System and method for characterizing by reflection an antenna system comprising a plurality of input / output ports

Abstract

System and method for reflective characterization of an antenna system comprising a plurality of input / output ports The invention relates to a system (300) for reflective characterization of an antenna system (100) comprising a plurality of input / output ports. Such a system comprises a measurement antenna (210) coupled to a network analyzer (220) for measuring a backscatter coefficient from the complex amplitude of an incident wave emitted by the measurement antenna towards the antenna system and the complex amplitude of the backscattered wave received by the measurement antenna. Such a system further comprises a circuit (310) comprising a delay line implemented between a first port and a second port of the plurality of ports.The delay line is configured so that an impulse response estimated from backscattering coefficients comprises a plurality of echoes, called useful echoes, having temporal supports distinct from each other, the useful echoes being associated with physical phenomena distinct from each other contributing to said backscattered wave. ABSTRACT FIGURE: [Fig.3].

Description

Title of the invention: System and method for characterizing by reflection an antenna system comprising a plurality of input / output ports Field of invention

[0001] The field of the invention is that of antenna systems comprising a plurality of input / output ports.

[0002] The invention relates more particularly to a system and a method for the characterization of such antenna systems.

[0003] The invention thus has applications in the fields in which such antenna systems are implemented. This is for example the field of aeronautics in which antenna systems comprising a plurality of antennas are integrated on a carrier. Prior art and its drawbacks

[0004] There are many ways to describe an antenna. For example, the following characteristics are commonly encountered: • Power gain, radiation pattern, directivity, polarization, in a given direction or over a given angular sector (2D or 3D); • Adaptation to the electronic system to which the antenna port(s) is connected; • Couplings between ports or between antennas where applicable.

[0005] To these usual characteristics, one can, for example in the field of radar discretion, add the radar equivalent surface (SER) specific to the antenna or the modification of that of the carrier after integration of the antenna. If the dimensions of the antenna and the distance between the antenna and the carrier are close or small compared to the wavelength, it becomes difficult to consider independently the antenna and the carrier on which the antenna is integrated. The same problem arises in the case of the integration of a plurality of antennas when the distances between antennas are close or small compared to the wavelength. In these different cases, the entire system comprising the antenna (or antennas) and the carrier radiates, and it is preferable to speak for example of a radiating antenna system. Such a system comprises a plurality of input / output ports if necessary.

[0006] Several formalisms exist to mathematically describe such antenna systems. For example, the multipole formalism expressed in the form of an extended 5-parameter matrix is ​​usually encountered. As illustrated in [Fig.l] and in [Fig. la], such extended 5-parameters connect the outgoing waves (i.e. the two waves in free space bH and bv according to the horizontal and vertical polarizations, as well as the N guided waves ... bN at the output of the N ports of the plurality of ports of the antenna system 100) to the incoming waves (i.e. the two waves in free space aH and av according to the horizontal and vertical polarizations, as well as the N guided waves ai... aN at the input of the N ports of the plurality of ports of the antenna system 100). According to such a formalism, the parameters S can be grouped into four blocks associated with distinct physical phenomena. More particularly ([Fig. la]): • the Sd parameters are representative of the structural component of the SER of the antenna system 100; • the parameters Se are representative of the capacity of the antenna system 100 to radiate the energy supplied to its ports; • the Sr parameters are representative of the capacity of the antenna system 100 to induce the captured energy on each of its ports; • the Sc parameters are representative of the difficulty of the antenna system 100 in radiating the energy supplied to its ports because of the existing couplings between radiating elements and between ports. It can be noted in particular that the coupling of a port towards itself can be interpreted as including the mismatch on the port in question.

[0007] The parameters Sj, Se and Sr depend on the angle of incidence of the incoming waves in free space. The parameters Sr and Se are related to the gain / diagram of the antenna system 100. The parameters 5^ do not depend on the angle of incidence.

[0008] In order to measure such parameters 5 for a given antenna system 100, different characterization techniques exist.

[0009] A known technique is based on a transmission measurement implementing, on the one hand, an antenna under test which is powered and, on the other hand, an already known (characterized) reference antenna which measures the wave radiated by the antenna under test.

