Abstract:
A system having a steerable antenna coupled to a temperature-dependent driver. The driver has a shape-memory element fabricated using a shape-memory alloy (SMA) and having the ability to change its shape as a function of temperature. The element is adapted to steer the antenna to improve signal reception and is controlled by a control circuit, which resistively heats the element while using the strength of the electrical signal generated by the antenna in response to a received radio-frequency signal as a feedback signal. The temperature of the element is adjusted to optimize the signal strength. Systems of the invention may enable customer-performed antenna alignment and are relatively simple and inexpensive to implement.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to wireless communication equipment.  
           [0003]    2. Description of the Related Art  
           [0004]    Medium-size (e.g., 10-50 cm) radio antennas are often used for wireless communication and various broadband applications. Such an antenna may be installed outside (e.g., on the roof) of a home or commercial building. During installation, the antenna is typically aligned, e.g., by manually pointing the antenna, for optimal signal strength. The antenna is then fixed in an optimal orientation. Special equipment and a qualified technician are often needed to properly align the antenna. In addition, it is not unusual that the alignment of the antenna needs to be adjusted weeks or months after the installation. This typically occurs due to changes in the surroundings (e.g., a new building) and/or changes in the network configuration (e.g., an added or moved base station).  
         SUMMARY OF THE INVENTION  
         [0005]    Problems in the prior art are addressed in accordance with the principles of the present invention by a system having a steerable antenna coupled to a temperature-dependent driver. The driver has a shape-memory element fabricated using a shape-memory alloy (SMA) and having the ability to change its shape as a function of temperature. The element is adapted to steer the antenna to improve signal reception and is controlled by a control circuit, which resistively heats the element while using the strength of the electrical signal generated by the antenna in response to a received radio-frequency signal as a feedback signal. The temperature of the element is adjusted to optimize the signal strength. Systems of the invention may enable customer-performed antenna alignment and are relatively simple and inexpensive to implement.  
           [0006]    According to one embodiment, the present invention is an apparatus for controlling orientation of an antenna, comprising: a shape-memory element mechanically coupled between the antenna and a mounting structure; and a control circuit electrically coupled to the shape-memory element, wherein: the control circuit is designed to control temperature of the shape-memory element; and in response to a change in the temperature, the shape-memory element changes shape, which changes the orientation of the antenna relative to the mounting structure.  
           [0007]    According to another embodiment, the present invention is a communication system, comprising: a steerable antenna; a shape-memory element mechanically coupled between the antenna and a mounting structure; and a control circuit electrically coupled to the shape-memory element, wherein: the control circuit is designed to control temperature of the shape-memory element; and in response to a change in the temperature, the shape-memory element changes shape, which changes the orientation of the antenna relative to the mounting structure.  
           [0008]    According to yet another embodiment, the present invention is a method of controlling orientation of an antenna, comprising changing temperature of a shape-memory element, wherein: the shape-memory element is mechanically coupled between the antenna and a mounting structure; and in response to a change in the temperature, the shape-memory element changes shape, which changes the orientation of the antenna relative to the mounting structure. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    Other aspects, features, and benefits of the present invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings in which:  
         [0010]    [0010]FIG. 1 shows a three-dimensional perspective view of a representative communication system according to one embodiment of the present invention;  
         [0011]    [0011]FIG. 2 shows an enlarged perspective view of the driver/antenna assembly used in the system of FIG. 1;  
         [0012]    FIGS.  3 A-B schematically illustrate antenna rotation in the assembly of FIG. 2;  
         [0013]    [0013]FIG. 4 schematically shows a perspective view of a driver/antenna assembly that can be used in a communication system similar to the system of FIG. 1 according to another embodiment of the present invention;  
         [0014]    FIGS.  5 A-B schematically illustrate antenna rotation in the assembly of FIG. 4;  
         [0015]    [0015]FIG. 6 schematically shows a temperature-dependent driver that can be used in the driver/antenna assembly of FIG. 4 according to another embodiment of the present invention;  
         [0016]    FIGS.  7 A-B schematically show perspective and side views of a driver/antenna assembly that can be used in a communication system similar to the system of FIG. 1 according to yet another embodiment of the present invention; and  
         [0017]    [0017]FIGS. 8-11 schematically show various shape-memory elements that can be used in the driver/antenna assembly of FIG. 7 according to certain embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0018]    Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments.  
