Abstract:
Described is a mobile radar system which provides both persistent surveillance and tracking of objects with adaptive measurement rates for both maneuvering and non-maneuvering objects. The mobile radar system includes a vehicle having mounted therein an active, electronically-steerable, phased array radar system movable between a stowed position and a deployed position and wherein the phased array radar system is operational in both the deployed and stored positions and also while the vehicle is either stationary or moving. Thus, the mobile radar system described herein provides for longer time on target and longer integration times, increased radar sensitivity and improved Doppler resolution and clutter rejection. This results in a highly mobile radar system appropriate for use in a battlefield environment and which supports single-integrated-air-picture metrics including but not limited to track purity, track completeness, and track continuity and thus improved radar performance in a battlefield.

Description:
FIELD OF THE INVENTION 
       [0001]    The system and techniques described herein relate generally to radar systems and more particularly to mobile radar systems. 
       BACKGROUND OF THE INVENTION 
       [0002]    As is known in the art, there is a great need for highly mobile, medium-range, tactical radar systems that provide information about enemy artillery, mortar and rocket launcher locations for counterattack and other significant threats to warfighters on the ground. Such a radar system must provide high operational availability and reduced maintenance costs. 
         [0003]    Conventional radar systems which attempt to serve this function are stowed and typically transported (e.g. towed) by so-called “high mobility multi-purpose wheeled vehicles” or HMMWV&#39;s or any other vehicle suitable for the transport task. Such mobile radar platforms are typically located proximate forward battle lines in direct support of brigade operations. Typically, the radar system must be capable of being set up and operational in approximately fifteen (15) minutes. Since such radars are in a fixed position when they are operating (i.e. they can only be operational when they are stationary), they eventually become a target for enemy attack. Thus, the radars must also be capable of moving from an existing location within five (5) minutes of a decision being made to evacuate a given position. This involves stopping radar operation and securing the radar in a stored position (e.g. on an HMMWV or a trailer attached to an HMMWV) for transport to a new position. 
         [0004]    Some tactical land based radars employ rotating antennas on stationary platforms during operation. There are a number of shortcomings to this mode of operation. First, the fixed radar position, located close to the forward battle line in direct support of brigade operations, becomes a possible enemy target. Second, forces which are on the move may not receive the benefits provided by a stationary radar and thus may be unprotected from enemy artillery, mortars and rockets. Third, a rotating antenna places limits on radar system performance (e.g. limits search time, reduces track signal-to-noise ratio, etc . . . ). Fourth, a rotating antenna system severely complicates signal routing to the antenna, degrades system reliability and availability and burdens life-cycle cost. 
       SUMMARY OF THE INVENTION 
       [0005]    In accordance with the concepts, techniques and systems described herein, a mobile radar system (also sometimes referred to herein as an “on-the-move” radar system) includes a phased array radar system configured to be mounted in a vehicle. The phased array radar system is movable between a stowed position and a deployed position; while on the vehicle the operation is in either the stowed or deployed position, and also while the vehicle is stationary or moving. 
         [0006]    With this particular arrangement, a highly mobile battlefield radar system suitable for use in a battlefield or other environment is provided. Since the phased array radar system is operational when it is in either a stowed position or a deployed position and also while the vehicle to which the phased array radar is mounted is stationary or moving, the mobile radar system can operate while travelling to, from and/or around a battlefield environment (i.e. the mobile radar is operational regardless of whether the vehicle is moving or stopped). Thus, the mobile radar system can avoid and evade enemy attacks while still operating and thus while supporting troops in a battlefield. 
         [0007]    In one embodiment, with the phased array radar system operational while in its stowed position, the vehicle can move at a top speed which is greater than a top speed of the vehicle when the phased array radar system is in its deployed position. In one embodiment, when the antenna platform is in its deployed position, the phased array radar system provides substantially 360 degrees of scan coverage (regardless of whether the vehicle is moving or stopped). In one embodiment, when the phased array radar system is in its stowed position, it provides substantially 270 degrees of scan coverage (regardless of whether the vehicle is moving or stopped). Since the phased array radar system provides substantially 270 or 360 degrees of coverage, the phased array radar system is able to track targets in a wide range of areas. In cases in which the phased array radar system includes an electronically-steerable phased array (AESA) antenna having substantially 270 or 360 degrees of coverage, search raster rates are not limited as in radar systems which utilize a mechanically rotating antenna to provide such coverage. Also, in the case where an AESA antenna is used, the mobile radar system described herein is adaptable to a current threat limited only by the speed at which beams can be switched. 
         [0008]    Since the mobile radar system provides 270° or 360° of scan coverage and can remain operational even while moving from one physical location to another, the mobile radar system provides for longer time-on-target, longer integration times, increased radar sensitivity and improved Doppler resolution and clutter rejection than prior art systems. 
         [0009]    The mobile radar system can provide, while stationary or in motion, persistent surveillance and tracking of objects with adaptive measurement rates for both maneuvering and non-maneuvering objects. In one embodiment, the phased array radar system comprises an active electronically-steerable, phased array (AESA) antenna mounted on an antenna platform movable between a stored position and a deployed position. Significantly, the AESA antenna is operational in both the deployed and stored positions of the movable antenna platform. 
         [0010]    Providing a mobile radar system which is operational while both stationary and moving results in a mobile radar system which supports the achievement of completely compliant single-integrated-air-picture (SIAP) metrics such as track purity, track completeness, track continuity. 
         [0011]    In one embodiment, the AESA antenna is provided as a solid state active array having a plurality of “array faces” (or more simply, “faces”) which provide 360 degrees of scan coverage. In one embodiment, the AESA antenna has four faces. The four faces are arranged such that the AESA antenna provides continuous 360 degrees of coverage. 
         [0012]    In one embodiment, the mobile radar system (aka the on-the-move radar system) may further include a generator coupled to an AESA antenna. The generator provides an amount of power to the AESA antenna which is sufficient to power the antenna. In one embodiment, the AESA antenna uses prime power provided by a vehicle on which the AESA antenna is mounted. In one embodiment, the AESA antenna comprises a plurality of faces and the primary power is shared among all the faces. Thus, the AESA antenna is provided as a self-contained antenna. In one embodiment, the AESA antenna is provided as a self-contained, four face, solid state AESA antenna. 
         [0013]    In one embodiment, the vehicle and phased array radar system which make up the mobile radar system do not require any set-up time to operate. That is, the phased array radar system is continuously operational regardless of vehicle motion or whether the phased array radar system is in a deployed position, a stowed position or some other position (e.g. neither fully deployed, nor fully stowed). Thus, the system has the flexibility needed to adapt to situational battlefield developments. 
