Abstract:
Exemplary systems and methods are disclosed for regulating the electrical length of an antenna. An exemplary method comprises transmitting communication signals over a transmission line at a predetermined frequency between a transceiver and an antenna, and with sufficient power to operate the antenna and radiate the communication signals; sensing transmission line signals reflected from the antenna; and modifying an electrical length of the antenna in response to sensing the transmission line signals, the transmission line signals being a reflection of the communication signals. Sensing transmission line signals typically means sensing transmission line signal power levels. In some aspects, the antenna impedance is modified. Alternately, it can be stated that the transmission line signal strength is optimized between the transceiver and the antenna.

Description:
RELATED APPLICATIONS  
       [0001]     This application is a continuation of U.S. application Ser. No. 10/407, 966, filed Apr. 3, 2003, which is incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention generally relates to wireless communication antennas and, more particularly, to a system and method for regulating the operating frequency of a portable wireless communications device antenna.  
       BACKGROUND  
       [0003]     The size of portable wireless communications devices, such as telephones, continues to shrink, even as more functionality is added. As a result, the designers must increase the performance of components or device subsystems while reducing their size, or placing these components in less desirable locations. One such critical component is the wireless communications antenna. This antenna may be connected to a telephone transceiver, for example, or a global positioning system (GPS) receiver.  
         [0004]     Wireless telephones can operate in a number of different frequency bands. In the US, the cellular band (AMPS), at around 850 megahertz (MHz), and the PCS (Personal Communication System) band, at around 1900 MHz, are used. Other frequency bands include the PCN (Personal Communication Network) at approximately 1800 MHz, the GSM system (Groupe Speciale Mobile) at approximately 900 MHz, and the JDC (Japanese Digital Cellular) at approximately 800 and 1500 MHz. Other bands of interest are GPS signals at approximately 1575 MHz and Bluetooth at approximately 2400 MHz.  
         [0005]     Conventionally, good communication results have been achieved using a whip antenna. Using a wireless telephone as an example, it is typical to use a combination of a helical and a whip antenna. In the standby mode with the whip antenna withdrawn, the wireless device uses the stubby, lower gain helical coil to maintain control channel communications. When a traffic channel is initiated (the phone rings), the user has the option of extending the higher gain whip antenna. Some devices combine the helical and whip antennas. Other devices disconnect the helical antenna when the whip antenna is extended. However, the whip antenna increases the overall form factor of the wireless telephone.  
         [0006]     It is known to use a portion of a circuitboard, such as a dc power bus, as an electromagnetic radiator. This solution eliminates the problem of an antenna extending from the chassis body. Printed circuitboard, or microstrip antennas can be formed exclusively for the purpose of electromagnetic communications. These antennas can provide relatively high performance in a small form factor.  
         [0007]     Since not all users understand that an antenna whip must be extended for best performance, and because the whip creates an undesirable form factor, with a protrusion to catch in pockets or purses, chassis-embedded antenna styles are being investigated. That is, the antenna, whether it is a whip, patch, or a related modification, is formed in the chassis of the phone, or enclosed by the chassis. While this approach creates a desirable telephone form factor, the antenna becomes more susceptible to user manipulation and other user-induced loading effects. For example, an antenna that is tuned to operate in the bandwidth between 824 and 894 megahertz (MHz) while laying on a table, may be optimally tuned to operate between 790 and 830 MHz when it is held in a user&#39;s hand. Further, the tuning may depend upon the physical characteristics of the user and how the user chooses to hold and operate their phones. Thus, it may be impractical to factory tune a conventional chassis-embedded antenna to account for the effects of user manipulation.  
       SUMMARY  
       [0008]     A wireless communication device system and method for sensing the electrical length of an antenna are disclosed. That is, the device senses antenna detuning, in response to user manipulation for example. Using the sensed information the device modifies characteristics of the antenna, to “move” the antenna, optimizing the tuning at its intended operating frequency.  
