PLANAR NET FIXTURE ANTENNA

Description

[0001] The invention lies in the field of planar antennas comprising an array of unitary radiating elements.

[0002] The invention applies to radiofrequency antennas, in particular, to microwave antennas. Such antennas can be used in various applications such as radar applications in avionics and aerospace, high-speed communication, beacons and space technologies.

[0003] It particularly concerns radars with active antennas also called AESA (acronym for the Anglo-Saxon expression "Active Electronically Scanned Array") and antennas with multiple inputs and outputs also called MIMO in reference to the Anglo-Saxon expression "Multiple-Input Multiple-Output".

[0004] When a planar antenna with a two-dimensional radiating element array emits a beam along a principal axis x1, it has a radiation pattern in dB in different directions formed around the center of the antenna in a plane perpendicular to the plane of the antenna. Such a pattern is shown in the figure 4 around a central point in a predetermined plane. The radiation pattern includes a main lobe radiated along the main axis x1. The x1 axis corresponds to the axis of the absolute maximum of the radiation pattern. The radiation pattern includes two secondary lobes on either side of the main lobe, radiated along respective x2, x2' axes of secondary lobes, corresponding to the radiation axes of the highest local maxima of the radiation pattern after the absolute maximum. The radiation pattern also includes diffuse lobes also called diffuse lobes along other axes corresponding to the other local maxima of the radiation pattern. The different lobes are separated by minimaxes of the radiation pattern.

[0005] There is a need to reduce the side lobes and diffuse lobes of a radar antenna. Indeed, r in directions other than the main lobe lead to the following disadvantages: the elements illuminated by the side lobes are seen as parasites and added, in reception, in the main lobe. A strong mobile echo is then amalgamated with the receptions of the main lobe, generating a detection ambiguity and, for example, a false alarm in the main lobe. This is highly problematic in the case of strong misalignment of the antenna beam, the side lobes and diffuse lobes rising to significant levels, in particular when the antenna is on board an aircraft at low altitude and a side lobe and diffuse lobes are directed towards the ground. Such a rise in the levels of the side and diffuse lobes prevents the use of the antenna for combat radars.Furthermore, emission in the side lobes and diffuse lobes limits the radar's discretion during transmission. Emissions from the side lobes allow jammers to synchronize a replica to generate false blips, which will appear in the main reception lobe. The radar is therefore deceived by such echoes. These are called angular jammers.

[0006] Side lobes at reception also cause disadvantages. The elements illuminated by the side lobes are seen and added, at reception, to the main lobe. Once the overall reception is carried out, it is no longer possible to separate the receptions in the axis of the main reception lobe from the receptions in the side and diffuse lobes.

[0007] Furthermore, there is a deformation of the secondary lobes depending on the pointing angle. This deformation leads to an asymmetry and a widening of the secondary lobes as well as variations in the gain of the lobes (secondary, diffuse and main) depending on the pointing angle.

[0008] A known solution to limit the secondary lobes in transmission is to choose pointing coefficients in such a way as to optimize the ratio between the main lobe and secondary lobes, for example of the Hann window type. However, this type of correction results in a widening of the main lobe and therefore a loss of power in the transmission axis of the main lobe and a slight loss of precision. Furthermore, this loss of radiated power results in a loss of received power which must be compensated by a need to increase the radiated power which results in heating of the antenna panel, attenuation of the signal and problems of different thermal regimes of the amplifiers and therefore phase corrections to be carried out according to the pointing directions and weightings.

[0009] For active antenna radars or AESA, it is possible to generate asymmetries of the emission pattern from emission pulse to emission pulse. This allows the levels of the right and left secondary lobes to be modified, but has the disadvantage of modulating the radiated levels and the received levels.

[0010] Another solution that can be used for both transmission and reception consists of coupling the main radar antenna to an auxiliary array antenna, called an ancillary antenna. The phase shifts and attenuations to be applied to the different channels of the ancillary antenna are determined so that the radar has secondary lobes and diffuse lobes of lower power than those of the main antenna without modifying the main lobe. However, this solution requires additional equipment, including the ancillary antenna, which has a certain size, which, when a predetermined size is assigned to the system, requires a reduction in the surface area of ​​the main antenna.

[0011] At the receiving end, methods are known to combat unintentional interference such as Side Lobe Opposition or OLS methods. However, these methods require additional antennas and additional receivers. This also requires significant signal processing that estimates the respective gains of the two receiving antennas (main and pseudo-omnidirectional auxiliary). The known principle is to match receptions made by the pseudo-omnidirectional (cardioid) antenna with the characteristics of the side lobes of the main antenna, both in amplitude and phase. This has a cost (consumption, weight and computing power, therefore dissipation). The attenuation depth of these methods is, moreover, limited.Furthermore, since electronic antennas are pointed at different angles, with variations in the gain of the side lobes (as well as the main lobe), it is not possible to use a fixed cardioid auxiliary antenna. The fluctuation of the side lobes and the widening of the main lobe depending on the pointing angle require dynamic calibration by pointing direction and inter-channel correction. This auxiliary antenna must follow the pointings of the main beam. In the event of side lobes rising, the usual solution is to tighten the mesh of the radiating element network, which has a cost and causes a density that is problematic at the level of the implementation (number of boxes, routing of components, cooling, etc.).

