Radar system and method for detecting occupied frequency channels

Abstract

A radar system (1) for detecting occupied frequency channels is proposed, comprising N reception channels (20n) each capable of receiving signals (Srn). The system comprises, for each channel (20n), a unit (22n) for converting said received signals (Srn) into the spectral domain to form a signal (Sn) converted onto an instantaneous frequency band associated with frequency channels (F), a module (24n) for determining correlation values ​​(Rn(F)) applying a power correlation between the spectrum of the converted signal (Sn) and the spectrum of an arbitrary reference signal chosen from one of the converted signals propagated on one of said channels, and an evaluation module (30) determining the values ​​of the sum channel from the correlation values ​​(Rn(F)), the frequency channel (F) being occupied if the value of the associated sum channel is greater than a predefined detection threshold value. Figure for the abstract: [Fig.1]

Description

Title of the invention: Radar system and method for detecting occupied frequency channels Technical field

[0001] The present invention relates generally to the field of passive multi-channel antenna systems, and in particular to a radar system and a method for detecting occupied frequency channels.

[0002] An antenna system can be disturbed when it is used in a dense electromagnetic environment, that is to say comprising numerous so-called occupied (or polluted) frequency channels each associated with emitted electromagnetic signals that can be received by the antenna system. Knowledge of the occupied frequency channels allows an operator of this antenna system to optimize the exploitation of the frequency channels in transmission and / or reception by choosing the so-called free frequency channels to transmit a new electromagnetic signal and / or process signals of interest.

[0003] Today there are systems for detecting occupied frequency channels, such as electromagnetic intelligence systems (also called SIGINT for Signal Intelligence according to the corresponding English acronym, or ESM for Electronic Support Measures according to the corresponding English acronym) making it possible to detect and locate electromagnetic signals in a very wide range of frequencies.

[0004] However, such systems present significant implementation complexity and high manufacturing costs. They also present strong constraints in terms of installation on a more global system such as an airborne vehicle for example. In particular, existing systems have a large footprint, a significant mass and coercive specifications concerning the specific installation areas of these systems on a carrier such as an airplane or a helicopter.

[0005] Furthermore, such systems installed on an airborne vehicle present limited results in terms of estimating the direction of arrival of a detected signal, in particular because the antennas used have limited directivity.

[0006] There is thus a need for an improved system and method for detecting busy frequency channels. Summary of the invention

[0007] For this purpose, a radar system for detecting occupied frequency channels is proposed, the system comprising N reception channels and a set (10) of radar antennas associated with each channel, N being an integer greater than or equal to 2, each channel being able to respectively receive signals by means of the associated radar antenna. The radar system comprises, for each reception channel, a conversion unit in the spectral domain of the received signals to form a converted signal defined on a given instantaneous frequency band associated with a set of frequency channels, and a module for determining correlation values ​​adapted to apply a power correlation between the spectrum of the converted signal propagated on the reception channel and the spectrum of an arbitrary reference signal chosen from one of the converted signals propagated on one of the reception channels. The radar system further comprises a module for evaluating occupied frequency channels adapted to determine the values ​​of the sum channel from the correlation values ​​of the N reception channels, the frequency channel being occupied if the value of the associated sum channel is greater than a predefined detection threshold value.

[0008] Advantageously, the correlation value determination module can be configured to determine a power spectral density of the signal propagated on the reception path relative to the arbitrary reference signal.

[0009] In embodiments, the correlation value determination module can be configured to apply an integration over several successive frames of the signal propagated on the reception path.

[0010] According to certain embodiments, the radar system may further comprise a calibration device comprising N calibration channels. For each calibration channel, the calibration device may be configured to determine correction coefficient values ​​of the converted signal to balance in amplitude and phase each of the reception channels of the radar system.

[0011] The radar system may be configured to apply a frequency sweep by repeating the evaluation of the detection of occupied frequency channels with respect to the detection threshold value, to cover an entire predefined frequency domain of interest.

