[0001] [The invention relates to the general field of radio detection and localization systems.

[0002] It relates in particular to the field of the operation of radar equipment, in particular of long-pulse radars with pulse compression and to the implementation, on such radars, of modes of

operation with temporally interlaced emissions.

Conventionally, the emissions from airborne patrol radars and

maritime surveillance are in Horizontal polarization (HH). The particular function of maritime surveillance radars is to explore the areas of space extending under the carrier over a given distance, as illustrated in Figure 1.

[0004] To do this, they use, in a known manner, waveforms of the bi-pulse type, emitted by means of active electronic scanning antennas which allow pointing in two different directions with a switching time. almost instantaneous. Such a hardware configuration makes it possible in particular to cover a vast distance range by taking advantage of the agility in electron beam elevation.

-As part of the emission of waveforms of the bi-pulse type, illustrated in Figure 2, a first beam 1 1 in which is emitted a so-called short pulse (IC), of pulse length LU, with a recurrence period TR1, illuminates an area at a close distance, while a second beam 12, in which is emitted a so-called long pulse (IL), of pulse length LI2, with a recurrence period TR2, illuminates a farther distance zone, contiguous with the near distance zone. All of the two programs 21 and 22,

temporally interlaced makes it possible in a known manner to cover a continuous distance domain devoid of blind zones.

The terms long pulse and short pulse reflect the respective durations of the pulses constituting each pattern emitted. In particular, the duration of the repetition period (PRI) of the short pulse must be greater than the duration of the long pulse, in order to be able to instrument the blind zone which corresponds to the emission time of the long pulse.

[0007] Such an operating mode, however, in a known manner

also, the disadvantage of causing, during the listening period, reception, which follows the emission of a long pulse 22, the appearance of echoes 23 consecutive to the reflection, by objects located in a distant area , of the short pulse 21 which preceded the considered pulse (echoes IC of nth traces).

[0008] These echoes, known as "nth traces", mingle with the echoes from the long pulse 22 and alter their use by causing parasitic signals to appear in the zone considered. These parasites, inherent in two-pulse operation as it is currently designed, must subsequently be detected in order to be eliminated. This role is generally devolved, after reception, to the signal processing means which implement various known algorithms which attempt with more or less success to proceed to the elimination of the nth trace echoes. For this purpose, for example, sweeping methods are used.

To limit the drawbacks brought about by the implementation of an interlaced operating mode, it is also known to associate a different coverage with each of the operating phases, operating phase in close zone using short pulses ( IC) or remote area operation using long pulses (IL).

Thus, for the transmission of a short pulse and the reception of echoes

corresponding (operation in close zone), the antenna of the radar (of the radioelectric detection system) considered is generally pointed at a determined site, in order to limit the reception of ground reverberation echoes which have a high amplitude in the near zone.

On the other hand, for the transmission of a long pulse and the reception of

corresponding echoes (operation in a remote area), the radar antenna (of the radioelectric detection system) considered is generally pointed at a weak site, close to the horizontal, allowing the transmitted radio wave to reach more distant areas .

[0012] As a result, for the remote zone operating mode, the reverberation echoes from the ground can be advantageously ignored because they mainly occur during the emission of the long pulse itself, at a time when the receiver is inactive.

On the other hand, due to the transition to low coverage, the echoes of

reverberation of the short pulse by the ground occurring during the implementation of the far-zone mode of operation, are also received by the receiver.

These echoes are liable to disturb, in particular, the operation of the compression of long pulses on reception, so that part of the compression gain may be lost.

Thus, by implementing the known techniques, the current systems cannot be completely free from the undesirable effects of the use of a temporal interlacing, such as that described above, interlacing necessary to ensure double coverage, in near area and in far area.

An object of the invention is to provide a solution allowing a detection system to adopt a dual operating mode allowing it to cover the near and far areas of its environment by emitting a waveform comprising a pulse short followed by a long pulse, without this operating mode affecting the detection performance expected for coverage of distant areas.

To this end, the invention relates to a radar transmission-reception method implementing a short-range operating mode with transmission of a short pulse and a long-range operating mode with transmission of a modulated long pulse, the short and long pulses transmitted being temporally interlaced, said method being characterized in that the

Short pulses and long pulses are emitted as waves with distinct polarizations.

