CN114355382B - Microwave photon MIMO radar receiving and transmitting system - Google Patents

Abstract

A microwave photon MIMO radar transceiver system belongs to the field of radar detection technology and solves the problems that a high repetition frequency optical frequency comb signal at a transmitting end is difficult to generate and the spurious amount of a de-skewed intermediate frequency signal at a receiving end is high. The transmitting end generates two optical frequency comb signals with different repetition frequencies, one optical frequency comb signal is used as a local oscillator optical frequency comb signal, and the other optical frequency comb signal is used as an optical carrier and modulated by a baseband linear frequency modulation signal. The modulated optical frequency comb signal is divided into two paths, one of which beats with the local oscillator optical frequency comb signal to obtain an up-converted M-path transmitting waveform, and the other is transmitted to a receiving subsystem as a reference optical signal. N receiving antennas at the receiving end receive radar echo signals and then modulate them onto an optical frequency comb signal coupled from a transmitting subsystem, and couple them with a reference optical signal and input them into a photoelectric detector for beat frequency, so as to obtain M×N de-skewed intermediate frequency signals of the echo signal, and then perform digital signal processing after analog-to-digital conversion to obtain target information carried in the echo signal.

Description

A microwave photon MIMO radar transceiver system

Technical Field

The invention belongs to the technical field of radar detection and relates to a microwave photon MIMO radar transceiver system.

Background Art

Radar plays an increasingly important role in military and civilian fields because it can still maintain excellent detection performance under extreme environmental and climatic conditions. Multiple input multiple output (MIMO) radar is a new radar technology that has attracted much attention in recent years. MIMO radar uses the advantages of antenna array spatial diversity and waveform diversity to have an overall performance far superior to single-input single-output radar in terms of target detection, parameter estimation, imaging recognition and anti-interference. Traditional radar systems are limited by electrical devices and it is difficult to achieve a large-bandwidth, multi-channel simultaneous transceiver MIMO radar system. Microwave photonic links have the advantages of low loss, electromagnetic interference resistance, small size, and large-bandwidth signal processing capabilities. In recent years, microwave photonic technology has been increasingly widely introduced in modern radar systems to solve the limitations of traditional electrical devices. In MIMO radar systems, the advantages of microwave photonic technology are used to generate multi-channel orthogonal broadband radar signals. As the amount of received data increases, how to achieve fast real-time processing of radar echo signals is a problem that needs to be solved in the current MIMO radar implementation scheme. In the prior art, the Chinese invention patent application "Microwave Photon MIMO Radar Detection Method and Microwave Photon MIMO Radar System" with application publication number CN108287349A and application publication date July 17, 2018 modulates M intermediate frequency linear frequency modulation signals with the same bandwidth, chirp rate and non-overlapping frequency on M optical carriers with different wavelengths to generate M optical signals that only retain positive and negative second-order sidebands; the M optical signals are combined through an optical wavelength division multiplexer and divided into two paths; one of the paths is divided into N beams of reference light; the other optical signal is photoelectrically converted and the M mutually orthogonal linear frequency modulation signals are separated and transmitted; N receiving antennas are used to receive the target reflection signals respectively, and de-skew processing and wavelength demultiplexing are performed, and the obtained M optical signals are photoelectrically converted, low-pass filtered and analog-to-digital converted respectively to obtain M×N digital signals, and the digital signals are processed to obtain target detection results. However, this document does not solve the problem that high repetition frequency optical frequency comb signals are difficult to generate in the transmitting subsystem and the spurious amount of the de-skewed intermediate frequency signal in the receiving subsystem is high.

Summary of the invention

The object of the present invention is to provide a microwave photon MIMO radar transceiver system to solve the problem that a high repetition frequency optical frequency comb signal is difficult to generate in a transmitting subsystem and the spurious amount of a de-skewed intermediate frequency signal is high in a receiving subsystem.

