A high-isolation secondary radar response transmitting circuit, a response transmitter and a transponder

Abstract

The application discloses a secondary radar response transmitting circuit with high state isolation, a response transmitter and a responder, and relates to the technical field of secondary radar. The response transmitting circuit comprises a frequency source unit, a modulation unit, a signal amplification unit, a transceiving diversity unit and a detection unit which are electrically connected in sequence. The frequency source unit is powered on when receiving a frequency source power control signal and outputs a carrier signal, and is powered off when the frequency source power control signal is invalid. The modulation unit is used for modulating the carrier signal when receiving a transmitting code signal, and outputs a modulated radio frequency signal. The transmitting code signal is sent later than the frequency source power control signal, so that the carrier leakage of the frequency source before the modulation transmitting signal is suppressed. Finally, the signal amplification unit is used for amplifying the radio frequency signal, and the amplified signal is output to an antenna through the transceiving diversity unit and the detection unit. The problems that the carrier leakage influences the receiver work and reduces the sensitivity of the receiver are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary radar, in particular to a secondary radar response transmitting circuit with high off-state isolation, a secondary radar response transmitter and a responder. BACKGROUND

[0002] With the increasing number of aircraft in airspace, the functional requirements of air control systems are also increasing, and the demand for devices that integrate the functions of the Automatic Dependent Surveillance-Broadcast (ADS-B) system and the secondary radar responder is becoming more and more widespread. The working schematic diagram of the secondary radar responder integrated with the ADS-B system is shown in FIG. 1. The transmitting frequency of the secondary radar responder is 1090 MHz ± 1 MHz, and the receiving frequency is 1030 MHz ± 3 MHz. The transmitting frequency and the receiving frequency are not at the same frequency point, but the receiving frequency of the ADS-B system is 1090 MHz ± 3 MHz, which is at the same frequency point as the transmitting frequency.

[0003] The receiving sensitivity of the ADS-B system in the integrated ADS-B system and secondary radar responder is not less than -84 dBm, and the tangent sensitivity is -90 dBm. Since the receiving frequency of the ADS-B system and the carrier signal of the transmitter are both 1090 MHz, the ADS-B and the secondary radar responder share the same receiving channel, so the radio frequency filter at the front end of the receiving channel is a wideband filter with a passband frequency covering 1090 MHz and 1030 MHz. In this case, the carrier signal leaked from the transmitter will affect the sensitivity of the receiver, causing insufficient sensitivity and response probability.

[0004] The main technical idea to solve the carrier leakage of the transmitter is to add a program-controlled attenuator in the transmitting link, change the gain of the transmitting link by switching the attenuation value, and isolate each circuit with a shielded cavity to prevent signal coupling from being transmitted to the receiving port through space radiation. The problem with this approach is that the program-controlled attenuator and the cavity structure increase the complexity of the circuit and the device. The radio frequency circuit has unpredictability during debugging, making it difficult to adjust the attenuation. There are differences in the carrier leakage amplitude of the device at room temperature and high and low temperatures, and the radio frequency circuit needs to repeatedly adjust the attenuator value and the shielding isolation, which is a large amount of work and has low reusability. Physical isolation measures cannot guarantee that the cavity structure has no gaps, and the shielding effect cannot fully play its role. SUMMARY

[0005] The present application provides a secondary radar response transmitting circuit with high off-state isolation, a secondary radar response transmitter and a responder to solve the problem of carrier signal leakage coupling to the receiving port, affecting the sensitivity of the receiver and the response rate.

[0006] The present application is achieved by the following technical solutions:

[0007] The application provides a high off-state isolation secondary radar response transmitting circuit, which comprises a frequency source unit, a modulation unit, a signal amplification unit, a transceiver diversity unit and a detection unit connected in sequence.

[0008] The frequency source unit is used for being powered on when receiving a frequency source power control signal and outputting a carrier signal, and being powered off when the frequency source power control signal is invalid and not outputting any signal.

[0009] The modulation unit is used for modulating the carrier signal when receiving a transmitting code signal and outputting a modulated radio frequency signal, and the transmitting time of the transmitting code signal is later than that of the frequency source power control signal.

[0010] The signal amplification unit is used for amplifying the radio frequency signal and outputting an amplified signal.

[0011] The transceiver diversity unit is used for transceiver switching and filtering the amplified signal and outputting a filtered amplified signal.

[0012] The detection unit is used for detecting the filtered amplified signal and transmitting the filtered amplified signal to an antenna for transmission.