         [0019]    [0019]FIG. 1 shows a three-dimensional perspective view of a representative communication system  100  according to one embodiment of the present invention. System  100  includes a steerable antenna  102  rotatably mounted on a frame  104  and connected to a signal processor (e.g., a local area network transceiver, not shown) by a cable  110 . Antenna  102  is coupled to a temperature-dependent driver  106 , which is configured to rotate the antenna about a vertical axis as indicated by the double-headed arrow in FIG. 1. The angle of rotation (i.e., the azimuth angle) is determined by the temperature of a shape-memory element  108  in driver  106 , the principle of operation of which will be described in more detail below. The temperature of shape-memory element  108  is controlled by a control circuit  114 , which resistively heats the element by passing current through it while using the strength of the signal received from antenna  102  as a feedback signal. Circuit  114  is designed to control the azimuth angle of antenna  102  to increase the signal strength by adjusting the current passing through element  108 .  
         [0020]    [0020]FIG. 2 shows an enlarged perspective view of the driver/antenna ( 106 / 102 ) assembly in system  100  of FIG. 1. Driver  106  is configured to rotate antenna  102  about axis AB and includes shape-memory element  108 , a bias spring  218 , and a pivot  220 . Shape-memory element  108  is a twisting strip-element connected between frame  104  (FIG. 1) and antenna  102 . Bias spring  218  is a helical spring connected between pivot  220  (which is rigidly connected to frame  104 ) and antenna  102  and configured to oppose the shape-restoring force generated by shape-memory element  108 . As a result, antenna  102  adopts an orientation in which the forces generated by element  108  and spring  218  compensate each other. In one embodiment, driver  106  includes an orientation-locking mechanism (not shown), e.g., a friction lock, that can be engaged to lock antenna  102  in position, e.g., to fix the antenna at a present azimuth angle. Control circuit  114  may include appropriate circuitry for controlling (i.e., engaging/disengaging) the orientation-locking mechanism.  
         [0021]    In one embodiment, shape-memory element  108  is fabricated using a shape-memory alloy (SMA), e.g., a nickel titanium alloy, available from Shape Memory Applications, Inc., of San Jose, Calif. SMA alloys belong to a group of materials characterized by the ability to return to a predetermined shape when heated. This ability is usually referred to as a shape-memory effect. The shape-memory effect occurs due to a phase transition in the SMA alloy between a weaker low-temperature (Martensite) phase and a stronger high-temperature (Austenite) phase. When an SMA alloy is in its Martensite phase, it is relatively easily deformed into a new shape. However, when the alloy is heated and transformed into its Austenite phase, it recovers its initial shape with relatively great force.  
         [0022]    The Martensite/Austenite phase transition occurs over a temperature range, within which the two phases coexist. Within this transition temperature range, the phase ratio and therefore the shape-restoring force generated by a shape-memory element are functions of temperature. In addition, the Martensite/Austenite phase transition exhibits a hysteresis, that is, the phase ratio and the force are functions of the transition direction, i.e., Martensite to Austenite or Austenite to Martensite. The upper and lower temperature bounds of the transition temperature range can themselves depend on the transition direction. For example, a first set of temperature bounds may characterize the Martensite-to-Austenite transition while a second set of temperature bounds, different from the first set, characterizes the Austenite-to-Martensite transition. The upper and lower temperature bounds can be selected during manufacture of the SMA alloy, e.g., based on the SMA composition and/or special heat treatment. In one implementation, shape-memory element  108  is fabricated using an SMA alloy having the transition temperature range of 95° C. to 100° C. In another implementation, element  108  is fabricated such that the corresponding transition temperature range is separated from the highest expected environment temperature for element  108  by about 10 degrees.  
         [0023]    FIGS.  3 A-B schematically illustrate rotation of antenna  102  by driver  106  in system  100 . More specifically, FIGS.  3 A-B show positions of antenna  102 , when shape-memory element  108  is at temperatures below and above, respectively, the SMA transition temperature range. Shape-memory element  108  is fabricated such that it has a twisted-strip shape in its high-temperature (Austenite) phase. When the temperature of shape-memory element  108  is lowered, e.g., below the lower transition temperature bound, shape-memory element  108  is untwisted by the action of bias spring  218  as illustrated in FIG. 3A, which rotates antenna  102  clockwise as viewed from the top of FIG. 3A. Similarly, when the temperature of shape-memory element  108  is elevated, e.g., above the upper transition temperature bound, element  108  overcomes the force of bias spring  218  to return to its original twisted shape as illustrated by FIG. 3B, which rotates antenna  102  counterclockwise as viewed from the top of FIG. 3B. Intermediate rotation angles (e.g., between the angles shown in FIGS.  3 A-B) can be obtained by appropriately selecting the temperature of shape-memory element  108 .  
