Abstract:
A radar system and method of cooling same. In the illustrative embodiment, the inventive system includes a radar array comprising a circuit board; a plurality of radiating elements printed on the circuit board; and a plurality of transmit and receive modules disposed on the circuit board in communication with the radiating elements. In a specific implementation, the invention further includes means for cooling the T/R modules. In the preferred embodiment, the modules are spray cooled. A particularly novel aspect of the invention is the provision of a mechanism for physically, electrically and hydraulically interconnecting the T/R modules or modules. The physical interconnect is achieved by rails mounted on the top bottom covers and sides of the circuit boards. The rails allow for the modules to be dovetailed together and thereby secured against vertical and lateral stresses.

Description:
This invention was made with Government support under a Government contract. The Government has certain rights in this invention. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to antennas. More specifically, the present invention relates to methods and apparatus for cooling active array radar antennas. 
     2. Description of the Related Art 
     Active array antennas allow for electronic steering of a radar beam. Active array antennas include a plurality of antenna sub-arrays commonly referred to as ‘sticks’ comprising 20 to 30 radiating elements. The stick has a finite thickness and a heat exchanger located in a central portion thereof. The heat exchanger is designed to remove heat from circuit components, particularly the transmit/receive (T/R) modules mounted on either side thereof. Unfortunately, the finite length of the heat exchanger imposes some limitations on the system insofar as there is a need to pump coolant therethrough same. In addition, the heat exchanger imposes the more general requirements of fabrication, installation and removal. These considerations limit the optimal size of the exchanger. 
     An additional problem is due to the physical limitations of the RF (radio frequency) feed located at the back end of the stick. The RF feed is split to distribute power to each radiating element in the array. Each layer of power division requires more physical depth. Unfortunately, the T/R module is conventionally built into a small package. The heat exchanger has walls with a certain thickness. The heat developed within the T/R modules within the high power amplifier (HPA) is considerable due to the high power densities of the modules (on the order of hundreds of watts/sq. cm) and the high associated junction temperatures within the component. Removal of heat is problematic in that the heat must be moved through several thermal/resistant layers. The inherent inefficiencies of the electronic components causes the generation of large amounts of thermal energy, the thermal energy causes an increase in the junction temperatures of the associated components. As the junction temperatures increase, the reliability of the component decreases. 
     In addition, as the junction temperature is lowered, the overall efficiency of the HPA increases. Hence, as the temperature of the HPA is lowered, the input powered required for a given amount of radiated output power is lowered as well. This is important for aircraft applications where power generation is limited. 
     Those skilled in the art will appreciate that the critical parameter is area, viz., the footprint of the HPA component verses the thermal resistance of the areas from which heat is being removed. 
     In addition, conventionally, the components of a T/R module are placed on a substrate mounted within a housing and the T/R module is attached to the heat exchanger. The housing is typically of metallic construction. The module must be physically attached to a sub-array using one of a number of mechanical attachment mechanisms (solder, bolts, etc.). Differing coefficients of thermal expansion between the module and the heat exchanger will cause the expansion and contraction of the heat exchanger to damage the module and/or break a bond line therebetween. 
     Another consideration has to do with thermal mismatch between a component of a T/R module and its substrate. 
     Further, lattice spacing is the location of one radiating element relative to the next. Smaller lattice spacing leads to a higher number of T/R modules and a higher antenna output power. Lattice spacing is also driven by antenna operating frequency. Unfortunately, lattice spacings of active array antennas designed in accordance with conventional teachings are constrained based on the projected footprint of the T/R module, notwithstanding the desirability of more flexible lattice spacing arrangements to accommodate frequency. 
     In summary, there are several problems with the conventional active array antenna design including: high heat density, excessive layers of thermal resistance, physical component assembly, mounting the T/R module to the subarray, lattice spacing, and thermal mismatch. 
     Hence, there is a need in the art to make smaller HPA components within T/R modules in radar and other electrical systems to achieve smaller denser lattice spacings. There is a further need for a system and technique to more efficiently remove heat from such components. There is also a compelling need to reduce the cost of radar antenna assemblies. 
     SUMMARY OF THE INVENTION 
     The need in the art is addressed by the radar system and method of cooling of the present invention. In the illustrative embodiment, the inventive system includes a radar array comprising a circuit board; a plurality of radiating elements printed on the circuit board; and a plurality of transmit and receive modules disposed on the circuit board in communication with the radiating elements. In a specific implementation, the invention further includes means for cooling the modules. In the preferred embodiment, the modules are spray cooled. 
     A particularly novel aspect of the invention is the provision of a mechanism for physically, electrically and hydraulically interconnecting the modules. The physical interconnect is achieved by rails mounted on the top and sides of the circuit boards. The rails allow for the modules to be dovetailed together and thereby secured against vertical and lateral stresses. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing an assembly of spray cooled modules in accordance with the teachings of the present invention, to form an antenna. 
