Method for detecting conflicts between the II / SI identification code of a Mode S radar and a nearby radar, and secondary radar implementing the method

Abstract

The present invention relates to a method for detecting a conflict in the II / SI identification code of a radar in the vicinity of a secondary S-mode radar, characterized in that the method comprises at least: a first step (31), in which the radar detects an unsolicited asynchronous reply, i.e., a fruit, in an area of ​​extended radar coverage; a second step (32), in which the radar detects a conflict in the II / SI code by analyzing a geographical area of ​​radar coverage shared by the radar and at least one nearby radar, a conflict being detected if the radar: detects the presence of a fruit of which the nearby radar is the source in the area of ​​the extended coverage; observes the absence of a fruit caused by the nearby radar in that area of ​​the radar coverage of the radar, which area of ​​the radar coverage of the radar does not overlap with an area of ​​the radar coverage of the nearby radar; the overlapping area between the radar coverage of the radar and the radar coverage of the nearby radar forming a conflict area in the II / SI code.

Description

Technical Field

[0001] The present invention relates to the field of air traffic control (ATC) where radar performance, most particularly with respect to detection of aircraft in Mode S, is extremely important, with an expected success rate of approximately 99%. Background Art

[0002] Air traffic control is primarily based on Mode S radars, which are widely recognized for their detection and decoding reliability. The performance achieved by Mode S radars is particularly related to the fact that they are identified by aircraft using their II / SI codes (II stands for Interrogator Identifier). To limit electromagnetic interference and thus increase the reliability of radar transactions, Mode S radars lock onto the II / SI identities of the targets they manage within their coverage and area of ​​responsibility, preventing these targets from responding to non-selective Mode S interrogations.

[0003] The following is a specific technical problem to be solved. In the case of overlapping coverage areas of nearby radars, the radars must have different I / S / I identities. In the opposite case, where two nearby radars share the same I / S / I code, each radar cannot see a target that has been locked onto by the other radar, resulting in a serious safety failure.

[0004] Various methods have been proposed in the prior art to detect the presence of aircraft within radar coverage that are not responding to all-call interrogations from a nearby radar using the same I / I code. The first solution is disclosed in GB201000946. By design, this solution only works for aircraft equipped with ADS-B Out. It requires the radar to be equipped with or associated with a local ADS-B_in receiver for communication.

[0005] Another solution is proposed in document GB201316553. It involves detecting conflicts in the Il / Sl codes between nearby interrogators by comparing the inbound and outbound detection ranges of the radars. Specifically, outbound aircraft leaving the coverage area of ​​radar A are managed in a selective manner, and thus until the limits of radar A's operational coverage are reached, while inbound aircraft entering the coverage area of ​​radar A (from radar B's coverage area) are only visible to radar A's station when the other radar (radar B) loses its lock on it. If there is overlap between the coverage areas of radars A and B, it occurs within the coverage area of ​​radar A and therefore at a distance less than the limits of its coverage area.

[0006] Therefore, in the prior art, the detection of conflicting regions in II / SI codes is limited:

[0007] - or through a device that needs to see the aircraft (ADS-B_out);

[0008] - or through hindsight of the difference between inbound and outbound coverage; and

[0009] - Finally, the prior art does not provide any means for avoiding collisions in II / SI codes to detect aircraft.

[0010] Another standardized approach used with Mode S stations is to coordinate radars using the same II / SI identifiers into SCN clusters (SCN stands for Surveillance Coordination Network). This requires a cross-border ground infrastructure so that radars can freely exchange the positions of targets in their common area via a high-reliability ground network. In addition to the drawback of using a complex structure, the problem of human error is also not addressed. Summary of the Invention

[0011] One object of the present invention is, in particular, to alleviate the problems associated with sharing Il / SI codes between nearby radars without the disadvantages of the prior art. To this end, a subject of the present invention is a method for detecting conflicts in Il / SI identification codes of radars in the vicinity of a Mode-S-2 radar, said method comprising at least:

[0012] - a first step, in which the radar detects an unsolicited asynchronous reply, i.e. a fruit (a temporally unsynchronized erroneous reply), in the area of ​​the extended radar coverage;

[0013] - a second step, wherein the radar detects conflicts in II / SI codes by analyzing a geographical area of ​​radar coverage common to the radar and at least one nearby radar, if the radar:

[0014] In a sub-area of ​​the extended coverage, the presence of a DF11 fruit with the same II / SI code as the radar is detected, and the nearby radar is the source;

[0015] Observing that no DF11 fruit is present in the area of ​​the radar coverage of the radar caused by the nearby radar, and that the area of ​​the radar coverage of the radar does not overlap with the area of ​​the radar coverage of the nearby radar;

[0016] A conflict is detected.

[0017] An overlapping area between the radar coverage of the radar and the radar coverage of the nearby radar forms a conflict area of ​​II / SI codes.

[0018] In a specific embodiment, the method includes a third step, wherein the radar detects a target locked by the nearby radar in the conflict area, and the detection of DF4, DF5, DF20 or DF21 fruit caused by the nearby radar in the conflict area indicates the presence of a target in the conflict area.

[0019] In said first step, in response to a UF11 all-call interrogation of said radar, listening for synchronized DF11 replies after an all-call period and during a roll call period provides, for example, additional synchronized replies in said extended area, said additional replies thus obtained being processed as other synchronized replies in the all-call period to construct a DF11 hit having the properties of a conventional S-mode hit.

[0020] The target is pre-positioned in an azimuth area inside the conflict area by, for example, utilizing the absolute value of the time difference between the target's fruit and each fruit of the targets in the extended area, the extended area generating the DF11 fruit caused by the nearby radar, the azimuth position of each of the targets being known.

[0021] Another subject matter of the invention is a radar capable of implementing the method.

[0022] The radar comprises, for example, means for continuously processing non-synchronized Mode S replies, the processing being independent of the listening period associated with the interrogations transmitted by the radar.

[0023] The processing means detects and decodes the asynchronous reply, for example by respectively utilizing the radiation pattern of the antenna of the radar:

[0024] - detecting all asynchronous and synchronous responses received via said antenna;

[0025] -Decode the data of any type of reply or message and extract the Mode S address from it;

[0026] - enriching each decoded response with its characteristics, at least the time of detection, the azimuth of the main lobe of the antenna at the time of detection and the power received by the antenna radiation pattern.

[0027] The radar comprises an extractor of DF11 hits, for example, in the area of ​​the extended coverage, extracting DF11 hits outside the operating range taking into account only the location and identification of the target via its Mode S address.

[0028] The radar comprises, for example, processing means for detecting conflicts in the II / SI codes and for detecting and locating targets locked by the nearby radar in any conflict area in the II / SI codes, said means:

[0029] - Associate fruit with sync hit;

[0030] - Perform geographical analysis on the source of DF11_R2 fruit. DF11_R2 indicates that the DF11 fruit is an asynchronous response from the nearby radar R2.