[0010] More particularly, from the measurement carried out in transmission, and knowing the equation which describes the physics (so-called Friis equation in the present case), it is possible to extract the gains / diagrams of the antenna under test. This requires knowledge of the characteristics of all the components used to carry out the measurement: e.g. network analyzer, cable, RF link on optical fiber, elbows, adapters, etc. Furthermore, such a transmission characterization technique requires having a compatible reference antenna. Such a technique is also intrusive at the level of the antenna system 100 under test since it is necessary to connect an RF link to it to power the antenna. This link must also be robust when it is moved in order to be able to characterize it in turn. Finally, such a technique is disruptive for the measurement of the SER and the gain, and makes it difficult to quickly access the phase of the S parameters sought.

[0011] Another known technique consists of measuring a backscattering coefficient (or the SER) of the antenna system 100 several times, by loading the antenna port(s) each time with a different load. From this set of measurements, and knowing the loads used, it is possible to go back to the desired antenna characteristics. This is therefore a characterization by reflection. For example, according to the configuration of the characterization system 200 illustrated in [Fig. 2], a measurement antenna 210 is intended to emit an incident wave in the direction of the antenna system 100 and to receive in return a wave backscattered by the antenna system 100. A network analyzer 220 is intended to measure a backscattering coefficient from the complex amplitude of the incident wave emitted by the measurement antenna 210 and the complex amplitude of the backscattered wave received by the measurement antenna 210.The radar equation is used here instead of the Friis equation.

[0012] This reflection characterization technique makes it possible to overcome the aforementioned problems associated with transmission characterization. However, reflection characterization requires measurements of backscattering coefficients, measurements which remain more difficult in principle than simple transmission measurements. Furthermore, reflection characterization requires a potentially complex algorithm to extract the antenna characteristics, because the measured backscattering coefficients depend non-linearly on the Sc parameters according to the following equation:

[0013] [Math.l] Mesurei = Sd+ 8^( IS.C^S,

[0014] where C, represents the loads placed on the N ports of the plurality of ports of the antenna system 100 during the i-th measurement. Thus, characterization by reflection requires an on-board load switching system, remotely controlled, or manual interventions between each measurement, which are tedious and detrimental to the accuracy of the measurements in question.

[0015] There is thus a need for a technique for characterizing an antenna system comprising a plurality of input / output ports that is simple to implement and facilitates the extraction of antenna characteristics, e.g. by avoiding the use of a complex algorithm. Statement of the invention

[0016] In one embodiment of the invention, there is provided a system for characterizing by reflection an antenna system comprising a plurality of input / output ports. The characterization system comprises a measurement antenna coupled to a network analyzer, the measurement antenna being intended to transmit, for at at least one given frequency of a frequency band of interest, an incident wave towards the antenna system and to receive a wave backscattered by the antenna system, the network analyzer being intended to measure a backscatter coefficient associated with the given frequency from the complex amplitude of the incident wave and the complex amplitude of the received wave. The characterization system further comprises a circuit, called a dissociation circuit, configured to load the plurality of input / output ports of the antenna system. The dissociation circuit comprises at least one delay line implemented between a first port and a second port of the plurality of ports.The delay line is configured so that an impulse response estimated from backscattering coefficients measured in the frequency band of interest comprises a plurality of echoes, called useful echoes, having temporal supports distinct from each other, the useful echoes being associated with physical phenomena distinct from each other contributing to said backscattered wave.

[0017] Thus, the invention proposes a new and inventive solution for characterizing an antenna system when the system in question comprises a plurality of input / output ports.

[0018] More particularly, the proposed solution is based on a characterization by reflection of the antenna system. Thus a phase coherence between the different parameters characterizing the antenna system, e.g. the S parameters, can be obtained.

[0019] Furthermore, the implementation of the dissociation circuit makes it possible to temporally isolate the different physical phenomena contributing to the backscattered wave, and therefore to the backscattering coefficients in the end. Thus, by temporal windowing it is possible to isolate the different physical contributions and thus to estimate in a simple manner and via a simplified formalism the parameters characterizing the antenna system.