         [0014]    For example, the mobile radar system can move to avoid or evade possible enemy attack while still remaining operational and providing information (e.g. target locations and tracks) to third parties. Also, since the AESA antenna provides substantially simultaneous 360 degrees of coverage, faster search rates are not limited as in radar systems which utilize phased array radars which mechanically rotate to provide 360 degrees of coverage. Furthermore, the ability to remain operational even while moving allows the mobile radar system to detect and track targets at all times during battlefield operations. Thus, the mobile radar system helps achieve completely compliant single-integrated-air-picture (SIAP) metrics including but not limited to total purity, track completeness, and track continuity. 
         [0015]    In one embodiment, the phased array radar system is provided having four faces. Each face of the phased array radar system may be provided as an AESA antenna and the phased array radar is configured such that it is possible to electronically switch between the faces in any sequence. Electronic scan by four AESA faces vastly enhances search update rates and allows greater flexibility in scheduling radar waveforms compared with mechanically rotating system. For example, since each AESA can be treated as a separate radar, each AESA face can be autonomously operated (i.e., one face can operate in a search mode at one instant, and a second different face can operate in a track mode at the next instant). This allows different sectors to be scanned according to threat. Thus, the mobile radar system provides substantially continuous 360 degree coverage capability even while tracking a threat in a given sector. It should be appreciated that a full operational face can only be performed in one instant of time with the limitation of an on-board generator. Without any such limitations, it would be possible to have one face operate in a search mode at one instant in time, and a second different face operate in a track mode at the same instant in time. 
         [0016]    Also, since each AESA antenna can be treated as a separate radar, the mobile radar system can simultaneously operate multiple sub-apertures on different faces of the phased array radar system to detect and track targets. 
         [0017]    This is in stark contrast to the operation of a rotating radar since once a rotating radar stops and focuses resources on a given sector, the radar is now completely blind to threats that may arise in other (now ignored) sectors. 
         [0018]    Also, since the radar described herein is a continuously operational system and provides substantially continuous 360 degree coverage while moving or stopped, it can track highly maneuvering, low radar cross-section (RCS) targets at rates which are orders-of-magnitude faster than that achievable in mechanically rotating radars. This capability enables high levels of track consistency, continuity, and clarity that can significantly contribute to the formation of a single-integrated-air-picture (SIAP) in complex, multiple threat, multiple-friendly environments. 
         [0019]    Furthermore, since the mobile radar system provides substantially continuous 360 degree coverage while moving or stopped (e.g. when the vehicle on which the phased array radar system is mounted is moving or parked), the mobile radar system need not stay in one location at all times. Since the mobile radar system need not stay in one location to be operational, the risk of the mobile radar system itself becoming a target is reduced. 
         [0020]    This is in contrast to prior art battlefield radar systems which operate at a fixed location for an amount of time which allows an enemy to identify the location of a battlefield radar and thus make the radar location a target. 
         [0021]    Since the mobile radar system utilizes an active, electronically steerable array (AESA) antenna having a size and shape configured to provide substantially continuous 360 degree coverage, the mobile radar system need not utilize a rotating antenna aperture. Elimination of a rotating antenna aperture significantly simplifies all signal interfaces between the solid-state AESA and a radar signal processor, prime power and receiver/exciter sub-systems. This results in a system having reliability which is greater than the reliability of prior art systems. 
         [0022]    In one exemplary embodiment, the mobile radar system comprises a solid state AESA having four faces with each of the faces having an area of approximately one square meter (1 m 2 ). In a preferred embodiment, each face of the mobile radar system is comprised of a panel array antenna disposed on a movable antenna platform. In this configuration, the mobile radar system provides almost instantaneous coverage in an approximately 360 degree range in a deployed mode and in an “on-the-move” mode (i.e. with movable antenna platform in a stowed position), the mobile radar system provides almost instantaneous coverage in an approximately 270 degree range. This is true regardless of varying terrain and climate conditions. Furthermore, each panel array antenna face is mounted to a frame which in turn is coupled to a telescoping platform or mast. Also, the panel array antennas are mounted in a manner which allows the panels to be removed and replaced without making or breaking power and signal cables. 
         [0023]    Utilizing panel arrays significantly reduces cost, weight and size of a mobile radar system while also providing an exceptional power-aperture-gain (PAG) sensitivity. In one embodiment, a 128 transmit-receive (TR) channel panel array comprises a “building-block” for an active electronically scanned array (AESA) antenna. The panel array integrates RF, DC and logic distribution to 128 TR channels. In addition, the 128 TR channel panel array integrates a three-channel monopulse network (transmit/sum channel, delta elevation channel and delta azimuth channel). 
         [0024]    In one embodiment, the panel array is conduction cooled by direct mechanical contact between backsides of flip-chip components and a brazement with a liquid pumped through the brazement. 
         [0025]    In one embodiment, thermal management of the array is addressed via component and subassembly packaging. In particular, in addition to the liquid cooled brazement, direct mechanical contact between flip-chip monolithic microwave integrated circuits (MMICs) and a finned heat sink is used. An intermediate “gap pad” layer may or may not be used between the MMICS and the heat sink. Ideally, each MMIC has substantially the same thermal resistance to a cold plate which reduces (or in some case may even minimize) the number of thermal interfaces between the source of heat (e.g. the MMICs) and the cold plate or other heat sinking source. Thus, a parallel cooling approach is used. 
         [0026]    In one embodiment, a centrally located heat exchanger provides the cooling for all four AESA faces. 
         [0027]    In one embodiment, the system also includes an active monopulse combiner network assembly. This assembly, which is part of an overall monopulse network, enables use of a single panel array design (i.e. a single panel array design part number), eliminates quantization lobes (resulting from correlated weighting at the sub-array level) and produces low sidelobes. This approach preserves panel array scalability and affordability and produces excellent monopulse patterns and an exemplary network is described in co-pending application Ser. No. 12/757,371, filed Apr. 9, 2010 which is assigned to the assignee of the present invention and which is incorporated herein by reference in it&#39;s entirety. 
         [0028]    In one embodiment, each panel comprises modular line replaceable units (LRUs). In one exemplary embodiment, a panel which is one (1) square meter (m 2 ) in area is comprised of four (4) weather-tight, electromagnetic interference (EMI) shielded LRU&#39;s. Each LRU comprises eight (8) sub-panels, a brazement to cool the sub-panels, four (4) active monopulse combiner network assemblies, four (4) power-logic circuit cards, one (1) distribution board, four (4) linear regulators (LR), eight (8) DC/DC converters, a brazement to cool the DC/DC converters and LR&#39;s, and a bus bar. In one particular embodiment, each LRU is approximately 46 in. (high)×10 in. (wide)×4 in. (deep) and the LRU weight is estimated to be 64 lbs. The LRU approach provides several advantages: (1) LRU&#39;s allow easy access to signal and coolant lines; (2) LRU&#39;s can be removed or inserted into the face of an AESA in a short amount of time; (3) LRU weight allows replacement to be accomplished manually (e.g. it is a two-man lift); and (4) the LRU approach reduces associated costs of packaging and cooling an array. 
