Patent Publication Number: US-2010127945-A1

Title: Apparatus for compensation of the impedance and the load phase of the antenna element

Description:
FIELD OF THE INVENTION 
     Embodiments of the present invention relate to an apparatus. In particular, they relate to a radio communication apparatus. 
     BACKGROUND TO THE INVENTION 
     Apparatus such as mobile cellular telephones usually have at least one antenna element by which they can communicate with other apparatus. If the context of the apparatus changes, the load phase and impedance of the antenna element at a desired frequency band may change. For example, if a user handles the apparatus, the antenna element may electromagnetically couple with the user and the load phase and the impedance of the antenna element at the desired frequency band may change as a consequence. 
     One problem associated with such an apparatus is that it may no longer be able to communicate efficiently in the desired frequency band. 
     Mobile cellular telephone operators usually require that a mobile cellular telephone within their network meet certain Total Transmission Power (TRP) and Total Received Sensitivity (TRS) requirements. When the context of a mobile cellular telephone changes, the TRP and TRS values for the mobile cellular telephone may change and no longer meet these requirements. Currently, in order to compensate for such changes in the TRP value, additional electrical energy may be supplied to the antenna element. This may result however in the battery life of the mobile cellular telephone being reduced. 
     Therefore, it would be desirable to provide an alternative apparatus. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one embodiment of the present invention there is provided an apparatus comprising: an antenna element having an impedance and a load phase; a phase shifter coupled to the antenna element; and a controller for controlling, in response to a change in a context of the apparatus, the phase shifter to compensate for a consequent change in the impedance and the load phase of the antenna element. 
     When the apparatus is in a first context, the antenna element may have a first load phase and a first impedance. When the context of the apparatus changes to a second context, the phase shifter may compensate for the consequent change in the load phase and impedance of the antenna element by bringing the load phase and the impedance of the antenna element towards the first load phase and the first impedance. 
     The context of the apparatus may be a physical environment of the apparatus. The context of the apparatus may be a physical mode of the apparatus. 
     The apparatus may further comprise one or more sensors for detecting the context of the apparatus and for providing detection information to the controller for identification of the context of the apparatus. The one or more sensors may be operable to detect the proximity of an object which is external to the apparatus. 
     The controller may be operable to detect and subsequently identify, using the detection information, the context of the apparatus. The controller may be operable to detect an operational mode of the apparatus. The apparatus may further comprise a memory for storing a database having information associated with at least one context of the apparatus. The controller may be operable to identify the context of the apparatus by comparing the detection information with the information in the database. 
     The predetermined information in the database may include phase shift information for at least one context. 
     The controller may be operable to control the phase shifter using the phase shift information in the database. The phase shifter may be coupled to the antenna element via a feed point of the antenna element. The phase shifter may be alternatively coupled to the antenna element via a ground point of the antenna element. 
     According to another embodiment of the present invention there is provided a method comprising: controlling, in response to a change in a context of an apparatus, including an antenna element, having an impedance and a load phase, and a phase shifter coupled to the antenna element, the phase shifter to compensate for a consequent change in the impedance and the load phase of the antenna element. 
     When the apparatus is in a first context, the antenna element may have a first load phase and a first impedance and when the context of the apparatus changes to a second context, the method may further comprise compensating for the consequent change in the load phase and the impedance of the antenna element by bringing the load phase and the impedance of the antenna element towards the first load phase and the first impedance. 
     The context of the apparatus may relate to the physical environment of the apparatus. The context of the apparatus may be a physical mode of the apparatus. 
     The method may further comprise detecting, via one or more sensors, the context of the apparatus and providing information to a controller of the apparatus. 
     The method may further comprise identifying, at the controller, the context of the apparatus using the detected information. 
     The one or more sensors may be operable to detect the proximity of an object which is external to the apparatus. 
     The method may further comprise detecting, at a controller, the context of the apparatus. The controller may be operable to detect an operational mode of the apparatus. 
     The method may further comprise identifying, at the controller, the context of the apparatus using the detection information. 
     The method may further comprise storing a database having information associated with at least one context of the apparatus. The method may further comprise comparing the detection information with the information in the database to identify the context of the apparatus. 
