Secondary radar response transmitting circuit with high off-state isolation, response transmitter and responder

Abstract

The invention discloses a secondary radar response transmitting circuit with high off-state isolation, a response transmitter and a responder, and relates to the technical field of secondary radars. The response transmitting circuit comprises a frequency source unit, a modulation unit, a signal amplification unit, a transmit-receive diversity unit and a detection unit which are electrically connected in sequence; the frequency source unit is powered on when receiving the frequency source power supply control signal, outputs a carrier signal, and is powered off when the frequency source power supply control signal is invalid; the modulation unit is used for modulating a carrier signal when receiving the transmitting coded signal and outputting a modulated radio frequency signal, and the transmitting time of the transmitting coded signal is later than that of the frequency source power supply control signal, so that the carrier leaked by the frequency source before the transmitting signal is modulated is inhibited; and finally, the signal amplification unit is used for amplifying the radio frequency signal, and the amplified signal is output to an antenna through the transmit-receive diversity unit and the detection unit. The problems that carrier leakage affects receiver work and reduces receiver sensitivity are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary radar, and in particular to a secondary radar response transmission circuit, a response transmitter and a response machine with high off-state isolation. Background Art

[0002] As the number of aircraft in the airspace increases, the functional requirements for air traffic control systems are also increasing. In particular, aircraft have an increasing demand for equipment that integrates the functions of the automatic dependent surveillance-broadcast system (ADS-B system) and secondary radar transponders. The working diagram of the transponder that integrates the ADS-B and secondary radar systems is shown in Figure 1. The transmitting frequency of the secondary radar transponder is 1090MHz±1MHz and the receiving frequency is 1030MHz±3MHz. The transmitting frequency and the receiving frequency are not at the same frequency point, but the receiving frequency of the ADS-B system is 1090MHz±3MHz, which is at the same frequency point as the transmitting frequency.

[0003] The receiving sensitivity of the ADS-B system in the fusion ADS-B system and the secondary radar transponder is not less than -84dBm, and the tangent sensitivity is -90dBm. Since the receiving frequency of the ADS-B system is the same as the transmitter carrier signal, 1090MHz, and the ADS-B and the secondary radar transponder share the same receiving channel, the RF filter at the front end of the receiving channel is a broadband filter with a passband frequency covering 1090MHz and 1030MHz, and the ADS-B system is always in the receiving state. In this case, the carrier signal leaked from the transmitter will affect the sensitivity of the receiver, resulting in reduced sensitivity and insufficient response probability.

[0004] The main technical idea for solving the current transmitter carrier leakage is to add a programmable attenuator to the transmission link, change the gain of the transmission link by switching the attenuation value, and isolate each circuit with a shielded cavity to prevent the signal from being coupled and transmitted to the receiving port through spatial radiation. The problems with this method are: the programmable attenuator and the cavity structure increase the complexity of the circuit and equipment; the RF circuit is unpredictable during debugging, making it difficult to adjust the attenuation; the equipment has different carrier leakage amplitudes at room temperature and high and low temperatures, and the RF circuit needs to repeatedly debug the attenuator value and shielding isolation, which has a large debugging workload and low reusability; the physical isolation measures cannot ensure that there are no gaps in the cavity structure, and the shielding effect cannot be fully exerted. Summary of the invention

[0005] The present invention provides a secondary radar reply transmission circuit, a reply transmitter and a reply machine with high off-state isolation, so as to solve the problem that the carrier signal leaks and couples to the receiving port, thus affecting the receiver sensitivity and reply rate.