         [0029]    In one embodiment, the system utilizes centralized prime power. The prime power source may be provided as part of the vehicle or as part of the phased array radar system. In one exemplary embodiment, a central 208 VAC 3-phase generator provides system prime power and is converted to +30V DC that is used to bus power to each face of the AESA (where each face is on the order of 1 m 2 ). This approach eliminates relatively expensive +30V DC/DC converters utilized in prior art approaches. 
         [0030]    Thus, described herein is a mobile radar system which, in one embodiment, is a self-contained, four face, solid state AESA radar disposed on a telescoping platform (or telescoping mast) mounted to a ground based vehicle (e.g. a HMMWV). The mobile radar system is coupled to the telescoping platform or mast in such a way that the AESA antenna is operational in at least two positions (e.g. AESA antenna fully raised and AESA antenna fully lowered). With this arrangement, a self-contained, four face, solid state phased array radar system on a telescoping platform or mast mounted to a ground based vehicle which is operational in at least two positions is provided. Since the phased array radar system is operational in at least two positions (e.g. AESA fully raised and AESA fully lowered), no set up time is required before operating the system. Furthermore, the mobile radar system operates in at least two different radar modes: 1) air surveillance and 2) small arms fire surveillance and tracking. 
         [0031]    Although the mobile radar system is described primarily in the context of being mounted on a mobile vehicle (e.g. a HMMWV), it should be appreciated that the mobile radar system can be placed on a wide variety of other vehicles. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]      FIG. 1  is a diagrammatic view of a mobile radar system travelling in a battlefield with the mobile radar system provided from a vehicle having a phased array radar system disposed thereon and operating while the vehicle is moving; 
           [0033]      FIG. 1A  illustrates a phased array radar system in a stowed position mounted on a ground based vehicle; 
           [0034]      FIG. 1B  illustrates a phased array radar system in a deployed position mounted on a ground based vehicle; 
           [0035]      FIG. 1C  illustrates a phased array radar system in a deployed position mounted on a ground based vehicle; 
           [0036]      FIG. 2  is a flow diagram of a method of operating a mobile radar system; 
           [0037]      FIG. 3  is a block diagram of a mobile radar system mounted on a ground based vehicle; 
           [0038]      FIG. 4  is a block diagram of mobile radar system electronics; 
           [0039]      FIGS. 5 and 5A  are block diagrams of an active, electronically-scanned array (AESA) antenna face made up of an array of individual panels and illustrating different active panels on the AESA antenna face; 
           [0040]      FIG. 6  is a front isometric view of an AESA antenna face made up of a plurality of panel arrays; 
           [0041]      FIG. 6A  is a rear isometric view of a panel array illustrating a line replaceable unit (LRU); 
           [0042]      FIG. 6B  is an isometric view of a portion of the panel array shown in  FIG. 6A ; 
           [0043]      FIG. 6C  is an isometric view of a portion of the panel array shown in  FIG. 6A ; and 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0044]    Referring now to  FIGS. 1-1C  in which like elements are provided having like reference designations throughout the several views, a mobile radar system  5  comprises a phased array radar system  10  disposed on a vehicle  12 . Vehicle  12  travels in and around a battlefield area  13 . Vehicle  12  may be provided, for example, as high mobility multi-purpose wheeled vehicle (HMMWV&#39;s) or any other vehicle suitable for a transport task. Vehicle  12  and phased array radar system  10  may travel in a variety of environments and terrains, with a clear battlefield environment (i.e. clear of fog, rain, snow, smoke, etc . . . ) and both a relatively flat beach terrain and a mountain range terrain here being show. A global positioning system (GPS) coupled to phased array radar system  10  or vehicle  12  communicates with a GPS satellite  15 . 
         [0045]    Mobile radar system  5  tracks aircraft  6  or other objects via phased array radar system  10 . Significantly, mobile radar system  5  is operational in either a fixed location (as shown in  FIG. 1 ) or while vehicle  12  is on-the-move (i.e. even while vehicle  12  traverses the beach, or the mountainous terrain or follows any other path). Since mobile radar system  5  need not be in a fixed position when operating, mobile radar system  5  can avoid enemy attack and move where needed and thus is suitable for use proximate forward battle lines in direct support of troop operations. 
         [0046]    Accordingly, troops which are on the move receive the benefits provided by mobile radar system  5  which can track a wide variety of objects such as enemy artillery, mortars and rockets and aircraft. 
         [0047]    As will become apparent from the description provided herein below, in one embodiment, phased array radar system  10  comprises a plurality of so-called “panel arrays” combined with resource management systems and signal processing systems to provide the radar system  10  as an integrated, four-faced, active, electronically-scanned array (AESA) radar system capable of performing radar functions regardless of whether vehicle  12  is moving (and thus, phased array radar system  10  is moving) or whether vehicle  12  is stationary (and thus, phased array radar system  10  is stationary). 
         [0048]    For an assortment of reasons including, but not limited to, mechanical difficulties, conventional, rotating single-faced antennas cannot operate while being transported. A rotating, single-face AESA, for example, is only operational when a vehicle transporting the rotating, single-face AESA is stationary (and thus the radar is at a fixed position). 
         [0049]    Referring now to  FIGS. 1A-1C , phased array radar system  10  comprises a movable antenna platform  16  ( FIGS. 1A-1B ) having an outer cover  17 . Antenna platform  16  has a first portion configured to be mounted and attached to vehicle  12  and having a second portion to which an AESA antenna  18  is coupled. Thus, antenna platform  16  can be removed from the vehicle and mounted on another structure (e.g., the roof of a building) to provide surveillance protection for a base or compound. Platform  16  is selected having a size and strength sufficient to raise and lower AESA antenna  18 . In one embodiment, platform  16  is provided as a telescoping platform. 
         [0050]    AESA antenna  18  comprises four apertures (or “faces”)  18   a - 18   d  with only face  18   a  visible in  FIG. 1A  and faces  18   a,    18   b  visible in  FIG. 1B . Preferably, the faces should be substantially identical in size and shape, but need not be so. In one embodiment, each aperture  18   a - 18   d  may be the same as or similar to panel array antennas  52  described below in conjunction with  FIGS. 6-60  which in turn may be the same as or similar to a panel array of the type described in co-pending U.S. patent application Ser. No. 12/694,450, filed Jan. 27, 2010 which is a divisional of application Ser. No. 11/558,126 filed Nov. 9, 2006 now U.S. Pat. No. 7,671,696; or U.S. Pat. No. 6,624,787; or co-pending U.S. patent application Ser. No. 12/484,626, filed Jun. 15, 2009 all of which are assigned to the assignee of the present invention and incorporated herein by reference in their entireties. 
