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Abstract

This disclosure relates to a secondary radar. The radar includes an antenna having a radiation pattern forming a channel SUM, a radiation pattern forming a differential channel DIFF, and a radiation pattern forming a control channel CONT. A first transmit-receive chain (4) is associated with the SUM channel, a second transmit-receive chain (4') is associated with the CONT channel, and a receive channel (4'') is associated with the DIFF channel. Each of the transmit-receive chains (4, 4') is capable of simultaneous transmission and reception. The transmit chain (401) includes filtering operations (4A, 4B) for a signal transmitted at 1090 MHz, and the receive chain (402) includes filtering operations (4C, 4D) for a signal transmitted at 1030 MHz, such that the chains operate independently of each other.

Description

Technical Field

[0001] This invention relates to the field of air traffic control (ATC). Background Technology

[0002] Currently, air control is primarily based on secondary radar, whose detection reliability is widely recognized. Secondary radar ensures synchronous mode surveillance of aircraft according to SSR and S-mode protocols. Furthermore, asynchronous reception of extended ADS-B (Automatic Dependent Surveillance-Broadcast) messages is employed in ground-based ATC. Extended ADS-B messages are provided to ensure onboard collision avoidance (TCAS: Traffic Warning and Collision Avoidance System), thus contributing to the interactive surveillance system.

[0003] This surveillance can be combined with IFF (Identification Friend or Foe) type surveillance, where the IFF interrogator ensures the identification of the aircraft in accordance with various military protocols.

[0004] Within a single structure that groups these sensors together, the operation of these various activities simultaneously requires:

[0005] - Simultaneously listen to the secondary radar and IFF interrogator (if used), these modes are limited by the target dwell time to ensure individual monitoring in time:

[0006] • In accordance with the user's traditional needs, SSR targets are monitored in S mode but ATC monitoring is performed, with each aircraft having two to three BDS (commB data selector) registers to be extracted sequentially;

[0007] • Optionally, IFF identification with protocols, whose main military protection lies in the long variable delay of the response in addition to the range-related duration, and therefore inherently requires a long target radiation time;

[0008] - In asynchronous mode, to listen to civilian ADS-B messages or military Mode 5 messages, the listening operation is as follows:

[0009] • Particularly affected by the polling of synchronous mode interrogation, especially in S mode, where there are many such polling (at least 2 or 3 interrogations per aircraft);

[0010] • Due to the lack of directional selectivity, it is associated with low detection and decoding probabilities when many targets are present, since asynchronous mode listening operations are inherently omnidirectional.

[0011] For example, considering 1200 aircraft per antenna rotation, with two BDS extracted per target, the re-interrogation rate is approximately 1.5 (depending on various external factors such as scrambled responses, transponder occupancy, target movement, etc.), which equates to approximately 3600 interrogations over 20 μs (duration taken from ICAO Annex 10, Volume IV). For the extended Mode S response, the duration of scrambled responses due to synchronous interrogation alone is approximately 140 μs, or 504 milliseconds of contamination per 4 seconds of antenna rotation, corresponding to approximately 13% of the listening operation duration. Specifically, due to its synchronous mode operation, the secondary radar does not require isolation between its transmit and receive chains, as they operate at different times; as a result, the leakage in the transmit chain typically has a level close to the highest amplitude response usually expected from the aircraft in the receive chain, thus making any simultaneous listening operation impossible during interrogation. Therefore, in existing radars, the disturbance caused by synchronous transmission will inevitably limit the detection probability of ADS-B messages to below 87% (this maximum does not take into account all other possible environmental factors that may result in undetected messages, such as response and ADS-B message corruption, multipathing, etc.).

[0012] Furthermore, the ATC secondary radar antenna is designed to operate in synchronous mode with the target located in the plane of the antenna's main panel normal; as a result, it has limitations in the 360-degree electromagnetic coverage required for asynchronous listening, which will be described in detail below.

[0013] To avoid these difficulties, existing technologies, such as those disclosed in FR 3 019 905A1 and FR 2 658 967A1, separate these various activities to ensure the highest possible performance, with the architecture matched to the specificity of each activity. Therefore, conventional ADS-B reception typically consists of two back-to-back 180° antennas associated with two independent receivers to ensure better detection compared to a single 360° omnidirectional antenna, which differs significantly from radar antennas when located in the same area. Furthermore, due to the lack of dwell time to perform both simultaneously at the azimuth angle required for IFF identification, IFF identification is largely detrimental to Mode S surveillance during antenna rotation and within the sectors associated with IFF identification.

