Abstract:
In order to create a compact antenna block a corner-shaped support is provided with a radiating area on an upper surface thereof and a transition area is provided on an underlying surface. The transition area is characterized in that it is triangular. The angle of the triangle forms a connection point for the antenna. The tapered part of the corner-shaped support is fitted with a pole enabling it to be lifted above the plane of the circuit to which the antenna block is connected, whereby the transition area extends gradually above said plane, the upper radiating area being substantially parallel to said plane. As a result the impedance of the antenna can be regulated more easily in such a way that it is continuously constant and the reflection coefficient is improved.

Description:
FIELD OF INVENTION 
   The subject of the present invention is a particularly compact antenna block for a wireless device, notably for a mobile telephone. The subject of the invention also is wireless devices for information networks, notably by transmission according to the Blue Tooth standard. The antenna block of the invention is designed to be used with one or the other of the involved frequencies, or even one and then the other successively. The invention principally seeks to simplify the creation of radiating devices, antenna blocks, while conferring broader-spectrum performance and a better adaptability to the medium in which these devices must radiate. 
   BACKGROUND OF THE INVENTION 
   In the mobile telephone field, particularly in Europe, the GSM standard at 900 MHz and the DCS standard at 1800 MHz are known. The frequency bands at which a mobile telephone must radiate, both in transmission and reception, are thus clearly distinct. Moreover, for third-generation mobile telephones, in addition to the PCS standard at 2100 MHz, there is also the UMTS standard at 2200 MHz. In the course of manufacture, mobile telephones must therefore now have available a radiating element, if possible a single one, capable of radiating in these three distinct frequency bands. In passing, it will be noted that the latter bands (1800 MHz to 2200 MHz) form a broad band, in particular by encompassing the DECT standard of 1800 MHz to 1900 MHz. 
   For complete interactivity of wireless devices, the necessity of satisfying the Blue Tooth standard or the IEEE802.11 standard is now added to the complexity of creating an antenna capable of these three frequency bands. To obtain such a variety of frequencies with a single aerial antenna is a problem that is currently unresolved. We therefore turn to multiple antenna structures. 
   An antenna permitting radiating in two bands, typically the GSM band at 900 MHz and the DCS band at 1800 MHz, is known from the document of the prior art “Dual-Frequency Planar Inverted-F Antenna”, of Zi Dong Liu and Peter S. Hall in “IEEE Transactions on antennas and propagation,” Vol. 45, No. 10, October 1997, pages 1451 and following. The geometry of the antenna, which is particularly simple and which is envisioned for such a situation of radiation over two bands, has a metallized zone in the shape of the letter L overall and a rectangular metallized area able to be positioned in the open space of the L shape. On the one hand, this solution has separate feeds for the different antenna elements so that switching circuits must be added to the electronic circuit to which this antenna is coupled. These switching elements themselves create operating difficulties. On the other hand, high bands such as UMTS and very high bands such as Blue Tooth are not possible with such a network. 
   Such solutions are therefore poor. They require connection switches, which generate problems for transmission or reception. 
   SUMMARY OF THE INVENTION 
   In the present invention, in order to remedy this problem, the creation of an antenna whose radiating part is formed by a flat metallized radiating layer is envisioned. The flat radiating layer has different patterns that form the surface radiating networks. These networks permit an amplification by adaptation of the length of conductive tracks which result from the patterns at the wavelength of the electromagnetic waves to be radiated by the antenna. In the invention, one can thus envision, for one example, an asymmetric H-shaped pattern, meaning that the insulating zones forming the legs of the H bound and define the conductive tracks. These legs are not symmetrically arranged relative to the horizontal insulating bar of the H. In this way, the offset would permit broadening the band around the frequencies considered, notably around 2400 MHz. 
   In a complementary manner, a good result can also be obtained by creating a radiating element with two insulating slots by another pattern and placing this radiating element with two slots between the asymmetric H pattern, on one side, and a principal radiating element, essentially a conductive strip, on the other side. In this case, it could be observed that a mutual controlled influence could be established between the radiating zones of the first pattern and those of the second pattern. This influence then modifies the frequency characteristic of the antenna in a very significant way by broadening the intermediate frequency band. This broadening of the band is used in the invention to comply with the frequency band corresponding to the DCS, PCS, UMTS, or even DECT standards. 
