Abstract:
A lightweight active phased array antenna including modular active electronics assemblies and passive radiating element aperture panels that are integrated into a lightweight support structure of a minimum depth which provides a cooling system for the electronics assemblies. The electronics assemblies and aperture panels are fully accessible from one or both faces of the antenna and can be readily removed/replaced as required.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to radar systems, and more particularly, to a lightweight active phased array antenna with forced convection cooling.  
       BACKGROUND OF THE INVENTION  
       [0002]     Mission requirements for near-future radars dictate high levels of operational capability provided by systems that are light in weight. Such radars must feature agile, reconfigurable beams coupled with high effective transmit power and high receive sensitivity.  
         [0003]     The operational requirements are fulfilled by adopting large aperture active phased array antennas having transmit/receive (TIR) electronics distributed with the radiating elements. Distributing the active TIR circuits over the array antenna also necessitates distributing their associated prime power converters and controllers, plus providing means for effective thermal management and conveying RF/power signals. It is desirable that these phased array antennas be realized with minimum weight to promote high mobility in ground radar applications and to minimize top-side mass for shipboard systems.  
         [0004]     Accordingly, there is a need for a lightweight active phased array antenna having distributed transmit/receive (T/R) electronics radiating elements, power converters, and controllers. Such a phased array antenna should also have effective thermal management and a mechanism for conveying the RF/power signals.  
       SUMMARY OF THE INVENTION  
       [0005]     According to an aspect of the invention, a lightweight active phased array antenna comprises modular active electronics assemblies and passive radiating element aperture panels that are integrated into a lightweight support structure of a minimum depth, which provides a cooling system for the electronics assemblies. The electronics assemblies and aperture panels are accessible from one or both faces of the antenna and can be readily removed/replaced as required. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a perspective view of an exemplary embodiment of a lightweight active phased array antenna according to an embodiment of the present invention.  
         [0007]      FIG. 2  is an enlarged perspective view of the lightweight active phased array antenna.  
         [0008]      FIG. 3  is a sectional view through two stacked, duct-like horizontal cross members of the antenna&#39;s support structure.  
         [0009]      FIG. 4  is a perspective view showing a vertical column member of the antenna&#39;s support structure.  
         [0010]      FIG. 5  is an enlarged perspective view showing a modular, active electronics assembly and a modular passive radiating element aperture panel of the antenna.  
         [0011]      FIG. 6  is an exploded perspective view of a multichannel transmitter/receiver (T/R) assembly which forms one of the antenna&#39;s modular, active electronics assemblies.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]      FIG. 1  shows an exemplary embodiment of a lightweight active phased array antenna according to an embodiment of the present invention. The lightweight active phased array antenna, denoted by numeral  10 , comprises a rigid, lightweight support structure  100  having a first side  101  and a second side  102 , and a plurality of modular, active electronics assemblies  200  and modular passive radiating element aperture panels  300  disposed on the first and second sides  101 ,  102  of the support structure  100 . A thin sheet-style radome  400  is attached directly to the aperture panels  300  disposed on each of the first and second sides  101 ,  102  of the support structure  100 , thereby protecting the aperture panels  300  from weather, chemical, and mechanical damage, and rejecting the majority of incident solar radiation.  
         [0013]     The support structure  100  comprises a perimeter frame  110 , a plurality of stacked, duct-like horizontal cross members  120  which are secured together by the perimeter frame  110 , and a plurality of intermediate, channel-shape vertical column members  130  that provide additional stiffness to the support structure  100  and form bays  140  on both the first and second sides  101 ,  102  of the structure  100  into which the modular active electronics assemblies  200  are mounted. The modular passive radiating element aperture panels  300  may be mounted to the modular active electronics assemblies  200  mounted in the bays  140 . The perimeter frame  110  may include an upper channel member  111 , a lower channel member  112 , and first and second side I-beam members  113  and  114  extending between the upper and lower channel members  111 ,  112 . The first and second side I-beam members  113 ,  114  each include a central web portion  113   a,    114   a  having a plurality of fan mounting apertures  113   b,    114   b  formed therein.  
