FR3144713A1 - Method for calibrating an AESA type phased transmission array antenna and associated calibration system - Google Patents

Abstract

Method for calibrating an AESA type phased transmission array antenna and associated calibration system The present invention relates to a method for calibrating a transmission array antenna, comprising the following steps: - selection (110) of an emission element to be tested; - introduction (120) of a particular modulation in the elementary signal to be transmitted by the transmission element to be tested; - emission (130) of a beam of elementary signals; - reception (140) by another antenna of a signal formed from the transmitted beam; - measurement (150) of an effect of the particular modulation introduced on the power of the received signal; - transmission (160) to a reception antenna connected to the transmission network antenna to be calibrated of the measured effect; - correction (170) of calibration parameters of the emission element to be tested. Figure for abstract: Figure 5

Description

TITLE :

Method for calibrating an array antenna resignation AESA type phase controlled And associated calibration system

The present invention relates to a method for calibrating an AESA type phased-controlled transmitting array antenna.

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

In particular, the technical field of the invention concerns phased array antennas (or “phased array antenna” in English) and in particular AESA type array antennas (from the English “Active Electronically Scanned Array”).

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

These amplitudes and phases can be generated by digital controls on analog components, also called ABF components (from the English “Analog Beam Forming”).

These components can include different amplifiers with controllable gain, programmable phase shifters, programmable delay lines, etc.

The aforementioned type of antenna can be used in radiocommunication in general (for example of the Satcom GEO, MEO, LEO type, X, Ku, Ka bands, etc.) as well as in radars.

For this type of antenna, there is a need to guarantee the secondary lobe levels with respect to radiocommunication standards.

For this, it is generally necessary to calibrate the different elements forming the antenna following variations occurring during its life cycle.

These variations can occur in the different components of the antenna and can be caused by multiple reasons.

Among these reasons, we can cite in particular external conditions (temperature, humidity, etc.), power supply, vibrations, aging of materials, etc.

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

So, one of these methods consists of carrying out a purely factory calibration in the hope that this calibration can last the entire life of the antenna.

Another calibration method consists of determining maintenance periods during which the antenna is not operational.

We can then see that the methods of the state of the art are not satisfactory and in particular do not allow regular calibration of the network antenna without interrupting its operation.

One of the objectives of the present invention is to provide regular calibration of an AESA type array antenna throughout its life cycle without interruption of its nominal operation.

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

- a plurality of emission elements;

- an analog beam forming module capable of forming for each transmission element an elementary signal to be transmitted from a radio frequency signal;

- a modem capable of generating the radio frequency signal.

The process includes the following steps:

- selection of an emission element to test;

- introduction of a particular modulation in the elementary signal to be transmitted by the transmission element to be tested;

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

- reception by another antenna of a signal formed from the transmitted beam;

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

- transmission to a reception antenna connected to the transmission network antenna to be calibrated of the measured effect;

- correction of calibration parameters of the emission element to be tested depending on the measured effect.

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

- each emission element corresponds to a radiating element or to a pattern formed of a plurality of radiating elements;

- the steps of the process are repeated for each transmitting element of the transmitting network antenna to be calibrated;

- the steps of the process are repeated during operation of the transmitting network antenna in nominal mode;

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

- the predetermined time interval ΔT is known to the other antenna;

- 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;

- the calibration parameters of a transmission element include phase and/or amplitude weights associated with this transmission element;

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

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

- a first module integrated in the transmitting network antenna to be calibrated and in the receiving antenna connected to the transmitting network antenna;

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

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

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

- there is a schematic view of a calibration system of a transmitting array antenna to be calibrated, according to the invention;

- there is a schematic view of a transmission module of the transmission network antenna of the ;

- there is a schematic view of a pattern forming part of the emission module of the ;

- there is a schematic view of a control unit associated with a group of radiating elements of the pattern of the ; And

- there is a flowchart of a calibration process implemented at least partially by the calibration system of the .

There illustrates in fact a calibration system 10 of a transmission network antenna to be calibrated 11 using a reception antenna 11' connected to this transmission network antenna 11 and another antenna 12 communicating with the reception antenna 11' .

This calibration system 10 comprises a first module 21 integrated into the antennas 11, 11' and a second module 22 integrated into the other antenna 12.

The transmitting array antenna to be calibrated 11 is an AESA (Active Electronically Scanned Array) type phased array antenna.

This network antenna 11 comprises a transmission assembly 25 adapted to transmit radio signals to another antenna.

The transmission assembly 25 comprises a transmission module 31 making it possible to transmit a beam of elementary signals, a beam forming module 32 making it possible to form a beam of elementary signals from a radio frequency signal, a modem 33 making it possible to generate the radio frequency signal from the useful data and a control module 34 making it possible to control the operation of the components of the transmission assembly 25.

