Antenna system and corresponding array antenna

Abstract

The invention relates to an antenna system comprising: - a primary antenna configured to operate in at least one frequency band; - at least one secondary antenna configured to be able to operate in the at least one frequency band. The secondary antenna is loaded by an impedance configured so that the radiation pattern of the system has, for at least one given frequency of the at least one frequency band, an attenuation in a predetermined direction. The secondary antenna is coupled to the primary antenna via an electromagnetic coupling device comprising at least one guided propagation line configured to transfer electromagnetic energy between the primary antenna and the secondary antenna, the guided propagation line having a characteristic impedance between 25 ohms and 100 ohms.

Description

[0001] DESCRIPTION

[0002] TITLE: Antenna system and corresponding array antenna.

[0003] Field of invention

[0004] The field of the invention is that of antennas with reconfigurable radiation patterns. The invention relates more particularly to an antenna allowing spatial filtering via the control of attenuations (or "nuis" or "dips" or "zeros") in its radiation pattern in corresponding angular directions.

[0005] The invention thus has applications, in particular, but not exclusively, in fields in which a desired signal from a given direction must be received in the presence of interfering signals from other directions, the adjustment of attenuations in the radiation pattern allowing the rejection of interfering signals. Such fields concern, for example, the reception of GNSS (Global Navigation Satellite Systems) signals, telecommunications networks, radar, etc.

[0006] Prior art and its drawbacks

[0007] In order to reject an interfering signal (or jamming signal) at a receiver, different techniques using the antenna system are known to obtain spatial filtering. For example, we can cite: beamforming by weighting digitized signals (or "Digital Beamforming" in the English literature). However, such a technique requires synchronous acquisition on several reception channels. Furthermore, such a technique requires maintaining the received signals in the linear range of each reception channel, otherwise it will no longer be possible to correctly estimate the weightings to be applied in order to obtain spatial filtering, or even to process the useful signal. However, the received signals can occupy a significant dynamic range. For example, the signal of interest may have a low amplitude while the interfering signals may have a high amplitude relative to the amplitude of the desired signal.This leads to having several acquisition chains with a large dynamic range of Analog Digital converters and therefore additional consumption and cost; the implementation of an antenna array, in which the module and phase weighting of the signal from each antenna in the array is implemented via a RF (radio frequency) path-forming circuit, aimed at controlling the position of an attenuation (or "null" or "dip" or "zero") in the radiation pattern of the antenna array in the direction of the interfering signal.However, such a path-forming circuit requires the implementation of reconfigurable RF components such as amplifiers, variable attenuators, and controllable phase shifters that are expensive and potentially not temperature stable; and the implementation of a reconfigurable geometry antenna, a solution that consists of changing the size or shape of a main radiating element by controlling, using radio frequency (RF) switches, e.g. using diodes, the RF current in certain parts of the antenna in order to create a radiation attenuation in a predetermined direction. However, in order to obtain different attenuations in azimuth and / or elevation, it is necessary to implement as many configurations and therefore switchable portions of antennas. The complexity and the surface area of ​​the overall antenna thus obtained makes such an approach non-competitive.

[0008] In order to overcome the limitations of the techniques listed above, it is possible to implement an antenna system from the family of parasitized antennas, or ESPAR (for "Electronically Steered Parasitic Antenna" in English. It should be noted that the term "Aerial beamforming by space-coupled parasites" is also found in the English literature). Such a system does not require a channel-forming circuit and maintains a reasonable implementation complexity.

[0009] For example, the antenna system 100 of the ESPAR type of [Fig.l] comprises: a primary antenna 110 intended to be connected to an RF receiver and / or transmitter; a secondary antenna 120 loaded by a load impedance 130 whose value impacts the radiation behavior of the antenna system 100 (directivity or on the contrary synthesis of attenuations in the radiation pattern).

[0010] More particularly, the RF currents induced on the secondary antenna 120 and incident on the load impedance 130 come from the electromagnetic (EM) coupling by proximity (eg by radiation) between the secondary antenna 120 and the primary antenna 110.

[0011] Calculating the value of the load impedance 130 for an angular direction of attenuation in the radiation pattern of the antenna system 100 is not straightforward. For this purpose, optimizers can be used as described eg in the article by M. Ohira, A. Miura, M.

[0012] Taromaru and M. Ueba, “Efficient Gain Optimization Techniques for Azimuth Beam / Null Steering of Inverted-F Multiport Parasitic Array Radiator (MuPAR) Antenna,” IEEE Transactions on Antennas and Propagation, vol. 60, no. 3, pp. 1352-1361, March 2012.