[0012] Advantageously, the radar system can be configured to apply a pointing antenna direction. The occupied frequency channel evaluation module can further be adapted to determine values ​​of the deviation channel from the correlation values ​​of the N reception channels, then values ​​of the ratio of the deviation channel from the values ​​of the sum channel and the values ​​of the deviation channel, the pointing antenna direction corresponding to the direction of arrival of the received signals relative to the orientation of the antennas of the radar system if the values ​​of the ratio of the deviation channel are less than a predefined lobe threshold value.

[0013] The occupied frequency channel evaluation module may further be adapted to determine at least one refined direction of arrival of the signals received with respect to to the orientation of the radar system antennas from the values ​​of the channel deviation ratio and the pointing antenna direction.

[0014] In some embodiments, the radar system may be configured to apply a spatial scan by repeating the evaluation of the direction of arrival of the received signals with respect to the lobe threshold value, to cover an entire predefined angular domain of interest.

[0015] The radar system may comprise a configuration operationally in “listening” mode in the radio frequency domain of the “X-band” type.

[0016] There is further provided a method for detecting frequency channels, implemented in a radar system comprising N reception channels, N being an integer greater than or equal to 2, the method comprising receiving, at each channel, signals. The method comprises, for each reception channel, the following steps consisting of:

[0017] - convert, in the spectral domain, the received signals to form N signals converts each defined on a given instantaneous frequency band associated with a set of frequency channels,

[0018] - determining correlation values ​​by applying power correlation between the spectrum of the converted signal propagated on the reception channel and the spectrum of an arbitrary reference signal chosen from one of the converted signals propagated on one of the reception channels.

[0019] The method further comprises an evaluation of the occupied frequency channels comprising the steps of:

[0020] - determine the sum channel values ​​from the correlation values ​​of the N reception channels,

[0021] - compare the value of the sum channel associated with a detection threshold value predefined, and

[0022] - determine that the frequency channel is occupied if the value of the sum channel associated is greater than the predefined detection threshold value.

[0023] The embodiments of the invention thus provide a radar system and a method allowing the detection and evaluation of occupied frequency channels according to a satisfactory estimation of the direction of arrival of a detected signal.

[0024] The embodiments of the invention also provide an efficient and affordable solution in terms of material complexity, while limiting manufacturing and installation costs, as well as energy costs of implementation. The proposed system advantageously has a reduced volume and mass compactness, as well as an optimized footprint. Description of the figures

[0025] Other characteristics, details and advantages of the invention will emerge on reading the description given with reference to the appended drawings given by way of example.

[0026] [Fig-1] [Fig. 1] is a diagram showing a radar system for detecting occupied frequency channels, according to embodiments of the invention.

[0027] [Fig.2] [Fig.2] consists of two diagrams (a) and (b) representing a module for measuring a reception channel of a radar system, according to embodiments of the invention.

[0028] [Fig.3] Fig. 3 is a diagram showing a calibration device for a radar system, according to embodiments of the invention.

[0029] [Fig.4] Fig. 4 consists of two diagrams (a) and (b) respectively showing a noise correction measurement module of a noise processing path and a calibration correction measurement module of a calibration device for a radar system, according to embodiments of the invention.

[0030] [Fig.5] Fig. 5 is a diagram showing a 4-channel 2D receiving antenna, according to embodiments of the invention.

[0031] [Fig.6] Fig. 6 is a flowchart showing a method for evaluating frequency channels of a received signal, according to embodiments of the invention.

[0032] [Fig.7] [Fig.7] is a flowchart representing a method for estimating the direction of arrival of a received signal, according to embodiments of the invention.

[0033] Identical references are used in the figures to designate identical or similar elements. For reasons of clarity, the elements shown are not to scale. Detailed description

[0034] [Fig.l] schematically represents a radar system for detecting occupied frequency channels 1 comprising a set 10 of N radar electromagnetic antennas (or a set 10 of N receivers of a radar electromagnetic antenna) each associated with a reception channel 20n and an evaluation module 30 of occupied frequency channels, according to embodiments of the invention.

[0035] The radar system 1 thus comprises a number N of reception channels 20n, each channel being capable of receiving one or more received signals (i.e. received time signals), denoted Srn, originating (i.e. by means of) one of the radar antennas of the set 10. The index 'n', associated with the reception channels, is an integer between 1 and N, and the value of N being an integer greater than or equal to 2.