[0006] The present invention is achieved through the following technical solutions:

[0007] In a first aspect of the present invention, there is provided a secondary radar transponder transmitting circuit with high off-state isolation, comprising a frequency source unit, a modulation unit, a signal amplification unit, a transceiver diversity unit and a detection unit electrically connected in sequence;

[0008] The frequency source unit is used to power on and output a carrier signal when receiving a frequency source power control signal, and to power off and not output any signal when the frequency source power control signal is invalid;

[0009] The modulation unit is used to modulate the carrier signal when receiving the transmission coding signal and output the modulated radio frequency signal, and the transmission time of the transmission coding signal is later than the transmission time of the frequency source power supply control signal;

[0010] The signal amplification unit is used to amplify the radio frequency signal and output an amplified signal;

[0011] The transmit / receive diversity unit is used for transmitting / receiving switching and filtering the amplified signal, and outputting the amplified signal after filtering out the stray signals;

[0012] The detection unit is used to detect the amplified signal after the spurious signals are filtered out, and send the amplified signal after the spurious signals are filtered out to the antenna for transmission.

[0013] The reply transmission circuit of the present invention 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 of the transmitter at the antenna port. The frequency source unit is controlled by the frequency source power supply control signal to power on, and the frequency source power supply control signal is powered off when it is invalid, so that the frequency source carrier can be completely shut down without the same-frequency interference problem, ensuring the receiving sensitivity of the ADS-B system.

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

[0015] The signal amplifier unit amplifies the modulated RF signal and is controlled by the transmission enable signal. When not transmitting, the amplifier drain power supply is turned off to reduce the transmitter power consumption while improving the circuit isolation. Through the above design, the amplitude of the carrier signal leaking to the receiver is much lower than the receiver sensitivity, ensuring the stable and reliable operation of the transponder integrating the ADS-B system and the secondary radar system.

[0016] As a preferred embodiment, the frequency source unit includes an electrically connected power modulator and a dielectric resonator, the power modulator is also connected to the processing module of the transponder, and is used to receive a frequency source power control signal issued 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 oscillates under the drive of the level signal, and outputs a continuous carrier signal.

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

[0018] As a preferred embodiment, the modulation unit includes an inverter and an amplitude modulator; the inverter is used to perform phase inversion when receiving the transmitted coded signal and phase modulate the carrier signal; the amplitude modulator is used to perform amplitude modulation on the carrier signal according to the amplitude modulation signal in the transmitted coded signal when receiving the transmitted coded signal.

[0019] As a preferred embodiment, the modulation unit further includes a high-pass filter, and the high-pass filter is used to process 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, and the second and third stages are GaN amplifiers; the drain power supply of the GaN amplifier is connected to the processing module of the transponder, and is used to turn on the drain power supply through the GaN power-on circuit for transmission when receiving the enable signal of the processing module, and turn off the drain power supply when it is invalid, so as to reduce the power consumption of the transmitter and improve the isolation of the transmission circuit; the sending time of the transmission enable signal is later than the frequency source power control signal.

[0021] As a preferred embodiment, there is matched attenuation between the first-stage amplifier and the second-stage amplifier, and an isolator is provided between the second-stage amplifier and the third-stage amplifier.

[0022] As a preferred embodiment, the transmit / receive diversity unit includes a circulator and a bandpass filter which are electrically connected, the circulator is used to realize the transmit / receive diversity function, and the bandpass filter is used to filter out out-of-band stray signals.

[0023] A second aspect of the present invention provides a secondary radar transponder transmitter, comprising the secondary radar transponder transmitting circuit with high off-state isolation as described in any one embodiment of the first aspect of the present invention.

[0024] A third aspect of the present invention provides a secondary radar transponder, comprising: a receiver, a processing module and the secondary radar transponder transmitter described in the second aspect of the present invention.

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

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

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

[0028] The signal amplification unit uses a cascaded GaN amplifier with high gain, high efficiency and high power density. When transmitting, the transmit enable signal is in an effective state, and the amplifier works normally to amplify the modulated RF signal to sufficient transmit power. After the transmission is completed, the transmit enable signal is in an invalid state, and the amplifier drain power supply is turned off through the GaN power-on circuit to reduce the power consumption of the transmitter and improve the isolation of the transmit circuit. The reverse isolation of the amplifier circuit is greater than 50dB. Within 1us after the frequency source is powered on, the carrier signal leaked from the frequency source can be further reversely suppressed, so that the carrier leakage amplitude from the power-on of the frequency source to the time when the transmit enable signal is in an effective state is lower than the receiving sensitivity of the air traffic control transponder, 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, low cost, etc. It reduces the complexity of the transmitter and effectively suppresses out-of-band spurious signals.

