The invention relates generally to radar technology and, more particularly, to active phased array antennas (APAA), namely to housings of high-power high-frequency transmit/receive modules (T/R) for APAA.

APAA includes a plurality (sometimes up to several thousand) of T/R modules or ultra-high frequency (microwave) transmitter modules. The main active electronic components of such APAA modules are microwave transistors or microwave monolithic integrated circuits of output power amplifiers. Since output power amplifiers have an efficiency factor from 25% to 40%, a significant part of the electrical energy consumed by the microwave module is converted into heat. The increase in temperature of the active electronic components results in the decrease in reliability of the microwave module and the APAA as a whole. To reduce the temperature of the active micro wave electronic components, the design of the APAA module is equipped with cooling devices.

A known hermetic electricity- and heat-conducting housing of the microwave module with hybrid microcircuits has a heat-conducting and shielding partition in its middle part dividing the housing into at least two sections (see patent of Ukraine for a utility model UA 14005 U, Int. Cl. H05K 7/20 "Module”, published 17.04.2006). In this design, each section is sealed with a separate lid. Thin printed circuit boards with hybrid microcircuits are glued or soldered to the opposite sides of the electricity- and heat-conducting partition of the housing. Heat from the hybrid microcircuits is carried away through the printed circuit boards to the electricity- and heat-conducting partition of the housing.

The disadvantage of this module housing is ineffective heat transport from the high- power hybrid microcircuits. This is due to the significant thermal resistance of the printed circuit board and the low efficiency of heat removal from the housing surface by natural convection with ambient air.

Another prior art housing design for the microwave transmitter module of S-band APAA (see article: O.T. Drak, V.G. Zhigalov, A.I. Zadorozhniy, M.D. Pames. Experience in solving the problem of heat dissipation from transmitter module of APAA. Microwave electronics and microelectronics, 2015, vol. 1, no 1, pp. 292-295, Fig. 3, in Russian) contains a 6 mm thick base plate made of thermally conductive material (aluminum alloy D16T). One side of this plate has a 2.6 mm recess for the installation of aluminum plates with active microwave electronic components, and the opposite side of the base carries 1 mm thick and 8 mm high cooling fins with intervals of 4 mm. To increase the cooling efficiency, the fins are cooled by airflow from a fan.

The disadvantage of this housing design is that the maximum overheat of the electronic components relative to the cooling air exceeds the allowable value by 5°C. This is caused by insufficient thermal conductivity of the base material of the module housing and insufficient base thickness. Apart from that, the housing has a significant aerodynamic drag, due to the small size of the air ducts between the cooling fins (3 mm). The high aerodynamic drag causes extra power consumption due to power required for the operation of the air duct fan.

Another prior art housing of the active phased array antenna module (patent of the Russian Federation RU 175877 Ul, Int. Cl. H01Q 21/00 (2006.01), Housing of active phased array antenna module, published 21.12.2017) comprises a heat-conducting base with sites for mounting cooled elements. Under said sites, in thermal contact with the module housing, heat pipes are located in such a way that their evaporation zones are positioned right under the sites for mounting cooled elements, while their condensation zones are outside the module housing and equipped with air cooling devices. The housing of the active phased array antenna module is an integral unit, with the heat pipes formed directly in parallel channels with a wick on the walls and a vapor duct. The heat pipes are in direct thermal contact with each other, and the module housing also serves as the walls of the heat pipes formed inside it. The minimum distance from the mounting site of the cooled element to the heat pipe is equal to the thickness of the heat pipe wall, considering the manufacturing process requirements.

The main disadvantage of this design is its low thermal characteristics due to the following reasons. Firstly, distilled water, which has the best thermophysical characteristics compared to other liquids, cannot be used as a working fluid in aluminum heat pipes. During long-term interaction between water and aluminum, they release hydrogen, which blocks the condensation zone of the heat pipe, significantly increasing its thermal resistance and the temperature drop across the heat pipe. Secondly, it is impossible to ensure reliable thermal contact between the aluminum housing and the wick of the heat pipe. Thirdly, placing air cooling devices on the outside of the base increases the length of the heat pipes, which reduces the maximum heat flux transferred by the pipes.