According to various embodiment, the method according to the invention can have various characteristics, each of which can be considered alone or in combination with other characteristics.

Thus, according to one characteristic of the invention, the polarization of each emitted wave is obtained by emitting simultaneously, by two co-located radiating sources, for each pulse, two signals having a phase shift Q whose value varies according to the short nature or long of the considered pulse.

According to another characteristic, in the case of a short pulse, the two signals emitted have a phase shift Q, the value of which induces a vertical polarization of the emitted wave and in that, for the long pulse, the two signals emitted have a phase shift whose value induces a horizontal polarization of the emitted wave.

According to another characteristic, the backscattered radio signals, consecutive to the emission of a pulse being picked up by each of the radiating sources, a phase shift q ′ of given value is applied to the radio signal received by this same source.

According to another characteristic, the phase shift q 'is equal to the phase shift Q.

The subject of the invention is also a radar transmission-reception device capable of implementing such a method, said device being configured to carry out the following operations:

producing two synchronous radiofrequency (RF) transmission signals, said signals exhibiting between them a phase shift Q of controllable given value, said signals exhibiting the amplitudes are also controllable;

- radiating two radio waves, each corresponding to one of the RF emission signals produced, by means of two radiating sources (two radiating elements), these sources each having a given axis of polarization;

- perform the reception of the backscattered radio signals picked up by each of the radiating sources and

- Deliver two radio frequency (RF) reception signals, each signal corresponding to the backscattered radio signal picked up by one of the radiating sources, to which a given phase shift q 'is applied.

According to various arrangements, each of which can be considered alone or in combination, the device according to the invention can have different

characteristics.

Thus, according to a first characteristic, the device comprises a radiating element and an electronic circuit integrating a first module

d'émission/réception, constitué d'une première voie d'émission et d'une première voie de réception et un second module d'émission/réception, constitué d'une seconde voie d'émission et d'une seconde voie de réception , les deux modules d'émission/réception présentent des structures identiques; chaque module d'émission/réception comportant un commutateur permettant de connecter alternativement la voie d'émission et la voie de réception du module considéré à l'élément rayonnant.

According to another characteristic, the radiating element is formed by a patch antenna, substantially planar, having a regular shape, comprising four connection points arranged two by two symmetrically with respect to the center of the patch, along two perpendicular axes, two connection points symmetrical forming a connection port of the antenna.

According to one embodiment, this radiating element is a square-shaped patch antenna.

According to another characteristic, the first and second modules

transmission / reception are each connected to the radiating element by a pair of supply lines, the connection points arranged symmetrically on the antenna patch are connected to the inputs / outputs of the same transmission-reception module via a switch.

According to another characteristic, the inputs of the first and second transmission channels of the two transmission / reception modules are configured to be driven by the same RF signal delivered by a waveform generator connected to the electronic circuit by an input, the transmission channel of the second transmission / reception module comprising at input a controllable phase shifter circuit, making it possible to introduce between the two transmission channels a given phase shift Q.

According to one embodiment, the electronic circuit comprises a control module configured to autonomously generate the commands of the phase shifters in charge of the phase shift Q, said module mainly comprising a memory and an address generator configured to carry out a circular addressing of the locations of Memory.

According to a first embodiment, the outputs of the first and second reception channels of the transmission / reception modules are summed by means of an adder circuit and then connected to a single receiver by a common output of the electronic circuit, the reception channel. of the second transmission / reception module comprising at its output a controllable phase shifter circuit making it possible to introduce, between the two reception channels, a given phase shift Q equal to the phase shift introduced between the two transmission channels.

According to one characteristic, the electronic circuit comprises controllable phase shifters configured to apply the same phase shift f to the RF signal delivered by the waveform generator and to the signals delivered by the two reception channels.

According to another embodiment, the outputs of the first and second reception channels of the transmission / reception modules are connected, by two outputs of the electronic circuit, to two separate reception channels of a same digital receiver configured to apply between the signals from the two reception channels a phase shift q '.

According to one characteristic, each of the reception channels comprises a controllable phase shifter, each of the phase shifters being configured to apply to the corresponding reception channel a same phase shift cp equal to the phase shift applied to the RF signal delivered by the waveform generator.