[0030] The detection unit couples out a portion of the energy of the transmission signal for detection and can convert the radio frequency signal into an analog signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0032] Figure 1 It is a working diagram of installing ADS-B and secondary radar system transponders;

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

[0034] Figure 3 It is a block diagram of a secondary radar response transmission circuit with high off-state isolation according to an embodiment of the present invention;

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

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

[0037] Figure 6 is a schematic diagram of an internal envelope of a modulated pulse according to an embodiment of the present invention;

[0038] Figure 7 It is a schematic diagram of a work flow of installing an ADS-B system and a secondary radar system transponder according to an embodiment of the present invention;

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

[0040] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0041] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to or inherent to other steps or units of the device.

[0042] The terms used in various embodiments of the present invention are only used for the purpose of describing specific embodiments and are not intended to limit various embodiments of the present invention. As used herein, the singular form is intended to also include the plural form, unless the context clearly indicates otherwise. Unless otherwise limited, all terms used here (including technical terms and scientific terms) have the same meaning as the meaning generally understood by those of ordinary skill in the art to which the various embodiments of the present invention belong. The terms (such as the terms defined in the dictionary generally used) will be interpreted as having the same meaning as the contextual meaning in the relevant technical field and will not be interpreted as having an idealized meaning or an overly formal meaning, unless clearly defined in various embodiments of the present invention.

[0043] The embodiments of the present invention provide a secondary radar transponder transmission circuit, a transponder transmitter and a transponder, which are suitable for processing transponder transmission signals, are beneficial to reducing carrier leakage, simplifying transmitter circuits, and can suppress the carrier leakage amplitude to be lower than -100dBm. They are particularly suitable for installation in ADS-B systems and secondary radar system transponders.

[0044] The transmitting frequency of the secondary radar transponder is 1090MHz±1MHz, and the receiving frequency is 1030MHz±3MHz. The transmitting frequency and the receiving frequency are not at the same frequency point. In the transmitter design, the internal carrier signal is usually generated by a phase-locked loop circuit. The frequency locking time of the phase-locked loop circuit is about ten microseconds to tens of microseconds. In order to meet the requirements of the A / C mode inquiry and response delay of 3us±0.5us and the S mode inquiry and response delay of 128us±0.25us in the civil aviation standard, the transmitter needs to be in a state of standby transmission 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 suppressed by the channel selection filter at the front end of the receiver, and the transmitter and receiver adopt a time-sharing mode, so there is no problem of the transmitting carrier signal interfering with the receiver.

[0045] However, as the number of aircraft increases, the functional requirements for air traffic control systems are higher, and the demand for equipment that integrates the functions of the ADS-B system and the secondary radar transponder is becoming more and more widespread. The ADS-B system and the secondary radar system share a receiving channel, and the secondary radar transponder transmission frequency is the same as the ADS-B system receiving frequency of 1090MHz, which leads to the problem of the transmitter carrier signal leaking to the receiving port. In response to this problem, the present invention proposes a secondary radar transponder transmitter transmission circuit with high off-state isolation. The transmitter equipped with the transmission 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 not to reduce the response probability.

[0046] See also Figure 2 , Figure 3 As shown, Figure 2 This is the block diagram of the secondary radar transponder. Figure 3 The block diagram of a secondary radar transponder transmitter circuit with high off-state isolation according to an embodiment of the present invention is applied to the transmitter of a secondary radar transponder. The basic components of the transponder include a receiver, a processing module, a transmitter and a power module. The power module converts the external input power into the voltage required by each internal module to complete the power conversion function.