   Providing an antenna having a radiating microband in the form of a flat metallized layer, placed in an elevated position relative to a circuit which bears it, notably a circuit provided with a continuous metal surface forming a ground plane, is known particularly, from the document “ New Considerations in the Design of Microstrip Antennas ” of Naftali Herscovici, “ IEEE Transactions on antennas and propagation ,” Vol. 46, No. 6, June 1998, pages 807 and following. The antenna pattern is connected to the circuit here by means of a transition connection between the circuit and the metallization of the antenna pattern. This transition connection is present in the form of a conductive part raised above the circuit support. However, the embodiment thus recommended does not benefit from a sufficient degree of freedom to also take into account a radiation parameter, in a supplemental manner. This radiation parameter to take into consideration is the impedance adaptation of the antenna to the medium in which it is supposed to radiate. 
   In fact, this antenna must be adapted to the impedance of air and, moreover, must take into account penalizing circumstances, such as the proximity or lack of proximity of the hand or the head of a mobile telephone user, or the proximity of other structures, notably metal ones. It is clear from the different possibilities for use of a mobile telephone that this impedance must be adaptable. It is particularly important to minimize losses in the transition zone between the waveguide means, electrically linked to the outlet of the electronic transmission and reception circuit, and the radiating element of the antenna. 
   In addition, another problem is posed, that of miniaturization. Such miniaturization limits foreseeable technical solutions. 
   The invention thus seeks to create a broadband multifrequency antenna. The interest of having broad bands is to preserve a large antenna gain even in the presence of disruptive elements such as metal structures that shift the tuning frequency of the antenna. Moreover, the invention seeks to minimize losses at the level of the transition between the waveguide means and a radiating or receiving element. 
   DETAILED DESCRIPTION OF THE INVENTION 
   In the invention, this is obtained by creating a progressive transition zone between these two parts. The progressive transition zone is a continuous transition zone minimizing losses by reflection and permitting a broadband functioning of the antenna. The transition zone preferably has a length equivalent to the length of the radiating zone. Their difference is due to an incline. 
   Thus, this problem is remedied in the invention by creating an antenna having a radiating zone and a transition zone, the transition zone being positioned under the radiating zone. It could thus be shown that by acting in this way, a greater transition zone is available, since it can practically occupy the same length as an antenna that it is supposed to connect. 
   According to the solution of the invention, the metallization of a radiating zone and of a transition zone, leading to an electronic circuit at the radiating zone, is formed by a layer, preferably metallized, borne by the same support (but on the bottom) as that which bears the radiating layer. A great ease of manufacture, transport and positioning of the antenna results from this, in addition to the solution to the problems stated above of band width and impedance adaptability. 
   The subject of the invention is therefore an antenna block for a wireless device, comprising a radiating zone and a transition zone, the transition zone serving to connect the radiating zone to an electronic transmitter and/or receiver circuit of the wireless device, the radiating zone comprising a first metal layer, characterized in that the transition zone has a second metal layer, and in that the two layers are superimposed and connected together electrically by a metal reversal piece. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention will be better understood upon reading the description that follows and examining the figures that accompany it. These figures are only shown by way of indication and do not at all limit the invention. The figures show: 
       FIGS. 1   a  to  1   d : an example of embodiment of an antenna pattern according to one aspect of the invention; 
       FIG. 2 : a spectral diagram of the measurements carried out with the antenna of  FIGS. 1   a  to  1   d  showing the ratio of energy reflected by the antenna to energy transmitted by the latter; 
       FIGS. 3   a  and  3   b : bottom and top views, respectively, in perspective of an antenna block according to one aspect of the invention; 
       FIG. 4 : a sectional view of the radiating and transition zones, the active zone of the antenna of  FIGS. 3   a  and  3   b.    
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1   a  shows an antenna block for a mobile telephone. For example, this antenna block has a metallization [conducting layer]  1  borne by a support  2 , for example of plastic or ceramics. Radiating zone  1  can thus be obtained by deposition, notably metal vapor deposition, then etching of the metallized layer in order to create patterns favoring resonance in this metallized zone, and therefore favoring transmission or reception of certain spectral components. The spectral components are precisely those mentioned above. 
   For this purpose, radiating zone  1  has a first pattern  3  in the shape of an asymmetric H. This pattern is also shown in  FIG. 1   b . In this pattern  3 , a metallized strip  4  is aligned with, but separated from another metallized strip  5 . The two strips  4  and  5  are bordered on either side by two etched slots  6  and  7 . The two etched slots, of roughly equal length, are connected by an etched bridge  8  permitting the two strips  4  and  5  to face each other. The two slots  6  and  7  and bridge  8  form insulating zones. Moreover, electrically, the two strips  4  and  5  are fed by two conduction channels  9  and  10  situated on the other side of the strips, respectively, relative to etched slots  6  and  7 . The conduction channels end at a base  11  for connection of the antenna. The offsetting of slots  6  and  7  is such that slot  7  is overall closer to base  11  than slot  6  is. The two strips  4  and  5  also have different lengths,  12  and  13 , respectively, corresponding to the wavelengths of the waves to be radiated by the antenna. 