[0020] In some embodiments, a first useful echo is associated with a physical phenomenon comprising the reflection of the incident wave on the structure of the antenna system.

[0021] In some embodiments, a second useful echo is associated with a physical phenomenon comprising transmission of the incident wave on the ports of the plurality, reflection of transmitted incident Fonde on the loads present on the ports of the plurality, and radiation by the antenna system of transmitted reflected incident Fonde.

[0022] In some embodiments, a third useful echo is associated with a physical phenomenon including transmission of incident Fonde on the ports of the plurality, propagation of incident Fonde transmitted between the ports of the plurality due to mismatches and couplings between the ports of the plurality, and radiation by the antenna system of transmitted incident Fonde propagated between ports.

[0023] In some embodiments, the delay line implements a device belonging to the group comprising:

[0024] - a device comprising a passive radiofrequency cable (500);

[0025] - a device comprising a passive radiofrequency cable and an amplifier (510);

[0026] - a device comprising a passive radiofrequency cable, an amplifier and at minus one attenuator (520);

[0027] - a device comprising a pair of RF to RF conversion devices (530) optics and an optical fiber (540).

[0028] In some embodiments, the characterization system further comprises an anechoic chamber. The characterization of the antenna system is implemented inside the anechoic chamber, the impulse response comprising at least one echo, called a direct echo, linked to the presence of the chamber. The delay line is configured so that the useful echoes are not temporally superimposed on said at least one direct echo.

[0029] Thus, there is no need to subtract the vacuum chamber to estimate the parameters characterizing the antenna system.

[0030] The invention also relates to a method for characterizing by reflection an antenna system comprising a plurality of input / output ports by implementing a characterization system as described previously (according to any one of the embodiments described above). Such a method comprises, for at least one given frequency of a frequency band of interest:

[0031] - an emission, by the measuring antenna, of the incident wave in the direction of the system antennal; and

[0032] - a reception, by the measuring antenna, of the wave backscattered by the system an tenary.

[0033] The method further comprises, for at least one time support associated with a useful echo of the plurality of echoes:

[0034] - a time windowing of the backscattered wave on the time medium delivering a windowed wave; and

[0035] - a measurement, by the network analyzer, of a backscattering coefficient from the windowed wave,

[0036] delivering at least one corresponding backscattering coefficient.

[0037] The method further comprises:

[0038] - an estimation of at least one characterization parameter of the antenna system to from said at least one backscattering coefficient.

[0039] In some embodiments wherein a first useful echo is associated with a physical phenomenon comprising the reflection of the incident wave on the structure of the antenna system, the time windowing and the measurement of a backscattering coefficient are implemented for a first time support associated with the first useful echo delivering a first backscattering coefficient. The estimation comprises the estimation, from the first backscattering coefficient, of at least one parameter S representative of the structural component of the radar equivalent surface of the antenna system.

[0040] In certain given embodiments in which a second useful echo is associated with a physical phenomenon comprising the transmission of the incident wave on the ports of the plurality, the reflection of the transmitted incident wave on the loads present on the ports of the plurality, and the radiation by the antenna system of the reflected transmitted incident wave, the time windowing and the measurement of a backscattering coefficient are implemented for a second time support associated with the second useful echo delivering a second backscattering coefficient. The estimation comprises the estimation, from the second backscattering coefficient and a transfer function of the dissociation circuit:

[0041] - of at least one parameter 5 representative of the capacity of the antenna system to induce the captured energy on each of its ports; and

[0042] - of at least one parameter 5 representative of the capacity of the antenna system to radiate the energy supplied to its ports.

