Method for calibrating a transmission array antenna with aesa-type phase control and associated calibration system

Abstract

The present invention relates to a method for calibrating a transmission array antenna (11), comprising the following steps: - selecting (110) a transmission element to be tested; - introducing (120) a particular modulation into the elementary signal to be transmitted by the transmission element to be tested; - transmitting (130) a beam of elementary signals; - receiving (140), by another antenna (12), a signal formed of the transmitted beam; - measuring (150) an effect of the introduced particular modulation on the power of the received signal; - transmitting (160) the measured effect to a reception antenna (11') connected to the transmission array antenna to be calibrated; and - correcting (170) calibration parameters of the transmission element to be tested.

Description

[0001] DESCRIPTION

[0002] TITLE :

[0003] Method for calibrating an AESA-type phased array transmitting antenna and associated calibration system

[0004] The present invention relates to a method for calibrating an AESA type phased array transmitting antenna.

[0005] The present invention also relates to a calibration system associated with such a method.

[0006] In particular, the technical field of the invention relates to phased array antennas (or “phased array antennas” in English) and in particular AESA (Active Electronically Scanned Array) type array antennas.

[0007] In a manner known per se, two-dimensional pointing in a direction by such an antenna is obtained by applying appropriate phase (and / or delay) and amplitude weights to the radiating elements.

[0008] These amplitudes and phases can be generated by digital commands on analog components, also called ABF (Analog Beam Forming) components. These components can include various controllable gain amplifiers, programmable phase shifters, programmable delay lines, etc.

[0009] The above-mentioned antenna type can be used in general radio communication (e.g. Satcom GEO, MEO, LEO, X, Ku, Ka bands, etc.) as well as in radars.

[0010] For this type of antenna, there is a need to guarantee the side lobe levels with respect to radiocommunication standards. For this, it is generally necessary to carry out a calibration of different elements forming the antenna following variations occurring during its life cycle.

[0011] These variations can occur in the various components of the antenna and can be caused by multiple reasons. These reasons include external conditions (temperature, humidity, etc.), power supply, vibrations, aging of materials, etc.

[0012] The state of the art already offers some methods for calibrating this type of antenna.

[0013] So, one of these methods is to perform a purely factory calibration with the expectation that this calibration will last the entire lifetime of the antenna. Another calibration method is to determine maintenance periods during which the antenna is not operational.

[0014] It is therefore clear that the methods of the state of the art are not satisfactory and in particular do not allow regular calibration of the network antenna to be carried out without interrupting its operation.

[0015] One of the objectives of the present invention is to propose regular calibration of an AESA type network antenna throughout its life cycle and without interruption of its nominal operation.

[0016] To this end, the invention relates to a method for calibrating an AESA type phased array transmitting antenna, the transmitting array antenna comprising:

[0017] - a plurality of emission elements;

[0018] - an analog beamforming module capable of forming for each transmission element an elementary signal to be transmitted from a radiofrequency signal;

[0019] - a modem capable of generating the radiofrequency signal.

[0020] The process includes the following steps:

[0021] - selection of an emission element to be tested;

[0022] - introduction of a particular modulation into the elementary signal to be emitted by the emission element to be tested;

[0023] - emission of a beam of elementary signals by all the radiating elements;

[0024] - reception by another antenna of a signal formed from the emitted beam;

[0025] - measurement of an effect of the particular modulation introduced on the power of the received signal;

[0026] - transmission to a receiving antenna connected to the transmitting network antenna to be calibrated of the measured effect;

[0027] - correction of calibration parameters of the emission element to be tested according to the measured effect.

[0028] According to other advantageous aspects of the invention, the method comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0029] - each emission element corresponds to a radiating element or to a pattern formed from a plurality of radiating elements;

[0030] - the steps of the method are repeated for each transmission element of the transmission array antenna to be calibrated; - the steps of the method are repeated during operation of the transmission array antenna in nominal mode;

[0031] - the introduction of the particular modulation comprises the introduction into the elementary signal to be transmitted of a code in phase and / or in delay and / or in amplitude in each predetermined time interval AT;

[0032] - the predetermined AT time interval is known to the other antenna;

[0033] - the measurement of the effect of the particular modulation comprises n power measurements of the received signal, n being advantageously greater than 1 and chosen according to a signal-to-noise ratio necessary to measure the particular modulation;

[0034] - the calibration parameters of a transmitting element include phase and / or amplitude weights associated with this transmitting element;

[0035] - the measured effect is transmitted with a date of reception of the signal by the other antenna.

