Radar system and method for detecting occupied frequency channels

Abstract

A radar system (1) for detecting occupied frequency channels is proposed, comprising N receiving channels (20n) capable of receiving each of the signals (Srn). For each channel (20n), the system includes a conversion unit (22n) in the spectral domain of said received signals (Srn) to form a converted signal (Sn) on an instantaneous frequency band associated with frequency channels (F), a correlation value determination module (24n) (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 sum channel values ​​from the correlation values ​​(Rn(F)). The frequency channel (F) is considered occupied if the value of the associated sum channel is greater than a predefined detection threshold value. [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 affected when used in a dense electromagnetic environment, that is, one 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 use of frequency channels in transmission and / or reception by selecting 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 Anglo-Saxon acronym, or ESM for Electronic Support Measures according to the corresponding Anglo-Saxon acronym) which allow the detection and localization of electromagnetic signals in a very wide range of frequencies.

[0004] However, such systems present significant implementation complexity and high manufacturing costs. They also present significant constraints in terms of installation on a larger system, such as an airborne vehicle. In particular, existing systems are bulky, heavy, and have restrictive specifications regarding the specific installation areas on a carrier such as an airplane or helicopter.

[0005] In addition, such systems installed on an airborne vehicle show 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 therefore a need for an improved system and method for detecting busy frequency channels. Summary of the invention

[0007] To this end, a radar system for detecting occupied frequency channels is proposed, the system comprising N receiving 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 capable of receiving signals respectively by means of the associated radar antenna. The radar system comprises, for each receiving 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 correlation value determination module adapted to apply a power correlation between the spectrum of the converted signal propagated on the receiving channel and the spectrum of an arbitrary reference signal chosen from one of the converted signals propagated on one of the receiving channels. The radar system further comprises an occupied frequency channel evaluation module adapted to determine the sum channel values ​​from the correlation values ​​of the N receiving 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 receiving channel relative to the arbitrary reference signal.

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

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

[0011] The radar system can be configured to apply a frequency scan by repeating the evaluation of the detection of occupied frequency channels against the detection threshold value, to cover an entire frequency range of predefined interest.

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

[0013] The busy frequency channel evaluation module can further be adapted to determine at least one refined direction of arrival of the received signals relative 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 can 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 include an operationally “listening” configuration in the “X-band” type radio frequency domain.

[0016] A method for detecting frequency channels is further proposed, implemented in a radar system comprising N receiving channels, where N is an integer greater than or equal to 2. The method comprises receiving signals at each channel. For each receiving channel, the method comprises the following steps:

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

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

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

[0020] - determine the values ​​of the sum path 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 for detecting and evaluating busy frequency channels according to a satisfactory estimation of the direction of arrival of a detected signal.

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

[0025] Other features, details and advantages of the invention will become apparent from the description made with reference to the accompanying drawings given by way of example.

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

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

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

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

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

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

[0032] [Fig.7] The [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 reference numerals are used in the figures to designate identical or analogous elements. For clarity, the elements shown are not to scale. Detailed description

[0034] Fig. 1 schematically represents a radar system for detecting occupied frequency channels 1 comprising an array 10 of N radar electromagnetic antennas (or an array 10 of N receivers of a radar electromagnetic antenna) each associated with a receiving 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 receiving channels 20n, each channel being capable of receiving one or more received signals (i.e. received time signals), denoted Srn, coming from (i.e. by means of) one of the radar antennas of the assembly 10. The index 'n', associated with the receiving 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 detecting and locating electromagnetic emissions in a dense electromagnetic environment.

[0037] Advantageously, the radar system 1 can be a multi-antenna (or multi-channel) system configured in "listening" mode, that is, according to an operational configuration that exploits signals from the antennas (or antenna) capturing the external environment and from the various receiving 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 range of such a system can include a very wide range of frequencies, and be located in the radio frequency (RF) range corresponding, for example and without limitation, to an RF band of type "X band" typically between 8 GHz and 12 GHz, to an RF band of type "K band" typically between 12 GHz and 18 GHz, to an RF band of type "K band" typically between 18 GHz and 26 GHz, or even to an RF band of type "Ka 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.1], each receiving 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 pass-through), in the spectral domain (i.e., the frequency domain), of the received signal(s) Srn to form a signal called the 'converted signal' and denoted Sn, to be propagated on the receiving 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 such as 'X-band', can be equal to 256 MHz, and comprise 256 associated frequency channels F, each frequency channel F being defined at 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 spectral analysis, defined in particular by applying a discrete Fourier transform to 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 Anglo-Saxon acronym).

