 7 and 8 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)  
      In  FIG. 1 , reference numeral  1  relates to an upper part of an apparatus casing for a cell or mobile telephone. This casing may be both an inner casing which, in such instance, is included in the mechanically bearing parts of the mobile telephone, and an outer casing which substantially fulfils aesthetic functions. Interiorly in this casing, there is disposed a circuit card  2  with the circuits of the apparatus. A first antenna element  3 , which is in the form of an inner or permanent antenna  3 , has two radiators  4  and  5 , where, for example, the longer radiator, which is designed as a meander, may be dimensioned for GSM bands (880-960 MHz), while the shorter radiator  5  which, in the illustrated embodiment, is a rod antenna, may be dimensioned for the DCS- or PCS bands or both (1710-1880 MHz and 1850-1990 MHz, respectively).  
      Both radiators  4  and  5  are interconnected to each other by the intermediary of a connecting member  21  which realises a galvanic parallel connection of the radiators whereby the impedance is reduced to such a low level that a specific matching network may many times be dispensed with. The radiators have a common supply section  6  which is galvanically connected to the two radiators and further galvanically connected to the circuits on the circuit card  2 . Between the two radiators  4  and  5 , there is a dielectric such as air, glass, a suitable plastic material etc. The inner antenna  3  is dimensioned in order alone to be able to function satisfactorily, at least in environments where the reception conditions are good or normal.  
      The first antenna element  3  is disposed in or on and positionally fixed by means of a retainer device which, in this embodiment, is an integral part of the casing  1  of the apparatus. In the illustrated embodiment, the retainer device is formed by the inside  14  of the upper end wall of the casing  1  and a wall  13  projecting from the inside of the casing. In other words, the antenna element is interlockingly fixed in tight connection to the inside  14  of the casing.  
      In addition to the galvanic interconnection of the radiators  4  and  5 , the connection  21  realises a separation of the radiators  4  and  5  so that, also in the longitudinal direction of the connecting member, they will be positioned closely adjacent inner surfaces, e.g. a rear surface  22  on the back portion of the casing  1 .  
      It will be apparent from  FIGS. 1 and 2  that the two radiators  4  and  5  are arcuate in shape, whereby their shape is adapted to closely conform with the configuration of adjacent inner surfaces of the casing.  
      An outer antenna  7  is disposed on or together with or integral in a wrist strap, a neck strap or some similar accessory to the mobile telephone itself. The outer antenna  7  may therefore be seen as an accessory which greatly improves antenna performance, and which may be important in areas where reception conditions are less satisfactory. If, for purposes of exemplification of the outer antenna  7 , we use a neck strap, this has a first part  8  and a second part  9  which are brought together in an eye  10  which is fixable in an anchorage  11  on the apparatus casing  1  physically close to the inner antenna  3 . While not being apparent from  FIG. 1 , the outer antenna has a lightly flexible, metallic conductor whose dimensioning is such that, when, as a result of its physical proximity to the inner antenna  3 , it is capacitatively/inductively connected to it and can operate with half wave operation in the frequency range to which the radiator  4  is set, up to full wave operation in the frequency range to which the radiator  5  is set. In one concrete example, the metallic conductor in the outer antenna  7  may be a thin, lightly flexible metal wire.  
      It is further apparent from  FIGS. 1 and 2  that the apparatus casing  1  has, just beneath the anchorage  11 , a through-going, elongate aperture  12  which, interiorly in the apparatus casing  1 , is defined by the surrounding wall  13 . Between the upper side of the surrounding wall  13  and the lower side or inside  14  of the apparatus casing, there is a space which, as was mentioned above, is dimensioned for mechanical retention of the inner antenna  3 .  FIG. 2  clearly shows how the antenna  3  is placed in this space and how it is shaped according to and follows the inner surfaces  14  and  22  of the casing  1 . The through-going and elongate aperture  12  is also intended for the passage of an alternative to the neck strap with the parts  8  and  9 , for example a wrist strap.  
       FIGS. 3 and 4  show one embodiment where there is disposed in the outer antenna  7 , a single conductor  15  which constitutes a second antenna element if the inner antenna  3  is considered as a first antenna element. The conductor  15  has an end region or a coupling portion  16  which is located physically proximal the first antenna element. The distance between the coupling portion  16  and the first antenna element should be of the order of magnitude of 0.01-0.03 wavelengths. In  FIGS. 1 and 2 , the embodiment according to  FIG. 3  has its counterpart in a situation where there is disposed in the outer antenna  7  a metallic conductor only in one of the two parts  8  and  9 .  
       FIG. 4  shows a similar embodiment with a single conductor  15  which constitutes the second antenna element. In this embodiment, the coupling portion  17  has, however, a different appearance and extends at least partly about the first antenna element  3 . In the embodiment according to  FIGS. 1 and 2 , this would imply that the neck strap or the wrist strap is passed through the through-going aperture  12  straight through the apparatus casing  1 .  
       FIG. 5  shows an embodiment where a double or duplex conductor  18  is employed as the second antenna element. This has its counterpart in  FIGS. 1 and 2  by the situation that both the first part  8  and the second part  9  of the neck strap or the wrist strap each have their part of the duplex conductor  18 . The region of union between these parts constitutes the coupling portion  19  of the second antenna element. In  FIGS. 1 and 2 , this embodiment has its counterpart in a situation where the outer antenna  7  is secured in the anchorage  11  of the apparatus casing.  
       FIG. 6  shows a similar embodiment where the outer antenna  7  is secured in the through-going aperture  12  of the apparatus casing so that the coupling portion  20  of the second antenna element at least partly extends around the first antenna element.  
