FR3056042B1 - REDUNDANT RADIOFREQUENCY RECEIVING CHAIN WITH CRYOGENIC TEMPERATURE COOLING - Google Patents

Abstract

The device (100) comprises a radiofrequency reception chain including at least two weak amplifiers (LNA1, LNA2) of the signals received by the same antenna and cooled to cryogenic temperatures. In the device, the two amplifiers (LNA1, LNA2) are maintained at temperatures in the same cavity (32) subjected to a high vacuum of a cryostat (30) in which are also arranged all the radio components between an input coupler (20) and low noise amplifiers. At least two cryogenerators (40a, 40b) cool the cryostat whose cooling capacity is determined to maintain a nominal temperature when two cryogenerators are in simultaneous operation and to maintain a degraded temperature, higher, when a single cryogenerator is in operation . A cold extension (61) of the cryogenerator, passing through the wall (31) of the cryostat (30), is confined in a sealed sleeve (51) allowing the disassembling of a cold head without breaking the vacuum and keeping the other cryogenerator in position. operation.

Description

Redundant radiofrequency receiver chain with cooling at cryogenic temperature

The present invention belongs to the field of low power radiofrequency signal receiving systems.

More particularly, the invention relates to a high-frequency, low-noise radio reception chain adapted to the reception of weak signals emitted in particular by spacecraft more or less distant.

With regard to communications in the radio frequency domain, it is sometimes necessary to detect and amplify signals of very low power.

This situation is particularly in cases where the signal transmitter, sometimes itself low power, is located at great distances or the conditions of transmission and / or reception are unfavorable.

Answers to improving the reception of radio signals are known and widely applied.

In general it is not or no longer possible to act on the transmission conditions, transmitter power, antennas gains ..., the transmitter being inaccessible.

The solution therefore consists in improving the signal-to-noise ratio of the ground receiver whose quality index is given by the ratio G / T where G represents the gain of the antenna and T (K) the noise temperature of the equipment of the reception chain.

The gain of the antenna G, which acts directly on the power of the received signal, is in practice improved by increasing the dimensions of the antenna and finds at a time operational limits and / or cost which lead to act on the temperature of the antenna. T noise to decrease the internal noise of the receiver.

In a reception chain, the components processing very low power signals are the most sensitive to the noise temperature. The most critical components are the first amplifiers connected to the antenna in the receive chain due to the low power of the received signals.

For these sensitive components, it is customary to lower the operating temperature at cryogenic temperatures, generally below 120 K, and in practice to temperatures of a few Kelvin.

Maintaining a reception chain at such low temperatures is achieved by placing the amplifiers in a cooled enclosure of a cryostat.

The known devices, as in the example of architecture shown schematically in Figure 1, in practice uses cryogenic amplifiers AC1, AC2, a cryogenic amplifier consisting of a low noise amplifier LNA1, LNA2 cooled in a cryostat having its cold generator.

In such an architecture the replacement of a cryogenic amplifier is easily achievable in case of failure, the low noise amplifier or the cold generator, without stopping the other amplifiers. But this architecture is penalizing in terms of integration of the reception chain and in terms of maintenance of the device.

Such a failure, especially when linked to a failure of the cold generator, is all the more troublesome that the different amplifiers are dedicated to the amplification of different signals, for example by their polarizations as in the example of Figure 1 .

In order to overcome the defects of the existing systems and to improve the operational availability of a device for receiving radio frequency signals, the device of the invention comprises a cryostat in a single enclosure of which are grouped the components of the reception chain of which the internal thermal noise substantially affects the signal-to-noise ratio of the receiver, which is cooled by a plurality of cryogenerators to provide continuity of reception.

According to the invention, the device for the reception of radio signals comprises a radiofrequency reception chain, said chain comprising functionally interconnected radioelectric components, of which at least two low noise amplifiers cooled to cryogenic temperatures below 120K, said at least two amplifiers low noise being arranged in said reception channel to receive radio signals picked up by the same antenna via a separator ,.

In addition: the two low noise amplifiers are maintained at cryogenic temperatures in the same cavity of a cryostat; the cavity of the cryostat furthermore contains, maintained at cryogenic temperatures, all the radioelectric components of the reception chain situated between on the one hand an input coupler, arranged in the cavity opposite a window; a wall of the cryostat, transparent to the radio signals coming from the antenna, and without contact with said wall, and on the other hand the at least two weak amplifiers noise.

By such an arrangement, a complete cooling by unitary means of all the components capable of raising the thermal noise level in the reception chain is achieved when the received signal has not yet been amplified.