Another disadvantage of this prior art design is the lack of maintainability. If one heat pipe fails, it cannot be repaired without dismantling the entire module. The closest analogue of the claimed invention is the module housing for the active phased array antenna (see patent of Ukraine UA 139015 U, Int. Cl. 92019.01) H01Q 21/00, H05K 7/20 (2006.01), F28D 15/02 (2006.01), Module housing for active phased array antenna, published 10.12.2019, bul. N°23). This housing has a two-sided base with straight longitudinal channels, sites for installation of cooled elements, and heat pipes with sintered capillary-porous metal fiber wick on their inner surface. The pipes are installed horizontally in thermal contact with the longitudinal channels of the base in such a way that their evaporation zones are positioned near the mounting sites for cooled microwave elements, while their condensation zones are equipped with air cooling devices. The sites for mounting cooled elements are located on the first (mounting) side of the base, and the air cooling devices are made integral with the housing base in the form of cooling fins on the second (opposite to the first) side of the base.

The longitudinal channels are open to the mounting side of the base and are horizontal. Copper heat pipes are flat with a rectangular or flat oval cross section. One flat surface of each heat pipe in the evaporation zone is where the cooled element is mounted, and the second flat surface of each heat pipe is in thermal contact with the air cooling devices. Same as with the longitudinal channels, the heat pipes are positioned horizontally on the mounting plane of the base. The base of the module housing is made of heat-conducting material. The distance between the flat heat pipes and the cooling fins is minimal, considering their manufacturing process requirements and the durability characteristics of the base of the module housing. This module housing is intended for use in both transmitting and transmit/receive modules for APAA.

The design of the closest analogue uses flat copper heat pipes in the module housing and creates a reliable thermal contact between the sintered metal fiber wick and the heat pipe wall, which increases the thermal characteristics of the module housing, improves its maintainability and reduces length and weight.

The disadvantage of the closest equivalent design is its complexity and low manufacturability. Particularly complex is the design of the flat heat pipes with sintered metal fiber wick inside. Thus, in order to manufacture such a flat copper heat pipe, its wick is made by sintering fragments of copper fibers with each other and with the pipe itself under high temperature close to the melting point of copper in a protective medium or in vacuum. The sintering process takes several hours and requires a significant amount of electricity. The claimed invention is intended to solve the problem of simplifying the design and improving the manufacturability of the housing of the T/R module for the phased array antenna with built-in flat heat pipes.

The problem is solved by the fact that in the housing of the T/R module for the array antenna, comprising a base with a mounting surface and a heat-transfer surface, straight channels and mounting sites for cooled elements located on said mounting surface, and cooling fins located on said heat-transfer surface, flat heat pipes with a wick on their inner surface installed in thermal contact with the straight channels of the base so that the evaporation zones of the flat heat pipes are positioned near the mounting sites for cooled elements, and the condensation zones of the heat pipes are positioned neat the heat-transfer surface with cooling fins; said wick, covering largely the evaporation zone of the flat heat pipes, is designed as threaded grooves with small intervals, and both the straight channels and the flat heat pipes are tilted relative to the horizon so that the condensation zones of the heat pipes are elevated over their evaporation zones in the tilted service position of the module housing; the value of the tilt angle of the straight channels and the flat heat pipes in the mounting surface plane of the base relative to the horizon is determined depending on the angle of the module casing in the service position by the formula: where a is the tilt angle of the straight channels and the flat heat pipes in the mounting surface plane of the base relative to the horizon, degrees; β is the tilt angle of the mounting plane of the base of the module housing to the horizon in the tilted service position, degrees.

The threaded grooves of the wick in the evaporation zone of the flat heat pipes are made with intervals from 0.05 mm to 0.5 mm. The pipes are partially filled with a working fluid, which is corrosion compatible with the material of the heat pipes.