[0043] In some of these given embodiments in which a third useful echo is further associated with a physical phenomenon comprising the transmission of the incident wave on the ports of the plurality, the propagation of the transmitted incident wave between the ports of the plurality due to mismatches and couplings between the ports of the plurality, and the radiation by the antenna system of transmitted incident wave propagated between ports, the time windowing and the measurement of a backscattering coefficient are implemented for the second time medium associated with the second useful echo and for a third time medium associated with the third useful echo delivering the second backscattering coefficient and a third backscattering coefficient.The estimation includes the estimation, from the second backscattering coefficient and the third backscattering coefficient, of at least one parameter S representative of the difficulty of the antenna system in radiating the energy supplied to its ports because of the existing couplings between radiating elements and between ports. List of figures

[0044] Other aims, characteristics and advantages of the invention will appear more clearly on reading the following description, given as a simple illustrative, and non-limiting, example, in relation to the figures, among which:

[0045] [Fig.l], described above in relation to the prior art, illustrates a system an- tenary comprising a plurality of input / output ports and the waves used for the definition of the extended parameters 5 characterizing the antenna system;

[0046] [Fig.1a], described above in relation to the prior art, illustrates the structure of a matrix comprising the extended parameters 5 characterizing an antenna system comprising a plurality of input / output ports;

[0047] [Fig.2], described above in relation to the prior art, illustrates the structure of a system for characterizing by reflection an antenna system comprising a plurality of input / output ports according to a known technique;

[0048] [Fig.3] illustrates the structure of a reflection characterization system of an antenna system comprising a plurality of input / output ports according to an embodiment of the invention;

[0049] [Fig.4] illustrates the impulse response measured by a characterization system by reflection of an antenna system comprising a plurality of input / output ports according to one embodiment of the invention;

[0050] [Fig.5] illustrates the structure of a dissociation circuit implemented in a reflection characterization system of an antenna system comprising two input / output ports according to a first embodiment of the invention;

[0051] [Fig.5a] illustrates the structure of a dissociation circuit implemented in a reflection characterization system of an antenna system comprising two input / output ports according to a second embodiment of the invention;

[0052] [Fig.5b] illustrates the structure of a dissociation circuit implemented in a reflection characterization system of an antenna system comprising two input / output ports according to a third embodiment of the invention;

[0053] [Fig.5c] illustrates the structure of a dissociation circuit implemented in a reflection characterization system of an antenna system comprising two input / output ports according to a fourth embodiment of the invention;

[0054] [Fig.6] illustrates the structure of a dissociation circuit implemented in a reflection characterization system of an antenna system comprising three input / output ports according to an embodiment of the invention;

[0055] [Fig.7] illustrates the steps of a method of characterization by reflection of a system antenna comprising a plurality of input / output ports by implementing a characterization system according to an embodiment of the invention.

[0056] Detailed description of embodiments of the invention

[0057] We now present, in relation to [Fig. 3], an example of the structure of a system 300 for characterizing by reflection an antenna system 100 comprising a plurality of input / output ports according to an embodiment of the invention.

[0058] More particularly, the characterization system 300 comprises, just like the characterization system 200 described above in relation to [Fig.2], an antenna measuring antenna 210 coupled to a network analyzer 220. The measuring antenna 210 is intended to emit, for at least one given frequency of a frequency band of interest, an incident wave in the direction of the antenna system 100 and to receive a wave backscattered by the antenna system 100. The network analyzer 220 is intended to measure a backscattering coefficient associated with the given frequency from the complex amplitude of the incident wave emitted by the measuring antenna 210 and the complex amplitude of the wave received by the measuring antenna 210. Thus, the proposed solution is based on a characterization by reflection of the antenna system 100. In this way, a phase coherence between the different parameters characterizing the antenna system 100, eg the S parameters, can be obtained.

[0059] However, unlike the characterization system 200 in which the input / output ports are loaded by simple charges changed at each measurement, the characterization system 300 comprises a circuit, called dissociation circuit 310, configured to load the plurality of input / output ports of the antenna system 100.

[0060] More particularly, such a dissociation circuit 310 comprises one (or more) delay lines implemented between a first port and a second port of the plurality of input / output ports. The delay line is configured so that an impulse response 410 estimated from backscattering coefficients measured in the frequency band of interest comprises a plurality of echoes, called useful echoes 412a, 412b, 412c, having temporal supports distinct from each other. The useful echoes 412a, 412b, 412c are associated with physical phenomena distinct from each other contributing to the backscattered wave. In practice, the radioelectric length of the delay line may depend on different criteria. According to a first example of criterion, the radio length is determined so as to place the useful echoes 412a, 412b, 412c in a predetermined zone of the impulse response 410.According to a second example of criterion, the radio length is determined as a function of the time resolution of the characterization system 300, and therefore of the frequency band of interest on which the backscattering coefficients are ultimately measured. The larger this frequency band of interest, the finer the time resolution of the impulse response 410, thereby relaxing the constraints on the radio length of the delay line. For example, the radio length of the delay line is determined to obtain such a time dissociation of the useful echoes 412a, 412b, 412c for a given time resolution.