         [0051]    In one embodiment, AESA antenna  18  can steer to any beam position within its hemispheric coverage within about 100 μsec. 
         [0052]    In contrast, conventional systems (e.g. a system having a mechanically rotating AESA) have a revisit time no faster than 1 sec due to a maximum rate or speed at which the AESA can be rotated. 
         [0053]    The advantages provided by electronic beam steering result in a number of radar performance advantages. For example, one advantage of mobile radar system  5  is an increase in “time-on-target” (which is one important radar parameter since signal-to-noise ratio (S/N), is a function of time-on-target). On a given search or track frame, the four-faced on-the-move radar can make up to 10,000 updates in 1 second. 
         [0054]    Conventional systems such as a mechanical rotating AESA, on the other hand, provide about 1 update per second for a rotating AESA. 
         [0055]    Another advantage of mobile radar system  5  described herein, is the ability to modify the electronic switch rate between AESA faces. In one embodiment, for example, a switching period of 100 μsec can be used for fast 360 degree volume sweeps or horizon-fence search sweeps. A slower electronic sweep rate (e.g., 1 millisecond) can be used when the AESA operates in a “track-while-scan” mode. 
         [0056]    Another advantage of the mobile radar system  5  as compared with conventional systems is reaction time. Electronic switching provides fast reaction time to targets which suddenly appear in a given volume search (so-called “pop-up” targets) and enables radar resources to be rapidly focused as needed on the sector in which a target appears. 
         [0057]    Another advantage of mobile radar system  5  is the ability to better track maneuvering targets with a revisit rate matched or substantially matched to estimated or measured acceleration profile(s) of the target(s) in track. Ultimately, this capability can result in a single-integrated-air-picture (SIAP) above a battlefield which is superior to that which can be provided by conventional systems. 
         [0058]    As will be described in more detail below in conjunction with  FIGS. 3 and 4 , mobile radar system  5  also includes an on-board power source such as a generator (i.e. a generator mounted on vehicle  12 ) Generator  12  provides electrical power to AESA antenna  18  and associated electronics with radar system  10  in an amount sufficient that phased array radar system  10  can operate without the aid of any external power source. Thus, the phased array radar system  10  is said to be self-contained. 
         [0059]    As evident from  FIGS. 1A and 1B , antenna platform  16  is movable between a stowed position ( FIG. 1A ) and a deployed position ( FIG. 1B ). Significantly, AESA, antenna  18  is operable while antenna platform  16  is in either of the stowed or deployed positions. It should be appreciated that in the exemplary embodiment of  FIGS. 1A and 1B , when antenna platform  16  is in its stowed position, one face (labeled with reference numeral  18   b  in  FIGS. 1A ,  1 B) of antenna  18  is obstructed by a portion of vehicle  12 . Thus, in this case, antenna  18  is operable to provide substantially 270 degrees of scan coverage. When antenna platform  16  is in its deployed position ( FIG. 1B ) however, antenna  18  is raised above a top-most surface of the vehicle  12  and thus is operable to provide substantially 360 degrees of scan coverage (i.e. when the movable platform raises the AESA antenna to a deployed position such that each face of said AESA antenna is above a top-most surface of the vehicle, the AESA antenna is able to electronically scan antenna beams substantially unobstructed by any portion of said vehicle). 
         [0060]    In one embodiment, the phased array radar system is configured on movable platform such that the phased array radar system is capable of rotating (i.e. turning) on the movable platform. In one embodiment, the movable platform itself turns while in another embodiment, the movable platform stays substantially fixed and the phased array radar system coupled to the movable platform turns. Thus, when the movable platform raises the AESA antenna to a deployed position such that each face of said AESA antenna is above a top-most surface of the vehicle, the AESA antenna can physically rotate in addition to electronically scanning antenna beams substantially unobstructed by any portion of said vehicle. 
         [0061]    Since antenna  18  is provided as a self-contained, four face, solid state AESA, phased array radar system  10  does not require any set up time to operate. That is, radar system  10  is operational when vehicle  12  is moving as well as when vehicle  12  is stationary. Thus, mobile radar  5  is continuously operational. 
         [0062]    Accordingly, if mobile radar system  5  is deployed in a battlefield, it can begin operating as soon as it is deployed and continue to operate as it travels to a desired location. Once mobile radar system  5  reaches its desired location, vehicle  12  stops but radar system  10  continues to operate. If battlefield conditions dictate that mobile radar system  5  should move (e.g. mobile radar system  5  becomes a target of enemy gunfire or other attack), then mobile radar system  5  can move to a different location and phased array radar system  10  but will continuously operate during any movement. Since the four AESA faces  18   a - 18   d  provide substantially continuous 270° or 360° of scan coverage, the mobile radar system  5  can maintain target tracks even if the vehicle must turn while moving. Thus, the mobile radar system  5  flexibility to adapt to situational battlefield developments. 
         [0063]    It should be appreciated that, in one embodiment, when a volume scan is being performed, a predetermined pattern (i.e., a pre-programmed beam scan pattern) is used. It should be appreciated that in a tracking mode while the vehicle is moving, it is possible to lose a track due to perturbances which occur from movement of the vehicle (i.e., bumps in a terrain being travelled, etc . . . ). Thus, in such cases, the mobile radar system utilizes the fact that there is a certain amount of predictability in target movement as well as the beam agility in an AESA antenna. Accordingly, if a target moves out of an antenna field of view (FOV), then the AESA antenna can, for example, switch to an adjacent aperture on the same face or can switch to a different aperture on a different face of the AESA antenna. 
         [0064]    By providing a mobile radar system  5  which can continuously operate, it is possible to achieve high levels of track consistency, continuity and clarity in a battlefield environment. This significantly contributes to the formation of a single-integrated-air-picture (SIAP) in a complex, multiple-threat, multiple-friendly environment. Thus, mobile radar system  5  provides enhanced radar performance in any environment or application in which ground radar systems may be used. 
         [0065]    Also, in embodiments in which phased array radar system  10  comprises four faces  18   a - 18   d  which provide substantially continuous 360 degrees of coverage (in the deployed antenna platform position), search raster rates are not limited as in conventional radars which utilizes a rotator antenna. Rather, mobile radar system  5  is adaptable to a current threat limited only by the speed at which beams can be electronically switched, targets can be acquired and tracks can be formed. 