[0013] The response transmitting circuit improves the off-state isolation of the transmitter through the design of the frequency source unit, the modulation unit and the signal amplification unit, and reduces the carrier leakage amplitude at the antenna port of the transmitter. The frequency source unit is powered on under the control of the frequency source power control signal and is powered off when the frequency source power control signal is invalid, so that the frequency source carrier can be completely turned off, there is no same frequency interference problem, and the receiving sensitivity of the ADS-B system is ensured.

[0014] When the transmitter is in a transmitting state, the frequency source unit is powered on under the control of the frequency source power control signal, and the frequency source can output a carrier signal. Since the frequency source needs about 1us from power-on to frequency locking, the frequency source needs to be turned on 1us before the transmitter outputs a response code. The modulation unit is controlled by the transmitting code signal, and the transmitting time of the transmitting code signal is later than that of the frequency source power control signal. Therefore, when the transmitter does not receive the transmitting code, the modulation circuit is in an off state, the leaked carrier signal is suppressed by the modulation circuit within the 1us, the amplitude of the leaked carrier signal is reduced, the reception of the S-mode P4 pulse is not affected, and the receiving sensitivity of the secondary radar responder is ensured.

[0015] The signal amplification unit amplifies the modulated radio frequency signal and is controlled by the transmission enable signal, and the amplifier drain source is turned off when not transmitting, thereby reducing the power consumption of the transmitter and improving the circuit isolation. Through the above design, the amplitude of the carrier signal leaked to the receiver is far lower than the sensitivity of the receiver, ensuring the stable and reliable operation of the transponder of the fusion ADS-B system and the secondary radar system.

[0016] As a preferred embodiment, the frequency source unit comprises a power modulator and a dielectric resonator connected electrically, the power modulator is further connected with the processing module of the transponder, and is used for receiving the frequency source power control signal issued by the processing module based on the received signal; the power modulator is powered on when receiving the frequency source power control signal, and outputs a level signal; the dielectric resonator is driven to vibrate by the level signal, and outputs a continuous carrier signal.

[0017] As a preferred embodiment, the frequency source unit further comprises a low-pass filter and a matching attenuator, the input end of the low-pass filter is connected with the output end of the frequency source, the output end of the low-pass filter is connected with the input end of the matching attenuator, and the output end of the matching attenuator is connected with the modulation unit.

[0018] As a preferred embodiment, the modulation unit comprises an inverter and an amplitude modulator; the inverter is used for phase inversion when receiving the transmission coding signal, and performs phase modulation on the carrier signal; the amplitude modulator is used for amplitude modulation on the carrier signal according to the amplitude modulation signal in the transmission coding signal when receiving the transmission coding signal.

[0019] As a preferred embodiment, the modulation unit further comprises a high-pass filter, and the high-pass filter is used for processing the modulated radio frequency signal.

[0020] As a preferred embodiment, the signal amplification unit adopts a three-stage amplifier, the first stage is a low-noise amplifier, the second stage and the third stage are GaN amplifiers; the drain source of the GaN amplifier is connected with the processing module of the transponder, and is used for turning on the drain source through the GaN power-on circuit to transmit when receiving the enable signal of the processing module, and turning off the drain source when invalid, so as to reduce the power consumption of the transmitter and improve the transmission circuit isolation; the transmission time of the transmission enable signal is later than that of the frequency source power control signal.

[0021] As a preferred embodiment, there is a matching attenuator between the first-stage amplifier and the second-stage amplifier, and an isolator is arranged between the second-stage amplifier and the third-stage amplifier.

[0022] As a preferred embodiment, the transceiving diversity unit comprises an electrically connected circulator and a band-pass filter, the circulator is used to realize the transceiving diversity function, and the band-pass filter is used to filter out the out-of-band spurious signals.

[0023] In a second aspect of the present application, a secondary radar response transmitter is provided, comprising the high-isolation secondary radar response transmitting circuit according to any one of the embodiments of the first aspect of the present application.

[0024] In a third aspect of the present application, a secondary radar responder is provided, comprising a receiver, a processing module and the secondary radar response transmitter according to the second aspect of the present application.

[0025] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0026] The frequency source unit is powered by the control signal, and is quickly started within 1us after power-on to output a 1090MHz continuous wave carrier signal for use by the transmitter. After power-off of the frequency source, no signal is output, so that the carrier leakage amplitude at the antenna port of the transmitter is lower than the sensitivity of the receiver, effectively avoiding repeated debugging caused by space radiation transmission, greatly reducing the debugging workload, and having high consistency, thereby fundamentally solving the problem of receiver co-channel interference and ensuring the sensitivity index of the ADS-B receiving function of the receiver.