[0061] In order to detail this phenomenon, we now consider the impulse response 410 illustrated in [Fig. 4]. More particularly, such an impulse response 410 is measured here in the particular case where the characterization system 300 further comprises an anechoic chamber 400. The characterization of the antenna system 100 is implemented inside the anechoic chamber 400. Thus, the impulse response ional 410 comprises one (or more) echoes, called direct echo 411, linked to the presence of the anechoic chamber 400. In the present case, the impulse response 410 is represented as the amplitude (Amp.) of the backscattered wave measured by the measuring antenna 210 as a function of the distance (d) traveled by the incident wave emitted by the measuring antenna 210 then backscattered by the antenna system 100 until its return to the measuring antenna 210. Thus, the direct echo 411, linked to the presence of the anechoic chamber 400, is located at a distance corresponding to a wall of the anechoic chamber 400.

[0062] Furthermore, the delay line(s) of the dissociation circuit 310 is configured so that the impulse response 410 comprises useful echoes 412a, 412b, 412c having temporal supports that are distinct from each other. The useful echoes 412a, 412b, 412c are associated with physical phenomena contributing to the backscattered wave and which are distinct from each other.

[0063] More particularly, the impulse response 410 comprises:

[0064] - a first useful echo 412a associated with a physical phenomenon comprising the reflection of the incident wave on the structure of the antenna system 100. Thus, a backscattering coefficient measured from the backscattered wave temporally windowed around the first useful echo 420a is representative of one (or more) parameters Sd;

[0065] - a second useful echo 412b associated with a physical phenomenon comprising the transmission of the incident wave on the input / output ports, the reflection of the transmitted incident wave on the loads present on the input / output ports, and the radiation by the antenna system 100 of the reflected transmitted incident wave. Thus, a backscattering coefficient measured from the backscattered wave temporally windowed around the second useful echo 412b is representative of one (or more) products of the SeySr type, with Y the transfer function of the dissociation circuit 310;

[0066] - a third useful echo 412c associated with a physical phenomenon comprising the transmission of the incident wave on the input / output ports, the incident Fonde propagation transmitted between the input / output ports due to mismatches and couplings between radiating elements and between input / output ports, and the radiation by the antenna system 100 of the transmitted incident wave propagated between ports. Thus, a backscattering coefficient measured from the backscattered wave temporally windowed around the third useful echo 420c is representative of one (or more) products of the type SeyS(ySr.

[0067] In the present embodiment, the delay line(s) of the dissociation circuit 310 is further configured so that the useful echoes 412a, 412b, 412c are not temporally superimposed on the direct echo (or direct echoes) 411. Thus, there is no need to subtract the empty anechoic chamber 400 to estimate the parameters characterizing the antenna system 100. In certain embodiments, the delay line(s) of the dissociation circuit 310 is further configured so that the useful echoes 412a, 412b, 412c are positioned after the end of the impulse response specific to the anechoic chamber 400 (i.e. in a time section of the impulse response 410 which no longer includes components linked to the anechoic chamber 400).

[0068] However, in other embodiments, the delay line(s) of the dissociation circuit 310 is configured only so that the useful echoes 412a, 412b, 412c have distinct temporal supports between them. In this case, the delay line(s) of the dissociation circuit 310 is not configured so that the useful echoes 412a, 412b, 412c are not temporally superimposed on the direct echo (or direct echoes) 411. This is for example a case where the vacuum anechoic chamber 400 is subtracted before the estimation of the parameters characterizing the antenna system 100.

