Patent Publication Number: US-8120544-B2

Title: Compact continuous ground plane system

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This work was sponsored under Department of Defense Contract No. F19628-00-C -0100-MP-RTIP, and subcontract A140000084-MP-RTIP. The government has certain rights in this invention. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to grounding systems. More specifically, the invention relates to a grounding system that provides for a continuous ground plane between components that move relative to one another. 
     BACKGROUND 
     A good ground plane is essential to proper operation of a number of antenna systems. Active array antennas in particular have a need for a continuous ground plane. Without such a ground plane, undesirable effects can disrupt received signals and impair antenna performance. The importance of ground planes for antennas is described in U.S. Pat. No. 6,100,855 to Vinson, et al., the entire content of which is expressly incorporated herein by reference. 
     Antenna systems can include a number of radiating elements. Examples of antenna systems can be found in U.S. Pat. No. 6,366,259 to Pruett et al. and U.S. Pat. No. 7,391,382 to Mason et al., the entire content of each is expressly incorporated herein by reference. The radiating elements can send and receive signals provided by way of a main feed network. Often, the radiating elements are mounted such that a small space, such as a gap, exists between the elements. In some applications, the antenna systems are mounted to moving devices, such as aircraft or other vehicles. In such case, the radiating elements can be exposed to significant vibration. Both the gaps in antenna structure and the vibration create challenges to implementing and maintaining a continuous ground plane for an antenna system. 
     Systems to account for vibration and/or gaps in a ground plane have been proposed. These systems include, for example, copper fingers, spiral gaskets, and metallized tape. Among other limitations, such systems are unable to provide a continuous ground plane for antennas having relative movement between radiating elements. 
     SUMMARY OF THE INVENTION 
     Aspects of the invention relate to a compact continuous ground plane system. In one embodiment, the invention relates to an assembly for forming a continuous ground plane for an antenna having at least two elements configured to move relative to one another, the ground assembly including a first element having a housing, a plunger disposed within the housing, a second element, a wear plate coupled to the second element, and a spring disposed between the plunger and the housing, the spring configured to urge the plunger toward the wear plate, where the plunger is configured to be moved within the housing and to make electrical contact with the wear plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of a antenna system having multiple radiating elements in accordance with one embodiment of the present invention. 
         FIG. 2  is a fragmentary isometric view of base sections of adjacent radiating elements of an antenna system and an assembly, including a plunger, a wear plate, a retaining housing and a spring, for forming a ground plane between the adjacent radiating elements in accordance with one embodiment of the present invention. 
         FIG. 3  is an enlarged side view of the grounding assembly of  FIG. 2 . 
         FIG. 4  is an isometric view of one end of a plunger in accordance with one embodiment of the present invention. 
         FIG. 5  is a end view of a plunger in accordance with one embodiment of the present invention. 
         FIG. 6  is a side view of the plunger of  FIG. 5 . 
         FIG. 7  is an isometric view of a wear plate in accordance with one embodiment of the present invention. 
         FIG. 8  is a top view of the wear plate of  FIG. 7 . 
         FIG. 9  is an enlarged view of a mounting hole of the wear plate of  FIG. 7 . 
         FIG. 10  is a side view of the wear plate of  FIG. 7 . 
         FIG. 11  is a cross sectional view of the wear plate of  FIG. 10  taken across the section A-A. 
         FIG. 12  is an isometric view of a wavy portion of a spring in accordance with one embodiment of the present invention. 
         FIG. 13  is a top view of a spring having both a flat portion and a wavy portion in accordance with one embodiment of the present invention. 
         FIG. 14  is a side view of the spring of  FIG. 13 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, embodiments of assemblies for forming continuous ground planes are illustrated. In many embodiments, the grounding assemblies include a plunger, a spring, a retaining housing and a wear plate for electrically coupling adjacent radiating elements to one another despite relative movement. The plunger can have a T-shaped “dove tail” end and a tapered end with a rounded contact point to minimize wear on the wear plate. The “dove tail” end can be retained within the retaining housing. 
     The spring can be a wavy spring mounted between the plunger and the retaining housing such that the spring provides a force to the plunger directed away from the radiating element. The retaining housing is mounted to a radiating element. The wear plate is mounted to an adjacent radiating element and configured to make contact with the plunger. The assembly can sustain electrical contact between the radiating elements despite a predetermined amount of relative motion between the radiating elements. In some cases, the relative motion can be caused by vibration. In several embodiments, the relative motion is caused when the radiating elements are part of an antenna that is mounted to a moving vehicle, such as an aircraft. In a number of embodiments, the relative motion can occur in different directions. In many embodiments, the ground plane assemblies are configured to sustain electrical contact despite the relative motion in different directions. 