         [0014]     The entire support structure  100  may be fabricated from a carbon-epoxy composite, which provides exceptional stiffness to weight characteristics. Alternatively, the entire support structure  100  may be fabricated from a low mass density metal alloy, such as aluminum. Still further, some of the members of the support structure  100  may be fabricated from the carbon-epoxy composite and other members of the support structure  100  may be fabricated from the low mass density metal alloy. In one exemplary embodiment, the support structure may have a width W of about 92 inches, a height H of about 87 inches, and a depth D of about 11.5 inches. Support structures of other dimensions are also contemplated.  
         [0015]     A back-to-back, dual-face phased array antenna may be realized using the shown support structure  100  which includes the bays  140  on both the first and second sides  101 ,  102  thereof and the modular active electronics assemblies  200  (mounting the modular passive radiating element aperture panels  300 ) mounted in the bays  140  on both the first and second sides  101 ,  102  of the structure  100 . Although not shown, a single-face phased array antenna may also be realized using an embodiment of the support structure  100  that includes the bays  140  on only one of the first and second sides  101 ,  102  thereof for mounting the modular active electronics assemblies  200  (and the modular passive radiating element aperture panels  300  mounted to the electronics assemblies  200 ).  
         [0016]     As best shown in  FIGS. 2 and 3 , the support structure&#39;s horizontal, duct-like cross-members have a “bow tie” sectional shape formed by a central main duct  121  and laterally extending, wing-like secondary ducts  122  that communicate with the central, main duct  121 . The upper and lower walls  122   a,    122   b  of the secondary ducts  122  include inner and outer air metering apertures  122   c    122   d.  The duct-forming design of the horizontal cross-members allow them to distribute a coolant, preferably air, to the array&#39;s modular active electronics assemblies  200 . In the case of an air coolant, intake cooling fans  160  and exhaust cooling fans  170  are placed at the ends of the horizontal cross-members, in the fan mounting apertures  113   b,    114   b  of the side I-beam members  113 ,  114 , to direct ambient or conditioned inlet or intake air into, and exhaust air out of the phased array antenna. The vertical stack of horizontal cross-members form alternating “intake” and “exhaust” ducts. As shown in  FIG. 3 , the lower wall  121   b  of the central duct portion  121  may be formed with an outdent  121   d  and the upper wall  121   a  of the central duct portion  121  may be formed with a correspondingly shaped indent  121   c  to maintain vertical alignment of the stacked, horizontal cross-members  120  and further rigidify the support structure  100 . The wing-like secondary ducts include cut-outs  123  which are dimensioned for receiving the vertical column members  130 .  
         [0017]     Referring to  FIG. 4 , the channel-like vertical column members  130  of the support structure  100  are each formed by bottom wall  131  and two depending side walls  132 . The side walls  132  each include openings  133  which are positioned to communicate with each of the bays  140  so that the vertical column members  130  may also operate as raceways for bus networks that distribute DC power, control, and RF signal to the modular active electronics assemblies  200  disposed in the bays  140 .  
         [0018]     Referring to  FIG. 5 , the modular active electronics assemblies  200  each of which includes a high power density DC to DC converter  210 , a panel electronics digital controller  220 , and a multichannel transmitter/receiver (TIR) assembly  230 , and the modular aperture panels  300  are integrated into the array as line replaceable units. The DC converter  210  and the digital controller  220  are disposed end to end in the innermost portion of each of the bays  1440  of the support structure  100  and may be secured by conventional fasteners. The DC converter  210  and the digital controller  220  are plugged into power and control signal buses disposed in the vertical column members  130 .  
         [0019]     Referring again to  FIG. 3 , the DC converter  210  includes a heat exchanger  211  that is aligined with the inner air metering, apertures  122   c  of two of the horizontal cross-members&#39; secondary ducts  122  that are immediately above and below the DC converter  210  in the bay  140  (one of the two cross-members  120  operates as an “intake” air duct and the other one operates as an “exhaust” air duct). Compliant gaskets  240  are provided for sealing the DC converter&#39;s heat exchanger  211  to the secondary ducts  122  of these two cross-members  120  to prevent coolant leakage between the secondary ducts  122  and the heat exchanger  211 . Cooling intake air ducted through the main and secondary ducts  121 ,  122  of the “intake” horizontal cross-member  120  (the cross-member  120  below the DC converter  210  in the shown embodiment) passes through the cross-member&#39;s inner air metering apertures  122   c  (the inner air metering apertures  122   c  that communicate with that DC converter&#39;s bay  140 ) into or across the fins or grid comprising the DC converter&#39;s heat exchanger  211 . The air (which now contains the heat drawn away from the heat exchanger  211 ) is exhausted through the inner air metering apertures  122   c  of “exhaust” air horizontal cross-member&#39;s secondary duct  122  (the cross-member  120  above the DC converter  210  in the shown embodiment) and exhausted through the main duct  121  thereof.  
