Abstract:
An actuator providing improved torque, control, and reduced motor and actuator size is provided. An actuator according to one example may include a base plate, a stationary ring gear on the base plate, the ring gear having an arc of substantially less than a conventional full circle ring gear, a pivot assembly and a drive shaft. In one example, the ring gear is approximately half a circle. The pivot assembly may be pivotally mounted on the base plate. The pivot assembly may also have a control board, a stepper motor and a drive gear coupled to an output shaft of the stepper motor, the drive gear mounted on the pivot assembly such that the drive gear engages the stationary ring gear. In one example, the stepper motor is coupled to the drive gear via a worm gear, spur gear, and a shaft. In another example, the drive gear is mounted directly on the output shaft of the stepper motor. The actuator also includes a drive shaft having an axis parallel to a pivot of the pivot assembly.

Description:
BACKGROUND 
       [0001]    Wireless mobile communication networks continue to evolve given the increased traffic demands on the networks, the expanded coverage areas for service and the new systems being deployed. Cellular (“wireless”) communications networks rely on a network of base station antennas for connecting cellular devices, such as cellular telephones, to the wireless network. Many base station antennas include a plurality of radiating elements in a linear array. Various attributes of the antenna array, such as beam elevation angle, beam azimuth angle, and half power beam width may be adjusted by electrical-mechanical controllers. See, for example, U.S. Pat. Nos. 6,573,875 and 6,603,436, both of which are incorporated by reference. For example, with respect to U.S. Pat. No. 6,573,875, a plurality of radiating elements may be provided in an approximately vertical alignment. A feed network may be provided to supply each of the radiating elements with a signal. The phase angle of the signals provided to the radiating elements may be adjusted to cause a radiated beam angle produced by the antenna array to tilt up or down from a nominal or default beam angle. 
         [0002]    Phase angles may be adjusted by mechanical phase shifters. In the example of the &#39;875 patent, phase shifters are coupled by a common mechanical linkage. An expected phase angle may be ascertained from markings on a linearly-reciprocal linkage rod or by a sensor in a linear motion electro-mechanical actuator located off the antenna panel extending beyond a bottom edge of the panel. However, known linear pushrod actuators, while having certain advantages, are not always well adapted to actuating variable elements such as phase shifters. Many antenna variable elements require rotational actuation, so a mechanism must be included to translate linear motion to rotational motion. Rotational stepper motors are also known, however, when selected to produce sufficient torque to drive the variable elements such motors may be undesirably large. Smaller motors may be used with gear reduction arrangements to multiply torque, however, known gear reduction arrangements may occupy undesirably large amounts of space. 
       SUMMARY 
       [0003]    An actuator providing improved torque, control, and reduced motor and actuator size is provided. An actuator according to one example of the present invention may include a base plate, a stationary ring gear on the base plate, the ring gear having an arc of substantially less than a conventional full circle ring gear, a pivot assembly and a drive shaft. In one example, the ring gear is approximately half a circle. The pivot assembly may be pivotally mounted on the base plate. The pivot assembly may also have a control board, a stepper motor and a drive gear coupled to an output shaft of the stepper motor, the drive gear mounted on the pivot assembly such that the drive gear engages the stationary ring gear. In one example, the stepper motor is coupled to the drive gear via a worm gear, spur gear, and a shaft. In another example, the drive gear is mounted directly on the output shaft of the stepper motor. The actuator also includes a drive shaft having an axis parallel to a pivot of the pivot assembly. 
         [0004]    The drive shaft may be formed as part of the pivot assembly. For example, the pivot assembly may further include a pivot bracket, wherein the control board is mounted on the pivot bracket, and the pivot bracket is pivotally mounted on the base plate at a point comprising a center of a circle defined by the stationary ring gear. The drive shaft may be formed as part of the pivot bracket. 
         [0005]    In various examples, the controller board may include several components, including a controller, a motor driver, and an accelerometer. The controller may be responsive to commands that conform with industry standards, such as AISG. The controller may be coupled to the accelerometer and coupled to ASIG connectors, and the motor driver may be coupled to the controller and to the stepper motor. 
         [0006]    In another example, the actuator of the present invention is incorporated on a panel antenna. The panel antenna may include a plurality of radiating elements, an input, a first feed network coupling the input to a first set of dipoles of the plurality of radiating elements, the first feed network comprising a plurality of transmission lines and at least a first variable element, the first variable element including a rotatable component; and an actuator according to one or more examples of the present invention, where the drive shaft of the actuator physically engages the rotatable component of the variable element. The panel antenna may also include a second feed network, where one or more variable elements of the second feed network are also driven by the actuator, typically by a cross link. 