[0031] - isolating targets present in the conflict zone that are not detected by the radar;

[0032] - evaluating the azimuth prepositioning of the target relative to the radar in the conflict zone;

[0033] - Detecting and locating the target in range and azimuth to allow the radar to continue its surveillance function for all other targets. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Other features and advantages of the present invention will become apparent from the following description given with reference to the accompanying drawings, which show:

[0035] Figure 1 is an exemplary overview of a prior art Mode S radar;

[0036] Figure 2 is an exemplary overview of a Mode S radar capable of implementing the present invention;

[0037] Figure 3 is a diagram of steps that can be used to implement the method according to the present invention;

[0038] Figure 4 is a view of the operating range and extended range of the secondary radar at a given altitude;

[0039] Figure 5 This is a view of the overlapping ranges of two secondary radars;

[0040] Figure 6a is a view of the electromagnetic impact of the reference radar from nearby radars;

[0041] Figure 6b Rather, it is a reference radar's view of the electromagnetic impact on nearby radars;

[0042] Figure 7 This view divides the overlapping area into multiple sub-areas based on the responses generated by the two radars.

[0043] Figure 8 is a representation of the replies sent by the targets to the radars R1 and R2 in the area where the sub-areas overlap;

[0044] Figure 9is a representation of the azimuth area according to the collision in the II / SI code of the radar R1 of the reply sent in the area where the sub-areas overlap;

[0045] Figure 10a is a view of the detection of DF11 hits outside the operational coverage of the reference radar achieved by increasing the duration of the All Call (AC) period;

[0046] Figure 10b is a view of the detection of DF11 hits outside the operational coverage of the reference radar, in parallel with the subsequent period and achieved without increasing the duration of the AC period;

[0047] Figure 11 This is a view of the asynchronous nature of the fruit due to nearby radars;

[0048] Figure 12 It is a view that searches and pre-locates targets in the conflict area of ​​II / SI codes through time and azimuth analysis of the results caused by nearby radars;

[0049] Figure 13 is a view for detecting locked targets without interrupting the operation of the reference radar;

[0050] Figure 14 is another illustration of the method according to the present invention. DETAILED DESCRIPTION

[0051] refer to Figure 1 , which shows an exemplary overview of a Mode S radar, the principles of this radar will be reviewed. The principles of a Mode S secondary radar (whose interface with the transponder is defined in detail by ICAO in Volume 4, Annex 10) are:

[0052] - Transmit Selective Interrogation:

[0053] or indicates the intended recipient: a single target specified by its Mode S address;

[0054] or an identifier indicating the sender;

[0055] -Receive Selective Acknowledgement:

[0056] or an identifier indicating the sender: the same Mode S address of the target;

[0057] or an indication of the intended recipient: the identifier of the interrogator;

[0058] - Its main content depends on the message:

[0059] o During the acquisition phase (temporary, at the runway threshold)

[0060] DF11: Mode S address of the target;

[0061] o In ELS (ELS is the acronym for elementary surveillance)

[0062] ■DF4: Altitude;

[0063] ■DF5: Identity (Mode A);

[0064] o In EHS (EHS is an acronym for enhanced surveillance)

[0065] ■DF20: Altitude + BDS register, whose quantity is known specifically by calling its query;

[0066] ■DF21: Identity (Mode A) + BDS register, the number of which is known in particular by the query that invokes it.

[0067] When used in a conventional manner, a secondary radar operates in synchronous mode, ie it transmits an interrogation and waits for a reply consistent therewith, which allows locating a target via measurements (of azimuth and range) and identifying it (via its Mode S address).

[0068] In order to perform this task effectively, the radar is equipped with an antenna 1 ( Figure 1 ), which usually does the following:

[0069] - Summation mode 11, hereinafter denoted as SUM, is used to interrogate and detect the target's synchronous response;

[0070] - Difference mode 12, denoted as DIFF, is used to finely locate the target in the SUM beam;

[0071] - a first control mode 15, denoted CONT_Front, for blocking and rejecting replies from targets facing the antenna but not present in the main SUM beam;

[0072] - A second control mode 14, denoted CONT_back, is used to block and reject replies from targets behind the antenna (and therefore not necessarily present in the main SUM beam).

[0073] Depending on the mission and therefore on the desired performance level of the radar, the antenna may have:

[0074] -Multiple radiation modes:

[0075] 4 modes: SUM, DIFF, CONT_Front, and CONT_Back;

[0076] 3 modes: SUM, DIFF, CONT (CONT_Front and CONT_Back grouped together at the antenna);

[0077] 2 modes: SUM, DIFF / CONT (DIFF, CONT_Front and CONT_Back grouped together at the antenna);

[0078] -Set the size of the pattern:

[0079] Width direction:

[0080] o in order to obtain a thin main beam that has a large width, provides high gain, and is selective and azimuthally precise;

[0081] Height direction:

[0082] o in order to achieve a high altitude (LVA antenna, LVA is the acronym for Large Vertical Aperture) and provide gain and protection against ground reflections (mainly ATC); or

[0083] o To obtain a small height (open array antenna providing mobility) (mainly used for IFF).

[0084] While the SUM and DIFF modes are typically narrow, with 3dB lobes between 2.4° and 10°, it is expected that for the CONT_Front and CONT_Back modes each mode will effectively cover 180°.

[0085] The antenna can also:

[0086] - have a fixed radiation pattern, i.e. a rotating "mechanical" pattern; or

[0087] -Has fixed or rotationally variable electronic scanning pattern, i.e. AESA.

[0088] In the remainder of this specification, the most complete antenna configuration will be described, namely a rotating antenna with 4 radiation patterns, and other configurations will be treated similarly, regardless of the number of antenna radiation patterns employed and whether the antenna is rotating or fixed. However, to simplify the description, a 3-mode configuration with CONT groups CONT_Front and CONT_Back will likely be used.

[0089] Antenna 1 transmits interrogating radiation at 1030 MHz and receives replies at 1090 MHz, via four radiation patterns: SUM, DIFF, CONT_Front and CONT_Back, or three radiation patterns (SUM, DIFF, CONT) or two radiation patterns (SUM, DIFF / CONT).

[0090] In the rotating antenna, the rotating joint 2 and the antenna down lead ensure:

[0091] - RF coupling of signals transmitted at 1030 MHz and received at 1090 MHz between the rotating and fixed parts of the radar, independent of the four radiation modes;

[0092] - A shift in the azimuthal position 201 of the axis of the antenna's main lobe.

[0093] The RF processing stage includes:

[0094] a duplexer or circulator 3 ensuring RF coupling between the signal transmitted at 1030 MHz and the signal received at 1090 MHz, independently of the four radiation modes;

[0095] - a transmitter 4 which:

[0096] Transmitting inquiries via SUM mode at 1030 MHz;

[0097] Block transponders outside the 1030MHz SUM lobe via CONT_Front and CONT_Back modes;

[0098] The transmitter does this for all the various auxiliary protocols: IFF, SSR, and Mode S.

[0099] - A receiver 5 which receives the 1090 MHz reply via the four modes SUM, DIFF, CONT_Front and CONT_Back and calculates the angle error for the various auxiliary protocols: IFF, SSR and S-mode.