[0047] In the transponder that integrates the ADS-B system and the secondary radar system, the receiver receives and preprocesses 1090MHz and 1030MHz signals, and sends the signals to the processing module for decoding to complete the signal reception function. The processing module completes the information decoding work, controls the transmitter state through low-frequency signals, and outputs the transmission code signal. The transmitter completes the carrier signal generation, signal modulation, amplification, filtering, and sends the RF signal through the antenna according to the input transmission code and control signal, and completes the transponder function.

[0048] like Figure 3 As shown, the secondary radar response transmission circuit with high off-state isolation 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 follows Figure 3 As shown. Among them, the frequency source unit is used to power on when receiving the frequency source power control signal and output the carrier signal. The modulation unit is used to modulate the carrier signal when receiving the transmission coding signal, and output the modulated radio frequency signal, and the transmission time of the transmission coding signal is later than the transmission time of the frequency source power control signal. The signal amplification unit is used to amplify the radio frequency signal and output the amplified signal. The transceiver diversity unit is used for transceiver switching and filtering the amplified signal, and outputs the amplified signal after filtering out the spurious. The detection unit is used to detect the amplified signal after filtering out the spurious, and send 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 after the signal is transmitted and the transponder is in the receiving state, 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 receiver's co-frequency receiving function.

[0050] The modulation unit is controlled to modulate the carrier signal when transmitting the coded signal. Since the frequency source needs to be turned on 1us before the transmitter outputs the response code, the modulation unit is in a non-working state within 1us from the time the frequency source unit is powered on to the time the modulation unit receives the transmission code sent by the processing module, thereby suppressing the carrier amplitude leaked from the frequency source unit, not affecting the reception of the S-mode P4 pulse, and ensuring the receiving sensitivity of the secondary radar transponder.

[0051] Different from the design of adding a programmable attenuator to the transmission link, the present invention achieves high off-state isolation through the design of the frequency source unit, modulation unit, and amplifier circuit unit, and the transceiver diversity circuit unit and detection unit are common components of the transmitter.

[0052] The front end of the transmitting circuit is connected to the processing module, and the back end is connected to the antenna. The response workflow is as follows: the processing module receives the signal from the receiver, which is judged and processed by the decoding processing unit, and the transmitter is controlled to be in the ready-to-transmit state. The encoding unit outputs the power control signal and the transmission coding signal to the transmitter. The transmitter outputs the carrier signal through the frequency source power-on, and the modulation unit modulates the carrier according to the transmission coding signal. Finally, the amplifier unit amplifies the output RF signal and sends it to the antenna output. Among them, the workflow of the transmitting circuit is as follows:

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

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

[0055] S130, the signal amplification unit amplifies the modulated RF signal. The amplification circuit can amplify the RF signal from -2dBm to +58dBm, fully improving the transmission efficiency, and turn off the amplifier drain power supply after the transmission is completed to reduce 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 is sent to the detection unit after the high-order harmonics are processed by a low-pass filter.

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

[0058] S160, the frequency source unit receives the frequency source power control signal from the processing module, indicating that the frequency source is powered off, and there is no carrier output, waiting for the next transmission.

[0059] Furthermore, the frequency source unit includes an electrically connected power modulator and a frequency source, the power modulator is connected to the processing module of the transponder, and is used to receive a frequency source power control signal issued 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 frequency source oscillates under the drive of the level signal, and outputs a continuous carrier signal.

[0060] The frequency source unit is the first key circuit to achieve high-off state isolation of the transmitter. The frequency source can use a dielectric resonator with fast oscillation. The working diagram of the frequency source unit is shown in Figure 4, which includes 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 on and off of the MOS tube inside the power modulator, thereby controlling the on and off of the power modulator VCC pin to the V_TTL pin, and then enters S230;

[0063] S230, the power modulator V_TTL pin outputs a V_TTL signal having a certain load capacity and being synchronized with the power modulation signal, and then proceeds to step S240;

[0064] S240, the V_TTL signal is connected to the power supply pin VCC of the frequency source, so as to control the power on / off of the frequency source, and then proceed to step S250;

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

[0066] S260, the frequency source is powered off and there is no carrier signal 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 co-frequency interference of the receiver, and ensures the receiving sensitivity of the receiver ADS-B system.