         [0066]    Furthermore, elimination of a rotating antenna aperture significantly simplifies signal interfaces between the AESA antenna and a radar signal processor, prime power and receiver/exciter sub-systems and thus mobile radar system  5  is provided having improved reliability compared with conventional systems which utilize a rotating antenna structure. 
         [0067]    Furthermore, by providing a plurality of AESA faces (e.g. four AESA faces) that can be electronically switched in any sequence, the mobile radar  5  also eliminates at least two drawbacks of so-called “sit-and-spin” radars. First, as previously mentioned, mobile radar system  5  is capable of operating while vehicle  12  is both in a fixed position and while vehicle  12  is in motion (e.g. using prime power provided by the vehicle). Second, electronic scan by a plurality of AESA faces vastly enhances search update rates and allows greater flexibility in scheduling radar waveforms. For example, since each AESA antenna can be treated as a separate radar, each AESA face can be autonomously operated (i.e., face  18   a  could be operating in a search mode at one instant while face  18   b  could be operating in a track mode at substantially the same instant). This allows different sectors to be scanned according to threat. Thus, mobile radar system  5  provides substantially continuous 360 degree coverage capability even while tracking a threat in a given sector. 
         [0068]    This is in stark contrast to the operation of a mechanically rotating radar which provides 360° of coverage since once a rotating radar stops and focuses resources on a given sector, the radar is now completely blind to target that may enter the now ignored sectors. 
         [0069]    Furthermore, the when mobile radar system  5  comprises a phased array radar system  10  made up of a plurality of panel arrays, mobile radar system  5  can track highly maneuvering, low radar cross-section (RCS) targets at rates which are orders-of-magnitude faster than that achievable in rotator radars. By mounting phased array radar system  10  in a highly mobile ground based vehicle  12  which can enter a battlefield area, a mobile radar system is provided which can achieve high levels of track consistency, continuity, and clarity that can significantly contribute to the formation of a single-integrated-air-picture (SIAP) in complex, multiple threats, multiple-friendly environments. 
         [0070]    Furthermore since mobile radar system  5  provides substantially 360 degree coverage while moving or stopped (e.g. parked), the threat of the radar itself becoming a target is reduced because the radar need not stay in one location at all times. 
         [0071]    This is in contrast to prior art systems which operate at a fixed location for an amount of time which allows an enemy to identify a location of the radar and thus make the radar location a target. 
         [0072]    Referring now to  FIG. 1C , in one embodiment, movable antenna platform  16  is provided as a scissors jack structure  19  which raises and lowers phased array radar systems  10 . In preferred embodiments, the telescoping structure is preferred given its rigidity and distributed support; in addition, it can enclose some of the electronics (e.g., beam steering computer and system monitoring/control; navigational equipment) from the weather. 
         [0073]    Referring now to  FIG. 2 , a flow diagram illustrating an exemplary technique for operating a mobile radar system, such as mobile radar system  5  described above in conjunction with  FIGS. 1-1C , is shown. It should be appreciated that unless otherwise specifically indicated, the order in which the individual steps are performed may be varied from that shown in  FIG. 2 . 
         [0074]    Turning now to  FIG. 2 , processing begins as shown in block  20  by determining a position, velocity and direction of a mobile radar system. In one embodiment, the position, velocity and direction are determined by acquiring the information from a navigation system and/or one or more other systems disposed in or on a ground based vehicle (e.g. vehicle  12  in  FIGS. 1-1C ) and/or disposed in or on a phased array radar system coupled to the vehicle such as phased array radar system  10  described above in conjunction with  FIGS. 1-1C . In one embodiment, the navigation system comprises an inertial measurement unit, (IMU) and a global positioning system (GPS). In one embodiment, the navigation system may also include one or more of: an internal and/or external accelerometer/speed sensors, a barometric system (for altitude correction) and a magnetic compass. 
         [0075]    Processing then flows to blocks  22  and  24  where one or more targets are acquired by the mobile radar system and target tracks are formed for each of the one or more acquired targets. 
         [0076]    In processing block  26 , since the radar system is mobile, position, velocity and direction of the mobile radar system is provided to a processor (e.g. a radar tracking processor) and in processing block  28  each of the one or more tracks are updated as needed to account for movement of the mobile radar system. In one embodiment, the mobile radar system uses a so-called “batch tracking algorithm” and the data provided to the radar tracking processor (or other processor) is used to correct and/or smooth target tracks. 
         [0077]    As shown in blocks  30 - 34 , periodically, the system may perform a built-in-test to determine if any action (e.g. re-calibration of a phased array antenna) is required. If any action is necessary, then processing flows to block  34  and if no action is necessary, then processing returns to the beginning of the process (which in this exemplary case is processing block  20 ). 
         [0078]    Referring now to  FIG. 3 , a phased array radar system  35  is disposed on a telescoping radar mounting platform  36  which can be raised and lowered thereby raising and lowering phased array radar system  35  between one of a stowed position  36   a  and a deployed position  36   b.  Significantly, phased array radar system  35  operates in both the stowed and deployed positions. Mounting platform  36  is, in turn, disposed on a mobile ground vehicle  37 . 
         [0079]    In the embodiment shown in  FIG. 3 , phased array radar system  35  is coupled, via a communication path  38  to a processor  39 , (e.g. a radar processor), a navigation system  40  and a display  41  all of which are disposed in or about a cab of vehicle  37 . Significantly, communication path  38  does not carry any high power RF or DC signals. 
         [0080]    Although radar processor  39 , navigation system  40  and display  41  are shown physically separate from, but electrically coupled to phased array radar system  35 , it should be appreciated that in some embodiments, some or all of radar processor  39 , navigation system  40  and display  41  may be provided as a physical part of phased array radar system  35  (i.e. electrical circuits and systems which make up radar processor  39 , navigation system  40  and display  41  may be disposed in the same physical structure which makes up phased array radar system  35 ). Operation of radar processor  39 , navigation system  40  and display  41  will be described below in conjunction with  FIG. 4 . 
         [0081]    Referring now to  FIG. 4 , in one embodiment, phased array radar system  35  ( FIG. 3 ) includes radar processor  39 , navigation system  40  and display  41 . Navigation system  40  measures and tracks current position and velocity of phased array radar system  35 . In one embodiment, navigation system  40  comprises inertial measurement unit (IMU)  40   a  and global positioning system (GPS)  40   b  (e.g. to conduct communications with a GPS Satellite such as Satellite  15  shown in  FIG. 1 ). 
         [0082]    As is known, IMU  40   a  measures and reports on an object&#39;s acceleration, velocity, orientation, and gravitational forces, typically using a combination of accelerometers and gyroscopes. IMU  40   a  also detects changes in rotational attributes like pitch, roll and yaw using one or more gyroscopes. 