[0100] The real-time processing phase includes:

[0101] - A space-time manager 6 that manages the interrogation periods and the associated listening periods in real time for the various auxiliary protocols: IFF, SSR and Mode S;

[0102] - a signal processor 7 which:

[0103] Processing replies during the listening period associated with an interrogation, for various auxiliary protocols: IFF, SSR, and Mode S;

[0104] Detecting and decoding synchronization replies in the main lobe of the antenna by utilizing four radiation patterns:

[0105] o SUM: detects the responses received in the main lobe;

[0106] o DIFF: pinpoints in azimuth the reply received in the main SUM lobe and potentially eliminates aliased replies;

[0107] o CONT_Front and CONT_Back: Reject replies received via the side SUM and DIFF lobes if detected in the main SUM lobe.

[0108] The antenna's main lobe processing stage includes:

[0109] - A manager 8 of the targets present in the lobe, which:

[0110] Preparation (challenge-response) for transactions to be performed in the next lobe, for various auxiliary protocols: IFF, SSR, and S-Mode;

[0111] Management lobe IFF, SSR, all-call Mode S, and roll call Mode S periods;

[0112] Dynamically set the selective Mode S interrogation and reply for the next roll call period based on the status of the transaction just performed and any new inbound aircraft entering the lobe;

[0113] An extractor 9 which generates hits for each of the various auxiliary protocols: IFF, SSR and S-Mode, based on the synchronization replies received in the lobes and depending on the protocol adopted by the interrogation.

[0114] The multi-rotation processing stage 10 includes:

[0115] - a manager (101) of Mode S missions to be performed on targets within coverage, predicting target positions (antenna crossings) and preparing the missions to be performed associated with these positions due to internal requests, external requests and the status of transactions from previous rotations;

[0116] - Correlating hits and tracking 102 targets in coverage, ensuring that targets are tracked to improve performance primarily but not exclusively in Mode S (especially by removing false hits and checking decoded data) and predicting their future positions.

[0117] The user interface allows the radar to consider various requests, as well as targets to be viewed and hits of tracked targets.

[0118] Recalling the operation of a Mode S secondary radar, and before describing the present invention in more detail, let's describe the principles of its implementation. The solution according to the present invention analyzes the environment of radar A by utilizing the fruits received by that radar (radar A), or more precisely, in the event of a conflict in the II / SI code, that radar A no longer receives. Fruits (an acronym for "false reply unsynchronized in time") are unsynchronized replies that were not caused by the radar. These fruits are:

[0119] - or caused by another interrogator sharing the same space (another radar, WAM, TCAS, etc.);

[0120] - or automatically generated by the target itself (ADS-B, etc.).

[0121] The characteristics of fruit are:

[0122] - Mode S address of the target;

[0123] - the power received via the antenna's radiation pattern;

[0124] - azimuth of the antenna;

[0125] -The time of the radar reception.

[0126] The Mode S fruit is a message (a Mode S reply in various downlink formats (DF)) transmitted by an aircraft to other radars R2, R3, R4, etc. Depending on the format of the message, it provides information about the identity of the aircraft and, depending on the nature of the reply, sometimes about the identity of the other radar (R2, R3, R4, etc.) with which the aircraft is communicating. If radar R1 refers to the aircraft using its Mode S address (which is also present in the fruit), this allows, via geographic analysis, to locate in near real time the spatial region where there is a conflict in the II / SI codes of radars R1 and R2.

[0127] Specifically, when the same II / SI code is used by nearby radars R1 and R2 sharing a common coverage area, differences are observed in the distribution of fruits in the environment compared to when different II / SI codes are used. These differences are as follows:

[0128] - Since both radars R1 and R2 locked the aircraft to the same II / SI code, no targets in the RF common area (outside the operating area) could generate DF11 results;

[0129] - Each target in the non-common coverage area of ​​each radar R1 or R2 produces the same II / SI code DF11fruit;

[0130] Because each radar R1, R2 locks the aircraft within its coverage area to the same II / SI code as the other radar, and aircraft outside the two coverage areas of the two radars R1, R2 use the II / SI codes of the two radars R1, R2 to generate DF11 fruit;

[0131] Because they are no longer locked to either radar, i.e. R1 and R2 are not locked.

[0132] This type of complete analysis allows marking and locating in azimuth relative to R1 (and R2, respectively) the areas where there are conflicts in the II / SI codes of the radars R1 and R2.

[0133] In addition, in the public area, radar R1 can detect the following fruits:

[0134] -DF4 fruit, given altitude,

[0135] -DF5 fruit, given identity (mode A),

[0136] -DF20 fruit, given altitude and requested BDS record,

[0137] -DF21 fruit, given altitude and required BDS record,

[0138] Generated by radar R2 in conjunction with an aircraft operating Mode S in ELS (Basic Surveillance) or EHS (Enhanced Surveillance):

[0139] - Allows detection of Mode S targets not yet known to Radar R1.

[0140] Using the same radar R2, the generation of DF4 / 5 / 20 / 21fruit of such targets and DF11fruit of other targets almost synchronously (time analysis) allows in a few rotations:

[0141] - Use radar R2 to isolate each target's DF4 / 5 / 20 / 21fruit;

[0142] - Pre-localization of new targets not yet detected in the II / SI conflict zone in azimuth of radar A:

[0143] or by temporal analysis based on the time difference between the DF4 / 5 / 20 / 21 fruit of the target and the DF11 fruit produced by other targets whose positions are known to R1;

[0144] or by the radar R1 assigning to each DFxx fruit a characteristic according to the energy received from the fruit via each antenna radiation pattern (SUM, DIFF, CONT) - see patent FR No. 1800657 for details of this principle applied to the ADS-B (DF17) squitter.

[0145] The collision in the II / SI code of the common area with R2 makes it meaningless to listen to the DF11 reply to the UF11 all-call of radar R1; however, it can still be used to acquire a new target that is closer. Therefore, in order to accurately locate this target in range (and better, in azimuth), radar R1 will supplement its all-call period with a third selective interrogation with the target's Mode S address only at the target's pre-located azimuth, within a considerable listening range (since the targets' interrogations are not synchronized, they do not provide information about their range). The third Mode S (UF4 or UF5) interrogation can be added to a given all-call period that already contains a non-selective (UF11) Mode S interrogation and an SSR (MA / MC / M1 / M2) interrogation, because these three interrogations are intended for different targets and, in addition, the associated synchronized replies have different formats, thus preventing any interpretation errors.

[0146] In order to reduce the size of the selective listening window, the range of the target can be estimated based on the power received in its fruit. To do this, for each fruit received from the target, once the azimuth of the target is determined, the range of the target is estimated by calculation, taking into account the antenna gain in the azimuth of the received fruit. This allows, in particular, to acquire and precisely locate targets in almost real time, even if they are locked by the UF11 all-call of the radar R2 to R1, and then to manage these targets like all other targets via selective transactions during the roll call (RC) period.