[0042] The measurement module 24n (also called the 'determination module' or 'calculation module') is configured to perform operations in the spectral domain, to determine the power correlation, denoted Rn, between the spectrum of the converted signal Sn propagated on the receiving 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 receiving 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 receiving channel denoted 20i. Each of the converted signals from another receiving channel can alternatively be used as the arbitrary reference signal Sref.

[0044] In some embodiments, the input signal of the measuring unit 24n can be the converted signal Sn propagated on the receiving channel 20n, as shown in [Fig.2](a).

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

[0046] The busy frequency channel evaluation module 30 of the radar system 1 is configured to determine (or reconstruct) the sum channel y of the N receive channels. In particular, the busy frequency channel evaluation module 30 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 receive channels, as defined according to the following equation (01):

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

[0048] Module 30 is further configured to evaluate (i.e., detect or determine) whether a specific frequency channel F is occupied by comparing the value of the associated sum channel y(F) to a predefined detection threshold Tthreshold. The frequency channel F can then be considered "occupied" (or "polluted") if the value of the sum channel y(F) is greater than the detection threshold Tthreshold. Alternatively, the specific frequency channel F can be considered "free" if the value of the sum channel y(F) is less than the detection threshold Tthreshold. For example, and without limitation, depending on the value of the predefined detection threshold Tthreshold, if the value of the sum channel y(F) is strictly greater than (or alternatively greater than or equal to) the detection threshold.Then the frequency channel F can be considered "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 "free".

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057] Advantageously, module 30 is configured to apply this occupancy assessment of all 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 system 1 is characterized by a direction of arrival 0 (or DOA for Direction of Arrival according to the corresponding Anglo-Saxon acronym, also called 'direction of origin') defined with respect to the orientation of the antenna, that is to say of the plane of the receivers of the set 10, as schematized on the [Fig.1]. For example, in the case of a one-dimensional (1D) antenna composed of receivers spaced a distance d apart, 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 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 and k-th receptors considered, and therefore the associated reception pathways, 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 difference coefficient equal to the following equation (04): A(p = ^.(18^( 9) The signal received by radar system 1, after demodulation and 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 An values ​​correspond to the level of the received signal S(t). multiplied by the antenna gain, denoted 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 the 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 arbitrary reference signal chosen (i.e., for example, the single reference channel 20i), up to a multiplicative constant, according to the amplitude An and the phase difference 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 direction of elevation and circular pointing can correspond to the direction of arrival of the received signal S(t); and if the absolute value of the circular deviation channel ratio ]ratioc(f) and / or the absolute value of the elevation deviation channel ratio ]ratio^F) is greater than or equal to (or alternatively strictly greater than) the lobe threshold ^obe, then the direction of elevation and circular pointing can correspond to the direction of arrival of the received signal S(t). In the case where the absolute values ​​of the channel ratio (circular deviation Iratio(F)) and elevation ratio Iratio(F)) are less than the lobe threshold (lobe threshold), i.e., the elevation and circular pointing direction (E0, E0) of antenna 10 corresponds to the arrival direction of the received signal S(t), the module 30 can be adapted to evaluate (i.e., estimate or determine) a refined elevation and circular direction (E0, E0) of arrival of the received signal S(t). Such a refined direction can be estimated from the value of the channel ratio (circular deviation ratio(F), the value of the channel ratio (elevation deviation ratio(F), and the elevation and circular pointing direction (E0, E0) of antenna 10. Thus, in some embodiments, the evaluation module 30 can be adapted to determine the value of the elevation-refined 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 refined circular direction 0c ... as a function of the value of the refined direction in state 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 the estimation of the direction of arrival of the received signal S(t) for a plurality of instantaneous LF frequency bands, in particular for several radar carrier frequencies within its agility band. This allows the radar system 1 to perform a frequency scan for signal detection by the antenna to cover an entire predefined frequency range of interest (for example, an entire frequency range associated with the RF band of the "X-band" type).

[0102] When estimating the arrival direction of the signal S(t) received by the antenna of system 1, if the elevation and circular pointing direction (0eo, ©co) of the antenna 10 does not correspond to this arrival direction, for example, the radar system 1 can be configured to apply a new antenna elevation and circular pointing direction before acquiring a new signal S(t) with the antenna and then performing another estimation of the signal's arrival direction. This allows the radar system 1 to perform a spatial scan of the signal detected by the antenna to cover a predefined angular domain of interest (antenna pointing direction).