     The predetermined information in the database may include phase shift information for at least one context. The phase shifter may be controlled by using the phase shift information in the database. 
     According to further embodiment of the present invention, there is provided a computer program comprising program instructions for causing a computer to perform the method as described in the above paragraphs. 
     According to another embodiment of the present invention, there is provided a computer program comprising program instructions for controlling the load phase and impedance of an antenna element and comprising means for controlling, in response to a change in a context of an apparatus, including an antenna element, having a load phase and an impedance, and a phase shifter coupled to the antenna element, the phase shifter to compensate for a consequent change in the load phase and impedance of the antenna element. 
     According to a further embodiment of the present invention, there is provided a physical entity embodying the computer program as described in the above paragraphs. 
     According to another embodiment of the present invention, there is provided an electromagnetic carrier signal carrying the computer program as described in the above paragraphs. 
     According to a further embodiment of the present invention there is provided an apparatus comprising: an antenna element having a first resonant frequency within a first operational frequency band when in a first context; a phase shifter coupled to the antenna element; and a controller for controlling, in response to a change in a context of the apparatus, the phase shifter to change the resonant frequency of the antenna element to a second resonant frequency within the first operational frequency band. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention reference will now be made by way of example only to the accompanying drawings in which: 
         FIG. 1  illustrates a schematic diagram of an apparatus according to an embodiment of the present invention; 
         FIG. 2  illustrates a flow diagram of a method according to an embodiment of the present invention; 
         FIG. 3  illustrates a schematic diagram of an apparatus according to another embodiment of the present invention; 
         FIG. 4  illustrates a graph of antenna load phase versus the receiver sensitivity and antenna load phase versus the overall Voltage Standing Wave Ratio of the receiver; 
         FIG. 5  illustrates a schematic diagram of an apparatus according to another embodiment of the present invention; 
         FIG. 6  illustrates a schematic diagram of an apparatus according to a further embodiment of the present invention; 
         FIG. 7  illustrates a schematic diagram of an apparatus according to another embodiment of the present invention; 
         FIG. 8  illustrates a schematic diagram of an apparatus according to a further embodiment of the present invention; and 
         FIG. 9  illustrates a schematic diagram of an apparatus according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     The figures illustrate an apparatus  10  comprising: an antenna element  24  having an impedance and a load phase; a phase shifter  30  coupled to the antenna element  24 ; and a controller  12  for controlling, in response to a change in a context of the apparatus  10 , the phase shifter  30  to compensate for a consequent change in the impedance and the load phase of the antenna element  24 . 
       FIG. 1  illustrates a schematic diagram of one embodiment of an apparatus  10  according to the present invention. In more detail, the apparatus  10  includes a controller  12 , a memory  14 , a display  16 , an audio output device  18 , an audio input device  20 , a transceiver  22 , an antenna element  24 , a user input device  26 , a power source  28 , a phase shifter  30  and one or more sensors  32 . 
     The apparatus  10  may be any electronic device and may be, for example, a portable apparatus such as a mobile cellular telephone, Personal Digital Assistant (PDA) or laptop computer. In the following embodiment which is described in detail with reference to  FIG. 1 , the apparatus  10  is a mobile cellular telephone. 
     The controller  12  may be any suitable processor and is, in this embodiment, a microprocessor. The controller  12  is connected to read from and write to the memory  14 . The memory  14  may be any suitable memory and may be, for example, permanent built-in memory such as flash memory or it may be a removable memory such as a hard disk, secure digital (SD) card or a micro-drive. 
     The display  16  is coupled to the controller  12  for receiving and displaying data. The controller  12  may read data from the memory  14  and provide it to the display  16  for display to a user of the cellular telephone  10 . The display  16  may be any suitable display and may be for example, a thin film transistor (TFT) display or a liquid crystal display (LCD). 
     The controller  12  is arranged to provide audio data to the audio output device  18 . The audio output device  18  is arranged to convert the audio data into acoustic waves, audible to the user of the cellular telephone  10 . The audio output device  18  may be, for example, a loudspeaker. 
     The audio. input device  20  is arranged to convert acoustic waves (for example, a voice of a user) into an electrical signal for input to the controller  12 . The audio input device  20  is in this embodiment a microphone. 