[0036] The radar system 1 can be used in various civil or military fields, in particular for applications of detection and localization of electromagnetic emissions in a dense electromagnetic environment.

[0037] Advantageously, the radar system 1 may be a multi-antenna (or multi-channel) system configured in “listening” mode, that is to say according to an operational configuration exploiting the signals coming from the antennas (or the antenna) capturing the external environment and from the different reception channels without emitting an electromagnetic signal. Thus, as used here, an 'operationally “listening” configuration' refers to a configuration in which the radar system operates in “listening” mode.The operational frequency domain of such a system may comprise a very wide range of frequencies, and be located in the radio frequency (RF) domain corresponding, for example and without limitations, to an “X band” type RF band typically between 8 GHz and 12 GHz, to a “Ku band” type RF band typically between 12 GHz and 18 GHz, to a “K band” type RF band typically between 18 GHz and 26 GHz, or to a “Ka band” type RF band typically between 26 GHz and 40 GHz.

[0038] The radar system 1 can in particular use a radar antenna device installed on board a carrier, of small size such as a helicopter for example, making it possible to provide an affordable system in terms of hardware implementation while limiting manufacturing and installation costs.

[0039] As shown in [Fig.l], each reception channel 20n of the radar system 1 comprises a conversion unit 22n and a measurement module 24n, according to embodiments of the invention.

[0040] The conversion unit 22n is configured to perform a conversion (or a passage), in the spectral domain (i.e. the frequency domain), of the received signal(s) Srn to form a signal called 'converted signal' and denoted Sn, to be propagated on the reception channel 20n, and defined on a given instantaneous frequency band, denoted BF. Such an instantaneous frequency band is associated with a set of frequency channels, denoted F. For example and without limitation, an instantaneous frequency band BF, defined in an RF band of the "X band" type, may be equal to 256 MHz, and comprise 256 associated frequency channels F, each frequency channel F being defined on 1 MHz. The remainder of the description will refer to the notation "Sn(F)" relating to the value of the converted signal defined on a specific frequency channel F.

[0041] Such a conversion unit 22n is implemented using a spectral analysis, defined in particular by applying a discrete Fourier transform of the received signal Srn. A Fourier transform can be implemented by an algorithm for calculating a fast Fourier transform (or FFT for Fast Fourier Transform according to the corresponding English acronym).

[0042] The measurement module 24n (also called 'determination module' or 'calculation module') is configured to implement operations, in the spectral domain, to determine the power correlation, denoted Rn, between the spectrum of the converted signal Sn propagated on the reception channel 20n and an arbitrary reference signal, denoted Sref. For each frequency channel F of the given instantaneous frequency band BF, the associated correlation value can be denoted Rn(F).

[0043] The arbitrary reference signal Sref is chosen from the set of N converted signals Sn propagated on the reception channels of the radar system 1. For example and without limitations, the arbitrary reference signal Sref can correspond to the converted signal Si to be propagated on a first reception channel denoted 20i. Each of the converted signals of another reception channel can alternatively be used as an arbitrary reference signal Sref.

[0044] In certain embodiments, the input signal of the measurement unit 24n may be the converted signal Sn propagated on the reception path 20n, as shown in [Fig.2](a).

[0045] In other embodiments, the signal at the input of the measurement unit 24n may be a signal calibrated in amplitude and phase, to be propagated on the reception channel 20n and noted Scn, as shown in [Fig.2](b).

[0046] The module 30 for evaluating occupied frequency channels of the radar system 1 is configured to determine (or reconstruct) the sum channel y of the N reception channels. In particular, the module 30 for evaluating occupied frequency channels is configured to determine, for each frequency channel F of the given instantaneous frequency band BF, the value of the sum channel, denoted y (F), from the correlation values ​​Rn(F) defined for each frequency channel F of the set of N reception channels, as defined according to the following equation (01):

[0047] y (F) = yn Rn(F) (01)

