Antenna system and corresponding network antenna

Abstract

Antenna System and Corresponding Array Antenna The invention relates to an 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 operate in at least one frequency band. The secondary antenna is loaded with an impedance configured such that the radiation pattern of the system exhibits, for at least one given frequency in the frequency band(s), 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 (210a) configured for the transfer of electromagnetic energy between the primary and secondary antennas. ABSTRACT FIGURE: [Fig. 3]

Description

Title of the invention: Antenna system and corresponding array antenna. Scope of the invention

[0001] The field of the invention is that of reconfigurable radiation pattern antennas.

[0002] The invention relates more particularly to an antenna allowing spatial filtering via the control of attenuations (or "nuisances" or "hollows" or "zeroes") in its radiation pattern in corresponding angular directions.

[0003] The invention thus has applications, in particular, but not exclusively, in fields where 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 enabling the rejection of the interfering signals. Such fields include, for example, the reception of GNSS (Global Navigation Satellite Systems) signals, telecommunications networks, radar, etc. Prior art and its drawbacks

[0004] In order to reject an interfering signal (or jamming signal) at a receiver, various techniques using an antenna system are known to achieve spatial filtering. Examples include:

[0005] - beamforming by weighting digitized signals (or “Digital” Beamforming (in Anglo-Saxon literature). However, such a technique requires synchronous acquisition on multiple receiving channels. Furthermore, this technique necessitates keeping the received signals within the linear range of each receiving channel; otherwise, it becomes impossible to correctly estimate the weightings required for spatial filtering, or even to process the desired signal. Yet, the received signals can have a significant dynamic range. For example, the signal of interest may have a low amplitude, while interfering signals may have a high amplitude relative to the desired signal. This leads to multiple acquisition chains with a wide dynamic range of Analog-to-Digital Converters, resulting in increased power consumption and cost.

[0006] - the implementation of an antenna array, in which the modulus weighting and phase of the signal from each antenna in the network, is implemented via an RF (radio frequency) channel-forming circuit, aimed at controlling the position of an attenuation (or "null" or "dip" or "zero") in the radiation pattern antenna arrays in the direction of the signal interfere. However, such a channel-forming circuit requires the implementation of reconfigurable RF components such as amplifiers, variable attenuators, and controllable phase shifters, which are expensive and potentially temperature-unstable; and

[0007] - the implementation of a reconfigurable geometry antenna, a solution which consists of Changing the size or shape of a primary radiating element by controlling the RF current in specific parts of the antenna using radio frequency (RF) switches, e.g., diodes, creates radiation attenuation in a predetermined direction. However, achieving different attenuations in azimuth and / or elevation requires implementing multiple configurations and therefore multiple switchable antenna segments. The resulting complexity and overall antenna size make this approach non-competitive.

[0008] In order to overcome the limitations of the techniques listed above, it is possible to implement an antenna system of the family of parasitic 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-language literature). Such a system does not require a channel-forming circuit and maintains a reasonable implementation complexity.

[0009] For example, the ESPAR-type antenna system 100 of [Fig. 1] comprises:

[0010] - a primary antenna 110 intended to be connected to a receiver and / or transmitter RF;

[0011] - a secondary antenna 120 loaded by a load impedance 130 of which the value impacts the radiation behavior of the antenna system 100 (directivity or on the contrary synthesis of attenuations in the radiation diagram).

[0012] 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 (e.g. by radiation) between the secondary antenna 120 and the primary antenna 110.

[0013] Calculating the load impedance value 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 e.g. in the article by M. Ohira, A. Miura, M. 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.

[0014] For example, a given value ZL of the load impedance 130 leads to the components Eg2 and E^ of the field radiated by the secondary antenna 120 substantially canceling the components Eg1 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 positive real-valued, which makes it, in practice, difficult or impossible to achieve.

[0015] There is therefore a need for an antenna system that allows for reconfigurable spatial filtering over a wide range of angular directions and that does not have the drawbacks of the prior art described above. Description of the invention

[0016] In one embodiment of the invention, an antenna system is proposed comprising:

[0017] - a primary antenna configured to operate in at least one band of frequencies;

[0018] - at least one secondary antenna configured to be capable of operating in said at least one frequency band.

