Abstract:
An arrangement designed for radio phones for integrating a mechanical structure of the antenna head of the phone. The mechanical structures of an antenna and a speaker of the radio phone are integrated so that a given planar component radiates both radio waves and sound waves. The radiator component ( 310 ) comprises a layer ( 315, 316 ) of a material, a shape of which can be controlled by means of a voltage. The sound waves, i.e. fluctuation of the air pressure are thus generated by causing the thickness or position of the layer to fluctuate according to the control voltage. The antenna head of the radio phone becomes more compact than in the prior art, and it takes up less space because the antenna and the speaker utilize same structural elements.

Description:
This application is a Continuation of International Patent Application No. PCT/FI02/00566, filed Jun. 26, 2002, which published in English on Jan. 9, 2003 as WO 03/003506 A1. 

   The invention relates to an arrangement, designed especially for mobile phones, for integrating the mechanical structure of the antenna head of a mobile phone. 
   BACKGROUND OF THE INVENTION 
   As mobile phones are becoming smaller, all arrangements that help reduce their size are recommendable. As regards antennas, an advantageous solution is a PIFA type (planar inverted F-antenna) structure. It is effective with respect to its size, and it does not create a protruding part in the phone. In an ordinary mobile phone structure, there is provided a speaker at the same end with the antenna, according to  FIG. 1 . Figure shows a mobile phone MS including a circuit board  105 , the top surface whereof is coated with a conductive layer. The conductive layer forms, among others, the ground plane of the antenna. A PIFA type antenna comprises a radiating plane  101  that is somewhat higher than the ground plane. Beside the radiating plane, there is a speaker capsule  102 , from which the sound is led to apertures provided in the mobile phone shell. 
   SUMMARY OF THE INVENTION 
   The object of the invention is to realize the mechanical structure of that end of a radio phone where the antenna is installed in a novel and more advantageous way. The antenna structure according to the invention is characterized by what is set forth in the independent claim  1 . Preferred embodiments of the invention are presented in the dependent claims. 
   The basic idea of the invention is as follows: In a radio phone, the antenna and the speaker/loudspeaker are integrated in their mechanical structure, so that a given planar component radiates both radio and sound waves. The radiator component contains a layer of material, the shape of which can be controlled by means of a voltage. Sound waves, or the air pressure fluctuation, is then generated by causing the layer thickness or position to fluctuate according to the control voltage. The antenna represents for instance the PIFA type. The feed conductor of the PIFA and one of audio conductors of the speaker are galvanically connected to one and the same conductor plane in the radiator component. 
   An advantage of the invention is that in an arrangement according to it, the antenna head of a radio phone becomes more compact than in the prior art, because the antenna and the speaker use same structural parts. Another advantage of the invention, for the same reason, is that the total space required by the antenna and the speaker is reduced. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in more detail below with reference to the appended drawings, where 
       FIG. 1  shows an example of a prior art arrangement at the antenna head of a radio phone, 
       FIG. 2   a  shows an example of an arrangement according to the invention at the antenna head of a radio phone, 
       FIG. 2   b  is a circuit diagram showing a feed arrangement of the structure shown in  FIG. 2   a,    
       FIG. 3   a  shows another example of an arrangement according to the invention at the antenna head of a radio phone, 
       FIG. 3   b  shows a feed arrangement of the structure shown in  FIG. 3   a  and a structure of the radiator component, 
       FIG. 4  shows a third example of an arrangement according to the invention at the antenna head of a radio phone, and 
       FIG. 5  shows an example of a radio phone provided with an arrangement according to the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 2   a  shows an example of an arrangement according to the invention at the antenna head of a radio phone. The arrangement comprises a conductive ground plane GND and a radiator component  210  that is parallel with the ground plane. In this example, the radiator component is formed of an electret layer  215 , the top surface whereof is coated with a first conductor plane  211  and the bottom surface whereof is coated with a second conductor plane  212 . The radiator component  210  is supported against the ground plane (or against the circuit board underneath the ground plane) with insulating elements, such as an element  271 . 
   In this description and in the claims, the prefix “top” refers to the opposite surface or side with respect to the ground plane, and the prefix “bottom” refers to the surface of side facing the ground plane. Respectively, a vertical direction means a direction that is perpendicular to the ground plane. 
