Abstract:
A mobile, telescoping radar array is disclosed. In some embodiments, the radar array has a plurality of support stages that fully nest when stowed and assume a telescoped form when deployed. A plurality of radiating elements depend from each stage. The support stages, as deployed, have a geometry that supports 360 degrees of radar coverage without rotating or otherwise repositioning the radar array.

Description:
FIELD OF THE INVENTION 
     The present invention relates to radar in general, and, more particularly, to ground-based mobile radar systems. 
     BACKGROUND OF THE INVENTION 
     Brigade-size and larger-size forces often use mobile radar systems to detect and track incoming artillery and rocket fire to determine the point of origin for counter-battery fire. These mobile radar systems are typically trailer mounted and towed by a vehicle, such as a HUMVEE. 
     These mobile radar systems usually take the form of a planar array that is either mechanically or electronically steered. In mechanically-steered systems, the planar array is continuously physically rotated 360° by a drive system. This enables the mechanically-steered radar to scan a full 360° of azimuth. Electronically-steered arrays, on the other hand, do not actually move while in operation. Rather, a sequence of electromagnetic “beams” is rapidly electronically swept over a 90° area. To scan a full 360° , the electronically-steered planar array must be physically repositioned (three times to scan the remaining 270° in 90° sectors) or supplemented by three additional systems, each scanning a different 90° sector of azimuth. Some electronically-steered mobile radar sets, such as the AN/TPQ-36 Firefinder radar, include a drive system for providing a 360° sectoring mode. In this mode, a first 90° sector is briefly electronically scanned and then the array is automatically rotated to sequentially scan, in turn, the three remaining 90° sectors. 
     Planar radar arrays have certain drawbacks. In particular, they are required to withstand wind loads and ice. Furthermore, to the extent that the arrays are rotated, they must be stable against off-axis rotation and tipping moments, etc. For mechanically-steered arrays, the actuation and drive systems are complex and expensive. And, to the extent that the issue of wind loads and ice is addressed by a more robust mechanical design (e.g., increased weight, etc.), the load on the drive system is increased, thereby requiring more power and heavier drive-system components. Additionally, it is difficult to provide sufficient cooling efficiency for air-cooled radar systems. Also, EMI shielding can be problematic for planar arrays. 
     In an attempt to reduce the weight and thereby increase the functionality and mobility of mobile radars, lightweight composite structures are being developed for this application. But it is proving to be problematic to implement planar radar antenna arrays using composite materials. In particular, it is proving to be difficult to develop composites that are adequately stiff to withstand deflection (e.g., weight, wind loads, ice, etc.), yet have suitable damage tolerance. 
     As a consequence, there is a need for a new design for a mobile radar array that addresses the shortcomings of the prior art, such as the tradeoff between weight and robustness, issues pertaining to cooling, EMI shielding, transportation, and the complexity of the drive system. 
     SUMMARY OF THE INVENTION 
     The present invention provides a mobile radar system that avoids some of the costs and disadvantages of the prior art. 
     In accordance with the illustrative embodiment, the mobile radar system has a plurality of “telescoping” support stages that fully nest when stowed and assume an extended, telescoped-form when deployed. The radar array includes a plurality of radiating antenna elements that depend from each of support stages. 
     In preferred embodiments, the deployed array has a geometry that supports 360 degrees of radar coverage without having to rotate or otherwise reposition the array. That is, the array is electronically steered through 360 degrees. Suitable array geometries for 360-degree coverage include, without limitation, cylindrical, pyramidal, conical, cubical, and the like. The array provides a varying amount of elevation coverage as a function of the precise positioning of the radiating elements and the amount of phase and amplitude pre-processing that is performed on the transmitted radar signals. 
     The telescoping radar array disclosed herein has a number of advantages in comparison with prior-art mobile radars. For example and without limitation, embodiments of the telescoping radar array described herein provide:
         A collapsible array. Since the array is collapsible and fully nests, it is better able to withstand the rigors of transport and requires less space than prior-art designs. In fact, the collapsible nature of the array provides significant advantages compared to the prior art in terms of C130 transport, rail transport, ground transport, and the like.   A non-rotating system. Since the array does not physically rotate, it provides superior performance in high-wind conditions, since rotating arrays are subject to inconsistent rotation in high winds. Furthermore, the system has greater stability, since there are no off-axis rotation concerns or tipping moments. Additionally, the telescoping radar array has greater reliability than prior-art rotating flat-planar arrays, since there are no moving parts to wear out. Specifically, a main bearing, slip ring, position encoder, and servo rotation speed control, which are normally required for rotating arrays, are used in the illustrative embodiment.   Resistance to deflection. The geometry of the telescoping array disclosed herein is inherently stiff and its symmetric structure results in more consistent and uniform wind loading, so that the array can operate in higher winds than flat planar arrays.   Simple actuation. Since the array does not rotate, but rather simply deploys in linear fashion, its actuating systems are less complex than for mechanically-rotated radars.   Low RCS. Due to its geometry, the telescoping radar array disclosed herein is expected to have a lower radar cross section than prior-art arrays.   Less weight. Since the telescoping radar array is not rotated, a drive system and associated controls are not required, thereby reducing weight relative to rotating flat planar arrays. Also, due to its geometry, the telescoping radar array is inherently stiff such that it can be formed from relatively light-weight composite materials. As previously noted, such composites are not well suited for use in conventional mobile radars because the stiffness/damage tolerance issue.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  depicts portable telescoping radar array  100  in accordance with the illustrative embodiment of the present invention.  FIG. 1A  depicts radar array  100  in a stowed state (for transport) on the back of a vehicle. 