     The transceiver  22  is connected to the antenna element  24  and to the controller  12 . The transceiver  22  includes radio frequency portions of the transmitter and receiver which are not illustrated in this figure. The controller  12  is arranged to provide data to the transceiver  22 . The transceiver  22  is arranged to encode the data and provide it to the antenna element  24  for transmission. The antenna element  24  is arranged to transmit the encoded data as a radio signal. 
     The antenna element  24  is also arranged to receive a radio signal. The antenna arrangement  24  then provides the received radio signal to the transceiver  22  which decodes the radio signal into data. The transceiver  22  then provides the data to the controller  12 . 
     It should be appreciated that the antenna element  24  may be a part of an antenna arrangement which includes a plurality of antenna elements. Each of the antenna elements in the antenna arrangement may be arranged in accordance with embodiments of the invention. The antenna element  24  may be any suitable antenna element and may be a monopole antenna, a dipole antenna, a helical antenna, a planar inverted F antenna (PIFA), a planar inverted L antenna (PILA) or a loop antenna. If the antenna element  24  is part of an antenna arrangement, it should be appreciated that the antenna arrangement may include any combination of the above antenna types. 
     The user input device  26  is operable by a user of the mobile cellular telephone to provide a control signal to the controller  12 . The user input device  26  may be any suitable device and may be a keypad in one embodiment. 
     The power source  28  is configured to provide electrical power to each of the components of the apparatus  10 . The controller  12  is operable to control the supply of electrical power from the power source  28  to the components of the apparatus  10 . In the embodiment where the apparatus  10  is a mobile cellular telephone the power source  28  is a battery. 
     The phase shifter  30  may be connected to the antenna element  24  via a feed point or a ground point of the antenna element  24 . If the phase shifter  30  is connected to a ground point of the antenna element  24  then the phase shifter  30  is not connected directly to the transceiver  22 . In this embodiment, data is exchanged between the controller  12  and the antenna element  24  via the transceiver  22  only (indicated by dotted line  34 ). If the phase shifter  30  is connected to the feed point of the antenna element  24  then the phase shifter  30  is also connected to the transceiver  22 . In this embodiment, data is exchanged between the controller  12  and the antenna element  24  via the transceiver  22  and the phase shifter  30  (indicated by dotted line  36 ). 
     Phase shifters are well known within the art of radio frequency circuitry and will not be discussed in detail here. Phase shifters may comprise, among other things, a plurality of transmission lines or comprise lumped components. Phase shifters can also be realised with active components such as transistor circuitry. Phase shifters are configured so that as they are switched between different configurations (for example, as they are switched between different lengths of transmission lines), they change the load phase of the antenna element to which they are connected. If a phase shifter is operating in a theoretically optimum way, then only the phase of the impedance of the antenna element is changed. However, since phase shifters are implemented with actual physical components there will always be an impedance change of the antenna element. 
     The one or more sensors  32  are connected to the controller  12  and are operable to detect the context of the apparatus  10  and provide the detection information to the controller  12 . In other embodiments of the invention, the controller  12  may be operable to detect the context of the apparatus  10 . 
     The context of the apparatus  10  may be defined by the physical environment of the apparatus  10 , for example, the proximity and spatial distribution of objects external to the apparatus  10 . In this embodiment, the one or more sensors  32  are proximity sensors. The context of the apparatus may also be defined by the operating mode of the apparatus  10 . For example, in the embodiment where the apparatus is a mobile cellular telephone, the context of the apparatus may be defined by the radio frequency protocol the apparatus is communicating in (for example, GSM, WCDMA, DVBH etc. . . . ). The context of the apparatus may also be defined by the physical mode of the apparatus. For example, if the apparatus is a mobile phone with a sliding mechanism, swivel mechanism or flip mechanism, then one physical mode may be the physical position of the slide mechanism, swivel mechanism or flip mechanism. The physical mode of the apparatus may be detected by the controller  12  or sensors  32  (e.g. HAL sensors). 
     The memory  14  stores computer program instructions  38  that control the operation of the apparatus  10  when loaded into the controller  12 . The computer program instructions  38  provide the logic and routines that enables the controller  12  to perform the method described in the following paragraphs of the description. 