[0048] The module 30 is further configured to evaluate (i.e. detect or determine) whether a specific frequency channel F is occupied from the comparison of the value of the associated sum channel y (F) with a predefined detection threshold T threshold. The frequency channel F can then be considered as “occupied” (or even “polluted”) if the value of the sum channel y (F) is greater than the detection threshold Tseiâl. Alternatively, the specific frequency channel F can be considered as “free” if the value of the sum channel y (F) is less than the detection threshold Tseuil. For example and without limitation, depending on the value of the predefined detection threshold Tseuil, if the value of the sum channel y (F) is strictly greater than (or alternatively greater than or equal to) the detection threshold ~ threshold.then the frequency channel F can then be considered as “occupied”; and if the value of the sum channel y (F) is less than or equal to (or alternatively strictly less than) the detection threshold Tseuii. then the frequency channel F can be considered as “free”.

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057] Advantageously, the module 30 is configured to apply this evaluation of the occupancy of all the frequency channels F defined in the given instantaneous frequency band BF. It should be noted that a signal S(t) received by the antenna of the system 1 is characterized by a direction of arrival 0 (or DOA for Direction of Arrivai according to the corresponding English acronym, also called 'direction of provenance') defined in relation to the orientation of the antenna, that is to say the plane of the receivers of the set 10, as shown diagrammatically in [Fig.l]. By way of illustration, in the case of a one-dimensional (1D) antenna composed of receivers spaced by a distance d, the receivers of the set 10 are configured to process the time signal S(t) received from the arrival direction 0. The path difference xk of reception of the received signal between a first receiver and a k-th receiver can be defined according to the following equation (02): xk = kdsin(0) (02) The index 'k' represents an integer between 2 and N. The phase difference A(|) between the first receiver and the k-th receiver considered, and therefore the associated reception channels, can thus be expressed according to the following equation (03): A(j) - x Xk - k. A(p In equation (03), the coefficient A(p) corresponds to the phase deviation coefficient equal to the following equation (04): A(p = ^.(18^( 9) The signal received by radar system 1, after demodulation then transformation of Fourier, that is to say converted into the frequency domain, can be represented for each frequency channel according to the following matrix expression (05), for each reception channel 20n:

[0058] Ape'% \ (05) \ s n / +

[0059] In formula (05), the values ​​An correspond to the level of the signal S(t) received multiplied by the antenna gain, noted Gn, predefined for each of the reception channels 20n of the radar system 1. Using the converted signal Si to be propagated on the first reception channel 20i as an arbitrary reference signal Sref, the set R relating to the power correlations Rn of the reception channels 20n can be represented according to the following relation (06):

[0060] R 1R{ 1 'e[sM] \ 1 A' 1 (06) — R2 — E[S2*Sj] _ ApA^e'^

[0061] Thus, for each of the reception channels 20n, the power correlation Rn can be defined, with respect to the chosen arbitrary reference signal (i.e. for example to the single reference channel 20i), to within a multiplicative constant, according to the amplitude An and the phase deviation coefficient A <p du signal reçu, tel que défini selon l’expression (07) suivante :

[0062] rn="AbAn.eX'"> W <p (07)

[0063] avantageusement, comme représenté sur les figures 2(a) et 2(b), le module de mesure 24n d’une voie réception 20n peut comprendre une première unité 24-ln configurée pour appliquer opération consistant à effectuer un produit corrélation entre signal converti sn référence arbitraire sref. une telle opération, encore appelé ‘opération produit’, correspondre densité spectrale puissance du propagé la par rapport sref, être représentée l’expression « sasj » présentée dans (06) précédente. le en outre deuxième 24-3n sommation dudit issu générer rn. post-intégration (ou d’intégration) plusieurs trames successives.

[0064] dans des modes réalisation, chaque 20n, calibré amplitude phase scn qui utilisé entrée l’unité , [fig.2](b), généré partir correction coefficient correction, noté cn (appelé également correction). en particulier, système radar 1 dispositif calibrage formation faisceau ic configuré calibration tel cn.

[0065] tel que [fig.3], nombre n voies 40n, étant apte recevoir ou signaux reçus srn provenant antennes l’ensemble 10 d’un récepteurs d’antenne radar), génération bruit 50 traitement 60.