         [0007]    In another example, an actuator may include a base plate, a stationary ring gear, on the base plate, and a pivot assembly. The ring gear having an arc of approximately 180°. The pivot assembly is pivotally mounted on the base plate. The pivot assembly may include a pivot bracket, a control board, and a stepper motor and drive gear. The pivot bracket comprises a drive shaft having an axis parallel to a pivot of the pivot assembly. The control board is mounted on the pivot bracket. The control board also includes an accelerometer, a controller coupled to the accelerometer, and a motor driver coupled to the controller. The drive gear is mounted on an output shaft of the stepper motor, and the stepper motor is coupled to the motor driver and mounted on the pivot bracket such that the drive gear engages the stationary ring gear. The controller is configured to obtain information from the accelerometer indicative of a physical angle of the pivot assembly, and the controller is further configured to operate the stepper motor until the pivot assembly reaches a desired physical angle with respect to vertical. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic diagram of a panel antenna. 
           [0009]      FIG. 2  is an illustration of a pair of phase shifters. 
           [0010]      FIG. 3  is a perspective drawing of a portion of a panel antenna having an actuator according to the present invention. 
           [0011]      FIG. 4  is a perspective view of an actuator according to the present invention with the cover removed for clarity. 
           [0012]      FIG. 5  is a bottom view of an actuator according to the present invention. 
           [0013]      FIG. 6  is a top view of a first example pivot assembly according to the present invention. 
           [0014]      FIG. 7  is a bottom view of the first example of a pivot assembly according to the present invention. 
           [0015]      FIG. 8  is a top view of a second example of a pivot assembly according to the present invention. 
           [0016]      FIG. 9  is a bottom view of the second example of a pivot assembly according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Referring to  FIG. 1 , a typical antenna array  10  may include an input  11 , a plurality of radiating elements  12  and a feed network  14  coupling the input  11  to the radiating elements  12 . A schematic diagram of a typical feed network  14  for an antenna array  10  is provided in  FIG. 1 . The feed network  14  may include a plurality of transmission lines  16  and one or more variable elements  18 . The transmission lines  16  have a nominal impedance which may be selected to match an impedance of a RF line that couples the antenna array  10  to a Low Noise Amplifier (not shown). Transmission lines  16  may be implemented as microstrip transmission lines, coaxial cables, or other impedance-controlled transmission media. The variable elements  18  may comprise one or more phase shifters, power dividers, a combination of the two, or another type of variable element. The variable elements  18  may comprise differential variable elements. In one example, first and second feed networks  14  are provided, with a first feed network  14  driving a first set of dipoles on radiating elements  12 , and a second feed network  14  driving a second set of dipoles on radiating elements  12 . 
         [0018]    In one example of the invention, the variable elements  18  comprise rotating-wiper type phase shifters  20 . Referring to  FIG. 2 , phase shifter  20 , in one example, may be implemented with first and second printed circuit boards (PCBs). In one illustrated example, the first PCB may comprise a stationary PCB  22 , and the second PCB may comprise a rotatable wiper PCB  24 . 
         [0019]    The stationary PCB  22  includes a plurality of transmission line traces  26 ,  28 . The transmission line traces  26 ,  28  are generally arcuate. The transmission line traces  26 ,  28  may be disposed in a serpentine pattern to achieve a longer effective length. In an illustrated example, there are two transmission line traces  26 ,  28  on the stationary PCB  22 , one transmission line trace  26  being disposed along an outer circumference of a PCB  22 , and one transmission line trace  28  being disposed on a shorter radius concentrically within the outer transmission line trace  26 . 
         [0020]    In the illustrated example, the stationary PCB  22  may include one or more input traces  40  leading from an input pad  42  near an edge of the stationary PCB  22  to where the pivot of the wiper PCB  24  is located. (The use of “input” and “output” herein refers to the radio frequency signal path as the panel antenna transmits. Radio frequency signals received by the panel antenna flow in the reverse direction.) Electrical signals on an input trace  40  are coupled to the wiper PCB  24 . The wiper PCB  24  couples the electrical signals to the transmission line traces  26 ,  28 . Transmission line traces  26 ,  28  may be coupled to output pads to which a coaxial cable may be connected. Alternatively, the stationary PCB  22  may be coupled to stripline transmission lines on a panel without additional coaxial cabling. As the wiper PCB  24  moves, an electrical length from the wiper PCB  24  to each output pad  44 , and therefore each radiating element served by the transmission lines  26 ,  28  changes. For example, as the wiper PCB  24  moves to shorten the electrical length from the input transmission line trace  40  to a first radiating element, the electrical length from the input transmission line trace end to a second radiating element increases by a corresponding amount. In the example illustrated in  FIG. 2 , an additional transmission line trace  29  is included on stationary PCB  22 . Transmission line trace  29  carries an unshifted signal. 