[0013] For example, a Z value Lgiven the load impedance 130 leads to having the components EQ2 and E2 of the field radiated by the secondary antenna 120 which substantially cancel the components E dl and E^ of the field radiated by the primary antenna 110 in a predetermined direction. However, the value of the load impedance 130 to be implemented for a given angular direction is not necessarily a positive real part, which makes it, in practice, difficult or impossible to achieve.

[0014] There is thus a need for an antenna system making it possible to implement spatial filtering in a reconfigurable manner over a wide range of angular directions and which does not have the drawbacks of the prior art described above.

[0015] Statement of the invention

[0016] In one embodiment of the invention, there is provided an antenna system comprising: a primary antenna configured to operate in at least one frequency band; at least one secondary antenna configured to be capable of operating in said at least one frequency band.

[0017] The secondary antenna is loaded by an impedance configured so that the radiation pattern of the system has, for at least one given frequency of said at least one frequency band, an attenuation in a predetermined direction. The secondary antenna is coupled to the primary antenna via an electromagnetic coupling device comprising at least one guided propagation line configured for the transfer of electromagnetic energy between the primary antenna and the secondary antenna. Such a guided propagation line has a characteristic impedance of between 25 Ohms and 100 Ohms, preferably 50 Ohms. Thus, the invention provides a novel and inventive solution for implementing spatial filtering in a reconfigurable manner over a wide range of angular directions.

[0018] More particularly, the proposed antenna system implements one (or more) guided propagation lines for the transfer of EM energy between the primary antenna and the secondary antenna. Indeed, such a coupling line makes it possible to obtain a sufficient coupling value between these antennas and thus to obtain load impedance values ​​of the secondary antenna with positive real parts for the creation of one (or more) attenuations in a predetermined direction of the radiation pattern, thereby making it possible to implement the antenna system. This remains true for a wide range of angular directions. Furthermore, a guided propagation line having a characteristic impedance between 25 Ohms and 100 Ohms makes it possible to overcome egof the inductive effect that a wire-type connection can provide, especially when the distance between the primary antenna and the secondary antennas increases, such an inductive effect being able to compromise the coupling (e.g. unwanted line radiation and coupled power loss) between the primary antenna and the secondary antennas. According to the present technique, it is thus possible to increase the distance between the primary antenna and the secondary antennas so as to reduce the EM coupling by proximity between the primary antenna and the secondary antennas. This allows fine control of the coupling between the primary antenna and the secondary antennas via the propagation line. This leaves more latitude in the formation of the radiation pattern (positioning of attenuations). Such a guided propagation line belongs for example to the group comprising: a micro-strip line, a coplanar line, a coaxial line, a slotted line and a stripline.

[0019] In some embodiments, the impedance is of variable value within a predetermined range of values.

[0020] Thus, the angular direction of attenuation (or attenuations) in the radiation pattern is variable within a range of angular directions corresponding to the predetermined range of values.

[0021] In some embodiments, the impedance is an impedance selectable from a set of predetermined discrete impedances. Each impedance of the set of impedances is configured so that the radiation pattern of the system exhibits, for a given frequency of said at least one frequency band, an attenuation in a predetermined direction. Thus, the impedance value is particularly stable with respect to environmental variations (e.g. temperature, level of received / transmitted RF signal).

[0022] In some embodiments, the at least one frequency band comprises a plurality of frequency bands. The impedance comprises a frequency multiplexing device configured to frequency multiplex unit impedances, each unit impedance being associated with a respective frequency band of the plurality and being configured such that the radiation pattern of the system exhibits, for a given frequency of the respective frequency band, an attenuation in a predetermined direction. Thus, attenuations are obtained simultaneously in different frequency bands. In some embodiments, at least one unit impedance associated with a respective frequency band is selectable from a set of unit impedances.

[0023] In some embodiments, the coupling device comprises, for the transfer of electromagnetic energy between, on the one hand, the guided propagation line and, on the other hand, the primary antenna or the secondary antenna, at least one element belonging to the group comprising; an electrical contact; an electrical probe; or a magnetic loop.