[0019] The secondary antenna is loaded with an impedance configured such that the radiation pattern of the system exhibits, for at least one given frequency within said at least one frequency band, 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 and secondary antennas.

[0020] Thus, the invention proposes a novel and inventive solution for implementing spatial filtering in a reconfigurable manner over a wide range of angular directions.

[0021] More specifically, the proposed antenna system implements one (or more) guided propagation lines for EM energy transfer between the primary and secondary antennas. 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 the implementation of the antenna system possible. This remains true for a wide range of angular directions.

[0022] In some embodiments, the impedance is variable in value within a predetermined range of values.

[0023] Thus, the angular direction of the attenuation (or attenuations) in the radiation diagram is variable in a range of angular directions corresponding to the predetermined range of values.

[0024] In certain embodiments, the impedance is a selectable impedance from a set of predetermined discrete impedances. Each impedance in the set of impedances is configured so that the radiation pattern of the system exhibits, for a given frequency in said at least one frequency band, an attenuation in a predetermined direction.

[0025] Thus, the impedance value is particularly stable with respect to environmental variations (e.g. temperature, received / emitted RF signal level).

[0026] In certain embodiments, said at least one frequency band comprises a plurality of frequency bands. The impedance comprises a frequency-multiplexing device configured to frequency-multiply 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, attenuation in a predetermined direction.

[0027] Thus, attenuations are obtained simultaneously in different frequency bands.

[0028] In certain embodiments, at least one unit impedance associated with a respective frequency band is selectable from a set of unit impedances.

[0029] In certain embodiments, the coupling device includes, for the transfer of electromagnetic energy between, on the one hand, the guided propagation line and, on the other hand, the primary or secondary antenna, at least one element belonging to the group comprising;

[0030] - an electrical contact;

[0031] - an electrical probe; or

[0032] - a magnetic loop.

[0033] In certain embodiments, the antenna system comprises a plurality of secondary antennas, the plurality comprising:

[0034] - 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 exhibits, 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;

[0035] - 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 exhibits, 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.

[0036] Thus, radiation attenuations can be obtained according to different polarizations.

[0037] In some embodiments, the first polarization and the second polarization are orthogonal polarizations.

[0038] In some embodiments, the first frequency and the second frequency are the same frequency.

[0039] In some embodiments, the first predetermined direction and the second predetermined direction are the same predetermined direction.

[0040] In certain 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.

[0041] Thus, the radiation attenuations can be substantially evenly distributed around the axis of revolution.

[0042] In some embodiments, the primary antenna and said at least one secondary antenna are of different natures.

[0043] Having primary and secondary antennas of different types (e.g., the primary antenna is a printed patch type and at least one secondary antenna is a folded printed dipole or magnetic loop type) further reduces proximity EM coupling between the primary and secondary antennas. Therefore, implementing a guided propagation line for the transfer of electromagnetic energy between the primary and secondary antennas makes it possible to overcome this problem and consider primary and secondary antennas of different types.

[0044] The invention also relates to a network antenna comprising a plurality of antenna systems according to any one of the aforementioned embodiments.

[0045] Thus, a second level of spatial filtering is obtained via the networking of antenna systems according to the invention (e.g. via a baseband beamforming implementation or via a channel-forming circuit implementation). List of figures

[0046] Other objects, features and advantages of the invention will become more apparent from the following description, given by way of simple illustrative, and not limiting, example, in relation to the figures, among which:

[0047] [Fig. 1], described above in relation to the prior art, illustrates an example of the structure of an antennal system according to a known technique;

[0048] [Fig.2] illustrates an example of the structure of an antenna system comprising an EM coupling device according to an embodiment of the invention;

[0049] [Fig.2a] illustrates an example of the structure of an antenna system comprising an EM coupling device according to another embodiment of the invention;