[0066] un permet calibrer 1, canaux fréquentiels bande fréquentielle instantanée donnée bf ensemble bandes fréquentielles instantanées associées rf spécifique, égalisant différents convertis propager réception.

[0067] l’unité ainsi bruit, sr0, large bande, c’est-à-dire couvrant exemple tout 10.

[0068] comme 40n conversion 42n 44n, selon réalisation l’invention.

[0069] de façon analogue, 60 62 64,

[0070] (c’est-à-dire assimilable équivalente) 22n 1. donc passage), domaine spectral, former défini prédéterminée bf, associée f.

[0071] sr0 so la suite description fera notation s0(f) relative au canal fréquentiel f spécifique.

[0072] 64 (encore ‘module détermination bruit’ calcul bruit’) mettre œuvre opérations spectral déterminer sc0. ce sc0 correspond l’inter-corrélation so.

[0073] 44n correction’ correction’) spectre il est noter valeurs coefficients complexes notées cn(f), peuvent aux estimations l’écart chacune spectral. tels permettent d’équilibrer toute bf.

[0074] pour calibrés définis appliqués alors utilisés

[0075] figure 4(a), 64-1 64-3. par sans limitations, d’inter-corrélation (issu 60), correspondant l’opération s0*sq »)• 64-3 postintégration 64-1,

[0076] [fig.4](a), 44-ln 44-3n. 42n) 60). 44-3n 44-ln.

[0077] troisième 44-5n division 20n.

[0078] ailleurs, cas où valeur somme £(f), définie f, supérieure seuil détection rseuil, occupé s(t) reçu, 30 évaluer direction d’arrivée 0 reçu l’antenne

[0079] modifier opérationnelle pointage antenne bidimensionnelle (2d) exemple, initialement élévation oeo circulaire oco, préalablement l’acquisition l’antenne.

[0080] selon variantes l’invention, 9 adapté si, occupé, coïncide (notamment approximativement) avec cette d’arrivée, puis estimer déterminer) affinée reçu.

[0081] cela, d’évaluation reconstituer) écart corrélations

[0082] 1d, déterminer, écart, notée a(f). 2d, circulaire, ac(f), qu’une élévation, ae(f). telles 2d définies équations (08) (09) suivantes :

[0083] ac(f)="£" n wc="{" ( ) ,rn(f)

[0084] ae(f)="£" we .rn(f)

[0085] (09), éléments wc(n) we(n) correspondent respectivement relatifs nieme récepteur associé limitation, [fig.5] représente illustration schématique 4 cas, exprimés expressions (10) (11)

[0086] + i, -i, +i, -i}(10)

[0087] we="{" _i, -i}(h)

[0088] ratio réception, £(f).

[0089] £(f)

[0090] faciliter compréhension l’invention titre simplification, sera faite principalement 2d. l’homme métier comprendra aisément s’appliquer type d’antenne, notamment 1d. ainsi, particulier ratioc(f), ratioe(f), (12) (13)

[0091] ratior(f) acw 112) ~ e(f)

[0092] ratioe(f) _ w —

[0093]

[0094] si (oeo, ^co) 10, comparaison prédéfinie, dite ‘seuil lobe’ ratioc(f) lobe prédéfinie ®co) absolue iratio^f)’ jratiop(f) sont inférieures

[0095]

[0096] eiobe. alternativement, ne pas ^-atioc(f)           est fonction siobe prédéfini, |ratioc(f) ^atiog(f) strictement alternativement égales) ew>e, then the pointing direction in elevation and in circular can correspond to the direction of arrival of the received signal S(t); and if the absolute value of the ratio of the circular deviation channel ]ratioc(f) and / °u the absolute value of the ratio of the elevation deviation channel Iratio^F) is greater than or equal to (or alternatively strictly greater than) the lobe threshold ^obe, then the pointing direction in elevation and in circular can correspond to the direction of arrival of the received signal S(t). In the case where the absolute values ​​of the ratio of the circular deviation channel IratiOcÜ7) and the elevation deviation channel Iratio^F) are lower than the lobe threshold ^obe, that is to say that the pointing direction in elevation and in circular (©eo, 9co) of the antenna 10 corresponds to the direction of arrival of the received signal S(t), the module 30 can be adapted to evaluate (that is to say estimate or determine) a refined direction in elevation and in circular (0EcsHm, $G,süir.) of arrival of the received signal S(t). Such a refined direction can be estimated from the value of the circular deviation channel ratio ratioc(F), from the value of the elevation deviation channel ratio ratioE(F), as well as from the pointing direction in elevation and in circular (OEo, ^co) of the antenna 10. Thus, in embodiments, the evaluation module 30 can be adapted to determine the value of the refined elevation direction ÔEesdm according to the following equation (14):