     The computer program instructions may arrive at the apparatus  10  via an electromagnetic carrier signal  40  or be copied from a physical entity  42  such as a computer program product, a memory device or a record medium. 
     The memory  14  also stores a database  39  which includes information for at least one context of the apparatus  10 . The controller  12  can interrogate the database  39  to identify the context of the apparatus  10  by comparing the detection information (obtained from the sensors  32  or obtained by the controller  12 ) with the information in the database. The database  39  also includes phase shift information for each context. The use of the database  12  will be explained in greater detail in the following paragraphs. 
       FIG. 2  illustrates a flow diagram of a method according to an embodiment of the present invention. Initially at step  44 , the apparatus  10  is in a first context. The phase shifter  30  is in a first configuration and consequently, the antenna element  24  has a first load phase and a first impedance at a first operational frequency band. The first load phase and first impedance are optimum for the antenna element  24  when operating in the first operational frequency band. At the first load phase and first impedance, the antenna element  24  resonates efficiently in the first operational frequency band because the capacitive and inductive components of the antenna element&#39;s  24  impedance effectively cancel one another out and the antenna element  24  becomes substantially only resistive. Consequently, the apparatus  10  consumes less electrical power from the power source  28  to transmit a signal. Additionally, at the first load phase and first impedance, the antenna element  24  receives signals more efficiently. 
     At step  46 , the sensors  32  and/or the controller  12  check to see if there has been a change in the context of the apparatus  10 . If there has not been a change in the context of the apparatus, then step  46  is repeated. If there has been a change in the context of the apparatus  10 , then the sensors  32  and/or the controller  12  detect the change and provide detection information to the controller  12 . 
     The sensors  32  and/or controller  12  may check to see if there has been a change in the context of the apparatus at predefined time intervals (for example, 5 seconds or 1600 times per second if it is performed at the base rate). In some embodiments, the sensors  32  and/or controller  12  may check at variable time intervals depending on the context of the apparatus. For example, if they detect that the context of the apparatus is likely to change frequently, they may decrease the time between the time intervals. 
     The proximity sensors  32  are arranged to detect the proximity and spatial distribution of objects which are external to the apparatus  10 . For example, the proximity sensors  32  may be arranged to detect if the user has placed the apparatus  10  next to his cheek (which is usually the case when the user is making a phone call on the apparatus) or if the user is holding the apparatus  10  in his hand away from his cheek (which is usually the case when the user is watching a film or television on the apparatus). 
     The controller  12  is arranged to detect if the operating mode of the apparatus  10  changes. For example, the controller  12  may detect if the operational mode of the apparatus  10  changes from a GSM voice call to a GSM data call. Additionally, the controller  12  can detect a change in the context of the apparatus  10  by measuring the power level of the power source  28 . If the electrical power output by the power source  28  increases, this may indicate that the load phase and impedance of the antenna element  24  (and in one embodiment, the impedance of the antenna element  24 ) have changed and that the antenna element  24  requires more electrical power to transmit a given signal. Such a change in the load phase and impedance of the antenna element  24  may indicate a change in the context of the apparatus  10 . 
     The load phase and impedance of the antenna element  24  at the first operational frequency band may change (due to a change in the context of the apparatus  10 ) so that they are no longer equal to the first load phase and first impedance respectively (i.e. the load phase of the antenna element  24  at the first operational frequency band is shifted away from the first load phase and the impedance of the antenna element  24  at the first operational frequency band is shifted away from the first impedance). For example, the load phase and impedance of the antenna element  24  may change if the apparatus  10  is moved to a position adjacent the user&#39;s cheek. The change in the load phase of the antenna element  24  may reduce the power of an output signal from the antenna element  24  and/or increase the power consumption of the antenna element  24 . 
     In step  48 , the controller  12  interrogates the database  39  and compares the detection information (obtained in step  46 ) with the information in the database  39  to identify the current context of the apparatus  10 . For example, the sensors  32  may detect that the apparatus  10  is placed in proximity to an object which is adjacent the user input device  26  of the apparatus (e.g. the keypad). When the controller  12  receives this detection information and interrogates the database  39 , it identifies that the apparatus  10  has been placed next to the user&#39;s cheek. As another example, the controller  12  may detect that the operational mode of the apparatus  10  has been changed from GSM voice call to GSM data call. When the controller  12  subsequently interrogates the database  39  and compares the detection information with the information in the database  39 , it identifies that the apparatus  10  is now being held in the user&#39;s hand away from the user&#39;s cheek. 