         [0083]    GPS  40   b  may be provided, for example, as a space-based global navigation satellite system that provides reliable location and time information in all weather and at all times and anywhere on or near the Earth when and where there is an unobstructed line of sight to four or more GPS satellites. GPS  40   b  provides a current position and a velocity of phased array radar system  35  to other system components as needed. The velocity and time data collected from navigation system  40  is fed to processor  39  (e.g. radar processor  39 ) which computes a current position and velocity of vehicle  37  ( FIG. 3 ) which is substantially the same as the current position and velocity of phased array radar system  35  ( FIG. 3 ). Data from navigation system  40  is used, for example, in a so-called “batch-tracking” processor  48  which functions to correct and/or smooth target tracks of the phased array radar. 
         [0084]    Navigation system  40  may also optionally include an external accelerometer/speed sensor  44 , a barometric system  45  (for altitude correction) and a magnetic compass  46  which provides direction information. 
         [0085]    Processor  39  performs AESA command, control and signal processing. Each AESA face of the phased array radar system  35  receives beam-steering commands (e.g. commands which control phase shifter and attenuator settings within the AESA) from a beam steering processor (BSP)  44 . BSP  44  also performs AESA built-in test (BIT) and fault status monitoring. 
         [0086]    As mentioned above, in one embodiment, phased array radar system  35  utilizes a form of radar signal processing referred to as “batch tracking” which is a known operational radar tracking algorithm used in radars. As is known, batch tracking is a self-correcting, or iterative, algorithm that corrects or smoothes the radar track measurement based on time stamped measurements provided by the processor  39  (which includes a signal data processor) and navigation system  40 . 
         [0087]    Referring now to  FIGS. 5 and 5A , an exemplary AESA face  45  which may be the same as or similar to AESA faces  18   a - 18   d  described above in conjunction with  FIG. 1-1C ), includes a plurality of rows and columns, here, eight (8) rows  46   a - 46   h  and four (4) columns  47   a - 47   d  which results in a total of thirty-two (32) individual panels  45   a - 45   ee.  Thus, AESA face  45  is made up of an array of individual panels, here thirty-two panels each of the thirty-two panels corresponding to a so-called “building block.” 
         [0088]    It should be understood that each of the individual panels  45   a - 45   e  acts as a so-called building-block which allows AESA faces of differing sizes to be built. Thus, the number of panels to include in any AESA face could be greater than or fewer than thirty-two. One of ordinary skill in the art will appreciate how to select a particular number of panels to use in an AESA face for a particular application. 
         [0089]    Each individual panel (or building block) is made up of a selected number of transmit-receive (TR) channels. The number of TR channels included in an individual panel is selected depending upon the needs of a particular application. One of ordinary skill in the art will understand how to select a number of TR channels to include in a panel for a given application. In one embodiment, each panel  45  is provided having thirty-two (32) individual TR channels. In another embodiment, each panel is provided having 128 TR channels. 
         [0090]    As discussed above, in a mobile radar system comprising a plurality of AESA faces (e.g. four AESA faces) which can be electronically switched in any sequence, each AESA can be treated as a separate radar. That is, each AESA face can be autonomously operated. For example, at one instant in time, one AESA face could be operating in a search mode while a second different AESA face could be operating in a track mode. This allows different sectors to be scanned according to threat. 
         [0091]    Accordingly, different panels on different AESA faces may be active (or energized) at the same (or different) points in time. For example, in  FIG. 5 , two rows of panels  46   d,    46   e  in AESA  45  can be active while in  FIG. 5A , a single column  47   d  of panels can be active. Thus,  FIGS. 5 and 5A  illustrate two different possibilities of energizing eight (8) panels in AESA faces. It should be noted that it is necessary to activate a certain minimum number of panels for proper radar operation in a particular application. For example, in some embodiments and applications, it is necessary to activate eight panels in EL or at least four (4) panels in AZ for proper operation of a monopulse network. 
         [0092]    Although  FIGS. 5 and 5A  illustrate rows and columns of AESA face  45  being active, it should be appreciated that any combination of panels on a given AESA face, or between AESA faces, may be active in a given time frame. Active panels on an AESA face need not be in the same column or row. Any (or in some instances, all) of the plurality of panels in given AESA face may be active. The ability to selectively turn on/off panel building-blocks in a mobile radar system results in a mobile radar system which can function in a plurality of different operating modes. 
         [0093]    For example, mobile radar system  5  ( FIGS. 1-1C ) may operate in a switched 360° radar coverage mode. In this mode, one AESA face is fully energized in a given time frame while the other three AESA faces (or two faces if the system is “on-the-move” and thus in a stowed position) are in standby power mode. Any sequence of turning on/off an AESA face is allowed. 
         [0094]    Mobile radar system  5  ( FIGS. 1-1C ) may also operate in a simultaneous, wide-area sector radar coverage mode. In this operating mode, the four-face mobile radar can have combinations of simultaneously energized AESA faces sharing the total available prime power in transmit and/or receive. For example, to achieve up to 180° coverage, one could energize two contiguous AESA faces. For example, sixteen panels can be turned on in a first AESA face and sixteen panels can be turned on in a second AESA face. To achieve up to 270° coverage, one could energize three AESA faces. For example, eight panels can be activated on a first AESA face, sixteen panels can be activated on a second AESA face and eight panels can be activated on a third AESA face. To achieve up to 360° coverage, one could energize all four AESA faces. For example, eight panels can be activated on each of the four AESA faces. 
         [0095]    Thus, by providing the mobile radar system as a self-contained, solid-state AESA having four faces, the radar can simultaneously operate sub-apertures for the following modes of operation: (1) transmit from one face and receive sub-aperture from any of the remaining three faces; (2) simultaneously operate sub-apertures on all four faces in a transmit mode; and (3) simultaneously operate sub-apertures on all four faces in a receive mode. 
         [0096]    Furthermore, the mobile radar system is capable of multi-face AESA operation. Any combination of AESA faces may be commanded in a given resource period. Digital commands are sent from the BSP to a given AESA face in a given resource period; status is sent from the AESA face to the BSP. 
         [0097]    Accordingly, a mobile radar system is provided which has the ability to rapidly adapt to the needs of many situational battlefield developments and scenarios. 
         [0098]    A central receiver/exciter (REX) provides frequency excitation and waveform generation in a radar transmit mode. The REX also provides matched filter/waveform processing and extraction on a radar receive mode. Transmit and receive ports are electronically switched between each AESA face and the REX. 
         [0099]    In single-face AESA operation, the REX communicates with a single AESA face in a given time frame. In this mode of operation, the REX is configured to provide one transmit port; three receive ports (three receive ports per AESA face for a three-channel monopulse system). In single-face AESA operation, in a given radar resource time frame, a single AESA face is energized and communicates with the BSP and REX and provides status. Three-channel monopulse receive data is processed by a processor such as a signal data processor (SDP). 