[0147] As shown in the rest of the description, the present invention has at least the following advantages:

[0148] The present invention is based on the complete concept of using II / SI codes to determine which radars lock onto a Mode S target: it is therefore applicable as long as the target has a Mode S transponder and does not require other types of onboard equipment (such as the ADS-B system);

[0149] - the analysis of the results of all targets in the area allows to define the conflict zone in II / SI code very quickly with greater geographical precision (through the location of all these targets) and even if the number of targets is high;

[0150] - the analysis of the target's position with the radar R2 allows the pre-positioning of said target in azimuth;

[0151] - Selective interrogation in all calls, with a large tolerance of the range of the target at the pre-positioned azimuth, allows its precise detection without affecting the operational performance of the radar R1.

[0152] Now think about it Figure 1An overview of the Mode S radar presented in and the changes required to implement the present invention. Figure 2 This new overview of a radar capable of implementing the present invention is shown in FIG. The main components and processing operations of an S-mode radar applied to an antenna with four radiation patterns added according to the present invention are shown in FIG. Figure 2 Indicated by bold lines.

[0153] Although the operation of the Mode S radar is synchronous, the processing operations added according to the present invention are independent of the transmission and only utilize the azimuth position of the axis of the antenna's main lobe. Most elements remain unchanged, and as a result:

[0154] -The present invention does not affect the operation of S-mode radar;

[0155] - Moreover, it uses the same components as those used in radar:

[0156] About antennas in a broad sense: antennas, rotary joints, antenna down leads, and duplexers;

[0157] · About processing: receiver.

[0158] This allows, in particular, the correlation of synchronized and unsynchronized replies from the same aircraft.

[0159] The main features added are described below.

[0160] In the real-time processing phase, and more specifically in the processing of signals:

[0161] - Added continuous processing 21 of asynchronous Mode S replies (independent of the listening period associated with the interrogation), ensuring detection and decoding of asynchronous replies by individually but also utilizing all 4 radiation patterns SUM, DIFF, CONT_Front and CONT_Back:

[0162] To detect all received responses: asynchronous and synchronous responses;

[0163] Decode the data of replies and messages in any format (DF4 / 5 / 11 / 20 / 21) and, most importantly, extract the Mode S address from them;

[0164] Enrich each decoded response with its characteristics: detection time, azimuth of the antenna's main lobe at the time of detection, power received via SUM, DIFF, CONT_Front, and CONT_Back;

[0165] - enrich the synchronization reply with the power measured via SUM, DIFF and CONT_Front and the antenna azimuth;

[0166] - Detection of synchronous replies outside the radar's operational coverage area.

[0167] In the stage of processing the main lobe, an S-mode extractor 22 is added of DF11 hits generated outside the operating range, outside which range the DF11 hits are extracted taking into account the positioning and identification of the target via its S-mode address.

[0168] During the multi-rotation processing stage:

[0169] - Adding process 23 to detect any conflicting areas in the II / SI code;

[0170] The association of the fruit (asynchronous response) with the synchronous hits in the coverage area (operating range and beyond);

[0171] Geographical analysis of the origin of DF11_R2 fruit (DF11_R2 means that DF11 fruit is an asynchronous reply whose origin is radar R2, i.e., an asynchronous reply after an all-call transmitted by radar R2, not caused by R1);

[0172] - Added accurate detection and location of targets locked by R2 in conflict zones in II / SI codes 23:

[0173] Isolate targets in the conflict zone that are not detected by radar R1 by analyzing DF4 / 5 / 20 / 21_R2 fruit (DF4 / 5 / 20 / 21_R2 indicates that the fruit is in DF4 format, DF5 format, DF20 format, or DF21 format, and is generated by targets managed by radar R2);

[0174] Evaluate its azimuth pre-positioning relative to R1 within the conflicting coverage area;

[0175] Detect and pinpoint the target in range and azimuth so that surveillance can then be continued as with all other targets.

[0176] Figure 3 The various steps for implementing the present invention are shown, which are performed by an operational radar 30. The radar 30 performs its normal task of monitoring its responsible (ELS or EHS) operational coverage area, namely, detecting and locating all possible Mode S targets through their enriched synchronous replies. The synchronous replies caused by the radar are received using an azimuthally selective SUM and DIFF radiation pattern.

[0177] Three possible steps for implementing the present invention are described below.

[0178] The first step 31 comprises three sub-steps SE1, SE2, and SE3. In the first sub-step SE1, the radar 30 detects fruit. These asynchronous replies, not caused by the radar, are received via the four radiation patterns SUM, DIFF, CONT_front, and CONT_back. According to the present invention, the processing performed by the radar specifically utilizes fruit, which has the same format as synchronous replies in terms of RF signal and reply structure.

[0179] In order to exploit the fruit, still in sub-step SE1, a phase of detecting and decoding these asynchronous replies, which conventional radars usually reject, is added to the process. These asynchronous replies have the properties of conventional replies, which are in particular the following:

[0180] - Detection time;

[0181] - the azimuth of the antenna at the moment of fruit;

[0182] - Mode S address of the transponder;

[0183] - the content of the message;

[0184] -The resulting power in each radiation mode of the antenna.

[0185] Depending on the distance of the target from the radar, the fruit can be detected simultaneously via multiple radiation patterns. Under these conditions, in a first step, multiple detections are cascaded (simultaneous detection) to ensure that there is only a single asynchronous reply message for each fruit. At this point, it is impossible to distinguish the source of the fruit, which can be:

[0186] - or caused by another interrogator sharing the same space (another radar, WAM, TCAS, etc.);

[0187] - or automatically generated by the target itself (ADS-B etc.), the present invention does not exploit this possibility.

[0188] In sub-step SE2, the radar's detection coverage is extended (knowing that the operational coverage is usually set by the user to be less than its guaranteed maximum range) to a much larger, or even maximum, synchronous detection range, in order to create a measurement area that allows the definition of the conflict area in the II / SI code. The additional synchronous reply thus obtained (interrogated using the same radar UF11 all-call operation and therefore without affecting the radar's operational work) is processed like the other synchronous replies of the radar's coverage area during the all-call (AC) period in order to produce a hit, which therefore has the normal basic properties of a basic Mode S hit, such as, in particular:

[0189] - detection time of the hit center;

[0190] - Mode S address of the transponder;

[0191] - azimuth of the impact center;

[0192] - Distance of hit;

[0193] -For each response that forms a hit:

[0194] Detection time (usually on the order of 50ns)

[0195] The azimuth of the antenna;

[0196] The success or failure of the query (whether a response was received);

[0197] Pointing errors in the lobes;

[0198] The content of the message;

[0199] • The reply power in each radiation pattern of the antenna (SUM, DIFF and CONT_Front).

[0200] In sub-step SE3, fruits are associated with Mode S hits of the radar's extended coverage area. With each target located by the radar through selective interrogation that generates a synchronous (DF4 / 5 / 11 / 20 / 21) reply in the extended or operational space of the radar's coverage area, the present invention associates the fruits it generates (based on the unique Mode S address of the transponder used as the target identifier):

[0201] - or between two consecutive synchronization detections in S mode (close to one rotation);

[0202] - or based on rotation for example.