The control module 34 is for example of the ACU type (from the English “Antenna Control Unit”) usable to point the transmitting antenna 11 in the desired direction.

This module 34 is in particular configured to control the operation of the beam forming module 32 and the emission module 31.

The control module 34 notably includes a calibration table comprising calibration parameters for each emission element explained in more detail below.

These calibration parameters include in particular phase (and/or delay) and amplitude weights which must be applied to the corresponding transmission element when transmitting an elementary signal.

The modem 33 is for example known per se.

In particular, it makes it possible to generate a radio frequency signal from useful data.

The useful data are the data to be transmitted by the transmitting antenna 11 which are generated for example by an external calculation unit.

There illustrates an example of the respective arrangement of the transmission module 31 and the beam forming module 32.

In the example of this , the transmission module 31 comprises a plurality of tiles 40-1, ..., 40-N.

The tiles 40-1, ..., 40-N present different physical entities arranged for example on a support of the transmitting antenna 11 separately from one another.

The slabs 40-1, ..., 40-N are for example substantially identical to each other.

For example, the number N of tiles varies for example between 1 to 10.

Each tile 40-1, …, 40-N comprises a plurality of patterns 41-1, …, 41-K arranged on an exterior surface of this tile.

As can be seen on the , these patterns form for example at least two lines and at least two columns on the surface of the corresponding slab.

According to other examples, the radiating elements can be arranged in a circle or have any other arrangement and the patterns can be adapted to this arrangement.

The size of a pattern can be chosen to avoid intra-pattern calibration such as radiating element by radiating element for example.

The number K of patterns per tile varies for example from 4 to 16.

Each pattern 41-1, ..., 41-K presents for example a printed circuit on which a plurality of radiating elements are arranged.

According to another example, the radiating elements can be horns.

The patterns 41-1, ..., 41-K are for example substantially similar to each other.

Thus, subsequently, only reason 41-1 will be explained in more detail with reference to the .

In reference to this , 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 the , 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.

The beam forming module 32 is an analog module making it possible to generate an elementary signal to be transmitted for each radiating element 42-1, ..., 42-M from the radio frequency signal delivered by the modem 33.

To do this, the beam forming 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 radio frequency signal delivered by the modem 33 into a frequency at transmit in a range, such as for example the “L”, “Ku” or “Ka” band.

The beam forming 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 amplifiers with controllable gain 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 the , 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 tiles 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 for each pattern 41-1, ..., 41-K in each tile 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 on the .

The beam forming 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 .

An example of such a control unit 55 is shown on the .

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 S 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.

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 reception assembly 26 is for example substantially symmetrical to the transmission assembly 25.

In particular, with reference to the , the reception assembly 26 comprises a reception module 61 making it possible to receive a beam of elementary signals, a radio frequency signal formation module 62 making it possible to form from the beam of elementary signals received a single radio frequency signal, a modem 63 capable to generate useful data from the received radio frequency signal and a control module 64 capable of controlling the operation of the different components of the reception assembly 66.

These different components are similar and symmetrical to those described previously in relation to the emission assembly 25 and will not be described in detail subsequently.

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 radio frequency antenna of the parabola type for example.

The antenna 12 (also designated by the term “other antenna”) presents any antenna capable of receiving and transmitting radio signals originating from and intended for the network antenna 11.

In the example of the , such communication between the two antennas 11, 12 is carried out via one or more satellites 70, for Satcom links.

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 useful data and of generating useful data from the signals received.

In certain examples, the antenna 12 is also an array antenna similar, for example, to the antennas 11, 11'.

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.

In particular, the first module 21 makes it possible to introduce a particular (or marking) modulation into the elementary signal emitted by each transmission element, according to a predetermined logic.

In the remainder of the description, by emission element, we mean either a radiating element 42-1, ..., 42-M, or a pattern 41-1, ..., 41-K.

To do this, the first module 21 includes 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 a particular desired modulation into the corresponding elementary signal.

In addition, 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.

The second module 22 comprises a measurement unit integrated into the transmission/reception module 72 of the other antenna 12 and a transmission unit integrated into 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 coming from the transmitting network antenna.

The transmission unit is capable of transmitting the measured effect to the reception antenna 11'.

The first module 21 and the second module 22 of the calibration system 10 are capable of implementing at least certain steps of the calibration process of the transmitting network antenna 11.

This process will now be described in detail with reference to the presenting a flowchart of its steps.

The purpose of this process is to calibrate the transmitting elements during operation in nominal mode of the transmitting network antenna 11.

In other words, the steps described below are implemented during the transmission of useful data by the transmitting antenna 11 without significant degradation of the quality of its service.

During an initial step 110, the first module 21 of the system 10 selects a transmission element to test.