[0036] The present invention also relates to a system for calibrating an AESA type phased array transmission antenna, comprising:

[0037] - a first module integrated into the transmission network antenna to be calibrated and into the reception antenna connected to the transmission network antenna;

[0038] - a second module integrated into another antenna capable of communicating directly or indirectly with the receiving antenna.

[0039] The first module and the second module are configured to implement at least certain steps of the method as defined previously.

[0040] These characteristics and advantages of the invention will appear on reading the description which follows, given solely as a non-limiting example, and made with reference to the appended drawings, in which:

[0041] - [Fig. 1] Figure 1 is a schematic view of a calibration system for a transmitting array antenna to be calibrated, according to the invention;

[0042] - [Fig. 2] Figure 2 is a schematic view of a transmitting module of the transmitting array antenna of Figure 1;

[0043] - [Fig. 3] Figure 3 is a schematic view of a pattern forming part of the emission module of Figure 2;

[0044] - [Fig. 4] Figure 4 is a schematic view of a control unit associated with a group of radiating elements of the pattern of Figure 3; and

[0045] - [Fig. 5] Figure 5 is a flowchart of a calibration method implemented at least partially by the calibration system of Figure 1. Figure 1 in fact illustrates a calibration system 10 of a transmission array antenna to be calibrated 11 using a reception antenna 11' connected to this transmission array antenna 11 and another antenna 12 communicating with the reception antenna 11'. This calibration system 10 comprises a first module 21 integrated in the antennas 11, 11' and a second module 22 integrated in the other antenna 12.

[0046] The transmitting array antenna 11 to be calibrated is a phased array antenna of the AESA (Active Electronically Scanned Array) type. This array antenna 11 comprises a transmitting assembly 25 adapted to transmit radio signals to another antenna.

[0047] The transmission assembly 25 comprises a transmission module 31 for transmitting a beam of elementary signals, a beam-forming module 32 for forming a beam of elementary signals from a radiofrequency signal, a modem 33 for generating the radiofrequency signal from the useful data and a control module 34 for controlling the operation of the components of the transmission assembly 25.

[0048] The control module 34 is for example of the ACU (Antenna Control Unit) type, usable to point the transmission antenna 11 in the desired direction. This module 34 is notably configured to control the operation of the beamforming module 32 and the transmission module 31.

[0049] The control module 34 comprises in particular a calibration table comprising calibration parameters for each transmission element explained in more detail below. These calibration parameters include in particular phase (and / or delay) and amplitude weights to be applied to the corresponding transmission element when transmitting an elementary signal.

[0050] The modem 33 is for example known per se. It makes it possible in particular to generate a radiofrequency signal from useful data. The useful data is the data to be transmitted by the transmission antenna 11 which is generated for example by an external computing unit.

[0051] Figure 2 illustrates an example of respective arrangement of the transmission module 31 and the beamforming module 32.

[0052] In the example of this figure 2, the transmission module 31 comprises a plurality of tiles 40-1, ..., 40-N. The tiles 40-1, ..., 40-N have different physical entities arranged for example on a support of the transmission antenna 11 separately from one another. The tiles 40-1, ..., 40-N are for example substantially identical to each other. By way of example, the number N of tiles varies for example between 1 and 10. Each tile 40-1, 40-N comprises a plurality of patterns 41-1, ..., 41-K arranged on an outer surface of this tile. As can be seen in figure 2, these patterns form for example at least two rows and at least two columns on the surface of the corresponding tile. In other examples, the radiating elements may be arranged in a circle or in any other arrangement and the patterns may be adapted to this arrangement.The size of a pattern can be chosen to avoid intra-pattern calibration of the radiating element by radiating element type for example. The number K of patterns per tile varies for example from 4 to 16.

[0053] Each pattern 41-1, ..., 41-K has, for example, a printed circuit on which a plurality of radiating elements are arranged. According to another example, the radiating elements may be horns. The patterns 41-1, ..., 41-K are, for example, substantially similar to each other. Thus, subsequently, only the pattern 41-1 will be explained in more detail with reference to FIG. 3.