[0097] ^E eslim = + ^ J i _ Q has i xratio E (Fy) ]

[0098] Furthermore, the evaluation module 30 can be adapted to determine the value of the circularly refined direction 0c ... as a function of the value of the circularly refined direction elevation 0Ee,ljm according to the following equation (15): [0°"] 0C^ = x [( cos (0^ sin ( 0co ) ) + ( x ratioc ( F ) ' ) ] ] (15)

[0100] In the preceding mathematical equations (14) and (15), the elements at are polynomial coefficients depending on predefined characteristics of the antenna 10, and the integer J corresponds to an order of the chosen polynomial.

[0101] It should be noted that the frequency band associated with the frequency channel F can advantageously correspond to the instantaneous frequency band centered on the predefined carrier frequency of the radar antenna for example, characterized by a particular pointing direction. Advantageously, the radar system 1 can be configured to apply the evaluation of the frequency channel F and / or to the estimation of the direction of arrival of the signal S(t) received for a plurality of instantaneous frequency bands BF, in particular for several carrier frequencies of the radar in its agility band. This thus allows the radar system 1 to perform a frequency sweep for signal detection by the antenna to cover an entire predefined frequency domain of interest (for example an entire frequency domain associated with the RF band of the “X band” type).

[0102] When estimating the direction of arrival of the signal S(t) received by the antenna of the system 1, in the case where the elevation and circular pointing direction (0eo, ©co) of the antenna 10 does not correspond to this direction of arrival for example, the radar system 1 can be configured to apply a new elevation and circular pointing antenna direction before acquiring a signal S(t) again by the antenna and then to perform a new estimation of the direction of arrival of the signal. This thus allows the radar system 1 to perform a spatial scan for detection of the signal by the antenna to cover an entire predefined angular domain of interest (antenna pointing direction).

[0103] In embodiments, the evaluation module 30 can be configured to roughly estimate the direction of arrival 0 of the signal S(t) received by a 1D antenna for example, from the measurement of the phase deviation coefficient A(p) of the received signal, the wavelength values ​​λ of the signal S(t) and the spacing d of the known receivers. According to the equation (04) defining this coefficient, the direction of arrival 0 can be deduced from the following expression (16):

[0104] sjn( gj _ Atp.^.d

[0105] It should be noted that the measurement of the phase deviation coefficient Aç> being defined between and 7', it can induce an ambiguity on the estimation of the direction of arrival 0 of the signal S(t) received. In this case, such a rough estimation can be carried out for an antenna 10 comprising very close receivers (i.e. comprising a maximum spacing of half a wavelength of the signal) or a digitization of the channels at the radiating element in the case of an array antenna.

[0106] [Fig.6] represents the method of evaluating a frequency channel of the received signal S(t), according to embodiments of the invention.

[0107] In step 600, each reception channel 20n receives signals Srn coming from one of the antennas of the set 10 (or from one of the radar antenna receivers) and coming from a signal S(t).

[0108] In step 620, on each reception channel 20n, the received signals Srn are converted into the spectral domain, to form the converted frequency signal Sn to be propagated on the channel 20n.

[0109] In step 640, for each reception channel 20n, for each frequency channel F of a given instantaneous frequency band BF, the correlation values ​​Rn(F) are determined by applying a power correlation between the spectrum of the signal propagated Sn on the channel 20n and an arbitrary reference signal Sref.

[0110] In step 660, for each frequency channel F of the given instantaneous frequency band BF, the values ​​of the sum channel £(F) are determined from the correlation values ​​Rn(F) defined for all of the N reception channels as defined according to the preceding equation (01).