[0203] Since the FRUIT is inherently asynchronous, the position of the target at the moment of detection of the FRUIT is determined by interpolating the target's position based on the trajectory of the target determined by the radar at the time the FRUIT is received as part of its operational function.

[0204] In a second step 32, the radar detects and characterizes potential conflicting areas in the II / SI code by analyzing the various geographical areas between the two radars. This operation corresponds to sub-step SE4, in which the radar performs this detection and characterization by analyzing the various geographical areas between the two radars:

[0205] - Two regions D1 and D2 flanking the conflicting region in the II / SI code ( Figure 7 The target DF11 fruit exists in regions D1 and D2;

[0206] - In the non-overlapping area A of the operational coverage of the radar R2 ( Figure 7 In region A), there is no DF11 fruit from the target;

[0207] - the II / SI code associated with the same fruit as that of the radar R1 in the zones D1 and D2;

[0208] - In area C( Figure 7 In region C), there are no simultaneous DF11 hits outside the radar's operational coverage.

[0209] In case of confirmation of a conflict in the II / SI code, the radar sends the area in question to the ATM manager in order to correct the problem.

[0210] The third step 33 comprises at least three sub-steps SE5, SE6 and SE7. In this step, in order to ensure the safety of radar monitoring (indispensable in ATC), in the event of any conflict in the II / SI code being detected, the present invention allows:

[0211] - the presence of targets not detected by radar in the conflict zone to be isolated;

[0212] - azimuth pre-positioning of the target in the conflict zone to be assessed;

[0213] - Detect and accurately locate the target in range and azimuth to allow it to be monitored like all other targets.

[0214] In sub-step SE5, the radar isolates the undetected targets present in the conflict area (in case of a conflict in the II / SI code). To this end, in order to detect the conflict area in the II / SI code ( Figure 7 If there is a target that may be locked by another radar R2 in area B or C in the image, the radar first isolates the DF4 / 5 / 20 / 21 fruits caused by the other radar R2 among all the captured fruits (i.e., the fruits caused by the other radar R2 during its operational interaction with the target), and R1 does not yet know the S-mode address of the other radar R2.

[0215] So, a target referenced by its S-mode address, some of its DF4 / 5 / 20 / 21 fruits:

[0216] - Temporally between the DF11_R2 fruit of the target known to R1 in regions D1 and D2,

[0217] - and, over P rotations of R1 (e.g., about ten rotations), time synchronization between the DF11_R2 fruits in regions D1 and D2,

[0218] is a potential lock target in area B or C, some of which is caused by this other radar R2 (these areas will be defined below).

[0219] The synchronization criterion between the fruit of this target and the fruit of each target in D1 and D2 takes into account the tolerance on the time difference between these fruits, allowing for the known azimuth variation of the targets in D1 and D2 over P rotations and their unknown position in the lobe of R2 for interrogation.

[0220] Since targets produce results with different radars, this time selection allows selecting only those due to R2 of targets in regions B or C.

[0221] In sub-step SE6, the radar pre-positions the target in azimuth in the conflict zone in the II / SI code. More precisely, the radar estimates the azimuth pre-positioning of the isolated target in the conflict zone by using the absolute value of the time difference between the fruit of the target under analysis and the fruit of the known targets in the zones D1 and D2. Considering that the rotation speed of R2 remains stable and that the targets in D1 and D2 are located in azimuth and range by R1 at each rotation, this makes it possible to estimate the azimuth of the target at each rotation by using the detection time of the fruit by R1 through analysis based on simple interpolation, and to do so over P rotations analyzed at the previous time (or more, depending on the desired accuracy). At each rotation, each pair consisting of the fruit of the target and the fruit of the known target of D1 or D2 allows an estimation of the azimuth. The azimuth pre-positioning of the target is the average of these estimates.

[0222] In sub-step SE7, the present invention performs, via R1, the detection of the azimuth position and calculation of the range of the target locked by R2, so that surveillance can then be continued as with all other targets. To this end, an additional selective interrogation of this Mode S address, known by its fruit, is located during the AC period (which is typically used for non-selective all-call interrogations), thus leaving the operation of selective surveillance of known targets via Roll Call (RC) interrogations unchanged. Specifically, since the range of this target is not yet precisely known, the associated listening window is larger in size. If this listening window were used during the RC period, it would occupy approximately half the sequence time, thus penalizing the other targets to be managed (areas A and B).

[0223] exist Figure 3In the process shown, sub-step SE4 of detecting a conflict in the Il / SI code forms a first processing stage 31, which allows the overall safety of ATC surveillance to be increased. This sub-step is followed by an external warning 39 indicating the conflict zone in the code. Sub-steps SE5, SE6 and SE7 form a second processing stage 32, which allows the radar 30 to maintain surveillance even in the event of a conflict in the Il / SI code, by detecting and locating the aircraft in the conflict zone in the Il / SI code.

[0224] The context and phases of the invention described above will now be described in more detail. First, the context of the fruits received by the secondary radar will be reviewed. These fruits are always generated by real targets, and are primarily generated by those targets within the electromagnetic coverage of the secondary radar.

[0225] Figure 4 The various ranges of the radar in the XY plane are shown. To ensure its surveillance function in a given area, the coverage area 41 of the secondary radar (hereinafter referred to as R1) generally includes an emission margin to ensure a detection probability greater than 99%. In this area 41, targets equipped with transponders with a sensitivity lower limit of 1030 MHz can correctly interpret S-mode interrogations, and transponders with a power lower limit of 1090 MHz can be correctly detected by the radar. As a result, targets with transponders that are more centered in the dispersion of 1030 MHz sensitivity and 1090 MHz power, or even transponders at the top of the range, can still correctly interpret (and therefore respond) at a maximum range far greater than that of the area 41. Thus, a larger area 42 is obtained in which most targets can still respond to interrogations. In addition, the radar must detect synchronous responses at 1090 MHz, which are caused by its interrogations at 1030 MHz. Therefore, its reception range is actually generally much greater than the maximum transmission range, resulting in a reception area 43 that is contained in the preceding areas 41 and 42. The transmission range corresponding to the limits of area 42 and the reception range corresponding to the limits of area 43 will be denoted below as range_TX and range_RX, respectively. The secondary radar in question is denoted as R1; it is located at the center of area 41, and with reference to this radar R1, its transmission and reception ranges are denoted as range_TX1 and range_RX1, respectively. Furthermore, radar operators typically employ the latter, which typically has a range less than the guaranteed electromagnetic range and, therefore, has an operational coverage area with a radius less than 41 with respect to locked targets, primarily due to limited target visibility from the radar's position.

[0226] Figure 5 A dual radar configuration is shown, with the second radar R2 located near radar R1. More precisely, Figure 5The overlap between the coverage areas of the two radars is shown. The analysis presented in the remainder of this specification is from the perspective of radar R1, and a reciprocal analysis can be performed from the perspective of radar R2. Radar R2 interrogates targets within the coverage area of ​​R1 until it transmits to the limit of Range_TX2.