         FIG. 1B  depicts portable telescoping radar array  100  in accordance with the illustrative embodiment of the present invention.  FIG. 1B  depicts radar array  100  in a deployed state (for use) on the back of a vehicle. 
         FIGS. 2A-2F  depict a reversible sequence showing the collapse (forward sequence) or deployment (reverse sequence) of radar array  100 . 
         FIGS. 3A-3C  depict details of flanges from adjacent support stages coming into contact. 
         FIG. 4  depicts radiating elements depending from the support stages of telescoping radar array  100 . 
         FIG. 5A  depicts a first embodiment of radar array  100  in which the radiating elements face the horizon (as in  FIG. 4 ). 
         FIG. 5B  depicts a second embodiment of radar array  100  wherein the radiating antenna elements face skyward. 
         FIG. 5C  depicts a third embodiment of radar array  100  wherein the radiating antenna elements are at an angle relative to the horizon. 
         FIG. 6  depicts fans for drawing air into radar array  100 , wherein the fans are disposed near the base of the radar array. 
         FIG. 7  depicts an embodiment of radar array  100  wherein the air that is drawn in by the fans vents from the top of the radar array. 
         FIG. 8  depicts an embodiment of radar array  100  wherein the air that is drawn in by the fans vents through the face of each support stage. 
         FIGS. 9A-12A  depict, via top views, various configurations of the support stages of radar array  100 . 
         FIGS. 9B-12B  depict side views that correspond to the top views shown in  FIGS. 9A-12A , respectively. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1A and 1B  depicts mobile telescoping radar array  100  in accordance with the illustrative embodiment of the present invention. 
     In these Figures, radar array  100  is situated on vehicle  102  for transportation and deployment.  FIG. 1A  depicts radar array  100  in a stowed state, which is used for transportation or storage. Radar array  100  is not operational in this state.  FIG. 1B  depicts radar array  100  in a deployed state for use. Radar processing electronics for data acquisition and processing, which is also a part of radar array  100 , is not depicted in  FIGS. 1A and 1B  (see,  FIG. 4 ). 
       FIGS. 2A through 2F  depict radar array  100 , sans vehicle  102 , in various stages of deployment. The ordered sequence FIG.  2 A→ FIG. 2F  depicts retraction of the radar array and the sequence FIG.  2 F→ FIG. 2A  depicts deployment of the array. For reference, in these Figures, the x-axis (i.e., horizontal) is the “radial” direction and the y-axis (i.e., vertical) is the “axial” direction. 
     The structural shell of radar array  100  comprises a plurality support stages  204   i . In the embodiment that is depicted in  FIGS. 2A through 2F , there are five support stages  204   1  through  204   5 . In some other embodiments, radar array  100  comprises fewer than five support stages  204   i . In still further embodiments, radar array  100  comprises more than five support stages  204   i . 
     Innermost support stage  204   5 , which upon deployment becomes the “top” of the telescoping array (see, e.g.,  FIGS. 2A and 2F ), includes cover  206 . Other support stages (e.g.,  204   1  through  204   4 for this embodiment) do not include a cover since they each must accommodate axial deployment of other stages. 
     Each support stage  204   i  preferably enables radar scanning of 360 degrees of azimuth. To that end, in the illustrative embodiment, each support stage is in the form of an annulus (i.e., each stage has a circular form). In some alternative embodiments, however, support stages are not circular. For example, as described in further detail later in this specification in conjunction with FIGS.  9 A/ 9 B through  12 A/ 12 B, support stages can have a polygonal shape (e.g., triangular, square, etc.; see, FIGS.  9 A/B,  10 A/B). 
     In the illustrative embodiment, the deployed array has a stepped “face” or profile. In some alternative embodiments, the profile is not stepped, but rather has a smoothly-tapering profile (see, e.g., FIGS.  11 A/B,  12 A/B). 
