Abstract:
A system and method for guiding an artillery shell in flight which includes a multi-element antenna having a large central access hole therein for receiving an airfoil actuator pin, the antenna array being switched during flight, as a function of the rotation of the shell, so that the upwardly directed portion of the radiation pattern predominates over a terrestrially directed segment of the radiation pattern.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present invention relates to a U.S. patent application Ser. No. 09/088,353 entitled “Artillery Fuse Circumferential Slot Antenna For Positioning and Telemetry” by James B. West filed on Jun. 1, 1998, now U.S. Pat. No. 6,098,547 which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to artillery shells and their fuses, and more particularly relates to antenna systems for use in an artillery shell, and even more particularly relates to methods and systems for guiding and communicating with an artillery shell. 
     BACKGROUND OF THE INVENTION 
     Artillery shells typically utilize a fuse installed at the leading end of the shell. The fuse is a mechanical or electronic device designed to control the detonation of the explosive charge of the shell. Modern artillery fuses further include electronics and telemetry systems for improved accuracy and detonation control. The electronic circuits disposed in the fuse remain in radio-frequency contact with a ground station after launch of the shell for coordinating the trajectory of the shell, making course corrections as necessary. Further, the artillery fuse may operate in conjunction with a satellite based positioning system, such as the NAVSTAR global positioning systems (GPS), maintained and operated by the United States government, for accurately determining the coordinates of the shell as it travels along its trajectory and reaches the point of impact, and for correcting the trajectories of subsequently fired munitions. GPS may also be used, as a positional reference, to deploy the flaps, from a previous free fall state, to more accurately control the downward descent to the target. 
     An artillery fuse having telemetry and positioning system electronics requires an antenna suitable for the application and environment to which an artillery shell is subject. The fuse antenna should be able to survive the extreme acceleration and high rotational velocities typical of gun launched projectiles. Further, the radiation pattern of the antenna should exhibit relatively high gain in the aft direction, the direction opposite to the direction of travel of the shell. The radiation pattern of the antenna should be minimal in the direction of travel of the shell to minimize or prevent jamming from the vicinity of the target area of the shell. Such an antenna should be of a sufficiently reduced size so as not to occupy a large of space within the interior of the fuse, and is desirably designed for operation with L-band and S-band signals. (“L” is the letter designation for microwave signals in the frequency range from 1 to 2 GHz, and “S” is the letter designation for microwave signals in the frequency range from 2-4 GHz.) 
     One prior art approach is described in the above-referenced patent application. While this design has considerable benefits, it does have some drawbacks. First of all, the size and shape of the antenna prohibit its use with some artillery shells having centrally disposed actuation pins for controlling airfoil surfaces on the artillery shell. The radiation pattern of the antenna is omni-directional in orthogonal directions about the shell trajectory and, therefore, is capable of being jammed from terrestrial positions. 
     Consequently, there exists a need for improved methods and systems for guiding artillery shells. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a system and method for guiding an artillery shell. 
     It is a feature of the present invention to utilize an array of antennas with an open central region. 
     It is another feature of the present invention to include a switching mechanism to control operation of particular antenna segments as a function of their orientation with respect to the ground. 
     It is an advantage of the present invention to achieve improved shell control by permitting a centrally disposed airfoil actuation pin to operate in the same cavity as the antenna. 
     The present invention is an apparatus and method for guiding artillery shells designed to satisfy the aforementioned needs, provide the previously stated objects, include the above-listed features, and achieve the already articulated advantages. The present invention is carried out in a “central obstruction-less” manner in a sense that the amount of centrally disposed obstructions in the artillery shell fuse has been greatly reduced. The present invention is also carried out in a “jam-free” manner in the sense that the susceptibility of the antenna to terrestrial-based jammers has been greatly reduced. 
     Accordingly, the present invention is a system and method for guiding an artillery shell which includes an array of separately controllable antennas disposed in an artillery shell fuse, with a central region therein which is available for location of an airfoil actuation pin. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may be more fully understood by reading the following description of the preferred embodiments of the invention, in conjunction with the appended drawings wherein: 
     FIG. 1 is a perspective view of an artillery shell of the present invention, which is shown having retractable airfoil flaps in a deployed configuration. 
     FIG. 2 is a plan view of an antenna array of the present invention, with a centrally disposed actuator pin. 
     FIG. 3 is a cross-sectional view of the antenna array of the present invention taken on line A—A of FIG.  2 . 
     FIG. 4 is a cut-away perspective view of the artillery shell of the present invention. 
     FIG. 5 is a view of the system of the present invention in which the antenna array of the present invention could be used. 
    
    
     DETAILED DESCRIPTION 
     Now referring to the drawings wherein like numerals refer to like matter throughout. 
     Referring now to FIG. 1, an artillery shell in accordance with the present invention is shown. The artillery shell  100  or similar munition is typically launched or fired from a cannon, mortar, or similar type of gun (not shown). A fuse  104  is disposed at the nose  102  of shell  100  and is typically physically contiguous with the body  108  of shell  100 . A fuse, or fuze, is a mechanical or electronic device utilized for detonating an explosive charge, such as the charge of an artillery shell or similar munition. Shell  100 , when launched or otherwise projected, travels in a forward direction  106  toward the vicinity of a target. During flight, the rear  110  of shell  100  generally points in the aft direction  112  toward the vicinity of origin of shell  100 ; i.e. toward the gun from which shell  100  is launched. During flight, retractable airfoil flaps  103  or any other selectively deployable airfoil mechanism are deployed to change the trajectory of the shell  100 . Retractable airfoil flaps  103  are shown as extending from slots  105  (behind flaps). 