     The controller  12  may identify the following contexts of the apparatus  10 : a voice call (via GSM, WCDMA and other protocols), a data call (via GSM, GPRS, EGPRS, WCDMA and other protocols), watching television content on the apparatus  10 , phone call with phone located on user&#39;s cheek, phone call with wireless headset, phone call with wired headset, phone call with integrated hands free speaker. 
     Once the context of the apparatus  10  has been identified, the controller  12  then extracts phase shift information for the identified context from the database  39  at step  50 . The phase shift information identifies the phase shift necessary for bringing the load phase and impedance of the antenna element  24  towards (and preferably at) the first load phase and the first impedance. 
     If the controller  12  determines that the load phase and impedance of the antenna element  24  have not substantially changed (for example, above a predetermined threshold) and it is not worth controlling the phase shifter  30  to change its configuration, the controller  12  goes back to step  46 . 
     At step  52 , the controller  12  sends a control signal to the phase shifter  30  to change the phase shifter  30  to a second configuration. At step  54 , the phase shifter  30  compensates for the change in the load phase and impedance of the antenna element  24 . The change in the configuration of the phase shifter  30  to the second configuration changes the load phase and impedance of the antenna element  24  to compensate for the change in the load phase and impedance due to the change in context. The second configuration of the phase shifter  30  brings the load phase and impedance of the antenna element  24  towards (and preferably at) the first load phase and the first impedance. 
     In one embodiment, the accuracy of the compensation performed by the phase shifter  30  is dependent upon the detected context of the apparatus  10 . For example, in some contexts only a minimal performance improvement may be needed and the accuracy of the compensation performed by the phase shifter  30  may be ±30 degrees. In other contexts, the performance improvement may be important and the accuracy of the compensation performed by the phase shifter  30  is less than ±30 degrees and may be less than ±5 degrees. 
     Embodiments of the present invention provide an advantage in that since the phase shifter  30  compensates for the change in the load phase and impedance of the antenna element  24  due to the change in the context of the apparatus  10 , the antenna element  24  is more efficient when transmitting and receiving signals. This may help to reduce the power consumption of the antenna element  24  and enable the apparatus  10  to achieve the required TRP and TRS values irrespective of its context. 
     The phase shifter  30  may be enabled at certain predetermined power levels depending on whether the antenna element  24  is receiving or transmitting a signal. For example, the phase shifter  30  may be enabled if the antenna element  24  is transmitting above a threshold power level (in order to conserve battery power) or it may be enabled if the antenna element  24  is expected to receive a signal below a threshold power level (so that it may receive the signal). 
     In one embodiment, the load phase and impedance for the optimum current consumption of the antenna element  24  and the load phase and impedance for the optimum antenna performance may not be the same. The controller  12  (or the user of the apparatus  10  via a software application) is arranged determine whether the load phase should be controlled to optimise the current consumption or optimise the antenna performance based on its knowledge of the context of the apparatus. 
     In another embodiment, the controller  12  may detect that the apparatus  10  is operating simultaneously in two or more similar operational frequency bands using two or more different antenna elements. In this embodiment, the controller  12  controls the phase shifter  30  to change the load phase and impedance of the antenna element  24  so that one of the antenna elements is resonant at a different frequency but within the same operational frequency band. This may help to reduce the interference between the two antenna elements. 
     For example, the antenna element  24  may be operating at GSM 850 or at GSM 900 and the controller  12  may detect that the user has requested that television content be downloaded via another antenna (not illustrated) using DVBH which has a similar operational frequency band (470 to 702 MHz). DVB-H is a mobile television standard which will be widely deployed within the next few years. DVB-H is an evolution of the European DVB-T digital television standard. The operational frequencies for DVB-T are from 470 MHz to 862 MHz. In this embodiment, the controller  12  controls the phase shifter  30  to change the load phase of the antenna element  24  so that it continues to operate in the GSM 850 band or in the GSM 900 band but at a different resonant frequency which does not substantially interfere with the download of the television content. 