[0024] In some embodiments, the antenna system comprises a plurality of secondary antennas, the plurality comprising: at least one first secondary antenna coupled to the primary antenna via a first electromagnetic coupling device, the first secondary antenna being loaded by a first impedance configured so that the radiation pattern of the system has, for a given first frequency of said at least one frequency band and for a first polarization of the radiated electromagnetic field, an attenuation in a first predetermined direction;at least one second secondary antenna coupled to the primary antenna via a second electromagnetic coupling device, the second secondary antenna being loaded by a second impedance configured so that the radiation pattern of the system has, for a second given frequency of said at least one frequency band and for a second polarization of the radiated electromagnetic field, an attenuation in a second predetermined direction.;

[0025] Thus, radiation attenuations can be achieved at different polarizations. In some embodiments, the first polarization and the second polarization are orthogonal polarizations.

[0026] In some embodiments, the first frequency and the second frequency are the same frequency.

[0027] In some embodiments, the first predetermined direction and the second predetermined direction are the same predetermined direction.

[0028] In some embodiments, a radiation pattern of the primary antenna has an axis of revolution. The antennas of the plurality of secondary antennas are equally distributed around the primary antenna in a plane substantially orthogonal to the axis of revolution.

[0029] Thus, the radiation attenuations can be substantially equally distributed around the axis of revolution. In certain embodiments, the primary antenna and said at least one secondary antenna are of different natures.

[0030] Having primary and secondary antennas of different natures (e.g. the primary antenna is of the printed patch type and the at least one secondary antenna is of the folded printed dipole or magnetic loop type) further reduces the EM coupling by proximity between the primary and secondary antennas. Thus, the implementation of a guided propagation line for the transfer of electromagnetic energy between the primary and secondary antennas makes it possible to overcome this problem and to envisage primary and secondary antennas of different natures. The invention also relates to an array antenna comprising a plurality of antenna systems according to any one of the aforementioned embodiments.

[0031] Thus, a second level of spatial filtering is obtained via the networking of antenna systems according to the invention (eg via an implementation of baseband beamforming or via an implementation of a channel forming circuit).

[0032] List of figures

[0033] Other aims, characteristics and advantages of the invention will appear more clearly on reading the following description, given as a simple illustrative, and non-limiting, example, in relation to the figures, among which:

[0034] [Fig.l], described above in relation to the prior art, illustrates an example of a structure of an antenna system according to a known technique;

[0035] [Fig. ] illustrates an example of a structure of an antenna system comprising an EM coupling device according to an embodiment of the invention;

[0036] [Fig.2a] illustrates an example of a structure of an antenna system comprising an EM coupling device according to another embodiment of the invention;

[0037] [Fig.3] illustrates an example of an antenna system according to an embodiment of the invention; [Fig.3a] illustrates an example of implementation of sets of load impedances of the secondary antennas of the antenna system of [Fig.3] according to an embodiment of the invention;

[0038] [Fig.3b] illustrates an example of a radiation pattern of the antenna system of [Fig.3] obtained for a given configuration of the load impedance sets of [Fig.3a];

[0039] [Fig.4] illustrates an exemplary structure of a set of load impedances for addressing the creation of attenuations in the radiation pattern of the antenna system of [Fig.3] in several frequency bands according to one embodiment of the invention; [Fig.4a] illustrates an exemplary load impedance structure for addressing the creation of attenuations in the radiation pattern of the antenna system of [Fig.3] in several frequency bands according to another embodiment of the invention; and

[0040] [Fig.5] illustrates an array antenna comprising a plurality of antenna systems according to one embodiment of the invention.

[0041] Detailed description of embodiments of the invention

[0042] We now present, in relation to [Fig. ], an example of the structure of an antenna system 200 comprising an EM coupling device 210 according to an embodiment of the invention.

[0043] More particularly, the antenna system 200 is configured to operate in one (or more) frequency bands. In other words, the antenna system 200 is configured to receive and / or transmit signals in the frequency band(s) in question. To do this, the antenna system 200 comprises, just like the antenna system 100 of [Fig.l]: a primary antenna 110 intended to be connected to an RF receiver and / or transmitter to receive and / or transmit signals in the frequency band(s) in question. The primary antenna 110 is thus configured to operate in the frequency band(s) in question; a secondary antenna 120 loaded by a load impedance 130 whose value impacts the behavior of the resulting radiation (directivity or on the contrary synthesis of an attenuation 350 (or “null” or “dip” or “zero”) in the radiation pattern of the antenna system 200).More particularly, the load impedance 130 is configured so that the radiation pattern of the antenna system 200 has, for at least one given frequency of the frequency band(s) considered, an attenuation 350 in a predetermined direction.

[0044] In other embodiments, eg the embodiment of [Fig. 3], the antenna system 200 comprises a plurality of secondary antennas 120 loaded by a respective load impedance 130.