         [0100]    In four-face AESA operation, the REX simultaneously communicates with any combination of AESA faces. In this mode of operation, the REX is configured to provide four transmit ports and twelve receive ports (three receive ports per AESA face for three-channel monopulse). In four-face AESA operation, in given radar resource time frame, up to four AESA faces are energized with simultaneous communication with the BSP and REX and each AESA face provides status. Again, three-channel monopulse receive data from each AESA face is processed by a processor such as a signal data processor (SDP). 
         [0101]    In one embodiment, the mobile radar system includes a scalable, three channel monopulse, which may be the same as or similar to the type described in co-pending U.S. application Ser. No. 12/757,371 assigned to the assignee of the present invention and incorporated herein by reference in its entirety. In one embodiment, each AESA face is one square meter (1 m 2 ) and is comprised of thirty-two 128 TR Channel Panel Array building-blocks, which incorporate a position-invariant monopulse beamforming network. 
         [0102]    The mobile radar system includes a resource management system to schedule and control the following radar system resources: prime power; radio frequency excitation, waveform and signal processing; computing; thermal management, mechanical sensing; built-in test. A resource management timeline is based upon radar resource period(s) and resource scheduling is controlled by the radar signal processor. Resource management is based upon various radar mission scenarios and is implemented to each AESA face through electronic switching of prime power, RF waveform excitation and control of the thermal management system and the central computer and REX. 
         [0103]    A prime power resource management system uses electronic commutation from a central prime power generator to each AESA panel. The speed of commutation is achieved by digital command recognition to allow a given AESA face (or one or more panels on an AESA face) to energize/de-energize in a desired (or required) time frame. In one embodiment of the mobile radar system, there are two basic modes of resource management. 
         [0104]    A first mode of resource management is referred to as “prime-power time-sharing.” In this mode, all available prime power is dedicated to a single AESA face, in transmit and/or receive, in a given time frame. The remaining three AESA faces are in standby power mode (e.g. a small amount of total prime power, for example, in the range of about 1%-5% of total prime power). 
         [0105]    A second mode of resource management is referred to as “prime-power splitting”. In any given time frame, prime power can be split between a plurality of AESA faces (e.g. four faces) in multiples of panel building-blocks. For example, in a system in which each AESA face comprises thirty-two panels, each having 128 TR channels, the total prime power usage is the same whether all thirty-two 128 TR channel panels on one given AESA face are energized in transmit (or receive) or, one-quarter (i.e. eight) of the 128 TR Channel Panels can be energized in Transmit (or Receive) on each of the four faces. 
         [0106]    In an AESA fault status monitoring mode, each AESA face is continuously monitored with status read-back provided to the BSP. Critical parameters such as power, coolant flow rate (for liquid-cooled version), fan status (for air-cooled version), temperature, are monitored and AESA antenna operation is shut-down if any parameter moves outside a desired range. 
         [0107]    Also each AESA face has an independent, embedded antenna element (e.g. a patch antenna element) measurement system used to perform built-in-test (BIT). 
         [0108]    For each AESA face, BIT is used to perform a variety of functions including, but not limited to: monitoring of TR channel RF performance and performance of re-calibration of active TR channels. In one embodiment, reference patches embedded around the periphery of each AESA face are used to couple portions of transmit and receive signals to each TR channel in the AESA antenna. These measurements are used to determine if a given TR channel on a given AESA face has degraded in performance (e.g., phase and/or receive amplitude drift or transmit output power degradation) or failed. The central computer computes the antenna pattern residual error between “in-field” reference patch measurements and factory reference patch measurements. Based upon this residual error, the central computer reports the new error floor and either: (1) performs a re-calibration of the degraded AESA face without replacement of a panel; or (2) performs a re-calibration of the degraded AESA face with replacement of one or more panels; or (3) does nothing. 
         [0109]    In one embodiment, BIT is performed at least in stand-by and operating modes. 
         [0110]    In stand-by mode, the AESA face is not in normal transmit/receive mode operation, but is supplied power to maintain digital control. In this mode, reference patch measurements are interleaved between radar resource periods. 
         [0111]    In normal operating mode, the AESA face is in normal transmit-receive mode and reference patch measurements are interleaved between radar resource periods. 
         [0112]    In one embodiment, a central receive-exciter (REX) provides frequency excitation and waveform generation in radar transmit mode; and provides matched filter/waveform processing on radar receive mode. Excitation of AESA face transmit and receive ports is performed by electronic switching between the AESA face and the REX. 
         [0113]    Referring now to  FIGS. 6-6C , in which like elements are provided having like reference designations throughout the several views, in one exemplary embodiment, phased array radar system  10  ( FIGS. 1-1C ), includes four faces  18   a - 18   d  ( FIGS. 1A-1C ) with each face corresponding to an AESA having an area of approximately one square meter (1 m 2 ). In a preferred embodiment, each of the ASEA&#39;s four faces  18   a - 18   d  are provided as panel array antennas  52  ( FIGS. 6-6C ). 
         [0114]    In one embodiment, each AESA antenna  50  is provided from a plurality (or array) of panel array antennas  52   a,  generally denoted  52  (sometimes referred to herein as a “panel arrays,” “antenna panels” or more simply as “panels  52 ”). Thus, AESA antenna  50  is said to have a “panel architecture.” One example of an antenna panel is described in U.S. Pat. No. 7,384,932 assigned to the assignee of the present invention. 
         [0115]    In preferred embodiments, the antenna panels  52  are stand alone units. That is, the panels  52  are each independently functional units (i.e. the functionality of one panel does not depend on any other panel). For example, the feed circuit for each panel  52  is wholly contained within the panel itself and is not coupled directly to any other panel. Thus, in the event that one panel  52  fails, the failed panel  52  may simply be removed from the array of panels which form AESA antenna  50  and another panel can be inserted in its place. This characteristic is particularly advantageous in RF transmit/receive systems deployed in sites or locations where it is difficult to service the RF system in the event of some failure. 
         [0116]    As described in the aforementioned U.S. Pat. No. 7,384,932, it is preferable for the antenna panels used in antennas having a panel architecture to maintain a low profile. This can be accomplished by utilizing a plurality of multilayer circuit boards which provide one or more circuit assemblies in which RF and other electronic components are disposed in close proximity with each other. The operation of such electronic components utilizes electrical power and thus the components dissipate energy in the form of heat. Thus, the antenna panels  52  must be cooled. 
