Improved hemispherical array antenna

Abstract

The present invention relates to an array antenna (1) comprising: a hemispherical radome (10); a plurality of radiating elements (20) carried by the radome; a plurality of transmitting / receiving modules (30), carried by the radome, each radiating element being associated with a transmitting / receiving module and electrically connected thereto. It is characterized by a common radiocommunication module, provided with a common antenna (44), placed at the center of the radome and connected to transmitting / receiving electronics of the common radiocommunication module, each transmitting / receiving module (30) comprising a communication module, equipped with an elementary antenna for bidirectional radiofrequency communication with the common radiocommunication module (40).

Description

[0001] The present invention relates to three-dimensional array antennas and, more particularly, to hemispherical array antennas.

[0002] As for example presented in patent application FR No. 22 05733, the radiating elements of an array antenna can be arranged on a curved support surface, in particular hemispherical.

[0003] Each radiating element is controlled by a transmit / receive module (or TR module). In the following, to simplify the description, we consider that a TR module is associated with a single radiating element. However, as a variant, a TR module can control a certain number of radiating elements.

[0004] A TR module is mounted immediately behind the associated radiating element, i.e. for example on an inner face of the support surface when the radiating elements are arranged on an outer face of this support surface.

[0005] Conventionally, each TR module is connected to low-level control electronics by a wired connection, such as a coaxial cable or an optical fiber. This connection allows the transmission chain of the TR module to receive the transmission signal to be transmitted and to shape it (amplification and / or phase shift) before applying it to the radiating element to emit an electromagnetic wave. This connection allows the transmission to the control electronics of the reception signal corresponding to an electromagnetic wave captured by the radiating element and processed (amplification and / or phase shift) by the reception chain of the TR module. This connection also allows the controllable components of the TR module to be controlled to compensate for a bias and / or participate in beam formation.

[0006] However, in the case of a hemispherical array antenna, such an arrangement has various disadvantages.

[0007] In particular, the internal volume delimited by the support surface is reduced, which makes the wiring of the TR modules extremely delicate to carry out. This is a manual operation that cannot be automated. This limits productivity, but above all the reproducibility of the manufactured network antennas. Each network antenna therefore requires a complex calibration operation.

[0008] The aim of the present invention is therefore to propose a network antenna making it possible to overcome these problems.

[0009] To this end, the invention relates to an array antenna comprising: a hemispherical radome, with center C and radius R; a plurality of radiating elements, the radiating elements being carried by the radome; a plurality of transmission-reception modules, the transmission-reception modules being carried by the radome, each radiating element being associated with a transmission-reception module and electrically connected to it by one or more power supply links, characterized in that the array antenna further comprises: a common radiocommunication module, provided with a common antenna, placed at the center C of the hemispherical radome and connected to transmission-reception electronics of the common radiocommunication module, each transmission-reception module comprising a communication module, equipped with an elementary antenna for bidirectional radiofrequency communication with the common radiocommunication module.

[0010] According to other advantageous aspects of the invention, the network antenna comprises one or more of the following characteristics, taken individually or in all technically possible combinations: the face radially inside the radome is a metallic layer electromagnetically insulating a cavity inside the radome. the cavity is provided with an electromagnetic wave absorption device to reduce background noise. the absorption device is a meta-material covering a floor of the cavity. the meta-material consists of the stack of a reflection layer, an absorption layer and a metallic plane, the metallic plane being perforated so as to present a periodic pattern adapted to trap the radiofrequency waves in the thickness of the meta-material according to their polarization. the common antenna is an omnidirectional antenna, having in any plane passing through an axis of symmetry of the array antenna an opening of at least 170° for an attenuation of -12dB. the common antenna is a "patch" type antenna.the radiating elements are covered with a matching layer, itself covered with a protective layer. in transmission, the common antenna emits a transmission signal that each transmission-reception module collects in order to be transmitted. in reception, the elementary reception signal at the output of each transmission-reception module is re-emitted in the cavity towards the common antenna, the different elementary reception signals superimposing themselves in the cavity so as to form an overall reception signal, the common antenna collecting the overall reception signal.

[0011] The invention will appear more clearly on reading the description which follows, given solely by way of non-limiting example, and made with reference to the drawings in which: there figure 1 is a perspective and partially exploded view of a preferred embodiment of an array antenna according to the invention; figure 2 is a partial cross-sectional representation of the radome structure of the array antenna of the figure 1 ; there figure 3 is a schematic representation in the form of functional blocks of the antenna of the figure 1 ; there figure 4 is a graph illustrating the radiation pattern of the central antenna of the array antenna of the figure 1 ; and, the figure 5 is a perspective and partial sectional representation of the absorption plane constituting the floor of the network antenna of the figure 1

[0012] The invention is based on the implementation of wireless communication, preferably radio frequency - RF, between each transmission / reception module of the network antenna and a central, common antenna, connected to the low-level electronics for controlling the network antenna.