[0050] [Fig.3] illustrates an example of an antenna system according to an embodiment of the invention;

[0051] [Fig.3a] illustrates an example of implementation of load impedance sets of secondary antennas of the antenna system of the [Fig.3] according to an embodiment of the invention;

[0052] [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];

[0053] [Fig.4] illustrates an example of the structure of a load impedance set allowing the creation of attenuations in the radiation pattern of the antenna system of [Fig.3] in several frequency bands according to an embodiment of the invention;

[0054] [Fig. 4a] illustrates an example of a 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

[0055] [Fig.5] illustrates an array antenna comprising a plurality of antenna systems according to an embodiment of the invention.

[0056] Detailed description of embodiments of the invention

[0057] We now present, in relation to [Fig.2] an example of the structure of an antenna system 200 comprising an EM coupling device 210 according to an embodiment of the invention.

[0058] More specifically, the antenna system 200 is configured to operate in one (or more) frequency band(s). 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. 1]:

[0059] - a primary antenna 110 intended to be connected to a receiver and / or transmitter RF to receive and / or transmit signals in the frequency band(s) question. The primary antenna 110 is thus configured to operate in the frequency band(s) in question;

[0060] - a secondary antenna 120 loaded by a load impedance 130 of which The value impacts the behavior of the resulting radiation (directivity or, conversely, synthesis of an attenuation 350 (or "null" or "dip" or "zero") in the radiation pattern of the antenna system 200). More specifically, the load impedance 130 is configured so that the radiation pattern of the antenna system 200 exhibits, for at least one given frequency of the frequency band(s) considered, an attenuation 350 in a predetermined direction.

[0061] In other embodiments, e.g. the embodiment of [Fig.3], the antenna system 200 comprises a plurality of secondary antennas 120 loaded by a respective load impedance 130.

[0062] Regardless of the embodiment considered, the secondary antenna (or antennas) 120 is an antenna configured to operate in the frequency band(s) in which the antenna system 200 (and therefore the primary antenna 110) is configured to operate. In this respect, the antenna system 200 according to the present technique differs from the reconfigurable geometry antennas described above in relation to the section "Prior Art and its Disadvantages." Indeed, in such a reconfigurable geometry antenna, the physical elements that are powered or not in order to change the overall geometry of the antenna are not elements capable of functioning by themselves, if only because of their dimensions, like an antenna in the operating frequency band(s) of the overall antenna.Conversely, the secondary antenna (or antennas) 120 according to the present technique is suitable for such operation in the operating frequency band (or bands) of the antenna system 200.

[0063] Returning to [Fig. 2], the load impedance value 130 required to obtain an attenuation 350 in a given angular direction is obtained using the technique described in the aforementioned article by M. Ohira, A. Miura, M. Taromaru, and M. Ueba. In practice, the load impedance value 130 required to obtain an attenuation 350 in a given angular direction depends on the coupling level between the primary antenna 110 and the secondary antenna 120 under consideration. More specifically, for low coupling values, the required load impedance value 130 often has a negative real part, which makes it difficult or impossible to achieve in practice. 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 . In some embodiments, the primary antenna (110) and secondary antenna (120) are of different types. Such embodiments are interesting, e.g.:

[0064] - when the primary antenna 110 has a clean radiation pattern optimized for receiving the desired signal from a given direction, while the secondary antenna (or antennas) 120 has a clean radiation pattern optimized for receiving (and therefore canceling in the complete system) an interfering signal from another direction. This is the case, for example, when receiving a GNSS signal in the presence of an interfering signal (or "jammer" in English-language literature). The GNSS signal is indeed transmitted from a satellite in Earth orbit, while the interfering signal is often transmitted from a device on the Earth's surface; or

[0065] - when several secondary antennas 120 are implemented with fields EM radiated with different polarizations in a given direction (as e.g. in the embodiment of [Fig. 3]). In such a configuration, attenuations of 350 in the radiation pattern of the antenna system 200 can be obtained depending on the different polarizations.