       FIG. 3  illustrates a schematic diagram of another embodiment of the present invention. In this embodiment, the antenna element  24  includes a planar element  56 , a feed point  58 , a ground point  60  and an additional ground point  62 . The additional ground point  62  is connected to an ESD filter  64  which is in turn connected to the phase shifter  30 . The phase shifter  30  is connected to a switching circuit  66  which is in turn connected to a first transmission line  68  and a second transmission line  70 . The remaining components (such as the controller  12 ) of the apparatus  10  are not illustrated to maintain the clarity of  FIG. 3 . 
     The switching circuit  66  (an SPDT switch in this embodiment) is configured to switch the phase shifter  30  between being connected to the first transmission line  68  and being connected to the second transmission line  70 . The length of the first transmission line  68  is selected so that when the phase shifter  30  is connected to the first transmission line  68 , the antenna element  24  is effectively connected to an open circuit at the additional ground point  62 . The length of the second transmission line  70  is selected so that when the phase shifter  30  is connected to the second transmission line  70 , the antenna element  24  is effectively connected to a closed circuit at the additional ground point  62 . 
     The antenna element  24  is arranged so that it is operable in two resonant modes. When the phase shifter  30  is connected to the first transmission line  68 , the antenna element  24  is operable in the GSM 850 and GSM 1900 bands. When the phase shifter  30  is connected to the second transmission line  70 , the additional ground point  62  changes the resonant modes of the antenna  24  so that it is operable in the GSM 900 and GSM 1800 modes. 
     The phase shifter  30  is arranged to receive control signals (indicated by arrow  72 ) from the controller  12  (illustrated in  FIG. 1 ). If the context of the apparatus  10  changes, the controller  12  can control the phase shifter  30  to compensate for the consequent change in the load phase and impedance of the antenna element  24  in each of the four resonant modes mentioned above. 
     This embodiment provides an advantage in that since the phase shifter  30  is connected to the additional ground point  62 , it does not introduce an additional insertion loss between the antenna element  24  and the transceiver  22 . Consequently, the antenna element  24  may operate more efficiently. 
       FIG. 4  illustrates a graph of antenna load phase versus the receiver sensitivity and antenna load phase versus the overall Voltage Standing Wave Ratio of the receiver. The graph includes a horizontal axis  74  for the antenna load phase angle and includes values from −180° to 180°. The graph also includes a vertical axis  76  for the receiver sensitivity and a vertical axis  78  for the standing wave ratio of the receiver. A solid line  80  represents a plot of the receiver sensitivity over the range of the antenna load phase angle and has a sinusoidal shape. At −180° the solid line  80  initially rises to a maxima  81  (at approximately −135°) and falls to a minima at approximately 60°. A dotted line  82  represents a plot of the receiver standing wave ratio over the range of the antenna load phase angle and also has a sinusoidal shape. At −180° the dotted line  82  initially starts at a position where it is falling towards a minima  83  at approximately −100° and then rises to a maxima at approximately 80°. 
     The receiver standing wave ratio represents the extent to which an incoming signal is reflected back to an antenna port. The standard wave ratio can be considered as a loss for the received signal path which degrades the receiver reception performance. 
     Advantages which are provided by embodiments of the present invention can be understood from  FIG. 4 . In  FIG. 4 , the first load phase mentioned above is approximately equal to the load phase at the minima  83  of the dotted line  82 . At this point, the sensitivity of the receiver indicated by the solid line  80  is also near its maxima  81 . If the context of the apparatus  10  changes, the load phase of the antenna element  24  changes so that it is no longer equal to the first load phase (and hence the impedance of the antenna element  24  is no longer equal to the first impedance). As can be appreciated from  FIG. 4 , if the load phase of the antenna element  24  changes, the standing wave ratio of the receiver increases and the sensitivity of the receiver decreases. This may result in a degradation in the performance of the receiver. Embodiments of the invention provide an advantage because the phase shifter  30  may shift the load phase and impedance towards the first load phase and the first impedance and thereby decrease the standing wave ratio and increase the sensitivity of the receiver. A similar graph to the one illustrated in  FIG. 4  may be plotted for the performance of a transmitter. 