[0013] In the embodiment of the Figure 1 , the network antenna 1 comprises a hemispherical radome 10.

[0014] The radome 10 takes the general shape of a half-sphere, with center C and radius R. It is delimited by a median plane P, constituting the floor of the antenna 1.

[0015] The axis A, normal to the plane P at the center C, is an axis of symmetry of revolution of the network antenna 1.

[0016] Radome 10 is for example a polyhedron with triangular facets inscribed in the half-sphere with center C and radius R. Alternatively, it is a question of hexagonal, or pentagonal, facets, or the equivalent.

[0017] On the figure 2 , illustratively, three adjoining facets, 10 i-1 , 10 i and 10 i+1 , of the radome 10 are represented in section along a plane passing through the axis A. i is an integer between 1 and N, total number of facets, but also of radiating elements and of TR modules.

[0018] A 10 i facet results from the superposition of several layers.

[0019] The junction of the layers of the different facets defines a plurality of layers in the radome, such as, from the inside to the outside of the hemisphere, a metallized layer 12, a substrate 14, an adaptation layer 16, and a protection layer 18.

[0020] The continuous metallized layer 12 defines a half-sphere, which delimits, externally, a radiation space 2 of the network antenna 10 and, internally, a cavity 4. The metallized layer makes it possible to electromagnetically isolate the volume of the cavity 4 from the space 2.

[0021] The metallized layer 12 is advantageously used to define a ground plane for the TR modules and the radiating elements.

[0022] The substrate layer 14 is made of dielectric material whose relative permittivity is adjusted.

[0023] The adaptation layer 16 is for example made of a radiofrequency foam having a relative permittivity close to unity. This is for example the Rohacell ®< HF / WF material.

[0024] The outer layer 18 is for example made of a material having mechanical properties suitable for providing the desired mechanical resistance and protecting the radiating elements from external aggression. This is for example the FR-4 material.

[0025] The radome 10 carries a plurality of radiating elements 20 and a plurality of TR modules 30, each TR module being associated with a radiating element in the present embodiment.

[0026] A radiating element 20 is for example a planar antenna (or “patch” antenna), single or multiport.

[0027] For example, each radiating element 20 of the array antenna 1 is carried by a facet. A radiating element 20 is for example arranged in the center of a facet. Advantageously, as shown in the figure 2 , each radiating element 20 i is mounted on an external face of the substrate 14 and is covered with the material constituting the adaptation layer 16.

[0028] There figure 3 is a schematic electrical representation of the antenna 1. Each TR module, such as the TR module 30 i, is for example a printed circuit integrating a transmission chain 32 i and a reception chain 33 i connected, via a duplexer 31 i , to the ports of the radiating element 20 i , by one or more supply lines.

[0029] Each TR module 30 i is mounted behind the associated radiating element 20i. It is for example mounted on an internal face of the metal layer 12, as shown in the figure 2 . It is therefore located inside cavity 4.

[0030] Advantageously, an additional support layer is provided on the inner side of the metallized layer 12 to support the electronics, in particular the TR modules 30 i and their power supply lines.

[0031] Vias are provided through the metal layer 12 and the substrate 14 to allow the passage of the power supply lines electrically connecting the TR module 30 i and the associated radiating element 20 i.

[0032] According to the invention, each TR module 30 i is provided with an elementary radiocommunication module 36 i for communication, inside the cavity 4, with a common radiocommunication module 40. The module 36 i is connected to the input of the transmission chain 32 i and to the output of the reception chain 33 i of the TR module 30 i.

[0033] An elementary radiocommunication module 36 i is equipped with an elementary radiofrequency antenna - RF 34 i.

[0034] As shown in the figure 3 , the network antenna 10 comprises a common radiocommunication module 40.

[0035] It allows two-way radio frequency communication with each of the 36 i radio communication modules of the TR modules 30 i.

[0036] The module 40 is equipped with a common antenna or source 44 and suitable electronics.

[0037] Communication must allow: in uplink communication, the transmission of the transmission signal SE from the source 44 to each TR module 30 i; in downlink communication, the reception of the reception signal SR i from each TR module 30 i to the source 44; and advantageously, in uplink communication, the exchange of additional information for controlling the TR modules, from the source 40 to each TR module 30 i (phase shift φ i and gain A i of the controllable components of the transmission and reception chains to perform beamforming, compensate for biases, etc.).

