Abstract:
A drive mechanism for an antenna array mounted on a moving vehicle. The antenna array is mounted on a disc having two motors which, cooperatively, rotate the disc and rotate a number of antenna elements mounted on the disc. By rotating the antenna elements, the main lobe of the array may be scanned towards a satellite in the elevation plane. To track a moving source from a moving vehicle, one of the motors rotates the disc as a whole, thereby scanning the beam in the azimuth plane. Each antenna element is at an angle to the vertical so that, by rotating the disc to face the direction of the signal source, such as a satellite, a better signal can be obtained.

Description:
FIELD OF THE INVENTION 
     The invention relates to rotating antenna arrays with plural antenna elements which can be individually rotated to change the phase of the signal of the individual antenna elements, altering the direction of the main lobe of the antenna. 
     BACKGROUND TO THE INVENTION 
     Current aircraft-satellite communications require an antenna design which is capable of phase scanning. On small aircraft, another requirement is that the physical dimensions of the design be small. Conventional phase scanned arrays use digitally controlled diode phase shifters that introduce substantial losses in the RF path. These losses degrade the antenna gain and increase the antenna noise temperature resulting in a very low gain/temperature characteristic for a given antenna size. 
     Future aeronautical satellite communications antennas will serve multiple purposes such as providing voice communications to the cockpit and cabin, data and internet services, and live video entertainment. The transmission of multiple simultaneous voice and data carriers can produce intermodulation products that may interfere with other navigation and communications systems on the aircraft and on the ground. 
     Transmission and reception over the Inmarsat network from aircraft demands an antenna whose beam can be scanned over most of the upper hemisphere, allowing the beam to be directed towards the satellite regardless of the aircraft orientation. This beam steering can be achieved using mechanically steered antennas. These are usually mounted inside the tail where size limitations are considerable. Access to the tail is quite difficult on large commercial aircraft due to the size and weight of the tail-fin radome and the height of the tail. 
     Current technologies in mechanically steered arrays do not allow for maximum flexibility in phase scanning and satellite tracking. One technology, disclosed in U.S. Pat. No. 4,427,984 issued to Anderson attempted to solve this problem. Anderson discloses an antenna array with rotatable antenna elements. The phase of the antenna elements are changed to move the lobe of the array to point towards a satellite or signal source. However, Anderson does not disclose how the whole array may be rotated to track a satellite in two planes from a mobile platform. As such, Anderson is only suitable for tracking in a single plane and cannot be used to scan a beam in both elevation and azimuth as required for mobile satellite communications. 
     Other technologies have tried to provide platforms for other antenna types. Specifically, dish antennas have been tried as the antenna element for numerous antenna platforms. German Patent DE 4 405 644 issued to Braun et al., UK Patent GB 2266 996 issued to Racal Research Limited have both tried this approach. Unfortunately, such an approach leads to complex mechanical systems which require time consuming and labour intensive maintenance. In addition, such antennas are very tall and are thus not suitable for mounting on top of most vehicles. 
     Another approach, shown in U.S. Pat. No. 4,771,290 issued to Storey, uses a rotating platform for a ranging system. However, Storey does not mention using such a platform for an antenna system for aircraft use. 
     From the above, there is a need for a low profile antenna drive system which is capable of tracking a satellite from a mobile platform. Such an antenna should be readily adaptable for aircraft use or for use with any other moving vehicle and must be of a low cost, reliable design. 
     SUMMARY OF THE INVENTION 
     The current invention provides a drive mechanism for an antenna array mounted on a moving vehicle. The antenna array is mounted on a disc having two motors which, cooperatively, rotate the disc and rotate a number of antenna elements mounted on the disc. By rotating the antenna elements, the main lobe of the array may be scanned towards a satellite in the elevation plane. To track a moving source from a moving vehicle, one of the motors rotates the disc as a whole, thereby scanning the beam in the azimuth plane. Each antenna element is at an angle to the vertical so that, by rotating the disc to face the direction of the signal source, such as a satellite, a better signal can be obtained. 
     In a first embodiment, the current invention provides a drive mechanism for rotating multiple rotatable antenna elements mounted on a rotatable pallet having a first side and a second side. The mechanism comprises a main motor for rotating the rotatable antenna elements, a secondary motor for rotating the pallet, and rotating means for rotating the rotatable antenna elements. The rotating means is coupled to the main motor and to each rotatable antenna element. 