[0111] In step 680, for each frequency channel F of the given instantaneous frequency band BF, the values ​​of the sum channel (F) are compared to a predefined detection threshold value TseM.

[0112] In step 682, if a value of the sum channel £(F) is greater than the detection threshold rsaâl, the associated frequency channel F is then considered “occupied”. Alternatively, in step 684, if a value of the sum channel £(F) is less than the detection threshold, the associated frequency channel F is then considered “free”.

[0113] Step 620 and / or 640 can subsequently be repeated to determine new correlation values ​​Rn(F) according to another given instantaneous frequency band BF to carry out a frequency sweep, on a predetermined RF band for example.

[0114] [Fig.7] represents the method for estimating the direction of arrival of the received signal S(t), according to embodiments of the invention.

[0115] The method may include an initial step 700 of applying the pointing antenna direction (in elevation Oeo and in circular Oco).

[0116] At step 720, for each frequency channel F of the given instantaneous frequency band BF, the values of the offset path (in circular AC(F) and in elevation AE(F)) can be determined from the correlation values Rn(F) of the set of N reception paths as defined for example by the previous equations (08) and (09).

[0117] At step 740, for each frequency channel F of the given instantaneous frequency band BF, the values of the offset path ratio (in circular ratioc(F) and in elevation ratioE(F)) can be determined from the values of the sum path )7 (F) and the values of the offset path (in circular AC(F) and in elevation AE(F) respectively) as defined for example by the previous equations (12) and (13).

[0118] In step 760, for each frequency channel F of the given instantaneous frequency band BF, the values ​​of the ratio of the deviation channel (in circular ratioc(F) and in elevation ratioE(F)) can be compared to a predefined lobe threshold value £Me.

[0119] In step 762, if the absolute values ​​of the ratio of the deviation channel (in circular ratioc(F) and in elevation ratioE(F)) are lower than the lobe threshold si»be, the pointing direction (in elevation 0Eo and in circular Oco) of the antenna can correspond to the direction of arrival of the signal S(t) received, and the values ​​of the refined direction (in elevation 0Et,,liu, and in circular 6cestjm respectively) can be determined from the absolute values ​​of the ratio of the deviation channel and the pointing direction as defined for example according to the preceding equations (14) and (15). Alternatively, in step 764, if at least one of the absolute values ​​of the ratio of the deviation path (in circular ratioc(F) and in elevation ratioE(F)) is greater than the lobe threshold eiobe, the pointing direction of the antenna may not correspond to the direction of arrival of the signal S(t) received.The initial step 700 may subsequently be repeated to apply a new pointing antenna direction.

[0120] Those skilled in the art will easily understand that certain steps of the methods relating to figures 6 and 7 can be carried out simultaneously, sequentially, independently or not, and / or in a different order, for example in an order defined by the radar system 1 or the evaluation module 30.

[0121] The system and methods described above according to the embodiments of the invention or sub-elements of this system can be implemented in various ways by hardware, software, or a combination of hardware and software, in particular in the form of program code which can be distributed in the form of a program product, in various forms. In particular, the methods of Figures 6 and 7 can for example be implemented in a computer system.

[0122] The invention is not limited to the embodiments described above as a non-limiting example. It encompasses all the variant embodiments that may be envisaged by those skilled in the art. In particular, those skilled in the art will understand that the invention is not limited to the different units, or to the different configurations of the reception channels described as a non-limiting example. In particular, certain embodiments of the invention may be combined.

Claims

Claims

1. Radar system (1) for detecting occupied frequency channels, the system comprising N reception channels (20n) and a set (10) of radar antennas associated with each channel, N being an integer greater than or equal to 2, each channel being capable of receiving signals (Srn) respectively by means of the associated radar antenna, characterized in that the radar system (1) comprises, for each reception channel (20n), a conversion unit (22n) in the spectral domain of said received signals (Srn) to form a converted signal (Sn) defined on a given instantaneous frequency band associated with a set of frequency channels (F), and a module (24n) for determining correlation values ​​(Rn(F)) adapted to apply a power correlation between the spectrum of the converted signal (Sn) propagated on said reception channel (20n) and the spectrum of an arbitrary reference signal (Sref) chosen from one of the converted signals propagated on one of said reception channels,the radar system (1) further comprising a module (30) for evaluating occupied frequency channels adapted to determine the values ​​of the sum channel (£ (F)) from the correlation values ​​(Rn(F)) of said N reception channels, the frequency channel (F) being occupied if the value of the associated sum channel Q2 (F)) is greater than a predefined detection threshold value (rseuil).,