[0054] With reference to this figure 3, the pattern 41-1 comprises a plurality of radiating elements 42-1, ..., 42-M. In the example of this figure, the number L of radiating elements is equal to 64. The radiating elements 42-1, ..., 42-M form a matrix on the corresponding pattern 41-1. Furthermore, the radiating elements 42-1, ..., 42-M are grouped into a plurality of groups within the same pattern 41-1. In the example of figure 3, each group is composed of four adjacent radiating elements 42-1, ..., 42-M. In this example, 16 groups of radiating elements are therefore formed. Each group of radiating elements is controlled by the same control unit, as will be explained in more detail later.

[0055] The beamforming module 32 is an analog module for generating an elementary signal to be transmitted for each radiating element 42-1, ..., 42-M from the radiofrequency signal delivered by the modem 33.

[0056] To do this, the beamforming module 32 comprises a conversion unit 45, for example of the BUC (Block Up Converter) type, making it possible to convert the frequency of the radiofrequency signal delivered by the modem 33 into a frequency to be transmitted in a range, such as, for example, the “L”, “Ku” or “Ka” band.

[0057] The beamforming module 32 further comprises at least three levels of signal separators making it possible to generate an elementary signal for each radiating element 42-1, ..., 42-M. These separators have controllable gain amplifiers and programmable phase shifters (and / or delays) making it possible to generate a beam of elementary signals according to techniques known per se. In particular, as can be seen in FIG. 2, a first level of separators comprises a single separator 51 making it possible to separate the signal delivered by the conversion unit 45 between the slabs 40-1, , 41-N. A second level of separators comprises N separators 52-1, ..., 52-N. Each separator of the second level 52-1, ..., 52-N is associated with one of the tiles 40-1, ..., 40-N and makes it possible to separate the signal received by this tile between the different patterns 41-1, ..., 41-K. Finally, a third level of separators comprises, by each pattern 41-1, ..., 41-K in each slab 40-1, ..., 40-N, a separator 53 making it possible to separate the signal delivered to the corresponding pattern between the different groups of radiating elements forming this pattern. Such a separator 53 is visible in Figure 3.

[0058] The beamforming module 32 further comprises a control unit 55 associated with each group of radiating elements and making it possible to generate an elementary signal for each radiating element of this group from the signal delivered by the corresponding separator 53 of the third level.

[0059] An example of such a control unit 55 is shown in Figure 4. According to this example, the control unit 55 is associated with a group of radiating elements formed of four radiating elements 42-1, ..., 42-M. Thus, from a signal delivered by the corresponding separator 53, this unit 55 makes it possible to generate 4 elementary signals for the corresponding radiating elements 42-1, ..., 42-M, according to a predetermined logic.

[0060] The receiving antenna 11' is for example also an array antenna. The receiving antenna 11' comprises a receiving assembly 26 adapted to receive radio signals from other antennas. The receiving assembly 26 is for example substantially symmetrical to the transmitting assembly 25.

[0061] In particular, with reference to FIG. 1, the reception assembly 26 comprises a reception module 61 for receiving a beam of elementary signals, a radiofrequency signal formation module 62 for forming a single radiofrequency signal from the received beam of elementary signals, a modem 63 capable of generating useful data from the received radiofrequency signal and a control module 64 capable of controlling the operation of the various components of the reception assembly 66. These various components are analogous and symmetrical to those described previously in relation to the transmission assembly 25 and will not be described in detail subsequently.

[0062] According to another embodiment, the reception assembly 26 may be different from the transmission assembly 25 and may have a simplified structure, for example a structure comprising a conventional radiofrequency antenna of the parabolic type for example.

[0063] The antenna 12 (also referred to as “other antenna”) has any antenna capable of receiving and transmitting radio signals originating from and intended for the network antenna 11. In the example of FIG. 1, such communication between the two antennas 11, 12 is carried out via one or more satellites 70, for Satcom links.

[0064] The antenna 12 comprises, for example, a transmission / reception module 72 capable of transmitting / receiving radio signals and a modem 73 capable of forming radio signals to be transmitted from the useful data and of generating useful data from the received radio signals.

[0065] In some examples, the antenna 12 is also an array antenna similar, for example, to the antennas 11, 11'.

[0066] As indicated previously, the first module 21 of the calibration system 10 is integrated into the antennas 11, 11' and the second module 22 is integrated into the other antenna 12.