[0045] Regardless of the embodiment considered, the secondary antenna (or antennas) 120 is an antenna configured to be able to operate in the frequency band (or bands) in which the antenna system 200 (and therefore the primary antenna 110) is configured to operate. In this, the antenna system 200 according to the present technique is distinguished from the antennas with reconfigurable geometries described above in relation to the section “Prior art and its drawbacks”. Indeed, in such an antenna with reconfigurable geometry, the physical elements that are supplied or not supplied with current in order to change the overall geometry of the antenna are not elements capable of operating by themselves, if only by their dimensions, like an antenna in the operating frequency band (or bands) of the overall antenna.Conversely, the secondary antenna (or antennas) 120 according to the present technique is capable of such operation in the operating frequency band(s) of the antenna system 200.

[0046] Returning to [Fig.2], the value of the load impedance 130 that must be implemented to obtain an attenuation 350 in a given angular direction is eg obtained via the technique described in the aforementioned article by M. Ohira, A. Miura, M. Taromaru and M. Ueba. In practice, the value of the load impedance 130 that must be implemented to obtain an attenuation 350 in a given angular direction is dependent on the coupling level between the primary antenna 110 and the secondary antenna 120 considered. More particularly, for low coupling values, the value of the load impedance 130 required often has a negative real part, which makes it, in practice, difficult or impossible to achieve. Such a coupling value is also naturally a function of the distance between the primary antenna 110 and the secondary antenna 120, but also a function of various parameters such as the nature of the primary antenna 110 and secondary antenna 120.For example, in certain embodiments the primary 110 and secondary 120 antennas are of different natures. Such embodiments are interesting e.g.: when the primary antenna 110 has a specific radiation pattern optimized for the reception of the desired signal coming from a given direction, while the secondary antenna (or antennas) 120 has a specific radiation pattern optimized for the reception (and therefore the cancellation in the complete system in the end) of an interfering signal coming from another direction. This is the case e.g. when receiving a GNSS signal in the presence of an interfering signal (or "jammer" in the English literature).The GNSS signal is in fact emitted from a satellite in Earth orbit while the interfering signal is often emitted from a device on the surface of the Earth; or when several secondary antennas 120 are implemented with radiated EM fields having different polarizations in a given direction (as eg in the embodiment of [Fig.3]). In such a configuration, attenuations 350 in the radiation pattern of the antenna system 200 can be obtained according to the different polarizations. Returning to [Fig.2], in order to overcome these weak coupling problems, unlike the antenna system 100 of [Fig.l], the secondary antenna 120 is here coupled to the primary antenna 110 via the EM coupling device 210.More particularly, the EM coupling device 210 comprises one (or more) guided propagation lines 210a configured for the transfer of EM energy between the primary antenna 110 and the secondary antenna 120.

[0047] Thus, a sufficient coupling value is obtained between the primary antenna 110 and the secondary antenna 120 to allow attenuations 350 to be created in the radiation pattern of the antenna system 200 by implementing load impedances 130 with positive real parts, and this in a wide range of angular directions of the attenuations 350.

[0048] More particularly, the coupling level must be neither too high (e.g. preferably the modulus of parameter S21 between the primary antenna 110 and the secondary antenna 120 is less than -10 dB), otherwise too much power will be coupled with the direct impact of a deterioration in the gain of the primary antenna 110, nor too low (e.g. preferably the modulus of parameter S21 between the primary antenna 110 and the secondary antenna 120 is greater than -15 dB) to ensure the proper operation of the secondary antennas 120.

[0049] Such a guided propagation line has a characteristic impedance of between 25 Ohms and 100 Ohms, preferably 50 Ohms. The guided propagation line is e.g. a microstrip line, a coplanar line, a coaxial line, a slotted line, a stripline, etc. More particularly, a line configured in this way makes it possible to overcome e.g. the inductive effect that a wire-type connection can provide, in particular when the distance between the primary antenna and the secondary antennas increases, such an inductive effect being able to compromise the coupling (e.g. unwanted line radiation and coupled power loss) between the primary antenna and the secondary antennas. According to the present technique, it is thus possible to increase the distance between the primary antenna and the secondary antennas so as to reduce the EM coupling by proximity between the primary antenna and the secondary antennas.This allows for fine control of the coupling between the primary antenna and the secondary antennas via the propagation line. This allows more latitude in the formation of the radiation pattern (positioning of attenuations).

