Patent ID: 12241962

DETAILED DESCRIPTION OF THE INVENTION

It is understood that the embodiments disclosed hereunder are by no means limiting. In particular, it is possible to imagine variants of the invention that comprise only a selection of the features disclosed hereinafter in isolation from the other features disclosed, if this selection of features is sufficient to confer a technical benefit or to differentiate the invention with respect to the prior state of the art. This selection comprises at least one preferably functional feature which lacks structural details, or only has a portion of the structural details if that portion is only sufficient to confer a technical benefit or to differentiate the invention with respect to the prior state of the art.

In the figures the same reference has been used for the features that are common to several FIGURES.

FIGS.1A and1Bare schematic depictions of a non-exemplary embodiment of a configuration for calibrating an airborne goniometry apparatus, seen from a side view and a top view, respectively.

FIGS.1A and1Bschematically show a goniometry apparatus102transported by an aircraft, such as for example an airplane, and helicopter, an airship, a balloon, etc.

A calibration transmitter106, of known position, is used to calibrate the airborne goniometry apparatus102. The calibration transmitter106can be stationary or mobile. The calibration transmitter106can for example be disposed on the ground.

The calibration of the goniometry apparatus102is performed as follows. A calibration signal of known frequency is sent by the calibration transmitter106to the goniometry apparatus102. The goniometry apparatus102measures the reception response of each antenna in the antenna array for the calibration signal, namely a complex vector whose real part is formed by an amplitude datum and whose imaginary part is formed by the phase datum. The measured data are stored associated with the known emission frequency, and the known angular position of the calibration transmitter106relative to the airborne goniometry apparatus102.

For each angular position of the calibration transmitter106, in one or more embodiments, with respect to the airborne goniometry apparatus102, the calibration is repeated for different frequencies, or frequency bands, with a view to scanning an entire broad range of frequencies, in the context of a calibration sequence.

The position of the goniometry apparatus is changed to repeat the calibration at a new angular position so as to scan a range of angular positions, for example along a calibration path.

Thus, in one or more embodiments, at the end of calibration, a calibration data table is obtained. This table comprises for each pair {frequency, angular position} a set of complex vectors, each complex vector corresponding to the response of an antenna of the antenna array to a calibration signal.

According to a non-limiting example according to one or more embodiments of the invention, a reference magnitude can be calculated, for each frequency and each angular position, from the data set associated with said frequency at said angular position. For example, the calculated reference magnitude can be, in an entirely non-limiting manner, a covariance matrix indicating the reception differences between said receiving antennas, that is, between the complex vectors.

The angular position of the calibration transmitter106with respect to the goniometry apparatus102can be given by a combination of two angles, namely:a bearing angle, denoted G, depicted inFIG.1B, which corresponds to the angle, in the horizontal plane, between on the one hand the direction connecting the aircraft and the calibration transmitter106, and on the other hand a reference direction, for example magnetic north; andan elevation angle, denoted S, depicted inFIG.1A, corresponding to the angle formed between on the one hand the vertical direction between the goniometry apparatus102(and thus the aircraft) and the ground, and on the other hand the direction connecting the goniometry apparatus102(and thus the aircraft) and the calibration transmitter106.

These angles can be provided or calculated from measured data, by sensors equipping the goniometry apparatus102or the aircraft, such as, for example:a GPS module indicating the position of the aircraft,an altimeter indicating the altitude of the aircraft, andoptionally an inertial unit indicating the attitude, that is, the spatial orientation of the aircraft with the goniometry apparatus102on board.

Each calibration signal emitted by the calibration generator106can be a signal burst.

As noted above, in one or more embodiments, the goniometry apparatus102comprises an antenna array formed by several antennas. During calibration, for each angular position and for each calibration signal, each antenna receives and measures a pair of data, namely an amplitude datum and a phase datum. Thus, for each angular position and for each calibration signal, the goniometry apparatus measures a data set formed by as many data pairs {Amplitude, Phase} as there are antennas in the antenna array. This set of measured data can then be used to calculate a calibration datum such as a covariance matrix, for example, between the measurements made by all the antennas of the antenna array.