The present invention solves the above technical problems through the following technical solutions:

A microwave photon MIMO radar transceiver system comprises: a transmitting subsystem (10) and a receiving subsystem (20); the transmitting subsystem (10) generates two optical frequency comb signals with different repetition frequencies, wherein one optical frequency comb signal is used as a local oscillator optical frequency comb signal, and the other optical frequency comb signal is used as an optical carrier of the transmitting subsystem (10) and is modulated by a baseband linear frequency modulation signal; the modulated optical frequency comb signal is divided into two paths, one of which beats with the local oscillator optical frequency comb signal to obtain an up-converted M-path radar transmission waveform, and the other is transmitted to the receiving subsystem (20) as a reference optical signal; the N-path receiving antennas of the receiving subsystem (20) receive radar echo signals, modulate them onto the optical frequency comb signals coupled from the transmitting subsystem (10), couple them with the reference optical signals, and then input them into a photoelectric detector for beat frequency processing to obtain M×N-path de-slanted intermediate frequency signals of the radar echo signals, and then perform digital signal processing after analog-to-digital conversion to obtain target information carried in the echo signals.

In order to realize the generation of large bandwidth transmission signal, the microwave photon MIMO radar transceiver system of the present invention needs to use high repetition frequency optical frequency comb signal at the transmitting end. However, high repetition frequency optical frequency comb is difficult to be directly generated through a simple photon link. The present invention uses a comb filter to filter the low repetition frequency optical frequency comb signal to suppress the frequency component of the original optical frequency comb signal, thereby increasing the repetition frequency of the optical frequency comb. The reference optical signal at the receiving end and the modulated radar echo signal are directly coupled to one channel through an optical coupler. Since the reference signal comes from a different source, the optical frequency comb signal modulated by the echo signal avoids the high-order optical sideband components generated by multiple modulations of the reference signal in the receiver. There are no extra stray optical sidebands between the reference signal and the echo signal in the receiver, so that the optical sideband spectrum of the reference signal and the echo signal entering the photoelectric detector for beat frequency has no other stray components, and finally suppresses the stray in the intermediate frequency signal after de-skewing.

Furthermore, the transmitting subsystem (10) comprises: a laser (301), two optical frequency combs (302), two comb filters (303), an electro-optic modulator (304), two beam splitters (305), an optical coupler (306), an amplifier (307), an arrayed waveguide grating (308), M detectors (309) and a transmitting front end (310); the output end of the laser (301) is respectively connected to the input end of the two optical frequency combs (302), and the output end of the two optical frequency combs (302) is connected to the input end of the two optical frequency combs (302). The output ends are respectively connected to the input ends of two comb filters (303), the output end of the first comb filter (303) is connected to the input end of the electro-optic modulator (304) of the transmitting subsystem (10), the output end of the electro-optic modulator (304) of the transmitting subsystem (10) is connected to the input end of the first beam splitter (305), the modulated wave input port of the electro-optic modulator (304) of the transmitting subsystem (10) inputs the baseband linear frequency modulation signal, and one output end of the first beam splitter (305) is connected to the input end of the first beam splitter (305) of the transmitting subsystem (10). The optical coupler (306) is connected to a first input end of the optical coupler (306), another output end of the first beam splitter (305) is connected to a receiving subsystem (20), the output end of the optical coupler (306) in the transmitting subsystem (10) is connected to an input end of an amplifier (307) in the transmitting subsystem (10), the output end of the amplifier (307) in the transmitting subsystem (10) is connected to an input end of an arrayed waveguide grating (308) in the transmitting subsystem (10), and the M output ends of the arrayed waveguide grating (308) in the transmitting subsystem (10) are connected to the receiving subsystem (20). The second optical coupler (306) is connected to the transmitting subsystem (10), and the output ends of the M detectors (309) in the transmitting subsystem (10) are connected to the transmitting front end (310); the output end of the second comb filter (303) is connected to the input end of the second beam splitter (305), one output end of the second beam splitter (305) is connected to the second input end of the optical coupler (306) in the transmitting subsystem (10), and the other output end of the second beam splitter (305) is connected to the receiving subsystem (20).