      In  FIG. 1 , the inner antenna, i.e. the first antenna element, has been shown as an antenna of sheet metal material produced, for example, by etching. This is not a critical requirement, but the inner antenna element  3  may be produced from a double-sided circuit card, a flexifilm secured on a suitably shaped carrier or vehicle of plastic or other suitable material, or a metalisation of the carrier, the retainer device or the inside of the casing. Further, the first antenna element may be a helical antenna which lies with its longitudinal direction approximately parallel with the width direction of the apparatus casing. Other configurations of the first antenna element are also possible.  
      According to the present invention, it is also possible to make the uppermost part of the apparatus casing  1  as a loose component which may be snapped in position on the rest of the apparatus casing. In such an embodiment, the counterpart to the anchorage  11  is located on this additional unit, this also accommodating the counterpart to the first antenna element.  
      A counterpart to the aperture  12  may be disposed either in the additional unit or in the joint between it and the apparatus casing proper, but possibly also in the apparatus casing itself. In addition to the first antenna element  3  interiorly in the additional unit, there may also be an additional antenna device interiorly in the apparatus casing.  
      In the embodiment according to  FIGS. 1 and 2 , the antenna element  3  is positionally fixed interiorly in the casing  1  by means of a retainer member which is designed as an integral part of the casing of the apparatus. In the described embodiment, the retainer member positionally fixes the antenna element by the intermediary of a mechanical, interlocking engagement. In another embodiment, where the retained member is an integrated part of the casing  1  of the apparatus, the radiators of the antenna element  3  are applied direct on interior surfaces in the apparatus casing  1 . The radiators will hereby have a surface extent which is adapted to follow the configuration of these interior portions of the inside of the casing  1 .  
      As a variation on this theme, a construction is conceivable where the radiators are disposed interiorly in the material of the casing.  
       FIGS. 7 and 8  show one embodiment with a retainer member  23  which is designed as a separate unit which is insertable interiorly in the casing  1 . The design of the retainer member  23  is such that at least parts of its surfaces connect to and are formed in accordance with adjacent, corresponding interior surfaces in the casing  1 .  
      In the illustrated embodiment, the retainer member  23  (see  FIG. 8 ) has an open interior in which a circuit card  2  may be insertable as is intimated by the arrow  24 . As a result, the retainer member  23  and the circuit card  2  are joined to form a unit which is insertable interiorly in the casing  1 .  
      It will further be apparent from the Figure that the retainer member  23  has a contact device  25  which is intended for contact with a corresponding contact device  26  on the circuit card  2 . When the contact device  25  of the retainer member  23  is in communication with radiators  27  and  28  disposed on the retainer member, it will be seen that the radiators can, in a very simple manner, be connected to those circuits which are disposed on the circuit card  2 .  
      The two radiators  27  and  28  are, in the illustrated embodiment, produced as meandering or zigzag shaped conductors which, in a practical embodiment, may be disposed on a flexifilm  29  disposed on the retainer member  23 .  
      Of the two radiators  27  and  28  illustrated in  FIGS. 7 and 8 , the radiator  27  will also be designated a first radiator, while the radiator  28  will also be designated a second radiator.  
      The first radiator  27  has a first surface portion  30  and a second surface portion  31  which substantially lie in two separate planes that intersect one another possibly, as shown in the Figure, approximately at a right angle. The first surface portion  30  is disposed closely adjacent a side surface of the inside of the casing  1 , while the second surface portion  31  is disposed closely adjacent an upper end surface  14  of the inside of the casing  1 . The transitional region between the two surface portions  30  and  31  is an arched region, in the embodiment with the flexifilm  29 , a single-arched region.  
      Correspondingly, the second radiator  28  has a surface portion  32  which substantially lies in a third plane that intersects the above-mentioned first and second planes, preferably as shown in the Figures at right angles.  
      The first portion  30  of the first radiator  27  is of a longitudinal extent which is intimated by a broken line  33 , and the second radiator  28  is of a longitudinal direction which is intimated by the broken line  34 . In the illustrated embodiment, these lines  33  and  34  make approximately a right angle with each other, but the present invention also encompasses embodiments where the second broken line  34  may be turned in accordance with the arrow  35  so that the angle between the two lines  33  and  34  is less than 90°, for example of the order of magnitude of 45°. By such a change of the embodiment, the second radiator  28  will be higher up, i.e. closer to the upper end of the mobile telephone and further away from its circuits.  
      The contact device  25  has a supply section  36  which, in the embodiment illustrated in  FIGS. 7 and 8 , is connected to the ends of the two radiators  27  and  28 . This alternative, which is a pure, galvanic parallel connection of the two radiators, is illustrated in  FIG. 9 .  
       FIG. 10  shows an alternative interconnection of the two radiators  27  and  28  and it will be apparent that the first radiator  27  has its one end connected direct to the contact device  25 , while the second radiator  28  has its supply end connected between the ends of the first radiator but preferably in the proximity of that end which is connected to the contact device  25 .  
       FIG. 11  shows the reverse situation in relation to  FIG. 10 , where the second radiator  28  is connected directly to the contact device  25  with its one end while the one end of the first radiator  27  is connected to the second radiator  28  between both of its ends but preferably more proximal that end which is connected to the contact device  25 .  
      In all of the embodiments illustrated in  FIG. 7  to  11 , both of the radiators  27  and  28  have one end free.  
      In those embodiments which are shown in FIGS.  7  to  11 , the first radiator  27 , i.e. the longer radiator, may be designed for a quarter wave resonance and a half wave resonance, for example quarter wave resonance in the GSM-band and half wave resonance in the DCS- or PCS-bands, while the second radiator  28 , the shorter radiator, may be designed for quarter wave resonance in the DCS-band. If, in such instance, the settings in the DCS-band are not made exactly alike as regards the shorter and longer radiator, an increase of the band width will be attained in the higher frequency range.