[0066] Returning to [Fig.2], in order to overcome these weak coupling problems, unlike the antenna system 100 of [Fig.1], the secondary antenna 120 is here coupled to the primary antenna 110 via the EM coupling device 210. More specifically, the EM coupling device 210 comprises one (or more) guided propagation line 210a configured for the transfer of EM energy between the primary antenna 110 and the secondary antenna 120.

[0067] Thus, a sufficient coupling value is obtained between the primary antenna 110 and the secondary antenna 120 to allow the creation of attenuations 350 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.

[0068] In particular, the coupling level must not be too high (e.g. preferably the magnitude of the S2i parameter 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 of the gain of the primary antenna 110, nor too low (e.g. preferably the magnitude of the S2i parameter between the primary antenna 110 and the secondary antenna 120 is greater than -15 dB) to ensure the proper functioning of the secondary antennas 120.

[0069] The EM 210 coupling device further comprises:

[0070] - an electrical probe 210b for EM coupling between the primary antenna 110 and the (or the) guided propagation line 210a; and

[0071] - an electrical probe 210b for EM coupling between the line(s) of guided propagation 210a and secondary antenna 120.

[0072] Conversely, in the embodiment of [Fig. 2a], the EM 210 coupling device comprises:

[0073] - an electrical contact 210c for EM coupling between the primary antenna 110 and the (or the) guided propagation line 210a; and

[0074] - a 210c electrical contact for EM coupling between the line(s) of guided propagation 210a and secondary antenna 120.

[0075] Alternatively, magnetic loop coupling can be considered for EM coupling between the primary antenna 110 and the guided propagation line(s) 210a, as well as for EM coupling between the guided propagation line(s) 210a and the secondary antenna 120.

[0076] Furthermore, couplings of different types (i.e., contact, probe, or loop) can be envisaged for 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 some 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:

[0077] - an electrical contact;

[0078] - an electrical probe; or

[0079] - a magnetic loop.

[0080] An example of an antenna system 200 according to an embodiment of the invention is now presented in relation to [Fig.3].

[0081] More specifically, the primary antenna 110 is a circular patch antenna. The rotational symmetry makes it easier, e.g., to address all possible directions for the attenuations 350 in the radiation pattern.

[0082] However, in some embodiments, other types of primary antennas 110 are used, e.g. dipole, spiral, horn antennas, etc. 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.

[0083] Returning to [Fig. 3], the primary antenna 110 is here a multi-band, right-hand 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 frequency bands El and E6, the primary antenna 110 comprises two circular patches, stacked and centered one above the other so as to ensure rotational symmetry over a sufficient frequency band (better axial ratio over the bands considered compared to a nearly square or even truncated patch antenna).

[0084] Furthermore, in order to reduce the dimensions of the primary antenna 110 by a factor of approximately two, the patch antennas are fabricated on a thick microwave substrate (e.g., reference RO4003CTM, sr = 3.38 and tan 5 = 0.0027 at 10 GHz). The center frequency and bandwidth are adjusted by the patch diameter and the substrate thickness, respectively. Here, the diameter is 70 mm with a thickness of 6.4 mm for the lower patch covering the E6 band (stacking four 1.524 mm substrates), and the diameter is 55.2 mm with a thickness of 3.15 mm for the upper patch covering the El band (stacking two 1.524 mm substrates).

[0085] To achieve right-hand circular polarization, the antennas are fed by four quadrature feed probes 300 located 8 mm from the center of the structure and with a diameter of 2.2 mm. These feed probes 300 excite the first transverse magnetic mode TM110 of the primary antenna 110.

[0086] The feed probes 300 are connected to a feed circuit located on the rear layer of the printed circuit board of the primary antenna 110 ([Fig. 3a]). The feed circuit includes a balun 320 (e.g., Mini-Circuits ADTL2-18+ reference) feeding two 3dB-90° hybrid couplers 330 (e.g., Mini-Circuits QCN-19+ reference) connected to the feed probes 300 so as to ensure that each feed probe 300 receives signals of the same amplitude but phase-shifted by 90° (0°; 90°; 180°; 270°). Finally, a connector 340 (e.g., SMA type) is connected to the input of the balun to connect the primary antenna 110 to a coaxial cable.