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

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

[0105] It should be noted that since the phase deviation coefficient Ac is defined between θ and θ', it can introduce ambiguity in the estimation of the arrival direction θ of the received signal S(t). In this case, such a rough estimate can be made for an antenna 10 comprising very close receivers (i.e., comprising a maximum spacing of half a wavelength of the signal) or a channel digitization at the radiating element in the case of an array antenna.

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

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

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

[0109] At step 640, for each receiving 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 propagated signal Sn on the channel 20n and an arbitrary reference signal Sref.

[0110] At 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 the set of N receiving channels as defined according to the preceding equation (01).

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

[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 perform a frequency sweep, on a predetermined RF band for example.

[0114] Figure 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 consisting 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 deviation channel (in circular AC(F) and in elevation AE(F)) can be determined from the correlation values ​​Rn(F) of the set of N receiving channels as defined for example according to the preceding equations (08) and (09).

[0117] In step 740, for each frequency channel F of the given instantaneous frequency band BF, the values ​​of the channel gap ratio (circular ratio c(F) and elevation ratio E(F)) can be determined from the values ​​of the sum channel )7 (F) and the track deviation values ​​(in circular AC(F) and in elevation AE(F) respectively) as defined for example according to the preceding equations (12) and (13).

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

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

[0120] A person skilled in the art will readily understand that certain steps of the processes 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 embodiments of the invention or sub-elements thereof, can be implemented in various ways by hardware, software, or a combination of hardware and software, in particular in the form of program code that can be distributed as 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 by way of non-limiting example. It encompasses all possible embodiments that can be envisioned by a person skilled in the art. In particular, a person skilled in the art will understand that the invention is not limited to the different units or configurations of the receiving channels described by way of non-limiting example. In particular, certain embodiments of the invention can be combined.

Claims

Demands

1. A radar system (1) for detecting occupied frequency channels, the system comprising N receiving 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 receiving 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 correlation value determination module (24n) (Rn(F)) adapted to apply a power correlation between the spectrum of the converted signal (Sn) propagated on said receiving channel (20n) and the spectrum of an arbitrary reference signal (Sref) chosen from one of the converted signals propagated on one of said receiving channels,the radar system (1) further comprising a module (30) for evaluating busy frequency channels adapted to determine the sum channel values ​​(£ (F)) from the correlation values ​​(Rn(F)) of said N receiving channels, the frequency channel (F) being busy 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 receiving channel (20n) with respect to said arbitrary reference signal (Sref).

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

4. Radar system (1) according to any 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 receiving channels (20n) of the radar system (1).

5. Radar system (1) according to any one of the preceding claims, wherein said radar system (1) is configured to apply a frequency scan by repeating the evaluation of the detection of busy frequency channels against said detection threshold value (rwM7), to cover an entire frequency range of predefined interest.

6. A radar system (1) according to any one of the preceding claims, wherein the radar system (1) is configured to apply a pointing antenna direction (Δεθ, Δεθ), and wherein said busy frequency channel evaluation module (30) is further adapted to determine channel gap values ​​(AC(F), AE(F)) from the correlation values ​​(Rn(F)) of said N receive channels, and then channel gap ratio values ​​(ratioc(F), ratioH(F)) from said sum channel values ​​(Σ(F)) and said channel gap values ​​(AC(F), AE(F)), said pointing antenna direction (Δεθ, Δεθ) corresponding to the direction of arrival of the received signals (Srn) relative to the orientation of said antennas of the radar system (1) if said channel gap ratio values ​​(ratioc(F), ratio^F)) are less than a value predefined threshold lobe (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 fine-tuned direction (Or, ©c.) of arrival of the received signals relative to the orientation of said antennas of the radar system (1) from said values ​​of the channel deviation ratio (ratioc(F), ratioE(F)) and said pointing antenna direction (0E0, Oco).

8. Radar system (1) according to any 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 angular domain of predefined interest.

9. Radar system (1) according to any one of the preceding claims, wherein the radar system (1) comprises an operationally “listening” configuration in the “X-band” type radio frequency range.

10. A method for detecting occupied frequency channels, implemented in a radar system (1) comprising N receiving channels (20n), where N is 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 receiving channel (20n), the following steps: - 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), - determine (640) correlation values ​​(Rn(F)) by applying a power correlation between the spectrum of the converted signal (Sn) propagated on said receiving channel (20n) and the spectrum of an arbitrary reference signal (Sref) chosen from one of the converted signals propagated on one of said receiving channels, the process further includes an evaluation of 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 receiving channels, - compare (680) the value of the sum channel (£ (F)) associated with a predefined detection threshold value ^seuiï), and - determine 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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