[0012] One aim of the invention is to limit at least one of the aforementioned drawbacks.

[0013] For this purpose, the invention relates to an array antenna comprising an array of radiating elements composed of N radiating elements, N being an integer greater than 1, each radiating element of the array of radiating elements comprising a main excitation port, the array of radiating elements comprising at least a first radiating element comprising only the main excitation port and a secondary sub-array composed of N1 second radiating element(s) taken from among the N radiating elements of the array, such that N1 is greater than or equal to 1 and less than N, each radiating element of the secondary sub-array comprising a secondary excitation port.

[0014] Advantageously, the antenna comprises a processing circuit configured to allow signals to be conveyed from and / or to the main excitation ports in the same main mode taken from among the common mode and the differential mode and allowing signals to be conveyed to and / or from the secondary excitation ports in the same secondary mode taken from among the common mode and the differential mode.

[0015] Advantageously, the antenna comprises a processing circuit comprising: N main transmission circuits capable of independently adjusting phases and amplitudes of main excitation signals from the respective main excitation ports so as to generate a main transmission beam along an adjustable predetermined main transmission direction and / or N main reception circuits capable of independently adjusting phases and amplitudes of main reception signals from the respective main excitation ports so as to generate a main reception beam along an adjustable predetermined main reception direction,and N1 secondary transmission circuits capable of independently adjusting phases and amplitudes of excitation signals of the respective secondary excitation ports so as to generate a secondary transmission beam according to an adjustable predetermined secondary transmission direction and / or N secondary reception circuits capable of independently adjusting secondary phases and secondary amplitudes of secondary reception signals from the respective secondary excitation ports so as to generate a secondary reception beam according to an adjustable predetermined secondary reception direction.

[0016] Advantageously, the antenna comprises several secondary sub-arrays, the array of radiating elements comprising a unitary sub-array composed of at least one first radiating element, the processing circuit making it possible to simultaneously generate secondary transmission beams from the respective secondary sub-arrays or to simultaneously generate secondary reception beams from the respective secondary sub-arrays.

[0017] Advantageously, the radiating elements of the secondary sub-network are arranged around the first radiating element or first radiating elements.

[0018] The invention also relates to a method for generating beams by an antenna according to the invention. The method comprises the following steps: exciting the main excitation ports of the N radiating elements of the array so as to generate a main transmission beam along a first predetermined transmission direction, exciting the secondary excitation ports of the secondary sub-array so as to generate, simultaneously with the main transmission beam, a secondary transmission beam along a second predetermined transmission direction, and / or shaping signals from the main excitation ports and summing them so as to generate a main reception beam along a first predetermined reception direction, shaping signals from the secondary excitation ports of the secondary sub-array and summing them so as to generate, simultaneously with the main reception beam, a secondary reception beam along a second predetermined reception direction.

[0019] The invention also relates to a method for limiting another lobe other than a main lobe of a main transmission beam by an antenna according to the invention, the method comprising the following steps: exciting the main excitation ports so as to generate the main emission beam according to the first predetermined emission direction, exciting the secondary excitation ports of the secondary sub-array so as to generate simultaneously with the main beam, a secondary emission beam having a main lobe of the secondary beam in phase opposition with the other lobe of the main emission beam according to the other emission direction of the other emission lobe and having an amplitude less than or equal to the amplitude of the other lobe of the main beam.

[0020] Other characteristics, details and advantages of the invention will emerge from reading the description given with reference to the appended drawings given by way of example and which represent, respectively: there figure 1 schematically illustrates an antenna according to the invention, the figure 2 schematically illustrates an example of a dual processing circuit coupled to a radiating element of the secondary network, the figure 3 illustrates an example of a simple processing circuit coupled to a radiating element comprising only the main excitation port, the figure 4 already described illustrates a classic radiation pattern of a planar antenna.

[0021] From one figure to another, the same elements are identified by the same references.

[0022] The invention relates to planar array antennas better known as patch antennas comprising a planar array of unitary radiating elements of the conductive patch type also called microstrip tiles (also called microstrip patches).

[0023] As visible on the figure 1 , the antenna A comprises an array R of radiating elements composed of a number N greater than 1 of substantially planar radiating elements E0, E1, extending substantially in the plane of the figure 1 . N is equal to 64 in the non-limiting example of the figure 1 .

[0024] The invention relates in particular to active antennas or AESA. The invention also relates to multiple-input, multiple-output antennas commonly called MIMO, an acronym for the English expression “Multiple-Input Multiple-Output”.

[0025] Preferably, each radiating element E0, E1 is a pad made of conductive material. Alternatively, at least one radiating element comprises several stacked conductive pads. In the non-limiting example of the figure 1 , the radiating elements E0, E1 have a square shape. Alternatively, the radiating elements have another shape, for example a disc shape or another parallelogram shape such as for example a rectangle or a rhombus.