[0038] In the particular embodiment illustrated in the figure 3 , the electronics of the module 40 comprises a circulator 41 connecting transmission means and reception means, on the one hand, and the antenna 44, on the other hand.

[0039] In this embodiment, the communication between the module 40 and each TR module 30 i is carried out along a dedicated channel, characterized by a particular frequency F i .

[0040] Consequently, the module 40 comprises a transmission / reception unit 70 i for addressing in transmission and reception each TR module 30 i .

[0041] Each unit 70 i comprises a waveform generator 73 i , capable of generating a suitable individual transmission signal SE i .

[0042] The different units 70 i are connected to the input of a summer 43, the output of which is connected to the circulator 41. The antenna 44 thus emits a global signal SE resulting from the sum of the individual emission signals SE i .

[0043] The antenna 44 is connected to the input of a distributor 42, the output of which is connected to the input of each of the units 70 i , so as to apply to each module the global reception signal SR resulting from the sum of the individual reception signals SR i picked up by the antenna 44.

[0044] The input of a 70 i module comprises a 72 i filter, centered on the characteristic frequency F i of the corresponding channel, so as to isolate the individual reception signal SRj.

[0045] A 74i demodulator then allows the SRj signal to be demodulated, possibly taking into account the waveform generated by the corresponding 73i generator.

[0046] The raw signal is then transmitted to a conventional processing chain.

[0047] In transmission, the module 40 transmits to the transmission-reception module 30 i, at the start of a recurrence period, the transmission signal SEj, then, at the end of the recurrence period, different control signals so that the module 30 i adjusts the value of its operating parameters for the following recurrence period.

[0048] In reception, the elementary reception signal SR i at the output of each transmission-reception module 30 i is re-emitted in the cavity 4 towards the common antenna 44, the different elementary reception signals superimposing in the cavity so as to form a global reception signal, the common antenna 44 collecting the global reception signal SR.

[0049] The common antenna 44 must make it possible to address the different elementary antennas 34 i (which are located on the same sphere) with an identical amplitude, phase and polarization.

[0050] Note that if it is planned to create only one type of beam, it is not necessary to provide data transmission to adjust the phases and amplitudes at the level of the 30 i modules, these values ​​can be fixed in the active modules.

[0051] In order to limit the number of electronic components downstream, i.e. at the level of the radiating elements, the phase and amplitude control devices can be moved from the TR module upstream of the waveform generator of the module 40. The components of the signals which must be radiated by each radiating element are therefore created upstream and transmitted to the TR module, whose only function is then to stimulate the corresponding radiating element.

[0052] The common antenna 44 is placed in the vicinity of the center C of the network antenna 1.

[0053] Various antennas are known which have, more or less precisely, the desired properties of hemispherical radiation, without phase shift, without polarity disturbance. The person skilled in the art knows dipole, monopole, collinear, helical antennas, etc.

[0054] For example, on the figure 4 , the radiation pattern of a patch type antenna is shown in an axial plane (i.e. containing the axis A). If at -3dB, the angular opening of the main lobe 45 is approximately 100°, at -6dB, the angular opening is approximately 130° and at -9dB, the angular opening is approximately 155°.

[0055] Thus, an antenna can approach an omnidirectional antenna provided that it works with strong attenuations.

[0056] But, in return, it is necessary to lower the noise level.

[0057] However, inside the cavity 4, the problem arises of the reflection of the radiofrequency electromagnetic waves emitted either by the source 40 or by the elementary antennas 34 i of the TR modules, insofar as it is a medium confined by the metal layer 12.

[0058] These reflections must therefore be attenuated so that the signal-to-noise level inside the cavity 4 is sufficient to allow communication between the communication modules 40 and 36 i.

[0059] This is the reason why, advantageously, the network antenna 1 is provided with a device 50 for absorbing electromagnetic waves.

[0060] As illustrated on the figure 1 , it is for example an absorption plane 50 covering the plane P forming the floor of the cavity 4 of the network antenna 1.

[0061] As illustrated on the figure 5 , the absorption plane 50 is for example a meta-material consisting of the superposition of a reflective layer 52, an electromagnetic wave absorbing layer 54 and a structured metallic layer 56.

[0062] A wave 60 coming from the cavity 4 and incident on the absorption plane 50 is transmitted by the structured metal layer 56 provided that it has a first polarity compatible with the layer 56 so that the latter is transparent.

[0063] The transmitted wave 61 then propagates a first time in the absorbent material 54.

[0064] At the interface with the reflective layer 52, the wave undergoes a modification of its polarization while being reflected.

[0065] The reflected wave 62 propagates a second time in the absorbing material 54.

