Interrogator device for a radar system, having improved performance

Abstract

An interrogator device (25) for a radar system (20) is configured to emit a multi-beam antenna pattern comprising a first beam (∑) and a second beam (Δ). The interrogator device comprises a signal generation stage (40, 30, 31, 33) configured to generate a first signal (P6) and generate a second signal (P5), wherein the first signal temporally overlaps, at least in part, with the second signal; and a radiating stage (34, 35) configured to receive a third signal (P5+P6) indicative of a sum of the first signal and the second signal and, in response, to emit the first beam (∑) so that the first signal is transmitted over the first beam (∑) and to emit the second beam (Δ) so that the second signal is transmitted over the second beam (Δ). The signal generation stage is configured to adjust at least one of phase and amplitude of at least one of the first signal and the second signal, so as that an amplitude of the third signal is constant during transmission of at least one of the first signal and the second signal.

Description

[0001] “INTERROGATOR DEVICE FOR A RADAR SYSTEM, HAVING IMPROVED PERFORMANCE”

[0002] Cross-Reference to Related Applications

[0003] This Patent Application claims priority from European Patent Application No. 24184935.5 filed on June 27, 2024 and from Italian Patent Application No. 102024000024660 filed on November 04, 2024 the entire disclosures of which are incorporated herein by reference.

[0004] Technical Field of the Invention

[0005] The present invention relates to an interrogator device for a radar system. The present invention finds preferred, although not exclusive, application to an interrogator device for a Secondary Surveillance Radar (SSR) system and, in particular, to an interrogator configured to perform a mode-S interrogation.

[0006] State of the Art

[0007] As is known, a Secondary Surveillance Radar (SSR) is a collaborative radar system wherein an interrogator device sends an interrogation signal and the target is provided with a transponder that is configured to receive the interrogation signal and, in response, to send an information signal back to the interrogator device.

[0008] SSR radars are mainly used in avionics and aeronautical applications, for example for air traffic control (ATC), and can be used for ground-aircraft communication or aircraft-aircraft communication.

[0009] Among the different interrogation techniques that can be used for the implementation of an SSR radar, mode-S interrogation is based on a two-beam antenna pattern in order to perform interrogation sidelobe suppression (ISLS).

[0010] In detail, mode-S interrogation provides for the emission, by the interrogator device, of an interrogation beam (also referred to as sum beam and usually indicated by ) and a control beam (also referred to as delta beam or difference beam and usually indicated by A).

[0011] As depicted in the illustrative Figures 1 and 2, the delta beam radiation pattern is designed to be below the sum beam radiation pattern within the main beam (e.g., within an angle deviation range of ±0.5° with respect to the signal source), and above the sum beam outside of the main beam. For mode-S interrogation, Figure 3, the interrogation signal (indicated herein by INT) comprises pulses Pl, P2 and P6 and is configured to carry interrogation data bits that are modulated during the P6 pulse in Differential Binary Phase Shift Keying (DBPSK); and the control signal (indicated herein by CTRL) is used to perform ISLS and comprises a pulse P5 that has a short duration with a very low duty cycle.

[0012] In the mode-S interrogation, as shown in Figure 3, the ISLS is performed by transmitting pulse P5 over the delta beam A and pulse P6 over the sum beam X, so that pulses P5 and P6 partially overlaps in time one with the other.

[0013] In detail, at the time of transmission of pulse P5, pulse P6 has a synch phase reversal event.

[0014] If a receiver device (for example a transponder of a target aircraft), when receives the mode-S interrogation waveform, is within the main beam, then the amplitude of pulse P5 is lower than the amplitude of pulse P6; therefore, the synch phase reversal event of P6 is correctly detected by the receiver device.

[0015] If, on the contrary, the receiver device is outside the main beam, then the amplitude of pulse P5 is higher than the amplitude of pulse P6; therefore, the synch phase reversal event of P6 is not detected by the receiver device.

[0016] This mechanism allows the receiver device to reply to the received mode-S interrogation, only when it recognizes to be in the main beam.

[0017] If the interrogator device has a mechanically-scanned (M-SCAN) antenna array or a passive electronically-scanned (P-ESA) antenna array, then the interrogator device needs to have two separate active RF transmitter units (e.g. two amplifiers HPAs), one for providing the interrogation pulses to the external antenna elements (e.g., SUM port) and one for providing the control pulse to the external antenna elements (e.g., DELTA port).