[0227] Figure 6a and 6b The collision zone between the two radars R1 , R2 is shown. Figure 6a The impact volume of R2 on R1 corresponding to region 61 is shown. Figure 6b The impact of R1 on R2 corresponding to region 62 is shown.

[0228] like Figure 7 As shown, the overlapping area between two radars (here, the case of R2 colliding with R1) is divided into different subareas A, B, C, D1 / D2, E, F1 / F2 according to the type of messages each radar exchanges with the target in the subarea. The principle of the present invention is to analyze in detail the presence or absence of such messages in order to define these subareas in azimuth, as in the device described in patent application FR 1800914. In this invention, the goal is to detect collisions in the II / SI code. The format of the responses exchanged between the radar and the aircraft's transponder is known to those skilled in the art. The type of response depends on the radar and the mission assigned to it in the radar area where the target is located.

[0229] In the case of a conflict in II / SI codes, the area in question is area B, where if a target comes inbound towards R1 from R2's coverage area (areas E, C, B), R1 will not detect it before area A because in area B it is locked by R2, it does not respond to R1's all-call (DF11) and R1 therefore cannot see it.

[0230] Table 1 below compares the respective tasks of R1 and R2 in a given area for an example of typical operation of a Mode S radar with different II / SI codes (II1 for R1 and II2 for R2).

[0231] [Table 1]

[0232]

[0233]

[0234] Figure 8The following table shows the response type by sub-region for different II / SI codes. More specifically, it shows the messages exchanged in the overlapping region according to the sub-region associated with Table 1 above. Responses synchronized with R1 are bolded, while responses asynchronous with R1 are not bolded, the latter being the result caused by R2. Furthermore, the extended ranges S and F indicate whether the response is synchronized or a result, respectively.

[0235] Table 2 below compares the corresponding tasks of R1 and R2 for targets belonging to a given sub-area when both radars use the same II / SI code, which is denoted as IIc.

[0236] [Table 2]

[0237]

[0238] Figure 9 The table shows the types of replies by sub-area for the same II / SI code. More specifically, it shows the messages exchanged in the overlapping area according to the sub-area associated with Table 2. The bold characters represent DF11 replies, which disappear in the case of the same II / SI code (IIc). The non-bold characters represent the synchronous and non-synchronous replies that still exist. The distribution of DF11 replies for the full calls of each radar is different due to the fact that radars R1 and R2 use the same II / SI code (IIc). Figure 8 Changed:

[0239] - In sub-areas D1 and D2, there are still replies that are synchronized with R1 and not synchronized with R2; moreover, they use the same code IIc;

[0240] - In sub-area A, the target or R1 within the coverage range does not produce any fruit DF11 with R2;

[0241] - In sub-area C, outbound targets from R1's coverage area (sub-area B) no longer answer R1's all calls, even if R1 is no longer locked to them.

[0242] Table 3 below compares the differences between sub-regions with and without collisions in II / SI codes for R1.

[0243] [Table 3]

[0244]

[0245] Based on the spatial distribution of aircraft among the four sub-areas 1 to 4, the following criteria can be met:

[0246] - Regions D1 and D2: the presence of a hit in R1 produces a fruit with the same IIc code as R2;

[0247] - Area C: R1's hit outbound from area B does not answer R1's all-call (UF11);

[0248] - Region A; a hit of R1 does not produce a fruit of code IIc, which is an identifier of R2;

[0249] - Inbound hits cannot be seen by R1 in region B, they only appear in AC in region A: outbound range > inbound range.

[0250] After this analysis, the radar R1 assumes the hypothesis that there is a conflict in the II / SI code in the azimuth zone included between the two zones D1 and D2, which is Figure 9 , which is schematically delimited by two straight lines 91 and 92. In practice, the positions of these lines are obtained by drawing a straight line through the radar R1, and:

[0251] - In D1: the target of R1 produces a fruit with the same code IIc, which has the maximum azimuth as seen from R1;

[0252] - In D2: The target of R1 produces a fruit with the same code IIc, which has the smallest azimuth as seen from R1.

[0253] refer to Figure 10a or Figure 10b , which shows the detection of a DF11 hit outside the radar's operating range, we will now describe the specific processing performed to determine the azimuth of the conflict in the II / SI code. In order to detect and define the azimuth of the conflict in the II / SI code, in the radar R1, it is necessary to process the simultaneous replies from the two zones D1 and D2 without interfering with the radar's operating conditions.

[0254] In its operational work, the radar manages two types of periods for aircraft within its coverage area (areas A and B):

[0255] - All Call (AC) period for detecting incoming aircraft in Mode S:

[0256] Mode S radar beam management issues a general UF11 interrogation call in each AC;

[0257] Mode S reply processing detects DF11 replies within the radar's operating range;

[0258] Mode S extractor reconstructs DF11 Mode S hits within radar operating range;

[0259] - Roll Call (RC) period, used to ensure surveillance of aircraft in Mode S (ELS or EHS):

[0260] Mode S radar beam management selectively interrogates aircraft previously detected in AC sequentially via UF4 / 5 / 20 / 21 requests;

[0261] Mode S reply processing detects DF4 / 5 / 20 / 21 replies within the radar operating range;

[0262] The Mode S extractor reconstructs enriched Mode S hits within the radar's operating range;

[0263] The radar then locks onto the target thus acquired in the RC, so that it no longer replies to the radar's all-calls and therefore no longer replies to its identifier, ie its II / SI code.

[0264] In the present invention, the S-mode function in the processing 21 of the asynchronous reply refers to all DF11 results with code III of R1 that are received after the last UF11 interrogation of the AC period of the radar of R1, even if they come from outside the operating range of the radar. Two methods are possible, as shown:

[0265] -exist Figure 10a medium (increase in the duration of the AC period);

[0266] - and in Figure 10b (the period for monitoring the synchronous DF11 response is outside the AC period and in the RC period).

[0267] Both solutions allow the DF11 extraction function 22 to be constructed outside the operational coverage (outside the regular listening phase of the AC period) and thus for simultaneous DF11 hits of the areas D1, C and D2. Figure 10a and 10b is characterized by an additional listening phase 110 outside the operational AC listening period (which is not an operational requirement of prior art radars) and thus Figure 10b This additional listening phase is performed for area 42 (see Figure 4 ). It should therefore be noted that synchronized DF11 replies within the operational coverage of the radar are not processed by this new function 22, as they are already utilized by the operational work of the radar in the AC.

[0268] The duration of this additional phase of listening for DF11 replies is practically limited only by the duration of the RC period, since Figure 10b In the case of an RC period, it runs in parallel with this period before the next AC period. In practice, since the duration of the RC period is approximately 1.5 to 2 times that of the AC period, it is possible to listen for replies from a distance that must be twice the operating range. Therefore, the maximum listening range is actually limited only by the electromagnetic range.