Furthermore, the receiving subsystem (20) comprises: N electro-optical modulators (304), N optical couplers (306), an amplifier (307), N arrayed waveguide gratings (308), M×N detectors (309) and a receiving front end (311); the output end of the amplifier (307) in the receiving subsystem (20) is respectively connected to the input end of the N electro-optical modulators (304) in the receiving subsystem (20), the second input end of the N optical couplers (306) in the receiving subsystem (20) is respectively connected to the output end of the N electro-optical modulators (304) in the receiving subsystem (20), and the receiving subsystem ( The modulated wave input ports of the N electro-optical modulators (304) in the receiving subsystem (20) are connected to the N output ports of the receiving front end (311) respectively, the output ports of the N optical couplers (306) in the receiving subsystem (20) are connected to the input ports of the N arrayed waveguide gratings (308) in the receiving subsystem (20), and the M output ports of each arrayed waveguide grating (308) in the receiving subsystem (20) are connected to the input ports of the M detectors (309) in the receiving subsystem (20); the other output port of the beam splitter (305) in the first path is connected to the first input port of the N optical couplers (306) in the receiving subsystem (20). The other output port of the beam splitter (305) in the second path is connected to the input port of the amplifier (307) in the receiving subsystem (20).

Furthermore, the working process of the transmitting subsystem (10) is as follows: the laser (301) generates a continuous wave laser signal and is divided into two paths, which are respectively injected into two locked optical frequency combs (302), so that the optical frequency comb signals generated by the two optical frequency combs (302) are phase-coherent, and the frequency intervals of the optical signals generated by the two optical frequency combs (302) are FSR1 and FSR2 respectively. The signals generated by the two optical frequency combs are respectively input into two comb filters (303), and the interval between adjacent channels of the comb filters (303) is twice the frequency interval of the optical frequency combs (302). Therefore, after the optical signals generated by the optical frequency combs (302) are filtered by the comb filters (303), the frequency interval becomes twice that of the original optical frequency combs; the signal of the first optical frequency comb (302) after passing through the comb filters (303) is input into the electro-optical modulator (304) in the transmitting subsystem (10) as an optical carrier signal, and the optical carrier signal is modulated by the linear frequency modulation signal in the electro-optical modulator. The modulated optical carrier signal is divided into two paths, one of which is input into the receiving subsystem (20) as reference light, and the other is input into one of the input ports of the optical coupler (306) in the transmitting subsystem (10); the optical frequency comb signal generated by the second optical frequency comb (302) is also divided into two paths after being filtered by the comb filter (303), one of which is input into the receiving subsystem (20) as an optical carrier signal, and the other is coupled with the modulated signal in the electro-optical modulator (304) in the transmitting subsystem (10) through the optical coupler (306) in the transmitting subsystem (10), and then amplified by the amplifier (307) in the transmitting subsystem (10) and input into the arrayed waveguide grating (308) in the transmitting subsystem (10). Different channels of the arrayed waveguide grating (308) in the transmitting subsystem (10) select M-channel modulation signals and optical frequency comb signals, which are converted into optical signals by M-channel detectors (309) in the transmitting subsystem (10), thereby obtaining M-channel frequency-orthogonal linear frequency modulation microwave signals. The M-channel orthogonal linear frequency modulation signals are filtered and amplified and then radiated into free space as the transmitting signals of the radar transmitting subsystem (10).

Furthermore, the working process of the receiving subsystem (20) is as follows: the echo signals are collected by N receiving antennas, filtered and amplified by the receiving front end (311), and then respectively input into the input ends of the N electro-optical modulators (304) in the receiving subsystem (20), the N echo signals are respectively modulated onto the optical carriers branched by the second optical frequency comb (302) after filtering, and then respectively input into the N arrayed waveguide gratings (308) in the receiving subsystem (20), each echo and reference optical signal is divided into M different channels for output, and input into the detector (309) in the receiving subsystem (20) for de-skewing operation, to obtain M×N de-skewing intermediate frequency signals, and then digital signal processing is performed after analog-to-digital conversion to obtain the target information carried in the echo signals. The M and N are both positive integers, and the sum of M and N is greater than 2.