[0014] Therefore, implementing all these surveillance and identification activities incurs high operating and maintenance costs. In particular, procurement costs, infrastructure costs, ownership costs, and network costs must be considered. Summary of the Invention

[0015] One object of the present invention is, in particular, to obtain a low-cost, integrated interrogation and surveillance system that provides performance nearly comparable to that of a standalone system. To this end, the subject of the invention is a secondary radar comprising an antenna having a radiation pattern forming a channel denoted as SUM, a radiation pattern forming a differential channel denoted as DIFF, and a radiation pattern forming a control channel denoted as CONT. A first transmit-receive chain is associated with the SUM channel, and a second transmit-receive chain is associated with the CONT channel. A receive chain is associated with the DIFF channel. In this radar:

[0016] - Each in the transmit and receive chains is capable of transmitting and receiving simultaneously. The transmit chain includes filtering operations for signals transmitted at 1090MHz and the receive chain includes filtering operations for signals transmitted at 1030MHz. The receive chain associated with the DIFF channel also includes filtering operations for signals transmitted at 1030MHz, such that the chains operate independently of each other and the receive-side signal level remains unchanged during synchronous interrogation transmission.

[0017] - The processing device includes a method for matching the receiving-side frequency band with the characteristics of each transaction protocol used;

[0018] The receiver chains of the SUM, DIFF, and CONT channels can simultaneously listen to signals received from the target via the SUM, DIFF, and CONT patterns in both synchronous and asynchronous modes. The listening operations in synchronous and asynchronous modes are independent of each other, and the signal level on the receiving side remains unchanged during synchronous interrogation.

[0019] In one specific implementation, the CONT pattern consists of a front radiation pattern forming a channel denoted as CONT_Front and a back radiation pattern forming a channel denoted as CONT_Back. The CONT_Front and CONT_Back patterns are processed separately such that each in the transmit-receive chain is applied to the CONT_Front channel and the CONT_Back channel.

[0020] The radar includes, for example, a kit for extending the radiation pattern of the CONT_Back channel, which is placed on the back of the antenna. The kit includes three radiating patches:

[0021] - The first patch is used to fill the elevation detection hole, which is called the stationary cone;

[0022] - The second patch is used to fill the detection hole at a 90° azimuth angle;

[0023] - The third patch is used to fill the detection hole at an azimuth angle of -90°.

[0024] Each of the transmission chains includes, for example, a filtering operation specifically designed to reject parasitic signals transmitted at 1090 MHz.

[0025] Each of the receiver chains includes, for example, a filtering operation specifically designed to reject parasitic signals originating from the 1030MHz transmission channel.

[0026] In the case of ATC surveillance as a mission, the radar, for example, performs simultaneous listening operations on ADS-B messages individually via a radiation pattern and independently of synchronous transactions.

[0027] In cases where IFF identification is a task, the radar performs synchronous IFF detection, for example, independently of synchronous SSR and S-mode transactions.

[0028] In cases where IFF identification is a task, the radar, for example, independently of synchronous transactions, performs simultaneous listening operations on mode 5 level 2 messages via the radiation pattern.

[0029] In situations where airborne environmental control is a mission, radar, for example, can perform simultaneous listening operations independently of synchronous operations, via a radiation pattern, targeting any type of secondary response.

[0030] The radar transmits continuously during the all-call interrogation period and the round-robin interrogation period, with the round-robin interrogation starting, for example, during the all-call interrogation period.

[0031] The radar transmits continuously during the all-call interrogation period and the round-robin interrogation period. The all-call listening operation that begins during the all-call period is, for example, continuing the round-robin period. Attached Figure Description

[0032] Other features and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawings, which illustrate:

[0033] Figure 1a A diagram illustrating an exemplary implementation of a conventional secondary radar;

[0034] Figure 1b A diagram illustrating an exemplary embodiment of the radar according to the present invention;

[0035] Figure 2a Possible steps for implementing the present invention;

[0036] Figure 2b An example of a sequence of transactions performed by radar according to existing technology;

[0037] Figure 2c An example of a transaction sequence executed by the radar according to the present invention;

[0038] Figure 3 A schematic diagram of one of the above steps;

[0039] Figure 4a , representing the gain of the antenna's three radiation patterns SUM, CONT_Front, and CONT_Back as a function of the azimuth angle between + / -180°;

[0040] Figure 4b This indicates the contribution of the CONT_Back pattern of the present invention to the azimuth extension;

[0041] Figure 4c , representing the gain of the antenna's three radiation patterns SUM, CONT_Front, and CONT_Back as a function of the elevation angle from -60° to +180°;

[0042] Figure 4d , indicating the contribution of the radiation pattern CONT_Back to the elevation angle extension according to the present invention;

[0043] Figure 5 The management of all-call and turn-call transactions based on existing technology;

[0044] Figure 6 An example of the management of all-call and turn-call transactions in a radar according to the present invention;

[0045] Figure 7 Another example of transaction management in radar according to the present invention;

[0046] Figure 8a A diagram of a kit for extending the CONT_Back pattern of an ATC secondary antenna;

[0047] Figure 8b The implementation principle of the kit used to extend the CONT_Back pattern on the ATC secondary antenna. Detailed Implementation

[0048] To reduce the various costs mentioned in the background art, the present invention proposes a given system, referred to as a full-duplex meta secondary sensor, which groups together all the activities of the following ground sensors:

[0049] - Traditional secondary radar: ensures synchronous mode monitoring of aircraft according to SSR and S-mode protocols;

[0050] -IFF interrogator, ensuring the identification of aircraft according to the Mode 4 and Mode 5 protocols;

[0051] - Asynchronous receiver for extended ADS-B messages (DF17 / 18);

[0052] -Asynchronous receiver for Mode 5 Level 2 messages;

[0053] They also utilize the same antenna structure (rotor, antenna, motor, rotary joint, and cables, etc.) and the same infrastructure.