[0026] As visible on the figure 1 , the antenna A comprises a processing circuit CT coupled to the radiating elements E0, E1 at respective excitation ports PP, PS so as to enable the excitation of the radiating elements E0, E1 at the respective excitation ports E0, E1 from at least one input signal and / or so as to enable the processing of signals resulting from the excitation of the respective excitation ports PP, PS so as to generate a reception signal.

[0027] The CT processing circuit is capable of conveying signals to or from each excitation port PP, PS in common mode, the excitation port PP, PS then comprises a single excitation point as shown in figure 1 , or in differential mode, the excitation port then includes two excitation points.

[0028] The coupling between the processing circuit and the respective ports is carried out in a manner known to those skilled in the art. This coupling is, for example, carried out by electromagnetic slot coupling. Alternatively, the coupling is carried out by electrically connecting the end of a transmission line to an excitation point. The coupling can alternatively be carried out on the plane of the planar radiating element, or "patch", by attacking it directly with a printed microstrip line, connected to the edge of the radiating element. The excitation can also be carried out by proximity coupling to a printed microstrip line at a level located between the "patch" and the layer forming the ground plane.

[0029] The coupling can be carried out in the same way or in a different way for the different excitation points.

[0030] As visible on the figure 1 , each radiating element E0, E1 includes an excitation port PP called, main represented by a cross.

[0031] According to the invention, among the N radiating elements E0, E1 of the network R, a number U greater than or equal to 1 of radiating elements E0 and less than N, called main, comprises a single excitation port which is the main excitation port PP. In the non-limiting example of the figure 1 , U is equal to 16. These elements E0 form a so-called simple subnetwork S0.

[0032] The network R of radiating elements E0, E1 also comprises at least one secondary sub-network Si of radiating elements taken from among the radiating elements of the network R (with i = 1 to S where S is the number of secondary sub-networks, equal to 1 in the non-limiting example of the figure 1 ). i is equal to 1 in the non-limiting example of the figure 1 .

[0033] The secondary sub-network Si is composed of Ni radiating elements Ei (Ei = E1 on the figure 1 ), with Ni greater than or equal to 1 and less than N. Ni=N1 is equal to 48 in the non-limiting example of the figure 1 and Ni= NU.

[0034] Each radiating element E1 of the secondary sub-assembly S1 comprises, in addition to the main excitation port PP, a second excitation port PS, called the secondary excitation port PS, represented by a point on the figure 1 .

[0035] Each of the excitation ports PP, PS is coupled to the processing circuit CT.

[0036] The antenna A according to the invention makes it possible in particular, by providing an appropriate processing circuit CT, to generate several beams, including a main transmission beam by exciting the main excitation ports PP and a secondary transmission beam by exciting the secondary excitation ports PS. It is also possible to generate a main reception beam from signals from the main excitation ports PP and a secondary reception beam from signals from the secondary excitation ports.

[0037] In particular, it is possible to generate a main beam in transmission by exciting the main excitation ports PP of antenna A and to generate a secondary beam by exciting the secondary excitation ports PS.

[0038] These beams have a main lobe, secondary lobes and diffuse lobes. The direction of a beam is the direction of the main lobe of this beam.

[0039] By adjusting the phases of the excitation signals of the respective main ports PP it is possible to adjust the direction of the main beam. By adjusting the phases and amplitudes of the excitation signals of the secondary excitation ports, it is possible to adjust the direction of the secondary beam and in particular to generate a secondary beam according to the direction of one of the secondary lobes of the main beam; in phase opposition with the latter and whose amplitude is defined so as to adjust the power emitted by the antenna according to this direction in order to attenuate the secondary lobe emitted by the antenna.

[0040] The antenna A according to the invention also makes it possible to benefit from the entire radiating surface of the antenna, i.e. all of the radiating elements PP, PS of the array of radiating elements R of the antenna A to generate the main beam. There is therefore no loss of power from the main beam. This solution is compact because it does not require an additional antenna to generate the two beams.

[0041] The CT processing circuit includes N main processing circuits TP, one of which is shown in the figure 2 , coupled to the respective main excitation ports PP and N1 secondary processing circuits TS, one of which is shown in the figure 2 , coupled to the respective secondary excitation ports PS.

[0042] The dynamics of the signals to be processed to attenuate a secondary lobe in the main processing circuits TP and the secondary processing circuits TS are more than 20 dB, the power of the secondary lobe of the order of 20 dB lower than that of the main lobe. The fact of generating the secondary beam having a main lobe of lower amplitude than the main lobe of the main beam by means of different processing circuits makes it possible to manage this dynamic more easily in a low-cost way, in particular it is not necessary to provide attenuators capable of supporting a large dynamic range.

[0043] Furthermore, this solution allows, by using fewer radiating elements to attenuate the secondary lobes and the diffuse lobes also called diffuse, to further limit the need for attenuators to perform this function. The gains of the chains of the reception or transmission circuits being proportional to the number of secondary radiating elements, this number can be configured so that these transmission / reception chains work in the useful gain zone. This allows this gain adjustment to be made without using electronic means (variable attenuators, variable gain amplifiers) acting on a large gain dynamic. This has the effect of limiting intermodulations by limiting the variations of the IP3 (3rd order intermodulation) known to those skilled in the art. This also contributes to limiting the variations in the noise factors of the transmission / reception chains.