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

[0069] In a preferred embodiment, the modulation unit includes an inverter and an amplitude modulator. The inverter is used to perform phase inversion when receiving a transmitted coded signal and 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 transmitted coded signal when receiving the transmitted coded signal.

[0070] The modulation unit is the second key circuit to achieve high-off state isolation of the transmitter. The modulation circuit is mainly composed of an RF switch, an inverter and a driving circuit. It 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 time from power-on to frequency locking of the frequency source is about 1us, the frequency source power supply modulation signal needs to be turned on 1us before the transmitter outputs the response code. The carrier leaked from the frequency source will raise the noise floor of the receiver and affect the receiver's reception of the last pulse P4 of the full call inquiry mode. At this time, the carrier leaked from the frequency source within this 1us needs to be suppressed by the modulation unit and the signal amplification unit. The working schematic diagram of the modulation unit is shown in Figure 5, which includes the following steps.

[0071] S310, the modulation circuit receives the transmission coding 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 then enters S330;

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

[0074] S340, transmitting the amplitude modulation signal in the coding to control the opening and closing of the radio frequency switch in the modulation circuit, completing the amplitude modulation of the carrier signal, and entering S350;

[0075] S350, the modulation circuit outputs the modulated RF signal, completing the function of moving the baseband signal to the carrier signal, and then proceeds to S360. Figure 6 The figure shows the internal envelope of the modulated pulse. Each modulated pulse signal contains several cycles of sine waves.

[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 50dB, which can reduce the amplitude of the carrier signal leaked from the frequency source by more than 45dB.

[0077] In a preferred embodiment, the modulation unit also includes 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, which is used to filter the modulated RF signal and send it to the signal amplification unit after filtering out the spurious signal in the low frequency band.

[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 to achieve high off-state isolation. It consists of a small signal amplifier and a two-stage GaN amplifier cascade (including a driver amplifier and a high-power final amplifier). Both the driver amplifier and the high-power final amplifier use 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. When powered on, the negative gate voltage is turned on first, and then the positive drain voltage is turned on. When powered off, the positive drain voltage is disconnected first, and then the positive gate voltage is disconnected.

[0080] The drain power supply of the GaN amplifier is connected to the processing module of the transponder, and receives the transmit enable signal from the processing module. The transmission enable signal is sent later than the frequency source power control signal, which can further improve the isolation of the transmit circuit. During the period from when the frequency source unit is powered on to when the transmit enable signal is received, since the drain power supply is still in the off state, the carrier signal leaked from the frequency source can be further reversely suppressed to improve the off-state isolation of the transmit circuit. The reverse isolation of the amplifier circuit can reach more than 45dB, which further reduces the carrier leakage amplitude during the period from when the frequency source is turned on to when the transmit enable signal is received, ensuring that the reception of the P4 pulse is not affected. After receiving the transmit enable signal, the GaN power-on circuit turns on the drain power supply, and the amplifier works normally. After the transmit enable signal is invalid, the drain power supply is disconnected to improve the off-state isolation.

[0081] The working steps of the three-stage amplifier 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 utilizing the above characteristics of the GaN amplifier, a special pulse drain adjustment method is adopted, that is, the negative voltage adopts direct current and the positive voltage adopts pulse, and then enters S420;

[0083] S420, when the amplifier is not transmitting, the transmission enable signal is in an invalid state, the amplifier drain is closed, and its reverse isolation performance is used to improve the turn-off ratio of the entire link channel. The reverse isolation of the two-stage GaN amplifier can reach 50dB, so that the amplitude of the carrier signal leaked from the frequency source is lower than the receiving sensitivity of the secondary radar transponder, and then enter S430;

[0084] S430, when the amplifier is working, the transmission enable signal is turned on, the drain provides voltage, the amplifier is in a state of waiting to transmit, and enters S440;

[0085] S440, the amplitude modulator outputs the modulated RF signal into the amplifier circuit for power amplification, and the power is amplified to about 600W, which can amplify the RF signal from -2dBm to +58dBm. The amplified RF signal is output to the transmit-receive diversity unit.