[0054] Therefore, given the shared resources of these various activities within a secondary sensor, the solution provided by this invention utilizes the specificity of these activities to orthogonalize them. Orthogonalization means making them independent of each other, thereby ensuring that each of them acquires the same performance, whether they operate independently or are all activated simultaneously.

[0055] Therefore, the element sensor:

[0056] - Simultaneously transmit and receive various signals by utilizing two frequency aspects (1030MHz transmission and 1090MHz reception) as characteristics of a secondary radar to ensure complete independence of transmission and reception tasks: the term "full-duplex" will be used below to refer to this operating mode in which transmission and reception are simultaneous.

[0057] - Perform filtering operations that match the characteristics of each adopted protocol, meaning that filtering operations are only allowed to process the frequency band containing the useful signal, such as... Figure 1b As shown below;

[0058] - Listen in synchronous mode for the purpose of simultaneously performing ATC surveillance (in SSR and S modes) and IFF identification (in military encryption mode);

[0059] - Listening is performed in asynchronous mode via various physically available antenna patterns (i.e., depending on the antenna architecture), but the radar's radiation characteristics are improved compared to asynchronous mode listening operations, only to ensure better coverage at high elevation angles and temporary listening operations at almost 100% azimuth angles.

[0060] Therefore, the "full-duplex" operation according to the present invention allows:

[0061] - Perform asynchronous mode listening operations (ADS-B or Mode 5 Level 2 message) without being interfered with by synchronous transmission;

[0062] - In the Mode S protocol, optimizing the duration of the call sequence (within the so-called call period (RC)) and thus reducing the lower limit of the dwell time on the target, while not unique, is particularly important in the case of high-speed rotating radars (e.g., in airport configurations, typically 4 seconds per antenna rotation (see...) Figure 6 ));

[0063] - Independent of RC optimization, it detects targets when they enter the radar's electromagnetic range without compromising radar operational performance; that is, it does not require modification of the duration of the all-call period dedicated to this purpose (see [link]). Figure 7 This subsequently allows these incoming targets to be locked earlier in order to eliminate their DF11 response generated after the radar's UF11 interrogation.

[0064] Otherwise, their response potential is unnecessarily consumed;

[0065] Otherwise, it would cause contamination, meaning that these responses would contaminate other radars, especially those closest to the target.

[0066] The filtering operations matched to each protocol employed allow for an analysis band in the receiver that is as wide as required, and this analysis band is accomplished by these filtering operations that match the useful signal band of each protocol (i.e., both its modulation spectrum and the frequency stability of the transponder carrier). This allows for a reduction in noise levels, which in turn allows for a lower detection threshold to handle weaker signals and thus further increases the range.

[0067] Therefore, independent asynchronous mode operation, which allows simultaneous listening to three or four patterns via a conventional ACT antenna, allows for:

[0068] - By independently processing the receiver-side radiation patterns SUM, DIFF, CONT_Front, and CONT_Back

[0069] • At a medium distance, ensure approximately 75% time coverage of synchronous mode listening operations (see...). Figure 4a ),

[0070] • By utilizing the difference in distance from the field of view (if present) between simultaneous messages, these messages can be detected more effectively, thereby reducing the overlap of responses (which is quite long (120 μs)), which is why messages cannot be detected.

[0071] - Furthermore, for its asynchronous mode detection function, the radiation pattern of the radar's ATC secondary antenna is completed:

[0072] • Ensure coverage in the static cone (Cos) (see Figure 4d );

[0073] • Ensure 100% time coverage at the maximum distance of both ADS-B and IFF (see Figure 4b ).

[0074] The features and advantages of the present invention described above will now be described with reference to the accompanying drawings.

[0075] Recall Figure 1aThis diagram illustrates a conventional ATC surveillance radar, which only expects synchronous operation under S-mode and SSR. Transmit / receive chains 401 and 402 have an isolation level sufficient to ensure no disruption occurs even with infinite SWR at the output of the processing cabinet. The radiation patterns CONT_Front and CONT_Back of the ATC secondary antennas are merged by antennas 1 and 2 (radius CONT) because any signals not perfectly aligned with the antenna axis, i.e., the SUM axis, are rejected, regardless of whether they originate from the front or rear.