[0050] The EM coupling device 210 further comprises: an electrical probe 210b for EM coupling between the primary antenna 110 and the guided propagation line(s) 210a; and an electrical probe 210b for EM coupling between the guided propagation line(s) 210a and the secondary antenna 120.

[0051] On the contrary, in the embodiment of [Fig.2a], the EM coupling device 210 comprises: an electrical contact 210c for the EM coupling between the primary antenna 110 and the guided propagation line(s) 210a; and an electrical contact 210c for the EM coupling between the guided propagation line(s) 210a and the secondary antenna 120.

[0052] Alternatively, a magnetic loop coupling may be envisaged for the EM coupling between the primary antenna 110 and the guided propagation line(s) 210a, as well as for the EM coupling between the guided propagation line(s) 210a and the secondary antenna 120. Furthermore, couplings of different natures (i.e. by contact, by probe or by loop) may be envisaged for the coupling between, on the one hand, the ends of the guided propagation line(s) 210a and, on the other hand, the primary antenna 110 or the secondary antenna 120. Thus, in embodiments, the EM coupling device 210 comprises, for the transfer of EM energy between, on the one hand, the guided propagation line(s) 210a and, on the other hand, the primary antenna 110 or the secondary antenna 120, at least one element belonging to the group comprising: an electrical contact; an electrical probe; or a magnetic loop.

[0053] We now present, in relation to [Fig. 3], an example of an antenna system 200 according to an embodiment of the invention.

[0054] More particularly, the primary antenna 110 is a circular patch antenna. The symmetry of revolution makes it possible eg to more easily address all possible directions for the attenuations 350 in the radiation pattern.

[0055] However, in some embodiments, other types of primary antennas 110 are used, e.g., dipole, spiral, horn, etc. antennas. Such antennas may or may not have rotational symmetry and are configured to operate in a single frequency band or in a plurality of frequency bands.

[0056] Returning to [Fig.3], the primary antenna 110 is here a multi-band right circularly polarized GNSS antenna. With a diameter of 131 mm and a height of 59 mm, it covers the E6 (1260 - 1300 MHz) and El (1559 - 1591 MHz) bands. To achieve the two El and E6 frequency bands, the primary antenna 110 comprises two circular patches, stacked and centered one above the other so as to ensure symmetry of revolution over a sufficient frequency band (better axial ratio over the bands considered compared to a quasi-square or even truncated patch antenna).

[0057] Furthermore, in order to reduce the dimensions of the primary antenna 110 by a factor close to two, the patch antennas are produced on a thick microwave substrate (e.g. reference R04003CTM, s r= 3.38 and tan ô = 0.0027 at 10 GHz). The adjustment of the center frequency and the bandwidth width is ensured by the diameter of the patch and the thickness of its substrate respectively. Its diameter here is 70 mm with a thickness of 6.4 mm for the lower patch covering the E6 band (stack of four 1.524 mm substrates) and diameter

[0058] 55.2 mm with a thickness of 3.15 mm for the upper patch covering the El band (stack of two 1.524 mm substrates).

[0059] In order to achieve right circular polarization, the antennas are fed by four 300 quadrature feed probes located 8 mm from the center of the structure and with a diameter

[0060] 2.2 mm. These feed probes 300 excite the first transverse magnetic mode TM110 of the primary antenna 110.

[0061] The feed probes 300 are connected to a feed circuit located on the rear layer of the printed circuit of the primary antenna 110 ([Fig.3a]). The feed circuit comprises a balun 320 (e.g. reference ADTL2-18+ from Mini-Circuits) feeding two 3dB-90° hybrid couplers 330 (e.g. reference QCN-19+ from Mini-Circuits) connected to the feed probes 300 so as to guarantee on each of the feed probes 300 signals of the same amplitude but phase shifted relative to each other by 90° (0°; 90°; 180°; 270°). Finally, a connector 340 (e.g. SMA type) is connected to the input of the balun so as to connect the primary antenna 110 eg to a coaxial cable.

[0062] Returning to [Fig. 3], in order to feed the secondary antennas 120 located around the primary antenna 110, electrical coupling probes 210b are arranged near the feed probes 300. These coupling probes 210b are identical, substantially parallel to the feed probes 300 and are positioned relative to the latter so as to ensure a coupling level substantially equal to -13 dB in the frequency bands E1 and E6. In general, the coupling probes 210b are positioned according to the desired coupling level. Furthermore, as described above in relation to [Fig. 2] and [Fig. 2a], in certain embodiments, other types of coupling between the primary antenna 110 and the guided propagation line 210a can be envisaged (e.g. an electrical contact 210c or a magnetic loop coupling).