     Regardless of actual configuration, it is desirable for support stage  204   i  to enable a radar scan of 360-degrees of azimuth without the need to rotate or otherwise re-position the array. For convenience, the term “ring” or “ring-shaped” will be used in the appended claims to refer generically to support stages  204   i  that have a form or shape that is suitable for covering 360 degrees of azimuth, irrespective of the actual geometric configuration of the support stage. 
     Support stages  204   i  are coaxial with respect to each other and radially-spaced apart from each other so that they are capable of nesting (see, e.g.,  FIG. 2F ). The nested arrangement provides a high-packing density and efficient use of space to address transportation and storage issues. 
     Support stages  204   i  are axially-deployable; axial deployment is depicted via the sequence of figures proceeding from  FIG. 2F  to  FIG. 2A . In the illustrative embodiment, actuator  214 , which can be, without limitation, a piston or a drive screw, is used to deploy or retract radar support stages  204   i . In various embodiments, actuator  214  can be driven hydraulically, pneumatically, electrically, magnetically, etc. Furthermore, actuation can be manual; that is, an operator can, for example, use a hand-crank to deploy/retract the array. 
     In the illustrative embodiment, mechanical actuator  214  directly drives support stage  204   5 , which is the innermost of the support stages and axially extends (and moves) the furthest during deployment. That is, support stage  204   5  is the “top” of the deployed radar array. For this embodiment, mechanical actuator  214  physically contacts undersurface  208  of cover  206  of support stage  204   5 ; there is no contact between actuator  214  and the other support stages. 
     As described further below, support stages  204   i  include mechanical coupling elements. These coupling elements are dimensioned and arranged so that a “temporary” physical coupling occurs between adjacent support stages during deployment. These temporary couplings enable the driven support stage (i.e., support stage  204   5 ) to effectively drag stages  204   4 ,  204   3 , and  204   2  to their deployed positions. 
     With reference to the sequence of  FIGS. 2F to 2A ,  FIG. 2A  depicts support stages  204   1  through  204   5  in a fully nested state.  FIG. 2E  depicts the beginning of the deployment operation wherein actuator  214  drives support stage  204   5  in an axial direction, which is typically “upward.” This is depicted via a perspective view in  FIG. 3A . For the sake of clarity, the remaining support stages are not depicted in  FIG. 3A .  FIGS. 2E and 3A  depict lower circumferential lip or flange  210  of support stage  204   5  approaching upper circumferential flange  212  of adjacent support stage  204   4 . In the illustrative embodiment, flanges  210  and  212  serve as the aforementioned mechanical coupling elements. 
     With increasing upward axial movement, lower flange  210  of support stage  204   5  contacts upper flange  212  of support stage  204   4 . This is depicted in  FIG. 3B  and schematically in  FIG. 3C  (slight gap shown for clarity). Contact between the two flanges  210  and  212  results in the creation of temporary seal  216 . This seal, which is created between all adjacent support stages (see, e.g.,  FIG. 2A ), keeps weather (e.g., rain, snow, ice, etc. out of the interior volume defined by the fully telescoped stages. This is beneficial since, in some embodiments, the radiating elements will be exposed on the interior surface of each support stage  204   i . Furthermore, the seals are advantageously EMI compliant. 
     As actuator  214  continues to drive support stage  204   5 , support stage  204   4  is lifted, as depicted in  FIG. 2D . Deployment continues as stage  204   3  ( FIG. 2C ) and stage  204   2  ( FIG. 2B ) are sequentially lifted. 
     The mechanical coupling elements can have a different physical configuration than the flanges depicted in the illustrative embodiment. In preferred embodiments, the mechanical coupling elements provide both a coupling and sealing functionality. In less preferred embodiments, different elements are used in combination to provide these two functions. 
     It will be appreciated that telescoping support stages  204   i  can be actuated via a means other than a rigid actuator such as depicted in the illustrative embodiment. For example, and without limitation, a cabled actuator can be used. In some embodiments (not depicted) that use a cabled actuator, each support stage  204   i  is coupled to all other support stages via an actuator cable akin to the arrangement of a multi-section extension ladder. 
       FIG. 4  depicts radiating elements disposed on interior surface of the various supports stages  204   i . Although only a single radiating element is depicted on each support stage, it will be understood that a plurality of such radiating elements are situated along the interior surface of each support stage, thereby providing 360 degrees of azimuth coverage. The actual number of radiating elements per stage is a function of the desired radar resolution, which is ultimately a function of the specific radar application. In conjunction with the present disclosure, those skilled in the art will be able to determine how many radiating elements should be used, per stage, as a function of application specifics and other considerations. 
     Electrical lines  420  lead from each radiating element  418  to radar processing electronics  422 . Radar processing electronics is typically located in the vicinity of the support stages (e.g., beneath them, or elsewhere on the radar-transport vehicle, etc.). In some embodiments, radar processing electronics are disposed directly behind radiating elements  418 . 