In particular, the radio components of the reception chain located between the input coupler and the at least two low noise amplifiers comprise at least one of: couplers, frequency filters, separators, single-stage switches, several inputs and one or more outputs. In this way, it is possible to carry out passive processing of the signals before amplification without introducing thermal noise and in particular to have the ability to reconfigure in operation the amplification channels in the cryostat.

The device also includes all or some of the following characteristics taken alone or in any technically possible configuration: the input coupler is a horn antenna which picks up the signals coming from the antenna through a transparent window without being necessary that the coupler is in contact with the wall of the cryostat. the reception chain comprises at least one amplifier mounted in the second amplification stage of a low-noise amplifier, arranged in the amplification system outside the cryostat in an annex box fixed to said cryostat. It is thus limited the number of components in the cryostat while maintaining short links between the internal components of the cryostat and the external components.

In one embodiment: each of the radioelectric components of the reception chain located in the cavity of the cryostat is fixed on a cold plate arranged in said cavity subjected to a high vacuum with a pressure of less than one microbar (0.1 Pa ); the or each of the cold plates is maintained at cryogenic temperatures by at least two cryogenerators whose cooling capacities are determined to maintain the low noise amplifiers at a first nominal cryogenic temperature when the at least two cryogenerators are in simultaneous operation and to maintain said low noise amplifiers at a second degraded cryogenic temperature, greater than the first nominal cryogenic temperature, when only one cryogenerator is in operation; each cryogenerator carrying out a pumping of the heat of the cold plate (s) by a cold extension, of a cold head of the cryogenerator, passing through the wall of the cryostat and confined in a sleeve fixed to the said wall to ensure a gastightness between the cavity, subjected to high vacuum, and a space surrounding the cryostat at atmospheric pressure.

According to this embodiment, it is ensured a maintenance at a cryogenic temperature of the components fixed on the cold plate or plates, even in the event of failure of a cryogenerator, which can be removed without stopping the device and without breaking the vacuum in the cavity of the cryostat.

According to one embodiment, each cold extension comprises at least one thermal connection with one or more cold plates, and or one or more antiradiation screens in the cavity of the cryostat, said thermal connection comprising: a connection element fixed to the cold plate; , or the antiradiation screen, to cool; a thermal bridge fixed to the sheath; a cold end piece integral with the cold head; said connecting elements, thermal bridge and cold end piece being in contact to ensure transmission of heat from the cold plate to the cold head in a first nominal position of said cold head and the connecting member and the thermal bridge being separated in a second position of said cold head fixed to the sleeve when said sleeve, held at the wall of the cryostat by an extensible connection of a barrel return, is partially extracted from the cryostat without being separated from it.

It is thus possible, without interrupting the operation of the device, in an intermediate position to heat the cold head to be disassembled and its sheath. Also in this intermediate position, it is avoided that the cold head at a standstill is a source of heat that would lead to oversizing of the cryogenerator to maintain the components of the receiver chain at a cryogenic temperature.

To carry out the complete disassembly of the cold head, the thermal bridge and the cold end piece are separated in a third position of the cold head at least partially extracted from the sleeve, said sleeve providing gastightness between the cavity and the nozzle. surrounding area.

In one embodiment, a thermal connection between a connecting member and a thermal bridge, and or between a thermal bridge and a cold end piece, is provided by a pin engaged in a radially elastic sleeve clamped to said pin by a contraction ring when said clamping ring is at cryogenic temperature, and releasing said pin when said clamping ring is at non-cryogenic temperature.

It is thus ensured a minimum contact heat resistance between the heat conducting elements that must remain disconnectable.

To ensure optimal reception of signals of very low power, advantageously the first cryogenic temperature, in nominal operation, is less than 10 K.

To ensure acceptable reception of these signals, the second cryogenic temperature, in degraded operation, is preferably less than 80 K. The invention also relates to a method for replacing a cold head of a device according to the invention.

According to the method it is compensated for the failure of a cold head without interruption of operation of the receiving chain by maintaining cryogenic temperature of the cooled components in the cryostat.

The method comprises a step in which the cold head, stopped and to be replaced, is dismounted while maintaining at least one other cooling head in operation so that a cryogenic cold is maintained in the cryostat without breaking the vacuum in the cryostat.