     In a second embodiment, the current invention provides a drive mechanism for rotating multiple antenna elements mounted on a first side of a pallet rotatable about an axis. The mechanism comprises a rotation mechanism for rotating said rotatable antenna elements, a main motor for rotating said rotatable antenna elements and coupled to at least a portion of each of said rotatable antenna element through the rotation mechanism, and a secondary motor for rotating the pallet. Also included in the mechanism are a plurality of shafts mounted on a second side of said pallet, each of the shafts being rotatable about its longitudinal axis with the axis being parallel to the pallet. Further included are a plurality of shaft gears, each shaft gear being mounted on a shaft such that a longitudinal axis of a shaft gear is parallel to the longitudinal axis of the shaft and such that rotation of the shaft causes rotation of the shaft gear, a plurality of antenna gears, each antenna gear being mounted on a distal end of a rotatable antenna element, the distal end protruding through a second side of the pallet, and at least one primary transmission means coupled to the main motor and to at least one of said shafts. Each shaft gear is in contact with an antenna gear such that a rotation of a shaft gear causes rotation of an associated antenna gear and a rotation of an antenna gear causes rotation of an antenna element. Activation of the main motor causes at least one primary transmission means to cause at least one of said shafts to rotate. 
     In a third embodiment, the current invention provides a mechanism for rotating multiple antenna elements mounted on a first side of a pallet rotatable about an axis. The mechanism comprises a main motor for rotating said rotatable antenna elements, a secondary motor for rotating the pallet, and a plurality of slots in the pallet. The rotating means includes a slider pallet located adjacent a second side of the pallet with the slider pallet being rotatable about a slider pallet axis. Also included in the rotating means are a plurality of slider mounts mounted on the first side of the pallet with each slider mount being slidably mounted inside a slot and a plurality of slider cords, each slider cord being wrapped around a portion of a rotatable antenna element. Each slider cord is attached to a slider mount such that slidably moving a slider mount within its associated slit causes its associated rotatable antenna element to rotate. The rotating means further includes a plurality of slider cars mounted on the slider pallet, each of said slider cars being coupled to at least one slider mount, first coupling means to couple the main motor to the slider pallet, and second coupling means to couple the secondary motor to the pallet. The axis of the pallet and the slider pallet axis are substantially collinear. The main motor is coupled to the slider pallet for rotating the slider pallet about the slider pallet axis and the secondary motor is coupled to the pallet for rotating the pallet about the pallet axis. Rotating the pallet and the slider pallet at different rotational speeds causes the rotatable antenna elements to rotate. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     A better understanding of the invention may be obtained by reading the detailed description of the invention below, in conjunction with the following drawings, in which: 
     FIG. 1 is a top view of a rotatable dual directional antenna array; 
     FIG. 2 is a first lower perspective view of the bottom of a pallet illustrating a mechanism for operating the antenna array of FIG. 1; 
     FIG. 3 is a second lower perspective view of the antenna array of FIG. 1 showing the bottom of the pallet illustrated in FIG. 2 from a different angle; 
     FIG. 4 is an exploded perspective view of a second embodiment of the mechanism illustrated in FIG. 2; and 
     FIG. 5 is a plan view of a portion of the embodiment illustrated in FIG. 4 illustrating the relationships between the distance travelled by a slider and the angular distance travelled by an element mounted on that slider. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a top view of an antenna array  10  is illustrated with rotatable antenna elements  20  mounted on a first side of a pallet  15 . Also mounted on the same side of the pallet  15  are nonrotatable antenna elements  30 . 
     Referring to FIGS. 2 and 3, different views of the second side of the pallet  15  of FIG. 1 are shown. A main motor  40 , having main motor shafts  50 , is mounted, along with a secondary motor  45  on the second side of the pallet  15 . Coupled to the main motor shaft  50  are belts  60 . The belts  60 , are coupled on their other end to array shafts  70  via connection points  80 . In the illustration, connection points  80  are embodied as pulleys. The array shafts  70  are rotatably mounted, using shaft mounts  90 , on the same side of the pallet  15  as the main motor  40 . Also illustrated in FIGS. 2 and 3 are secondary belts  100 , which couple two array shafts  70  together. These secondary belts  100  couple two array shafts  70  via secondary connection points  110 , also embodied as pulleys in the illustration. Tensioners  115  are also shown in FIG.  2 . These tensioners provide tension to secondary belts  100 . As shown in FIG. 3, on each array shaft  70  is at least one shaft gear  120 . This shaft gear  120  is in contact with an antenna gear  130 . Each antenna gear  130  is mounted on one end of a rotatable antenna element  20 . The antenna gear  130  and shaft gear  120  assembly is embodied as a worm gear in the illustration. 