[0069] In some embodiments, the characterization system 300 does not include an anechoic chamber 400. In such cases, the impulse response 410 does not include direct echo(es) 411.

[0070] We now present, in relation to [Fig.5], [Fig.5a], [Fig.5b] and [Fig.5c] examples of dissociation circuit structures 310 according to different embodiments of the invention.

[0071] More particularly, in these different embodiments the dissociation circuits 310 are configured to load an antenna system 100 comprising two input / output ports. The dissociation circuits 310 each comprise a delay line implementing a device belonging to the group comprising:

[0072] - a device comprising a passive 500 radiofrequency cable ([Fig.5]);

[0073] - a device comprising a passive 500 radiofrequency cable and an amplifier 510 ([Fig.5a]);

[0074] - a device comprising a radiofrequency cable 500, an amplifier 510 and at minus one attenuator 520 ([Fig.5b]);

[0075] - a device comprising a pair of RF to RF conversion devices 530 optical and a 540 optical fiber ([Fig.5c]).

[0076] For example, a passive radiofrequency cable 500 has a given radioelectric length and thus makes it possible to add a propagation delay. In this way, such a passive radiofrequency cable 500 makes it possible to temporally dissociate the useful echoes 412a, 412b, 412c in a simple manner. However, such a passive cable provides an attenuation which reduces the amplitude of the temporally dissociated useful echoes 412a, 412b, 412c. In practice, such an attenuation is all the greater as the frequency is high and / or the cable length is high (one can have tens of meters of cable in practical implementations). Conversely, a radiofrequency cable 500 associated with an amplifier 510 makes it possible to compensate for the attenuation of the cable. Furthermore, such an amplifier-based assembly is unidirectional, which makes it possible to differentiate the contributions linked, on the one hand, to the path between the first port and the second port and, on the other hand, to the path between the second port and the first port within the parameters characterizing the antenna system 100.

[0077] The presence of attenuators 520 makes it possible to mask multiple reflections linked to load mismatches.

[0078] The use of optical fibers 540 allows long propagation delays to be achieved while having low losses, which allows minimizing the reduction in the amplitude of the useful echoes 412a, 412b, 412c. For example, the use of optical fibers 540 allows the implementation of amplifiers, which also leads to unidirectional behavior as described above.

[0079] We now present, in relation to [Fig.6], an example of the structure of a dissociation circuit 310 according to another embodiment of the invention.

[0080] More particularly, in this embodiment the dissociation circuit 310 is configured to load an antenna system 100 comprising three input / output ports. The dissociation circuit 310 comprises different delay lines configured to delay the different possible paths between the different input / output ports of the antenna system 100.

[0081] To do this, the dissociation circuit 310 comprises three passive radiofrequency cables 500, each cable being electrically connected, on the one hand, to an input / output port of the antenna system 100 and, on the other hand, to an RF splitter 550. The RF splitter 550 is in turn electrically connected to two RF to optical conversion devices 530 connected to respective optical fibers 540. The optical fibers 540 are configured so that all or part of the delays associated with the different possible paths between the different input / output ports are different.

[0082] We now present, in relation to [Fig. 7], the steps of a method for characterizing by reflection an antenna system 100 comprising a plurality of input / output ports according to an embodiment of the invention. More particularly, such a method implements the characterization system 300 (according to any one of the aforementioned embodiments).

[0083] More particularly, for a given frequency of a frequency band of interest:

[0084] - during a step E700, the measuring antenna 210 emits an incident wave in direction of the antenna system 100; and

[0085] - during a step E710, the measuring antenna 210 receives the wave backscattered by the antenna system 100.

[0086] For at least one temporal support associated with a given useful echo 412a or 412b or 412c of the impulse response 410:

[0087] - during a step E720, a time window is applied to the backscattered background on the temporal support of the given useful echo 412a or 412b or 412c delivering a windowed wave; and

[0088] - during a step E730, the network analyzer 220 measures a retro coefficient diffusion from the windowed wave.

[0089] At the end of the execution (or executions depending on the number of time supports considered) of steps E700 to E730, at least one backscattering coefficient is obtained.

[0090] Then, during a step E740, at least one characterization parameter of the antenna system 100 is estimated from said at least one backscattering coefficient.