         [0009]     Accordingly, a method is provided for regulating the electrical length of an antenna. An exemplary method comprises transmitting communication signals over a transmission line at a predetermined frequency between a transceiver and an antenna, and with sufficient power to operate the antenna and radiate the communication signals; sensing transmission line signals reflected from the antenna; and modifying an electrical length of the antenna in response to sensing the transmission line signals, the transmission line signals being a reflection of the communication signals.  
         [0010]     In some aspects, modifying the electrical length of the antenna in response to sensing the transmission line signals includes modifying the antenna impedance. Alternately, it can be stated that modifying the electrical length of the antenna includes optimizing the transmission line signal strength between the transceiver and the antenna.  
         [0011]     More specifically, communicating transmission line signals at a predetermined frequency between a transceiver and an antenna includes accepting the transmission line signal from the transceiver at an antenna port. Then, sensing transmission line signals includes measuring the transmission line signal reflected from the antenna port.  
         [0012]     In some aspects of the method, the antenna includes a radiator, a counterpoise, and a dielectric proximately located with the radiator and the counterpoise. Then, modifying the electrical length of the antenna in response to sensing the transmission line signals includes changing the dielectric constant of the dielectric. In some aspects, the antenna dielectric includes a ferroelectric material with a variable dielectric constant.  
         [0013]     Alternately, the antenna includes a radiator with at least one selectively connectable microelectromechanical switch (MEMS). Then, modifying the electrical length of the antenna in response to sensing the transmission line signals includes changing the electrical length of the radiator in response to connecting the MEMS. In other aspects, a MEMS can be used to change the electrical length of a counterpoise.  
         [0014]     Additional details of the above-described method and an antenna system for regulating the electrical length of an antenna are provided below.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is a schematic block diagram of the present invention antenna system for regulating the electrical length of an antenna.  
         [0016]      FIG. 2  is a partial cross-sectional view of the antenna of  FIG. 1  enabled with a ferroelectric dielectric material.  
         [0017]      FIG. 3  is a plan view of the antenna of  FIG. 1  enabled with a microelectromechanical switch (MEMS).  
         [0018]      FIG. 4  is a schematic block diagram illustrating variations of the present invention antenna system for regulating the electrical length of an antenna.  
         [0019]      FIGS. 5   a  and  5   b  are flowcharts illustrating the present invention method for regulating the electrical length of an antenna.  
         [0020]      FIG. 6  is a flowchart illustrating the present invention method for controlling the efficiency of a radiated signal.  
         [0021]      FIG. 7  is a flowchart illustrating the present invention method for regulating the operating frequency of an antenna.  
       DETAILED DESCRIPTION 
    
    
       [0022]      FIG. 1  is a schematic block diagram of the present invention antenna system for regulating the electrical length of an antenna. The system  100  comprises an antenna  102  including an active element  104  having an electrical length responsive to a control signal, an antenna port connected to a transmission line  106  to transceive transmission line signals. The antenna  102  has a control port on line  108  that is connected to the active element and accepts control signals. Especially in the context of a wireless telephone system, active element operating frequencies of interest include 824 to 894 megahertz (MHz), 1850 to 1990 MHz, 1565 to 1585 MHz, and 2400 to 2480 MHz. It should be understood that an antenna electrical length has a direct relationship with (optimally tuned) antenna operating frequencies. For example, an antenna designed to operate at a frequency of 1875 MHz may have an effective electrical length of a quarter wavelength of an electromagnetic wave propagating through a medium with a dielectric constant. The electrical length may be considered to be an effective electrical length that is responsive to the characteristics of the proximate dielectric.  
         [0023]     A detector  110  has an input on line  112  operatively connected to the transmission line  106  to sense transmission line signals and an output on line  114  to supply detected signals. Operatively connected, as used herein, means either a direct connection or an indirect connection through an intervening element. A regulator circuit  116  has an input connected to the detector output on line  114  to accept the detected signals and a reference input on line  118  to accept a reference signal responsive to the intended antenna electrical length, which is related to the frequency of the conducted transmission line signals on line  106 . The regulator circuit  116  has an output connected to the antenna on line  108  to supply the control signal in response to the detected signals and the reference signal. Note that a wireless telephone application of the system  100  may further include filters, duplexers, and isolators (not shown).  