       FIG. 1  is an isometric view of a antenna system  100  having multiple radiating elements  102  in accordance with one embodiment of the present invention. In the illustrated embodiment, the multiple radiating elements  102  are disposed vertically and adjacent to one another in an array architecture. In one embodiment, the antenna system can be an active electronically scanned array (AESA). In some embodiments, the antenna system can be used with an aircraft such as a military jet. In several embodiments, the antenna system is a component of a radar system for tracking objects, terrain, weather and a speed of the objects. In some embodiments, the antenna system can be used with other vehicles such as a ship. In one embodiment, the antenna system is used with a stationary system. 
       FIG. 2  is a fragmentary isometric view of base sections of adjacent radiating elements of an antenna system and an assembly, including a plunger, a wear plate, a retaining housing and a spring, for forming a ground plane between the adjacent radiating elements in accordance with one embodiment of the present invention. The antenna system  200  includes a base portion of a first radiating element  202  and a base portion of a second radiating element  204  separated by a gap  206 . The radiating elements are electrically coupled by a grounding assembly. The grounding assembly includes a plunger  208 , a spring  210 , a wear plate  212  and a retaining housing  214 . The plunger  208  and spring  210  are disposed within the rectangular retaining housing  214  of the first radiating element  202 . The plunger  208  has a T-shaped “dove tail” end  208   a  that is retained within a cavity  224  formed by the retaining housing  214 . 
     A first housing  216  is coupled to a side of the first radiating element  202 . Similarly, a second housing  218  is coupled to a side of the second radiating element  204 . The first radiating element  202  is mounted to a first antenna support structure  220 , and the second radiating element  204  is mounted to a second antenna support structure  222 . In most embodiments, the second antenna support structure has a chamfer disposed along a lower edge of the structure (not visible) and the gap  206 . 
       FIG. 3  is an enlarged side view of the grounding assembly of  FIG. 2 . The retaining housing  214  includes a rear wall  214   a , a top wall  214   b , a bottom wall  214   c , a top retaining wall  214   d , and a bottom retaining wall  214   e  which form the retaining cavity  224 . The top retaining wall  214   d  and bottom retaining wall  214   e  are disposed on the top and bottom, respectively, of an opening  226  through which a shaft  208   b  of the plunger  208  can be moved. The shaft  208   b  and head  208   a  are disposed below the top wall  214   b  and above the bottom wall  214   c  within the cavity  224 . The spring  210  is disposed between a flat rear surface of the head  208   a  and the rear wall  214   a  of the retaining cavity  224 . 
     When compressed, the spring  210  is configured to provide a force on the plunger  208  directed away from the first radiating element  202  and toward the adjacent second radiating element  204 . In effect, the spring  210  can urge the plunger toward the wear plate  212 . The plunger  208  can move laterally within the retaining housing  214  for a distance limited by the width of the cavity within the housing  214  and the width of the spring  210  in a compressed state. The spring  210  resists movement of the plunger  208  toward the first radiating element  202 . In one embodiment, such movement can be caused by a vibrational force applied to the grounding assembly. 
     In some embodiments, the spring  210  is a wavy spring having a number of wave-like bends in a thin flat metallic material. In one embodiment, the spring  210  is made of tin plated steel. In other embodiments, the spring is made of other suitably conductive and compression resistant materials. In one embodiment, the spring is made of a non-conductive material. In such case, an alternate means of making an electrical connection between the plunger and the first radiating element can be used. In one embodiment, the alternate means includes one or more wires coupling the retaining housing and the plunger. 
     In some embodiments, the spring is a leaf spring. In several embodiments, the spring has an elongated body that extends approximately the length of the first radiating element. In other embodiments, the spring may be replaced by a number of discrete springs having a similar structure in a shorter form factor. In one embodiment, the spring can be replaced with a number of coil springs. 
     In the exploded side view of  FIG. 3 , the plunger  208  features a cross section having a T-shape (e.g., like a short nail) resting horizontally within the retaining housing  214 . As depicted in  FIG. 3 , the T-shape includes a rectangular head  208   a , positioned such that the longer sides are disposed vertically within the cavity  224 , and a pointed shaft  208   b  disposed horizontally. The end of the shaft is chamfered and comes to a beveled or rounded point  208   c . In many embodiments, the beveled point (or blunt end)  208   c  of the plunger  208  makes contact with the wear plate  212  in an assembled configuration. In many embodiments, head portion  208   a  of the plunger makes electrical contact with the retaining housing, by both direct physical contact and indirectly by way of the spring  210 . 