Furthermore, the de-skewing operation is to modulate the radar echo signal onto an optical carrier and input it into the array waveguide grating together with the reference light, and the corresponding optical sidebands of the echo signal and the reference light signal are subjected to beat frequency processing in a photodetector to obtain a difference frequency signal between the echo signal and the reference signal.

Furthermore, the laser (301) is used to generate a continuous wave laser signal as an injection reference light source for the optical frequency comb (302).

Furthermore, the comb filter (303) is composed of a plurality of passbands and stopbands periodically arranged at certain frequency intervals. The comb filter (303) is used to filter the low repetition frequency optical frequency comb, suppress specific frequency spectrum components in the original optical frequency comb, and allow the spectrum of specific frequencies to pass, thereby realizing the conversion of the low repetition frequency optical frequency comb to the high repetition frequency optical frequency comb.

Furthermore, the electro-optic modulator (304) operates at a minimum bias point, suppressing the optical carrier signal and retaining only the modulated optical frequency comb signal of the positive and negative first-order optical sidebands.

Furthermore, the linear frequency modulation signal is generated by a digital frequency synthesizer.

The advantages of the present invention are:

In order to realize the generation of large bandwidth transmission signal, the microwave photon MIMO radar transceiver system of the present invention needs to use high repetition frequency optical frequency comb signal at the transmitting end. However, high repetition frequency optical frequency comb is difficult to be directly generated through a simple photon link. The present invention uses a comb filter to filter the low repetition frequency optical frequency comb signal to suppress the frequency component of the original optical frequency comb signal, thereby increasing the repetition frequency of the optical frequency comb. The reference optical signal at the receiving end and the modulated radar echo signal are directly coupled to one channel through an optical coupler. Since the reference signal comes from a different source, the optical frequency comb signal modulated by the echo signal avoids the high-order optical sideband components generated by multiple modulations of the reference signal in the receiver. There are no extra stray optical sidebands between the reference signal and the echo signal in the receiver, so that the optical sideband spectrum of the reference signal and the echo signal entering the photoelectric detector for beat frequency has no other stray components, and finally suppresses the stray in the intermediate frequency signal after de-skewing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram showing that an optical carrier generated by a laser is modulated by a baseband signal and a local oscillator signal;

FIG2 is a schematic diagram of the de-skewing process principle;

FIG3 is a schematic diagram of conventional MIMO radar echo reception;

FIG4 is a schematic diagram of low spurious reception of MIMO radar echoes according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a comb filter filtering a low repetition rate optical frequency comb.

DETAILED DESCRIPTION

In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments:

Embodiment 1

1. Photon-assisted radar signal generation

In radar systems, parameters such as the power, time width, bandwidth, and coding form of the transmitted signal determine the detection distance, detection accuracy, and anti-interference capability of the system. As the next generation of radar systems places increasingly higher demands on detection capabilities, traditional electronic waveform generation technology has become increasingly difficult to meet the needs of radar systems. Photon-assisted signal generation is to modulate the baseband waveform generated in the electrical domain onto an optical carrier through electro-optical conversion, and obtain high-order optical modulation components in the optical domain through operating point control or optical domain filtering. This modulation component is demodulated with the local oscillator signal in the photodetector to generate an up-conversion component of the baseband signal, thereby multiplying the center frequency of the signal. Compared with electronic frequency conversion solutions, photon frequency conversion technology has better amplitude flatness and lower phase nonlinearity.