Thus, the method comprises at least the steps of: controlling the temperature in the cryostat, then when said temperature is substantially stabilized around the second degraded cryogenic temperature; - Loosen screws immobilizing a sleeve flange of the barrel return, relative to a ferrule, fixed to the wall of the cryostat, the cold head being fixed on a cold head flange solidarisant the sleeve and said sheath return; - Applying a tensile force on the cold head, still attached to the sleeve, to a partial extraction of said sleeve, the cavity of the cryostat, permitted by an elongation of the extensible sealing connector; measuring the temperature of the sleeve, which, following the partial extraction of said sleeve, the thermal bridges are no longer in contact with still cooled parts of the device; - When the barrel temperature has reached or exceeded a dew point temperature in the environment of the cryostat, break the vacuum in said sleeve, detach the cold head from the cold head flange and extract the cold extension of said sleeve.

It is thus ensured disassembly without risk of damage neither the cryostat nor the cold head and bring the possibility of easy and quick reassembly of a replacement cold head. The operating time of the reception channel in degraded mode can be minimized.

The description of the invention is made with reference to the figures which illustrate schematically and in a nonlimiting manner: FIG. 1: already cited, a schematic representation of a reception chain comprising several cryogenic amplifiers; FIG. 2a: a schematic representation of an exemplary device of the invention in which a reception channel receiving several low noise amplifiers is arranged in a single cryostat; Figure 2b: a schematic representation of another embodiment of the device according to the invention incorporating a device similar to the device of Figure 2a in a set also comprising transmitting means; FIG. 3a: in a simplified isometric view, a device such as the device of the diagram of FIG. 2a, showing the cryostat with a window transparent to radio radiation and two cryogenerators for cooling the cryostat; FIG. 3b: in isometric view, an illustration of an exemplary interior arrangement of the cryostat of FIG. 3a, the side exterior wall and the side antiradiation shields being removed, all the detail elements or accessories not being shown; Figure 4a: a purified section of a cryogenerator, along a longitudinal axis of its cold extension, in operative position on a cryostat;

4b: a representation of the cryogenerator of FIG. 4a in which the cold head is still attached to the cryostat but whose thermal bridges of the sleeve, still connected to the cold ends of the cold head, are disconnected from the cold plate connection elements; FIG. 4c: a representation of the cryogenerator of FIG. 4a whose cold head, disconnected from the sleeve, is in a position partially extracted from the sleeve of the cryogenerator.

The present invention relates to a device for receiving radio signals comprising a radio frequency signal reception and amplification system maintained at cryogenic temperature.

For the purposes of the detailed description of an exemplary embodiment of the device, it will be considered the case of a reception chain comprising two low noise amplifiers (LNA).

The temperatures are here considered cryogenic for values below 120K, higher value which corresponds substantially to the liquefaction of air gases under atmospheric pressure conditions.

FIG. 2a schematically represents a device 100 comprising the reception chain, at least its initial high frequency amplification part.

The device comprises a cryostat 30, a wall 31 defines a cavity 32 in which the components of the receiving chain must be maintained at a cryogenic temperature.

The reception chain also comprises, inside the cavity 32: an input coupler 20, in the form of a horn antenna, located opposite a window 33, transparent on the radio plane, of the wall 31; two low-noise amplifiers LNA1, LNA2; - Output couplers IEC, CE2 amplified signals through the wall 31 of the cryostat.

Between the input coupler 20 and the low-noise amplifiers LIMAI, LNA2, the reception chain also comprises: a tracking coupler 21; one or more filters 22, for example band-pass filters, radiofrequency signals; a separator 23 for discriminating the waves of different polarizations; a switch 24 with two inputs connected to outputs of the separator and with two outputs each connected to an input of a low-noise amplifier via a test coupler 251, 252.

Incidentally, the cavity 32 also contains components of a tracking system 26 receiving signals from the tracking coupler 21.

The components of the tracking system 26 are not interposed in the reception chain, outside the tracking coupler 21. The signal-to-noise ratio requirements in the tracking system are not as severe as for the signals to be analyzed and said Tracking system components are here integrated into the cavity of the cryostat for convenience.

The mounting of the switch 24 in the cryostat makes it possible, without using mechanical traversing in the wall 31 of the cryostat, to switch each of the polarizations of the signal, discriminated by the separator 23, towards one or the other of the low-noise amplifiers. LNA1 or LNA2. Thus, each low-noise amplifier can alternately amplify the radio signal according to one or the other of the polarizations, and thus occasionally replace the other low-noise amplifier in the event of a failure of the latter, without it being in the reception channel introduced by thermal noise or amount of heat by conduction to the inside of the cryostat.

In the diagram of FIG. 2a, amplifiers mounted in the second amplification stage, which are less sensitive to noise of thermal origin because of the pre-amplified signal they receive, are arranged in the amplification chain outside. cryostat 30, advantageously in an annex box 90 attached to the cryostat 30 to minimize the lengths of the connections between the different amplification stages.