     Radar processing electronics  422  provides data acquisition and processing. The radar processing electronics is typically electrically connected to a screen (not depicted), so that a view of the search volume (e.g., showing radar contacts) is displayed to an operator. Those skilled in the art will know how to specify and use radar processing electronics  422 . 
       FIG. 5A  depicts the direction of radiation when radiating elements  418  face the horizon, as in  FIG. 4 . This configuration provides radar detection in a search volume that extends below the horizon to some elevation angle, as determined by system requirements and the amount of pre-processing and post-processing that is available to telescoping radar array  100  via radar processing electronics  422 . 
     In some other embodiments, radiating elements  418  are arranged against each support stage  204   i  such that they face skyward. The direction of radiation for such embodiments is depicted in  FIG. 5B . This configuration provides efficient coverage of the airspace overhead with radar detection capability down toward the horizon. 
     In yet some further embodiments, radiating elements  418  are mounted on a sloped face (or at an angle to a non-sloped face). This configuration provides radar detection in a search volume that extends below the horizon to some elevation angle, as determined by system requirements and the amount of pre-processing and post-processing that is available to telescoping radar array  100 . Several embodiments of telescoping radar arrays in accordance with the present invention and having sloped faces are depicted in FIGS.  12 A/B and  13 A/B. In some embodiments, the sloped face of the support stages and, consequently, the radiating elements, are set back 22.5 degrees relative to vertical. 
     In view of the present disclosure, those skilled in the art will know how to arrange radiating elements  418  to cover a desired search volume as a function of post- and pre-processing capabilities, among other considerations. 
     Telescoping radar array  100  incorporates shielding from electromagnetic interference (“EMI”). In some embodiments, each support stage  204   i  comprises a non-conductive composite material that includes a conductive material (e.g., embedded mesh, etc.) suitable for providing EMI shielding. The shielding is located throughout the support stage, but is not continuous so that apertures through which each radiating element transmits and receives radiation are provided. 
     Radar processing electronics  422  generate considerable heat; as a consequence, cooling must be provided. In embodiments in which radar processing electronics  422  are disposed directly behind radiating elements  418 , such cooling is particularly important. 
     In some embodiments, especially those in which radar processing electronics  422  are disposed directly behind radiating elements  418 , telescoping radar array  100  is air cooled via a forced-air cooling system. In the embodiment that is depicted in  FIG. 6 , the forced-air cooling system includes cooling fans  624  for drawing air into the space defined by the deployed support stages. In some embodiments, cooling fans  624  are disposed in base  626 , which couples to the bottom of the radially-outermost support stage (the support stage at the bottom of deployed radar array  100 ). 
     In the embodiment that is depicted in  FIG. 7 , air is drawn through base  626  via fans  624  and is vented through cover  206  at the top of telescoping radar array  100 . In this embodiment, cover  206  includes a louvered vent, etc., with EMI shielding and dust/sand filtration. 
     In the embodiment that is depicted in  FIG. 8 , air is drawn through base  626  via fans  624  and forced past radiating elements  418  and vented through each support stage  204   i . In this embodiment, each support stage has an open frame or lattice-like design wherein a “breathable” (i.e., air-permeable) material is wrapped over the frame. The material is suitably-treated for water resistance. See, U.S. patent application Ser. No. 11/427,225 entitled “Breathable Radome,” incorporated by reference herein. 
     As previously noted, support stage  204   i  can have any one of variety of geometric configurations. FIGS.  9 A/ 9 B,  10 A/ 10 B,  11 A/B, and  12 A/ 12 B depict respective top and side views of some embodiments of telescoping radar arrays in accordance with the present invention that have a different configuration than the illustrative embodiment (e.g., see  FIG. 1B : radar array  100  having circular-shape support stages  204   i  wherein telescoped array  100  has a stepped profile). 
       FIGS. 9A and 9B  depict respective top and side views of triangular-shape support stages  204   i  wherein telescoped array  900  has a stepped, three-sided pyramidal profile  928 .  FIGS. 10A and 10B  depict respective top and side views of square-shape support stages  204   i  wherein telescoped array  1000  has a stepped profile  1028 . 
       FIGS. 11A and 11B  depict respective top and side views of square-shape support stages  204   i  wherein telescoped array  1100  has a smoothly-tapered, four-sided pyramidal profile  1128 . And  FIGS. 12A and 12B  depict respective top and side views of circular-shape support stages  204   i  wherein telescoped array  1200  has a smoothly-tapered profile  1228  that results in a conical shape. 
     It is to be understood that the disclosure teaches just one example of the illustrative embodiment and that many variations of the invention can easily be devised by those skilled in the art after reading this disclosure and that the scope of the present invention is to be determined by the following claims.