A further subject of the invention is a radar surveillance system comprising a waveform generator, an array of patch antennas and a receiver, said system comprising a set of transmission-reception devices according to the invention, the generator waveform and the receiver being connected to each of the patch antennas of the network by means of a transceiver device.

The characteristics and advantages of the invention will be better appreciated thanks to the following description, description which is based on the appended figures.

The accompanying figures illustrate the invention:

[0019] [Fig.1] and [Fig.2], mentioned in the preamble of this description,

present schematic illustrations showing the technical problem to which the invention provides a solution.

[0020] [Fig.3] and [Fig.4] show illustrations, in the form of timing diagrams, of the general principle of operation of the invention.

[0021] [Fig.5] shows a block diagram of the structure of a device

transmission / reception allowing the implementation of the method according to the invention, device disclosed in patent application FR 15 01644, filed

previously by the plaintiff.

[0022] [Fig.6] shows a block diagram of the structure of the device

transmission / reception according to the invention.

[0023] [Fig.7] shows a partial block diagram of the structure of the device

transmission / reception of figure 6 detailing the structure of the

commande de phase et son positionnement dans les voies émission et réception du dispositif.

[0024] [Fig.8] présente un synoptique partiel de la structure du dispositif

d'émission/réception de la figure 6 illustrant une forme alternative de réalisation des voies de réception.

[0025] [Fig.9] présente une illustration sous forme de chronogrammes, d'un mode de mise en oeuvre du dispositif selon l'invention adapté à la détection de la présence de câbles électriques.

[0026] Il est à noter que, sur les figures annexées, un même élément fonctionnel ou structurel porte, de préférence, un même symbole repère.

[0027] Comme cela a été dit précédemment, un des objets de l'invention est de faire face, dans le cadre notamment de systèmes de détection radar fonctionnant en mode bi-pulse pour supprimer les zones aveugles, aux problèmes consécutifs à la présence d'échos de Nièmes traces provenant d'une impulsion courte reçus durant la phase de réception des échos provenant de l'impulsion longue qui suit ladite impulsion courte.

[0028] Pour ce faire le procédé selon l'invention consiste, comme l'illustre les figures 3 et 4, à différentier la polarisation de l'onde électromagnétique émise suivant que l'impulsion émise est une impulsion courte 21 ou une impulsion longue 22. Cette modification de la polarisation est réalisée en émettant simultanément pour chaque impulsion, par deux sources rayonnantes co-localisées, deux signaux présentant un déphasage dont la valeur varie selon que l'impulsion considérée est une impulsion courte ou longue. Par recombinaison dans l'air des ondes rayonnées correspondant aux deux signaux émis, le procédé selon l'invention permet de générer une onde résultante polarisée selon une polarisation donnée qui dépend de la phase relative des signaux rayonnés par les deux sources.

[0029] De manière préférentielle, en fonctionnement courte portée, on exploite une polarisation P1 verticale, de façon à minimiser l'effet des réflexions multiples, grâce à l’incidence de Brewster, et en fonctionnement longue portée, on exploite une polarisation P2 horizontale de façon à créer des franges d’interférence propres à augmenter avantageusement la portée radar.

[0030] La mise en oeuvre du procédé selon l'invention est réalisée en utilisant un dispositif configuré pour réaliser les opérations suivantes:

- Producing two synchronous radiofrequency (RF) transmission signals, exhibiting between them a phase shift of given value, the value of the phase shift being controllable. It is, in this way, possible to program a set of polarizations with a discretized step dependent on the digital phase shift control, a discretization in steps of 3 degrees for example.

- produce two transmission signals whose amplitudes are also controllable;

- radiating two radio waves each corresponding to one of the RF transmission signals, by means of two radiating sources (ie two radiating elements) each having a given axis of polarization;

- Perform the reception of the backscattered radio signals picked up by each of the radiating sources and deliver two radio frequency (RF) reception signals each corresponding to a radio signal; a relative phase shift equal to the phase shift introduced at transmission being applied to the RF reception signals.

According to the invention, this device is configured to receive an RF signal

corresponding to the waveform to be transmitted, this signal being for example synthesized by the waveform generator of the radar, and to deliver, to the two radiating sources, two RF transmission signals produced from the received RF signal, said RF transmission signals being phase shifted with respect to each other by a given phase shift.