When the calibration is performed in-flight, the measured angular positions do not necessarily correspond exactly to those desired. Thus, at the end of an acquisition phase, the measured angular positions are not distributed in the desired way, for example, with a desired angular pitch. In other words, in one or more embodiments, in-flight calibration does not allow obtaining a complete, even and balanced calibration table with a constant angular pitch because the trajectory of the air carrier with the goniometry apparatus on board is not totally predictable, particularly because of drifts related to winds for example.

At least one embodiment of the invention makes it possible to overcome this drawback by proposing a method for calculating calibration data for at least one unmeasured angular position, called “estimated angular position” or “estimated position”, by interpolating data measured in-flight for several measured angular positions, also called “measured position” herein.

FIG.2is a schematic depiction of a non-limiting example of a method according to one or more embodiments of the invention.

The method200ofFIG.2allows calculating calibration data for an estimated angular position, for which no calibration data measured in-flight are available, from in-flight measured calibration data for several measured angular positions at the same frequency.

Preferably, in one or more embodiments, the measured angular positions whose calibration data are used to calculate the calibration data of the estimated position are angular positions close to, or around, or surrounding said estimated position.

The method200depicted inFIG.2is described for an estimated position. The method200can be repeated as many times as desired to calculate, individually, calibration data for several estimated positions.

The method200includes a step202in which measured data for several measured angular positions are extracted. These measured data will be used to calculate by interpolation calibration data for an estimated angular position. For example, in step202, the measured data for M positions POSM1-POSMMare extracted. Considering that the antenna array comprises K antennas, the data measured for each position POSMmcorrespond to a set of K data pairs, each pair corresponding to one of the K antennas and comprising an amplitude datum and a phase datum measured by said antenna. Thus, in one or more embodiments, the measured data set for the position POSMmcorresponds to:
POSMm={(AM1m,PH1m), . . . ,(AMkm,PHkm), . . . ,(AMKm,PHKm)}wherein 1≤m≤M and 1≤k≤K

In step204, the measured data set for each measured position POSMmis normalized with respect to the phase measured by each antenna in the antenna array. Normalization of the data set with respect to the phase of an antenna can be performed by dividing the phase data measured by all antennas by the phase data of said antenna. Thus, in this step204, K data sets are obtained for each measured position POSMm. For example, for the data set POSMm, measured for the “m” measured position, the following K normalized data sets are obtained:
POSMm/1={(AM1m,1), . . . ,(AMkm,PHkm/PH1m), . . . ,(AMKm,PHKm/PH1m)},
normalized with respect to the antenna phase 1
POSMm/k={(AM1m,PH1m/PHkm), . . . ,(AMkm,1), . . . ,(AMKm,PHKm/PHkm)},
normalized with respect to the antenna phase k
POSMm/K={(AM1m,PH1m/PHKm), . . . ,(AMkm,PHkm/PHKm), . . . ,(AMKm,1)},
normalized with respect to the antenna phase K

In step206, K candidate datasets are calculated by interpolation for the estimated position, considering the normalized antenna-by-antenna data.

In other words, in one or more embodiments, for all measured positions, the data normalized with respect to the antenna1are considered first: POSM1/1-POSMM/1. These normalized data POSM1/1-POSMM/1are used to calculate by interpolation a candidate data set, denoted POSE/1, for the estimated position POSE. The candidate data set POSE/1is thus obtained by taking antenna1as phase reference. The same operation is repeated with the data set normalized with respect to antenna2: POSM1/2-POSMM/2to calculate a candidate data set POSE/2obtained by taking as phase reference the antenna2, and so forth so that step206provides K candidate data sets POSE/1-POSE/K, each obtained by taking as phase reference one of the antennas of the antenna array. Note that each candidate data set POSE/k, wherein 1≤k≤K, provides as many data pairs (AM, PH) as there are antennas in the antenna array so that the obtained candidate data set with respect to antenna k can be:
POSE/k={(AM1/k,PH1k), . . . ,(AMk/k,PHk/k), . . . ,(AMK/k,PHK/k)}wherein 1≤k≤K

In this step206, each candidate data set is calculated using an interpolation function, such as for example the GRIDDATA function, in MATLAB.

In step208, the energy of each candidate data set POSE/k, wherein 1≤k≤K, is calculated. This energy can be calculated in different ways.