[0066] Its polarization having changed, the structured metallic layer 56 does not transmit it into the cavity 4, but reflects it.

[0067] The reflected wave 63 propagates a third time in the absorbing material 54.

[0068] At the interface with the reflective layer 52, it undergoes a modification of its polarization, while being reflected.

[0069] The reflected wave 64 propagates a fourth time in the absorbing material 54.

[0070] Its polarization having changed a second time, the structured metal layer 56 transmits it towards the cavity 4.

[0071] Wave 65 emerges in cavity 4 after four passes through the absorbing material. It is therefore strongly attenuated.

[0072] Thus, the background noise level can be very significantly lowered in cavity 4.

[0073] By implementing a wireless connection between the low-level electronics and the front-end electronics (transmission / reception modules and radiating elements), the presence of cables and consequently the additional weight that this represents is eliminated. This network antenna is therefore lightweight and compatible with carriers such as aerial drones.

[0074] Furthermore, implementing a wireless connection avoids phase disparities. Indeed, electromagnetic radiation is homogeneous in phase regardless of its direction, whereas a multitude of cables will present disparities along their lengths, and therefore on the phases of the signals they transmit.

[0075] In the antenna according to the invention, several radiating elements can be grouped together to emit together so as to form a beam in an emission direction.

[0076] This grouping can be predefined. The radiating elements participating in beamforming (and therefore their number) are fixed by the initial configuration of the array antenna. For example, a group is formed by several radiating elements connected to the same TR module. The transmission direction is then fixed. For example, a group is formed by associating the different TR modules of the radiating elements to the same communication channel with the common antenna. In this case, the transmission direction can be modified by beamforming.

[0077] This grouping can be defined dynamically, by appropriately controlling the TR modules of the grouped radiating elements. In this case, the radiating elements participating in the formation of a beam are selected according to the need (for example according to the direction in which the beam must point or the power to be transmitted).

[0078] At any one time when using the antenna, only one group can be activated, with the antenna emitting only one beam, or several groups can be activated simultaneously, with the antenna emitting several beams.

[0079] The array antenna just presented finds applications in all applications requiring detection over a wide area. This is the case, for example, of airborne radar antennas, particularly for ground-to-air detection, electronic warfare systems, telecommunications antennas, etc.

Claims

1. Network antenna (1) comprising: - a hemispherical radome (10), with center C and radius R; - a plurality of radiating elements (20 i ), the radiating elements being carried by the radome; - a plurality of transmission reception modules (30 i ), the transmission-reception modules being carried by the radome, each radiating element being associated with a transmission-reception module and electrically connected to it by one or more power supply links, characterized in that the network antenna further comprises: - a common radiocommunication module (40), provided with a common antenna (44), placed at the center C of the hemispherical radome and connected to a transmission reception electronics of the common radiocommunication module, each transmission reception module (30 i ) comprising a communication module (36 i ), equipped with an elementary antenna (34 i) for two-way radio frequency communication with the common radio communication module (40).

2. An array antenna according to claim 1, wherein the face radially inside the radome (10) is a metal layer (12) electromagnetically insulating a cavity (4) inside the radome.

3. Antenna according to claim 2, in which the cavity (4) is provided with an absorption device (50) for electromagnetic waves to reduce background noise.

4. Antenna according to claim 3, in which the absorption device is a meta-material covering a floor of the cavity (4).

5. Antenna according to claim 4, in which the meta-material consists of the stacking of a reflection layer (52), an absorption layer (54) and a metallic plane (56), the metallic plane being perforated so as to present a periodic pattern adapted to trap the radiofrequency waves in the thickness of the meta-material according to their polarization.

6. Antenna according to any one of claims 2 to 5, in which, on reception, the elementary reception signal (SRj) at the output of each transmission reception module (30 i ) is re-emitted in the cavity (4) towards the common antenna (44), the different elementary reception signals superimposing themselves in the cavity so as to form a global reception signal (SR), the common antenna collecting the global reception signal.

7. Antenna according to any one of the preceding claims, in which the common antenna (44) is an omnidirectional antenna, having in any plane passing through an axis of symmetry (A) of the network antenna (1) an opening of at least 170° for an attenuation of -12dB.

8. Antenna according to claim 7, in which the common antenna (44) is a “patch” type antenna.

9. Antenna according to any one of the preceding claims, in which the radiating elements (20 i ) are covered with an adaptation layer (16), itself covered with a protective layer (18).

10. Antenna according to any one of the preceding claims, in which, in transmission, the common antenna (44) transmits a transmission signal (SE) that each transmission reception module (30 i ) collection for issue.

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