The causal relationship between the essential aspects of the invention and the achieved technical result is as follows. The threaded groove wick is made mainly within the evaporation zone of the flat heat pipes using a machine tap or a cutter and is simple in design, easy to manufacture, and, unlike the closest analogue, does not require a time-consuming high-temperature power-intensive sintering process. The simplified design and the increased manufacturability do not impinge on the heat transfer efficiency of the pipes. The threaded groove wick with small intervals increases the number of nucleation sites and thus intensifies the heat transfer processes in the evaporation zone. The condensate is returned from the condensation zone to the evaporation zone of the flat heat pipes in the tilted service position of the mounting plane of the module base due to the fact that the straight channels made in the mounting plane of the module base and the flat heat pipes in them are positioned at a tilt angle relative to the horizon determined by the formula: where a is the tilt angle of the straight channels and the flat heat pipes in the mounting surface plane of the base relative to the horizon, degrees; β is the tilt angle of the mounting plane of the base of the module housing to the horizon in the tilted service position, degrees.

Angle a determined by this formula, when the mounting plane is in its service position tilted at an angle β to the horizon, allows ensuring the required orientation of the flat heat pipes in space, with their condensation zones elevated above their evaporation zones. This provides minimum heat resistance in the heat pipes with threaded grooves with small intervals, stable reliable performance of the heat pipes in the tilted service position of the module, and efficient heat dissipation from the mounting sites for cooled elements. Otherwise, if the proposed technical solution did not provide efficient heat dissipation, it would neither make sense nor have any industrial applicability.

Since this set of essential aspects is not known from the prior art, the proposed technical solution is new.

Since the proposed new technical solution is not obvious for the specialist, i. e., it is not clearly inferred from the prior art base, an inventive step is involved.

The proposed technical solution is also industrially applicable and can be used to develop new and modernize the existing array antennas with T/R modules.

Compared to the closest analogue, the essential aspects of the invention make it possible to simplify the design and increase the manufacturability of the housing of the T/R module for array antennas while effectively removing heat from the sites for mounting cooled elements in the tilted service position of the module housing.

The essence of the claimed invention is illustrated by schematic drawings.

Fig. 1 shows a general view of the housing of the T/R module for the array antenna with the top lid removed.

Fig. 2 shows a cross-sectional view of the module housing along the A-A line. Fig. 3 shows enlarged fragment I of the cross-sectional view of the T/R module housing along the A-A line.

Fig. 4 shows the module housing in the tilted service position, side view in section.

Fig. 5 shows the geometry of the mounting surface of the module housing with straight channels and built-in heat pipes in the tilted service position relative to the horizontal plane, indicating, in particular, the angles needed to determine the tilt angle of the heat pipes in the mounting plane of the module housing.

The housing of the T/R module for the array antenna is made of heat-conducting material, such as aluminum or aluminum alloy. It contains a base 1 with two surfaces 2 and 3 (see Fig. 1 and Fig. 2). The first surface 2 is for mounting, and the second surface 3 is for heat-transfer. The first surface 2 of the base 1 has mounting sites 4 for the most heatgenerating microwave elements (Fig. 1 does not show said microwave elements). The second surface 3 (opposite to the first surface) of the base 1 carries longitudinal cooling fins 5 (see Fig. 2), for example, forming an integral unit with the base 1 of the module housing.

Straight channels 6 and 7 having, for example, a rectangular cross-section (see Fig. 3), are made in the base 1 (see Fig. 1). The straight channels 6 and 7 are open to the first, mounting, surface 2 of the base 1 and are tilted at an angle a to the horizontal axis OX (in Fig. 1, for example, the origin point O corresponds to the lower edge of the straight channel 7 and is denoted by an arrow), which is parallel to the horizon and the lower horizontal face of the base 1. Heat pipes 8 and 9 are mounted in thermal contact to the straight channels 6 and 7, respectively, on both sides of the mounting sites for cooled elements 4.