         [0117]    As shown in  FIGS. 6-6C , array antenna  50  (and more specifically RF panels  52 ) are coupled to a panel heat sink  54 . In this exemplary embodiment, heat sink  54  is comprised of a plurality, here four, separate sections  54   a - 54   d.  A first surface of each heat sink section  54   a - 54   d  is designated  55   a  and a second opposing surface of each heat sink section  54   a - 54   d  is designated  55   b.  Thus, RF panels  52  are coupled to the first surface  55   a  of heat sink  14 . 
         [0118]    A rear heat sink  56  is coupled to surface  55   b  of heat sink  54 . In this exemplary embodiment, rear heat sink  56  is comprised of a plurality, here four, separate sections  56   a - 56   d  ( FIG. 3A ). A first surface of each heat sink section  56   a - 56   d  is designated  57   a  and a second opposing surface of each heat sink section  56   a - 56   d  is designated  57   b.  Thus, portions of heat sink surface  55   b  contact portions of heat sink surface  57   a.    
         [0119]    A set or combination of heat sink sections and associated panels can be removed from the array and replaced with another set of heat sink sections and associated panels. Such a combination is referred to as a line replaceable unit (LRU). For example, heat sink sections  54   a,    56   a  and the panels dispose on heat sink section  54   a  form a LRU  60   a.  Thus, the exemplary system of  FIG. 1  comprises four LRUs  60   a - 60   d  with each of the LRUs comprised of eight panels  52 , one of panel heat sink sections  54   a - 54   d  and a corresponding one of rear heat sink sections  56   a - 56   d.    
         [0120]    In one embodiment, each 1 m 2  AESA face is comprised of thirty-two 128 TR channel panel array “building-blocks” using a position-invariant analog monopulse beamforming network. All active and passive components are surface mounted to the panel array. Each TR channel uses “flip-chip” mounted monolithic microwave integrated circuits (MMIC) with an integral heat spreader attached to the backside of each MMIC. The mobile radar system combines hardware (e.g. a modular, scalable panel array combined with an on-board navigation system, a central computer system, a receiver-exciter, and a thermal management system) with resource control to produce an on-the-move radar capability. 
         [0121]    Referring now to  FIG. 6A , panel  50  includes a modular line replaceable unit (LRU)  60 . In this exemplary embodiment, there are four weather-tight, electromagnetic interference (EMI) shielded LRU&#39;s per each square meter. The LRU includes eight panels, a brazement  62  to cool the panels, four active monopulse combiner network assemblies, four power-logic circuit cards, four distribution boards, four linear regulators (LR), eight DC/DC converters, a brazement to cool the DC/DCs and LR&#39;s, and a bus bar. In one exemplary embodiment, the LRU is approximately 46 in (high)×10 in (wide)×4 in (deep) and the LRU weight is estimated to be 64 lbs. The LRU approach provides several advantages: (1) LRU&#39;s allow easy access to signal and coolant lines; (2) LRU&#39;s can be removed or inserted into the face of an AESA in a short amount of time; (3) LRU weight allows replacement to be accomplished manually (e.g. it is a two-man lift); and (4) the LRU approach reduces associated costs of packaging and cooling an array. 
         [0122]    In one embodiment, panel heat sink sections  54   a - 54   d  and rear heat sink sections  56   a - 56   d  are provided having a “U” shaped cross sectional shape. Thus, when the panel heat sink sections  54   a - 54   d  and corresponding rear heat sink sections  56   a - 56   d  are coupled an internal cavity is formed therebetween in which power and logic circuits/electronics are disposed. 
         [0123]    It should be appreciated that in other embodiments other heat sink configurations may be desired or required. For example, only one of the heat sinks  54 ,  56  may be provided having a recess region with electronics disposed therein. Alternatively, in some embodiments, neither of the heat sinks  54 ,  56  may be provided having a recess region. The particular manner in which to provide the heat sinks and in which to couple the electronics depends upon the particular application and the factors associated with the application. 
         [0124]    In one embodiment, heat sinks  54 ,  56  are provided as so-called cold plates which utilize fluid to cool any heat generating structures (such as panels  52  and electronics) coupled thereto. A fluid is fed through channels (not shown) provided in the heat sinks  54 ,  56  via fluid fittings  69  and fluid paths  58 . It should be appreciated that each of the heat sinks  54 ,  56  may be comprised of a plurality of different components or subassemblies coupled together or alternatively heat sinks  54 ,  56  may be provided as monolithic structures. In other embodiments, air cooling can be used. 
         [0125]    Since the electronics are disposed between a surface of the panel heat sink and an internal surface of the rear heat sink, the electronics are not accessible when the panel heat sink  54  and rear heat sink  56  are coupled as shown in  FIGS. 3-3C . Thus, to provide access to the recess region of the rear heat sink  56  (and thereby provide access to the electronics disposed in the recess region of rear heat sink  56 ), one or more translating hinges  70  couples panel heat sinks  54   a - 54   d  to respective ones of rear heat sinks  56   a - 56   d.  Thus, the translating hinges allow access to the electronics disposed in recess regions thereby facilitating disassembly and rework of the electronics (or portions thereof) and/or heat sinks (or portions thereof) when needed. The translating hinges  70  may be the same as or similar to the type describe in co-pending U.S. patent application Ser. No. 12/465,120 filed May 13, 2009, assigned to the assignee of the present invention and incorporated herein by reference in its entirety. 
         [0126]    Heat sinks  54   a - 54   d  are coupled to heat sinks  56   a - 56   d  via a plurality of fasteners  76  and a plurality of translating hinges  70 . In the exemplary embodiment shown herein, fasteners  76  are provided as screws which are captive in heat sink  56  and which mate with threaded holes provided in heat sink  54 . It should be appreciated that one of ordinary skill in the art will understand how to select an appropriate type and number of fasteners  76  to use in any particular application. In one embodiment, fasteners  76  may be provided as spring-loaded, captive screws. 
         [0127]    Referring now to  FIG. 6B , a portion of a panel  50  includes a plurality, here three, RF connectors  72 . RF transmit and receive signals, e.g. Az, EL and sum monopulse signals, are coupled to panel  50  via RF connectors  72 . DC and logic signals are coupled to panel  50  via connector  74 . With this approach, by simply disconnecting each RF connector  72  and each DC/logic connector  74  on panel  50 , panel  50  may be removed from an array of panels which form a multi-faced phased array antenna (e.g. such as phased array antenna  18  described above in conjunction with  FIG. 1 ) without making or breaking RF or DC/logic connections to any other panel. This approach allows panels to be repaired or exchanged while the radar is still operational. 
         [0128]    Having described preferred embodiments which serve to illustrate various concepts, structures and techniques which are the subject of this patent, it will now become apparent to those of ordinary skill in the art that other embodiments incorporating these concepts, structures and techniques may be used. Accordingly, it is submitted that that scope of the patent should not be limited to the described embodiments but rather should be limited only by the spirit and scope of the following claims.