[0027] The modulation unit is controlled by the transmission encoding signal to perform carrier modulation. When the transmitter does not receive the transmission encoding signal, the modulation circuit is in an off state, and the isolation degree is greater than 50dB, which can reduce the carrier amplitude by more than 45dB, effectively suppress the carrier amplitude leaked by the transmitter when the frequency source is turned on 1us before the output of the response code, and avoid affecting the reception of the P4 pulse.

[0028] The signal amplification unit adopts a cascaded GaN amplifier with high gain, high efficiency and high power density. During transmission, the transmission enable signal is in an active state, the amplifier works normally, and the modulated radio frequency signal is amplified to sufficient transmission power. After transmission, the transmission enable signal is in an inactive state, and the GaN power-on circuit turns off the drain power supply of the amplifier to reduce the power consumption of the transmitter and improve the isolation degree of the transmission circuit. The reverse isolation degree of the amplification circuit is greater than 50dB, and within 1us after the frequency source is powered on, the carrier signal leaked by the frequency source can be further suppressed in reverse, so that the carrier leakage amplitude within the time from the power-on of the frequency source to the active state of the transmission enable signal is lower than the receiving sensitivity of the air traffic control responder, ensuring that the reception of the P4 pulse is not affected.

[0029] The use of loop filtering has the advantages of simple circuit, high reliability and low cost, reduces the complexity of the transmitter, and effectively suppresses the out-of-band spurious signals.

[0030] The detection unit realizes coupling of a part of energy of the transmitting signal for detection, and converting the radio frequency signal into an analog signal. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments, and it should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be considered as a limitation to the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor. In the drawings:

[0032] Figure 1 is a working schematic diagram of the ADS-B and secondary radar system transponder;

[0033] Figure 2 is a block diagram of the secondary radar transponder;

[0034] Figure 3 is a block diagram of a high-isolation secondary radar transponder transmitting circuit according to an embodiment of the present application;

[0035] Figure 4 is a working schematic diagram of a frequency source unit according to an embodiment of the present application;

[0036] Figure 5 is a working schematic diagram of a modulation unit according to an embodiment of the present application;

[0037] Figure 6 is an internal envelope diagram of a modulation pulse according to an embodiment of the present application;

[0038] Figure 7 is a working flow diagram of the ADS-B system and secondary radar system transponder according to an embodiment of the present application;

[0039] Figure 8 is a timing comparison diagram of a frequency source power supply control signal, a transmitting enable signal and a transmitting code signal according to an embodiment of the present application. DETAILED DESCRIPTION

[0040] In order to make the objects, technical solutions and advantages of the present application more clear, the following will further describe the present application in combination with the embodiments and drawings, and the exemplary embodiments of the present application and the description are only used to explain the present application, and should not be considered as a limitation to the present application.

[0041] It has to be noted that the terms "comprising", "having" and "including" and any variations thereof used in the present specification and in the claims are intended to cover both the case where the step or the unit is present and the case where it is not present. The terms "comprising", "having" and "including" and any variations thereof used in the present specification and in the claims are intended to cover both the case where the step or the unit is present and the case where it is not present.

[0042] The terminology used in the description of the various embodiments herein is for the purpose of describing particular embodiments only and is not intended to limit the various embodiments of the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the various embodiments belong. The terms, such as "include", "comprise", "have", and / or "contain", are used herein to describe both qualitative and quantitative composition of the subject matter. The terms "comprise", "comprising", "include", "including", and "contain", "containing" as used herein are used in their broadest sense and are used in conjunction with open-ended language such as "comprising" and "containing" to describe features that can be added and features that can be additional to those present.

[0043] The embodiment of the present application provides a secondary radar response transmitting circuit, a response transmitter and a responder, which are suitable for processing of the response signal transmitted by the responder, and are beneficial to reduce carrier leakage, simplify the transmitter circuit, and inhibit the carrier leakage amplitude to be lower than -100dBm, and are particularly suitable for adding the ADS-B system and the secondary radar system responder.