The heat pipes 8 and 9 are straight and flat with a thickness, for example, from 3 to 6 mm. The cross-section of the heat pipes may be rectangular or flat-oval (see Fig. 3). In other embodiments, the cross section of the heat pipe may have a different shape, for example, partially round with a flat face, square, trapezoidal, polyhedron, etc. In this particular embodiment of the invention, flat heat pipes are considered to be the pipes with at least one flat face. On the inner surface of the heat pipe 10, mostly in the evaporation zone, a wick 11 is made, for example, in the form of threaded grooves with small intervals, for example, from 0.05 mm to 0.5 mm, according to the technology known from the patent of Ukraine for a utility model UA 133241 U, Int. Cl. (2006.01) F28D 15/02, B23P 15/22 (Method of manufacturing gravitational heat pipes. National Technical University of Ukraine "Igor Sikorsky Kyiv Polytechnic Institute". Yu. Ye. Nikolaenko, V. A. Rogachev. Published 03/25/2019, bull. N°6. Application u201811023, November 8, 2018). The flat heat pipes 8 and 9 are partially filled with a working fluid (Fig. 1 and Fig. 3 do not show the level of the fluid), which is corrosion compatible with the material the heat pipe walls 10 are made of. In copper heat pipes, the working fluid may be, for example, freon R141b.

The heat pipes 8 and 9 are installed and fixed in the straight channels 6 and 7, respectively, of the base 1 in such a way that their evaporation zones are positioned near the mounting sites 4 for cooled microwave elements. The mounting sites 4 for the most heatgenerating microwave elements may be arranged, for example, in a row, perpendicular to the length of the base 1 (see Fig. 1). The thickness of the flat heat pipes 8 and 9 is not less than the depth of the straight channels 6 or 7, respectively (see Fig. 2 and Fig. 3). Due to this, one (first) flat surface of the wall 10 of each heat pipe in the evaporation zone is actually the mounting site 4 for a cooled microwave element. If a particular T/R module design uses pallets with several microwave elements, for example, two, the site for mounting such a pallet with two microwave elements covers two adjacent heat pipes (as shown in Fig. 1 with dotted lines).

The second, opposite to the first, flat surface of the wall 10 of each heat pipe is in thermal contact with the heat-transfer surface and the cooling fins 5, which, for example, form an integral unit with the base 1 (see Fig. 3). Thus, the length of the condensation zones of the heat pipes 8 and 9 is virtually equal to the entire length of the heat pipes, except for the small length of the evaporation zones in the mounting sites 4 for cooled elements. Reliable thermal contact between the heat pipes 8 and 9 and the walls of the straight channels 6 and 7 of the base 1 is provided, for example, by a layer of heat-conducting glue or solder 12. The distance between the second flat surface 10 of the heat pipes 8 and 9 and the heat exchange surface 3 of the base 1 with the cooling fins 5 is minimal, taking into account their manufacturing process requirements and the durability characteristics of the base of the module housing, and can be, for example, from 1.5 to 3 mm.

The service position of the T/R module in the APAA is tilted (see, for example, the patent of Ukraine for a utility model UA 123372 U. Antenna hardware module for mobile radar station, Int. Cl. (2018.01) H01Q 1/27 (2006.01), H01Q 21/00, owner: KP "NVK Iskra", Zaporozhye, inventors: L.V. Bortyuk, A.A. Deneka, V.Y. Kononovich, I.S. Presnyak, V.F. Trailin, O.L. Hara, published February 26, 2018, bull. N°4) at a certain angle β to the horizon (see Fig. 4 and Fig. 5). Fig. 5 uses the following notation:

0 is the origin of the coordinate axes;

X, Y, Z are the coordinate axes; d is the elevation of the condensation zone over the evaporation zone of the heat pipe (distance from the end point of the heat pipe to the XOY plane), m;

1 is the length of the heat pipe and the length of the channels (same), m; a is the tilt angle of the straight channels and the flat heat pipes in the plane of the mounting surface of the base of the module housing relative to the horizon, degrees; β is the tilt angle of the mounting plane of the base of the module housing to the horizon in the tilted service position, degrees (angle between the plane with heat pipes and the XOY plane); φ is the tilt angle of the heat pipe in space relative to the horizon (in Fig. 5, the plane of the horizon XOY is shown with dotted lines) in the service position of the mounting surface of the module housing tilted at an angle p to the horizon (angle between the heat pipe and the pipe projection on the XOY plane), degrees.