To be maintained at low temperature, the components of the reception chain, essentially grouped in the center of the cryostat, visible but not marked in FIG. 3b, are intimately fixed on a cold plate 34 formed in a material that is highly heat-conductive, for example copper example, itself cooled by cryogenerators 40a, 40b, ie cold sources that pump the heat of said cold plate, heat that is provided by the operation of electronic components, by the conduction via the structures of the device, the convection by the residual gases in the cavity 32 of the cryostat and the thermal radiation.

To keep the temperature in operation as low as possible, it is naturally desirable to minimize all the heat gains from the outside to the inside of the cryostat and to maximize the inverse heat transfer from the thermal pumping.

Thus, the input coupler 20 horn antenna placed vis-à-vis the transparent window 33 of the wall is fixed without contact with the wall 31 to prevent direct heat transfer by conduction with said wall.

Also, it is operated and maintained a high vacuum, corresponding to a pressure of less than one microbar (0.1 Pa), to limit the heat exchange by conduction and convection.

Advantageously, antiradiation screens 35 are arranged between the parts to be kept cold and the wall 31 of the cryostat to limit radiative heating of the external heat heating said wall.

The combination of the high vacuum and the implementation of anti-radiation screen thus makes it possible not to penalize the thermal balance of the cryostat by the temperature of the wall 31 of the cryostat which is advantageously made of aluminum alloy to withstand atmospheric pressure. , when a vacuum is made in the cavity 32, without excessive mass penalty.

The various elements, in particular cold plates and antiradiation screens are mechanically held in the cavity 32 attached indirectly to the wall 31 by supports 36, such as columns, which, without affecting their mechanical functions, are made of a material as much as possible thermally insulating to prevent heat input into the enclosure by conduction.

Taken individually, the various components of the reception chain are known, but here they are assembled and arranged in a single cavity 32 of a cryostat 30 in an arrangement adapted to the reconfiguration of said reception chain, and their cooling is carried out by two cryogenerators 40a, 40b independent.

It must be understood here that the two cryogenerators are independent in that each can be in operation or not independently of the other.

It should also be noted that more than two cryogenerators can be arranged to cool the components in the cryostat, but to avoid an interruption of the reception due to an excessive rise in temperature, at least two cryogenerators are in operation simultaneously, out of case of failure, so that a failure of a cryogenerator in operation does not completely interrupt the cooling of the components inside the cryostat and that it can be started a cold redundant cryogenerator and or proceeded to change the defective cryogenerator.

In addition, if it is necessary to dismantle a cryogenerator 40a, 40b, for example for a repair following a breakdown, a maintenance operation or a replacement at the end of operational life, disassembly must be able to be performed without interrupting the operation of the reception chain which implies without heating the components beyond a defined maximum cryogenic temperature and, consequently, to continue the cooling without breaking the vacuum pushed into the cavity 32 of the cryostat.

To achieve, with a minimum cooling power, a temperature in cryogenic operation, in particular less than 10K, it is necessary that the cooling of the cold plate 34 is effected effectively, which implies on the one hand that a cold termination 41, 42 of a cryogenerator is brought to a sufficiently low temperature to reach the desired temperature for the cold plate and that on the other hand all the mechanical connections by which the heat is pumped have a low thermal resistance to ensure a transfer effective heat.

In the example of the cryogenerator 40a, 40b illustrated in simplified section in FIGS. 4a, 4b and 4c, the cryogenerator used has two stages operating at different temperatures.

Such a known configuration with two cooling stages is not mandatory but is suitable for cooling an amplification system at the temperatures considered.

Figures 4a, 4b and 4c also show elements in contact with the cryogenerator, namely the cold plate 34 to be brought to the lowest temperature, the anti-radiation screen 35 and the wall 31 of the cryostat.

In this chapter devoted to cryogenerators, the term "resistance" refers to the thermal resistance that opposes heat transfer, in particular to the thermal contact resistance resulting from the joining of two parts. through which the heat must pass.

The cryogenerator comprises three main subassemblies shown in FIG. 4a in the operating configuration of the cryogenerator: a first subassembly in contact with the other parts of the device; a second subassembly 50 comprising a sealed sleeve; a third subassembly forming a cold head 60 for the generation of cold and the pumping of heat in the cryostat.

The first subassembly mainly comprises the parts of the cryogenerator directly attached to the parts to be cooled or to the wall 31 of the cryostat.

In said first subassembly, there is a first connecting element 41 to the cold plate 34, a second connecting element 42 to the antiradiation shield and a shell 43 through which the sleeve, and indirectly the cold head of the cryogenerator, is fixed. at the wall 31.