   It can be shown that this off-setting of the slots and also the difference in lengths  12  and  13  can lead to a broadening of the first very-high-frequency pass-band, notably for the radiating band corresponding to the Blue Tooth standard. 
   Metallization  1  forming the antenna also has a second pattern, also shown by itself in  FIG. 1   c . This pattern is formed of two insulating etched slots  14  and  15  together creating a strip  16  between them and, on either side, two conduction channels  17  and  18 , all three having their source in base  11 . Channels  17  and  18  and strip  16  are connected together at their top by an electric bridge. The two slots  14  and  15  permit defining a second length  20  corresponding to an average wavelength of a second resonance pass-band. 
   Antenna  1  finally has a third pattern created principally by a broad band  21  whose length  22  permits defining a third average wavelength of a third resonance band of the antenna.  FIG. 1   d  shows the third individual pattern. 
   In fact, the three metallization patterns are connected together by base  11 , but are separated from one another by insulating zones. These insulating zones fundamentally comprise three arms  23 ,  24  and  25 , respectively, together emerging into an insulating arm  26 . The second pattern  14 – 20  is thus contained between arms  24  and  25 , between the first pattern  3 – 13  and the second pattern of the band  21 – 22 . 
   The large band  21  is also continued, on the side opposite base  11 , by a connection  27  perpendicular to band  21 . Connection  27  is itself continued by a half-band  28  (of the quarter-wave type). Bands  21 ,  27  and  28  are linked by connection zones  29  and  30  both comprising the particular feature of having a cut section  31  and  32 , respectively. Cut sections  31  and  32  permit transporting the signal by preventing reflections that can damp signal transmission. It could be determined that these cut sections promoted a gain of antenna  1  in the low-frequency band. 
   The interlacing of the patterns thus created is also of a nature to favor a broadening of the pass-band of the second pass-band by coupling with the second pattern. The proximity of the asymmetric H pattern and the second double-slot pattern thus induces a broadening of the second resonance pass-band. 
   In the same way, insulation arm  24  situated between the first and the second pattern has an insulating zone  33  in the region of base  11  in the form of a triangle extending in the direction of the first asymmetric H pattern, away from the second pattern of double slots  14  and  15 . In the same way, triangle  33  has a cut section  34  favorable to the attenuation of reflections as well as a means for controlled coupling of the radiation induced by the second pattern to the radiation induced by the first pattern. 
     FIG. 2  shows a result of measurement of the ratio value of the signal reflected by the antenna to the signal transmitted by the antenna. The peaks represented definitively show the frequencies in which the antenna resonates correctly.  FIG. 2  thus shows a first peak  35  corresponding to frequencies of the GSM 900 MHz type. It also has second and third peaks  36  and  37  due to the presence of the second pattern, as well as the coupling with strip  4  of the first pattern. Finally, the diagram of  FIG. 2  shows a fourth peak  38  corresponding to the Blue Tooth standard and induced by strip  5 . It will be noted that the two peaks  36  and  37  are connected by a broad band (with rejection and reflection levels of less than −10 dB) permitting functioning of the antenna with an acceptable gain in all the intermediate bands mentioned above. 
   The fact of having placed the radiating element with two slots between the asymmetric H element on one side and the principal radiating element on the other side modifies the frequency characteristic of this element by significantly broadening the frequency band. 
   In one example, antenna  1  has dimensions of 3.5 cm long by 2.5 cm wide. 
     FIG. 3   a  and  FIG. 3   b  show, conforming to one subject of the invention, a preferred coupling circuit for an antenna in a mobile telephone.  FIG. 3   a  is a view of the antenna from the bottom of its radiating face.  FIG. 3   b  is a perspective view of the same antenna viewed from the top, with the radiating zone visible. The radiating pattern shown on the radiating zone is a particular case. The antenna block for a mobile telephone thus embodied has a metallized and flat radiating zone  40 . Possibly, zone  40  could be made in the form of a metal plate. In practice, metallized zone  40  is borne by a support  41  of plastic or ceramics. Making it of ceramics could permit making a smaller support due to the difference in the dielectric constant of the material. Radiating zone  40  is coupled to a transition zone  42 ,  FIG. 3   a , also preferably borne by support  41 . In one example, the two zones are metallizations, notably created by MID technology, then finally etched. The pattern of metallization area  40  is preferably that of  FIG. 1   a.    