[0086] In a preferred embodiment, an isolator is provided between the first-stage amplifier and the second-stage amplifier, and between the second-stage amplifier and the third-stage amplifier. Figure 3 As shown, a matching attenuator can also be set between the first-stage amplifier and the second-stage amplifier. By adjusting the inter-stage matching through the matching attenuator and the isolator, the amplifier reflection coefficient can be reduced, and the standing wave ratio can be prevented from increasing after the failure of the subsequent amplifier, causing the fault to continue to be transmitted to the previous amplifier, thereby protecting the amplifier.

[0087] In a preferred embodiment, the transmit / receive diversity unit adopts a loop filter circuit including a circulator and a bandpass filter electrically connected.

[0088] The loop filter circuit is a universal transmitter circuit, consisting of a three-port or four-port circulator and a bandpass filter. The circulator mainly realizes the function of transmit and receive diversity. Compared with the use of transmit and receive switches, the circulator, as a passive device, has the advantages of simple circuit, high reliability and low cost. The filter is an LC bandpass filter composed of capacitors and inductors. The appropriate filter order can be selected by comprehensively considering the requirements of volume, out-of-band suppression, insertion loss, etc., to achieve the function of effectively suppressing out-of-band spurious signals.

[0089] The detection unit is also a commonly used circuit in transmitters, which consists of a coupler, a detector diode, a voltage comparator, etc. In the design, a microstrip parallel line coupler is selected. Compared with a coupling bridge, a microstrip coupler can be flexibly designed according to the size of the transmitter. It has the advantages of high reliability, low insertion loss, and low cost, and can realize the function of coupling out a part of the energy of the transmission signal. The detector diode can convert the RF signal into an analog signal. The comparator can determine whether the input signal is normal according to the set threshold level, completing the transmitter self-test function.

[0090] The embodiment of the present invention further provides a secondary radar transponder transmitter, comprising the secondary radar transponder transmitter circuit with high off-state isolation described in any one of the above embodiments of the present invention. The secondary radar transponder transmitter can be used in a transponder of a secondary radar system and in a transponder equipped with an ADS-B system and a secondary radar system.

[0091] The embodiment of the present invention further provides a secondary radar transponder, comprising a receiver, a processing module and the secondary radar transponder transmitter of the above embodiment of the present invention. The secondary radar transponder is equipped with a secondary radar transponder system or an ADS-B system and a secondary radar system at the same time.

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

[0093] The working modes of the transponders equipped with the ADS-B system and the secondary radar system include conventional A, C and S transponder modes. The working procedures for different transponder modes are as follows: Figure 7 As shown, S502-S512 are the transmitter working process, S504-S507 are the conventional A and C response mode working processes, and S508-S512 are the S response mode working process.

[0094] S501, the receiver receives the inquiry signal P1, P3 pulses, decodes them through the processing module, controls the transmitter state through the low-frequency signal, and outputs the transmission coded signal.

[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, starts working, and outputs a carrier signal.

[0096] S503, determine whether the P4 pulse is received, and determine whether the response mode is A, C normal response mode or S response mode. The response delays of A, C, and S mode response 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, the transmission enable signal is turned on, and the amplifier is in a state of waiting to transmit.

[0098] S505, the transmitter receives the normal mode transmission code and transmits the signal in a fixed format.

[0099] S506, outputting a response signal to complete the A and C normal mode responses.