         [0021]    In one example illustrated in  FIG. 2 , two phase shifters  20  are illustrated. The wiper PCBs  24  are mechanically coupled by wiper link  30  such that the wiper arm PCBs move in unison. 
         [0022]    Referring to  FIG. 3 , in one embodiment of the present invention, an actuator  110  is directly coupled to one of the phase shifters  20 . The actuator  110  is mounted on an actuator mount  108 , which is mounted to a radome back panel (not shown for clarity). The phase shifters  20  are mounted on a reflector  106 . Referring to  FIG. 4  and  FIG. 5 , the actuator  110  comprises a baseplate  112 , a connector bracket  114 , a top cover  120 , a drive shaft  122  and a pivot assembly  124 . The connector bracket  114  may comprise a molded AISG connector bracket. Male AISG connector  116  and female AISG connector  118  may be installed on the connector bracket  114 . A ring gear  126  may be attached to the baseplate  112 . In the illustrated example, the baseplate  112  is semi-circular and the ring gear  126  comprises a half ring gear, with gear teeth on an inner circumference of the gear. In this regard the ring gear  126  comprises only a portion of a conventional circular ring gear. The ring gear  126  may also include additional supporting structure which connects ends of the ring gear  126  to provide additional mechanical strength and facilitate mounting of the ring gear  126  on the baseplate  112  in an appropriate orientation. The baseplate  112  may be thermo molded plastic, metal, or any other suitable material. The ring gear  126  may be formed integrally with the baseplate  112 , for example, the ring gear  126  may be molded as a single unit with the baseplate  112 . Alternatively, the ring gear  126  may be separately formed and fixedly attached to the baseplate  112 . 
         [0023]    Referring to  FIGS. 4 ,  6  and  7 , the pivot assembly  124  includes a pivot bracket  132 , a control board  134 , drive gear  136 , and a stepper motor  138 . Operation of the stepper motor  138  is controlled by the control board  134 , and the stepper motor  138  and control board  134  are mounted on the pivot bracket  132 . The pivot bracket  132  engages the drive shaft  122 . In one example, the drive shaft  122  may be molded as a unitary piece with pivot bracket  132 . In a preferred example, an output shaft of stepper motor  138  drives worm gear  140 . Worm gear  140  meshes with and drives spur gear  142 . A shaft couples spur gear  142  to drive gear  136 . This arrangement reduces the likelihood that the variable elements will be able to back-drive the stepper motor  138 . 
         [0024]    In an alternate example, referring to pivot assembly  224  on  FIGS. 8 and 9 , stepper motor  238  and control board  234  are on one side of the pivot bracket  232 , and the drive gear  236  is on the other side of the pivot bracket  232 . This alternate example has fewer moving parts and allows good transfer of rotational force, because a rotor shaft of the stepper motor  238  passes through the pivot bracket  232 . The stepper motor  238  may include additional securing brackets and fasteners. Additional alternate physical relationships between the stepper motor and the drive gear may be implemented without departing from the scope of the invention. 
         [0025]    The ring gear  126  is located such that a circle defined by the radius of the ring gear  126  is concentric with the drive shaft  122 . Additionally, the length of the pivot bracket  132  and the location of the drive gear  136  are dimensioned such that the drive gear  136  engages the ring gear  126 , and, as the stepper motor  138  is operated, the drive gear  136  moves the pivot board through an arc defined by the ring gear  126  and the radius of the pivot bracket  132 . In the illustrated example, the rotation of the pivot board is approximately 180 degrees. Other amounts of rotation may be implemented without departing from the invention. 
         [0026]    The male AISG connector  116  and the female AISG connector  118  are coupled to the control board  134 . The control board  134  includes a controller  144 , which may be a microprocessor or microcontroller, and a motor driver  146 . These devices are configured to operate the stepper motor  138 . The controller may also be configured to receive and transmit commands and information according to AISG protocols. 