[0269] refer to Figure 11 Now, we will describe the search for targets in area B by using a time method for the target. For this time method, the radar will be assumed to be a mechanical rotating antenna, which is the assumption for most ATC radars. Figure 11 This simplified diagram shows an example of what happens when all targets in a common RF coverage area are:

[0270] - Northeast of radar R1;

[0271] - Southwest of radar R2,

[0272] The situation of the aforementioned radars R1 and R2 when .

[0273] An additional assumption is made (in this example) that the rotation period of R2's antenna is approximately ¾ of the rotation period of R1.

[0274] Figure 11 Shown are replies 111 that are synchronized with R1 and replies 112 that are synchronized with R2, as well as replies 113 that are not synchronized with R1 (fruit) of a target in the common area. Due to the natural motion between the rotations of the two antennas, it can be seen that the fruit due to R2 is also not synchronized in azimuth relative to R1, however, this allows the fruits to be accurately timestamped so that their azimuths can be subsequently calculated.

[0275] The principle of the invention for detecting the presence of targets potentially locked by R2 in zone B requires first of all to isolate, among all the fruits acquired by R1, the DF4 / 5 / 20 / 21 fruits due to radar R2 that caused them during its operational interaction with targets including those in zones B or C. It should be noted that the DF4 / 5 / 20 / 21 messages do not contain an identifier of R2, but only the Mode S address of the target, and therefore they do not by themselves identify the radar that caused them: they only allow identification of the target.

[0276] To achieve this isolation, Figure 12 As shown, the present invention exploits the fact that from one rotation of antenna R2 to the next, the fruits of R2 are nearly synchronized with each other.

[0277] exist Figure 9 In the example, the preceding analysis allows R1 to locate targets that produce DF11 fruit due to R2 (according to its identifier) ​​in regions D1, southeast of R1 (southwest of R2), and D2, northeast of R1 (west of R2).

[0278] The next step of the analysis consists in searching for DF4 / 5 / 20 / 21 fruits synchronized with these DF11 fruits of R2 by analyzing those fruits over multiple rotations whose time differences relative to the targets or fruits of areas D1 and D2 remain almost constant when taking into account the movement of these targets (R1 can calculate this movement because these targets produce hits synchronized with R1 outside the operational coverage).

[0279] Therefore, these DF4 / 5 / 20 / 21 fruits are due to potential targets in regions B and C and caused by R2. These DF4 / 5 / 20 / 21 fruits are:

[0280] - in time between the DF11_R2fruit of the target known by R1 in the regions D1 and D2 from one rotation to the next,

[0281] - and are synchronized in time between fruitDF11_R2 in regions D1 and D2 over P rotations of R1 (about ten rotations - parameter of the invention).

[0282] Figure 12 Successive scans by the antenna of R2 are shown along the time axis and in azimuth of R1, starting from scan N (labeled scan_N), the figure shows successive time zoom-ins on the passage of the antenna of R2 from the area "D1, southwest of R2" to the area "D2, west of R2" and thus through areas B and C. The dotted line shows the remainder of the rotation of the antenna of R2 to other azimuths of R2 on a time scale that is intentionally reduced to highlight the zoomed-in portion.

[0283] In the areas "D1, southwest of R2" and "D2, west of R2", only targets (indicated by solid circles) that emit DF11_R2fruit caused by R2 are shown.

[0284] In the central time period between areas D1 and D2, there are two types of DF4 / 5 / 20 / 21 fruits captured by R1. The radar according to the present invention analyzes these fruits (S-mode addresses available in DF4 / 5 / 20 / 21 messages) on a target-by-target basis to determine their time difference relative to the DF11_R2 fruits of the two areas D1 and D2 at each rotation:

[0285] - For targets in regions B or C, the fruit induced by R2 remains almost stable relative to the DF11 fruit of R2, since they are induced by the same radar (fruit is indicated by a bold circle);

[0286] After allowing for the rotational differences of these radars and R2's antenna, for a target at any azimuth that R1 will still detect via its omnidirectional antenna (radiation pattern CONT), the fruits due to the other radars are unstable as a function of time relative to those of R2 (fruits are indicated by circles that are not bolded).

[0287] exist Figure 12 The target indicated by the bold circle at the S-mode address MS1 (@MS1) is considered to be in region B or C. For the analysis at the P (parameter) rotation depth, the S-mode address MS1 is relative to the DF11_R2 fruit (@MS A and D2's @MS B ) remains stable (with a parameterizable time tolerance ΔT). Therefore, Figure 12 The analysis allows positioning of fruits relative to each other.

[0288] To pre-position a potential locked target in azimuth to be in region B without replying to R1's UF11 all-call, at least two methods may be used: azimuth pre-positioning via time difference or azimuth pre-positioning via use of antenna radiation pattern.

[0289] For azimuth pre-positioning, it should be noted that in the previous step, the stability of the time difference between the fruit of the target at address MS1 (@MS1) and the DF11_R2 fruit of areas D1 and D2 was used to isolate whether it belongs to area B or area C. Now, radar R1 knows the azimuth position of the targets in areas D1 and D2 that have generated DF11_R2 fruit in its reference frame.

[0290] The target under analysis (@MS1) is relative to each target in region D (@MS A and @MS B ) allows estimating the azimuth of target @MS1 for each of the P previously analyzed rotations (or more, depending on the desired accuracy). The azimuth pre-position of target @MS1 in a given rotation is the average of these estimates. Linear regression over the P rotations allows refinement of the azimuth and, in addition, estimation of the target's angular velocity relative to R1.

[0291] The principle of another way in which azimuthal pre-positioning can be determined is described in particular in patent application FR 1 800 657, namely using the radiation pattern of an antenna.

[0292] Once the target, potentially in region B, has been located in azimuth, all that remains is to locate it in range. In the remainder of the foregoing example, target @MS1 will be considered. This target @MS1 located in range relative to R1:

[0293] - is not in area A, because if it were, it would reply to R1's UF11 query R1;

[0294] - possibly in region B, and therefore in the area for which R1 is responsible (in which case it must be detected);

[0295] - possibly in region C, and therefore outside the area for which R1 is responsible (in which case it is not necessary to detect it).

[0296] The target @MS1 must be searched for outside the maximum distance of area A and below the minimum distance of area B. Target @MS1 can be detected and accurately located using at least two of the following methods:

[0297] - or by utilizing the functionality of the Mode S protocol;

[0298] - or by utilizing selective interrogation of Region B targets.

[0299] In the event of a conflict in the II / SI code, the Mode S protocol provides for forced unlocking of the target receiving the UF11 all-call interrogation, forcing the locked transponder to respond to the UF11 requested II / SI code. This method not only:

[0300] - a lot of clutter echoes are generated, since all those targets in areas A and B, which are already known to the radar R1 and which are at the azimuth of the transmission called by UF11 or covered by the azimuth width of the lobe of the transmitting antenna (EBW_TX close to 6°), will reply;

[0301] - and won't always work, because all of these Mode S responses will also overlap:

[0302] If the number of targets is high in that azimuth direction;

[0303] Or even simply if the target is close in range @MS1,

[0304] Therefore @MS1 will have a high probability of not being detected on the first attempt, and will require multiple attempts over multiple rotations, each causing multiple unnecessary replies from the known target.