[0076] Figure 1b A schematic diagram of the device according to the invention is shown. The properties of the "full-duplex" secondary sensor described above can be obtained through the proposed architecture. In particular, this architecture ensures the simultaneous operation of various secondary protocols with minimal interference between them. Therefore, for each protocol, the same performance achievable in the sensor's antenna structure is guaranteed when operating simultaneously with other protocols, even when other protocols are inactive. Figure 1b The architecture is Figure 1a The following describes the evolution of the conventional architecture of a secondary radar. Some of the descriptions below illustrate this. Figure 1a The components that already exist in conventional radar are highlighted by using thicker lines to show additional elements.

[0077] In its normal operating configuration, the secondary radar operates in synchronous mode, that is, it issues an interrogation and waits for a consistent response, which allows it to locate and identify targets by measurement (in terms of azimuth and range) and (usually via addresses in the Mode S protocol).

[0078] To effectively perform this task, the radar is equipped with antenna 1 having multiple radiation patterns 11, 12, 13, and 14, whose traditional function is:

[0079] - and direction diagram 11, hereinafter referred to as SUM, to query and detect the target's synchronous response;

[0080] - Difference pattern 12, denoted as DIFF, is used to precisely locate the target within the SUM beam;

[0081] - Control direction diagram, represented as CONT (see...) Figure 1a In the context of one option of the invention, it can advantageously be divided into two radiation patterns (therefore this option can employ separate treatment of three or four radiation patterns of the antenna):

[0082] ○ The first control pattern 13, denoted as CONT_Front, is used to block and reject responses from targets facing the antenna that are not present in the main SUM beam;

[0083] ○ The second control pattern 14, denoted as CONT_Back, is used to block and reject responses from targets at the rear of the antenna (therefore, this response may not necessarily exist in the main SUM beam).

[0084] In the remainder of this invention, this configuration using the radiation patterns CONT_Front and CONT_Back is considered, as these two radiation patterns may be processed separately. For Figure 1b For example, a reference to the channel CONT would likely include channels CONT_Front and CONT_Back.

[0085] For rotating antennas, ensure the following for rotary connector 2 and the antenna under-cable:

[0086] - RF coupling of signals transmitted at 1030MHz and received at 1090MHz independently between the rotating and stationary sections of the radar, using four radiation patterns (SUM, DIFF, CONT_Front, and CONT_Back).

[0087] - The distribution of the azimuth position 201 of the main lobe axis of the antenna.

[0088] Duplexer 3 ensures RF coupling between signals transmitted at 1030 MHz and received at 1090 MHz independently for each of the four radiation patterns. To this end, duplexer 3 includes a circulator associated with each channel. Figure 1b In the example, three circulators 311, 313, and 314 decouple the transmission at 1030MHz and reception at 1090MHz for the SUM, CONT_Front, and CONT_Back channels, respectively. In pure synchronous operation, after the transmission phase via the SUM and DIFF channels, listening is performed only via the radar's main lobe, i.e., via the SUM and DIFF channels. Since the DIFF channel operates only in reception, circulator 312 operates in only one manner, routing only the received signal obtained via the antenna (the circulator is optional, and its use on the DIFF has no other purpose than balancing the signals between SUM and DIFF to measure angular errors). In synchronous mode, listening via the CONT channel serves no other purpose than rejecting responses received with more energy under the CONT pattern than under the SUM pattern.

[0089] Filters 311', 313', and 314' are placed upstream of the circulators on the SUM, CONT_Front, and CONT_Back channels. These filters are primarily used downstream of the transmitter to filter harmonics of the transmitted signal. The same filters are also used in the receiver to protect against frequencies outside the secondary radar's useful band (i.e., approximately 1020 to 1100 MHz).

[0090] Therefore, the SUM and CONT channels are used for both sending and receiving. For readability reasons, Figure 1b (and Figure 1a Only the transmit / receive circuit 4 for the SUM channel is shown in the diagram (these circuits are the same for the CONT channel, or for the CONT_Front and CONT_Back channels):

[0091] -CONT channel ( Figure 1a ) and CONT_Front / CONT_Back channels ( Figure 1b The architecture of the transmitting and receiving circuit 4' is similar to that of the transmitting and receiving circuit of SUM.

[0092] The circuit 4' of the -DIFF channel is not shown and is the same as the circuit for the SUM receiver.

[0093] Space-time management 5 ensures real-time management of interrogation periods and associated listening periods for various secondary protocols: IFF, SSR, and S-mode protocols. Specific protocol-specific signal processing 6 utilizes signals obtained via various pattern SUM, DIFF, CONT_Front, and CONT_Back.

[0094] Refer again Figure 1b The transmit / receive unit 4, associated with the SUM channel and located between the circulator 311 of the replicator and the space-time management 5 and signal processing 6, will now be described. This transmit / receive unit 4 includes an adaptation specific to the present invention. Specifically, the SUM transmit chain 401, transmitting at 1030 MHz, incorporates additional filtering operations 4A, 4B, dedicated to reducing transmit noise, and more specifically rejecting parasitic signals at 1090 MHz, to maintain the residual noise level at the receiver's noise level after coupling 311. The transmit chain includes a first amplifier 8 performing a first amplification; it is followed by a first filter 4A. The latter is followed by a second amplifier 8', which is a power amplifier and delivers the transmit signal, and this amplifier is followed by a second filter 4B.