2. Radar system (1) according to claim 1, wherein said determination module (24n) is configured to determine a power spectral density of the signal propagated on said reception path (20n) with respect to said arbitrary reference signal (Sref).

3. Radar system (1) according to one of the preceding claims, wherein said determination module (24n) is configured to apply an integration over several successive frames of the signal propagated on said reception channel (20n).

4. Radar system (1) according to one of the preceding claims, wherein the radar system (1) further comprises a calibration device (IC) comprising N calibration channels (40n), and wherein, for each calibration channel (40n), the calibration device (IC) is configured to determine correction coefficient values (Cn(F)) of said converted signal (Sn) to balance in amplitude and phase each of said reception channels (20n) of the radar system (1).

5. Radar system (1) according to one of the preceding claims, wherein said radar system (1) is configured to apply a frequency sweep by repeating the evaluation of the detection of occupied frequency channels with respect to said detection threshold value (rwM7), to cover an entire predefined frequency domain of interest.

6. Radar system (1) according to one of the preceding claims, wherein the radar system (1) is configured to apply a pointing antenna direction (©eo, ^co), and wherein said occupied frequency channel evaluation module (30) is further adapted to determine values ​​of the deviation channel (AC(F), AE(F)) from the correlation values ​​(Rn(F)) of said N reception channels, then values ​​of the ratio of the deviation channel (ratioc(F), ratioH(F)) from said values ​​of the sum channel (£ (F)) and said values ​​of the deviation channel (AC(F), AE(F)), said pointing antenna direction (®eo, ^co) corresponding to the direction of arrival of the received signals (Srn) with respect to the orientation of said antennas of the radar system (1) if said values ​​of the ratio of the deviation channel (ratioc(F), ratio^F)) are lower to a predefined lobe threshold value (siobe).

7. Radar system (1) according to claim 6, wherein said occupied frequency channel evaluation module (30) is further adapted to determine at least one refined direction (Or , ©c . ) of arrival of the received signals with respect to the orientation of said antennas of the radar system (1) from said values ​​of the ratio of the deviation path (ratioc(F), ratioE(F)) and said pointing antenna direction (0E0, Oco).

8. Radar system (1) according to one of claims 6 or 7, wherein said radar system (1) is configured to apply a spatial scan by repeating the evaluation of the direction of arrival of the received signals with respect to said lobe threshold value (e^), to cover an entire predefined angular domain of interest.

9. Radar system (1) according to one of the preceding claims, in which the radar system (1) comprises a configuration operationally in "listening" mode in the radio frequency domain of the "X-band" type.

10. Method for detecting occupied frequency channels, implemented in a radar system (1) comprising N reception channels (20n), N being an integer greater than or equal to 2, the method comprising the reception, at each channel, of signals (Srn), characterized in that said method comprises, for each reception channel (20n) the following steps consisting of: - convert (620), in the spectral domain, the received signals (Srn) to form N converted signals (Sn) each defined on a given instantaneous frequency band associated with a set of frequency channels (F), - determining (640) correlation values ​​(Rn(F)) by applying a power correlation between the spectrum of the converted signal (Sn) propagated on said reception channel (20n) and the spectrum of an arbitrary reference signal (Sref) chosen from one of the converted signals propagated on one of said reception channels, the method further comprising an evaluation of the occupied frequency channels comprising the steps of: - determine (660) the values ​​of the sum channel (£ (F)) from the correlation values ​​(Rn(F)) of said N reception channels, - compare (680) the value of the sum channel (£ (F)) associated with a predefined detection threshold value ^seuiï), and - determining that the frequency channel (F) is occupied (682) if the value of the associated sum channel (£(F)) is greater than said predefined detection threshold value.

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