         [0024]     In some aspects of the system  100 , the antenna port reflects transmission line signals in response to changes in the electrical length of the active element  104 . Then, the detector  110  senses transmission line signals reflected from the antenna port on transmission line  106 . That is, the antenna port reflects transmission line signals at a power level that varies in response to changes in the electrical length of the active element  104 , and the detector  110  senses transmission line signals responsive to changes in the reflected power levels. Alternately stated, the antenna port has an input impedance on transmission line  106  that varies in response to changes in the electrical length, or optimally tuned operating frequency of the active element  104 . The detector  110  senses transmission line signals responsive to changes in the antenna port impedance changes. The changes in the electrical length are typically due to changes in the proximate dielectric medium(s). That is, the effective electrical length changes as the dielectric medium near the active element changes. For example, a wireless telephone antenna may have a first electrical length responsive to being placed on a table, and a second electrical length responsive to being held in a user&#39;s hand or placed proximate to a user&#39;s head. It is the change in the dielectric constant of the surrounding dielectric medium that causes changes in the antenna&#39;s electrical length.  
         [0025]     Also shown is a transceiver  120  with a port connected to the transmission line  106  to supply a transmission line signal. The detector  110  senses transmission line signals supplied by the transceiver  120  and reflected from the antenna port.  
         [0026]      FIG. 2  is a partial cross-sectional view of the antenna of  FIG. 1  enabled with a ferroelectric dielectric material. The active element  104  includes a counterpoise  200  and a dielectric  202 , proximately located with the counterpoise  200 , with a dielectric constant responsive to the control signal on line  108 . The active element also includes a radiator  204  with an electrical length responsive to changes in the dielectric constant. In some aspects, the dielectric  202  includes a ferroelectric material  206  with a variable dielectric constant that changes in response to changes in the control signal voltage levels on line  108 .  
         [0027]     A dipole antenna is specifically shown where the radiator and counterpoise are radiating elements with an effective electrical length at the antenna electrical length that is an odd multiple of a quarter-wavelength (2n+1) (λ/4), where n=0, 1, 2, . . . That is, the wavelength is responsive to the dielectric constant of the proximate dielectric material, and the operating frequency can be modified by changing the dielectric constant. The operating frequencies of monopole and patch antenna can likewise by changed by applying different control signal voltages to (on opposite sides of) the ferroelectric material. An inverted-F antenna can be tuned using a ferroelectric capacitor between the end of the radiator and the groundplane and/or in series to the radiator from the antenna port. Additional details of ferroelectric antenna designs that are suitable for use in the context of the present invention can be found in the applications cited as Related Applications, above. These related applications are incorporated herein by reference.  
         [0028]      FIG. 3  is a plan view of the antenna of  FIG. 1  enabled with a microelectromechanical switch (MEMS). The active element  104  includes at least one selectively connectable MEMS  300  responsive to the control signal. In one aspect, such as when the active element is a monopole or patch antenna, a radiator  302  has an electrical length  304  that varies in response to selectively connecting the MEMS  300 .  
         [0029]     In other aspects when the antenna is a dipole, as shown, the antenna active element  104  includes a counterpoise  306  with an electrical length  308  that varies in response to selectively connecting the MEMS  310 . Although only a dipole antenna is specifically depicted, the MEMS concept of antenna tuning applies to a wide variety of antenna styles that are applicable to the present invention. The control signal is used to selectively connect or disconnect MEMS sections. Note that although only a single MEMS is shown included as part of radiator  302 , the radiator may include a plurality of MEMSs in other aspects. Additional details of MEMS antenna designs can be found in the MICROELECTROMECHANICAL SWITCH (MEMS) ANTENNA application cited as a Related Application, above. This application is incorporated herein by reference.  