[0063] Returning to [Fig. 3], the secondary antennas 120 are configured to be capable of operating in the E6 and E1 frequency bands and comprise: four first secondary antennas 120a, each first secondary antenna 120a being coupled to the primary antenna 110 via a respective first EM coupling device 210; and four second secondary antennas 120b, each second secondary antenna 120a being coupled to the primary antenna 110 via a respective second EM coupling device 210.

[0064] More particularly, the first secondary antennas 120a and the second secondary antennas 120b are of different natures. Furthermore, the first secondary antennas 120a and the second secondary antennas 120b radiate EM fields having orthogonal polarizations in at least one radiation direction. This makes it possible to obtain attenuations 350 in the radiation pattern of the antenna system 200 according to different polarizations in the direction(s) in question.

[0065] The first secondary antennas 120a are here dipoles printed on a substrate. The second secondary antennas 120b are here magnetic loops printed on a substrate. However, in embodiments, other types of secondary antennas 120a, 120b are used, e.g. dipole, spiral, horn antennas, etc.

[0066] In embodiments, the first secondary antennas 120a and the second secondary antennas 120b are of the same nature. In embodiments, the first secondary antennas 120a and the second secondary antennas 120b radiate EM fields having the same polarizations.

[0067] Returning to [Fig. 3], the first secondary antennas 120a and the second secondary antennas 120b are loaded by load impedances 130 located on the rear face of the antenna system 200 ([Fig. 3a]).

[0068] More particularly, the load impedance 130 of a given secondary antenna 120a, 120b is of variable value within a predetermined range of values. Thus, the angular direction of the attenuation (or attenuations) 350 in the radiation pattern of the antenna system 200 is variable within a range of angular directions related to the predetermined range of values.

[0069] More particularly, the load impedance 130 of a given secondary antenna 120a, 120b is here an impedance selectable from a set of predetermined discrete impedances. Each impedance of the set of impedances is configured so that the radiation pattern of the antenna system 200 has, for a given frequency of the frequency band El or of the frequency band E6, an attenuation 350 in a predetermined direction.

[0070] For example, a load switching circuit associated with each secondary antenna 120a, 120b comprises an RF switch 310 of the SP8T type (e.g. reference PE42282 from PSemi) in order to select up to eight different load impedance values ​​130 (possibility of creating e.g. up to seven different attenuations 350 in the radiation pattern, the last value allowing nominal operation of the antenna system 200, i.e. without attenuation 350). Each load line is loaded by a resistor and a reactance (e.g. capacitance or inductance) connected in series on a microstrip line terminated by a ground return. The advantage of switching discrete values ​​of the load impedance 130 compared to a continuous variation lies in the high stability of the impedance values ​​obtained with respect to operational variations (e.g. temperature, RF signal level).This makes it possible to guarantee stability of the performance of a product implementing such an antenna system 200.

[0071] Thus, according to such an approach, in some embodiments the load impedance 130 is an impedance selectable from a set of predetermined discrete impedances. Each impedance of the set of impedances is configured so that the radiation pattern of the antenna system 200 has, for a given frequency of the frequency band(s) in which the antenna system 200 is configured to operate, an attenuation 350 in a predetermined direction in the radiation pattern. However, in some embodiments, the value of the load impedance 130 varies continuously within the predetermined range of values ​​considered.

[0072] Returning to [Fig.3], the secondary antennas 120a, 120b are equally distributed around the primary antenna 110 in a plane (here the xoy plane) substantially orthogonal to the axis of revolution (here the z axis) of the radiation pattern of the primary antenna 110. Thus, the attenuations 350 obtained in the radiation pattern are substantially equally distributed around the axis of revolution as illustrated in [Fig.3b].

[0073] However, in some embodiments, the secondary antennas 120 are not equally distributed around the primary antenna 110. Furthermore, in some embodiments the secondary antennas 120 are not implemented in a plane. Returning to [Fig. 3b], four first secondary antennas 120a and four second secondary antennas 120b are coupled to the primary antenna 110. However, in some embodiments, another number of secondary antennas 120 are implemented.