     To explain the workings of the platform  10 , the starting point must necessarily be the main motor  40 . Upon activation of the main motor  40 , the main motor shaft  50  rotates, thereby causing the belts  60  to turn. When the belts  60  turn, this in turn causes all the array shafts  70  to rotate, either by being directly driven by belts  60  or driven by secondary belts  100 . (The secondary belts  100  are turned by the rotation of the shafts  70 . Any shafts  70  coupled to secondary belts  100  are therefore rotated as well). Once a shaft  70  is rotated, the contact between a shaft gear  120  and its associated antenna gear  130  causes the antenna gear  130  to rotate about its longitudinal axis. Since the rotatable antenna element  20  is free to rotate, rotation of its antenna gear  130  directly rotates the rotatable antenna element  20  about its longitudinal axis. To control the amount of rotation of each rotatable antenna element  20 , specific gear ratios between the shaft gear  120  and the antenna gear  130  must be chosen. By judiciously choosing such gear ratios, fixed incremental rotations can be achieved. As an example, the rotatable antenna elements  20  farthest from the centre of the platform could have the smallest gear ratios between its shaft gears  120  and its antenna gears  130 . This would cause these outermost rotatable antenna elements to have the largest amount of rotation per turn of the main motor shaft. The innermost rotatable antenna elements could have the largest gear ratio between its shaft gears  120  and its antenna gears  130 , thereby causing these innermost rotatable antenna elements to have the smallest amount of rotation per turn of the main motor shaft. 
     Because of the above arrangement, and by choosing the right gear ratios, one rotatable antenna element can, for every rotation of main motor shaft, rotate N degrees. Another element can rotate −N degrees and yet another can rotate N/2 degrees. To facilitate this incremental rotation, the belts  60  can be attached to a well known motor pulley which rotates in precise increments. A stepping motor can be used as the main motor  40  to allow precise incremental rotation of the main motor shaft  50 . The belts  100  are well known timing belts, transmitting the motion of the belts  60  to the array shafts  70 . At connection points  80 , a shaft pulley is used in cooperation with the timing belt (belt  100 ) to rotate the array shaft  70 . This shaft pulley transmits the motion from the timing belts to the shaft and maintains a fixed turns ratio (gear reduction) when appropriately selected with the motor pulley. As noted above, the shaft gear  120  and antenna gear  130  assembly can be implemented using a worm gear and a drive worm. Each shaft gear  120  can be a drive worm and each antenna gear  130  can be a worm gear. The drive worm distributes rotational energy to the worm gear and changes the rotational axis through 90 degrees to the shaft  70 . The worm gear, depending on the orientation of the rotatable antenna element relative to vertical, can be at an angle other than 90 degrees to the drive worm. In the embodiment illustrated in FIG. 2 and 3, the worm gear is 45 degrees to the drive worm. The secondary belts  100  cooperate with shafts  70  at secondary connection points  110 . Connection points  110  can be shaft pulleys which transfer the rotational energy of one shaft to another shaft further away from the main motor  40 . 
     As noted above, the worm gear can be at an oblique angle to the drive worm if the rotatable antenna element is at an angle to the platform. As can be seen from FIG. 1, the antenna elements, both rotatable and non-rotatable, are at an angle to the plane of the pallet  15 . In the embodiment illustrated in the FIGS. 2 and 3, the elements are angled at 45 degrees to the pallet. 
     In the embodiment illustrated in FIGS. 2 and 3, both clockwise and counter clockwise rotation of the rotatable antenna elements can be obtained for a given turn of the main motor shaft. Depending on which side of the shaft gear the antenna gear is mounted on, a fixed turn of the main motor shaft will produce either a clockwise or a counterclockwise rotation of a rotatable antenna element. 
     It should be noted that the drive worm/worm gear arrangement can be replaced by bevel gears or any other suitable gearing mechanism. 
     Another mechanism for rotating the antenna elements mounted on the pallet  15  is illustrated in FIG.  4 . FIG. 5 is a more detailed view of this mechanism. The pallet  15  has a number of slots  140 . Within each slot  140  is a slider mount  150 , each slider mount  150  being slidable within a slot  140 . Wrapped around the rotatable antenna element  20  is a slider cord  160 . Both ends of a slider cord  160  are attached to a slider mount  150 . The slider cord  160  is wrapped around the rotatable antenna element  20  such that the rotatable antenna element  20  rotates when the slider mount is moved either left or right. When the slider mount  150  is slid across the slot  140 , this causes the rotatable antenna element  20  to rotate about its longitudinal axis. 
     Also in this embodiment, a slider pallet  170  is located beneath the pallet  15 . Mounted on the slider pallet  170  are slider cars  180 , each of which is fixedly attached to a slider mount  150  through holes in the pallet  15 . The slider pallet  170  is rotatable about its central axis independently of the pallet  15 . The pallet  15  is also rotatable about its central axis. Ideally, the central axes of the pallet  15  and the slider pallet  170  are collinear so that the pallet  15  and the slider pallet  170  may rotate about the same axis. Located away from the pallet  15  and the slider pallet  170  are the main motor  40  and the secondary motor  45 . The main motor  40  rotates the slider pallet  170  about its axis and the secondary motor  45  rotates the pallet  15  about its axis. By judiciously rotating the pallet  15  and the slider pallet  170  at different speeds, the slider mounts  150 , because they are attached to the slider cars  180 , slide within their respective slots  140 . In doing so, the associated rotatable antenna element is rotated. 