[0091] In certain embodiments in which the dissociation circuit 310 is configured so that the impulse response 410 comprises a first useful echo 412a associated with a physical phenomenon comprising the Fonde reflection incident on the structure of the antenna system 100, the time windowing step E720 and the step E730 of measuring a backscattering coefficient are implemented for a first time support associated with the first useful echo 412a delivering a first backscattering coefficient. The estimation step E740 comprises the estimation, from the first backscattering coefficient, of at least one parameter 5 representative of the structural component of the SER of the antenna system 100, eg of at least one parameter Sd.

[0092] In certain embodiments in which the dissociation circuit 310 is configured so that the impulse response 410 comprises a second useful echo 412b associated with a physical phenomenon comprising the transmission of incident Fonde on the input / output ports of the antenna system 100, the reflection of incident Fonde transmitted on the loads present on the input / output ports of the antenna system 100, and the radiation by the antenna system 100 of transmitted reflected incident Fonde, the step E720 of time windowing and the step E730 of measuring a backscattering coefficient are implemented for a second time medium associated with the second useful echo 412b delivering a second backscattering coefficient.

[0093] The estimation step E740 comprises the estimation, from the second backscattering coefficient and the transfer function of the dissociation circuit 310:

[0094] - of at least one parameter 5 representative of the capacity of the antenna system 100 to induce on each of its ports the captured energy, eg of at least one parameter Sr; and

[0095] - of at least one parameter S representative of the capacity of the antenna system 100 to radiate the energy supplied to its ports, eg of at least one Se parameter.

[0096] For example, the transfer function of the dissociation circuit 310 is predetermined prior to the implementation of the characterization method, e.g. via a characterization of the dissociation circuit 310 on a table before mounting on the input / output ports of the antenna system 100.

[0097] In some embodiments in which the dissociation circuit 310 is configured so that the impulse response 410 includes, in addition to the second useful echo 412b, a third useful echo 412c associated with a physical phenomenon including the transmission of the incident wave on the input / output ports of the antenna system 100, the propagation of the transmitted incident wave between the input / output ports of the antenna system 100 due to mismatches and couplings between the input / output ports of the antenna system 100, and the radiation by the antenna system 100 of the transmitted incident wave propagated between ports,the step E720 of time windowing and the step E730 of measuring a backscattering coefficient are implemented for the second time support associated with the second useful echo 412b and for a third time support associated with the third useful echo 412c delivering the second backscattering coefficient and a third backscattering coefficient.

[0098] The estimation step E740 comprises the estimation, from the second backscattering coefficient and the transfer function of the dissociation circuit 310, of at least one parameter 5 representative of the difficulty of the antenna system 100 in radiating the energy supplied to its ports because of the existing couplings between radiating elements and between ports, eg of at least one parameter Sc.

[0099] Thus, the implementation of the dissociation circuit 310 makes it possible to temporally isolate the different physical phenomena contributing to the backscattered wave, and therefore to isolate the different contributions to the backscattering coefficients characterizing the antenna system 100. Thus, by temporal windowing it is possible to isolate the different physical contributions and thus to estimate in a simple manner, and via a simplified formalism, the parameters characterizing the antenna system 100.

Claims

Claims

1. System (300) for characterizing by reflection an antenna system (100) comprising a plurality of input / output ports, the characterization system comprising a measurement antenna (210) coupled to a network analyzer (220), the measurement antenna being intended to emit, for at least one given frequency of a frequency band of interest, an incident wave in the direction of the antenna system and to receive a wave backscattered by the antenna system, the network analyzer being intended to measure a backscatter coefficient associated with the given frequency from the complex amplitude of the incident wave and the complex amplitude of the received wave, characterized in that it further comprises a circuit, called a dissociation circuit (310), configured to load the plurality of input / output ports of the antenna system,the dissociation circuit comprising at least one delay line implemented between a first port and a second port of the plurality of ports, the delay line being configured so that an impulse response (410) estimated from backscattering coefficients measured in the frequency band of interest comprises a plurality of echoes, called useful echoes (412a, 412b, 412c), having temporal supports distinct from each other, the useful echoes being associated with physical phenomena distinct from each other contributing to said backscattered wave.,

2. The system of claim 1, wherein a first useful echo (412a) is associated with a physical phenomenon comprising the reflection of the incident wave on the structure of the antenna system.