[0018] Thus, the total available power Pafrom the interrogator device is:

[0019] Pa=PHPA wherein PHPA is the power of each transmitter unit.

[0020] However, since the interrogation data are carried only by the sum beam, the usable power Puof the interrogator device which determines the beam-range of the interrogator device, is only half of the available power Pa, in fact:

[0021] In avionics applications, where SWaP (Size, Weight and Power) is a crucial figure of merit, the fact that only one half of the hardware is fully used, is a significant drawback. Since several years, radar systems are become more and more diffused wherein the antenna array is an active electronically scanned array (AESA). AESA systems have been employed in ground equipment and recently is being applied also inside aircrafts.

[0022] Figure 4 shows the block diagram of a known interrogator device 1 of an SSR radar system that is configured to perform mode-S interrogation and is based on AESA antenna array.

[0023] The interrogator device 1 is configured to emit a total RF output signal including the sum beam and the delta beam discussed above.

[0024] The interrogator device 1 transmits the interrogation signal over the sum beam X and the control signal over the delta beam A.

[0025] In detail, the interrogator device 1 comprises a sum beamformer 3, a delta beamformer 4 and an antenna array 5 that has a number N of transmitters ‘HP A’ and antenna elements ‘Ant’ couples.

[0026] The sum beamformer 3 receives the interrogation signal X, the delta beamformer 4 receives the control signal A and each provide N copies of the respective signals X, one for each of the N antenna couples.

[0027] The outputs of the sum and delta beamformers 3, 4 are summed together and each resulting signal is then amplified (amplifiers HP A) and transmitted to a respective antenna radiating element, for the emission of the total output RF signal.

[0028] If the antenna array 5 has N antenna elements, then the total available power Pafrom the interrogator device 1 is

[0029] Pa=PHPA, wherein PHPA is the maximum output power of each transmitter HP A.

[0030] Since the maximum power of each transmitter HP A is PHPA, when the interrogator device 1 transmits pulses P5 and P6 simultaneously, the RF power used for the sum and delta beam has the following limit:

[0031] Therefore, the RF power transmitted over the sum beam X, which is the one carrying the information to be transmitted to the target’s receiver, is one half of the available power Pa, similarly to the M-SCAN or P-ESA radar systems.

[0032] Based on the above, the interrogator device 1 is configured so that the envelope output signal (RFout) that is emitted by the interrogator device 1 has a non-constant amplitude over time, as illustrated in Figure 5.

[0033] This leads to the problem, also in the case of AESA radar systems, that the range of the interrogation achievable by the interrogator device is 0.7 times the maximum available, similarly to the M-SCAN and P-ESA radar systems.

[0034] Moreover, as shown in Figure 5, the known interrogator device 1 works with two different working points: one outside pulse P5, wherein the RF amplifiers work at half power; and one inside pulse P5 (i.e., during the transmission of pulse P5), wherein the RF amplifiers work at full power. However, this causes calibration issues of the interrogator device 1.

[0035] Therefore, the need is felt to improve the performance of the known interrogator devices that are configured to emit a multi -beam antenna pattern for the interaction with a target device.

[0036] Subject and Summary of the Invention

[0037] The aim of the present invention is to overcome the disadvantages of the prior art and satisfy at least in part the above-mentioned needs.

[0038] The present invention relates to an interrogator device, a method and a software, as claimed in the appended claims.

[0039] Brief Description of the Drawings

[0040] Figure 1 shows an example of a radiation pattern of a known interrogator device for mode-S interrogation.

[0041] Figure 2 shows a zoomed-in portion of an example of a radiation pattern of a known interrogator device for mode-S interrogation.

[0042] Figures 3 shows an example of mode-S interrogation waveforms provided by a known interrogator device.

[0043] Figure 4 shows the block diagram of a known interrogator device for mode-S interrogation having an AESA antenna array.

[0044] Figure 5 shows an example of an output envelope of the known interrogator device of Figure 4, during performance of mode-S interrogation.

[0045] Figure 6 shows the block diagram of a radar system, according to the invention.

[0046] Figure 7 shows the block diagram of an interrogator device of the radar system of Figure 6, for mode-S interrogation and having an AESA antenna array, according to an embodiment of the invention.

[0047] Figure 8 shows an example of waveforms of the interrogator device of Figure 7, in use, during a mode-S interrogation, according to an embodiment.