     Fig,  5  illustrates a schematic diagram of an apparatus  10  according to another embodiment of the present invention. The apparatus  10  is similar to the apparatus illustrated in  FIG. 1  and where features are similar, the same reference numerals are used. In this embodiment, the apparatus  10  includes a directional coupler  84 , an (optional) RF to DC rectifier  86  and an (optional) RF to DC rectifier  88  and a transmission line  90 . The remaining components of the apparatus  10  are not illustrated to maintain the clarity of  FIG. 5 . 
     The transmission line  90  is connected to the transceiver  22  and to the phase shifter  30  via the directional coupler  84 . The directional coupler  84  produces a signal  92  which includes a portion of a transmitted signal and a signal  94  which contains a portion of the transmitted signal which is reflected from the antenna element  24  due to load phase of the antenna element  24 . The signals  92  and  94  are provided to the transceiver  22  and to the controller  12  via the rectifiers  86  and  88  which convert RF frequency information to baseband frequency information. The rectifiers  86  and  88  are optional since the controller  12  and the transceiver  22  may be able to process RF frequency information. 
     The controller  12  is arranged to process the signals  92  and  94  to detect if there has been a change in the load phase and impedance of the antenna element  24 . The controller  12  may determine the phase shift required in order to change the load phase and impedance of the antenna element  24  to an optimum load phase and impedance and provide a control signal  13  to the phase shifter  30  to change the configuration of the phase shifter  30  to achieve the optimum load phase and impedance. 
     In order to achieve an optimum load phase and impedance for the antenna element  24 , the controller  12  may carry out an iterative process where it controls the phase shifter  30  to rotate the phase in a first direction and then monitors the reflected power from the antenna element  24  (using signal  94 ). If the reflected power increases, the controller  12  controls the phase shifter  30  to rotate in a second direction (opposite to the first direction). If the reflected power decreases, the controller  12  controls the phase shifter  30  to rotate once again in the first direction. By using an iterative process, the accuracy of the compensation performed by the phase shifter  30  may be improved because the controller  12  continuously controls the phase shifter  30  towards the optimum load phase and impedance. 
       FIG. 6  illustrates an apparatus according to a further embodiment of the present invention. The apparatus  10  is similar to the apparatus illustrated in  FIG. 1  and where the features are similar, the same reference numerals are used. In this embodiment, the apparatus  10  includes a switch  96 , a transmission line  98 , a transmission line  100  and a transmission line  102 . 
     The transceiver  22  includes a transmitter  104  and a receiver  106 . The transmitter  104  is connected to the switch  96  via the transmission line  98  and the receiver  106  is connected to the switch  96  via the transmission line  100 . The switch  96  is connected to the phase shifter  30  via the transmission line  102 . 
     When a signal is transmitted from the transmitter  104  to the antenna element  24 , some of the reflected signal is leaked to the transmission line  100  (when the switch  96  connects the transmission line  100  to the phase shifter  30 ). The leaked signal on the transmission line  100  can be compared to the transmission signal in the transmitter  104  and the controller  12  may control the phase shifter  30  to change its configuration so that the load phase compensates for a change in the context of the apparatus  10 . 
     The controller  12  determines if the phase shifter  30  is providing an optimum compensation for the antenna element  24  by comparing the phase and amplitude of the leaked signal on the transmission line  100  with stored optimum phase and amplitude values. If the phase and amplitude of the leaked signal are the same as the stored optimal phase and amplitude values, the controller  12  determines that the phase shifter  30  is providing optimal compensation of the load phase and impedance of the antenna element  24 . The optimum antenna load phase can be determined during development of the apparatus  10  and can be stored in the memory  14 . The optimum load phase value can be considered as a target value when an iterative process is performed. 
       FIG. 7  illustrates an apparatus according to another embodiment of the present invention. The apparatus  10  is similar to the apparatus  10  illustrated in  FIG. 5  and where the features are similar, the same reference numerals are used. In this embodiment, the transceiver  22  includes a mixer  108 , a voltage controlled oscillator  110  and a phase comparator  112 . 