The shape and dimensions of the first and second connecting elements are adapted to form contact surfaces on which the cold plate and the antiradiation shield are respectively supported and said connection elements are tightened by means of fasteners, such as screws 411. , respectively against the cold plate or said anti-radiation shield to obtain the lowest possible contact resistance.

The ferrule 43 mainly ensures the maintenance of the sheath and the cryogenerator and simultaneously the sealing at the crossing of the wall 31 by the sheath, which is necessarily sealed to maintain the vacuum produced in the cavity 32.

As seen in FIG. 4a, these three elements are not in direct contact with each other and form a unit in that they are fixed with respect to a structure of the cryostat, when the device is in operation.

The second subassembly 50 mainly comprises the sheath 51, a first thermal bridge 52, a second thermal bridge 53, a sheath return 54, outside the sheath, comprising a tight fitting extension 55, for example an accordion bellows.

The sheath 51 and the sheath return 54 comprising the extensible connector 55 form a gas-tight envelope which rests on the shell 43 and provides the seal to maintain the vacuum in the cavity 32.

A cold head flange 56 is arranged at the junction of the sleeve 51 and the barrel return 54, the function of which will be explained later.

A sleeve flange 57 is arranged on the sleeve return, between the extensible connector and the cold head flange, so as to immobilize the sleeve by screws, not shown in FIGS. 4a, 4b and 4c, maintaining a position close to said sleeve flange with the ferrule 43 in nominal operation.

The first and second thermal bridges are in thermal contact with the first connecting element 41 and the second connecting element 42 respectively.

According to a similar arrangement for the two thermal bridges, a thermal connection is made by a sleeve 522, 532, radially elastic, the thermal bridge 52, 53 fitted on a pin 411, 421 of the connecting element with which the thermal connection is performed.

To ensure a quality of the contact between the sleeve and the pin a clamping ring 523, 533 is arranged around the sleeve 522, 532.

This type of assembly for the cold termination junction allows insertion or disengagement of the sleeve on the lug easily at room temperature, the ring then having a diameter sufficient to allow elastic expansion of the sleeve during the insertion of the nipple, and cryogenic temperature clamping by thermal contraction of the clamping ring. The clamping ring is for example made of PTFE (polytetrafluoroethylene).

The cold head 60 is a conventional device for generating cold and pumping heat by a cold extension 61, in the embodiment with two cold ends, a cold first end at low temperature, here to reach a temperature below 10K and a second cryogenic intermediate temperature cold end used to cool parts not requiring a temperature as low as critical components, such as low noise amplifiers.

In the example shown, the cold extension corresponds to a form of revolution, as in practice the sleeve 51 and the shell 43, of which only the contour is shown in Figure 4a.

Cold end pieces 62, 63 are thermally connected to the thermal bridges 52, 53 in a manner similar to thermal connections between said thermal bridges 52, 53 and the connecting elements 41, 42, i.e. by sleeves 622, 632, radially resilient, fitted on the pins 521, 531 of the thermal bridge 52, 53 with which the thermal connection is made.

A clamping ring 623, 633 is arranged around the sleeve 622, 632 to provide a low-resistance contact between the sleeve and the pin.

It should be noted that in the cryogenerator 40a, 40b, the contacts between the connecting elements 41, 42 and the thermal bridges 52, 53 are located inside the cavity 32 of the cryostat in which a high vacuum is maintained, and that the contacts between said thermal bridges and the cold end pieces 62, 63 are located inside the sleeve 51 sealed with respect to the cavity 32.

According to another characteristic, when the device is in operation and the cryogenerator considered is also in function, the sleeve 51 is sealed and it is also maintained the vacuum in said sealed sleeve to limit heat losses.

This form of assembly thus makes it possible to maintain the tightness of the cavity 32 of the cryostat, and thus the vacuum in said cavity when the cold head 60, that is to say the part of the cryogenerator that produces the cold and pumps the heat in the cryostat, which is the part of the cryogenerator that may need to be replaced in operation of the device, is removed.

This embodiment also makes it possible to disassemble and reassemble the cold head 60 when the device is still cooled at cryogenic temperature by another cryogenerator.

In the case of operating stoppage of a cryogenerator, the cryogenic temperature of the cryostat will be ensured only by the generator (s) remaining in operation.

In practice the temperature maintained below 10K with two cryogenerators will rise and will only be maintained at a higher temperature, for example a specified temperature of 80K which will be used to determine a minimum power of a cryogenerator to ensure the operation of the device in degraded mode.

This rise in temperature is sufficient to ensure expansion of the various clamping rings which would allow disassembly of the cold head. However, the thermal bridges 52, 53 of the sheath are still in contact with the connecting elements 41, 42 themselves in contact with the parts cooled by the other cryogenerator: the cold plate 34 and the antiradiation shield 35.

Under these conditions, a disassembly of the cold head 60 would have the consequence, on the one hand, of heat exchanges with the outside air which would be in direct contact with the surfaces of said thermal bridges inside the sleeve 51 and would bring heat to the elements cooled by the other cryogenerator and on the other hand an ice formation from the water present in vapor form in the atmosphere.

It would therefore be caused a heat flow towards the cold parts and the formed ice would oppose a reassembly of a cold head.

The described embodiment makes it possible to escape these difficulties by the double thermal junction made at each of the cold terminations and by the extensible connector 55.

The advantages will be better understood from the description of a procedure illustrated in the sequence of FIGS. 4a, 4b and 4c for the replacement of a cold head 60 when the device is in operation.

The initial assembly carried out at room temperature does not pose any particular problem for the skilled person who will ensure the appropriate assembly order and the necessary sealing mechanical connections. When the assembly is completed, the vacuum is produced in the cavity 32 of the cryostat and in the sleeve 51. Given the temperatures desired during operation, a high vacuum will be achieved. The temperature is then lowered and maintained on the cooled parts of the device by the simultaneous operation of at least two cryogenerators.

To dismantle a cold head from a cryogenerator at standstill, breakdown or voluntary stop, without interrupting the operation of the device, it is then proceeded as follows: in a first step, starting from the configuration illustrated in FIG. 4a , it is expected that the temperatures in the cryostat at the cooled parts back because of the stop cryogenerator whose cold head must be dismantled; - When this temperature is raised, in practice a few tens of Kelvin and still in the field of cryogenic temperatures thanks to the cryogenerator still in operation, the expansion of the clamping rings 523, 533 is sufficient for an ordinary tensile force on the sleeve 51 ensures the separation of the sleeves 522, 532 of the thermal bridges with the pins 411, 421 of the connecting elements. This force is applied in the form of traction, performed by hand or with specialized tools, when the screws holding the sleeve flange 57 to the shell 43 have been sufficiently loosened, the cold head still being fixed on the flange of cold head 56. The partial extraction of the sleeve 51 is allowed by the deformation of the extensible connector 55 which allows movement of the sleeve while maintaining the seal of the cavity 32 of the cryostat. At this stage, the inner volume of the sheath, in which the cold extension 61 is located, is always under vacuum although the sheath is partially extracted from the cryostat; - Following this maneuver partial extraction of the sheath, in the configuration of Figure 4b, the thermal bridges 52, 53 are no longer in contact with the still cooled parts of the device and the temperature of the assembly, sheath, thermal bridges , and cold head, thus thermally disconnected, separations indicated by the double arrows in Figure 4b, can be brought to room temperature, naturally or by active heating to accelerate said heating, maintaining the operation of the device. At this stage, the vacuum pushed into the cavity 32 of the cryostat prevents excessive heating of the components of the reception chain by diffusion of the temperature of the sleeve; - When the temperature of the sleeve 54 is in the vicinity of the ambient temperature, in practice at least above the dew point temperature in the environment of the cryostat, it is then broken the vacuum in said sleeve, and the cold head can be disassembled by detaching said cold head from the cold head flange 56 without fear of condensation of water or ice formation in the sheath.

During this disassembly, although in degraded conditions, the reception chain is still functional and cooled to a cryogenic temperature.

The reassembly of a cold head 60, when the device is in operation, is performed in the reverse order of disassembly operations: - the cold extension 61 of the replacement cold head 60 is inserted into the sleeve 51 until with engagement of the sleeves 622, 632 of the cold end pieces 62, 63 on the pins 521, 531 of the thermal bridges 52, 53. This engagement is made practically without effort due to the expansion of the clamping rings 623, 633 whose Expansion at room temperature is important at the scale considered; the cold head is fixed on the cold head flange 56 reconstituting the imperviousness of the sleeve 51 in which the vacuum can be restored; - The sheath 51 can then be pushed back to engagement of the sleeves 522, 532 of the thermal bridges 52, 53 on the pins 411, 421 of the connecting elements 41, 42. As when mounting the cold head in the sleeve, this engagement is achieved virtually effortless due to the expansion of the clamping rings 523, 533 still substantially at room temperature; - Once this contact established with the parts cooled by the other cryogenerator in operation, the heat conduction parts begin to cool and the clamping rings to tighten by thermal contraction. The commissioning of the cryogenerator that has just been mounted then makes it possible to lower the temperature in order to bring the device back to nominal temperature conditions.

Simultaneously with the lowering of the temperature of the cooled parts in the cryostat, the various clamping rings contract again and restore contacts with reduced thermal resistance.

In the description just given, when the term "temperature" or "cryogenic temperature" and generally the term "temperature" are used, the skilled person understands that, because of the sources of warming and thermal pumping in the cryostat, the temperature is not identical in every way even if the singular is used.

The device of which an example has just been described is capable of variants without departing from the invention.

For example, the reception chain may comprise only part of the components illustrated in the example described and, as in the example illustrated in FIG. 2a, be associated with a transmission channel 91 coupled to the same antenna. .

As already mentioned, the device comprises at least two independent cryogenerators that are in simultaneous operation, but it may include more operating simultaneously or occasionally when one of the cryogenerators in operation fails or must be stopped.

The cold heads described have two stages, but the principles of connection and disconnection explained can be transposed to a cold head with any number of stages.

The device described is shown schematically with a single cold plate on which are fixed the components to be maintained at low temperatures, and with a cooled antiradiation screen functionally acting as a cold plate with respect to thermal pumping, however the device may comprise several cold plates, and or several antiradiation screens, interconnected by thermal connectors, some of which are visible in Figure 3b, and or connected to different stages of the cold heads, depending on desired temperatures. The expression "cold plate", even used in the singular, must therefore be considered here generally as structures to be cooled to cryogenic temperature by a pumping of heat, in particular a set of supports on which are fixed components in front of to be maintained at cryogenic temperatures, the expression cold plate in the singular being more particularly used when the supports of this set are thermally connected to each other.

In the thermal junctions "connecting element - thermal bridge" and "thermal bridge - cold end piece", made by fitting a nipple in a sleeve and clamping by thermal contraction of a clamping ring, the positions of the nipple and the sleeve can be inverted with respect to the illustrated cases in any possible combination. For example the sleeve may be on the connecting element and the pin on the thermal bridge.

The temperatures and pressures involved in the device are given by way of example corresponding to a realistic operation for a device such as that of the invention but may however evolve more or less according to the specifications and requirements of the case. the species, provided that the operation assumes a cryogenic temperature of the sensitive components and the maintenance of a vacuum at least partial, if not pushed, in the cryostat.

The device of the invention is therefore particularly efficient in ensuring the operation of the reception channel for the reception of weak radio signals, in particular in the S band (2.2-2.3 GHz), the X band ( 8.4-8.5 GHz) and the Ka band (31.8-32.3 GHz), even in the event of a cryostat failure and allowing the change of the failed cryostat without stopping the reception chain.

Claims (11)

1 - Device (100) for receiving radio signals comprising a cryostat (30) having a cavity (32), a radio frequency reception chain, said chain comprising functionally interconnected radioelectric components, including an input coupler (20) receiving radio signals picked up by an antenna outside the device (100), at least two weak noise amplifiers (LNA1, LNA2) cooled to cryogenic temperatures below 120K in the cavity (32) of the cryostat (30), characterized in that: the cavity (32) of the cryostat (30) furthermore contains, maintained at cryogenic temperatures, all the radio components of the receiving channel of the device (100) situated in said chain between, on the one hand, the input coupler (20); ), arranged in the cavity (32) vis-à-vis a window (33) of a wall (31) of the cryostat (30), transparent to the radio signals from the antenna, and without contact with said wall, and that; the at least two low noise amplifiers (LIMAI, LNA2) are arranged in parallel in said reception channel to receive the radio signals picked up by the input coupler (20) via a splitter (23). 2 - Device according to claim 1 wherein the radio components of the reception chain located between the input coupler and the at least two weak amplifiers (LNA1, LNA2) comprise at least one of: couplers (21, 251, 252), frequency filters (22), separators (23), switches (24) with one or more inputs and one or more outputs. 3 - Device according to claim 1 or claim 2 wherein the input coupler (20) is a horn antenna. 4 - Device according to one of the preceding claims wherein the receiving chain comprises at least one amplifier mounted second amplification stage of a low noise amplifier (LNA1, LNA2) arranged in the amplification chain outside the cryostat (30) in an auxiliary housing (90) attached to said cryostat. 5 - Device according to one of the preceding claims wherein: -the cryostat (30) comprises at least two cryogenerators (40a, 40b) capable of operating independently of one another, arranged to pump heat from one or several cold plates (34) where each of the compounds of the reception chain are fixed -the cavity (32) of the cryostat (30) is subjected to a high vacuum of a pressure lower than a microbar (0.1 Pa) - the or each of the cold plates (34) is maintained at cryogenic temperatures jointly by the at least two cryogenerators (40a, 40b) whose cooling capacities are determined to maintain the low noise amplifiers (LNA1, LNA2) at a first nominal cryogenic temperature when the at least two cryogenerators are in simultaneous operation and to maintain said low noise amplifiers at a second degraded cryogenic temperature, higher than the first nominal cryogenic temperature, when only one cryogenerator is in operation; the device also comprises, for each cryogenerator, a sheath (51) fastened to the wall (31) of the cryostat (30) so as to ensure a gastight seal between the cavity (32), subjected to high vacuum, and a space surrounding the cryostat at atmospheric pressure, and whose sheath (51) passes through said wall (31) and confines to its interior a cold head (60) of a cryogenerator; each cryogenerator (40a, 40b) simultaneously pumps the heat of the cold plate (s) by a cold extension (61) of the cold head (60) of the cryogenerator, passing through the wall (31) of the cryostat (30) and confined in the sleeve (51). 6 - Device according to claim 5 wherein: -the sleeve (51) passing through the wall (31) of the cryostat comprises, on its outside, a barrel return (54) secured to said sleeve (51) by a cold head flange ( 56), and on which sleeve return (54) are arranged an extensible coupling (55) and a ferrule (43) sealing the cavity of the cryostat (32) and; the sleeve (51) is fixed to the wall (31) of the cryostat by a sleeve flange (57) arranged on the sleeve return (54), between the extensible connector (55) and the cold head flange (56) immobilizing the barrel return (54) relative to the barrel (43) and the expandable coupling (55); each cold extension (61) comprises at least one thermal connection with the cold plate or plates (34), and or one or more antiradiation screens (35) in the cavity (32), said thermal connection comprising: a connecting element (41, 42) attached to the cold plate, and or the antiradiation screen, to cool; - a thermal bridge (52, 53) fixed to the sheath (51); - a cold end piece (62, 63) integral with the cold head (60); the connecting elements, thermal bridge and cold end piece being in contact to ensure the transmission of heat from the cold plate to the cold head in a first nominal position of said cold head and the connecting element and the thermal bridge being separated in a second position of said cold head fixed to the sheath (51) when said sheath is partially extracted from the cryostat without being separated from it. 7 - Device according to claim 6 wherein the thermal bridge (52, 53) and the cold end piece (62, 63) are separated in a third position of the cold head (60) at least partially extracted from the sleeve (51). ), said sleeve providing gastightness between the cavity (32) and the surrounding space. 8 - Device according to claim 6 or claim 7 wherein a thermal connection between a connecting element (41, 42) and a thermal bridge (52, 53), and or between a thermal bridge (52, 53) and a part the cold end (62, 63) is formed by a stud (411, 521, 421, 531) engaged in a radially resilient sleeve (522, 622, 532, 632) clamped to said stud by a clamping ring (523 , 623, 533, 633) by contraction when said clamping ring is at cryogenic temperature, and releasing said pin when said clamping ring is at non-cryogenic temperature. 9 - Device according to one of claims 5 to 8 wherein the first cryogenic temperature in nominal operation is less than 10 K. 10 - Device according to one of claims 5 to 9 wherein the second cryogenic temperature in degraded operation is less than 80 K. 11 - Method for replacing a cold head (60) of a device (100) according to one of claims 8 to 10 without interruption of operation of the receiving chain by a cryogenic temperature maintenance components cooled in the cryostat (30), said method comprising disassembling the stopped cold head to be replaced by maintaining at least one other cold head in operation, said method comprising at least the steps of: - controlling the temperature in the cryostat, then when said temperature is substantially stabilized around the second degraded cryogenic temperature; - loosen screws immobilizing the sleeve flange (57), the barrel return (54), relative to the shell (43), fixed to the wall (31) of the cryostat, the cold head being fixed on the head flange cold (56) solidarisant the sheath (51) and said sheath return; - Applying a tensile force on the cold head (60), still attached to the sleeve (51), to a partial extraction of said sleeve, the cavity of the cryostat, permitted by an elongation of the extensible fitting (55) sealed; - Measuring the temperature of the sleeve (51), following the partial extraction of said sleeve, the thermal bridges (52, 53) are no longer in contact with still cooled parts of the device; when the temperature of the sleeve (51) has reached or exceeded a dew point temperature in the environment of the cryostat, breaking the vacuum in said sleeve, detaching the cold head (60) from the cold head flange (56) and extracting the cold extension (61) of said sheath.