         [0030]     Returning to  FIG. 1 , a coupler  130  has an input connected to the transmission line  106  and an output connected to the detector input on line  112 . The detector  110  converts the coupled signal to a dc voltage and supplies the dc voltage as the detected signal on line  114 . A variety of coupler and detector designs are known by those skilled in the art that would be applicable for use in the present invention.  
         [0031]     Typically, the detector  110  includes a rectifying diode and a capacitor (not shown). Therefore, the detector  110  has a non-uniform frequency response. In some aspects, the regulator circuit  116  includes a memory  132  with dc voltage measurements cross referenced to the frequencies of coupled signals. Typically, the calibration might be made to create a 0 volt offset at a bandpass center frequency (f1), with plus or minus voltage offsets for frequencies either above or below f1. However, other calibration schemes are possible. Regardless, the regulator circuit  116  supplies a frequency offset control signal on line  108  that is responsive to the reference signal on line  118 .  
         [0032]     Typically, the coupler  130  has a non-uniform frequency response. In other aspects of the system  100 , the regulator circuit  116  includes a memory  134  with coupler signal strength measurements cross referenced to the frequencies of coupled signals. As above, the calibration might be made to create a zero offset at a bandpass center frequency (f1), with plus or minus offsets for frequencies either above or below f1. The offsets could be added either to the detected signal to indirectly modify the control signal, or be added to directly modify the control signal. Regardless, the regulator circuit  116  supplies a frequency offset control signal on line  108  responsive to the reference signal on line  118 . The reference signal on line  118  may be an analog voltage that represents the intended antenna operating frequency. Alternately, the reference signal may be a digital representation of the intended antenna operating frequency. Note that the regulator circuit  116  may have mechanisms for calibrating both the detector and the coupler.  
         [0033]     In some aspects of the system  100 , the regulator circuit  116  includes a memory  136  for storing previous control signal modifications. Than, the antenna active element  104  can be initialized with the stored control signal modifications upon startup. In the context of a wireless telephone, the memory  136  may be used to store the average modification, in response to the user&#39;s normal hand position for example. Using the average modification as an initial value may result in greater resource efficiencies.  
         [0034]      FIGS. 4   a  and  4   b  are schematic block diagrams illustrating variations of the present invention antenna system for regulating the electrical length of an antenna.  FIG. 4   a  depicts a time-duplexing transceiver. A time-duplexing transceiving system is understood to be a system where the transmit and receive signals have the same frequency, but are time division multiplexed. For example, the time-duplexing transceiver describes a time division multiple access (TDMA) wireless telephone system protocol. The system  400  comprises an antenna  402  including an active element  404  having an electrical length responsive to a control signal, an antenna port connected to a transmission line  406  to transceive transmission line signals, and a control port connected to the active element  404  and accepting control signals on line  408 . A half-duplex transmitter  410  has a port on transmission line  412  to supply a transmission line signal to the antenna port. A half-duplex receiver  414  has an input port on transmission line  416  to receive the transmission line signals reflected from the antenna port and an output port on line  418  to supply an evaluation of received transmission line signal.  
         [0035]     The transmitter  410 , receiver  414 , and antenna  402  are shown connected to a duplexer  420 . Then, the receiver  414  measures transmitter signals reflected by the antenna  402 , that “leak” through the duplexer. Alternately but not shown, an isolator (or circulator) can have a first port connected to the antenna port on line  406  and a second port connected to the transmitter port on line  412  that is minimally isolated from the first port. The isolator can have a third port connected to the receiver port on line  416  that is minimally isolated from the first port and maximally isolated from the second port.  
         [0036]     A regulator circuit  422  has an input connected to the receiver output on line  418  to accept the transmission line signal evaluations and a reference input on line  424  to accept a reference signal responsive to the antenna electrical length, which is in turn related to the frequency of the conducted transmission line signal supplied by the transmitter  410 . The regulator circuit  422  has an output connected to the antenna on line  408  to supply the control signal in response to the signal evaluations and the reference signal.  