This device is also configured to transmit to the radar receiver the RF reception signals corresponding to the radio signals picked up.

Figure 5 illustrates the basic structure of an embodiment of a

transmission / reception device capable of implementing the method according to the invention. This basic structure, further described in detail in French patent application FR 15 01644 filed on 07/31/2015 by the applicant, is recalled here so as to allow the clear presentation of the specific elements introduced into this structure in the within the scope of the present invention.

This basic structure, illustrated in Figure 5, comprises a radiating element 52 and an electronic circuit 51, integrating a first transmission / reception module, consisting of a transmission channel 54 and a transmission channel reception 56 and a second transmission / reception module consisting of a transmission channel 55 and a reception channel 57. The two modules

transmission / reception have identical structures.

Each transmission / reception module comprises a switch 515 or 516 respectively, making it possible to alternately connect the transmission channel and the reception channel of the module in question to the radiating element 52.

Furthermore the inputs of the transmission channels 54 and 55 of the two modules

transmission / reception are configured to be driven by the same RF signal 534 delivered by the waveform generator of the radar 531 connected to the electronic circuit 51 by an input 53. However, the transmission channel 55 of the second module d 'transmission / reception comprises, at input, a controllable phase shifter circuit 512, making it possible to introduce between the two transmission channels a given phase shift Q.

Similarly, the two reception channels 56 and 57 are summed by means of a summing circuit 514 to form a common reception channel 58 connected to the radar receiver 532 delivering to the radar receiver 532, an RF reception signal 535 corresponding to the sum of the radio signals delivered by the radiating element 52. The reception channel 57 of the second transmission / reception module however comprises at its output, before summation, a controllable phase shifter circuit 513 making it possible to introduce between the two channels reception a given phase shift Q equal to the phase shift introduced between the two transmission channels.

The first and second transmission / reception modules mainly have the function of transforming the signal transmitted by the waveform generator of the radar, into radio frequency signals, or RF transmission signals, intended to be transmitted under differential form to the radiating element 52, respectively via the inputs / outputs 521 -522 of the electronic circuit for the first module and the inputs / outputs 523-524 for the second module.

The radiating element 52, shown schematically in Figure 5, consists of a substantially planar "patch" antenna, having a regular shape, a square shape for example and having four connection points (ports) arranged in pairs symmetrically relative to the center of the patch, along two perpendicular axes, each group of two symmetrical connection points forming a connection port of the antenna. As detailed in the patent application cited above, such an antenna makes it possible to radiate

an excitation RF signal along two distinct perpendicular polarization axes.

As illustrated in Figure 5, the first and second modules

transmission / reception are each connected to the radiating element 52 by a pair of supply lines, 525 and 526 respectively. The symmetrically arranged ports are connected to the inputs / outputs of the same transmit / receive module via a switch 515 or 516.

The electronic circuit 51 also includes control inputs allowing a control module 533, the computer responsible for managing the transmission and reception within the radar equipment for example, to control it by applying on these entries the appropriate commands. The electronic circuit 51 thus comprises:

- une entrée 517 dédiée à la commande d'un circuit déphaseur commandable 59, configuré pour appliquer un déphasage f au signal délivré par le générateur de forme d'onde 531 avant son application aux voies d'émission 54 et 55 des deux modules d'émission/réception, et à la commande d'un circuit déphaseur commandable 51 1 , configuré pour appliquer ce même déphasage f aux signaux de réception RF issus des voies de réception 56 et 57 de ces mêmes modules;

- une entrée 518 dédiée à la commande d'un circuit déphaseur commandable 512, configuré pour appliquer au niveau de la voie d'émission 55 du second module d'émission/réception, un déphasage Q donné au signal délivré par le générateur de forme d'onde 531 ; et à la commande d'un circuit déphaseur commandable 513, configuré pour appliquer ce même déphasage Q aux signaux de réception RF issus de la voie de réception 57 de ce même module;

- une entrée 519 dédiée à la commande des circuits de commutation 515 et 516 qui permet de placer alternativement les entrées/sorties 521 -524 des commutateurs 515 et 516 du circuit électronique 51 en entrée ou en sortie.