[0087] Returning to [Fig. 3], in order to supply power to the secondary antennas 120 located around From 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 them to ensure a coupling level of approximately -13 dB in the frequency bands E1 and E6. Generally, 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 some embodiments, other types of coupling between the primary antenna 110 and the guided propagation line 210a can be considered (e.g., an electrical contact 210c or magnetic loop coupling).

[0088] Returning to [Fig. 3], the secondary antennas 120 are configured to be capable of operate in the E6 and El frequency bands and include:

[0089] - 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

[0090] - four second secondary antennas 120b, each second secondary antenna 120a being coupled to the primary antenna 110 via a second respective EM coupling device 210.

[0091] In particular, the first secondary antennas 120a and the second secondary antennas 120b are of different types. Furthermore, the first secondary antennas 120a and the second secondary antennas 120b radiate EM fields with 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.

[0092] The first secondary antennas 120a are here printed dipoles on a substrate. The second secondary antennas 120b are here printed magnetic loops on a substrate. However, in some embodiments, other types of secondary antennas 120a, 120b are used, e.g. dipole, spiral, horn antennas, etc.

[0093] In some embodiments, the first secondary antennas 120a and the second secondary antennas 120b are of the same type. In some embodiments, the first secondary antennas 120a and the second secondary antennas 120b radiate EM fields having the same polarizations.

[0094] 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]).

[0095] More specifically, the load impedance 130 of a given secondary antenna 120a, 120b is variable 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.

[0096] More specifically, the load impedance 130 of a given secondary antenna 120a, 120b is here a selectable impedance from a set of predetermined discrete impedances. Each impedance in the set of impedances is configured so that the radiation pattern of the antenna system 200 exhibits, for a given frequency in the El or E6 frequency band, an attenuation 350 in a predetermined direction.

[0097] For example, a load switching circuit associated with each secondary antenna 120a, 120b includes an RF switch 310 of the SP8T type (e.g., PSemi reference PE42282) to select up to eight different load impedance values ​​130 (making it possible to create, 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 The load line is loaded by a resistor and a reactance (e.g., capacitor or inductor) connected in series on a microstrip line terminated with a ground connection. The advantage of switching discrete values ​​of the load impedance 130 compared to a continuous variation lies in the high stability of the resulting impedance values ​​with respect to operational variations (e.g., temperature, RF signal level). This ensures stable performance of a product implementing such an antenna system 200.

[0098] Thus, according to such an approach, in certain embodiments the load impedance 130 is a selectable impedance from a set of predetermined discrete impedances. Each impedance in the set of impedances is configured so that the radiation pattern of the antenna system 200 exhibits, for a given frequency in 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 certain embodiments, the value of the load impedance 130 varies continuously within the range of predetermined values ​​considered.

[0099] 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].

[0100] However, in some embodiments, the secondary antennas 120 are not equidistributed around the primary antenna 110. Furthermore, in some embodiments the secondary antennas 120 are not implemented in a plane.

[0101] 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 is implemented.

[0102] Thus, in certain embodiments, the antenna system 200 is configured to operate in one (or more) frequency bands and comprises:

[0103] - 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 exhibits, for a first given frequency of the frequency band(s) and for a first polarization of the radiated EM field, an attenuation 350 in a first predetermined direction;

[0104] - 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 exhibits, for a second given frequency of the frequency band(s) and for a second polarization of the radiated EM field, an attenuation of 350 in a second predetermined direction.

[0105] Thus, radiation attenuations of 350 can be obtained according to different polarizations.

[0106] In some embodiments, the first and second polarizations are orthogonal polarizations (e.g., the first polarization is right-hand circular (or elliptical) polarization and the second polarization is left-hand circular (or elliptical) polarization. Alternatively, the first and second polarizations are orthogonal linear polarizations). In some embodiments, the first and second polarizations are different polarizations (orthogonal or not). In some embodiments, the first and second polarizations are the same polarizations.