[0044] The transmitting frequency of the secondary radar responder is 1090MHz±1MHz, and the receiving frequency is 1030MHz±3MHz. The transmitting frequency and the receiving frequency are not at the same frequency point. The internal carrier signal in the transmitter design is usually generated by a phase-locked loop circuit. The frequency locking time of the phase-locked loop circuit is about several microseconds to tens of microseconds. In order to meet the requirements of the A / C mode inquiry response delay of 3us±0.5us and the S mode inquiry response delay of 128us±0.25us in the civil aviation standard, the transmitter needs to be in a standby transmitting state at all times, so the frequency source circuit needs to be powered at all times. In this state, the transmitter carrier signal always exists, and the amplitude leaked to the receiving port is about -50dBm. This signal can be effectively inhibited by the channel selection filter in the front end of the receiver. Therefore, there is no problem of the transmitting carrier signal interfering with the receiver, and the transmitter and the receiver adopt a time-sharing working mode.

[0045] However, with the increasing number of aircraft, the function of the air control system is higher and higher, and the device that combines the ADS-B system and the secondary radar transponder function is more and more widely needed, the ADS-B system and the secondary radar system share the receiving channel, the secondary radar transponder transmitting frequency and the ADS-B system receiving frequency are both 1090MHz, which causes the problem of transmitter carrier signal leakage to the receiving port. In view of this problem, the application provides a high off-state isolation secondary radar transponder transmitter circuit, the transmitter equipped with the transmitter circuit can suppress the carrier leakage to below-100dBm, which is much lower than the receiving sensitivity of the ADS-B system-84dBm, so as to not reduce the response probability.

[0046] Referring to Figure 2 , Figure 3 , Figure 2 is a secondary radar transponder block diagram, Figure 3 is a high off-state isolation secondary radar transponder transmitting circuit block diagram of an embodiment of the application, and the application of the transponder transmitting circuit is applied to the transmitter of the secondary radar transponder. The basic components of the transponder include a receiver, a processing module, a transmitter and a power module, the power module realizes the conversion of the external input power into the voltage required by each module inside, and completes the power conversion function.

[0047] In the transponder that combines the ADS-B system and the secondary radar system, the receiver realizes the reception and preprocessing of 1090MHz and 1030MHz signals, and sends the signals to the processing module for decoding, to complete the signal receiving function. The processing module completes the information decoding work, and outputs the transmitting coded signal through the low-frequency signal control transmitter state. The transmitter completes the carrier signal generation, signal modulation, amplification, filtering according to the input transmitting coded and control signal, and sends the radio frequency signal through the antenna, to complete the response function.

[0048] As shown in Figure 3 , the high off-state isolation secondary radar transponder transmitting circuit mainly includes a frequency source unit, a modulation unit, an amplification circuit unit, a transceiver diversity circuit unit and a detection unit, and the connection relationship is as shown in Figure 3 . Among them, the frequency source unit is used for power-on when receiving the frequency source power control signal, and outputs the carrier signal. The modulation unit is used for modulating the carrier signal when receiving the transmitting coded signal, and outputs the modulated radio frequency signal, and the transmitting time of the transmitting coded signal is later than that of the frequency source power control signal. The signal amplification unit is used for amplifying the radio frequency signal, and outputs the amplified signal. The transceiver diversity unit is used for transceiver switching and filtering the amplified signal, and outputs the filtered amplified signal. The detection unit is used for detecting the filtered amplified signal, and sending it to the antenna for transmission.

[0049] The frequency source unit is powered off when the frequency source power control signal is invalid, and does not output any signal, so that when the transponder is in a receiving state after the signal is transmitted, the carrier leakage amplitude at the antenna port is lower than the receiving sensitivity of the receiver ADS-B system, and does not affect the function of the receiver.

[0050] The modulation unit is controlled to modulate the carrier signal when transmitting the coded signal, and since the frequency source needs to be turned on 1us before the transponder outputs the reply code, the modulation unit is in an inoperative state within 1us before the frequency source unit is powered on to the modulation unit receives the transmission code sent by the processing module, so as to suppress the carrier amplitude leaked by the frequency source unit, does not affect the reception of the S-mode P4 pulse, and ensures the receiving sensitivity of the secondary radar transponder.

[0051] Unlike the design of adding a programmable attenuator on the transmission link, the present application realizes high off-state isolation through the design of the frequency source unit, the modulation unit, and the amplification circuit unit, and the transceiver diversity circuit unit and the detection unit are general components of the transmitter.

[0052] The front end of the transmission circuit is connected to the processing module, and the rear end is connected to the antenna. The reply working process is as follows: the processing module receives the signal from the receiver, judges and processes through the decoding processing unit, and controls the transmitter to be in a standby transmission state, the power control signal and the transmission code signal are output from the coding unit to the transmitter, the transmitter outputs the carrier signal through the power-on of the frequency source, the modulation unit modulates the carrier according to the transmission code signal, and finally the amplified radio frequency signal is output to the antenna output through the amplification unit. The working process of the transmission circuit is as follows:

[0053] S110, the frequency source unit receives the frequency source power control signal from the processing module, the frequency source power control signal is the power-on of the frequency source, and the frequency source outputs a 1090MHz carrier signal.

[0054] S120, the modulation circuit modulates the carrier signal according to the received transmission code signal and sends it to the signal amplification unit,

[0055] S130, the signal amplification unit amplifies the modulated radio frequency signal, and the amplification circuit can amplify the radio frequency signal from -2dBm to +58dBm, which fully improves the transmission efficiency, and turns off the drain power supply of the amplifier after transmission, thereby reducing the power consumption of the transmitter.

[0056] S140, the amplified radio frequency signal is sent to the transceiver diversity unit, the radio frequency signal is transmitted along a fixed path, and after being processed by a low-pass filter, the radio frequency signal is sent to the detection unit.

[0057] S150, the detection unit couples out a small part of the signal from the main transmission signal through the coupler and demodulates the envelope signal through the detection diode, and sends it into the voltage comparator for BIT detection, and sends most of the radio frequency signal to the antenna port for transmission. Finally, the received signal is sent to the secondary radar receiver through the circulator, and the response is completed.

[0058] S160, the frequency source unit receives the frequency source power control signal from the processing module to power off the frequency source, and no carrier output is output, and the next transmission is waited.

[0059] Further, the frequency source unit comprises a power modulator and a frequency source connected electrically, the power modulator is connected with the processing module of the transponder, and is used for receiving the frequency source power control signal sent by the processing module based on the received signal; the power modulator is powered on when receiving the frequency source power control signal, and outputs a level signal; the frequency source is driven by the level signal to oscillate and output a continuous carrier signal.

[0060] The frequency source unit is the first key circuit to realize high off-state isolation of the transmitter, and the frequency source can adopt a medium resonator with fast oscillation. The working schematic diagram of the frequency source unit is shown in FIG. 4, comprising the following steps.

[0061] S210, the power modulator receives the frequency source power control signal, and enters S220;

[0062] S220, the frequency source power control signal controls the opening and closing of the MOS tube in the power modulator, and further controls the on-off of the VCC pin to the V_TTL pin of the power modulator, and enters S230;

[0063] S230, the power modulator V_TTL pin outputs a V_TTL signal with certain load capacity and synchronized with the power modulation signal, and enters step S240;

[0064] S240, the V_TTL signal is connected to the power supply pin VCC of the frequency source, that is, the power on / off of the frequency source can be controlled, and enters step S250;

[0065] S250, after the frequency source is powered on, it can quickly oscillate within 1us, and output a continuous wave carrier signal of 1090MHz for use of the transmitter, and enter S260;

[0066] S260, the frequency source is powered off, and no carrier signal is output.

[0067] The design of the frequency source unit effectively avoids repeated debugging caused by space radiation transmission, greatly reduces the debugging workload, makes the module port carrier leakage amplitude lower than the receiver sensitivity, and has high consistency, fundamentally solves the problem of receiver co-channel interference, and ensures the receiving sensitivity of the ADS-B system of the receiver.

[0068] In a preferred embodiment, the frequency source unit further comprises a low-pass filter and a matching attenuator for filtering out the harmonics in the carrier signal. The input of the low-pass filter is connected to the output of the frequency source, the output of the low-pass filter is connected to the input of the matching attenuator, and the output of the matching attenuator is connected to the modulation unit.

[0069] In a preferred embodiment, the modulation unit comprises an inverter and an amplitude modulator. The inverter is used to perform phase inversion when receiving the transmission code signal, and to perform phase modulation on the carrier signal; the amplitude modulator is used to perform amplitude modulation on the carrier signal according to the amplitude modulation signal in the transmission code signal when receiving the transmission code signal.

[0070] The modulation unit is the second key circuit for achieving high off-state isolation of the transmitter. The modulation circuit mainly consists of a radio frequency switch, an inverter, and a driving circuit, which can perform phase and amplitude modulation on the continuous carrier signal output by the frequency source circuit to generate a modulated signal. At the same time, since the frequency source takes about 1us from power-on to frequency locking, the frequency source needs to be powered on 1us before the transmitter outputs the response code to modulate the signal. The carrier leaked by the frequency source will raise the noise floor of the receiver, affecting the receiver to receive the last pulse P4 of the full call inquiry mode. At this time, the carrier leaked by the frequency source in the 1us needs to be suppressed by the modulation unit and the signal amplification unit. The working schematic of the modulation unit is shown in FIG. 5, which includes the following steps.

[0071] S310, the modulation circuit receives the transmission code signal sent by the processing module, and enters S320;

[0072] S320, the continuous wave carrier signal output by the frequency source circuit is sent to the modulation circuit, and enters S330;

[0073] S330, the phase modulation signal in the transmission code controls the inverter in the modulation circuit to perform phase inversion, and completes the phase modulation on the carrier signal, and enters S340;

[0074] S340, the amplitude modulation signal in the transmission code controls the opening and closing of the radio frequency switch in the modulation circuit, and completes the amplitude modulation on the carrier signal, and enters S350;

[0075] S350, the modulation circuit outputs the modulated radio frequency signal, completes the function of moving the baseband signal to the carrier signal, and enters S360. As shown in FIG. 6, it is a schematic diagram of the internal envelope of the modulation pulse. Each modulation pulse signal contains several periods of sine wave inside. Figure 6

[0076] ​S360, when the transmitter does not receive the transmission code or the received transmission code is invalid, the modulation circuit is turned off. The modulation circuit has a turn-off ratio of more than 50 dB, which can reduce the carrier signal amplitude leaked by the frequency source by more than 45 dB.

[0077] In a preferred embodiment, the modulation unit further comprises a high-pass filter, the input end of the high-pass filter is connected to the output end of the amplitude modulator, and the output end of the high-pass filter is connected to the signal amplification unit, for filtering the modulated radio frequency signal, and sending the signal to the signal amplification unit after filtering out the low-frequency stray signals.

[0078] In a preferred embodiment, the signal amplification unit adopts a three-stage amplifier, the first stage is a low-noise amplifier, and the second and third stages are GaN amplifiers.

[0079] The signal amplification unit is the third key circuit for realizing high off-state isolation, which is composed of a small-signal amplifier and two GaN amplifiers in cascade (including a driver amplifier and a high-power final amplifier). Both the driver amplifier and the high-power final amplifier adopt GaN amplifiers with high gain, high efficiency, and high power density, which can amplify the modulated signal to sufficient transmission power. At the same time, the GaN device has a power-on sequence, that is, when powered on, the gate negative voltage is turned on first, and then the drain positive voltage is turned on; when powered off, the drain positive voltage is turned off first, and then the gate positive voltage is turned off.

[0080] The drain level power supply of the GaN amplifier is connected to the processing module of the transponder, and the transmission enable signal is received from the processing module. The transmission time of the transmission enable signal is later than that of the frequency source power control signal, which can further improve the isolation of the transmission circuit. During the period from the power-on of the frequency source unit to the reception of the transmission enable signal, the drain power supply is still in the off state, which can further suppress the carrier signal leaked by the frequency source in the reverse direction and improve the off-state isolation of the transmission circuit. The reverse isolation of the amplification circuit can be more than 45 dB, which can further reduce the carrier leakage amplitude during the period from the power-on of the frequency source to the reception of the transmission enable signal, and ensure that the reception of the P4 pulse is not affected. After receiving the transmission enable signal, the GaN power-on circuit turns on the drain power supply, and the amplifier works normally. After the transmission enable signal is invalid, the drain level power supply is turned off, which plays a role in improving the off-state isolation.

[0081] The working steps of the three-stage amplification circuit are as follows:

[0082] S410, the GaN device is powered on, the gate negative voltage is turned on first, and then the drain positive voltage is turned on. By using the above-mentioned characteristics of the GaN amplifier and adopting a special way of pulse drain modulation, that is, the negative voltage adopts direct current, and the positive voltage adopts pulse, S420 is entered.

[0083] S420, when the amplifier is not transmitting, the transmit enable signal is in an inactive state, the amplifier drain is off, and the reverse isolation of the amplifier is used to improve the off ratio of the entire link channel. The reverse isolation of the two-stage GaN amplifier can reach 50 dB, so that the amplitude of the frequency source leakage carrier signal is lower than the receiving sensitivity of the secondary radar transponder, and the process goes to S430;

[0084] S430, when the amplifier is working, the transmit enable signal is turned on, the drain provides a voltage, and the amplifier is in a standby transmitting state, and the process goes to S440;

[0085] S440, the amplitude modulator outputs the modulated radio frequency signal to the amplification circuit for power amplification. The radio frequency signal is amplified from -2 dBm to +58 dBm, and the amplified radio frequency signal is output to the transmit-receive diversity unit.

[0086] In a preferred embodiment, an isolator is arranged between the first-stage amplifier and the second-stage amplifier and between the second-stage amplifier and the third-stage amplifier. As shown in Figure 3 A matching attenuator can also be arranged between the first-stage amplifier and the second-stage amplifier. The matching attenuator and the isolator are used to adjust the inter-stage matching, reduce the reflection coefficient of the amplifier, and prevent the standing wave ratio from increasing when the subsequent-stage amplifier fails, so that the failure is not transmitted to the previous-stage amplifier, thereby protecting the amplifier.

[0087] In a preferred embodiment, the transmit-receive diversity unit adopts a loop filter circuit, which includes a circulator and a band-pass filter connected in an electrical manner.

[0088] The loop filter circuit is a general circuit of the transmitter, which includes a three-port or four-port circulator and a band-pass filter. The circulator mainly realizes the function of transmit-receive diversity. Compared with using a transmit-receive switch, the circulator has the advantages of simple circuit, high reliability, and low cost as a passive device. The filter is an LC band-pass filter composed of a capacitor and an inductor. The filter order can be selected according to the requirements of size, out-of-band suppression, insertion loss, and the like, so as to realize the function of effectively suppressing out-of-band spurious signals.

[0089] The detection unit is also a common circuit of the transmitter, which includes a coupler, a detection diode, a voltage comparator, and the like. In the design, a microstrip parallel line coupler is selected. Compared with a coupling bridge, the microstrip coupler can be designed flexibly according to the size of the transmitter, has the advantages of high reliability, low insertion loss, and low cost, and realizes the function of coupling a part of the transmitted signal energy. The detection diode can convert the radio frequency signal into an analog signal. The comparator can judge whether the input signal is normal according to the set threshold level, and complete the function of self-checking of the transmitter.

[0090] Embodiments of the present invention also provide a secondary radar transponder transmitter, including the high off-state isolation secondary radar transponder transmitter circuit described in any one of the above claims. This secondary radar transponder transmitter can be applied to the transponder of a secondary radar system and to the transponder in which an ADS-B system is added to the secondary radar system.

[0091] Embodiments of the present invention also provide a secondary radar transponder, including a receiver, a processing module, and a secondary radar transponder transmitter as described in the above embodiments of the present invention. The secondary radar transponder may be equipped with a secondary radar transponder system or simultaneously equipped with an ADS-B system and a secondary radar system.

[0092] Furthermore, the secondary radar transponder also includes a power module for supplying power to the transmitter, processing module, and receiver.

[0093] The operating modes of the transponders equipped with the aforementioned ADS-B system and secondary radar system include conventional A and C response modes and S response mode. The workflow for each response mode is as follows: Figure 7 As shown, S502 to S512 are the transmitter operation procedures, S504 to S507 are the conventional A and C response modes operation procedures, and S508 to S512 are the S response mode operation procedures.

[0094] S501: The receiver receives interrogation signals P1 and P3 pulses, which are then decoded by the processing module. The transmitter status is controlled by a low-frequency signal, and the transmitted coded signal is output.

[0095] S502: After the transmitter receives the frequency source power control signal (power modulation signal) from the processing module, the frequency source is powered on and starts working, outputting a carrier signal.

[0096] S503: Determine whether a P4 pulse has been received. Determine whether the response mode is A / C normal response mode or S response mode. The response delays for A, C, and S modes are different. If it is A / C response mode, execute S504 to S507. If it is S response mode, execute S508 to S512.

[0097] S504, transmit enable signal is turned on, at this time the amplifier is in transmit ready state.

[0098] The S505 transmitter receives conventional mode transmission codes and transmits signals in a fixed format.

[0099] S506 outputs an answer signal to complete the A and C normal mode answer.

[0100] S507: Frequency source power control signal and transmit enable signal are off; frequency source power is off; amplifier is off.

[0101] S508, when S3 detects that P4 pulse is not received, the frequency source power control signal is off, the frequency source is powered off, and the carrier leakage is reduced.

[0102] S509, when P4 signal is received, information is read.

[0103] S510, the frequency source power control signal and the transmission enable signal are turned on, and the amplifier is in a standby transmission state.

[0104] S511, the transmitter receives S-mode transmission code and transmits signals in a fixed format.

[0105] S512, an answer signal is output, and S-mode answering is completed.

[0106] S513, after the transmitter completes A, C normal mode answering or S-mode answering, the receiver is in an ADS-B receiving or air traffic control receiving state.

[0107] Figure 8 The timing diagram of the frequency source power control signal, the transmission enable signal, and the transmission code signal is shown. Through the timing control of the frequency source power control signal, the transmission enable signal, and the transmission code signal, when the transmitter is in a receiving state, the frequency source carrier can be completely turned off, and there is no co-frequency interference problem. When the transmitter does not receive the transmission code, the modulation circuit is in an off state, and the leaked carrier signal can be suppressed. Through the state control of the amplifier by the transmission enable signal, the frequency source leaked carrier signal is further suppressed in reverse, and high off-state isolation is achieved.

[0108] The above specific embodiments further illustrate the purpose, technical solutions, and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A high on-state isolation secondary radar transponder transmitting circuit, characterized in that, The frequency source unit, the modulation unit, the signal amplification unit, the transceiving diversity unit and the detection unit are sequentially electrically connected; The frequency source unit is used for being powered on when receiving the frequency source power control signal and outputting a carrier signal, and being powered off when the frequency source power control signal is invalid and not outputting any signal; The modulation unit is used for modulating the carrier signal when receiving a transmission code signal and outputting a modulated radio frequency signal, and being in an off state when not receiving the transmission code signal, and the transmission time of the transmission code signal is later than the transmission time of the frequency source power control signal; The signal amplification unit adopts a cascade GaN amplifier, and the GaN amplifier is controlled by a transmission enable signal, and the drain power supply is turned on to amplify the radio frequency signal and output an amplified signal during transmission, and the drain power supply is turned off during non-transmission. The transceiving diversity unit is used for transceiving switching and filtering the amplified signal, and outputting the amplified signal filtered from the stray. The detection unit is used for detecting the amplified signal filtered from the stray and transmitting the amplified signal filtered from the stray to an antenna for transmission.

2. The high side isolation secondary surveillance radar transponder transmit circuit of claim 1, wherein, The frequency source unit includes a power modulator and a dielectric resonator which are electrically connected, and the power modulator is further connected with a processing module of a transponder for receiving a frequency source power control signal sent by the processing module based on a received signal; The power modulator is powered on when receiving the frequency source power control signal and outputs a level signal; The dielectric resonator is quickly vibrated under the driving of the level signal and outputs a continuous carrier signal.

3. The high caseness isolation secondary radar reply transmitting circuit according to claim 2, characterized in that, The frequency source unit further includes a low-pass filter and a matching attenuator, the input end of the low-pass filter is connected with the output end of the dielectric resonator, the output end of the low-pass filter is connected with the input end of the matching attenuator, and the output end of the matching attenuator is connected with the modulation unit.

4. The high caseness isolation secondary surveillance radar transponder transmit circuit of claim 1, wherein, The modulation unit includes an inverter and an amplitude modulator; The inverter is used for phase inversion when receiving the transmission code signal and phase modulation of the carrier signal; and the amplitude modulator is used for amplitude modulation of the carrier signal according to an amplitude modulation signal in the transmission code signal when receiving the transmission code signal.

5. The high caseness isolation secondary radar reply transmitting circuit according to claim 4, characterized in that, The modulation unit further includes a high-pass filter for processing the modulated radio frequency signal.

6. The high caseness isolation secondary surveillance radar reply transmitting circuit according to claim 1, characterized in that, The signal amplification unit adopts a three-stage amplifier, the first stage is a low-noise amplifier, the second stage and the third stage are GaN amplifiers; the drain power supply of the GaN amplifier is connected with the processing module of the transponder, and is used for turning on the drain power supply through a GaN power-on circuit when receiving a transmission enable signal sent by the processing module, and the transmission time of the transmission enable signal is later than the transmission time of the frequency source power control signal, so as to improve the isolation degree of the transmission circuit.

7. The high caseness isolation secondary radar reply transmitting circuit according to claim 6, characterized in that, Isolators are arranged between the first-stage amplifier and the second-stage amplifier and between the second-stage amplifier and the third-stage amplifier.

8. The high caseness isolation secondary surveillance radar reply transmitting circuit according to claim 1, characterized in that, The transceiving diversity unit comprises a circulator and a band-pass filter, the circulator is used to realize the transceiving diversity function, and the band-pass filter is used to filter out the out-of-band stray signals.

9. Secondary radar transponder transmitter, characterized in that A secondary radar transponder transmission circuit with high state isolation according to any one of claims 1-8.

10. A secondary surveillance radar transponder, characterized by Comprising: A receiver, a processing module and a secondary radar transponder transmitter according to claim 9.

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