   To the first conductor plane  211  there is connected a first feed conductor  221  and to the second conductor plane  212  at a same vertical line as the first feed conductor, there is connected a second feed conductor  222  of the antenna. Respectively, in another spot of the radiator component, in the first conductor plane there is connected a first short-circuit conductor  231  of the antenna, and in the second conductor plane  212  at a same vertical line as the first short-circuit conductor, there is connected a second short-circuit conductor  232  of the antenna. The second short-circuit conductor is connected to ground plane via a condensator C 24 . In a similar way, also the first short-circuit conductor and both the first and second feed conductors have a serial condensator. The feed conductors are connected, via the serial condensators, to the antenna port of a radio transmitter. The described structure serves as a PIFA type antenna, where instead of one radiating plane, there is a dual plane formed of a first and a second conductor plane. In the example of  FIG. 2   a , the first conductor plane  211  includes a slot that divides it, viewed from the feed point, into two branches of different lengths. The second conductor plane  212  is provided with a similar slot at the same location. Thus the PIFA is a dual-frequency antenna. 
   The electret layer  215  is for instance electromechanical film EMFi. The thickness of this type of film is reduced owing to the effect of an electric field. An inner static electric field can be generated in the material, which field causes a constriction of a given magnitude in the direction of the film thickness. External electric fields directed to this film cause additional changes. In the structure of  FIG. 2   a , these additional changes are provided with an audio signal. In the first conductor plane  211 , there is connected, in addition to the aforementioned conductors, a first audio conductor  241 , and in the second conductor plane  212  there is connected a second audio conductor  242 . Consequently, the strength of the electric field affecting the electret layer can be made to fluctuate according to the audio signal. It is alternatingly higher and alternatingly lower than the strength of the inner field of the electret layer. Thus the radiator component  210  causes a fluctuation of pressure in the ambient air, said fluctuation corresponding to the audio signal. Thus the structure serves as a speaker or a loudspeaker. 
     FIG. 2   b  shows an example of a circuit diagram of the feed arrangement of the structure illustrated in  FIG. 2   a . In the figure is seen a terminal amplifier AA of the receiver&#39;s audio part, and a terminal amplifier RA of the radio transmitter. The output of the audio amplifier AA is connected to the conductor planes of the radiator component  210  in a balanced way, so that neither of the output conductors, i.e. audio conductors, is connected to ground. The “hot” conductor of the output of the radio-frequency amplifier RA is connected to the conductor planes of the radiator component capacitively via the condensators C 21  and C 22 . Thus both of the conductor planes get a similar feed, but they are galvanically separated from each other. The galvanic separation is needed because of the audio feed. The drawing does not show other such elements between the amplifier RA and the antenna that are inessential from the point of view of the present invention. At the short circuit points, the conductor planes of the radiator component are connected to ground capacitively via the condensators C 23  and C 24 . Also here the capacitive coupling is due to the galvanic separation of the conductor planes. The capacitances of the condensators C 21 –C 24  are chosen so that their impedances are very high at audio frequencies, and very low at radio frequencies. The value of the capacitance is for example 1 nF. Thus the condensators C 23  and C 24  realize a short circuit only at very high frequencies. 
   The circuit of  FIG. 2   b  is drawn from the point of view of the audio amplifier. The equivalent circuit of the radiator component depends on frequency. At radio frequencies, for example between the condensators C 21  and C 23 , as well as between condensators C 22  and C 24 , there prevails a given impedance. The whole radiator component represents a given sound radiation resistance at audio frequencies, and a given radio radiation resistance at radio frequencies. The impedances of the output conductors of the audio amplifier AA with respect to ground must at radio frequencies be arranged to be as high as possible in order to prevent the audio amplifier from remarkably affecting the antenna matching. Another possibility is to choose the location of the audio connection of the radiator component and to arrange the impedances of the output conductors of the audio amplifier with respect to ground so that the audio connection of the radiator component replaces the whole short circuit connection of the PIFA. 
     FIGS. 3   a  and  3   b  show another example of the arrangement according to the invention at the antenna head of a radio phone. The arrangement comprises a conductive ground plane GND and a radiator component  310  that is parallel with the ground plane. The inner structure of the radiator component appears from  FIG. 3   b , where it is illustrated as a longitudinal section. As a loudspeaker solution, the structure is known as such for instance from the article “ElectroMechanical Film—a new multipurpose electret material” [Sensors and Actuators 84 (2000), pp. 95–102]. 