As shown in FIG1 , the laser generates a single-frequency continuous wave laser signal, such as the waveform shown at point a in FIG1 , which is divided into two paths and input into the electro-optical modulator as an optical carrier signal, wherein the upper optical carrier is modulated by the baseband microwave signal, and the lower optical signal is modulated by the local oscillator signal. The generated optical carrier is as shown in the waveforms at points b and c in FIG1 . The modulated baseband signal is coupled with the local oscillator signal as one path, such as the waveform shown at point d in FIG1 . After being filtered by an optical filter, such as the waveform shown at point e in FIG1 , the required optical sideband is selected, and the local oscillator and the corresponding optical sideband of the microwave signal output by the filter are injected into the photodetector for demodulation, and finally an up-converted microwave signal is obtained. Compared with the original baseband signal, the center frequency of the obtained RF signal can be increased several times.

2. Radar echo signal de-slant reception

De-skewing technology uses homodyne reception to process broadband linear frequency modulation waveforms. The de-skewing intermediate frequency signal can be collected by a low-speed analog-to-digital converter, which greatly reduces the difficulty of subsequent signal processing. In microwave receivers, microwave mixers are used to complete the de-skewing of the local oscillator and echo signal, but the amplitude and phase characteristics of the broadband mixer are inconsistent and intermodulation interference is difficult to eliminate, which limits the dynamic range of the de-skewing system. Microwave photon de-skewing technology has the advantages of high broadband consistency and low spurious. By modulating the radar's reference signal and echo signal onto an optical carrier and using the square-law detection characteristics of the photodetector, the de-skewing output intermediate frequency signal of the reference signal and echo signal can be obtained. Similar to the de-skewing result of electrical devices, the frequency of the intermediate frequency signal corresponds one-to-one to the distance (delay) of the detection area, that is, the broadband transmission signal can be converted into a narrowband intermediate frequency signal, thereby greatly reducing the requirements for the analog-to-digital converter.

As shown in Figure 2, in order to ensure the range resolution index of the radar, the radar's transmitting waveform is required to have a large transmitting bandwidth. The radar echo signal has a certain time delay t compared to the transmitting signal. It is not difficult to see that at the same time, the frequency difference f between the transmitting signal and the echo signal remains unchanged, and the frequency difference corresponds to the target distance. In the radar receiver, if the echo signal is directly sampled and received, due to its large bandwidth, the receiver is required to have a very large sampling rate, which places high demands on the receiver's analog-to-digital converter. The de-skewing receiving process is to mix the radar transmitting signal with the echo signal to obtain the frequency difference between the transmitting signal and the echo signal, that is, to convert the broadband transmitting signal into a narrowband intermediate frequency signal, and then sample the intermediate frequency signal. Since the intermediate frequency signal has a very low frequency, it can be collected with a low-speed analog-to-digital converter, reducing the amount of data after sampling.

Microwave photon de-skewing technology modulates the radar's transmission signal and echo signal onto an optical carrier respectively, and controls the operating point of the electro-optic modulator through a DC voltage, so that the electro-optic modulator works at the minimum bias point. At this time, both the optical carrier and the high-order optical sidebands are suppressed, leaving only the positive and negative first-order optical sidebands modulated by the transmission signal and the echo signal. The modulated optical carrier is filtered to retain the positive first-order optical sidebands of the transmission and echo signals. The positive first-order sidebands of the transmission signal and the echo signal beat in the photoelectric detector to obtain the intermediate frequency signal after the two sidebands are mixed, and finally collected by a low-speed ADC for subsequent digital signal processing.

3. Typical microwave photon radar system

As shown in Figure 3, at the transmitting end, the baseband linear frequency modulation signal is modulated onto the optical carrier generated by the laser. By controlling the working point of the dual parallel modulator, only the positive and negative second-order sidebands of the linear frequency modulation signal are retained at the modulator output end. The modulated optical signal is divided into two paths through an optical coupler, one of which is input to the receiving end as a reference optical signal, and the other is injected into the detector at the transmitting end for photoelectric conversion. The input positive and negative second-order sidebands beat each other to obtain a quadruple frequency signal of the original linear frequency modulation signal, which is amplified and input to the transmitting antenna to radiate into free space.