3. The system of claim 1 or 2, wherein a second useful echo (412b) is associated with a physical phenomenon comprising the transmission of incident wave on the ports of the plurality, the reflection of the transmitted incident wave on the loads present on the ports of the plurality, and the radiation by the antenna system of the reflected transmitted incident wave.

4. The system of any one of claims 1 to 3, wherein a third useful echo (412c) is associated with a physical phenomenon comprising transmission of the incident wave on the ports of the plurality, propagation of incident Fonde transmitted between the ports of the plurality due to mismatches and couplings between the ports of the plurality, and radiation by the Fonde antenna system. incident transmitted propagated between ports.

5. System according to any one of claims 1 to 4, wherein the delay line implements a device belonging to the group comprising: - a device comprising a passive radio frequency cable (500); - a device comprising a passive radio frequency cable and an amplifier (510); - a device comprising a passive radio frequency cable, an amplifier and at least one attenuator (520); - a device comprising a pair of RF to optical conversion devices (530) and an optical fiber (540).

6. System according to any one of claims 1 to 5, the characterization system further comprising an anechoic chamber (400), the characterization of the antenna system being implemented inside the anechoic chamber, the impulse response comprising at least one echo, called direct echo (411), linked to the presence of the chamber, in which the delay line is configured so that the useful echoes are not temporally superimposed on said at least one direct echo.

7. Method for characterizing by reflection an antenna system (100) comprising a plurality of input / output ports by implementing a characterization system (300) according to any one of the preceding claims, characterized in that it comprises, for at least one given frequency of a frequency band of interest: - a transmission (E700), by the measurement antenna (210), of the incident wave in the direction of the antenna system; and - a reception (E710), by the measurement antenna, of the wave backscattered by the antenna system, in that it comprises, for at least one time medium associated with a useful echo of the plurality of echoes: - a time windowing (E720) of the backscattered wave on the time medium delivering a windowed wave;and - a measurement (E730), by the network analyzer (220), of a backscattering coefficient from the windowed background, delivering at least one corresponding backscattering coefficient, and in that it comprises: - an estimation (E740) of at least one characterization parameter of the antenna system from said at least one backscattering coefficient; broadcast.

8. Method according to claim 7, in which the characterization system is according to claim 2 or according to any one of claims 3 to 6 in that it depends on claim 2, in which the time windowing and the measurement of a backscattering coefficient are implemented for a first time support associated with the first useful echo (412a) delivering a first backscattering coefficient, and in which said estimation comprises the estimation, from the first backscattering coefficient, of at least one parameter 5 representative of the structural component of the radar equivalent surface of the antenna system.

9. Method according to claim 7, in which the characterization system is according to claim 3 or according to any one of claims 4 to 6 in that it depends on claim 3, in which the time windowing and the measurement of a backscattering coefficient are implemented for a second time support associated with the second useful echo (412b) delivering a second backscattering coefficient, and in which said estimation comprises the estimation, from the second backscattering coefficient and a transfer function of the dissociation circuit: - of at least one parameter S representative of the capacity of the antenna system to induce on each of its ports the captured energy; and - of at least one parameter 5 representative of the capacity of the antenna system to radiate the energy supplied on its ports.

10. Method according to claim 9, in which the characterization system is according to claim 4 in that it depends on claim 3 or according to claims 5 or 6 in that it depends on claim 4 and claim 3, in which the time windowing and the measurement of a backscattering coefficient are implemented for the second time medium associated with the second useful echo and for a third time medium associated with the third useful echo (412c) delivering the second backscattering coefficient and a third backscattering coefficient, and in which said estimation comprises the estimation, from the second backscattering coefficient and the third backscattering coefficient, of at least one parameter S representative of the difficulty of the antenna system to radiate the energy supplied to its ports because of the existing couplings between radiating elements and between ports.

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