     FIG. 2 is a diagram of a single module in accordance with the teachings of the present invention. 
     FIG. 3 is a diagram that illustrates how the rails of each module interlock in a dovetail manner to secure the modules against vertical, horizontal (lateral) and rotational stresses. 
     FIG. 4 is a diagram, which depicts a dual circuit board construction of a T/R module constructed in accordance with the teachings of the present invention. 
     FIG. 5 is an exploded view of the T/R module of FIG.  4 . 
     FIG. 6 is a diagram showing one of the printed circuit boards of FIGS. 4 and 5. 
     FIG. 7 a  is an isolated, rear perspective view of the center spray cover of the cooling system constructed in accordance with the teachings of the present invention. 
     FIG. 7 b  is an isolated, front perspective view of the center spray cover of the cooling system constructed in accordance with the teachings of the present invention. 
     FIG. 8 is a sectional side view of the cooling system cover of FIG. 2 taken along the line  8 — 8  thereof. 
     FIG. 9 is a sectional side view of the cooling system cover and PCB of FIG. 2 taken along the line  9 — 9  thereof. 
     FIG. 10 is a magnified view showing the HPA nozzle in greater detail. 
     FIG. 11 is a detailed view of the front cover of the cooling system of the present invention. 
     FIG. 12 is a detailed view of the back cover of the cooling system of the present invention. 
    
    
     DESCRIPTION OF THE INVENTION 
     Illustrative embodiments and exemplary applications will now be described with reference to the accompanying drawings to disclose the advantageous teachings of the present invention. 
     While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility. 
     FIG. 1 is a diagram showing an assembly of T/R modules in accordance with the teachings of the present invention. The assembly  10  includes a base  12 , which supports a shear panel  14 . FIG. 1 shows the typical assembly/interlocking modules assembled to create a portion antenna aperture. Using this interlocking method an N×M array can be constructed. Approximately 30 single sided modules  100  (of which one is removed) are interfaced to the shear panel  14  of the assembly of FIG.  1 . Those skilled in the art will appreciate that the teachings of the present invention are not limited to 30 modules. Any N×M array can be built, where N and M are integers, without departing from the scope of the present teachings. The shear panel  14  supports a module interface  16 , which is plug compatible with each module  100 . 
     FIG. 2 is a diagram of a single module in accordance with the teachings of the present invention. The module  100  includes a single printed circuit board  110  on which a plurality of individual radiating elements  120  are disposed. The printed circuit board  110  may be of conventional design, fabrication and construction e.g., fiberglass, Teflon®, Duroids etc. Those skilled in the art will appreciate that the invention is not limited to the design of the radiating elements shown. Numerous antenna patterns may be used without departing from the scope of the present teachings. 
     A plurality of components (not shown in FIG. 2) are mounted on the circuit board  110  in electrical communication with the radiating elements  120 . Heat generated by these components is dissipated by a cooling system  130 . The cooling system  130  is disposed beneath a cover  132 . 
     FIG. 1 shows the modular nature and interlocking capabilities of the structure  10 . As shown in FIG. 2, and in accordance with the present teachings, the modular and interlocking capabilities are afforded by the provision of upper ( 134 ), lower ( 136 ) and lateral ( 138  and  140 ) integrated guide rails can be molded, machined or attached into each cover  132  of each module  100 . Holes  139  are provided for jackscrews. 
     FIG. 1 shows the typical assembly/interlocking modules assembled to create a portion of the antenna aperture. As mentioned above, using this interlocking method, an N×M array can be constructed. 
     FIG. 3 is a diagram that illustrates how the rails  134 - 140  of each module interlock in a dovetail manner to secure the modules  100  against vertical, horizontal (lateral) and rotational stresses. The modules  100  are secured in place via jackscrews  143  that serve to hold the modules to a coolant distribution panel as discussed more fully below. 
     In FIG. 3, it is understood that a second cover  132  would be disposed on the back side of each board as would be the case with the alternative module implementation of FIG. 4 below which shows a dual printed circuit board construction. 
     FIG. 4 is a diagram, which depicts a dual circuit board construction of a T/R module constructed in accordance with the teachings of the present invention. The module  100 ′ of FIG. 4 includes first and second printed circuit boards  110  and  112  mounted back-to-back on either side of a center cover  144  of a cooling system  130 . The boards  110  and  112  are secured to each other with snap clips  148  or bolts or other suitable attachment mechanism. The embodiment of FIG. 4 enables two circuit boards to be cooled by one cooling system  130 . In addition, the design of FIG. 4 enables the inlet and outlet to be distributed to prevent interference with the respect flow paths as discussed more fully below. A front cover  142  is provided along with a back cover  146  (not shown in FIG.  4 ). Note the provision of the top rail  134 . Note the provision of male and female lateral rails  138  and  140 , respectively, and a DC signal connector  150 . Note also the provision of the printed feed radiators  120  and printed aperture radiators  122 . 