     In some embodiments, the plunger is made of aluminum. In several embodiments, the plunger is plated with a material including both nickel and chrome. In such case, the material is conducive to establishing good electrical continuity between the plunger and those objects that come in contact with the plunger. In other embodiments, the plunger is made of other conductive materials and/or coated with other conductive materials. In some embodiments, the plunger is hollow. In many embodiments, the plunger has an elongated body that extends approximately the length of the first radiating element. In some embodiments, a number of discrete plungers can be used that are shorter in length than the first radiating element. In other embodiments, the plunger can take other shapes providing for constant electrical contact with the wear plate. 
     In the embodiment illustrated in  FIGS. 2 and 3 , the wear plate  212  has a rectangular cross section with a beveled front corner. A front surface of the wear plate  212  faces the plunger  208  and is configured to make contact with the beveled or rounded point of the plunger  208 . In several embodiments, the flat front surface of the wear plate allows for relative motion between in the radiating elements in a vertical direction (e.g., up and down motion). The wear plate  212  extends longitudinally for approximately the length of the second radiating element  204 . In some embodiments, a number of discrete wear plates can be used instead of a single elongated wear plate. In many embodiments, the wear plate is made of aluminum and is plated with nickel. In some embodiments, the wear plate is made and/or coated with other conductive materials. In several embodiments, the wear plate is hollow. In the embodiment illustrated in  FIGS. 2 and 3 , the wear plate has a rectangular cross section with a beveled corner. In other embodiments, the wear plate can take other shapes suitable for providing electrical connectivity between adjacent radiating elements. 
     In several embodiments, the materials for the wear plate, the plunger and their respective coating materials are selected to prevent galling. Galling can be thought of as a condition where excessive friction between high spots results in localized welding with subsequent splitting and a further roughening of rubbing surfaces of one or both of two mating parts. In practice, galling can be caused when the same materials come in contact with one another on the adjacent mating parts. To prevent galling, embodiments of the grounding assembly can avoid using common metals for mating parts (e.g., plunger and wear plate). In the embodiment illustrated in  FIG. 2 , for example, the plunger can be made of a core metal that is chrome plated, while the wear plate is made of nickel plated aluminum. In such case, the metals in contact with one another are chrome and nickel, and galling between components having substantial contact is prevented. In this case, the prevention of galling can allow mating parts (e.g., the plunger and the wear plate) to move smoothly relative to one another for a longer period of time than they would if no steps to prevent galling were taken. 
     Returning to  FIG. 2 , a plunger cover plate  226  can be fastened by two mounting bolts to secure ends of the spring  210  and the plunger  208  within the retaining housing  214 . In many embodiments, a similar cover plate is fastened to the opposite side of the first radiating element. 
     In some embodiments, the radiating elements and coupled housings are made of hollow aluminum. In several embodiments, the antenna support structures are made of hollow aluminum. In other embodiments, other suitable materials can be used for the radiating elements, the plunger, the spring, and the wear plate. 
     In a number of embodiments, the components of the grounding assembly effectively provide self-contained connection systems and thus the final antenna system can be assembled and unassembled easily as opposed to antenna systems using prior art technologies (e.g., conductive tapes or gaskets). In one embodiment, for example, the components of the grounding assembly include the plunger in its retaining housing fully installed on the first radiating element and the wear plate fully installed on the second radiating element. In such case, after components of the grounding assembly have been fully assembled on the first radiating element and second radiating elements, the radiating elements can be installed on the antenna system by placing the first radiating element into a first slot and by sliding the second radiating element into an adjacent slot on the antenna system while allowing the plunger to retract whereby an elongated point of contact between the plunger and wear plate is achieved. In one embodiment, the first radiating element and second radiating elements are components of a first antenna assembly and a second antenna assembly, respectively, where each assembly includes components in addition to the radiating elements. 
     In a number of embodiments, the final assembly step for the antenna system therefore requires no tools and the system can be uninstalled just as easily without tools. Prior art systems, on the other hand, such as those using conductive tapes, gaskets, and the like are generally not capable of being easily uninstalled and reinstalled. For example, prior art technologies such as copper finger gaskets, conductive plates or the like can require one or more fasteners for installation of the grounding assembly. In such case, additional time and tools are required for installation, disassembly and any subsequent reassembly of the grounding system or antenna. 