[0044] In addition, the phase shift induced by the different attenuation values ​​of the main and secondary processing circuits is limited.

[0045] Furthermore, this solution allows the power received by the ports of the same radiating element to be summed, in the radiating element and in the air, which limits intermodulation problems and increases the radiated power. It avoids dissipation in the integrated circuits and / or in the antenna. Furthermore, since the summation of the powers of the main and secondary channels is done at the level of the radiating element and not via an electronic circuit comprising power, gain and amplitude linearity limitations, this limits the aforementioned IP3 variations and the need to dissipate power unnecessarily in the electronic components.

[0046] The proposed solution consumes low power of the order of the power emitted in the secondary lobes of the main beam, in the case of a secondary lobe suppression application.

[0047] The proposed solution also allows the use of a mesh larger than λ / 2 where λ is the wavelength of the beam or a triangular mesh since it allows the elimination of annoying secondary or diffuse lobes.

[0048] The number N1 of radiating elements E1 of the secondary sub-array depends on the dynamics required for the suppression of the corresponding secondary lobe or diffuse and the desired elimination accuracy.

[0049] On the figure 2 , an example of a processing circuit called double CD coupled to the excitation ports PP, PS, of one of the radiating elements E1 comprising two excitation ports PP, PS is shown.

[0050] The dual processing circuit CD comprises a main processing circuit TP coupled to the main port PP of the radiating element E1 and a secondary processing circuit TS coupled to the secondary excitation port PS of the same radiating element E1. The single processing circuit shown in figure 3 , coupled to one of the radiating elements E0, comprising only the main excitation port PP, comprises only the main processing circuit TP.

[0051] Advantageously, the respective main processing circuits TP coupled to the respective main excitation ports PP are identical. The same is advantageously true for the secondary processing circuits TS coupled to the respective secondary ports PS of the sub-network S1.

[0052] Advantageously, the N main processing circuits TP comprise N main transmission circuits CPE capable of independently adjusting phases and amplitudes of excitation signals of the respective main excitation ports PP so as to enable the generation of a main transmission beam having a main lobe of predetermined amplitude adjustable according to a predetermined main transmission direction adjustable.

[0053] The main CPE transmission circuit comprises, in the non-limiting example of the figure 2 , a controllable phase shifter FPE capable of applying an adjustable phase shift to an input signal SE. The main transmission circuit CPE comprises a controllable amplitude adjuster GPE for adjusting the amplitude of the signal output from the controllable phase shifter FPE. The amplitude adjuster is, for example, a controllable attenuator or a controllable gain amplifier. The main transmission circuit CPE further comprises an output amplifier APE, for example, a high-power amplifier amplifying the signal output from the controllable amplifier.

[0054] Advantageously, the N main processing circuits TP comprise N main reception circuits CPR capable of independently adjusting the phases and amplitudes of the reception signals from the respective main excitation ports PP so as to enable the generation of a main physical reception beam having a main lobe, of adjustable predetermined amplitude, according to an adjustable predetermined main reception direction.

[0055] The main CPR reception circuit comprises, in the non-limiting example of the figure 1 , an input amplifier receiving a signal generated by the excitation of the excitation port by a radio wave. The main receiving circuit CPR comprises a controllable amplitude regulator GPR, for example a controllable attenuator or a controllable gain amplifier, receiving the output signal of an input amplifier EPR receiving a signal from the main excitation port PP. The controllable amplitude regulator GPR acts on the amplitude of the output signal of the input amplifier APR so as to deliver an output signal of adjustable amplitude. The main receiving circuit CPR comprises a controllable phase shifter FPR applying an adjustable phase shift to the output signal of the amplitude regulator CPR.

[0056] Advantageously, the N1 secondary processing circuits TS comprise N1 respective secondary transmission circuits CSE capable of independently adjusting phases and amplitudes of excitation signals of the respective secondary excitation ports PS so as to enable generation of a secondary transmission beam whose main lobe has a predetermined amplitude adjustable according to a predetermined secondary transmission direction adjustable and having a predetermined phase shift relative to the main transmission beam.

[0057] The secondary emission circuit CSE comprises, in the non-limiting example of the figure 1 , a controllable phase shifter FSE capable of applying an adjustable phase shift to an input signal SE. The secondary transmission circuit CSE comprises an amplitude regulator GSE, acting on the amplitude of the signal output from the controllable phase shifter FSE so as to generate a secondary beam having a main lobe of adjustable predetermined amplitude. The amplitude regulator GSE is, for example, an adjustable gain amplifier or an adjustable attenuator. The secondary transmission circuit CSE further comprises an output amplifier ASE, for example, a high-power amplifier amplifying the signal output from the controllable amplifier GSE.

[0058] Advantageously, the N1 secondary processing circuits TS comprise N1 secondary reception circuits CSR capable of independently adjusting the phases and amplitudes of the reception signals coming from the respective secondary excitation ports PS so as to enable the generation of a secondary reception beam whose main lobe has a predetermined amplitude adjustable according to a predetermined secondary reception direction adjustable and having a predetermined phase shift with the main reception beam.