[0042] D'un point de vue fonctionnel, la mise en oeuvre des déphaseurs

commandables 59 et 51 1 permet d'appliquer un même déphasage f aux signaux délivrés à l'élément rayonnant 52 par les deux modules d'émission/réception ainsi qu'aux signaux de réception RF correspondant au signaux radioélectriques

captés par l'élément rayonnant 52. Cette fonctionnalité permet avantageusement de réaliser une antenne multisources en associant en réseau les éléments rayonnants 52 d'une pluralité de dispositifs tels que celui représenté sur la figure 5, chaque dispositif étant affecté d'un déphasage f fonction de la direction pointée par l'antenne.

[0043] Dans une telle structure, chaque dispositif reçoit le signal produit par un

même générateur de signaux et applique audit signal un déphasage f fonction de la position du dispositif dans le réseau avant de transmettre celui-ci, sous forme différentielle à l'élément rayonnant 52.

[0044] Inversement chaque dispositif reçoit les signaux délivrés sous forme

différentielle par l'élément rayonnant 52 et le transforme en signal RF non différentiel et applique à ce dernier un déphasage cp fonction de la position du dispositif dans le réseau avant de transmettre celui-ci au récepteur.

[0045] Par ailleurs, la mise en oeuvre des déphaseurs commandables 512 et 513 permet avantageusement d'appliquer un déphasage complémentaire Q sur les voies d'émission 55 et de réception 56 du second module d'émission/réception, de sorte que les signaux délivrés par le circuit électronique 51 sur les lignes 525 et 526 d'alimentation de l'élément rayonnant 52, de même que les signaux de réception RF correspondant aux signaux radioélectriques délivrés par l'élément rayonnant 52, présentent entre eux un déphasage de valeur donnée Q.

[0046] Comme cela est détaillé dans la demande française mentionnée

précédemment, la mise en oeuvre des déphaseurs commandables 512 et 513 permet ainsi avantageusement de rayonner deux signaux radioélectriques dont la recombinaison dans l'espace produit un signal présentant une polarisation dont la nature est fonction de la valeur du déphasage complémentaire Q appliqué au signal d'émission RF délivré par le second module d'émission réception.

[0047] Inversement cette mise en oeuvre permet, en réception, de ne prendre en compte que les signaux de réception RF correspondant aux signaux

radioélectriques reçus présentant une polarité donnée déterminée par le déphasage Q.

[0048] Comme cela a été dit précédemment, les commandes de déphasage appliquées aux différents déphaseurs sont en principe délivrées au dispositif d'émission réception par un module de contrôle 533 intégré fonctionnellement sinon physiquement au système de gestion des émissions/réceptions de l'équipement radar auquel le dispositif est intégré. Ces commandes sont transmises aux déphaseurs par un bus de commande la valeur de la commande de déphasage étant maintenue constante entre deux changements de valeur.

[0049] Or, concernant notamment les déphaseurs 512 et 513 qui assurent le

relative phase shift Q between the transmission channels 54 and 55 and between the reception channels 56 and 57, the time lapse between two changes of the load value may prove to be short and the rate of these changes high, so that the control which conveys these values ​​can present a sustained electrical activity during the reception phases of the radio signals backscattered by the environment, and cause the appearance of parasitic signals on the reception channels. This can also be the case for the phase shifters 59 and 51 1.

Consequently, the basic structure presented in FIG. 5, in which the commands of the phase shifters, the phase shifters 512 and 513 in particular, are delivered directly by the control module 533, appears more suited to systems in which the rate changes in the value of the phase shift commands remain low and / or in which these changes may take place outside the reception phases of the backscattered echoes.

In the context of the method according to the invention, the value of the phase shift Q is caused to vary, as a minimum, at the rate of the alternation of the short and long range treatments. Consequently, the value of the phase shift command Q applied to the phase shifters 512 and 513 is likely to change frequently, this variation causing frequent data exchanges on the control bus via which the control module 533 controls each of the phase shifters 512 and 513.

This is why, in the context of the invention, an adaptation

functional structure of the device described in the French application cited above and illustrated in Figure 5.