   Transition zone  42  serves to connect zone  40  to an electronic transmitter and/or receiver circuit of a mobile telephone (not shown) and accessible by a connection  43 . Antenna block  40 – 42  has the particular feature that both layers  40  and  42  are superimposed overall and electrically joined together by a metal (or metallized) reversal piece. The fact of supporting metallizations areas  40  and  42  and reversal piece  44  on the same support  41  confers a great reproducibility to the mounting of the antenna and its behavior once mounted. The superimposition of the invention thus permits having a long transition zone, for example, longer than the radiating zone, which is favorable to a better impedance adaptation. The superimposition is such that, for example, the incline of the transition zone on the electronic circuit, or under the radiating zone, is of the order of or less than 30 degrees of angle, in any case less than 45 degrees. Due to the fact of this superimposition, the transition layer is sandwiched between the electronic circuit and the radiating zone. With the superimposition, the transition zone does not occupy any additional space above the electronic circuit. 
   For example, very simply, one end of support  41 , in the place where reversal piece  44  is designed to be positioned has a finer rounded edge in order to make the two surfaces communicate with each other, the one bearing metallization area  40  and the one bearing metallization area  42 . In this case, this rounded edge forms a reversal piece permitting assuring to a metallization area  44  continuity between a transition zone  42  and a radiating zone  40 . The fact of making zone  42  subjacent to zone  41  permits having a significant length available for zone  42 , for example, and preferably the length of zone  40 . This length is measured in the direction of propagation of the signal to be radiated, from connection  43  to zone  40 . In this case, it is possible to adopt a gentle progression of width for zone  42 , between a width at the place for joining to connection  43  and a width at the location of reversal piece  44 , equal to the width of the radiating zone. In this way, with progressive broadening, a better capability is shown for adapting the impedance to an impedance to be obtained. Reversal piece  44  is also shown as ending up at base  11  of the antenna of  FIG. 1   a.    
   Support  41 , moreover, has the particular feature that it has the shape of a corner overall. The corner has a shape pointing to the place of reversal piece  44 . At the other end, support  41  has a right foot  45  designed to be raised roughly perpendicular to a circuit  46  on which the antenna block will be mounted. Circuit  46  notably bears connection  43 . For this purpose, right foot  45  is provided with a console  47  itself pierced with an opening  48  for engaging a screw for holding antenna block  40 – 45  onto circuit  46 . The bond between transition zone  42  and connection  43 , for example, can be made by a solder bead placed between this track and a beginning part  49  of zone  42  at the place of console  47 . This solder bead is then melted during connection. The corner shape of support  41  thus confers to transition zone  42  the particular feature of being progressively raised above the plane of circuit  46 . This progressive elevation, as well as the overall triangular shape of transition zone  42  and height  50  above circuit  46  where radiating zone  40  is situated also have parameters that permit adapting the impedance of the antenna, particularly taking into account the conditions of use invoked above. 
   The width of the transition zone thus increases the width of connection  43  until the width of base  11  of the radiating zone is reached. The increasing function is a linear function, varying with the length of zone  42  and with the height  50  of the transition zone. In this way, a constant impedance of the connection in all sections of zone  42  is obtained. The width of a section at each place of zone  42  is calculated principally as a function of the height of this section relative to the ground plane, for the desired impedance. 
   Due to the use of a progressive transition, it was possible to use the antenna in broadband mode by making cut-outs creating segments tuned to the frequencies considered on surface  40  of the antenna. 
   In a preferred case, circuit  46  bears a ground plane  51  on which the antenna block  40 – 45  is placed. In the case where ground plane  51  is present, on one hand, the length of the radiating element must be close to a quarter of the minimal wavelength to be transmitted and/or received, or if there is no ground plane  51 , it must be close to a half-wavelength. Moreover, in a way notably to assure the stability of mounting of support  51 , the latter may be provided with a pole  52  situated near the edge of reversal piece  44 . This pole  52  can also serve to electrically couple reversal piece  44  (and also base  11 ) to ground plane  51 . For this purpose, pole  52  can have a metallization area  53  communicating with radiating zone  40 . Possibly a second pole can be envisioned for the other side of support  41 . 
     FIG. 4  shows the overall appearance of the metallization areas borne by support  45  in the form of a corner. For example, the curve of metallization area  44  has a radius roughly equal to a third of height  50 . In a preferred example, this height  50  is equal to 0.8 cm.