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.

The selection can be done for example according to a predetermined rule.

This rule can for example include the selection of an emission element according to an order defined by its position on the tile and/or the corresponding pattern.

During a following step 120, the first module 22 introduces a particular modulation into the elementary signal to be transmitted 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 transmitted by this transmitting element.

This particular modulation comprises 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 ΔT.

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.

In particular, a particular modulation may present an amplitude-phase code, or amplitude/delay or combined amplitude-phase-delay which is superimposed on the elementary signal which should normally be emitted by the corresponding transmitting element depending on the operating mode. nominal of the transmitting network antenna 11.

The rhythm of the code (change frequency) is chosen for example double the level rhythm or the frame rhythm of the modem 34 of the transmitting 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 a phase alternation, for example of -45°/+45°.

During the next step 130, the transmitting network antenna 11 emits a beam of elementary signals (that is to say nominal elementary signals except one which is modified) by all of the radiating elements 42-1, …, 42-M.

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 transmitting network antenna 11.

During the next step 140, the other antenna 12 receives a signal formed from the beam emitted by the transmitting network antenna 11.

During 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, for example, than 1000.

Generally speaking, 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 emitting element (radiating element or pattern).

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

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

For example, let α be the phase error in radians to be corrected linked to the emission element under test, assumed to be small.

In this case, the powers P1 and P2 can be written as follows:

P1= P _received @t=t0+ nΔT= [a*b +1*cos(45°+ α)]2 ~ (a*b +0.7)2 + 2*0.7*180/pi α

P2= P _received @t=t0+ (n+1)ΔT = [a*b +1*cos(45°- α)]2 ~ (a*b +0.7)2 – 2*0.7sin(α ) where a*b is the total number of patterns (a patterns in a row and b patterns in a column) or the total number of radiators minus the selected radiator.

The error α, relative to +45/-45˚, is characterized by the power ratio 1- (P1/P2).

During the next step 160, the second module 22 of the calibration system 10 transmits the measured effect to the reception antenna 11'.

This effect is dated for example from the date of reception of the corresponding signal.

This effect is transmitted in the form of useful data using the radio frequency link between the two antennas 11', 12 in a conventional manner.

During the next step 170, the first module 21 of the calibration system 10 analyzes the measured effect received, determines the emission element corresponding to this effect using the date thereof and corrects the calibration parameters of this emission element.

In particular, these parameters are, for example, corrected so as to minimize the measured effect.

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

We can then see that the present invention presents a certain number of advantages.

In particular, the invention makes it possible to calibrate a transmitting network antenna throughout its life cycle without degradation of the service provided.

Indeed, during calibration, the transmitting network 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 emission elements.

Finally, each particular modulation introduced can be controlled and varied for example to adapt the calibration to a particular type of variations which may occur throughout the life cycle of the array antenna.

Claims (10)

Method for calibrating an AESA type phase-controlled transmission array antenna (11), the transmission array antenna (11) comprising:
- a plurality of transmission elements;
- an analog beamforming module (32) capable of forming for each transmission element an elementary signal to be transmitted from a radio frequency signal;
- a modem (33) capable of generating the radio frequency signal;
the process comprising the following steps:
- selection (110) of a transmission element to test;
- introduction (120) of a particular modulation into the elementary signal to be transmitted by the transmission element to be tested;
- emission (130) of a beam of elementary signals by all the transmission elements;
- reception (140) by another antenna (12) of a signal formed from the transmitted 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 for the measured effect;
- correction (170) of calibration parameters of the emission element to be tested depending on the measured effect. 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 of a plurality of radiating elements (42-1, …, 42-M). Method according to claim 1 or 2, in which the steps of the method are repeated for each transmitting element of the transmitting array antenna (11) to be calibrated. 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. 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 phase and/or delay and/or amplitude code in each time interval ΔT predetermined. Method according to claim 5, in which the predetermined time interval ΔT is known to the other antenna (12). Method according to any one of the preceding claims, in which the measurement of the effect of the particular modulation comprises n measurements of power of the received signal, n being advantageously greater than 1 and chosen according to a signal-to-noise ratio necessary for measure the particular modulation. Method according to any one of the preceding claims, in which the calibration parameters of a transmitting element comprise phase and/or amplitude weights associated with this transmitting element. 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). Calibration system (10) of an AESA type phased transmission array antenna (11), comprising:
- a first module (21) integrated in the transmitting network antenna (11) to be calibrated and in the receiving antenna (11') connected to the transmitting network antenna (11);
- a second module (22) integrated into another antenna (12) capable of communicating directly or indirectly with the reception antenna (11');
the first module (21) and the second module (22) being configured to implement at least certain steps of the method according to any one of the preceding claims.