Patent Publication Number: US-2010127953-A1

Title: Antenna, antenna arrangement and radio communication apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to an antenna, an antenna arrangement with such an antenna, and a radio communication apparatus with such an antenna arrangement. 
     BACKGROUND 
     Antenna characteristics are very much depending on geometrical properties, such as position and form of antenna elements, position of feeding, and position and form of parasitic elements, which can be both intended and unintended. By changing any of these properties, the antenna characteristics can be tuned such that the antenna works as intended. This is normally done when designing the antenna, or by switching in and out antenna elements and/or parasitic elements. However, there is a desire to provide a less complex way of after-design tuning of an antenna. 
     SUMMARY 
     The present invention is based on the understanding that an electroactive polymer can be arranged to change its form when applying a suitable voltage across it. The inventor has found that by applying antenna elements on mutual sides of an electroactive polymer element, geometrical properties of these can be changed by applying a voltage across the electroactive polymer element. 
     According to a first aspect, there is provided an antenna comprising a first antenna element; a second antenna element arranged along the first antenna element; and an electroactive polymer element arranged between the first and the second antenna elements, wherein the electroactive polymer element is connected to electrodes through which a voltage is applicable across the electroactive polymer element such that the distance between the first and the second antenna elements is adjustable by changing the voltage. 
     At least one of the first and second antenna element may be a conductive coating on the electroactive polymer element. 
     The antenna may be a planar inverted F antenna. The antenna may further have capacitive feeding. 
     At least one of the first and the second antenna element may be fed via a spring contact such that feeding is ensured upon the adjustment of position of the antenna element. 
     According to a second aspect, there is provided an antenna arrangement comprising an antenna comprising a first antenna element; a second antenna element arranged along the first antenna element; and an electroactive polymer element arranged between the first and the second antenna elements, wherein the electroactive polymer element is connected to electrodes through which a voltage is applicable across the electroactive polymer element such that the distance between the first and the second antenna elements is adjustable by changing the voltage. 
     The antenna arrangement may further comprise a controller arranged to provide the voltage based on a received tuning parameter. 
     According to a third aspect, there is provided a radio communication apparatus comprising an antenna arrangement comprising an antenna comprising a first antenna element; a second antenna element arranged along the first antenna element; and an electroactive polymer element arranged between the first and the second antenna elements, wherein the electroactive polymer element is connected to electrodes through which a voltage is applicable across the electroactive polymer element such that the distance between the first and the second antenna elements is adjustable by changing the voltage. 
     The communication apparatus may further comprise a controller arranged to provide the voltage based on a received tuning parameter. The tuning parameter may be provided by a radio circuitry of the communication apparatus. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS. 1   a  and  1   b  are sectional views of an antenna according to an embodiment in different operation states. 
         FIGS. 2   a  and  2   b  are sectional views illustrating an antenna according to an embodiment in different operation states. 
         FIG. 3  schematically illustrates an antenna arrangement according to an embodiment. 
         FIG. 4  schematically illustrates a radio communication apparatus according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1   a  and  1   b  are sectional views of an antenna  100  according to an embodiment in different operation states. The antenna  100  comprises a first antenna element  102 , a second antenna element  104 , and an electroactive polymer element  106  arranged between the first and the second antenna elements  102 ,  104 . The electroactive polymer element  106  has electrodes  108 ,  110  arranged on mutual sides such that a voltage V can be applied across the electroactive polymer element  106 . Upon application of the voltage, the electroactive polymer changes size and applies a force on the antenna elements  102 ,  104  such that they are displaced, as illustrated in  FIG. 1   b.  Thus, geometry and characteristics of the antenna is changed by applying suitable voltage between the electrodes  108 ,  110 , and thus across the electroactive polymer. 
       FIGS. 2  are sectional views illustrating an antenna  200  according to an embodiment. The antenna  200  is a planar inverted F antenna. The antenna  200  comprises a first antenna element  202 , a second antenna element  204 , and an electroactive polymer element  206  arranged between the first and the second antenna elements  202 ,  204 . The electroactive polymer element  206  has electrodes  208 ,  210  arranged on mutual sides such that a voltage can be applied across the electroactive polymer element  206 . Upon application of the voltage, the electroactive polymer changes size and applies a force on the antenna elements  202 ,  204  such that they are displaced. Thus, geometry and characteristics of the antenna is changed by applying suitable voltage between the electrodes  208 ,  210 , and thus across the electroactive polymer. A spring contact  212  is arranged to feed the antenna elements  202 ,  204 . This provided for proper feeding although the antenna elements  202 ,  204  are displaced, as illustrated in  FIG. 2   b.  Such a spring contact  212  is also suitable for other embodiments for providing proper feeding to displaced antenna elements. 
       FIG. 3  schematically illustrates an antenna arrangement according to an embodiment. The antenna arrangement comprises an antenna  300  having displacable antenna elements by an electroactive polymer element, e.g. according to any of the embodiments demonstrated above with reference to  FIGS. 1 and 2 . A voltage is provided across the electroactive polymer element by a controller  302 , which provides the voltage based on a received tuning signal  304 . Thereby, the antenna  300  can be tuned for desired properties. 
       FIG. 4  schematically illustrates a radio communication apparatus  400  according to an embodiment. The radio communication apparatus  400  comprises an antenna  402  having at least one of its antenna elements displaceable such that its distance to the other antenna element is adjustable, as demonstrated above, by an electroactive polymer element. This is performed by provision of a voltage across the electroactive polymer element, where the voltage is provided by a controller  404 . The controller  404  can provide this voltage based on a tuning signal that can be provided by a radio circuitry  406 . The radio circuitry  406  is arranged to send and/or transmit via the antenna  402 . Optionally, signal processing means  408 , which can be a general processor or dedicated signal processing circuitry, is connected to the radio circuitry for provision of signals to the radio circuitry for transmission, reception of received and demodulated signals, and/or provision of control signals to the radio circuitry. Optionally, the tuning signal is provided by the signal processing means  408  instead of the radio circuitry  406 . The tuning signal can be used to adjust center frequency, directional properties, impedance, etc. of the antenna  402 . Further elements  410 , such as memory, user interface, interfaces, etc. can be connected to the signal processing means  408 .