         [0037]     In some aspects, the receiver evaluation is a measurement of the automatic gain control voltage. That is, the receiver  414  supplies an evaluation that is responsive to the signal strength of the received signal. If the antenna is well matched, that is, tuned to operate at the frequency of the conducted transmission line signals receiving from the transmitter, then very little signal is reflected. As a result, when the receiver  414  measures low signal strength reflected power levels, the antenna is properly tuned. The antenna tuning can be improved by searching to find the minimum signal strength level.  
         [0038]     Alternately, the receiver may decode the received signal and use the decoded bit error rate (BER) to evaluate the antenna matching. As above, when the antenna is well matched, the reflected signal strength will be low. As a result, the BER rate for a well-matched antenna will be high. The antenna tuning can be improved by searching the find the maximum BER. In another variation, the received demodulated signal can be compared to the (pre-modulated) transmitted signal to evaluate antenna matching. As in the system of  FIG. 1 , the regulator circuit  422  may include a memory (not shown) with previous antenna modification to use at system initialization.  
         [0039]      FIG. 4   b  depicts an isolator  430  having ports connected on lines  412  and  406  to pass transmitted transmission line signals to the antenna port. The isolator  430  also has port on line  112  to supply transmission line signals reflected by the antenna port. The detector  110  is connected to the isolator  430  to accept the reflected transmission line signals. As in  FIG. 1 , the detector  110  supplies detected signals to the regulator circuit  116 , and the regulator circuit  116  generates a control signal in response to the detected signals.  
         [0040]      FIGS. 5   a  and  5   b  are flowcharts illustrating the present invention method for regulating the electrical length of an antenna. Although the method (and the method of  FIGS. 6 and 7 , below) is depicted as a sequence of numbered steps for clarity, no order should be inferred from the numbering unless explicitly stated. It should be understood that some of these steps may be skipped, performed in parallel, or performed without the requirement of maintaining a strict order of sequence. The method starts at Step  500 .  
         [0041]     Step  502  communicates transmission line signals at a predetermined frequency between a transceiver and an antenna. Step  504  senses transmission line signals. Step  506  modifies the electrical length of an antenna in response to sensing the transmission line signals. In some aspects related to use in a wireless communications device telephone, modifying the antenna electrical length in Step  506  includes modifying the antenna electrical length to operate at a frequency such as 824 to 894 megahertz (MHz), 1850 to 1990 MHz, 1565 to 1585 MHz, or 2400 to 2480 MHz.  
         [0042]     In some aspects of the method, sensing transmission line signals in Step  504  includes sensing transmission line signal power levels. In other aspects, modifying the electrical length of the antenna in response to sensing the transmission line signals in Step  506  includes modifying the antenna impedance. Alternately, Step  506  modifies the antenna electrical length by optimizing the transmission line signal strength between the transceiver and the antenna.  
         [0043]     In some aspects, the antenna has an antenna port and communicating transmission line signals at a predetermined frequency between a transceiver and an antenna in Step  502  includes accepting the transmission line signal from the transceiver at the antenna port. Then, sensing transmission line signals in Step  504  includes measuring the transmission line signal reflected from the antenna port.  
         [0044]     In other aspects, the antenna includes a radiator, a counterpoise, and a dielectric proximately located with the radiator and the counterpoise. Then, modifying the electrical length of the antenna in response to sensing the transmission line signals in Step  506  includes changing the dielectric constant of the dielectric. In one aspect, the antenna dielectric includes a ferroelectric material with a variable dielectric constant. Then, changing the dielectric constant of the dielectric in Step  506  includes substeps. Step  506   a  supplies a control voltage to the ferroelectric material. Step  506   b  changes the dielectric constant of the ferroelectric material in response to changing the control voltage.  
         [0045]     In other aspects, the antenna includes a radiator with at least one selectively connectable microelectromechanical switch (MEMS). Then, modifying the electrical length of the antenna in response to sensing the transmission line signals in Step  506  includes changing the electrical length of the radiator in response to connecting the MEMS. In some aspects, the antenna includes a counterpoise with at least one selectively connectable MEMS. Then, modifying the antenna electrical length in Step  506  includes changing the electrical length of the counterpoise in response to connecting the (counterpoise) MEMS.  