[0305] exist Figure 13 In another method shown, in order to prevent replies from known targets in area A or area B, the target @MS1 is selectively interrogated at its pre-positioned azimuth. Figure 13 As shown, the selective interrogation of the target of Mode S address MS1 is located in the AC period (which is usually intended for non-selective all-call interrogation) and therefore does not require modification of the operation of selective surveillance of known targets by roll call. Figure 13In the example of AC period, at the azimuth of the target, a UF4 query selective for address MS1 is added to AC m+2 period (i.e., it is the complement of the UF11 all-call).

[0306] According to the description of the embodiment of the present invention just given, Figure 14 The principle of the invention is shown in the case of three radars, and more specifically the second step 32 and the third step 33 (see Figure 3 The secondary radar under consideration is still radar R1, but here there are two nearby radars, radar R2 and radar R3. The principles described for R2 apply to R3. Radar R1 thus detects targets that may be present in its coverage area and do not respond to all calls, targets that are locked onto by radar R2 due to conflicts in the II / SI codes. In a first step 31, radar R1 has previously extended its range to an extended area 42 and has detected fruit in this area. Detection is performed as follows:

[0307] - Radar R1 detects 141 (detected in sub-area D) a DF11_R2 fruit (whose origin is radar R2) in the extended area 42 outside the coverage area 41 and having the same II / SI code as R1;

[0308] - Radar R1 observes that there is no 142DF11_R2 fruit in R1’s coverage area that does not overlap with R2’s coverage area (sub-area A);

[0309] - Radar R1 observes the absence of synchronous DF11_R1 replies from aircraft leaving its operational coverage area (sub-area C).

[0310] Under these conditions, the radar R1 concludes from the above that there is a collision of II / SI codes between the two radars R1 and R2 (R2 locks the response), which corresponds to sub-step SE4.

[0311] From the presence of a DF4, DF5, DF20 or DF21 fruit whose origin is R2 in the overlapping area B or C between the coverage areas of the two radars R1 and R2, the radar R1 infers 143 the presence of an aircraft in this area B or C. The azimuth and range of this unseen target are then determined as described above.

Claims

1. A method for detecting conflicts in the II / SI identification codes of radars in the vicinity of a Mode-2 S radar (R1), characterized in that The method at least comprises: - A first step (31), wherein: - expanding (SE2) the coverage of the radar (R1) to obtain a synchronous response within the expanded radar coverage; - the radar (R1) detecting (SE1) an unsolicited asynchronous reply, namely fruit, in an area (42) of extended radar coverage; - associating the fruit with a Mode S target within the extended radar coverage area (SE3), determining the position of the fruit by interpolating using synchronous detections of the target based on the Mode S address of the target; - a second step (32) in which the radar (R1) detects conflicts in the II / SI codes by analyzing the geographical area (A, B, C, D1 and D2) of radar coverage common to the radar (R1) and at least one nearby radar (R2), if the radar (R1): - in the sub-area (42, area_D1, area_D2) of the extended radar coverage, the presence of DF11 fruit with the same II / SI code as the radar (R1) is detected (141), the nearby radar (R2) being the source; - observing (142) that there is no DF11 fruit caused by the nearby radar (R2) in that area (41, area B) of the radar coverage of the radar (R1), and that area of ​​the radar coverage of the radar does not overlap with the area of ​​the radar coverage of the nearby radar (R2); - No simultaneous DF11 hits were observed outside the radar's operating range (area C); A conflict is detected, An overlapping area (area_B) in the radar coverage of the radar (R1) and the radar coverage of the nearby radar (R2) forms a conflict area in the II / SI code; - a third step (33) in which the radar (R1) detects (SE5) a target locked by the nearby radar (R2) in the conflict area (area_B, area_C) based on the detection (143) of a DF4, DF5, DF20 or DF21 fruit caused by the nearby radar (R2) in the conflict area (area_B, area_C), thereby indicating the presence of a target in the conflict area; The target is pre-positioned (SE6) in an azimuth area within the conflict area (area_B, area_C) by utilizing the absolute value of the time difference between each of its DF4, DF5, DF20 or DF21 fruits of the target due to the nearby radar (R2) and each of the DF11 fruits of other targets in the area (area_D1, area_D2) of the extended radar coverage caused by the nearby radar (R2), the azimuth position of each of the other targets being known.

2. The method according to claim 1, characterized in that The precise range and azimuth position of a target is obtained by positioning a selective UF4 or UF5 interrogation (131, SE7) in the pre-positioned azimuth region of the target associated with a listening window in which a reply is listened for, the interrogation being transmitted to the target during a roll call period or during an all-call period in addition to or in lieu of a UF11 all-call Mode S interrogation, taking into account the uncertainty of the range of the target, the interrogation being transmitted to the target during a roll call period or during an all-call period in addition to or in lieu of a UF11 all-call Mode S interrogation, the range of the target being estimated based on the power of the target's fruit and the characteristics of the radar.

3. The method according to claim 2, characterized in that The radar transmits a UF11 all-call interrogation, and in the first step (31), in response to the UF11 all-call interrogation of the radar, listening for synchronized DF11 replies after the all-call period and during the roll call period provides additional synchronized replies (110) in the area (42) of the extended radar coverage, the additional synchronized replies thus obtained being processed as other synchronized replies in the all-call period to construct a DF11 hit having the attributes of a conventional S-mode hit.

4. A secondary radar, characterized in that: The secondary radar is configured to implement the method according to any one of claims 1-3.

5. The radar according to claim 4, characterized in that A listening period is included in association with interrogations transmitted by the radar, the radar comprising first processing means (21) for continuously processing non-synchronized Mode S replies independently of the listening period.

6. The radar according to claim 5, characterized in that The radar comprises an antenna (1) having an antenna radiation pattern (11, 12, 14, 15), the first processing device detecting and decoding the asynchronous Mode S reply by respectively utilizing the radiation patterns of the radar's antenna: - detecting all asynchronous and synchronous responses received via said antenna; -Decode the data of any type of reply or message and extract the Mode S address from it; - enriching each decoded response with its characteristics, at least the time of detection, the azimuth of the main lobe of the antenna at the time of detection and the power received by the antenna radiation pattern.

7. The radar according to any one of claims 4 to 6, characterized in that The radar includes an extractor (22) of DF11 hits in the extended coverage area (42), extracting DF11 hits outside the radar's operating range only with regard to locating and identifying a target via its Mode S address.

8. The radar according to any one of claims 4 to 6, characterized in that The radar comprises second processing means (23) for detecting conflicts in the II / SI code and for detecting and locating targets locked by the nearby radar in any conflict area in the II / SI code, the second processing means (23): - Associate fruit with sync hit; - Geographical analysis of the origin of DF11 fruit as an asynchronous response caused by a nearby radar (R2); - isolating targets present in the conflict zone that are not detected by the radar; - evaluating the azimuth prepositioning of the target relative to the radar in the conflict zone; - Detecting and locating the target in range and azimuth to allow the radar to continue its surveillance function as it does for all other targets.

Images