         [0024]    The following describes a representative alignment procedure for antenna  102  (FIGS. 1-3) according to one embodiment of the present invention. When shape-memory element  108  is at a temperature below the SMA transition temperature range (e.g., ambient temperature) and the orientation-locking mechanism (not shown) is disengaged, the action of bias spring  218  deforms shape-memory element  108  and moves antenna  102  into a first terminal position, e.g., shown in FIG. 3A. Next, control circuit  114  is turned on and begins to pass current through and increase the temperature of shape-memory element  108 . When the temperature reaches the lower transition temperature bound, shape-memory element  108  begins to recover its original shape and thereby rotate antenna  102  toward a second terminal position, e.g., shown in FIG. 3B, which position corresponds to the original shape of shape-memory element  108 . In a preferred implementation, the second terminal position corresponds to a 360° turn of antenna  102  with respect to the first terminal position. During the rotation, control circuit  114  monitors the signal strength from antenna  102  and adjusts the temperature of shape-memory element  108  accordingly to find an azimuth angle corresponding to optimal signal reception. Control circuit  114  is preferably designed to implement one or more side-lobe avoiding techniques, as known in the art, to ascertain that antenna  102  is steered into an orientation corresponding to the main lobe and not to a side lobe. When an optimal azimuth angle is found, control circuit  114  engages the orientation-locking mechanism to fix that azimuth angle for antenna  102 , after which control circuit  114  may be turned off until the antenna needs to be realigned.  
         [0025]    [0025]FIG. 4 schematically shows a perspective view of a driver/antenna assembly  400  that can be used in a communication system similar to system  100  of FIG. 1 according to another embodiment of the present invention. Assembly  400  includes a steerable antenna  402  mounted on two pivots  420   a - b.  Antenna  402  is coupled to a temperature-dependent driver  406  configured to rotate the antenna about the axis defined by pivots  420   a - b.  Driver  406  includes a shape-memory coil-element  408  and a bias coil-spring  418 . Each of element  408  and spring  418  is connected between antenna  402  and a housing (not shown) such that the shape-restoring force generated by element  408  opposes the spring force generated by spring  418 . Similar to shape-memory element  108  (FIGS. 1-3), shape-memory element  408  is fabricated using an SMA alloy and can be resistively heated, e.g., using a control circuit similar to circuit  114  of system  100 .  
         [0026]    FIGS.  5 A-B schematically illustrate rotation of antenna  402  using driver  406  in assembly  400 . More specifically, FIGS.  5 A-B show positions of antenna  402 , when shape-memory element  408  is at temperatures below and above, respectively, the SMA transition-temperature range. Shape-memory element  408  is fabricated such that it has a tightly coiled shape in the high-temperature (Austenite) phase. At a low temperature illustrated by FIG. 5A, shape-memory element  408  is deformed into a loosely coiled shape by the action of bias spring  418 . However, as the temperature of shape-memory element  408  is elevated, element  408  begins to recover the original tightly coiled shape due to the above-described shape-memory effect. As a result, antenna  402  will rotate counterclockwise as indicated by the arrow in FIG. 5B. Antenna  402  will return to the position shown in FIG. 5A when the temperature is lowered.  
         [0027]    [0027]FIG. 6 schematically shows a temperature-dependent driver  606  that can be used in driver/antenna assembly  400  of FIG. 4 according to another embodiment of the present invention. Driver  606  is similar to driver  406  except that, instead of coil spring  418  of driver  406 , driver  606  has a U-shaped strip spring  618 . As can be appreciated by one skilled in the art, in different embodiments, differently shaped and configured shape-memory elements and/or bias springs can be used.  
         [0028]    FIGS.  7 A-B schematically show a driver/antenna assembly  700  that can be used in a communication system similar to system  100  of FIG. 1 according to yet another embodiment of the present invention. More specifically, FIG. 7A shows a perspective view of assembly  700 , and FIG. 7B shows a side view of that assembly. Assembly  700  is designed to provide a capability to adjust both the azimuth angle and the tilt angle of a steerable antenna  702 . Antenna  702  is mounted on a movable support plate  704 , which is coupled to a first temperature-dependent driver  706 . Driver  706  has a shape-memory element  708  and a bias spring  718  and is similar to driver  106  of FIGS. 1-3. A second temperature-dependent driver  726  is coupled between support plate  704  and antenna  702 . Driver  726  has a shape-memory element  728  and a bias spring  738  and is similar to driver  606  of FIG. 6. Driver  706  is configured to rotate support plate  704  (and therefore antenna  702 ) about axis AB as indicated in FIG. 7A. Similarly, driver  726  is configured to rotate antenna  702  with respect to support plate  704  about axis CD. Therefore, by independently controlling the temperatures of shape-memory elements  708  and  728 , one can adjust both azimuth and tilt angles of antenna  702 . In one configuration, elements  708  and  728  are controlled by a control circuit analogous to control circuit  114  of FIG. 1.  