         [0027]    In one example, the control board  134  includes an accelerometer  150 , such as a 3-axis MEMS accelerometer  150 . The controller  144  on the control board  134  may be configured to read register information from the accelerometer, thereby determining the orientation of the pivot assembly  124 , and therefore drive shaft  122  position. From this, phase adjuster position may be determined. 
         [0028]    Preferably, the accelerometer  150  comprises a multiple-axis digital accelerometer, such as Digital Accelerometer ADXL345, from Analog Devices, Inc. In this example, the accelerometer  150  is a digital 3-axis accelerometer. However, other accelerometers may be acceptable in alternate embodiments. The accelerometer provides angle information for the three axes of rotation as serial data. In one example, the serial data conforms to the I 2 C digital interface. X-axis data, y-axis data, and z-axis data may be obtained by reading appropriate registers in the accelerometer  150 . The controller  144  interfaces with the accelerometer  150  and reads the data registers. 
         [0029]    The accelerometer  150  is mounted on the wiper control board  134  such that it may detect a physical angle of the control board  134  with respect to vertical. Control board  134  physical angle  0  may be determined by a first axis of the accelerometer  150 . If control board  134  angle with respect to vertical is the only angle to be determined, the solution may be had with a single axis of the accelerometer  150  and the following trigonometry relationship: 
         [0000]      V OUTX =V OFF   +S  sin θ
 
         [0000]    Where V OUTX  is the voltage output from the X-axis of the accelerometer, V OFF  is the an offset voltage and S is the sensitivity of the accelerometer. The acceleration on the x-axis due to gravity is: 
         [0000]        A   X =(V OUTX −V OFF )÷ S  
 
         [0000]    In this case, the solution for control board  134  angle is: 
         [0000]      θ=sin −1 ( A x)
 
         [0000]    In another example, the actuator is mounted such that the axis of rotation of the default angle of the panel antenna is on a different axis (e.g., the y-axis) from an axis of rotation of the control board  134 . 
         [0030]    In an alternative embodiment, a rotary potentiometer may be attached to the drive shaft  122  and coupled to the controller. In another alternate embodiment, pivot assembly  124  position sensing may be accomplished with pressure sensitive potentiometer tape extending the length of the ring gear  126 . 
         [0031]    In one example, the actuator  110  is directly coupled to a first phase shifter. The first phase shifter may be mechanically linked to additional phase shifters such that, by driving the first phase shifter, all phase shifters are driven simultaneously. 
         [0032]    The pivot bracket  132  may be rotationally fixed to the drive shaft  122 . The pivot bracket  132  and drive shaft  122  may be arranged such that they fit together in only one orientation, so that a risk of misalignment of the drive shaft  122  and pivot assembly  124  is minimized. In one example, the drive shaft  122  may have a D-shaped output side  123 , so that, once again, a risk of misalignment is minimized when the drive shaft  122  is connected to a phase shifter or linkage to operate one or more phase shifters. 
         [0033]    In operation, commands indicating a desired antenna beam downtilt angle are received via the AISG connector. The controller determines an appropriate actuator  110  position (for example, a position of the pivot assembly  124 ) that corresponds to the desired beam downtilt angle. The controller may determine the appropriate actuator position by retrieving from a look-up table a physical actuator  110  position that corresponds to a desired beam downtilt angle. The relationship between downtilt angle and pivot assembly  124  angle actuator  110  position may have been previously determined empirically and stored in the look-up table in the firmware for the controller. The controller then operates the stepper motor  138  until the pivot assembly  124  reaches the appropriate orientation. In the case of position being determined by an accelerometer, registers providing x-axis, y-axis, and z-axis information may be read periodically while the motor is moving the pivot assembly  124 . The registers may also be read when the motor is not in operation to determine actuator  110  position, true mechanical tilt of the panel antenna, or for other reasons. 
         [0034]    Various examples of the actuator  110  described herein benefit from improve torque. The torque of the stepper motor  138  is multiplied by the lever arm of the pivot bracket  132 . Thus, for a desired torque to operate a series of phase shifters, a proportionately smaller motor may be used. Additionally, the present invention requires only half a ring gear  126 , and that half ring gear  126  is stationary while the motor moves. This difference from conventional reduction gearing means that the actuator  110  takes up less space than a conventional reduction gear setup. If, for example, the motor were fixed and the ring gear  126  rotated, it would require 360 degrees of clearance to achieve 180 degrees of rotation.