[0095] The SUM receiver chain 402, operating at 1090MHz, typically includes a low-noise amplifier 9 and an analog-to-digital converter (ADC) 9'. It also includes, as with the transmit chain, additional filtering operations 4C, 4D, specifically designed to reject parasitic signals originating from the transmit channel at 1030MHz, in order to maintain the coupling level at the circulator (or due to antenna SWR) and to maintain baseband aliasing at the receiver's noise level. In particular, the receive channel includes an input filter 4C upstream of the low-noise amplifier 9. This filter is a bandpass filter designed to:

[0096] - Select a receiving signal within a frequency band of approximately 1090MHz;

[0097] - A very strong rejection of the approximately 1030MHz band originating from the transmit chain.

[0098] Figure 1b The configuration is a specific exemplary implementation, including a local oscillator (LO) 10 (oscillating at 1030 MHz) shared between transmit channel 401 and receive channel 402.

[0099] In the transmit channel upstream of the first amplifier 8, the transmit signal is modulated by modulator 12 at the frequency of local oscillator 10, i.e., 1030MHz. Filter 4E is inserted between the oscillator and modulator to filter noise at 1090MHz. In the receive channel, before analog-to-digital conversion 9', the received signal is mixed with the signal from the local oscillator by mixer 11 and then filtered by bandpass filter 13. Filter 4D is placed at the output of ADC 9' to filter the signal at 1030MHz.

[0100] The DIFF channel, which operates only in reception, includes a receive chain similar to the SUM channel's receive chain 402; specifically, it includes filtering operations 4C and 4D, which filter the signal transmitted at 1030 MHz. All SUM, DIFF, and CONT transmit and / or receive chains operate independently of each other.

[0101] The four radiation patterns of a civilian ATC antenna are processed separately, requiring a 4-channel receiver (if, as is usually the case, and as...). Figure 1a As shown, CONT_Front and CONT_Back are combined into a single CONT, which results in a 3-channel receiver.

[0102] Before any decoding of the response, each signal processing operation 6 independently matches its analysis band with the characteristics of the protocol it detects. This filtering operation, matched to each protocol used, allows for better performance by reducing noise levels, and thus allows for independent reduction of the detection threshold for each protocol to handle weaker signals.

[0103] Figure 2a The steps for implementing the present invention are shown. This implementation requires at least two steps.

[0104] Step 21 allows the conversion of a conventional S-mode secondary radar into a "full-duplex" meta-secondary sensor according to the present invention. In this step 21, various protocols are orthogonalized and the radar is adapted for asynchronous reception. Orthogonalization here means making the processing operations of the protocols completely independent. In practice, the orthogonalization of the protocols is implemented as follows:

[0105] - In 211 of the 1090MHz receive chain, by rejecting the query on the noise level of the 1090MHz chain at 1030MHz, as... Figure 1b The filters 4C and 4D are shown;

[0106] - In 212 of the 1030MHz transmission chain, signals transmitted at 1090MHz are rejected due to noise levels below 1090MHz, such as... Figure 1b The filters 4A and 4B are shown;

[0107] - On the receiving side, by matching the analysis band (BeamWidth_BW) with the characteristics of the adopted protocol 213, specifically making:

[0108] ○BW_IFF>BW_SSR>BW_MS>BW_ADS-B, where BW_IFF, BW_SSR, BW_MS and BW_ADS-B are the bandwidths of IFF, SSR, S mode and ADS-B, respectively.

[0109] - By listening simultaneously in asynchronous mode:

[0110] • The largest number of independent radiation patterns detected by secondary radar;

[0111] • Optionally, 214, the direction graphs CONT_Front and CONT_Back can be processed separately;

[0112] ·Also optional 215, only the CONT_back pattern receiver side can be extended to ensure RF coverage at high elevation angles and a complete kit at 360° azimuth angle.

[0113] In step 22, the orthogonality of the protocol is utilized operationally:

[0114] - In the field of civil air control 23 or ATC surveillance:

[0115] • Listen to ADS-B messages in asynchronous mode via three or four direction maps, independently of synchronous activities;

[0116] • By optimizing the duration of the sequence of round-call transactions, there are no other major restrictions except for the absence of overlapping listening periods, in order to avoid “response confusion” and non-overlapping of queries (achieved essentially due to the singleness of the sender), and this is done when all-call listening periods and round-call sending periods are performed simultaneously.