[0059] The secondary reception circuit CSR comprises, in the non-limiting example of the figure 1 , an input amplifier ASR receiving a signal from the secondary excitation port PS. The secondary receiving circuit CSR also comprises an amplitude adjuster GSR, for example a controllable attenuator or a controllable gain amplifier GSR, receiving the output signal from the input amplifier ASR. The amplitude adjuster GSR acts on the amplitude of the signal at the output signal of the input amplifier ASR to deliver an output signal having an adjustable amplitude. The secondary receiving circuit CSR comprises a controllable phase shifter FSR applying an adjustable phase shift to the output signal of the amplitude adjuster GSR.

[0060] Each of the main processing circuits TP or secondary TS comprises a signal steering device, CP and respectively CS, for example a switch or a circulator, making it possible to switch between a transmission mode in which the transmission circuit CPE, respectively CSE, is able to excite the associated excitation port PP, respectively PE, and a reception mode in which the reception circuit CPR, respectively CSR, is able to shape a signal coming from the associated excitation port PP or PS. The steering device CP, respectively CS, is able to alternately be in a first state in which it steers a signal coming from the main port PP, or respectively secondary port PS, towards the input amplifier APE, or respectively ASE, and in a second state in which it steers a signal coming from the output amplifier APR, or respectively ASR, towards the main port PP, or respectively the secondary port PS.

[0061] Alternatively, each main TP or secondary TS processing circuit comprises a transmission circuit or a reception circuit.

[0062] The proposed solution allows, by adequately controlling the phase shifters and the controllable amplifiers associated with the different radiating elements and the orientation devices, to simultaneously generate two transmission beams along respective adjustable transmission axes with adjustable relative amplitudes and phases and two reception beams along respective adjustable reception axes with adjustable relative amplitudes and phases between a secondary or diffuse lobe of the main beam and the main lobe of the secondary beam.

[0063] The invention relates to a method for the simultaneous generation of physical transmission beams using an antenna according to the invention.

[0064] The process includes the following steps: exciting the N main excitation ports PP of the N radiating elements of the network R so as to generate a main emission beam in a first predetermined emission direction, exciting the N1 secondary excitation ports PS of the secondary sub-network S1 so as to generate, simultaneously with the main emission beam, a secondary emission beam in a second predetermined emission direction.

[0065] To this end, the process includes: adjusting phases and amplitudes of the excitation signals of the respective N main excitation ports PP so as to generate the main emission beam according to the first predetermined emission direction, adjusting phases and amplitudes of the excitation signals of the respective N1 secondary excitation ports N1 of the secondary sub-array S1 so as to generate, simultaneously with the main emission beam, the secondary emission beam according to the second emission direction, possibly with a predetermined phase shift relative to the main beam, and possibly so that the ratio between the amplitude of the main lobe of the main beam and the amplitude of the main lobe of the secondary beam is predetermined.

[0066] The adjustment of the phases and amplitudes of the excitation signals of the respective main excitation ports so as to generate the main transmission beam is carried out by the main circuits CPE transmission circuits of the respective main circuits TP.

[0067] The adjustment of the phases and amplitudes of the excitation signals of the respective secondary excitation ports so as to generate the secondary beam is carried out by the CSE transmission circuits of the respective TP secondary circuits.

[0068] The processing circuits apply, for example, adjustable phase shifts and / or adjustable attenuations or amplifications to the same input signal SE coming from a distributor R distributing an initial signal SI coming from a source or to different synchronized input signals having the same frequency.

[0069] In this case, the main emission beam is generated by exciting the N main excitation ports PP of order i with i = 1 to N by the following respective so-called main excitation signals Vpi(t): Vpi t = e iωt ∗ A i ∗ e iφ i

[0070] Where ω is the pulsation of the excitation signal, Ai is the amplitude of the excitation signal of the i-order PP excitation port and ϕ i is the phase of the excitation signal of the i-order PP excitation port. This signal Vpi(t) is one of the N components intended to form the main beam according to the first emission direction.

[0071] The secondary beam is generated by exciting the N1 main excitation ports PS of order j by the following excitation signals: VSj t = e iωt ∗ A j ∗ e iφ j

[0072] Where ω is the pulsation of the excitation signal, Aj is the amplitude of the excitation signal of the PS excitation port of order j and ϕ j is the phase of the excitation signal of the PS excitation port of order j. This signal VSj(t) is one of the Si components intended to form the secondary beam according to the second emission direction.

[0073] Alternatively, the secondary beam is emitted at a different frequency from the main beam. For this purpose, the secondary transmission circuits are, for example, connected to a secondary source generating a secondary input signal and the main transmission circuits are connected to a main source generating a main input signal of a frequency distinct from that of the secondary input signal at a frequency distinct from the frequency of the secondary input signal. The main input signal then passes through a main distributor of the processing circuit dividing the secondary input signal into excitation signals respectively injected at the input of the respective main transmission circuits.

[0074] In the latter case, the signals generated by the primary and secondary sources must be phase coherent.

[0075] The device advantageously comprises a clock configured to synchronize the signals delivered by the two sources.