[0067] In particular, the first module 21 makes it possible to introduce a particular modulation (or marking) into the elementary signal emitted by each transmission element, according to a predetermined logic. In the remainder of the description, by transmission element, we mean either a radiating element 42-1, ..., 42-M, or a pattern 41-1, ..., 41-K.

[0068] To do this, the first module 21 comprises a training unit in each separator of each level of separators as well as in the control unit 55 of each group of radiating elements. In particular, in the example of the figures, a training unit 81 is associated with the separator 51, a training unit 82-1, ..., 82-N is associated with each separator 52-1, ..., 52-N, a training unit 83 is associated with each separator 53 and a training unit 84 is associated with each control unit 55 of the group of corresponding radiating elements. Each of these training units 81 to 84 is capable of introducing into the corresponding elementary signal a particular desired modulation.

[0069] Furthermore, the first module 21 comprises a control unit (not shown) capable of controlling the operation of all the training units 81 to 84. This control unit is integrated for example in the control module 34 of the transmission assembly 25.

[0070] The second module 22 comprises a measurement unit integrated in the transmission / reception module 72 of the other antenna 12 and a transmission unit integrated in the modem 73 of the other antenna 12. The measurement unit is capable of demodulating the effect of a particular modulation introduced into one of the elementary signals composing the signal from the transmission network antenna. The transmission unit is capable of transmitting the measured effect to the reception antenna 11'.

[0071] The first module 21 and the second module 22 of the calibration system 10 are capable of implementing at least certain steps of the method for calibrating the transmission array antenna 11. This method will now be described in detail with reference to FIG. 5 showing a flowchart of its steps.

[0072] The purpose of this method is to calibrate the transmission elements during operation in nominal mode of the transmission network antenna 11. In other words, the steps described below are implemented during the transmission of useful data by the transmission antenna 11 without significant degradation of the quality of its service.

[0073] In an initial step 110, the first module 21 of the system 10 selects a transmission element to be tested. As indicated previously, such an element to be tested corresponds either to a radiating element 42-1, ..., 42-M, or to a pattern 41-1, ..., 41-K.

[0074] The selection may be made, for example, according to a predetermined rule. This rule may, for example, include the selection of a transmission element according to an order defined by its position on the panel and / or the corresponding pattern.

[0075] In a subsequent step 120, the first module 22 introduces a particular modulation into the elementary signal to be emitted by the transmission element to be tested, through the training units explained previously. This is then done in place of or in addition to the nominal elementary signal to be emitted by this transmission element.

[0076] This particular modulation includes, for example, the introduction into the elementary signal to be transmitted of an additional phase (and / or delay) and amplitude, in each predetermined time interval AT.

[0077] When the transmitting element corresponds to a pattern, such a particular modulation is introduced into the elementary signals of all the radiating elements forming such a pattern. When the transmitting element corresponds to a radiating element, such a particular modulation is introduced into the elementary signal of this radiating element.

[0078] In particular, a particular modulation may have an amplitude-phase, or amplitude / delay or combined amplitude-phase-delay code which is superimposed on the elementary signal normally to be emitted by the corresponding transmitting element according to the nominal operating mode of the transmitting array antenna 11.

[0079] The code rate (change frequency) is chosen, for example, to be twice the step rate or the frame rate of the modem 34 of the transmission network antenna 11 and is synchronous with the modem 73 of the other antenna 12. For example, the particular modulation introduced into the elementary signal at this stage may include an alternation in phase, for example -45° / +45°.

[0080] During the following step 130, the transmitting network antenna 11 transmits a beam of elementary signals (i.e. nominal elementary signals except one which is modified) by all of the radiating elements 42-1, ..., 42-M.

[0081] In particular, during this transmission, only one elementary signal is modified and the other elementary signals are transmitted according to the nominal operating mode of the transmission network antenna 11.

[0082] In the next step 140, the other antenna 12 receives a signal formed from the beam emitted by the transmission array antenna 11.

[0083] In the next step 150, the second module 22 of the calibration system 10 performs n power measurements of the received signal and measures an effect of the particular modulation on this signal. The number n of measurements is advantageously greater than 1 and less than, for example, 1000. Generally, the number n of measurements is adapted to the signal-to-noise ratio necessary to correctly measure the particular modulation. The number n also depends on the nature of the emission element (radiating element or pattern).

[0084] This can be done by analyzing the n successive powers received over time, every AT, by normalizing them in power every 2AT, in order to be independent of variations in propagation and frequencies emitted, for example.