[0117] -In the field of military air control 24 or IFF identification:

[0118] • Via the IFF interrogator, which performs its identification transaction and uniquely restricts access to the transmission resources shared with SSR / S mode monitoring;

[0119] • Listen to Mode 5 Level 2 messages simultaneously via three or four directional maps, independently of synchronous activities;

[0120] -In the field of airborne environmental control 25:

[0121] • Listen simultaneously via three or four directional diagrams, independently of synchronous activities, for any type of secondary response (including time-asynchronous error responses (FRUIT)).

[0122] Figure 2b and Figure 2c Sequences of interrogation in IFF and SSR / S modes are shown respectively for radar according to the prior art and radar according to the present invention. Therefore, Figure 2b An example of a sequence of three consecutive time periods illustrates the conventional operation according to the prior art:

[0123] - Period N+2: All Call (AC), dedicated to All Call SSR and S Mode transactions;

[0124] - Period N+3: Round Robin (RC), dedicated to Round Robin S mode transactions;

[0125] - Period N+1: IFF, specifically for military mode.

[0126] If the dwell time on the target allows, the radar can at most [based on] Figure 2b The sequences shown above interweave time periods.

[0127] If the dwell time is not allowed, i.e., the antenna rotation speed is high (the most common case), the radar will perform military IFF identification, which is detrimental to civilian surveillance. These three time periods cannot occur within the available dwell time.

[0128] Figure 2c An example of operation according to the invention is shown. In this case, transactions can overlap from one time period to the next, and in particular, IFF identification can be extended to time periods N+2 and N+3. Specifically, the radar according to the invention performs IFF transactions independently of the AC and RC time periods at their own specific rates (completely different from the rates of SSR and S-mode transactions), while the AC and RC time periods remain dedicated to SSR and S-mode. This function is orthogonalized (see...). Figure 2a ) Utilize RF isolation between transmission and reception (see Figure 1b This allows for both of the following:

[0129] - IFF detection is still performed despite numerous S-mode transmissions (see...) Figure 2c (Time periods N+1 and N+3);

[0130] -S mode detection is still performed despite a small number of IFF transmissions (see...) Figure 2c (Time periods N+1 and N+2).

[0131] Even with the use of high-speed rotating radar, this enables simultaneous IFF military identification and civilian surveillance.

[0132] Figure 3 An example of the operation according to step 23 above is shown, which optimizes ATC surveillance. This example of utilization is shown for three aircraft 31, 32, and 33 present in the environment of the radar according to the invention. ADS-B messages are simultaneously listened to via the radar's SUM pattern, DIFF pattern, CONT_Front pattern, and CONT_Back pattern. These simultaneous listening operations allow for the avoidance of overlap of asynchronous responses from targets located at different off-axis angles, thereby improving their detection and decoding. The aircraft broadcast asynchronous ADS-B responses 30 omnidirectionally. The response of the first aircraft 31 is therefore received via the SUM pattern, the response of the second aircraft 32 is therefore received via the CONT_Front pattern, and the response of the third aircraft 33 is therefore received via the CONT_Back pattern. Thus, in this example, the independent ADS-B reception of each pattern of the antenna allows for the detection of these three messages even though they are simultaneous in time.

[0133] Figure 4a It shows the function of azimuth. Figure 1a The gain of the radiation pattern of a traditional ATC secondary antenna. More accurately, Figure 4a The signal amplitude received from a given target is quantized via a curve along 360° (relative to + / - 180° of the antenna), depending on its azimuth angle of 40° relative to the radar's antenna axis. In synchronized radar operation, the dominant radiation pattern is SUM, which ensures the transmission of useful interrogations and the reception of useful responses. The CONT_Front and CONT_Back radiation patterns are used to guarantee higher SUM sidelobes, i.e., to provide relative gain to avoid erroneous radar detection (from targets not on the axis).

[0134] In contrast, in asynchronous mode reception of ADS-B and IFF messages, CONT_Front and CONT_Back play a dominant role: their absolute gain defines the range of the ADS-B receiver, and their 360° coverage is reflected in the time coverage of the listening operation. At medium ADS-B range, the time coverage level of the listening operation performed via CONT_Front and CONT_Back is 75%, a result of conventional ATC secondary antenna designs, which yield the following results:

[0135] - In its principal plane, that is, at azimuth angles of +90° and -90°, radiation is zero, which will not impair the synchronous operation of the radar perpendicular to the antenna plane.

[0136] - On the antenna axis, the gain of CONT_Front is intentionally attenuated in synchronization mode: This intentional reduction in CONT_Front gain is provided to ensure that the azimuth angle between CONT_Front and the radar beam is completely different in synchronization mode.

[0137] Therefore, in addition to listening via CONT_Front, listening is also performed via SUM (or even via DIFF), ensuring approximately 5% time coverage by filling the gain drop of the CONF_Front pattern perpendicular to the antenna plane. Overall, listening independently and therefore simultaneously in asynchronous mode via two or three antenna patterns (SUM, CONT or SUM, CONT_Front, CONT_Back) ensures that the time coverage of asynchronous mode listening operation is approximately 80% in the medium ADS-B range and at least 50% in the maximum ADS-B range.