[0076] The invention also relates to a method for attenuating the power radiated by the antenna in the direction in which another lobe is radiated, which is a lobe of the main transmission beam other than the main lobe emitted by the antenna and which is emitted in another transmission direction (dependent on the direction of the main lobe, for example, a lobe directed towards a direction forming an angle of 30° relative to the direction in which the main lobe is directed. In this case, the main beam and the secondary beam are generated at the same frequency.

[0077] The mitigation process includes the following steps: exciting the N main excitation ports PP so as to generate the main emission beam according to the first predetermined emission direction, exciting the N1 secondary excitation ports PS of the secondary sub-array S1 so as to generate simultaneously with the main beam, a secondary emission beam in the same direction as the other lobe, and having a main lobe having an amplitude less than or equal to the amplitude of the other lobe to be attenuated and in phase opposition with the main lobe of the main beam.

[0078] Advantageously, the amplitude of the main lobe of the secondary beam is substantially equal to the amplitude of the other lobe of the main beam to be attenuated. This makes it possible to substantially cancel the power radiated by the antenna in the direction of the other lobe.

[0079] To this end, the process includes: adjusting phases and amplitudes of the excitation signals of the respective N main excitation ports PP so as to generate the main transmission beam along the first transmission direction at a predetermined frequency, adjusting phases and amplitudes of the excitation signals of the respective secondary excitation ports of the secondary sub-array so as to generate the secondary transmission beam along the other transmission direction, having a main lobe in phase opposition with the other lobe of the main transmission beam and having a main lobe of amplitude less than or equal to the amplitude of the other lobe of the main beam, so as to attenuate or substantially cancel the power radiated by the antenna along the other transmission direction.

[0080] For this purpose, for example, the phases of the excitation signals of the secondary excitation ports are first varied simultaneously in the same way, i.e. by the same amount, for fixed phases and amplitudes of the excitation signals of the main excitation ports and fixed amplitudes of the excitation signals of the secondary excitation ports, until the lowest possible radiated power is obtained in the direction of the other lobe of the main beam. The secondary lobe of the main beam and the main lobe of the secondary beam are then in phase opposition.

[0081] The amplitudes of the excitation signals of the secondary excitation ports are then varied simultaneously in the same way, that is to say by the same value, for fixed phases and amplitudes of the excitation signals of the main excitation ports and fixed phases of the excitation signals of the secondary excitation ports, until, depending on the direction of the other lobe of the main beam, a radiated power lower than the power radiated by the main lobe, or even substantially zero.

[0082] The waves radiated by the antenna in the other direction are destructive and the secondary beam attenuates or cancels the power emitted by the antenna in the other direction.

[0083] In the non-limiting example of the figure 2 , the controllable phase shifters and controllable amplifiers of the transmission paths of the different processing circuits are controlled so as to apply the desired phase shifts and amplifications to generate the desired main transmission beam and to simultaneously generate the secondary transmission beam in the other transmission direction so as to attenuate the other lobe.

[0084] The antenna according to the invention can further be used to simultaneously generate transmission beams in different directions for another purpose, for example to deceive another radar, or for example, to use the main beam for Air-Air applications and simultaneously the secondary beam for Air-Ground applications which require less energy.

[0085] The same beam generation process can be implemented at the reception. The process then comprises the following steps: shaping signals from the main excitation ports PP and summing them so as to generate a main beam for reception in a first predetermined reception direction, shaping signals from the secondary excitation ports PS of the secondary sub-network and summing them so as to generate, simultaneously with the main reception beam, a secondary beam for reception in a second predetermined reception direction.

[0086] To this end, the process includes the following steps: adjusting phases and amplitudes of the signals from the respective main excitation ports PP and summing them so as to generate the main reception beam according to the first predetermined reception direction, adjusting phases and amplitudes of the signals from the respective secondary excitation ports PS of the secondary sub-array and summing them so as to generate the secondary reception beam according to the second reception direction.

[0087] The adjustment of the phases and amplitudes of the signals from the respective main excitation ports PP so as to generate the main receiving beam according to the first predetermined receiving direction is carried out by the receiving circuits CPR of the respective main circuits TP.

[0088] The adjustment of the phases and amplitudes of the excitation signals of the respective secondary excitation ports PS so as to generate the secondary transmission beam according to the second predetermined direction is carried out by the receiving circuits CSR of the respective secondary circuits TS.

[0089] This makes it possible to generate reception beams in different directions and therefore to receive simultaneously in different directions, although with lower gains than that of the main beam because the secondary beam is generated by a smaller number of radiating elements than the main beam.

[0090] For example, it may be interesting to use the main receiving beam for Air-Air applications and the secondary receiving beam for Air-Ground applications which require less energy.

[0091] The processing circuits apply, for example, adjustable phase shifts and amplifications to the same input signal or to different synchronized input signals having the same frequency.

[0092] Alternatively, the input signals may have distinct frequencies such that the main beam and the secondary beam have distinct frequencies.