From Fig. 5, the projection of the heat pipe on the plane YOZ: l _p = I • sinα .

Distance from the end point of the heat pipe to the XOY plane (elevation of the condensation zone over the evaporation zone): d = l _p - sin β = / • sinα • sinβ .

The sine of the angle φ between the heat pipe and the projection of the pipe on the

XOY plane:

Then the formulas for the sine of the angle α and the angle a itself, depending on the ratio of other angles, have the following forms: The thermal resistance of heat pipes depends on their orientation in space. For example, if the heat pipe with a threaded groove wick is positioned horizontally (cp = 0°), there is no elevation of the condensation zone over the evaporation zone and gravity does not return condensate to the evaporation zone. Therefore, a copper heat pipe 250 mm long (the most rational size to be used in the basic version of the T/R module) with R141b as a working fluid was experimentally studied to determine the allowable value of the angle (p at which the condensate returns from the condenser to the evaporator under the influence of gravity providing an acceptable value of thermal resistance of the heat pipe, its stable performance in the module housing, and thus efficient heat dissipation from the mounting sites for cooled elements. For heat dissipation in the module to be efficient, the thermal resistance of the heat pipe should not excess 0.35°C/W.

The results of the study are shown in the table.

Table

The table shows that the heat pipe has the acceptable values of thermal resistance when it is oriented at a tilt angle φp of 15° or more to the horizon. Based on the fact that the sine of the 15° angle is equal to 0.2588, the formula for determining the angle a of the straight channels and flat heat pipes in the mounting surface plane of the base of the module housing relative to the horizon (degrees) will take the following form:

Using this formula and knowing the specified value of the angle β of the module housing (in degrees), the specialist designing the T/R module will be able to determine the angle a of the straight channels and the flat heat pipes in the mounting surface plane of the module housing relative to the horizon (degrees) .

The proposed housing of the T/R module for the array antenna operates as follows. When the heat from the cooled microwave elements is transferred to the mounting sites 4 in the evaporation zone of the heat pipes 8 and 9, the heat flux, due to the thermal conductivity of the material of the wall 10 of the heat pipe, is transferred to the wick 11. The working fluid in the threaded grooves 11 begins to boil, intensively absorbing the heat. The vapor of the working fluid moves along the vapor space of the heat pipes and condenses on the inner surface of the heat pipes in the condensation zone, giving off the heat of vaporization to the wall 10 of the flat heat pipe in the condensation zone. The heat is transferred through the heat-conducting wall 10 of the heat pipe and the layer of heat- conducting glue or solder in the contact zone to the base 1 of the module housing and through the body of the base 1 to the heat-transfer surface 3 with the fins 5 cooled by the airflow from fans (Fig. 1-4 do not show the fans). Due to the placement of the flat heat pipes in the mounting plane of the base of the module housing with a tilt angle α to the horizon, so that the condensation zone is positioned above the evaporation zone in the service position of the mounting surface of the module housing tilted at an angle β to the horizon (Fig. 4 and Fig. 5), gravity returns the condensed working fluid to the evaporation zone of the heat pipes and the heat transfer cycle is repeated.

Compared with the closest analogue, the claimed housing of the T/R module for the array antenna has a simplified design and is easier to manufacture while being efficient at heat dissipation. The design of the module becomes simpler and easier to manufacture due to a simpler design of heat pipes with a threaded groove wick in the evaporation zone, which is manufactured using a machine tap or a cutter and does not require a time-consuming power- intensive high-temperature sintering process. At the same time, the set of essential aspects of the proposed design provides efficient heat dissipation from the mounting sites for cooled elements in the tilted service position of the module.

Thus, the proposed housing of the T/R module for the array antenna is new, involves an inventive step, is an industrially applicable technical solution with a simplified design and improved manufacturing technology, and can be used to efficiently remove heat from high- power microwave elements of T/R modules for APAAs both in new radars and in upgrades of the existing radar designs.