     In this embodiment, the controller  12  sends transmission data  114  to the transceiver  22  where it is provided to the mixer  108  and converted to a transmission frequency (determined by the voltage controlled oscillator  110 ). The phase comparator  112  is arranged to compare the signal  94  (from the directional coupler  84 ) with the output of the voltage controlled oscillator  110  and provide an output  116  to the controller  12  which indicates the phase difference between the output of the voltage controlled oscillator  110  and the signal  94 . The controller  12  processes the output  116  of the phase comparator  112  to determine how to control the phase shifter  30  to change the load phase of the antenna element  24 . 
       FIG. 8  illustrates an apparatus according to a further embodiment of the present invention. The apparatus  10  is similar to the apparatus illustrated in  FIG. 1  and where the features are similar, the same reference numerals are used. 
     In this embodiment, the apparatus  10  includes a second transceiver  23 , a second phase shifter  31  and a second antenna element  25 . The second phase shifter  31  can be controlled by the controller  12  or by the transceiver  23  (via signals  15  and  37  respectively). The transceivers  22  and  23  may have similar functionalities and include transmitter and receiver portions. The transceiver  22  may be, for example, a GSM/WCDMA transceiver and the transceiver  23  may be WLAN transceiver. The controller  12  may control the phase shifters  30  and  31  using the same control signal  13  if they are both operating at substantially the same operational frequency band. 
       FIG. 9  illustrates an apparatus according to another embodiment of the present invention. The apparatus  10  is similar to the apparatus illustrated in  FIG. 5  and where the features are similar, the same reference numerals are used. In this embodiment, the apparatus  10  includes a third antenna element  118 , a third phase shifter  120 , a directional coupler  122  and a directional coupler  124 . 
     The third antenna element  118  is a diversity reception antenna and is used to increase the operational frequency range of the apparatus  10 . The third antenna element  118  may be used, for example, to receive signals in a WLAN frequency band. The third antenna element  118  is connected to the transceiver  22  via the third phase shifter  120  and the directional couplers  122  and  124  and may be controlled via a signal  128 . 
     The directional coupler  122  is arranged to detect the signal reflected from the third antenna  118  and provide it to the transceiver  22  as signal  126 . The directional coupler  124  provides a portion of the signal sent to the antenna element  24  to the transceiver  22 . 
     The transceiver  22  receives the signal  126  and compares it to the signal  128  to determine if the context of the apparatus  10  has changed. If the context of the apparatus  10  has changed, the controller  12  and the transceiver  22  can control the phase shifters  120  (via control signal  17 ) and  30  to compensate for the change in the context. 
     In order to improve the performance of the third antenna element  118 , the signals received by the antenna elements  24  and  118  should be 90° phase off-set relative to one another. This can be achieved by locating the antenna elements  24  and  118  λ/4 apart from one another. Since this may not be possible in all apparatus&#39;, the phase shifter&#39;s  30  and  120  can be controlled to ensure that there is a 90° phase difference between the signals received from the antenna elements  24  and  118 . 
     It should be appreciated that embodiments of the present invention are not limited to the resonant frequency bands mentioned above. For example, the different frequency bands and protocols may include (but are not limited to) DVB-H 470 to 702 MHz, US-GSM 850 (824-894 MHz); EGSM 900 (880-960 MHz); GPS 1572.42 MHz, PCN/DCS1800 (1710-1880 MHz); US-WCDMA1900 (1850-1990) band; WCDMA21000 band (Tx: 1920-1980I Rx: 2110-2180); PCS1900 (1850-1990 MHz); 2.5 GHz WLAN/BT, 5 GHz WLAN, DRM (0.15-30.0 MHz), FM (76-108 MHz), AM (0.535-1.705 MHz), DVB -H[US] (1670-1675 MHz), WiMax (2300-2400 MHz, 2305-2360 MHz, 2496-2690 MHz, 3300-3400 MHz, 3400-3800 MHz, 5150-5875 MHz), RFID (LF [125-134 kHz], HF[13.56 MHz]) UHF [433 MHz, 865-956 MHz or 2.45 GHz), and UWB 3.0 to 10.6 GHz. 
     Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed. For example, phase shifters may be provided at the feed point and the ground point of each antenna element of an antenna arrangement. 
     Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.