[0093] The invention relates, for example, to a method of attenuating another lobe, for example a secondary lobe, which is a lobe of the main beam other than the main lobe transmitted by the antenna. The method of attenuating a lobe other than the main lobe at reception comprises: shaping signals from the N main excitation ports PP so as to generate a main reception beam along a first predetermined reception direction, shaping signals from the secondary excitation ports PS of the secondary sub-array so as to generate, simultaneously with the main reception beam, a secondary reception beam along the other reception direction of the other lobe, the main lobe of which is in phase opposition with the secondary lobe of the main beam and so that the main lobe of the secondary beam has an amplitude less than or equal to the amplitude of the other lobe of the main reception beam. In this way, the amplitude of the signals received by the antenna in the other direction is less than or equal to the amplitude of the other lobe of the main reception beam and, preferably, substantially zero.These steps are performed by the receiving circuits of the main and secondary processing circuits.

[0094] The processing circuits apply, for example, adjustable phase shifts and adjustable amplifications or attenuations to the signals coming from the different excitation ports PP, PS of the different radiating elements before summing these signals by a summer S.

[0095] In the non-limiting example of the figure 2 , the controllable phase shifters and controllable amplitude adjusters of the reception channels of the different treatments are controlled so as to apply the desired phase shifts and amplifications / attenuations to generate the desired main reception beam and to simultaneously generate the secondary reception beam in the other direction so as to attenuate the other lobe.

[0096] In the non-limiting realization of the figures 2 And 3, the processing circuits include transmitting and receiving circuits each comprising a controllable phase shifter and a controllable attenuator or a controllable gain amplifier. The phase shifters and amplifiers are controlled by a common computer called a pointer. These channels are used to generate physical transmitting and receiving beams.

[0097] The processing of the signals transmitted and received by transmitting and receiving circuits with controllable phase shifters and amplitude adjusters, i.e. in hardware mode, makes it possible to avoid the backscattering of energy towards the receiver and therefore the harmful effects linked to parasitic emissions at the receiver level.

[0098] When the attenuation of a secondary lobe is carried out at transmission and reception, the remainder of parasitic signals is linked to the resolution of the transmission and reception circuits and is linked to the amplitude and phase resolution of these circuits.

[0099] The antenna advantageously comprises a computer for digitally processing the signals at the output of the reception circuits and, more precisely, for applying adjustable phase shifts and adjustable amplifications to these signals so as to form the main reception beam and the secondary reception beam by calculation, using techniques known to those skilled in the art. This makes it possible to limit or eliminate the remaining parasitic signals.

[0100] This type of processing circuits is not limiting.

[0101] For example, it is possible to envisage transmission circuits each comprising a waveform generator produced by direct digital synthesis (DDS) which make it possible to generate signals of the same frequency and with adjustable phases and amplitudes without resorting to the use of controllable attenuators or controllable phase shifters.

[0102] The coefficients (amplification / attenuation and phase shifts) to be applied to the input signals to generate the excitation signals of the respective main excitation ports to generate a main beam (in transmission or reception) in a given direction and at a given frequency are then, for example, determined by recording the diagram (of transmission or respectively reception) of the main beam according to the different pointing directions, and possibly at different frequencies, in phase and in amplitude and by modifying the coefficients iteratively until the desired main diagram is obtained for a given direction and a given frequency.

[0103] The different coefficients (amplification / attenuation and phase shifts) to be applied to the excitation signals of the respective secondary excitation ports to generate a secondary beam (in transmission or reception) attenuating a predetermined lobe of a main beam generated (in transmission or respectively in reception) in a given direction and at a given frequency can be determined by recording the diagram (of transmission or respectively of reception) of the main beam in the pointing direction at the determined frequency, in phase and in amplitude,to record the radiation patterns (transmission or reception) of the antenna generating the main beam and the secondary beam (transmission or reception) at the given frequency by applying predetermined coefficients to the secondary excitation ports and modifying them until a desired antenna radiation pattern is obtained in which the amplitudes of the signals radiated or received in the direction of the lobe in question are less than or equal to those of the secondary lobe of the main transmission and reception beams and preferably substantially zero.,

[0104] Alternatively, the different coefficients are determined analytically from a model of the antenna.

[0105] Alternatively, coefficients are determined analytically and then refined iteratively by measuring radiation patterns.

[0106] In the embodiment of the figures, the antenna comprises a sub-array of secondary radiating elements but may alternatively have several sub-arrays of secondary radiating elements so as to enable several secondary beams to be generated simultaneously. The array of radiating elements always comprises main radiating elements E0 comprising a single excitation port which is the main excitation port. Some radiating elements may have several secondary excitation ports.

[0107] In the embodiment of the figures, the processing circuits are configured to enable the excitation ports to be excited or the signals from the excitation ports to be processed in common mode. Alternatively, the processing circuits coupled to the main excitation ports and / or those coupled to the secondary excitation ports of at least one of the secondary sub-networks are configured to enable the excitation ports in question to be excited or the signals from the excitation ports in question to be processed in differential mode.

[0108] In the realization of the figure 1 , the radiating elements E1 of the secondary sub-network S1 and the elements E0 of the simple sub-network S0 are distributed on coplanar surfaces SU1 and SU0 respectively separated by a closed line CA represented in dotted lines on the figure 1 . The first surface SU1 completely surrounds the central surface SU0. In other words, the surface SU1 is a crown or a frame.