[0048] Figure 9 shows an example of an I-Q diagram of the waveforms of Figure 8, according to an embodiment.

[0049] Figures 10A-10D show examples of I-Q diagrams of the waveforms of Figure 8, during different steps of a mode-S interrogation, according to an embodiment.

[0050] Figure 11 shows an example of an output signal envelope of the interrogator device of Figure 7 during mode-S interrogation.

[0051] Detailed Description of Preferred Embodiments of the Invention

[0052] The following description is provided to enable a person skilled in the art to make and use the invention. Various modifications to the embodiments will be readily apparent to those skilled in the art, without departing from the scope of the claimed invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein and defined in the appended claims.

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments disclosed belongs. In the case of conflict, the present specification, including definitions, will prevail. In addition, the examples are illustrative only and not intended to be limiting.

[0054] For the purposes of facilitating understanding of the embodiments described herein, reference will be made to certain embodiments and specific language will be used to describe the same. The terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present disclosure.

[0055] Figure 6 shows schematically a radar system 20 comprising an interrogator apparatus 21 and a target 22, wherein the interrogator apparatus 21 is configured to emit an output electromagnetic signal (e.g., radio-frequency signal RFout) and detect an incoming electromagnetic signal (e.g., radio-frequency signal RFin) coming from the target 22.

[0056] The radar system 20 is for avionics or aeronautics applications; for example, the interrogator apparatus 21 may be a ground station communication, an aircraft or the like, and the target 22 may be an aircraft or the like.

[0057] Preferably, the radar system 20 is a Secondary Surveillance Radar (SSR) radar system.

[0058] In detail, the interrogator apparatus 21 comprises an interrogator device 25 that is configured to perform an interrogation, e.g. by emitting the output signal RFout, of the target 22. The target 22 comprises a receiving device 26, for example a transponder, that is configured to receive the output signal RFout emitted by the interrogator device 25 and, in response, send back a response signal (e.g., signal RFin) to the interrogator apparatus 21.

[0059] The interrogator device 25 is configured to emit a two-beam antenna pattern that comprises a sum beam X and a delta beam A, for interacting with the receiver 26 of the target 22.

[0060] In particular, reference will be made hereinafter, with reference to Figure 7, to the case in which the interrogator device 25 is configured to perform a mode-S interrogation.

[0061] The interrogator device 25 is configured to transmit interrogation data through the sum beam

[0062] The delta beam A is configured to be used for sidelobe suppression. In detail, the interrogator device 25 is configured so that the radiation pattern of the delta beam A is below (e.g., has a lower amplitude than) the sum beam X inside the main beam, and over (e.g., has a higher amplitude than) the sum beam X outside the main beam.

[0063] For example, the expression “main beam” is used to indicate an angular deviation, measured with respect to the emission source of the interrogator device 25, that is within a desired range. For example, the angular deviation may be within few degrees, for example ±0.5°.

[0064] The interrogator device 25 comprises a signal generation stage having an interrogation-signal generation stage 30 that is configured to generate an interrogation signal INT to be transmitted over the sum beam X, and a control -signal generation stage 31 that is configured to generate a control signal CTRL to be transmitted over the delta beam A.

[0065] The signal generation stage also comprises an adder 33 that is configured to sum the interrogation signal INT and the control signal CTRL.

[0066] In the present disclosure, wherein reference is made to mode-S interrogation, with the expression interrogation signal INT, it is intended to indicate in particular the respective pulse P6 of the mode-S interrogation and, with the expression control signal CTRL, it is intended to indicate in particular the respective pulse P5 of the mode-S interrogation.

[0067] The interrogator device 25 comprises a beamforming network (or beamformer) 34, and an antenna array 35.

[0068] Preferably, the antenna array 35 is an AES A (“Active Electronically-Scanned Array”) antenna array comprising a plurality of transmitters, in particular N transmitters 36_1,...,36_N, coupled to a plurality of antenna radiating elements, in particular N antenna elements 37_1 , . . . ,37N.

[0069] Each transmitter 36_1,... ,36_N may comprise a respective RF amplifier, e.g., a high-power amplifier HPA.

[0070] In detail, each transmitter 36 1,. . ,,36_N is coupled to a respective antenna element 37_1 , . . . ,37_N for feeding thereof.