[0100] S507, the frequency source power control signal and the transmission enable signal are turned off, the frequency source is powered off, and the amplifier is turned off.

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

[0102] S509, when receiving the P4 signal, read the information.

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

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

[0105] S512, output a response signal to complete the S-mode response.

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

[0107] Figure 8 The figure shows the timing comparison of the frequency source power supply control signal, the transmission enable signal and the transmission coding signal. Through the timing control of the frequency source power supply control signal, the transmission enable signal and the transmission coding signal, when the transmitter is in the receiving state, the frequency source carrier can be completely shut down without the problem of co-channel interference. When the transmitter does not receive the transmission code, the modulation circuit is in the off state, which can suppress the leaked carrier signal, and through the state control of the amplifier by the transmission enable signal, the carrier signal leaked from the frequency source can be further reversely suppressed, achieving high off-state isolation.

[0108] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A secondary radar response transmission circuit with high off-state isolation, characterized in that: It includes a frequency source unit, a modulation unit, a signal amplification unit, a transceiver diversity unit and a detection unit which are electrically connected in sequence; The frequency source unit is used to power on and output a carrier signal when receiving a frequency source power control signal, and to power off and not output any signal when the frequency source power control signal is invalid; The modulation unit is used to modulate the carrier signal when receiving the transmission coding signal, and output the modulated radio frequency signal, and the transmission time of the transmission coding signal is later than the transmission time of the frequency source power supply control signal; The signal amplification unit is used to amplify the radio frequency signal and output an amplified signal; The transmit / receive diversity unit is used for transmitting / receiving switching and filtering the amplified signal, and outputting the amplified signal after filtering out the stray signals; The detection unit is used to detect the amplified signal after the spurious signals are filtered out, and send the amplified signal after the spurious signals are filtered out to the antenna for transmission.

2. The secondary radar response transmitting circuit with high off-state isolation according to claim 1, characterized in that: The frequency source unit includes a power modulator and a dielectric resonator that are electrically connected, and the power modulator is also connected to a processing module of the transponder to receive a frequency source power control signal sent by the processing module based on a received signal; The power modulator is powered on upon receiving the frequency source power control signal, and outputs a level signal; The dielectric resonator is driven by the level signal to oscillate quickly and output a continuous carrier signal.

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

4. The secondary radar response transmitting circuit with high off-state isolation according to claim 1, characterized in that: The modulation unit includes an inverter and an amplitude modulator; The inverter is used to perform phase inversion when receiving the transmitted coded signal and 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 transmitted coded signal when receiving the transmitted coded signal.

5. The secondary radar response transmitting circuit with high off-state isolation according to claim 4, characterized in that: The modulation unit further includes a high-pass filter, and the high-pass filter is used to process the modulated radio frequency signal.

6. The secondary radar response transmitting circuit with high off-state isolation according to claim 1, characterized in that: 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; the drain power supply of the GaN amplifier is connected to the processing module of the transponder, and is used to turn on the drain power supply through the GaN power-on circuit when receiving the transmission enable signal sent by the processing module. The transmission enable signal is sent later than the frequency source power control signal to improve the isolation of the transmission circuit.

7. The secondary radar response transmitting circuit with high off-state isolation according to claim 6, characterized in that: Isolators are provided between the first-stage amplifier and the second-stage amplifier, and between the second-stage amplifier and the third-stage amplifier.

8. The secondary radar response transmitting circuit with high off-state isolation according to claim 1, characterized in that: The transceiver diversity unit includes a circulator and a bandpass filter which are electrically connected. The circulator is used to realize the transceiver diversity function, and the bandpass filter is used to filter out out-of-band stray signals.

9. A secondary radar transponder transmitter, characterized in that: A secondary radar response transmitting circuit with high off-state isolation comprising the circuit described in any one of claims 1 to 8.

10. Secondary radar transponder, characterized in that: include: A receiver, a processing module and a secondary radar transponder transmitter as claimed in claim 9.

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