According to at least one embodiment, the energy of each candidate data set POSE/kis calculated as follows. First, in one or more embodiments, the energy of each pair of data (AMk/k,PHk/k) forming the candidate data set is calculated. For each pair of data, the energy can for example correspond to the modulus of the complex vector formed by this pair of data. Then, in one or more embodiments, the energy of the candidate data set POSE/kcan be calculated based on the energy of each data pair forming said candidate data set. For example, the energy of the candidate data set may correspond to the average of the energies of the data pairs forming said candidate data set.

The method200then includes a step210, in which the candidate data set having the highest energy level is selected as the estimated data set for the POSE estimated position.

Optionally, in one or more embodiments, the method200may advantageously comprise a step212for calculating a calibration magnitude for the estimated position POSE. This calibration magnitude can be a covariance matrix obtained from the estimated data set selected in step210. Thus, at the end of step212, a calibration magnitude is obtained by interpolation for an estimated angular position and for a frequency for which no calibration data has been measured in-flight.

The method200can be repeated for as many estimated angular positions as desired to build a complete and balanced calibration table in terms of angular positions.

According to at least one embodiment of the invention, such a calibration table can be obtained without using one single phase reference for all estimated angular positions. Thus, for each estimated angular position, the phase reference used for interpolation can potentially be different. Furthermore, according to one or more embodiments of the invention, the phase reference used for each estimated position will always be the one with the highest energy level. Thus, one or more embodiments of the invention makes it possible to obtain, for (each) estimated angular position, estimated calibration data which are more accurate because they are less affected or tainted by noise which would be due to a phase reference whose energy is too low. Consequently, in one or more embodiments, the calibration data obtained by the method according to the invention are more accurate.

FIG.3is a schematic depiction of a non-limiting example of a method according to one or more embodiments of the invention for determining calibration data table of an airborne goniometry apparatus according to one or more embodiments of the invention.

The method300ofFIG.3makes it possible to determine a calibration data table comprising, for a multitude of given angular positions and frequencies, calibration data for an airborne goniometry device.

The method comprises a phase302of measuring calibration data for a plurality of measured angular positions. This acquisition phase302is performed in the configuration shown inFIGS.1A and1B, that is, whereupon the goniometry apparatus is on board an airborne carrier. The acquisition phase provides data for a plurality of angular positions that are not unevenly distributed.

An example of the distribution of measured angular positions402is shown inFIG.4A. Each measured angular position is represented by a rectangle. It can clearly be seen that the angular positions are not evenly distributed, that there are areas where there are no measured angular positions and areas comprising too many measured angular positions.

The method300next includes at least one iteration of a calibration data calculation for at least one estimated angular position, based on data measured in-flight during the acquisition phase. In particular, in one or more embodiments, the calculation of estimated calibration data for an estimated position may be performed according to the method200ofFIG.2.

Preferably, in one or more embodiments, the method200can be repeated for a plurality of angular positions so as to obtain a multitude of angular positions, for which calibration data are available, which are evenly distributed according to a desired constant or variable pitch.

An example of the angular position distribution thus obtained is shown inFIG.4B. Each measured angular position402is represented by a rectangle and each estimated angular position404is represented by a circle. It can be clearly seen that in the calibration table inFIG.4B, the angular positions are evenly distributed and according to a desired, and in particular constant, pitch. Furthermore, all areas are covered and there are no areas for which calibration data are not available.

In the method300, in one or more embodiments, the acquisition phase is performed before the first iteration of the method200. The first iteration of the method200may be performed after the acquisition phase is complete. Alternatively, in one or more embodiments, the first iteration of the method200can be performed/triggered without waiting for the completion of the acquisition phase.

Furthermore, in one or more embodiments, the method300can be repeated for each radio frequency involved in the calibration. In this case, the acquisition phase302can be common to several or even all radio frequencies.

At least one embodiment of the invention also relates to a data processing device configured to implement all the steps of the method according to one or more embodiments of the invention, and in particular the method200ofFIG.2. Such a device, not shown in the FIGURES, may be a computer, server, processor, programmable electronic chip, etc. configured to implement all the steps of the method, for example by virtue of a computer program.

The device according to one or more embodiments of the invention can be a physical machine or a virtual machine.

The invention in one or more embodiments also relates to a goniometry apparatus configured, or comprising a calibration table calculated, by a method according to one or more embodiments of the invention, and in particular by the method200ofFIG.2.

Of course, the invention is not limited to the examples detailed herein before given for purposes of illustration and the general scope of the invention is defined in the claims.