[0138] Figure 4b The complementarity of the azimuth radiation 41 of the CONT_Back pattern according to the present invention is shown. The aim is to ensure that the 1090 MHz receiver-side radiation pattern has the same level across the entire coverage area of ​​CONT; thus, to ensure that the reception of ADS-B and IFF messages reaches the maximum ADS-B and IFF range, with 100% time-of-use coverage.

[0139] Figure 4c It shows the function of elevation angle. Figure 1a The gain of the radiation pattern of a conventional ATC secondary antenna is shown. The radiation patterns for SUM, CONT_Front, and CONT_Back are illustrated, with their maximum azimuth angles as follows:

[0140] - Typically, the maximum value of the SUM pattern (see...) Figure 4a It is approximately 15 to 20 dB higher than CONT_Front;

[0141] - Leakage of the SUM pattern of the front panel opposite the antenna plane normal is typically below -35dB.

[0142] As can be seen from the design, the ATC secondary antenna exhibits a significant gain drop at high elevation angles, i.e., elevation angles exceeding 50°. Therefore, secondary radars typically do not detect within the stationary cone of space (CoS) extending from a 45-degree elevation angle. The ADS-B function, integrated into the radar and using the same antenna, has the same type of CoS.

[0143] Figure 4d The complementarity of the elevation radiation 43 of the CONT_Back pattern according to the invention is shown. The aim is to ensure a receiver-side radiation pattern of 1090 MHz even at very high elevation angles (>85°), allowing for the reception of ADS-B and IFF messages via this extension of the CONT_Back pattern to high elevation angles.

[0144] Figure 5 and Figure 6 This demonstrates the advantages of the present invention regarding the sequence of round-robin and all-call transactions. More precisely, relative to a reference... Figure 2a The second step 22 described, Figure 5 The conventional sequence used with radar according to existing technology is shown, and Figure 6 A sequence optimized for use with the radar according to the present invention is shown.

[0145] exist Figure 5 In this context, the time periods for all-call (AC) transactions and round-robin (RC) transactions are consecutively at rates 51 and 52. As an example, Figure 5 The diagram shows four consecutive time periods, m, m+1, m+2, and m+3, during the dwell time of the radar antenna lobe, corresponding to the AC and RC time periods, respectively. These AC and RC time periods are separate, as are the transmission and reception phases they contain.

[0146] Figure 6 The rates 61 and 62 for AC and RC interrogation, as shown and corresponding to the radar according to the invention, are different. The RC period is shorter. In particular, the invention advantageously allows for optimization of the duration of the paging transaction sequence, since paging transmissions may or may not be sent during the paging or all-call listening phase. More specifically, the invention allows:

[0147] - Reduce the duration of the RC period.

[0148] - Interweaving AC and RC sessions (selectively listening to RC begins during the AC session),

[0149] Therefore, the lower limit of the dwell time on the target is reduced: the antenna lobes now cover seven AC or RC phases (m to m+6).

[0150] Figure 7 Another possibility for the sequence of AC and RC time periods of the radar according to the invention is shown. The sequence of AC and RC time periods, for example, is... Figure 5 The situation is the same. In order to allow the aircraft to be managed before entering the radar's operational coverage, the RC listening operation 71, which begins in the AC period, continues during the start of the RC transaction phase, which must begin with an interrogation (synchronization mode), so there is no loss of dwell time with respect to targets present in the operational coverage.

[0151] The goal here is to optimize independently of the previous RC period (see...). Figure 6 This system detects targets outside the radar's operating range but within its electromagnetic range, thereby reducing the number of DF11 responses generated by these targets in response to the radar's interrogation.

[0152] -It unnecessarily consumes their response potential;

[0153] Their responses contaminate other radars, especially those closest to the target.

[0154] Figure 8a A diagram of kit 215 is shown, which is used to extend the 1090MHz receiver-side CONT_Back pattern in both the azimuth (approximately -90° and +90°) and elevation angles exceeding 50° in a 3-pattern antenna configuration presented in an illustrative manner (see [reference]). Figure 2a The kit 215 is added to the conventional structure of antenna 1, which includes:

[0155] -N column P-radiative dipole group 80 front face (forming radiation patterns SUM, DIFF and CONT_Front),

[0156] -P radiation dipoles on the back side of column 90 form the radiation pattern CONT_Back.

[0157] The distribution circuit 800, well known in the art, distributes signals to channels SUM, DIFF, and CONT (CONT_Front and CONT_Back).

[0158] As described below, this kit for expanding the CONT_Back pattern is designed to fill the detection aperture, especially in Figures 4a to 4d As shown in the image.

[0159] To avoid interrupting radar synchronization, pattern extension 215 is limited to requirements related to the reception of ADS-B and IFF messages. For example... Figure 8b As shown in the exemplary embodiment, the extension is positioned opposite the front panel and thus extends CONT_Back. The radiating portion of the extension kit is divided into three directional patches 81, 82, and 83 in the plane (e.g., lobes of + / -35°):

[0160] - An 81, used to fill the static cone with an elevation angle of approximately 110° at its azimuth and 180° azimuth.