         [0029]    [0029]FIG. 8 schematically shows a sectional shape-memory element  808  that can be used as element  708  in antenna assembly  700  according to one embodiment of the present invention. Sectional shape-memory element  808  is a twisting strip-element comprising n sections  810 - 1   810 -n. Each section  810  has a specific SMA composition and therefore specific properties such as, for example, the transition temperature range and value of spring constant. By appropriately choosing the SMA composition for each segment, shape-memory element  808  can be designed to have a linear temperature-force or current-force behavior. In addition or alternatively, element  808  may be designed to exhibit reduced hysteresis. Element  808  can be fabricated, for example, by mechanically fastening segments  810  together or by a controlled alloying process.  
         [0030]    [0030]FIGS. 9-11 schematically show various shape-memory elements, each of which can be used in antenna assemblies (e.g., assembly  700 ) according to certain embodiments of the present invention. More specifically, FIG. 9 shows a multi-strip (two or more) shape-memory element  908 . Illustratively, element  908  is shown as comprising three twisting strip-elements  910 - 1 ,  910 - 2 , and  910 - 3  bundled together. Each element  910  is similar to shape-memory element  108  (FIGS. 1-3). However, different elements  910  can have different SMA compositions and mechanical properties. FIG. 10 shows a sectional shape-memory coil-element  1008  comprising four coil sections  1010 - 1 - 1010 - 4 , each having a different SMA composition and mechanical properties. FIG. 11 shows a multi-coil shape-memory element  1108  illustratively comprising two shape-memory coil-elements  1110 - 1  and  1110 - 2 , one inside the other and each having a different SMA composition and mechanical properties.  
         [0031]    Different modes of operation may be implemented for communication systems employing driver/antenna assemblies of the present invention. For example, system  100  of FIG. 1 can be configured to operate in a continuous feedback mode, during which the azimuth angle of antenna  102  is continuously adjusted in real time to maintain optimal signal strength. This mode may be useful, for example, when antenna  102  is employed for communication with a mobile station. Depending on the location of (direction to) the mobile station, system  100  dynamically adjusts the azimuth angle of antenna  102  for optimal signal reception. Alternatively, system  100  can be configured to operate in an open-loop mode, during which control circuit  114  steers antenna  102  independent of the received signal strength. This feature may be useful, for example, if it is desired to reduce the number of remote stations accessing a particular base station that is over capacity by temporarily diverting part of the communication traffic to a different base station.  
         [0032]    In one embodiment, a temperature-dependent driver of the present invention is configured with an element similar to one of elements  808 ,  908 ,  1008 , and  1108 , which element is designed to have a substantially linear dependence of the shape-restoring force on the current passing through the element within specified current and ambient temperature ranges. As a result, the angle of rotation of the corresponding steerable antenna becomes a linear function of the current. As can be appreciated by one skilled in the art, this linearity significantly simplifies the circuitry for the corresponding control circuit (analogous to control circuit  114  of system  100 ), e.g., for implementing the above-mentioned open-loop mode. In addition, orientation of the antenna coupled to such a linear shape-memory element can be determined (monitored) very straightforwardly by observing the current.  
         [0033]    In another embodiment, a temperature-dependent driver of the present invention is configured with a two-state shape-memory element. As known in the art, material (typically an SMA alloy) of the two-state shape-memory element is formulated and treated to “remember” two different shapes (states), a low-temperature shape and a high-temperature shape. As a result, the two-state shape-memory element adopts the low-temperature shape upon cooling and the high-temperature shape upon heating, thereby providing a bi-directional actuator even without the use of a bias spring. Consequently, in a temperature-dependent driver having a two-state shape-memory element, a bias spring is optional.  
         [0034]    While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Differently shaped and configured shape-memory elements and/or bias springs can be used without departing from the principle of the invention. In certain embodiments, instead of a bias spring, a second, separately controlled shape-memory element can be used, e.g., spring  418  of FIG. 4 may be a second shape-memory element, where the memorized shape of shape-memory element  418  corresponds to the antenna orientation shown in FIG. 5A. In operation, only one of the shape memory elements might be heated at a time. Although the present invention was described in reference to shape-memory elements fabricated using SMA alloys, different shape-memory materials, e.g., shape-memory polymers may also be used. A different heater may be used for temperature regulation of a shape-memory element in addition to or instead of resistive heating. A control circuit analogous to control circuit  114  may be implemented in an integrated circuit and combined with an antenna package, e.g., mounted on support plate  704  or included into antenna  702 . Various modifications of the described embodiments, as well as other embodiments of the invention, which are apparent to persons skilled in the art to which the invention pertains are deemed to lie within the principle and scope of the invention as expressed in the following claims.