   In this example, in the middle of the radiator component  310 , there are superimposed a first electret layer  315  and a second electret layer  316 , between which layers there is a conductive film  313 . In both electret layers, there is formed an inner vertical electric field, so that the directions of these fields are opposite. Above the first electret layer, there is a sound-permeable first support layer  318 , made of a porous and flexible material. Respectively, underneath the second electret layer, there is a sound-permeable second support layer  319 , made of a porous and flexible material. The surfaces of both support layers facing the electret layers are designed to be corrugated, so that said surfaces only touch the electret layers at a relatively small area. These corrugated inner surfaces are coated with a conductive material, so that there are created a first conductor plane  311  that is in contact with the first electret layer  315 , and a second conductor plane  312  that is in contact with the second electret layer  316 . The first and second conductor planes are provided with tiny perforations, so that even these layers are sound-permeable. The antenna feed conductor  320  is connected at a certain point to the first conductor plane  311 , and also at the same vertical line to the second conductor plane  312 . Respectively, the antenna short circuit wire  330  is connected at a certain point to the first conductor plane  311 , and also at the same vertical line to the second conductor plane  312 . Thus the structure serves as a PIFA type antenna, where instead of one radiating plane, there is a dual plane formed of the first and second conductor planes. 
   The first output conductor of the audio amplifier AA, i.e. the first audio conductor  341 , is connected to the first and second conductor layer that are galvanically interconnected according to the description above. The second output conductor of the audio amplifier, i.e. the second audio conductor  342 , is connected to the conductive film  313 . When the output voltage of the audio amplifier is zero, the electret layers  315 ,  316  are in their middle position. When the output voltage of the audio amplifier deviates from than zero, the corresponding electric field strengthens the electric field of one electret layer and weakens the electric field of the other electret layer. Now the electrostatic force that draws the plane formed by the electret layers towards the first conductor layer  311  is for instance higher than the electrostatic force that draws the plane formed by the electret layers towards the second conductor layer  312 . For this reason, said plane moves forward, until a force balance is reached. When the output voltage of the audio amplifier deviates from zero in the opposite direction, also the changes in the forces have opposite signs, and the plane formed by the electret layers moves downwards. Consequently, the motion of the plane  315 ,  313 ,  316  conforms to the fluctuations of the output voltage of the audio amplifier. 
   The radio-frequency amplifier RA is connected to the radiator component capacitively. In between the “hot” conductor of the audio amplifier output and the antenna feed conductor  320 , there is a condensator C 31 , and between the ground plane GND and the antenna short-circuit conductor  330 , there is a condensator C 33 . The impedances of the condensators are fairly low at radio frequencies, but fairly high at audio frequencies. Their purpose is to separate the amplifiers feeding the radiator component from each other. For the same reason, the impedance of at least the first output conductor  341  of the audio amplifier with respect to ground is relatively high. 
   In  FIG. 3   a , the radiator component  310  is at the edges supported against the plane provided underneath it by means of a dielectric frame  370 , only a small part of which is illustrated in the drawing. Owing to the frame  370 , there is formed a closed or nearly closed box, which is advantageous for the sound reproduction. Without said box, the radiator component would be shorted acoustically, particularly at low audio frequencies. 
   The conductor layers  311 ,  312  radiating electromagnetic energy can be provided with similar double/multiband arrangements as in the example of  FIG. 2   a.    
     FIG. 4  shows a third example of an arrangement according to the invention at the antenna head of a radio phone. For the most part, the arrangement is similar to the one shown in  FIGS. 3   a ,  3   b . The difference is that the top surface of the radiator component  410  is now coated with a sound-permeable conductor layer  411 . This layer is galvanically connected to the antenna input conductor  420  and to the antenna short-circuit conductor  430  at the same vertical lines as the conductor layers inside the radiator component. Thus there is created a radio radiator that can be made better, as regards conductivity, than the conductor layers inside the component. In  FIG. 4 , in the conductor layer  411  there is drawn a slot starting from the edge thereof in order to form a double band antenna. 
     FIG. 5  shows a radio phone MS. It is provided with a radiator component  510 , which according to the invention forms a substantial part of both the antenna and the loudspeaker. 
   In the above specification, we have described antenna head structures according to the invention. The invention is not limited just to these. The inventive idea can be applied in many ways within the scope of the independent claim  1 .