       FIG. 4  is an isometric view of one end of a plunger  408  in accordance with one embodiment of the present invention. The plunger  408  features a cross section having a T-shaped body including a head and a relatively wide shaft extending from the head and coming to a beveled point. The head has a rectangular shape where each corner of the rectangle has been chamfered at roughly 30 degrees from the surfaces of the shorter sides (e.g., top and bottom) of the rectangle. The shaft extends from the head for a predetermined distance until it is chamfered at approximately 45 degrees. The chamfered portion of the shaft comes to a beveled point. The end points of the 45 degree chamfered surface are beveled as well. In other embodiments, more edges and corners can be chamfered and/or rounded for best fit and function. Chamfering and rounding can enable smooth movement within an opening of a retaining housing and can enable good electrical contact with a wear plate. 
       FIG. 5  is an end view of a plunger  508  in accordance with one embodiment of the present invention. In the embodiment illustrated in  FIG. 5 , the head of the plunger  508  has a width of 0.054 inches and a length of 0.144 inches. The shaft can have a width, from top to bottom, of 0.085 inches. The shaft can have a length of 0.076 inches extending from the head to the beveled point at the end of the shaft. The head can have a length, from top to bottom, of 0.144 inches. Thus, in a number of embodiments, the length of the head is greater than the width of the shaft.  FIG. 6  is a side view of the plunger  508  of  FIG. 5 . 
       FIG. 7  is an isometric view of a wear plate  712  in accordance with one embodiment of the present invention. In a number of embodiments, the wear plate is a solid bar having a number of recesses for mounting. In other embodiments, the wear plate can be a hollow bar.  FIG. 8  is a top view of the wear plate  712  of  FIG. 7 .  FIG. 9  is an enlarged view of a mounting hole of the wear plate of  FIG. 7 .  FIG. 10  is a side view of the wear plate  712  of  FIG. 7 . The wear plate  712  includes a number of mounting holes for attaching the wear plate to a radiating element.  FIG. 11  is a cross sectional view of a section of the wear plate  712  of  FIG. 10  taken across the section A-A. In the embodiment illustrated in  FIG. 11 , the wear plate  712  is hollowed at the mounting hole to accommodate a mounting fastener (not shown). The upper front corner of the wear plate  712  is chamfered at approximately 45 degrees. The end points of the chamfered surface on the corner of the wear plate are rounded. In other embodiments, other surfaces can be beveled and/or rounding to improve fit and function for making ground plane contact. In the embodiment illustrated in  FIGS. 7-11 , the wear plate is a single elongated unit. In other embodiments, the wear plate includes multiple discrete units performing a similar function. In some embodiments, the wear plate can take any number of shapes suitable for providing electrical connectivity between adjacent radiating elements. 
       FIG. 12  is an isometric view of a wavy portion of a spring  1210  in accordance with one embodiment of the present invention. The spring includes a number of sections bent at a small angle where the apex of adjacent bends is rounded or beveled. The resulting shape is wavy and resists compression by opposing flat surfaces. 
       FIG. 13  is a top view of a spring  1310  having both a flat portion and a wavy portion in accordance with one embodiment of the present invention. In many embodiments, the spring  1310  can be used in conjunction with the grounding assembly of  FIG. 2 . In such case, the plunger can be inserted into the retaining housing first. After the plunger has been inserted, the flat portion of the spring  1310  can be inserted into the retaining housing in the empty space behind the plunger. In such case, once the flat portion has been inserted into one side of the retaining housing, the flat portion can be pulled out of the other side and then severed from the remaining wavy portion of the spring. In such case, the only the wavy portion of the spring  1310  remains in the retaining housing. This two part spring structure and method of insertion can minimize difficulty associated with installation of the spring within the grounding assembly. 
       FIG. 14  is a side view of the wavy spring  1310  of  FIG. 13 . 
     Proper grounding can also be important in dealing with electromagnetic interference (EMI) problems. Electromagnetic interference, or radio frequency interference (or RFI), is generally defined as an unwanted disturbance that affects an electrical circuit due to electromagnetic radiation emitted from an external source. The disturbance can interrupt, obstruct, or otherwise limit the effective performance of the electrical circuit. The source can be any object that carries rapidly changing electrical currents, such as an electrical circuit. In certain circumstances, an antenna transmitting and receiving signals at a relatively fast rate is such an electrical circuit and can be a troublesome source of EMI. 
     Improper grounding can be a primary means of noise coupling and other interference. The embodiments of grounding assemblies described herein are useful for preventing the unintended radiation of signals that would effectively become EMI. In systems demonstrating EMI problems, the grounding assemblies described herein can be used to minimize such EMI, especially in circumstances where the specific components responsible for EMI generation move relative to one another. 
     While the above description contains many specific embodiments of the invention, these should not be construed as limitations on the scope of the invention, but rather as examples of specific embodiments thereof. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their equivalents.