     FIG. 5 is an exploded view of the T/R module  100 ′ of FIG.  4 . First and second electromagnetic interference shield inserts  152  and  154  are provided to protect the T/R components from electromagnetic interference. In practice, the shield inserts  152  and  154  may be implemented with a single element. An inlet quick disconnect  156  is shown along with a plurality of recovery quick disconnects  155 . The T/R modules are shown generally at  160 . Boltholes are shown in the exploded view of FIG. 5, in lieu of the snap clips  148  of FIG. 4, for the purpose of illustration. 
     FIG. 6 is a diagram showing one of the printed circuit boards of FIGS. 4 and 5. The board  110  includes printed flared radiators  120 , T/R components  160 , the DC signal connector  150 , clearance for a structural septum  164  an access for a coolant supply crossover  166  and printed feed radiators  122 . In accordance with the present teachings, all of the T/R components required for a radar system are integrated onto the printed circuit board. In addition, the printed radiators  122  form first level feeds for the radiating elements  120 . 
     FIG. 7 a  is an isolated, rear perspective view of the center spray cover  144  of the cooling system  130  constructed in accordance with the teachings of the present invention. In accordance with the present teachings, coolant is sprayed onto the components  160  by a cooling system  130  to remove heat generated by the components  160 . The cooling system  130  is disposed within the center cover and includes a plurality of nozzles  170 . Each of the nozzles  170  receives coolant via the distribution channels provided in the center cover  144  and sprays the coolant onto the components  160  as disclosed more fully below. The coolant is brought into the center spray cover by two inlets  166 . From the inlet  166 , the coolant moves into a plenum or chamber. The chamber provides a means to distribute the coolant along the length of the inlet  166  to the rear nozzles  170   b . One rear nozzle is provided for each channel. The septum  176  has a hole bored down its length. This hole provides a means for the jackscrew to pass through the inlet  166 . A cavity formed in the inlet  166  provides means for the coolant to be moved from the chamber to the HPA distribution chambers and thus to the HPA nozzles  170   a.    
     A coolant recovery chamber  172  is provided within the center cover  144  along with a plurality of collector holes  174  and a structural septum  176 . The center cover  144  is provided with a cross vent cutout in the septum  176 . Note the provision of a component chamber area  180 . 
     FIG. 7 b  is an isolated, front perspective view of the center spray cover  144  of the cooling system  130  constructed in accordance with the teachings of the present invention. The rear perspective view of FIG. 7 b  shows a coolant outlet  182  and an aft nozzle  184  within the cover  144 . The electromagnetic-interference shield insert  152  is shown in place. 
     FIG. 8 is a sectional side view of the cooling system cover  144  of FIG. 7 b  taken along the line  8 — 8  thereof. FIG. 9 is a sectional side view of the cooling system cover  144  and  110  of FIG. 4 taken along the line  9 — 9  thereof. In FIGS. 8 and 9, reference is made to the cover  144  of FIG. 4 to assist the reader. The sectional view of FIG. 8 shows a first (main) fluid delivery module  186  which communicates with a second (HPA) fluid delivery manifold  188 . The second manifold  188  communicates coolant to the HPA nozzles  170 . The sectional view of FIG. 9 reveals the main coolant plenum  187  and the HPA supply plenum  189 . 
     FIG. 10 is a magnified view showing the HPA nozzle in greater detail. The nozzle  170  receives coolant via the supply plenum  189  and ejects the coolant through an aperture  171  in said nozzle to spray a cone of vapor or mist onto the components  160  mounted on the board  110 . 
     Returning to FIGS. 8 and 9, the vapor flows over the components and is collected by inlets  200  and  202  and moves via fluid outlets  200   a ,  202   a  into a collection chamber  190 . Within the collection chamber  190  is a cross-over pressure equalization aperture  204 . The crossover pressure equalization apertures  224  allow for the hydraulic communication of fluid therebetween. The outputs of the component chambers are  180 . A second chamber  206  leads to a coolant quick disconnect plumbing fixture  208  such as that sold by the Aeroquip Corporation. 
     FIG. 11 is a detailed view of the outer cover of the cooling system of the invention. The covers  142 ,  144  and  146  are made of plastic or other suitable material. Note the provision of a molded supply inlet  210  and a recess  212  for the supply inlet of the next adjacent spray cooled module  100 ′. 
     FIG. 12 is a detailed view of the inside of the outer cover of the cooling system of the present invention. The outer cover  146  includes side clearance areas for uncooled electronic components  214 , a supply crossover aperture  216 , a lateral guide  218 , a supply inlet quick disconnect  220  and a cutout for a DC signal connector  222 . 
     In the preferred embodiment, liquid such as FC-72 by Florinert is used as a coolant. Those skilled in the art will appreciate that other coolants could be used such as water or inert liquids. 
     Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications, applications and embodiments within the scope thereof. 
     It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention.