An antenna array for a transmit-array antenna system

Abstract

According to an example aspect of the present invention, there is provided an antenna array for a transmit-array antenna system with a fixed feed antenna, comprising an inner radiating surface for receiving a first signal from the fixed feed antenna, an outer radiating surface for emitting a second signal from the antenna array, and at least two platforms, wherein the at least two platforms are substantially parallel to one another and each of the at least two platform comprises multiple electrical integrated circuits, for operatively connecting the inner and outer radiating surfaces, the antenna array further comprising at least two thermally insulated heat pipes between adjacent platforms of the at least two platforms, wherein a first part of each thermally insulated heat pipe is arranged to transfer heat from one electrical integrated circuit or two consecutive electrical integrated circuits of one platform to a second part of the thermally insulated heat pipe, and the second part of the thermally insulated heat pipe is substantially in a direction perpendicular to the normal of the inner and outer radiating surfaces and arranged to transfer heat from said one or two consecutive electrical integrated circuits to outside of the antenna array via a side of the antenna array to which the at least two platforms extend.

Description

AN ANTENNA ARRAY FOR A TRANSMIT-ARRAY ANTENNA SYSTEMFIELD

[0001] Embodiments of the present invention relate in general to an antenna array and in particular to an antenna array for a transmit-array system.BACKGROUND

[0002] An antenna array comprises multiple antennas for transmission or reception of radio waves. In an antenna array multiple antennas are connected and arranged such that the antennas are used in cooperation to basically work as a single transmitter or receiver at a time. In general, antenna arrays may be used to achieve higher gains, by exploiting a narrower beam of radio waves compared to transmitting or receiving with a single antenna. Antenna arrays may also be used, for example, to improve reliability by utilizing two or more wireless communication channels with different characteristics, and to mitigate interference coming from certain directions.

[0003] In the field of wireless communications beamforming generally refers to directing transmission or reception of radio signals using an antenna array. Direction of transmission or reception may be controlled by modifying the phase and amplitude of a signal at each antenna to increase the performance of transmission or reception for a single wireless signal.

[0004] Exploitation of millimetre waves is one aspect considered for improving the performance of wireless communication systems, because it enables the use of additional frequency spectrum. The use of higher frequencies makes building of antenna arrays comprising more antennas feasible as well, which can be used to enhance achievable gain. The achievable gain depends, at least partly, on the used antenna array. In some applications it is also desirable to have a large beam steering angle range.

[0005] However, at least in some antenna arrays and applications thereof, considerable heat may be generated and accumulated which may be problematic for theoptimal operation of said antenna array. There is therefore a need to provide cooling for an antenna array, in particular for a transmit-array system.SUMMARY OF THE INVENTION

[0006] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0007] According to an aspect of the present invention, there is provided an antenna array for a transmit-array antenna system with a fixed feed antenna, comprising an inner radiating surface for receiving a first signal from the fixed feed antenna, an outer radiating surface for emitting a second signal from the antenna array, and at least two platforms, wherein the at least two platforms are substantially parallel to one another and each of the at least two platform comprises multiple electrical integrated circuits, for operatively connecting the inner and outer radiating surfaces, the antenna array further comprising at least two thermally insulated heat pipes between adjacent platforms of the at least two platforms, wherein a first part of each thermally insulated heat pipe is arranged to transfer heat from one electrical integrated circuit or two consecutive electrical integrated circuits of one platform to a second part of the thermally insulated heat pipe, and the second part of the thermally insulated heat pipe is substantially in a direction perpendicular to the normal of the inner and outer radiating surfaces and arranged to transfer heat from said one or two consecutive electrical integrated circuits to outside of the antenna array via a side of the antenna array to which the at least two platforms extend.

[0008] Embodiments of the present invention may comprise at least one feature from the following bulleted list or any combination of the following features:• wherein the at least two platforms extend to a direction perpendicular to the normal of the inner and outer radiating surfaces;• wherein the first part of each thermally insulated heat pipe is substantially in a direction of the normal of the inner and outer radiating surfaces;• wherein the first part of each thermally insulated heat pipe is at an angle, wherein the angle is defined between the normal of the platform and the normal of the innerradiating surface or the normal of the outer radiating surface, and the angle is between 0 and 90 degrees;• wherein a length of a first part of a first thermally insulated heat pipe arranged to transfer heat from a centre of one platform is longer than a length of a first part of a second thermally insulated heat pipe arranged to transfer heat from closer to an edge of said one platform than the first thermally insulated heat pipe;• wherein a length of a second part of a first thermally insulated heat pipe arranged to transfer heat from a centre of one platform is longer than a length of a second part of a second thermally insulated heat pipe arranged to transfer heat from closer to an edge of said one platform than the first thermally insulated heat pipe;• wherein at least one of the at least two thermally insulated heat pipes comprises a first non-insulated end and a second non-insulated end, wherein the first noninsulated end is attached to said one or two consecutive electrical integrated circuits and the second non-insulated end is located outside of the antenna array;• wherein the thickness of the at least two thermally insulated heat pipes is less than a distance between adjacent platforms;• wherein the at least two thermally insulated heat pipes are from 3 mm to 8 mm in thickness, and 10 cm to 30 cm in length;• wherein the antenna array comprises a support structure between adjacent platforms;• wherein the thickness of the support structure is from 2 mm to 15 mm;• wherein the at least two thermally insulated heat pipes comprise polyimide as thermal insulation;• the antenna array comprising a plurality of platforms arranged as a stack of platforms;• wherein the antenna array comprises 8 platforms and 8 electrical integrated circuits on said platforms, forming thereby an 8 x 8 array;• wherein said antenna array is configured to operate at an at least one frequency of at least 2 GHz, such as from 10 GHz to 40 GHz.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIGURE 1 illustrates a transmit-array antenna system in accordance with at least some embodiments of the present invention;

[0010] FIGURE 2 illustrates an antenna array in accordance with at least some embodiments of the present invention;

[0011] FIGURE 3 A illustrates one view of an antenna array in accordance with at least some embodiments of the present invention;

[0012] FIGURE 3B illustrates another view of an antenna array in accordance with at least some embodiments of the present invention;

[0013] FIGURE 4A illustrates top-down perspective of a first example of an antenna array capable of supporting at least some embodiments of the present invention;

[0014] FIGURE 4B illustrates a top-down perspective of a part of a second example antenna array capable of supporting at least some embodiments of the present invention; and

[0015] FIGURE 5 illustrates a sideview of an example antenna array capable of supporting at least some embodiments.EMBODIMENTS

[0016] Demand for additional frequency spectrum is constantly increasing and hence it is desirable to use higher, millimetre-wave frequencies for wireless communications. Such frequencies are considered, e.g., in the context of 5G and 6G networks and for future cellular networks as well. Nevertheless, the embodiments of the invention are not limited to cellular networks and can be exploited in any system that uses antenna arrays. Millimetre-wave frequencies can be used for all kinds of transmissions between wireless devices, including radio access and backhaul connections. The proposed antenna solution is applicable also at least to military communications and radar systems.

[0017] For example, wireless backhaul connections typically require high gain antennas to achieve the required signal-to-noise ratios. In some applications an antenna gain of 30 - 44dBi may be required. On top of this requirement the beam-steering range of the antennas should be as large as possible. Certain applications, such as, for example, mesh backhaul networks may require broad beam-steering angles, e.g., at least + / -30 degrees.

[0018] FIGURE 1 illustrates a transmit-array antenna system in accordance with at least some embodiments of the present invention. The transmit-array antenna system 10 maycomprise a fixed feed antenna 20 and an antenna array 100. The fixed feed antenna 20 may be, for example, a feed horn or a fixed beam antenna. The position of the antenna 20 may be fixed, i.e., the fixed feed antenna 20 does not move, or cannot be moved, during the operation. The antenna array 100 may comprise a waveguide transmit-array with monolithic microwave integrated circuits, MMICs, such as integrated phase shifters and, possibly amplifiers.

[0019] The antenna array 100 comprises an inner radiating surface 110 for receiving a first signal from the fixed feed antenna 20 and an outer radiating surface 120 for emitting a second signal from the antenna array 100. The inner radiating surface 110 and the outer radiating surface 120 may comprise end-fire type radiators. In some embodiments of the present invention an open-ended waveguide may be preferred. However, in some embodiments of the present invention other end-fire elements, such as, for example, dipole, yagi and Vivaldi may be preferred. A side of the antenna array 100 is denoted by 115.

[0020] In FIGURE 1, a denotes the distance between the fixed feed antenna 20 and the inner radiating surface 110, i.e., inner aperture, of the antenna array 100, b denotes the thickness of the antenna array 100 from the inner radiating surface 110 of the antenna array 100 to the outer radiating surface 120, i.e., outer aperture, of the antenna array 100 and c denotes the width of the antenna array 100.

[0021] The distance between the fixed feed antenna 20 and the inner radiating surface 110 may be denoted by the focal distance a and the width of the antenna array 100 may be denoted by c. The geometry of the antenna array 100 may be characterized by the a / c ratio, wherein D may be the diameter of the aperture of the antenna array 100. For example, dimensions of the antenna array 100 for the transmit-array antenna system 10 operating in E band (frequencies from 60 GHz to 90 GHz) may be between 30-100 mm for a, 5-20 mm for b and 20-150 mm for c. The width of the antenna array 100 of 20 mm may correspond to an antenna array of 8*8 unit cells while 150 mm may correspond to an antenna array of 60*60 elements.

[0022] The feed system of the transmit-array antenna system 10 may be considered as a spatial feeding technique, because the transmitted signal propagates in free space and resembles light in character and behaviour. Such feeding techniques do not suffer from feed line losses which are pronounced in millimetre-wave frequencies like planar antenna array feeding networks. Hence, large and varying losses in the feed system may be avoided, whena large antenna array is implemented. Consequently, it is possible to reduce limitations related to the size of the antenna array 100 imposed by complex and lossy feed networks. The inner radiating surface 110 of the antenna array 100 may be illuminated by a spatial feeding technique using the fixed feed antenna 20 and hence the feed network of the antenna array 100 does not set any limitation to the size of the antenna array 100. Thus, very high antenna gains are feasible. On the other hand, the amplitude and phase of each antenna element on the outer radiating surface 120 of the antenna array 100 may be controlled at the input of the element. Therefore, the direction of the antenna beam can be steered and the achieved beam-steering angle range may be equal to a phased array antenna. The use of phase-shifters, as well as other radio frequency circuits RFICs and / or monolithic microwave integrated circuits, MMICs, may however, cause heat build-up and accumulation, which may be especially problematic for centre regions of an antenna array, for example, having a stacked configuration transmit-array having a plurality of platforms, such as PCBs stacked on top of one another.

[0023] The antenna array 100 may be configured to operate at an at least one frequency of at least 2 GHz, such as 10 GHz to 40 GHz. In such cases, for example, heat may build-up especially near centre portions of the antenna array 100. Because of the relatively small dimensions of such operational devices, such as waveguides, heat build-up may be mitigated with at least some embodiments of the present disclosure.

[0024] FIGURE 2 illustrates an antenna array accordance with at least some embodiments of the present invention. In FIGURE 2 the dashed lines 130 demonstrate platforms, such as a fin-line substrate Printed Circuit Board, PCB, which are set horizontally in each row of the antenna array 100. The example of FIGURE 2 presents an antenna array 100 with 8*8 unit cells 140, i.e., there are 8 unit cells 140 on the x-axis and 8 unit cells 140 on the y-axis.

[0025] In other words, one platform may connect all the unit cells 140 in one row of the antenna array 100. In some embodiments the platform may be set horizontally to the middle, or about middle, of the unit cell 140. The platform may be located equidistant from the inner radiating surface and the outer radiating surface of the antenna array. That is to say, platform 130 may be located about middle of the unit cell 140 in a longitudinal direction. The unit cell 140 may be referred to as a square waveguide or an open-ended waveguide as well.

[0026] In some embodiments the lengths of the x- and y-axes may be 20 mm, wherein the x-axis corresponds to parameter c in FIGURE 1. In such case the width x2 and length y2 of unit cells 140 would be 2.5 mm. The antenna array 100 of FIGURE 2 comprises 64 open- ended square unit cells installed in an 8*8 matrix form. One ends of each unit cells 140 may form an inner antenna array (inner radiating surface 110, which is closer to the fixed feed antenna 20) and the other ends of each unit cell 140 may form an outer antenna array (outer radiating surface 120, which is further away from the fixed feed antenna 20 than the inner radiating surface 110). Each unit cell 140 may comprise a first antenna element on the inner radiating surface 110 of the antenna array 100 and a second antenna element on the outer radiating surface 120 of the antenna array 100.

[0027] Distance x3 between two platforms 130 may be equal to the width x2 of a unit cell 140. So as an example, if the width x2 of a unit cell 140 is 2.5 mm, then the distance x3 between two platforms 130 may be 2.5 mm as well. The thickness of a metallic waveguide wall between consecutive unit cells 140 may be taken into account in the calculation.

[0028] In general, “vertical” is to be understood as a direction defined by the column, namely the direction in which the elements of the column are stacked on each other (denoted by x in FIGURE 2). On the other hand, “horizontal” is to be understood as a direction defined by the row (denoted by y in FIGURE 2), namely the direction in which the elements of the row are stacked on each other. One platform, such as a PCB, may connect all the inner and outer radiating elements of one column or row to each other. Thus, FIGURE 2 demonstrates an embodiment, wherein one platform, such as a PCB, connects unit cells 140 horizontally. However, in some embodiments one PCB may be set vertically for connecting the inner and outer radiating elements of unit cells 140 of one row.

[0029] The antenna array 100 may be used for beam steering, for example, by using a plurality of MMICs, comprised in the antenna array 100. Such an antenna array, however, produces heat during operation, and in the event of a large array and / or high frequencies, and thereby small dimension of unit cells 140, may be problematic to mitigate. At least in some antenna arrays and applications thereof, considerable heat may be generated and accumulated which may be problematic for the optimal operation of said antenna array. Embodiments of the present invention therefore provide cooling for an antenna array, such as the antenna array 100, in particular for the transmit-array antenna system 10.

[0030] For example, beam steering requires many MMICs (e.g., amplifiers) that produce lots of heat within the antenna array 100. Due to the structure, especially during operation, or prolonged operation of the antenna array 100, the coolest part of the antenna array 100 is the outer edge of the supporting structure. Moreover, the MMICs in the center of the antenna array 100 would be the hottest.

[0031] In some embodiments of the present invention, the inner radiating surface 110 and outer radiating surface 120 of the antenna array 100 may be connected to each other by at least one platform 130, for example a Printed Circuit Board, PCB. The at least one platform 130 may be located perpendicular to the two radiating surfaces 110 and 120. In general, the number of platforms 130 may be equal to the number columns or rows of the antenna array 100, depending on whether the platforms 130 are set vertically or horizontally in the array antenna 100. At least some embodiments of the present disclosure comprise multiple MMICs comprised in such platforms. An antenna array 100 according to at least some embodiments therefore comprises at least two such platforms 130 comprising each said MMICs.

[0032] A plurality of devices and components may generate and accumulate heat in the antenna array 100, e.g., due to multiple MMICs and operation thereof. In some embodiments, each of the multiple MMICs comprises at least one of a power amplifier, a low-noise amplifier or a phase shifter. For example, each of the multiple MMICs may include a power amplifier, a low noise amplifier and a phase shifter. As the MMICs operatively connect the inner radiating surface 110 and the outer radiating surface 120, heat may accumulate due to the operation of said MMICs. For example, phase shifters utilized for beam-steering generate heat as a by-product of their operation which may not necessarily be easily re-located or transferred, for example, in a compact structure (i.e., a structure having “closely-packed” RFICs, MMICs and / or other components). Therefore, thermal management and cooling may be especially important at least in such circumstances.

[0033] In some embodiments, one platform 130 may connect unit cells 140 of a column or row of the antenna array 100. Moreover, the platform 130 may comprise one or more MMICs for each unit cell 140. For example, such MMICs may comprise a phase shifter and, possibly, an amplifier. In some embodiments the phase shifter may be a vector modulator type phase shifter and it may be used for providing a continuous control of a phase and amplitude of a signal. Furthermore, in some embodiments the amplifier may be a PowerAmplifier and Low-Noise Amplifier, PALNA, amplifier, which may be used with vector modulators for enabling a bi-directional operation (reception and transmission) using the same antenna array.

[0034] In some embodiments, at least two platforms 130 of the antenna array 100 may be substantially parallel to one another, and the at least two platforms 130 may be perpendicular to the normal of the inner radiating surface 110 and the normal of the outer radiating surface 120. Substantially, as used here, it is to be understood that said at least two platforms 130 are parallel such that their surface normal vectors deviate from one another less than 10 degrees, or less than 5 degrees, such as less than 1 degrees, for example 0 degrees.

[0035] FIGURE 3 A illustrates one view of an antenna array in accordance with at least some embodiments of the present invention. The antenna array 100 of FIGURE 3 A comprises multiple platforms 130a-h. Each of the multiple platforms 130a-h comprises a plurality of MMICs 150 on, or integrated to, the platforms 130a-h of the antenna array 100. FIGURE 3A illustrates an antenna array 100 of size 8*8, which comprises 64 MMICs, one for each unit cell 140 illustrated in FIGURE 2.

[0036] With reference to FIGURE 1, the antenna array 100 comprises the inner radiating surface 110 and the outer radiating surface 120 at opposing faces of the antenna array 100. Sides of the antenna array 100 are denoted by 115a and 115b. The sides 115a and 115b are the sides to which the platforms 130a-h extend. That is, in the example of FIGURE 2, the sides 115a and 115b would be the sides in the horizontal direction. However, in some embodiments, the sides 115a and 115b would be the sides in the vertical direction, if the platforms 130a-h are in the vertical direction.

[0037] In FIGURE 3A, a support structure between two adjacent platforms 130 is denoted by 160. The antenna array 100 may comprise a support structure 160 between each adjacent platform 130. The support structure 160 may be arranged to provide structural support for the antenna array 100. As illustrated in FIGURE 3A, the platforms 130a-130h are arranged as a stack, forming thereby the antenna array 100 together with MMICs 150 and unit cells 140 of the antenna array 100. In other words, the antenna array 100 may comprise a stack of platforms 130a-130h, such as PCBs, as well as support structures 160 interleaved between two adjacent platforms 130.

[0038] The antenna array 100 may comprise a stacked configuration comprising a plurality of MMICs 150 on each of the plurality of platforms 130a-h, such that said platforms 130a-h form a stack. Moreover, the antenna array 100 may comprise the inner radiating surface 110 and the outer radiating surface 120 comprising waveguides on opposing surfaces. The normal of the inner surface 110 and the outer radiating surface 120 may be perpendicular to the stacked configuration, i.e., the platforms 130a-h may extend in a direction perpendicular to the normal of the inner radiating surface 110 and the outer radiating surface 120 of the antenna array 100.

[0039] In case of such a stacked configuration of the antenna array 100, heat may be profoundly generated and accumulated at the centre portion of the antenna array 100 but less at the edges of the antenna array 100. Such an uneven temperature distribution, or temperature gradient, may typically provide limitation on the size of the antenna array 100 and / or limit operation of the antenna array 100. Therefore, at least in some instances, the number of platforms 130a-h and / or number of MMICs 150 within a platform 130 may become limited due to heat build-up within such a construction. Thus, there is a need for heat management and cooling for the antenna array 100. FIGURE 3B illustrates another view of an antenna array in accordance with at least some embodiments of the present invention. More specifically, FIGURE 3B illustrates a side view of the antenna array 100, i.e., a view perpendicular to the inner radiating surface 110 and the outer radiating surface 120. The antenna array 100 of FIGURE 3B illustrates the antenna array 100 at the side of the outer radiating surface 120. As with FIGURE 3 A, the platforms 130a- 13 Oh are illustrated together with support structures 160a- 160g interleaved between the platforms 130a- 13 Oh.

[0040] FIGURE 4A illustrates a top-down perspective of a first example part of an antenna array capable of supporting at least some embodiments of the present invention. In FIGURE 4 A, the inner radiating surface 110 and the outer radiating surface 120 of the antenna array 100 are illustrated. The first example part of the antenna array comprises one platform 130 and support structure 160. The platform 130 further comprises multiple MMICs 150a-d. The part of the antenna array 100 may be a part of a larger structure, such as a stacked antenna array, such as the antenna array 100 of FIGURES 3 A and 3B.

[0041] In FIGURE 4A, a first thermally insulated heat pipe is denoted by 410a and a second thermally insulated heat pipe is denoted by 410b. The thermally insulated heat pipes 410a and 410b are between adjacent platforms 130 of the antenna array 100. That is, theantenna array 100 comprises another platform on top of the platform 130 illustrated in FIGURE 4 A and the thermally insulated heat pipes 410a and 410b are between the platform 130 and said another platform.

[0042] The first thermally insulated heat pipe 410a comprises a first part 412a and a second part 414a. The first part 412a of the first heat pipe 410a is arranged to transfer heat from two consecutive MMICs 150a and 150b of the platform 130 to the second part of 414a of the first heat pipe 410a. The second part 414a of the first thermally insulated heat pipe 410a is substantially in a direction perpendicular to the normal of the inner radiating surface 110 and the outer radiating surface 120 of the antenna array. The second part 414a of the first thermally insulated heat pipe 410a is arranged to transfer heat from the two consecutive MMICs 150a and 150b to outside of the antenna array 100 via the side 115a of the antenna array 100. Consecutive MMICs are to be understood as MMICs on a same platform and arranged next to one another. The platform 130 extends to the side 115a of the antenna array 100 from the side 115b of the antenna array. Moreover, the second parts of the thermally insulated heat pipes extend outside the antenna array 100 via the sides 115a, 115b of the antenna array 100.

[0043] As illustrated in FIGURE 4 A, the first part 412a of the first thermally insulated heat pipe 410a may be substantially in a direction of the normal of the inner radiating surface 110 and the outer radiating surface 120. Alternatively, the first part 412a of the first thermally insulated heat pipe 410a may be at an angle, wherein the angle is defined between the normal of the platform 130 and the normal of the inner radiating surface 110 or the normal of the outer radiating surface 120, and the angle is between 0 and 90 degrees (not depicted in FIGURE 4A).

[0044] In some embodiments, the first part 412a of the first thermally insulated heat pipe 410a may be towards a platform that is above the platform 130 illustrated in FIGURE 4 A. That is, the first part 412a of the first thermally insulated heat pipe 410a may be substantially in a direction of the normal of the platform 130, e.g., in a vertical direction in case of an antenna array comprising platforms 130 in a horizontal direction or in a horizontal direction in case of an antenna array comprising platforms 130 in a vertical direction. In such cases, the second part 414a of the first thermally insulated heat pipe 410a may be located in the support structure 160 between adjacent platforms, i.e., between unit cells.

[0045] The support structure 160 may be beneath, or above, the platform 130 to separate the platform 130 of FIGURE 4 A from an adjacent platform in the stacked configuration. The thermally insulated heat pipes 410a and 410b may be embedded, and / or traverse through, the support structure 130.

[0046] The second thermally insulated heat pipe 410b comprises a first part 412b and a second part 414b. Similarly, as in case of the first thermally insulated heat pipe 410a, the first part 412b of the second thermally insulated heat pipe 412b is arranged to transfer heat from two consecutive MMICs 150c and 150d of the platform 130 to the second part of 414b of the second thermally insulated heat pipe 410b. A length of the second part 414a of the first thermally insulated heat pipe 410a arranged to transfer heat from a centre of the platform 130 is longer than a length of the second part 414b of the second thermally insulated heat pipe 410b arranged to transfer heat from closer to an edge of the platform 130 than the first heat pipe 410a. The thermal insulation of the thermally insulated heat pipes 410a and 410b, for example in such embodiments, ensures that heat from other MMICs located at the platform 130 along or near the path of said thermally insulated heat pipe, do not at least greatly affect the heat transfer from the MMIC located in a centre of the platform, such as the MMIC 150a. Thus, efficient cooling of the antenna array 100 is enabled.

[0047] The thermally insulated heat pipes, such as thermally insulated heat pipes 410a and 410b, may be arranged to extend along the route along a plane parallel to the platform 130. That is, the thermally insulated heat pipes 410a and 410b may be arranged to extend along the route comprising a part that is substantially perpendicular to the normal of the inner radiating surface and the normal of the outer radiating surface and substantially parallel to the surface of the platform 130.

[0048] The thermally insulated heat pipes 410a and 410b may have an elongated geometry with a thermally insulated outer shell in at least a portion of the length of the heat pipes 410a and 410b. The elongated geometry is substantially along the platform and perpendicular to the surface normal of the inner radiating surface 110 and the outer radiating surface 120. Heat is therefore transferred from the MMICs 150a and 150b outside of the antenna array 100 along the platform via said thermally insulated heat pipe 410a extended along said platform 130. The thermally insulated heat pipes 410a and 410b are arranged along a plane parallel to the platform 130, and are configured such that they transfer heat outside the antenna array from two consecutive MMICs.

[0049] The term “heat pipe”, as to be understood in the context of the present disclosure, is a device designed to transfer heat. The heat pipe may comprise a structure having a hermetically sealed hollow outer shell. The heat may be transferred using a phasetransition within such a heat pipe. An example heat pipe structure comprises an elongated and thermally conducting outer shell as well as a phase transition substance delimited by said outer shell. In other words, heat pipe comprises a sealed exterior (i.e., an outer shell) that contains a substance that is configured to experience phase transitions. The outer shell material may comprise copper or alloys thereof, for example. The substance contained in a heat pipe may be a volatile liquid (and vapor thereof), or water, for example. In some embodiments, a heat pipe may comprise a tubular structure.

[0050] In some embodiments, the thermally insulated heat pipes comprise a liquid or gas as phase transition material.

[0051] The term “vapor chamber”, occasionally also known as a “planar heat pipe” is to be understood as a heat device, having a planar geometry for heat transfer. Because of at least their geometry, vapor chambers may be problematic for transferring heat from a singular location and / or a pinpointed location. As such, such structures are at least typically used for a large planar areas and large planar surfaces.

[0052] The term “thermally insulated heat pipe” as used in the context of the present disclosure is to be understood as a heat pipe which is configured such that it is at least in part thermally insulated from the surroundings of said heat pipe. In some embodiments, a thermally insulated heat pipe may comprise a thermally insulated middle portion as well as a non-insulated first end and / or a non-insulated second end. As such, a thermally insulated heat pipe comprises a heat pipe having a thermal insulator on the outer shell of said heat pipe, or portion(s) thereof. It is further noted that a person skilled in the relevant art understands that thermal insulation and effectiveness thereof, depends on the use case, and as such absolute thermal insulation is not necessarily applicable. In some embodiments, the thermally insulated heat pipe comprises polyimide, e.g., with 0.12 W / (mK), as thermal insulation.

[0053] The first thermally insulated heat pipe 410a may comprise a thermally insulated middle portion, as well as a non-insulated first end 416a and a non-insulated second end 418a. Similarly, the second heat pipe 410b may comprise a thermally insulated middle portion, as well as a non-insulated first end 416b and a non-insulated second end 418b. Thenon-insulated first ends 416a and 416b of the first heat pipe 410a and the second thermally insulated heat pipe 410b may be attached to two consecutive MMICs so as to thermally conduct and transfer heat from, and / or generated by, said MMICs, to outside of the antenna array 100. Thus, heat may be transferred via a thermally insulated heat pipe, namely the thermally insulated middle portion of such a heat pipe, without being affected by, or significantly affected by other MMICs of the antenna array 100.

[0054] Furthermore, as the heat pipes are thermally insulated from one another at least in the middle portions of said thermally insulated heat pipes, the effect of heat transfer of such a thermally insulated heat pipe is sufficiently unaffected regarding other thermally insulated heat pipes or MMICs, and heat thereof. Thus, a temperature gradient is maintained along the thermally insulated heat pipe. This may be especially beneficial for MMICs located in the centre portion of the antenna array 100, wherein heat build-up and accumulation may be otherwise significant, and cooling may be needed. Thus, the first part 412a of the first thermally insulated heat pipe 410a, having the first end 416a closer to the centre of the antenna array 100, is longer than the first part 412b of the second thermally insulated heat pipe 410b having the first end 416b closer to the edge of the antenna array 100, i.e., the side 115a.

[0055] In some embodiments, the ends of a thermally insulated heat pipe may be at least in part thermally exposed. In other words, the ends of a thermally insulated heat pipe in accordance with at least some embodiments lack thermal insulation. A benefit of such a construction is that heat may be transferred more effectively from the antenna array 110 to the outside of the antenna array 110 than using non-insulated heat pipes. It may be beneficial to obtain a direct contact between two MMICs, such as MMICs 105a and 105, and a noninsulated first end of a thermally insulated heat pipe, such as the end 416a of the first thermally insulated heat pipe. However, it is noted that although in some embodiments the non-insulated first ends of thermally insulated heat pipes may be in physical contact to two consecutive MMICs, in other embodiments a portion of a heat pipe, such as the first end, may not necessarily be in such a direct contact. In other words, the first end of a thermally insulated heat pipe may be near two consecutive MMICs so as to transfer heat from, and generated by, said consecutive MMICs.

[0056] FIGURE 4B illustrates a top-down perspective of a part of a second example antenna array capable of supporting at least some embodiments of the present invention. Thepart of the second example antenna array 100 is otherwise the same as the part of the first example antenna array 100 illustrated in FIGURE 4B, but in the part of the second example antenna array 100 each thermally insulated heat pipe is arranged to transfer heat from one MMIC to outside of the antenna array 100.

[0057] The first part 412a of the first thermally insulated heat pipe 410a is arranged to transfer heat from one MMICs 150a of the platform 130 to the second part of 414a of the first heat pipe 410a. The second part 414a of the first heat pipe 410a is arranged to transfer heat from the MMIC 150a to outside of the antenna array 100 via the side 115a of the antenna array 110. Similarly, the first part 412b of the second thermally insulated heat pipe 410b is arranged to transfer heat from one MMICs 150b of the platform 130 to the second part of 414b of the second thermally insulated heat pipe 410b. The second part 414b of the second thermally insulated heat pipe 410b is arranged to transfer heat from the MMIC 150b to outside of the antenna array 100 via the side 115a of the antenna array 110.

[0058] A benefit of thermally insulated middle portions of thermally insulated heat pipes, such as those depicted in FIGURES 4A and 4B, is that heat accumulated from other MMICs do not affect, or merely marginally affect, the heat transfer properties of the thermally insulated heat pipe. Therefore, heat may be thermally conducted outside of the antenna array 100 with an improved temperature gradient along a heat pipe. In other words, the temperature gradient within the heat pipe stays sufficiently large for heat transfer, whereas heat transfer between the middle portion and surroundings of the heat pipe is reduced and / or minimized.

[0059] In accordance with the present disclosure, in at least some embodiments the decrease in “hot spot” temperature of an antenna array 100 allows scaling to larger antenna arrays and transmit-arrays. In other words, larger number of MMICs 150a-d may be incorporated to the antenna array 100 because of the disclosed cooling and heat management. The use of thermally insulated heat pipes minimizes heat transfer to and from outside of said thermally insulated heat pipe along the length of the thermally insulated portion. Without such thermal insulation, a heat pipe would transfer heat on the whole length of the heat pipe and thermal gradient along the length of the heat pipe would be lower, thereby reducing the effectiveness of heat transfer outside the antenna array 100.

[0060] FIGURE 5 illustrates a sideview of an example antenna array capable of supporting at least some embodiments. FIGURE 5 illustrates an antenna array 100comprising at least three platforms. The platform 130 comprises MMICs 150a and 150b, the support structure 160 and the thermally insulated heat pipe 410a. The thermally insulating heat pipe 410a is within the support structure 160a, respectively. Similarly, thermal management and heat transfer may be needed from a plurality of MMICs of an antenna array.

[0061] The thermally insulated heat pipe 410a comprises a first end 416a and the thermally insulated heat pipe 410a is arranged such that the first end 416a is attached to two MMICs 150a and 150b. In other words, the first end 416a of the thermally insulated heat pipe 410a is attached to two MMICs 150a and 150b. A first part of the thermally insulated heat pipe 410a is connected to the first end 416a and the first part of the thermally insulated heat pipe 410a is arranged to transfer heat from the MMICs 150a and 150b to a second part 414a of the thermally insulated heat pipe 410a. The second part 414a of the thermally insulated heat pipe 410a extends outside the antenna array 100 via the side 115b to which the platforms extend.

[0062] The interleaved construction of an antenna array, such as the interleaved construction of the antenna array 100 depicted, may limit thermal conductivity and cooling options between said interleaved layers, as plurality of interfaces along such a path are present. Therefore, heat conduction along routes parallel to platforms, or routes along such a platform, may be feasible for thermal management of the antenna array 100. Therefore in at least some embodiments, the thermally insulated heat pipes 410a, 410b extend along a route substantially parallel to the platform 130, such as a PCB, such that said thermally insulated heat pipes 410a and 410b, or second parts 414a and 414b of said thermally insulated heat pipes 410a and 410b, respectively, are substantially perpendicular to the inner and outer radiating surfaces 110 and 120 of the antenna array 100.

[0063] With especially large antenna arrays having a large number of platforms and / or MMICs therein, significant heat may be formed and accumulated within, for example, a centre portion of such a large antenna array. This heat formation may be especially prominent at a centre portion of an antenna array 100 operating at high frequencies and having small dimensions of MMICs and waveguides attached thereto. Therefore, for example, the embodiments of the present disclosure may be beneficial in mitigating such heat formation and accumulation by transferring heat from MMICs and their surroundings to outside the antenna array 100.

[0064] In at least some embodiments, thermally insulated heat pipes may be at least in part integrated and / or embedded to support structures between two adjacent platforms of an antenna array. Such support structures may comprise, for example, aluminium or brass as a material. In some embodiments a thickness of a support structure is from 2 mm to 15 mm. At least in some embodiments, a thermally insulated heat pipe, or plurality thereof, may be embedded to, or otherwise extend through, such a support structure, whereby dimension of a thermally insulated heat pipe is delimited by the thickness of the support structure. In some embodiments, the thickness of the at least two thermally insulated heat pipes is less than a distance between adjacent platforms and / or less than the thickness of the support structure therebetween. The at least two thermally insulated heat pipes may be from 3 mm to 8 mm in thickness, and 10 cm to 30 cm in length. It is noted that 3 mm is not a lower limit for the thickness though. The thickness of a heat pipe may refer to an outer diameter of the heat pipe.

[0065] Thermally insulated heat pipes in accordance with the present disclosure may have varying configurations, routes and arrangements through which heat transfer may be achieved. For a stacked configuration of an antenna array, heat transfer outside antenna array may not necessarily be applicable along the normal of the inner radiating surface or the outer radiating surface because such an approach may hinder the operation of the antenna array, for example. Alternatively, heat transfer along the stacking direction of a stacked transmitarray may not necessarily be applicable because of the plurality of interfaces and structures. As such, in at least some embodiments, the thermally insulated heat pipes are arranged to traverse along a platform perpendicular to the radiating surfaces, and along a platform of the antenna array.

[0066] It is noted that even though MMICs are used as an example in various embodiments of the present disclosure, said embodiments of the present disclosure may be applied similarly for RFICs, or any other suitable electrical integrated circuits in general. That is, MMICs are used as an example of electrical integrated circuits which are suitable for operatively connecting the inner and outer radiating surfaces, such as RFICs.

[0067] For example, MMICs may be defined as electrical integrated circuits operating on a frequency range comprising frequencies substantially from 300 MHz to substantially 300GHz. RFICs may be defined as electrical integrated circuits which are suitable forwireless transmission and reception. In some embodiments, there may be multiple circuits in serial on a path of a signal from the inner radiating surface to the outer radiating surface.

[0068] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0069] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

[0070] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0071] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0072] While the forgoing examples are illustrative of the principles of the presentinvention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0073] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e. a singular form, throughout this document does not exclude a plurality.INDUSTRIAL APPLICABILITY

[0074] At least some embodiments of the present invention find industrial application in wireless communication systems. An antenna array described herein may be utilized for enabling wireless communications between various devices. The wireless communications may comprise communications between a user device, for example a smart phone, and a base station of a communications network. The wireless communications may also comprise backhaul connections between base stations or between a base station and a relay node. In addition to wireless communications the concept of the presented invention can be applied to radar antennas.ACRONYMS LISTIC integrated circuitMMIC monolithic microwave integrated circuitPCB printed circuit boardPALNA power amplifier and low-noise amplifierRF radio frequencyRFIC radiofrequency integrated circuitWLAN wireless local area networkREFERENCE SIGNS LIST

Claims

CLAIMS:

1. An antenna array for a transmit-array antenna system with a fixed feed antenna, comprising: an inner radiating surface for receiving a first signal from the fixed feed antenna, an outer radiating surface for emitting a second signal from the antenna array, and at least two platforms, wherein the at least two platforms are substantially parallel to one another and each of the at least two platform comprises multiple electrical integrated circuits, for operatively connecting the inner and outer radiating surfaces, the antenna array further comprising: at least two thermally insulated heat pipes between adjacent platforms of the at least two platforms, wherein a first part of each thermally insulated heat pipe is arranged to transfer heat from one electrical integrated circuit or two consecutive electrical integrated circuits of one platform to a second part of the thermally insulated heat pipe, and the second part of the thermally insulated heat pipe is substantially in a direction perpendicular to the normal of the inner and outer radiating surfaces and arranged to transfer heat from said one or two consecutive electrical integrated circuits to outside of the antenna array via a side of the antenna array to which the at least two platforms extend.

2. The antenna array according to claim 1, wherein the at least two platforms extend to a direction perpendicular to the normal of the inner and outer radiating surfaces.

3. The antenna array according to claim 1 or claim 2, wherein the first part of each thermally insulated heat pipe is substantially in a direction of the normal of the inner and outer radiating surfaces.

4. The antenna array according to claim 1 or claim 2, wherein the first part of each thermally insulated heat pipe is at an angle, wherein the angle is defined between the normal of the platform and the normal of the inner radiating surface or the normal of the outer radiating surface, and the angle is between 0 and 90 degrees.

5. The antenna array according to any one of the preceding claims, wherein a length of a first part of a first thermally insulated heat pipe arranged to transfer heat from a centre of oneplatform is longer than a length of a first part of a second thermally insulated heat pipe arranged to transfer heat from closer to an edge of said one platform than the first thermally insulated heat pipe.

6. The antenna array according to any one of the preceding claims, wherein a length of a second part of a first thermally insulated heat pipe arranged to transfer heat from a centre of one platform is longer than a length of a second part of a second thermally insulated heat pipe arranged to transfer heat from closer to an edge of said one platform than the first thermally insulated heat pipe.

7. The antenna array according to any one of the preceding claims, wherein at least one of the at least two thermally insulated heat pipes comprises a first non-insulated end and a second non-insulated end, wherein the first non-insulated end is attached to said one or two consecutive electrical integrated circuits and the second non-insulated end is located outside of the antenna array.

8. The antenna array according to any one of the preceding claims, wherein the thickness of the at least two thermally insulated heat pipes is less than a distance between adjacent platforms.

9. The antenna array according to any one of the preceding claims, wherein the at least two thermally insulated heat pipes are from 3 mm to 8 mm in thickness, and 10 cm to 30 cm in length.

10. The antenna array according to any one of the preceding claims, wherein the antenna array comprises a support structure between adjacent platforms.

11. The antenna array according to claim 8, wherein the thickness of the support structure is from 2 mm to 15 mm.

12. The antenna array according to any one of the preceding claims, wherein the at least two thermally insulated heat pipes comprise polyimide as thermal insulation.

13. The antenna array according to any one of the preceding claims, comprising a plurality of platforms arranged as a stack of platforms.

14. The antenna array according to any one of the preceding claims, wherein the antenna array comprises 8 platforms and 8 electrical integrated circuits on said platforms, forming thereby an 8 / 8 array.

15. The antenna array according to any one of the preceding claims, wherein said antenna array is configured to operate at an at least one frequency of at least 2 GHz, such as from 10 GHz to 40 GHz.

Images