     Now referring to FIG. 2, there is shown a top view of an antenna array  210  of the present invention, including a centrally disposed airfoil actuator pin  211 , a first antenna element  220 , a second antenna element  230 , a third antenna element  240  and a fourth antenna element  250 , having disposed therein and showing the top portions of first coaxial feed input  222 , second coaxial feed input  232 , third coaxial feed input  242 , and fourth coaxial feed input  252 , respectively. The antenna array is formed from a single dielectric disk having a central hole therein. The disk is divided into separate antenna elements by radiating element separation ground via walls  260 , which are plated through holes, which form shorting walls to isolate the neighboring antenna elements from each other. Each antenna element is separated from the central airfoil actuator pin  211  by an inner via ground isolation ring  270 , which is similar to radiating element separation ground via wall  260 . 
     Now referring to FIG. 3, there is shown a cross-sectional view of the antenna of FIG. 2 taken on line A—A. The antenna array  210  can be clearly seen to have a top ground plane  302 , an antenna dielectric  304  in the form of a disk with a central hole therein, a middle ground plane  306 , a splitter/combiner dielectric  308  and a micro strip line  310 , which can also be strip line. Known techniques of antenna manufacture, design and tuning, etc., such as those used in conjunction with the above-referenced patent application, can be employed to arrive at a particular design for a particular need. Known techniques of impedance matching can be employed in designing and feeding the antenna array  210  of the present invention. First coaxial feed input  222 , second coaxial feed input  232  (FIG.  2 ), third coaxial feed input  242  (FIG.  2 ), and fourth coaxial feed input  252  may be combined through an impedance matching/power splitter circuit and/or switching circuit. The diameter and location of the coaxial feed inputs within the pie-shaped antenna elements can be adjusted to facilitate impedance matching. Slot aperture coupling between the antenna and the matching/circuit/switch can be used in place of the coax feeds. 
     An omni-directional mode can be realized when all antenna elements are fed in phase. This can be accomplished with an N way Wilkenson, or equivalent splitter network located on the underside of the antenna array  210 . Microstrip line  310  could be a component of such an N way Wilkenson splitter network. 
     Antenna array  210  can also be configured with an adjustable switching network and/or phase shifting network to perform radiation pattern synthesis. This can be done with known techniques employed in electronic circuit board  212  (FIG.  4 ). The number of antenna elements is shown here as being four, but other numbers can be used as well. If lesser numbers of elements are arrayed together, for example  2  elements, a directional pattern perpendicular to the artillery shell  100  fuselage can exist. This could be maintained skyward in a non-spinning missile application to reject ground based, or low altitude jammer signals, as well as terrestrial ground noise. 
     If artillery shell  100  is a spinning shell, the sectoral antenna elements first antenna element  220 , second antenna element  230 , third antenna element  240 , and fourth antenna element  250  could be commutated in synchronous with the rotation rate of the artillery shell  100 , such that only upward directed radiating elements would be enabled at any point in the trajectory of the artillery shell  100 . 
     Now referring to FIG. 4, there is shown a partially cut-away view of the artillery shell  100  of the present invention, where the scalloped cut-away line  418  reveals an interior cavity  416  with GPS receiver electronic circuit boards  212  coupled to the antenna array  210  via a perpendicular mating of the antenna combing/splitter assembly&#39;s circuit trace layer or microstrip line  310  to the GPS receiver electronic circuit boards  212 . Retractable airfoil flaps  103  are shown removed from slots  105 . Various types of retractable airfoil flaps  103  could be employed. 
     Now referring to FIG. 5, there is shown a system of the present invention, which includes an artillery shell  100 , which has been launched in a usual manner. Artillery shell  100  is moving in forward direction  106  along a trajectory generally directed toward target  510 . Artillery shell  100  has come from a rearward direction  112  along the trajectory. It may be desirable to change the trajectory of artillery shell  100  while in flight to assure proper interaction with target  510 . Artillery shell  100  with its on-board GPS receiver continuously monitors its position via space directed signal  518  from satellite  520 . Antenna array  210  receives these GPS or other signals and can make course corrections either locally or via telemetry and other communications with base station  512 , through terrestrial RF signal  516 , and base station antenna  514 . A command may be sent to artillery shell  100  to deploy its retractable airfoil flaps  103  so as to change the aerodynamics, speed, and, therefore, trajectory. Other signals, such as detonation commands for airborne detonation, could be sent as well. 
     Throughout this description, reference is made to a four element antenna array because it is believed that the beneficial aspects of the present invention would be most readily apparent when used in connection with a spinning artillery shell  100  using GPS; however, it should be understood that the present invention is not intended to be limited to four element antenna arrays, spinning artillery shells, or use with GPS and should be hereby construed to include other designs as well. 
     It is thought that the method and apparatus of the present invention will be understood from the foregoing description and that it will be apparent that various changes may be made in the form, construct steps, and arrangement of the parts and steps thereof, without departing from the spirit and scope of the invention or sacrificing all of their material advantages. The form herein described is merely a preferred exemplary embodiment thereof.