[0074] Thus, in some embodiments, the antenna system 200 is configured to operate in one (or more) frequency bands and comprises: at least one first secondary antenna 120a coupled to the primary antenna 110 via a first EM coupling device. The first secondary antenna 120a is loaded by a first impedance 130 configured so that the radiation pattern of the system has, for a first given frequency of the (or more) frequency band and for a first polarization of the radiated EM field, an attenuation 350 in a first predetermined direction; at least one second secondary antenna 120b coupled to the primary antenna 110 via a second EM coupling device.The second secondary antenna 120b is loaded by a second impedance 130 configured so that the radiation pattern of the system has, for a second given frequency of the frequency band(s) and for a second polarization of the radiated EM field, an attenuation 350 in a second predetermined direction.

[0075] Thus, 350 radiation attenuations can be obtained according to different polarizations.

[0076] In some embodiments, the first polarization and the second polarization are orthogonal polarizations (e.g., the first polarization is a right-hand circular (or elliptical) polarization and the second polarization is a left-hand circular (or elliptical) polarization. Alternatively, the first polarization and the second polarization are orthogonal linear polarizations). In some embodiments, the first polarization and the second polarization are different polarizations (orthogonal or not). In some embodiments, the first polarization and the second polarization are the same polarizations.

[0077] In some embodiments, the first frequency and the second frequency are the same frequency. In some embodiments, the first frequency and the second frequency are different frequencies.

[0078] In some embodiments, the first predetermined direction and the second predetermined direction are the same predetermined direction. In some embodiments, the first predetermined direction and the second predetermined direction are different predetermined directions.

[0079] In some embodiments, the antenna system 200 comprises secondary antennas 120 all of the same nature. In some embodiments, the secondary antennas 120 are, at least in part, of different natures.

[0080] In some embodiments, the antenna system 200 includes a single secondary antenna 120.

[0081] We now present, in relation to [Fig. 4], an example of the structure of a set of load impedances 130 making it possible to address the creation of attenuations 350 in the radiation pattern of the antenna system 200 in several frequency bands according to an embodiment of the invention.

[0082] More particularly, the structure of [Fig. 4] is particularly suitable for sequentially addressing the creation of attenuations 350 in a plurality of frequency bands. To do this, an RF switch 400 (or an arrangement of several RF switches) is configured to be connectable to different load impedances 130 corresponding to the attenuations 350 to be created in the different frequency bands. In the case illustrated in [Fig. 4], two load impedances 130 are considered per frequency band: Zon1 and Zoff1 for a first frequency band, Zon2 and Zoff2 for a second frequency band, and Zon3 and Zoff3 for a third frequency band.More particularly, a load impedance 130 is configured for the creation of an attenuation 350 for a given frequency of the respective frequency band and in a given direction of the radiation pattern of the antenna system 200 (Zonl for the first frequency band, Zon2 for the second frequency band and Zon3 for the third frequency band). The other load impedance 130 is configured for the nominal operation of the antenna system 200, i.e. without attenuation 350 (Zoffl for the first frequency band, Zoff2 for the second frequency band and Zoff3 for the third frequency band).

[0083] However, in some embodiments, another number of load impedances 130 per frequency band and / or another number of frequency bands is considered.

[0084] We now present, in relation to [Fig. 4a] an example of a load impedance structure 130 making it possible to address the creation of attenuations 350 in the radiation pattern of the antenna system 200 in several frequency bands according to another embodiment of the invention. More particularly, the structure of [Fig. 4a] is particularly suitable for addressing the simultaneous creation of attenuations 350 in a plurality of frequency bands. To do this, the load impedance 130 comprises a frequency multiplexing device 410 (e.g. a duplexer for two frequency bands or a triplexer for three frequency bands, etc.) configured to frequency multiplex different unit impedances 430.Each unit impedance is associated with a respective frequency band of the plurality and is configured so that the radiation pattern of the antenna system 200 has, for a given frequency of the respective frequency band, an attenuation 350 in a predetermined radiation direction.

[0085] In some embodiments, at least one unit impedance 430 associated with a respective frequency band is selectable (eg via the implementation of an RF switch) from a set of unit impedances 430.

[0086] For example, in the case illustrated in [Fig.4a], two unit impedances 430 are considered per frequency band (Zonl and Zoffl for a first frequency band, Zon2 and Zoff2 for a second frequency band and Zon3 and Zoff3 for a third frequency band), selectable via an RF switch 420. One unit impedance 430 is configured for the creation of an attenuation 350 for a given frequency of the respective frequency band and in a given direction of the radiation pattern (Zonl for the first frequency band, Zon2 for the second frequency band and Zon3 for the third frequency band). The other unit impedance 430 is configured for the nominal operation of the antenna system 200 without radiation attenuation 350 (Zoffl for the first frequency band, Zoff2 for the second frequency band and Zoff3 for the third frequency band).In some embodiments, another number of unit impedances 430 per frequency band and / or another number of frequency bands is considered.