[0107] 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.

[0108] 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.

[0109] In some embodiments, the antenna system 200 comprises secondary antennas 120 all of the same type. In some embodiments, the secondary antennas 120 are, at least in part, of different types.

[0110] In some embodiments, the antenna system 200 comprises a single secondary antenna 120.

[0111] We now present, in relation to [Fig.4] an example of the structure of a set of load impedances 130 allowing 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.

[0112] More particularly, the structure of [Fig. 4] is especially suited for sequentially addressing the creation of attenuations 350 in a plurality of frequency bands. To this end, an RF switch 400 (or an arrangement of several RF switches) is configured to be connected 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 are used for a third frequency band. More specifically, a load impedance 130 is configured to create an attenuation 350 for a given frequency in the respective frequency band and in a given direction of the radiation pattern of the antenna system 200 (Zon1 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 (Zoff1 for the first frequency band, Zoff2 for the second frequency band, and Zoff3 for the third frequency band). However, in some embodiments, a different number of load impedances 130 per frequency band and / or a different number of frequency bands are considered.

[0113] An example of a load impedance structure 130 is now presented in relation to [Fig.4a] allowing the creation of attenuations 350 to be addressed in the radiation pattern of the antenna system 200 in several frequency bands according to another embodiment of the invention.

[0114] More particularly, the structure of [Fig. 4a] is especially suited to address the simultaneous creation of attenuations 350 in a plurality of frequency bands. To this end, the load impedance 130 includes a frequency multiplexing device 410 (e.g., a duplexer for two frequency bands or a triplexer for three frequency bands, etc.) configured to multiplex different unit impedances 430 into different frequencies. 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 exhibits, for a given frequency in the respective frequency band, an attenuation 350 in a predetermined radiation direction.

[0115] In some embodiments, at least one unit impedance 430 associated with a respective frequency band is selectable (e.g. via the implementation of an RF switch) from a set of unit impedances 430.

[0116] For example, in the case illustrated in [Fig. 4a], two unit impedances 430 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), selectable via an RF switch 420. One unit impedance 430 is configured to create attenuation 350 for a given frequency in the respective frequency band and in a given direction of the radiation pattern (Zon1 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 nominal operation of the antenna system 200 without radiation attenuation 350 (Zoff1 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.

[0117] Thus, attenuations of 350 can be obtained simultaneously in different frequency bands.

[0118] [Fig. 5] illustrates a 500 network antenna comprising a plurality of systems antenna 200 according to an embodiment of the invention.

[0119] More specifically, the 500 array antenna implements beamforming, e.g., via the implementation of an analog or digital channel-forming circuit. In this way, additional attenuations of 350 in the overall radiation pattern of the 500 array antenna can be obtained in addition to those related to the radiation patterns of the 200 antenna systems. Thus, a second level of spatial filtering is obtained in addition to that related to the implementation of the 200 antenna systems.

[0120] Depending on the implementations, such a 500 network antenna implements 200 antenna systems according to any one of the embodiments described above.

Claims

Demands

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 such that the radiation pattern of the system exhibits, for at least one given frequency of said at least one frequency band, an attenuation (350) in a predetermined direction, wherein 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, characterized in that the primary antenna and said at least one secondary antenna are of different natures.

2. Antenna system according to claim 1, wherein the impedance is variable in 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 in the set of impedances being configured so that the radiation pattern of the system exhibits, for a given frequency in said at least one frequency band, attenuation in a predetermined direction.

4. 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 exhibits, for a given frequency of the respective frequency band, attenuation in a predetermined direction.

5. 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, wherein 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 or secondary antenna, at least one element belonging to the group comprising: - an electrical contact; - an electrical probe; or - a magnetic loop.

7. 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 such that the radiation pattern of the system exhibits, 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 exhibits, 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. 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, wherein a radiation pattern of the primary antenna has an axis of revolution, and wherein 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 array (500) comprising a plurality of antenna systems according to any one of claims 1 to 11.

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