         [0020]     Referring to  FIG. 6 , the T/R assemblies  230  are constructed as two-sided tile-assemblies to minimize the depth of the phased array antenna. Specifically. each T/R assembly  130  comprises a heat exchanger  231  formed by an extruded or cast metal structure having a plurality of transverse air passages  232  extending therethrough, a conventional low power circuit board  233  forming a low power T/R channel is mounted on a first side surface of the heat exchanger  231 , and a conventional high power circuit board  234  forming a high power transmit amplifier is mounted on a second opposite side surface of the heat exchanger  231 . The low power circuit board  233  forming the T/R channel may include, without limitation, multi-layer interconnect circuits  233   a  and microwave monolithic integrated circuits (MMICs)  233   b.  The high power circuit board  234  forming the high power transmit amplifier may include, without limitation, a Si bi-polar junction transistor (BJT)  234   a,  a circulator  234   b,  and a band pass filter  234   c.  Because TIR assemblies  230  are well known to those skilled in the art, a further discussion of tile details of the low and high power circuit boards are unnecessary herein.  
         [0021]     Still referring to  FIG. 6 , covers  235  for shielding the low and high power circuit boards  233 ,  234  from electromagnetic interference and the environment are disposed over the circuit boards  233 ,  234 . Each T/R assembly  230  is disposed in the outermost portion of the bay  140  and may be secured by conventional fasteners and plugged into the array antenna&#39;s RF bus disposed in the vertical column members  130 . The T/R assembly  230  is also connected to the DC converter  210  and controller  220  disposed in the innermost portion of the corresponding bay  140  via plunge-style connectors or a short cable  236 .  
         [0022]     Referring again to  FIG. 6  and  FIG. 3 , the transverse air passages  232  of the T/R assembly&#39;s heat exchanger  231  are aligned with the outer air metering apertures  122   d  of the two horizontal cross-members&#39; secondary ducts  122  that are immediately above and below the T/R assembly  230  in the bay  140 . Compliant gaskets are provided for sealing the T/R assembly&#39;s heat exchanger to the secondary ducts of these cross-members to prevent coolant leakage between the secondary ducts  122  and the T/R heat exchanger  231 . As with the DC converter  210 , cooling intake air ducted through the main and secondary ducts  121 ,  122  of the “intake air” horizontal cross-member  120  passes through that cross-member&#39;s outer air metering apertures  122   d  and through the transverse air passages  232  of the T/R assembly&#39;s heat exchanger  231 . The heated air is exhausted through the outer air metering apertures  122   d  of “exhaust air” horizontal cross-member&#39;s secondary duct  122  and exhausted through its main duct  121 .  
         [0023]     As one of ordinary skill in the art will appreciate, the vertical stack of duct-like horizontal cross-members  120  provide a reliable and effective means for cooling the electronics assemblies  200 . The specialized connections, leak issues, and air purge requirements associated with conventional liquid cooled methods are obviated with the phased array antenna of the present invention.  
         [0024]     Referring again to  FIG. 5 , the modular aperture panels  300  each comprise a plurality of radiating elements. Their associated feed networks and optional signal sampling couplers which provided for a calibration system, are realized in the multiple layers of the panels  300 . The modular aperture panels  300  also comprising a plurality of RF signal input ports that may be embodied, for example, as RF plunge-style connectors  301  ( FIG. 3 ), so that when the panels  300  are attached at their periphery to the edges of the horizontal cross-members  120  and vertical column members  130  on one or both sides  101 ,  102  of the array antenna&#39;s support structure  100 , direct connections are made to the T/R assemblies  230 .  
         [0025]     While the foregoing invention has been described with reference to the above, various modifications and changes can be made without departing from the spirit of the invention. Accordingly, all such modifications and changes are considered to be within the scope of the appended claims.