         [0046]     In other aspects of the method, sensing transmission line signals in Step  504  includes substeps. Step  504   a  couples to the transmission line signal. Step  504   b  generates a coupled signal. Step  504   c  converts the coupled signal to a dc voltage. Step  504   d  measures the magnitude of the dc voltage. In some aspects, the antenna is connected to a transmitter through an isolator. Then, sensing transmission line signals includes detecting the power level of transmitted transmission line signals, through the isolator.  
         [0047]     Other aspects of the method include additional steps. Step  501   a  calibrates the dc voltage measurements to coupled signal frequencies. Step  501   b  determines the frequency of the coupled signal. Then, sensing transmission line signals in Step  504  includes offsetting the dc voltage measurements in response to the determined coupled signal frequency. In some aspects, Step  501   c  calibrates coupled signal strength to coupled signal frequency. Then, sensing transmission line signals in Step  504  includes offsetting the dc voltage measurements in response to the determined coupled signal frequency.  
         [0048]     Other aspects of the method include additional steps. Step  508  stores previous antenna electrical length modifications. Step  510  initializes the antenna with the stored modifications upon startup.  
         [0049]     In some aspects, Step  501   d  initially calibrates the antenna electrical length to communicate transmission line signals with a transceiver in a predetermined first environment of proximate dielectric materials. Step  501   e  changes from the antenna first environment of proximate dielectric materials to an antenna second environment of dielectric materials. Then, sensing transmission line signals in Step  504  includes sensing changes in the transmission line signals due to the antenna second environment. Modifying the electrical length of antenna in Step  506  includes modifying the antenna electrical length in response to the antenna second environment.  
         [0050]     In some aspects, the transceiver and antenna are elements of a portable wireless communications telephone. Then, changing from the antenna first environment of proximate dielectric materials to an antenna second environment of dielectric materials in Step  501   e  includes a user manipulating the telephone.  
         [0051]     In other aspects of the method, the antenna is connected to a half-duplex transceiver with a transmitter and receiver. Then, sensing transmission line signals in Step  504  includes alternate substeps. Step  504   e  receives the communicated transmission line signals at the receiver. Step  504   f  demodulates the received transmission line signals. Step  504   g  calculates the rate of errors in the demodulated signals, by comparing the received message to the transmitted message, or by using FEC to correct the received message.  
         [0052]      FIG. 6  is a flowchart illustrating the present invention method for controlling the efficiency of a radiated signal. The method starts at Step  600 . Step  602  radiates electromagnetic signals at a predetermined frequency. Step  604  converts between radiated electromagnetic signals and conducted electromagnetic signals. Step  606  senses the conducted signals. Step  608  increases the radiated signal strength in response to sensing the conducted signals.  
         [0053]     In some aspects, sensing the conducted signals in Step  606  includes sensing conducted signal power levels. In other aspects, increasing the radiated signal strength in response to sensing the conducted signals in Step  608  includes improving the impedance match at the interface between the radiated and conducted signals. Alternately, it can be stated that Step  608  increases the radiated signal strength by minimizing the signal strength of reflected conducted signals at the interface between radiated and conducted signals.  
         [0054]      FIG. 7  is a flowchart illustrating the present invention method for regulating the operating frequency of an antenna. The method starts at Step  700 . Step  702  communicates transmission line signals at a predetermined frequency between a transceiver and an antenna. Step  704  senses transmission line signals. Step  706  modifies the antenna operating frequency in response to sensing the transmission line signals.  
         [0055]     A system and method have been provided for altering the operating frequency of a wireless device antenna in response to sensing the antenna mismatch. Examples have been given of sensing techniques to illustrate specific applications of the invention. However, the present invention is not limited to merely the exemplary sensing means. Likewise, examples have been given of antennas that have selectable electrical lengths. However, once again the invention is not limited to any particular antenna style. Finally, although the invention has been introduced in the context of a wireless telephone system, it has broader implications for any system using an antenna for radiated communications. Other variations and embodiments of the invention will occur to those skilled in the art.