This functional adaptation, illustrated by Figures 6 and 7, consists in controlling the phase shifters 512 and 513 via a control module 62 mainly comprising a memory 621 and an address generator 622. This results in a transmission-reception device 61 capable of directly managing the phase change sequences required by the desired operating mode (bi-pulse mode), without transit of digital data between the control module 533 and the device 61 during the operating phases in reception of the latter.

According to the invention, the address generator 622 is configured so as to

perform, periodically, a circular addressing of the memory 621, each memory location 623 being addressed successively.

Advantageously, the address generator 612 used can be programmed according to the operating mode considered, to perform a cyclic reading of the memory locations in a constant order in increasing or decreasing order of addresses or in a variable order, alternately in order of. addresses ascending then descending.

From a functional point of view, the memory 621 can be of different types.

It can consist of a preprogrammed memory containing different phase shift control values ​​intended to be transmitted in sequence to phase shifters 512 and 513.

Alternatively, it can consist of a reprogrammable memory, the content of which is for example loaded by the controller 533. The memory 621 is then provided with a control input RA N 63 allowing the controller 533 to access it in writing.

The arrangement of the data inside the memory 621 is also

realized in such a way that it is possible, by carrying out a circular addressing, to reproduce a given sequence of phase shift command values ​​which induces a periodic variation of the phase shift Q applied to the transmission 55 and reception 57 channels.

Also from a functional point of view, the size of the memory 621 is

determined according to the number of distinct values ​​that the orders of

phase shift can take, as well as the length of time a given command must be held.

Thus, if, as illustrated in FIG. 7, the address generator 622 is clocked by a constant clock H, a given phase control can be written into several successive memory locations, the number

of locations being a function of the ratio of the duration during which the command must be applied to the duration of the period H, the period of the clock H being appropriately defined.

The implementation of a memory 621 and of a loop addressing (circular addressing), thus makes it possible to make changes in the value of the

phase control applied to phase shifters 512 and 513, at a rate that is both variable and rapid, without having, during operation, to circulate fluctuating digital data in the vicinity of the reception channels 56 and 57 of the device. This advantageously avoids the generation of interference likely to alter the reception of the signals.

In the operating configuration illustrated by the timing diagrams of Figures 3 and 4, the memory 621 could for example be programmed to vary the phase control Q applied to the phase shifters 512 and 513, at the rate of the alternation of successive emissions short pulses 21 and long pulses 22.

Likewise, in the operating configuration illustrated by

timing diagram of FIG. 8, the memory 621 could for example be

programmée pour faire varier la commande de phase Q appliquée aux

déphaseurs 512 et 513, au rythme des émissions successives des impulsions courtes 21 et des impulsions longues 22 et, pour une impulsion longue 22, au rythme de la variation de phase appliqué au signaux d'émission RF constituant l'impulsion longue; les signaux d'émission RF constituant l'impulsion longue étant par exemple affectés d'un déphasage relatif Q prenant, par alternance, une valeur choisie dans un ensemble de valeurs, de façon à constituer un signal

radioélectrique dont la polarisation varie pendant la durée d'émission de l'impulsion longue.

[0063] La figure 9 présente de manière schématique une forme alternative, une variante, de réalisation du dispositif d'émission-réception 61 , illustré par les figures 6 et 7.

[0064] Selon cette variante, plus particulièrement adaptée à un dispositif d'émission- réception associé à un récepteur radar numérique 93, les deux voies de

réception 56 et 57 du dispositif selon l'invention ne sont pas recombinées et les signaux de réception RF 96 et 97 issus des signaux radioélectriques captés par l'élément rayonnant 52 sont transmis par deux canaux distincts 94 et 95 au récepteur 93, ce dernier étant configuré pour réaliser un traitement séparé des deux voies.

[0065] Dans cette variante de mise en oeuvre, la commande de déphasage f est appliquée sur les deux voies séparément au moyen de deux déphaseurs 91 et 92. L'application d'un déphasage entre les deux voies de réception est, dans ce cas, déportée au niveau du récepteur 93 et traité numériquement.

This variant implementation advantageously makes it possible to apply

digitally between the signals corresponding to each of the reception channels 56 and 57, a phase shift q 'which can take different values, depending on the direction of polarization in which it is desired to analyze the received signals; q 'may be identical to or different from Q.