[0085] In the previous example with an alternation in amplitude, two power levels P1 and P2 at successive times can then be measured.

[0086] For example, let a be the phase error in radians to be corrected related to the emission element under test, assumed to be small. In this case, the powers P1 and P2 can be written as follows: a*b is the total number of patterns (a patterns in a row and b patterns in a column) or the total number of radiating elements minus the selected radiating element.

[0087] The error a, relative to +45 / -45°, is characterized by the power ratio 1 - (P1 / P2).

[0088] In the following step 160, the second module 22 of the calibration system 10 transmits the measured effect to the receiving antenna 11'. This effect is dated, for example, with the date of reception of the corresponding signal. This effect is transmitted in the form of useful data using the radiofrequency link between the two antennas 11', 12 in a conventional manner. In the following step 170, the first module 21 of the calibration system 10 analyzes the measured effect received, determines the transmission element corresponding to this effect using the date thereof and corrects the calibration parameters of this transmission element. In particular, these parameters are, for example, corrected so as to minimize the measured effect.

[0089] Then, steps 110 to 170 are repeated in relation to another emission element.

[0090] It is therefore understood that the present invention presents a certain number of advantages.

[0091] In particular, the invention makes it possible to calibrate a transmitting array antenna throughout its life cycle without degradation of the service provided. Indeed, during calibration, the transmitting array antenna operates normally and the particular modulation introduced at the level of a single transmitting element does not degrade the quality of service provided by this antenna. In addition, the method according to the invention can be applied an unlimited number of times for all the transmitting elements. Finally, each particular modulation introduced can be controlled and varied, for example, to adapt the calibration to a particular type of variations that may occur throughout the life cycle of the array antenna.

Claims

CLAIMS 1. Method for calibrating a phased array transmitting antenna (11) of the AESA type, the transmitting array antenna (11) comprising: - a plurality of emission elements; - an analog beamforming module (32) capable of forming for each transmission element an elementary signal to be transmitted from a radiofrequency signal; - a modem (33) capable of generating the radiofrequency signal from useful data to be transmitted; the method comprising the following steps: - selection (110) of a transmission element to be tested; - introduction (120) of a particular modulation into the elementary signal to be emitted by the emission element to be tested; - emission (130) of a beam of elementary signals by all of the emission elements; - reception (140) by another antenna (12) of a signal formed from the emitted beam; - measurement (150) of an effect of the particular modulation introduced on the power of the received signal; - transmission (160) to a reception antenna (11') connected to the transmission network antenna (11) to be calibrated of the measured effect; - correction (170) of calibration parameters of the emission element to be tested according to the measured effect.

2. Method according to claim 1, in which each emission element corresponds to a radiating element (42-1, 42-M) or to a pattern (41-1, ..., 41-K) formed from a plurality of radiating elements (42-1, ..., 42-M).

3. Method according to claim 1 or 2, in which the steps of the method are repeated for each transmission element of the transmission array antenna (11) to be calibrated.

4. Method according to any one of the preceding claims, in which the steps of the method are repeated during operation of the transmitting array antenna (11) in nominal mode.

5. Method according to any one of the preceding claims, in which the introduction of the particular modulation comprises the introduction into the elementary signal to be transmitted of a code in phase and / or in delay and / or in amplitude in each predetermined time interval AT.

6. Method according to claim 5, wherein the predetermined time interval AT is known to the other antenna (12).

7. Method according to any one of the preceding claims, in which the measurement of the effect of the particular modulation comprises n power measurements of the received signal, n being advantageously greater than 1 and chosen according to a signal-to-noise ratio necessary to measure the particular modulation.

8. Method according to any one of the preceding claims, in which the calibration parameters of a transmission element comprise phase and / or amplitude weights associated with this transmission element.

9. Method according to any one of the preceding claims, in which the measured effect is transmitted with a date of reception of the signal by the other antenna (12).

10. Calibration system (10) of a transmitting array antenna (11) with phased control of the AESA type, comprising: - a first module (21) integrated in the transmission network antenna (11) to be calibrated and in the reception antenna (1T) connected to the transmission network antenna (11); - a second module (22) integrated into another antenna (12) capable of communicating directly or indirectly with the receiving antenna (11'); the first module (21) and the second module (22) being configured to implement the steps of the method according to any one of the preceding claims.

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