[0161] - The second 82 is used to fill the right detection hole at an azimuth angle of 90°, with its directional plane having an elevation angle tilt of approximately 0°.

[0162] - The third 83 is used to fill the left detection hole with an azimuth angle of -90°, and its directional plane has an elevation angle tilt of about 0°.

[0163] The signal is routed between the distribution circuit and column 90 (normal CONT_Back) and the three patches 81, 82, and 83 are handled in a normal manner by a set of circulators, couplers, and summers.

[0164] Figure 8b This diagram illustrates a possible arrangement of the radiating elements 81, 82, and 83 according to the invention on a conventional ATC secondary antenna 1. The "right" patch 82 and the "left" patch 83 are located at the rear end of the antenna plane, respectively. The patch 81, assigned to the stationary cone, is located at the center of the rear end of the antenna plane.

Claims

1. Secondary radar, including an antenna (1), the antenna having radiation patterns forming a SUM channel, a radiation pattern forming a DIFF channel, and a pattern forming a CONT channel, a first transmit-receive chain (4) associated with the SUM channel, and a second transmit-receive chain (4') associated with the CONT channel, and a receive chain (4'') associated with the DIFF channel, characterized in that: - Each of the transmit-receive chains (4, 4') includes a transmit chain (401) and a receive chain (402) capable of simultaneous transmission and reception, the transmit chain (401) including filtering operations (4A, 4B) for filtering signals transmitted at 1090 MHz and the receive chain (402) including filtering operations (4C, 4D) for filtering signals transmitted at 1030 MHz, and the receive chain (4'') associated with the DIFF channel includes filtering operations (4C, 4D) for filtering signals transmitted at 1030 MHz, such that the transmit chain (401), the receive chain (402), and the receive chain (4'') associated with the DIFF channel operate independently of each other, and during synchronous interrogation transmission, the received-side signal level remains unchanged; - The processing device (6) includes matching the received-side frequency band to the characteristics of each transaction protocol used; - The receive chains of the SUM channel, the DIFF channel, and the CONT channel are each capable of simultaneously listening in synchronous and asynchronous modes to signals received from a target via the SUM pattern, the DIFF pattern, and the CONT pattern respectively, the operations of listening in synchronous and asynchronous modes are independent of each other, and during synchronous interrogation transmission, the received-side signal level remains unchanged.

2. The secondary radar according to claim 1, wherein The CONT pattern includes a front radiation CONT_Front pattern forming a channel and a back radiation CONT_Back pattern forming a channel, and the CONT_Front pattern and the CONT_Back pattern are processed separately such that each of the transmit-receive chains (401, 402) is applied to the CONT_Front channel and the CONT_Back channel.

3. The secondary radar according to claim 2, wherein It includes a kit for expanding the radiation pattern of the CONT_Back channel, which is placed on the back of the antenna (1), and the kit includes three radiation patches: - A first patch (81) for filling an elevation detection hole called a quiet cone; - A second patch (82) for filling a detection hole at an azimuth of 90°; - A third patch (83) for filling a detection hole at an azimuth of -90°.

4. The secondary radar according to any one of the preceding claims, characterized in that, Each of the transmit chains includes filtering operations (4A, 4B) dedicated to rejecting parasitic signals transmitted at 1090 MHz.

5. The secondary radar according to claim 1 or 2, characterized in that, Each of the receive chains includes filtering operations (4C, 4D) dedicated to rejecting parasitic signals at 1030 MHz originating from the transmit channel.

6. The secondary radar according to claim 1 or 2, characterized in that, Having an ATC surveillance (23) task, the secondary radar performs simultaneous listening operations separately for ADS-B messages via the pattern and independently of synchronous transactions.

7. The secondary radar according to claim 1 or 2, characterized in that, Having an IFF recognition task, the secondary radar performs synchronous IFF detection independently of synchronous SSR and S-mode transactions.

8. The secondary radar according to claim 1 or 2, characterized in that, Having an IFF recognition task, the secondary radar performs a simultaneous listening operation for Mode 5 level 2 messages separately via the pattern independently of synchronous transactions.

9. The secondary radar according to claim 1 or 2, characterized in that, Having an air environment control (25) task, the secondary radar performs a simultaneous listening operation for any type of secondary response separately via the pattern independently of synchronous transactions.

10. The secondary radar according to claim 1 or 2, characterized in that, The radar transmits continuously during the all-call interrogation period and the selective-call interrogation period, and the selective-call interrogation (63) starts during the all-call interrogation period.

11. The secondary radar according to claim 1 or 2, characterized in that, The radar transmits continuously during the all-call interrogation period and the selective-call interrogation period, and the all-call listening operation (71) starting during the all-call period continues during the selective-call period.

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