It is thus possible, at the level of each transceiver module 61, to analyze the backscattered signal picked up by the radiating element 52 simultaneously in different polarization directions, by playing at the reception level, on the relative phase applied signals received as well as the relative amplitude of the latter.

This variant implementation also allows, advantageously, in the context of a multisource antenna consisting of a plurality of transmission-reception devices 61 forming a network of radiating sources, to analyze the received signal. by the global multisource antenna simultaneously in different polarization directions. To do this, it suffices to perform the separate summations of all the first reception channels of the different devices on the one hand and of all the second reception channels of the different devices on the other hand, and to apply processing to the resulting signals. in phase identical to that described above.

This variant implementation also advantageously makes it possible to vary the polarization of the pulse in steps or linearly in order to seek the most favorable polarization for the detection of cables in airborne systems, in particular helicopters; the scanning of all the polarizations making it possible to find the optimum polarization for the cable, it being understood that all the polarizations are digitally calculated on reception. Thus, since the reflection of the signals on the cables depends on the

geometry of the cables (section and direction of the strand), the possibility of being able to use all the polarizations by scanning at the emission will make it possible to benefit from an improved detection capacity compared to that offered by the known solutions that can be envisaged in 'species, solutions which only allow switching polarization changes, at best from pulse to pulse.

This method also makes it possible to benefit from the two polarizations

simultaneously, which is particularly useful when one seeks to carry out a "Spot SA R" for which it is necessary to have all the power of the radar to focus the signal, so that it is not possible to separate the antenna in two, one part for the reception in H, another for the reception in V. The proposed method makes it possible to have the two simultaneous polarizations in reception without reduction of gain or widening of the beam of the antenna.

The search by scanning for the optimal polarizations for a given application, in other words for the polarizations making it possible to benefit from an improved detection capacity compared to that offered by the known solutions that can be envisaged in this case, can in particular be carried out by using a heuristic-type determination process.

Such a process consists, firstly, in transmitting pulses assigned with randomly determined polarities and then, secondly, in carrying out an evaluation of the quality of the reception for the choice of current polarizations. This choice is evaluated, depending on the distance and the type of target, by measuring the false alarm rate and the probability of detection. If the selected criteria are not optimally satisfied, a new printing is carried out giving rise to new polarization values. The polarizations giving the best results can then be, moreover, stored in order to be able to be reused according to the context considered.

Thus, a set of polarizations deemed optimal for a given distance, type of target and type of clutter (ie clutter) can advantageously be stored in a database. A stored set of polarizations can subsequently be applied as is in similar circumstances or be used as the starting point for a refining process implementing partial and random polarization changes making it possible to optimize the quality in real time. reception obtained, the refinement of the stored data making it possible to enrich and improve the database.

The choice of polarization thus made also makes it possible to improve the

contrast between targets and clutter (ie clutter).

WE CLAIMS

[Claim 1] [Radar transmission-reception method implementing a short-range operating mode with transmission of a short pulse and a long-range operating mode with transmission of a modulated long pulse, the short and long pulses transmitted being

temporally interlaced, characterized in that the short pulses and the long pulses are emitted in the form of waves having distinct polarizations, the polarization of each emitted wave being obtained by emitting simultaneously, by two co-located radiating sources, for each pulse, two signals exhibiting a phase shift Q, the value of which varies according to the short or long nature of the pulse considered.

[Claim 2] Method according to claim 1, characterized in that, for the short pulse, the two signals transmitted have a phase shift Q, the value of which induces a vertical polarization of the transmitted wave and in that, for the long pulse, the two signals emitted have a phase shift, the value of which induces a horizontal polarization of the emitted wave.

[Claim 3] A method according to any one of claims 1 or 2, characterized in that the backscattered radio signals

consecutive to the emission of a pulse being picked up by each of the radiating sources, a phase shift q 'of given value is applied to the radio signal received by this same source.

[Claim 4] A method according to claim 5, characterized in that the phase shift q 'is equal to the phase shift Q.