[0087] Thus, 350 attenuations can be obtained simultaneously in different frequency bands.

[0088] [Fig.5] illustrates an array antenna 500 comprising a plurality of antenna systems 200 according to one embodiment of the invention.

[0089] More particularly, the array antenna 500 implements beamforming, e.g. via an implementation of an analog or digital channel forming circuit. In this way, additional attenuations 350 in the overall radiation pattern of the array antenna 500 can be obtained in addition to those linked to the radiation patterns of the antenna systems 200. Thus, a second level of spatial filtering is obtained in addition to that linked to the implementation of the antenna systems 200.

[0090] According to the implementations, such an array antenna 500 implements antenna systems 200 according to any of the embodiments described above.

Claims

CLAIMS 1. Antenna system (200) comprising: - a primary antenna (110) configured to operate in at least one frequency band; - at least one secondary antenna (120, 120a, 120b) configured to be capable of operating in said at least one frequency band, the secondary antenna being loaded by an impedance (130) configured so that the radiation pattern of the system has, for at least one given frequency of said at least one frequency band, an attenuation (350) in a predetermined direction, characterized in that the secondary antenna is coupled to the primary antenna via an electromagnetic coupling device (210) comprising at least one guided propagation line (210a) configured for the transfer of electromagnetic energy between the primary antenna and the secondary antenna, the guided propagation line having a characteristic impedance of between 25 Ohms and 100 Ohms.

2. Antenna system according to claim 1, wherein the impedance is of variable value within a predetermined range of values.

3. Antenna system according to claim 1 or 2, wherein the impedance is an impedance selectable from a set of predetermined discrete impedances, each impedance of the set of impedances being configured so that the radiation pattern of the system has, for a given frequency of said at least one frequency band, an attenuation in a predetermined direction.

4. An antenna system according to claim 1 or 2, wherein said at least one frequency band comprises a plurality of frequency bands, and wherein the impedance comprises a frequency multiplexing device (410) configured to frequency multiplex unit impedances (430), each unit impedance being associated with a respective frequency band of the plurality and being configured so that the radiation pattern of the system has, for a given frequency of the respective frequency band, an attenuation in one direction predetermined.

5. An antenna system according to claim 4, wherein at least one unit impedance associated with a respective frequency band is selectable from a set of unit impedances.

6. Antenna system according to any one of claims 1 to 5, in which the coupling device comprises, for the transfer of electromagnetic energy between, on the one hand, the guided propagation line and, on the other hand, the primary antenna or the secondary antenna, at least one element belonging to the group comprising: - an electrical contact; - an electrical probe; or - a magnetic loop.

7. An antenna system according to any one of claims 1 to 6, comprising a plurality of secondary antennas, the plurality comprising: - at least one first secondary antenna (120a) coupled to the primary antenna via a first electromagnetic coupling device, the first secondary antenna being loaded by a first impedance configured so that the radiation pattern of the system has, for a first given frequency of said at least one frequency band and for a first polarization of the radiated electromagnetic field, an attenuation in a first predetermined direction; - at least one second secondary antenna (120b) coupled to the primary antenna via a second electromagnetic coupling device, the second secondary antenna being loaded by a second impedance configured so that the radiation pattern of the system has, for a second given frequency of said at least one frequency band and for a second polarization of the radiated electromagnetic field, an attenuation in a second predetermined direction.

8. An antenna system according to claim 7, wherein the first polarization and the second polarization are orthogonal polarizations.

9. Antenna system according to claim 7 or 8, wherein the first frequency and the second frequency are the same frequency.

10. Antenna system according to any one of claims 7 to 9, wherein the first predetermined direction and the second predetermined direction are the same predetermined direction.

11. Antenna system according to any one of claims 7 to 10, in which a radiation pattern of the primary antenna has an axis of revolution, and in which the antennas of the plurality of secondary antennas are equally distributed around the primary antenna in a plane substantially orthogonal to the axis of revolution.

12. Antenna system according to any one of claims 1 to 11, in which the primary antenna and said at least one secondary antenna are of different natures.

13. Antenna system according to any one of claims 1 to 12, in which the primary antenna is of the printed patch type and the at least one secondary antenna is of the folded printed dipole or magnetic loop type.

14. An array antenna (500) comprising a plurality of antenna systems according to any one of claims 1 to 13.

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