     To rotate the rotatable antenna elements, the pallet  15  and the slider pallet  170  are rotated at varying velocities relative to each other. If they are rotated at the same speed, then the slider cars experience no relative motion and the rotatable antenna elements remain stationary on their respective axes. If one of the pallets  150  or  170  is rotated at a velocity different from the other pallet, then the slider cars experience motion relative to the pallet  15 . This causes the slider mounts  150  to slide in their slots  140 . When this occurs, the rotatable antenna elements are rotated by way of the slider cords. To control the rate or angular distance of rotation of each rotatable antenna element, the distance of the slider mount from the central axis of the two pallets determines how far the slider mount moves in its slot. Accordingly, this also determines how much the associated rotatable antenna element rotates. Thus, the farther the slider mount is from the central axis, the more its associated rotatable antenna element rotates for a given differential in speed between the pallet and the slider pallet. 
     It should be clear that both clockwise and counterclockwise rotation of the antenna elements are possible with the embodiment in FIG.  4 . Sliders on opposite sides of the center of the rotating pallet would have opposite directions of rotation. The sliders are driven from the “neutral” or central axis of the pallet. (It should be noted that in FIG. 4, the nonrotatable elements  30  are on a centerline of the pallet. The middle nonrotatable element is at the center axis of the pallet.) FIG. 5 illustrates the mechanism of the sliders and how they operate. It should be noted that FIG. 5 does not illustrate the whole pallet and is only provided to clarify the relationships and interactions between the sliders and the rotation of the pallet. A slider that is a distance D from the center of the pallet would rotate its attached element R degrees in one direction. A slider that is a similar distance D from the center but is on the opposite side of the central axis would have its element experience a rotation of R degrees in the other direction. Thus, if a slider A is D units away from the center, then the element A 1  attached to slider A would rotate R degrees. Slider B, also a distance D units away from the center but on the opposite side of the centerline, would have its element B 1  rotate R degrees in a direction opposite to that of element A 1 . On the other hand, if element C is 2D units away from the center, its attached element C 1  would experience a rotation of 2R degrees. Thus, the amount of rotation that an element undergoes is directly proportional to the distance between its associated slider and the center of the pallet. 
     To further clarify the explanation, if the pallet shown in FIG. 5 rotates in a clockwise manner relative to the lower pallet (not shown in FIG.  5 ), the slider A will slide to the left as indicated by arrow  300 . Slider C, because it is twice as far from the center of the pallet as slider A, will slide in the same direction (arrow  310 ) but will travel twice the distance of slider A. Thus, since the amount of rotation that an antenna element is dependent on the amount of distance travelled by the slider to which it is attached, element C 1  rotates twice as much (2R) as element A 1  (R). 
     To keep each slider aligned within its slot, each slider has at least one pin protruding into and slidable within the slot. This pin or pins provides the attachment to the slider pallet  170 . Thus, as the slider pallet  170  moves relative to the pallet  15 , the pins slide within each slot, thereby causing each slider to move within each slot as well. This causes each rotatable antenna element to travel down its slider cord, thereby rotating the rotatable antenna element. 
     The slider pallet  170  and the pallet  15  are rotated respectively by the main motor  40  and the secondary motor  45  by means of a pulley and belt system. 
     From the above, it is therefore clear that each rotatable antenna element can be rotated about its longitudinal axis. In the embodiments illustrated, the antenna elements are angled away from the plane of the pallet  15 . This provides a much better pointing capability than the prior art. To track a signal source or target, such as a satellite, the secondary motor  45  can rotate the whole pallet  15  about its axis. This way, by rotating the pallet  15  and fixing the antenna elements to angle towards a certain point, a much better signal response can be obtained from a signal source. If the signal source or target were to move to the left of the pallet  15 , the secondary motor  45  can rotate the pallet  15  to keep the antenna elements pointed at the source or target. If the source or target were to move towards the horizon of the pallet  15  or towards the centre axis of the pallet  15 , rotating the rotatable antenna elements would change the phase of the antenna elements. This would effectively change the direction of the main lobe of the array formed by the antenna elements, thereby changing the direction targeted by the array. 
     It should also be noted that, while the embodiments described above have their rotation mechanisms underneath the pallet, it is also possible to have such mechanisms mounted atop the pallet. 
     A person understanding the above-described invention may now conceive of alternative designs, using the principles described herein. All such designs which fall within the scope of the claims appended hereto are considered to be part of the present invention.