[0071] The beamformer 34 is configured to receive the summed output signal (INT+CTRL) from the adder 33, generate a plurality of copies of the summed signal and provide the pluralities of copies of the summed signal each to a respective couple of the antenna array 35, so as to obtain the desired radiating pattern out of the interrogator device 25.

[0072] In detail, each of the RF amplifiers 36 1,. . ,,36_N receives a respective copy of the summed signal from the beamformer 34 and feeds the respective antenna element 37_1,...,37_N.

[0073] A local oscillator 40 may generate a source signal SRC, for example an RF electric signal, from which the interrogation-signal generation stage 30 and the control -signal generation stage 31 each generate the respective signals INT and, respectively, CTRL.

[0074] The source signal SRC may be for example a clock signal, a continuous signal or a pulsed signal, for example having a sinusoidal or square-wave waveform, depending on the specific application and implementation.

[0075] The interrogation-signal generation stage 30 comprises a modulator 42 and an attenuation stage 43 cascaded one with the other.

[0076] The modulator 42 is configured to generate a modulated signal containing interrogation information to be carried by the interrogation signal INT, in particular to be carried during pulse P6 of the mode-S interrogation.

[0077] In detail, the modulator 42 may be configured to modulate the source signal SRC.

[0078] Preferably, the modulator 42 is configured to perform a Differential Binary Phase Shift Key (DBPSK) modulation. However, the modulator 42 may be configured to perform other known kind of modulations, depending on the specific type of the radar system 20, specific application and the like.

[0079] The attenuation stage 43 is configured to provide a variable attenuation during the mode-S interrogation, depending on the current step of the mode-S interrogation.

[0080] The attenuation stage 43 is configured to apply one of a plurality of attenuation values, depending on the current step of the interrogation. The attenuation values may depend also on the phase relation between the interrogation signal INT and the control signal CTRL; in particular, the phase relation between pulses P6 and P5. In the embodiment of Figure 7, the attenuation stage 43 comprises a first branch 44 that is configured to provide an attenuation value of 1 (that is, not to provide any attenuation), a second branch 45 that is configured to provide an attenuation of 1 / V2 , and a switch 46 that is configured to select either the first branch 44 or the second branch 45 based on the attenuation to be provided.

[0081] The control -signal generation stage 31 comprises a phase shifter 50, a pulse modulator 51 and an attenuator 52.

[0082] The phase shifter 50 is configured to introduce a phase shift, so that the control signal CTRL is phase-shifted with respect to the interrogation signal INT; in particular, so that pulse P5 is phase-shifted with respect to pulse P6.

[0083] Preferably, the phase shifter 50 is configured to introduce a phase shift of 90°; this can simplify the design and application of the interrogator device 25. In particular, the phase shift may be substantially equal to 90°; that is, comprised within a range comprising the value 90°. The range may be centered around 90° or not centered around 90°. For example, the phase shift may be comprised within 80° and 100° and, in particular, between 85° and 95°.

[0084] The pulse modulator 51 modulates the waveform of the source signal so as to obtain the desired waveform for the control signal CTRL (i.e., pulse P5).

[0085] In the embodiment of Figure 7, the attenuator 52 provides a fixed attenuation; however, the attenuator 52 may provide a variable attenuation depending on the specific application and implementation of the interrogator device 25.

[0086] In particular, the attenuator 52 is configured to provide an attenuation of 1 / V2. However, the attenuation value may be different and depend on the phase relation between the interrogation signal INT and the control signal CTRL.

[0087] A method for performing an interrogation by the interrogator device 25 will be described hereinafter.

[0088] In detail, the method will be described with reference to a case wherein the interrogator device 25 is configured to perform a mode-S interrogation and, in particular, the disclosure herein will be limited to the transmission of pulses P5 and P6 of the mode- S interrogation.

[0089] It will be clear that, during a mode-S interrogation, the interrogator device 25 may be configured to transmit also pulses Pl and P2, as discussed with reference to Figure 3 and / or perform any other that can be useful for the execution of a mode-S interrogation, which are per se known and therefore not explicitly disclosed herein. If not explicitly mentioned otherwise herein, the mode-S interrogation described herein may be compliant with the mode S-interrogation as disclosed in Annex 10, Volume IV, of the International Civil Aviation Organization (ICAO), in particular in the most recent version thereof at the date of filing of the present patent application.

[0090] Figure 8 shows the waveforms of the interrogation signal INT and the control signal CTRL during transmission of pulses P6 and P5, respectively.

[0091] The transmission of pulses P6 and P5 may be divided into four steps: 60, 61, 62, 63.

[0092] During step 60, the interrogator device 25 starts transmission of pulse P6. In detail, pulse P6 starts at time instant ti, at an edge (in particular here a rising edge) of the interrogation signal INT.

[0093] During step 60, the interrogator device 25 transmits the interrogation signal INT at full power or amplitude (indicated by way of example by ‘ 1’ in Figure 8). In practice, during step 60, the attenuation stage 43 of the interrogation-signal generation stage 30 keeps the switch 46 to select the first branch 44.

[0094] During step 60, the control signal CTRL does not have any pulse. In other words, the amplitude of the control signal CTRL may be zero.

[0095] Step 60 starts at time instant ti and ends at time instant t2, wherein the interrogator device 25 starts transmission of pulse P5.

[0096] Figure 10A shows the interrogation signal INT in a phasor LQ diagram.

[0097] Step 61 starts at time instant t2.

[0098] In detail, pulse P5 starts at time instant t2, at an edge (in particular here a rising edge) of the control signal CTRL.

[0099] The control-signal generation stage 31 generates pulse P5 so that the amplitude or power of pulse P5 is 1 / V2 with respect to the full available amplitude or power.

[0100] Moreover, during step 61, the interrogation-signal generation stage 30 attenuates pulse P6 with respect to step 60, in particular by 1 / V2 (that is, 3dB in terms of power or 6dB in terms of voltage). In detail, the attenuation stage 43 of the interrogation-signal generation stage 30 keeps the switch 46 to select the second branch 45.

[0101] Since the interrogation signal INT and the control signal CTRL have a phase shift of, substantially, 90° one from the other, the sum of pulses P5 and P6 is still 1 (that is, they sum to full power), as also graphically shown in the phasor diagram of Figure 10B.

[0102] In practice, during step 61, the total amplitude of the sum of pulses P5 and P6 is the same as the one of step 60. At a time instant t3, pulse P6 has a synch phase reversal event (for example, because of the modulation introduced by the modulator 42). The first synch phase reversal event of pulse P6 (at instant ts) may be at a fixed time distance with respect to start of pulse P6 (instant ti) and may be configured to fall within pulse P5. The first synch phase reversal event at instant t3 may be used by the receiver device 26 of the target 22 for synchronization thereof.

[0103] Step 62 starts at time instant t3.

[0104] Figure IOC shows the phasor diagram of signals INT, CTRL during step 62. As shown in Figure IOC, the phase of interrogation signal INT is 180° shifted with respect to step 61 (Figure 10B).

[0105] During step 62, the interrogator device 25 keeps the same amplitude as in step 61.

[0106] Therefore, also during step 62, the total amplitude of the sum of pulses P5 and P6 is kept at 1.

[0107] At time instant t4, the interrogator device 25 interrupts transmission of pulse P5 (falling edge of the control signal CTRL).

[0108] Step 63 starts at time instant t4. During step 63, the interrogator device 25 transmits only pulse P6. Therefore, the interrogation-signal generation stage 30 generates the interrogation signal INT without any power reduction with respect to full power. In practice, during step 63, the attenuation stage 43 of the interrogation-signal generation stage 30 keeps the switch 46 to select the first branch 44.

[0109] Figure 10D shows the phasor diagram of the interrogation signal INT and the control signal CTRL during step 63.

[0110] The interrogator device 25 transmits the interrogation data bits over the interrogation signal INT (e.g., through the DBPSK modulation) during pulse P6 and after transmission of pulse P5. In other words, the interrogation data bits are transmitted during step 63.

[0111] The interrogation data bits are the information to be communicated to target 22 for performing the interrogation.

[0112] Figure 9 shows, in one phasor diagram, both signals INT and CTRL during all the four steps 60-63.

[0113] It emerges from the above that the envelope of the total RF output signal emitted by the interrogator device 25 during the mode-S interrogation (and in particular during transmission of pulses P5 and P6) has a constant amplitude during performance of the whole interrogation, as also schematically shown in Figure 11.

[0114] In detail, RF power is kept constant during transmission of all pulse P6. For example, the RF power may be kept constant at its maximum available power or at a different selected output power. Therefore, in case it is required to transmit a Mode-S interrogation at full power, the invention allows to use the whole available power from the RF amplifiers 36_1,...,36_N, that is:

[0115] Pu = PHPA.

[0116] Taking advantage of the entire available power, the range of the interrogation obtainable by the interrogator device 25 is increased up to a V2 factor compared to a traditional system (for example, the system of Figure 4).

[0117] Moreover, the fact that the amplitude of the summed signal INT+CTRL is kept constant for the whole length of pulse P6, implies that the input signal level received by the RF amplifiers 36_1,..,36_N is also kept constant; this allows to use only one calibration point for the RF amplifiers 36_1,..,36_N over the whole length of P6. Therefore, the interrogator device 25 has a simplified designing and a higher reliability.

[0118] In other words, the fact that the envelope amplitude of the sum of the interrogation signal INT and control signal CTRL is kept constant for whole transmission of pulses P5 and P6, allows to improve the performance of the interrogator device 25 and, accordingly, of the radar system 20.

[0119] Moreover, the fact that the phase shift during transmission of pulses P5 and P6 is kept at 90° further allows to use the same attenuation value of 1 / V2 for both the interrogation signal INT and the control signal CTRL, thereby further simplifying the design of the interrogator device 25.

[0120] In view of the above disclosure, it would be clear to the person skilled in the art that the invention may be applied to any interrogator device for a radar system wherein the interrogator device is configured to emit a multi-beam antenna pattern comprising a plurality of output beams (e.g., X and A beams) for the interaction with target device 22 and wherein two signals (e.g., pulses P5 and P6) are transmitted simultaneously over the different output beams.

[0121] Finally, it is clear that modifications and variations may be made to what has been described and illustrated herein, without thereby departing from the scope of the present invention, as defined in the annexed claims.

[0122] The orthogonality between the interrogation signal INT and the control signal CTRL may be generated by a different architecture than the one described with reference to Figure 7. For example, the interrogator device 25 may comprise the architecture described with reference to Figure 3 of EP3374790B 1, with the addition of the attenuators (43, 52) described herein with reference to Figure 7.

[0123] The interrogator device 25 may be configured to adjust only the phase shift or only the amplitude attenuation of either one or both of pulses P5 and P6, depending on the specific implementation, as long as the phase and / or amplitude are modified so as to keep the amplitude of the summed signal P5+P6 constant over the transmission of pulse P6 and / or P5.

[0124] For example, the interrogator device 25 may keep the phase shift between the interrogation signal INT and the control signal CTRL at a value different from 90°. In this case, the values of attenuation provided by the attenuation stage 43 and attenuator 52 may be modified accordingly, so as to maintain the total amplitude or power of the sum of the interrogation signal INT and control signal CTRL constant during transmission of pulses P5 and P6.

[0125] For example, the interrogator device 25 may be configured to apply the phase shift by means of the interrogation-signal generation stage 30 (i.e., apply the phase shift on the integration signal INT) and not by means of the control-signal generation stage 31. Alternatively, both the interrogation-signal generation stage 30 and the control-signal generation stage 31 may be configured to apply each a respective phase shift, so that the total phase shift between signals INT and CTRL corresponds to the desired one.

[0126] For example, the present interrogator device may have a radiating stage that comprises an antenna array different from what has been described herein, for example an M-SCAN or P-ESA type of antenna array.

[0127] The interrogator device 25 may be implemented by using digital, analogic and / or mixed signal electronics, depending on the specific application. In particular, the interrogation-signal generation stage 30, the control -signal generation stage 31, and preferably also the adder 33, may be implemented by using digital electronics, for example by means of FPGAs.

[0128] The beamformer 34 may be digital or analogic.

[0129] In case of digital implementation, the interrogator device 25 may also comprise one or more DACs, arranged before the amplifiers 36 1,. . . ,36_N.

[0130] In view of the above disclosure, the interrogator device according to the invention is configured to perform a method that comprises: generating first signal (P6) and second signal (P5), wherein the first signal temporally overlaps, at least in part, with the second signal; generating a third signal (P5+P6) indicative of a sum of the first signal and the second signal; emitting the third signal through a multi-beam antenna pattern comprising a first beam Qj) and a second beam (A), so that the first signal is transmitted over the first beam ( ) and the second signal is transmitted over the second beam (A); and adjusting at least one of phase and amplitude of at least one of the first signal and the second signal, so as that an amplitude of the third signal is constant during transmission of at least one of the first signal and the second signal.

[0131] The interrogator device according to the present invention may also comprise electronic resources such as one or more memories and processors, so that the interrogator device may store and execute a software adapted to cause the interrogator device to carry out the above-mentioned method.

[0132] Finally, the described embodiments may be combined to provide further solutions.

Claims

CLAIMS1. An interrogator device (25) for a radar system (20), configured to emit a multibeam antenna pattern comprising a first beam (X) and a second beam (A), wherein the interrogator device comprises: a signal generation stage (40, 30, 31, 33) configured to generate a first signal (P6) and generate a second signal (P5), the first signal temporally overlapping, at least in part, with the second signal; and a radiating stage (34, 35) configured to receive a third signal (P5+P6) indicative of a sum of the first signal and the second signal and, in response, to emit the first beam Qj) so that the first signal is transmitted over the first beam Qj) and to emit the second beam (A) so that the second signal is transmitted over the second beam (A), wherein the signal generation stage is configured to adjust at least one of phase and amplitude of at least one of the first signal and the second signal, so as that an amplitude of the third signal is constant during transmission of at least one of the first signal and the second signal.

2. The interrogator device (25) according to claim 1, wherein the signal generation stage (40, 30, 31, 33) is configured to adjust the phase of at least one of the first signal and the second signal and to adjust the amplitude of at least one of the first signal and the second signal.

3. The interrogator device according to claim 1 or 2, wherein the signal generation stage (40, 30, 31, 33) is configured to provide a phase shift between the first signal and the second signal that is comprised between 80° and 100°, in particular substantially equal to 90°.

4. The interrogator device according to any of the preceding claims, wherein the signal generation stage (40, 30, 31, 33) is configured, during an overlap period (t2-t4) wherein the first signal (P6) temporally overlaps with the second signal (P5), to set the amplitude of the first signal to a first attenuated value that is lower than a maximum amplitude value and to set the amplitude of the second signal to a second attenuated value that is lower than the maximum amplitude.

5. The interrogator device according to the preceding claim, wherein the firstattenuated value is the same as the second attenuated value.

6. The interrogator device according to any of the preceding claims, configured to emit the first beam and the second beam for performing an interrogation of a target device (26).

7. The interrogator device according to any of the preceding claims, wherein the first signal (P6) carries interrogation data and the second signal (P5) is a control signal configured to be used for sidelobe suppression.

8. The interrogator device according to any of the preceding claims, being configured to perform a mode-S interrogation, the first signal comprising pulse P6 of the mode-S interrogation and the second signal comprising pulse P5 of the mode-S interrogation.

9. The interrogator device according to any of the preceding claims, wherein the radiating stage comprises an Active Electronically-Scanned Array, AESA, antenna array (35).

10. The interrogator device according to any of the preceding claims, wherein the signal generation stage is configured to adjust at least one of phase and amplitude of at least one of the first signal and the second signal, so as that the amplitude of the third signal is constant during transmission of the first signal and the second signal.

11. The interrogator device according to the preceding claim when dependent on claim 8, wherein the signal generation stage is configured to adjust at least one of phase and amplitude of at least one of the first signal and the second signal, so as that the amplitude of the third signal is constant during whole transmission of pulses P5 and P6.

12. An apparatus (21) for avionics application, for example a ground station or an aircraft, comprising the interrogator device (25) according to any of the preceding claims.

13. A radar system (20), in particular a Secondary Surveillance Radar, SSR, comprising the apparatus according to the preceding claim.

14. A method, performed by an interrogator device (25) of a radar system (20), comprising: generating a first signal (P6); generating a second signal (P5), the first signal temporally overlapping, at least in part, with the second signal; generating a third signal (P5+P6) indicative of a sum of the first signal and the second signal; and emitting the third signal through a multi-beam antenna pattern comprising a first beam Qj) and a second beam (A), so that the first signal is transmitted over the first beam ( ) and the second signal is transmitted over the second beam (A), the method further comprising adjusting at least one of phase and amplitude of at least one of the first signal and the second signal, so as that an amplitude of the third signal is constant during transmission of at least one of the first signal and the second signal.

15. A software comprising instructions that, when executed by electronic resources of an interrogator device (25) for a radar system (20), cause the interrogator device to perform the method according to the preceding claim.

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