[Claim 5] Radar transceiver device, capable of implementing the method according to any one of claims 1 to 4,

characterized in that it is configured to perform the following operations:

producing two synchronous radiofrequency (RF) transmission signals, said signals exhibiting between them a phase shift Q of controllable given value, said signals exhibiting the amplitudes are also controllable;

- radiating two radio waves, each corresponding to one of the RF emission signals produced, by means of two radiating sources each having a given axis of polarization;

- perform the reception of the backscattered radio signals picked up by each of the radiating sources and

- Deliver two radio frequency (RF) reception signals, each signal corresponding to the backscattered radio signal picked up by one of the radiating sources, to which a given phase shift q 'is applied.

[Claim 6] Device according to claim 5, characterized in that it comprises a radiating element (52) and an electronic circuit (51, 61) incorporating a first transmission / reception module, consisting of a first channel of transmission (54) and a first reception channel (56) and a second transmission / reception module, consisting of a second transmission channel (55) and a second reception channel (57), the two transmission / reception modules have an identical structure; each transmission / reception module comprising a switch (515, 516), making it possible to connect

alternatively the transmission channel and the reception channel of the module considered at the radiating element (52).

[Claim 7] Device according to one of claims 5 or 6,

characterized in that the radiating element (52) is formed by a patch antenna, substantially planar, having a regular shape, comprising four connection points arranged two by two symmetrically with respect to the center of the patch, along two perpendicular axes, two points of

balanced connections forming an antenna connection port.

[Claim 8] Device according to claim 7, characterized in that the radiating element (52) is a square-shaped patch antenna.

[Claim 9] Device according to one of claims 7 or 8,

characterized in that the first and second transmit / receive modules are each connected to the radiating element (52) by a pair of supply lines (525, 526), ​​the connection points arranged symmetrically on the patch of antenna (52) are connected to the inputs / outputs of the same transmission / reception module via a switch (515, 516).

[Claim 10] Device according to any one of claims 5 to

9, characterized in that the inputs of the first and second channels

transmission (54, 55) of the two transmission / reception modules are configured to be driven by the same RF signal delivered by a waveform generator (531) connected to the electronic circuit (51) by an input (53 ), the transmission channel (55) of the second transmission / reception module comprising at input a controllable phase shifter circuit (512), making it possible to introduce between the two transmission channels a given phase shift Q.

[Claim 1 1] Device according to any one of claims 5 to

10, characterized in that the outputs of the first and second reception channels (56, 57) of the transmission / reception modules are summed by means of an adder circuit (514) then connected to the same receiver (532) by a common output (58) of the electronic circuit (51), the reception channel (57) of the second transmission / reception module comprising at its output a controllable phase-shifter circuit (513) making it possible to introduce, between the two reception channels, a given phase shift Q equal to the phase shift introduced between the two transmission channels (54, 55).

[Claim 12] Device according to one of claims 5 to 1 1,

characterized in that the electronic circuit (61) comprises a control module (62) configured to autonomously generate the

controls the phase shifters (512, 513) in charge of the Q phase shift, said module mainly comprising a memory (621) and an address generator (622) configured to carry out a circular addressing of the locations (623) of the memory.

[Claim 13] Device according to one of claims 1 1 or 12,

characterized in that the electronic circuit (51) comprises controllable phase shifters (59, 511) configured to apply a same phase shift f to the RF signal (534) delivered by the waveform generator (531) and to the signals delivered by the two reception channels (56, 57).

[Claim 14] Device according to any one of claims 5 to 10, characterized in that the outputs of the first and second reception channels (56, 57) of the transmission / reception modules are connected by two outputs (96, 97) of the electronic circuit (51, 61), with two distinct reception channels of the same digital receiver (93) configured to apply a phase shift q 'between the signals from the two reception channels.

[Claim 15] Device according to claim 14, characterized in that each of the reception channels (56, 57) comprises a phase shifter

controllable (91, 92), each of the phase shifters being configured to apply to the corresponding reception channel a same phase shift f equal to the phase shift applied to the RF signal (534) delivered by the waveform generator (531).

[Claim 16] Radar surveillance system comprising a waveform generator (531), an array of patch antennas (52) and a receiver (532), characterized in that it comprises a set of transmitting devices - reception according to any one of claims 6 to 16, the waveform generator (531) and the receiver (532) being connected to each of the patch antennas (52) of the network by means of a device for 'transmission-reception j