[0109] The surfaces SU1 and SU0 are, advantageously, but not necessarily, concentric.

[0110] If the crown of radiating elements E0, E1 which constitutes the ancillary antenna, i.e. which generates the secondary beam, has the same perimeter as the array of radiating elements E1 which generates the main beam, the secondary beam has the same angular aperture as the main beam, i.e. the smallest aperture achievable with the geometry of the available antenna. This makes it possible to cancel the lobes in the smallest angular zone (achievable with the geometry of the available antenna).

[0111] Alternatively, the antenna comprises several secondary arrays. The radiating elements of the different secondary arrays are distributed over respective disjoint coplanar surfaces separated two by two by closed lines so as to form radiating beams having different angular apertures. This makes it possible, for example, to avoid the elimination of lobes pointing towards the sky and to process only the lobes pointing towards the ground or laterally.

[0112] Respective surfaces on which radiating elements of respective secondary networks are distributed have, for example, crown shapes. They are advantageously concentric but not necessarily. They can have different thicknesses (distance between an internal diameter facing a central zone surrounded by the crowns and an external diameter, facing the outside of the antenna).

Claims

1. An array antenna (A) comprising an array (R) of radiating elements (E0, E1) consisting of N unitary radiating elements, with N being an integer greater than 1, characterised in that each radiating element (E0, E1) of the array (R) of radiating elements (E0, E1) comprises a main excitation port (PP), the array (R) of radiating elements (E0, E1) comprising at least one first radiating element (E0) comprising only the main excitation port (PP) and a secondary sub-array (S1) consisting of N1 second radiating elements (E1) taken from among the N radiating elements of the array, such that N1 is greater than or equal to 1 and is less than N, each radiating element (E1) of the secondary sub-array (S1) comprising a secondary excitation port (PS), the array antenna being adapted to generate a main beam in a first predetermined direction using said main excitation ports (PP) and to generate, simultaneously with the main beam, a secondary beam in a second predetermined direction using said secondary excitation ports.

2. The array antenna according to the preceding claim, comprising a processing circuit (CT) configured to allow signals to be conveyed from and / or to the main excitation ports in a same main mode taken from among the common mode and the differential mode and allowing signals to be conveyed to and / or from the secondary excitation ports in a same secondary mode taken from among the common mode and the differential mode.

3. The array antenna according to any one of the preceding claims, comprising a processing circuit comprising: - N main emission circuits capable of independently adjusting phases and amplitudes of main excitation signals of the respective main excitation ports (PP) so as to generate a main emission beam in a main predetermined adjustable emission direction and / or N main reception circuits capable of independently adjusting phases and amplitudes of the main reception signals originating from the respective main excitation ports (PP) so as to generate a main reception beam in a main predetermined adjustable reception direction, and - N1 secondary emission circuits capable of independently adjusting phases and amplitudes of excitation signals of the respective secondary excitation ports (PS) so as to generate a secondary emission beam in a secondary predetermined adjustable emission direction and / or N secondary reception circuits capable of independently adjusting secondary phases and secondary amplitudes of secondary reception signals originating from the respective secondary excitation ports (PS) so as to generate a secondary reception beam in a secondary predetermined adjustable reception direction.

4. The array antenna according to any one of the preceding claims, comprising several secondary sub-arrays Si, the array of radiating elements comprising a unitary sub-array consisting of U first radiating elements, with U being an integer greater than or equal to 1, the processing circuit allowing secondary emission beams to be simultaneously generated from the respective secondary sub-arrays or allowing secondary reception beams to be simultaneously generated from the respective secondary sub-arrays.

5. The array antenna according to the preceding claim, wherein the radiating elements of the secondary sub-array are disposed around the first radiating element or the first radiating elements.

6. A method for generating beams by an array antenna according to any one of the preceding claims, comprising the following steps of: - exciting the main excitation ports (PP) of the N radiating elements of the array (R) so as to generate a main emission beam in a first predetermined emission direction, - exciting the secondary excitation ports (PS) of the secondary sub-array (S1) so as to generate, simultaneously with the main emission beam, a secondary emission beam in a second predetermined emission direction, and / or comprising the following steps of: - shaping signals originating from the main excitation ports (PP) and adding them so as to generate a main beam at reception in a first predetermined reception direction, - shaping signals originating from the secondary excitation ports (PS) of the secondary sub-array and adding them so as to generate, simultaneously with the main reception beam, a secondary beam at reception in a second predetermined reception direction.

7. A method for limiting another lobe other than a main lobe of a main emission beam by an array antenna according to any one of claims 1 to 5, the method for limiting comprising: - exciting the main excitation ports (PP) so as to generate the main emission beam in the first predetermined emission direction, - exciting the secondary excitation ports (PS) of the secondary sub-array so as to generate, simultaneously with the main beam, a secondary emission beam having a main lobe of the secondary beam in phase opposition with the other lobe of the main emission beam in the other emission direction of the other emission lobe and having an amplitude that is less than or equal to the amplitude of the other lobe of the main beam.