At the receiving end, the receiving antenna collects the echo signal reflected by the target. After being amplified, the echo signal is modulated by an electro-optical modulator to the reference optical signal coupled from the transmitting end. Since the reference signal is modulated by the echo again, unnecessary high-order sidebands will be generated. After being filtered by an optical filter, it is input into the detector for photoelectric conversion. The echo signal is de-skewed in the detector and finally sampled by the ADC for digital signal processing.

4. Solution of the present invention

As shown in FIG4 , a microwave photon MIMO radar transceiver system includes a transmitting subsystem 10 and a receiving subsystem 20; the transmitting subsystem 10 includes: a laser 301, two optical frequency combs 302, two comb filters 303, an electro-optic modulator 304, two beam splitters 305, an optical coupler 306, an amplifier 307, an arrayed waveguide grating 308, M detectors 309 and a transmitting front end 310; the receiving subsystem 20 includes: N electro-optic modulators 304, N optical couplers 306, an amplifier 307, N arrayed waveguide gratings 308, M×N detectors 309 and a receiving front end 311.

The output end of the laser 301 is connected to the input end of two optical frequency combs 302 respectively. The laser 301 is used to generate a continuous wave laser signal as an injection reference light source of the optical frequency comb 302. The output ends of the two optical frequency combs 302 are connected to the input ends of two comb filters 303 respectively. The output end of the first comb filter 303 is connected to the input end of the electro-optical modulator 304 of the transmitting subsystem 10. The output end of the electro-optical modulator 304 of the transmitting subsystem 10 is connected to the input end of the first beam splitter 305. The modulation wave input port of the electro-optical modulator 304 of the transmitting subsystem 10 inputs the baseband linear frequency modulation signal. An output end of the first beam splitter 305 is connected to a first input end of an optical coupler 306 in the transmitting subsystem 10, another output end of the first beam splitter 305 is respectively connected to the first input ends of N optical couplers 306 of the receiving subsystem 20, an output end of the optical coupler 306 in the transmitting subsystem 10 is connected to an input end of an amplifier 307 in the transmitting subsystem 10, an output end of the amplifier 307 in the transmitting subsystem 10 is connected to an input end of an arrayed waveguide grating 308 in the transmitting subsystem 10, and M output ends of the arrayed waveguide grating 308 in the transmitting subsystem 10 are respectively connected to the transmitting subsystem 10. The output ends of the M detectors 309 in the transmitting subsystem 10 are connected to the transmitting front end 310; the output end of the second comb filter 303 is connected to the input end of the second beam splitter 305, one output end of the second beam splitter 305 is connected to the second input end of the optical coupler 306 in the transmitting subsystem 10, and the other output end of the second beam splitter 305 is connected to the input end of the amplifier 307 in the receiving subsystem 20, and the output ends of the amplifier 307 in the receiving subsystem 20 are respectively connected to the input ends of the N electro-optical modulators 304 in the receiving subsystem 20. The second input ends of the N optical couplers 306 in the receiving subsystem 20 are respectively connected to the output ends of the N electro-optical modulators 304 in the receiving subsystem 20, the modulated wave input ports of the N electro-optical modulators 304 in the receiving subsystem 20 are correspondingly connected to the N output ends of the receiving front end 311, the output ends of the N optical couplers 306 in the receiving subsystem 20 are respectively connected to the input ends of the N arrayed waveguide gratings 308 in the receiving subsystem 20, and the M output ends of each arrayed waveguide grating 308 in the receiving subsystem 20 are respectively connected to the input ends of the M detectors 309 in the receiving subsystem 20.

How the system works

1. Transmission: The laser 301 generates a continuous wave laser signal and is divided into two paths, which are respectively injected into two locked optical frequency combs 302, so that the optical frequency comb signals generated by the two optical frequency combs 302 are phase-coherent. The frequency intervals of the optical signals generated by the two optical frequency combs 302 are FSR1 and FSR2 respectively. The signals generated by the two optical frequency combs are respectively input into two comb filters 303. The interval between adjacent channels of the comb filters 303 is twice the frequency interval of the optical frequency combs 302. Therefore, after the optical signal generated by the optical frequency comb 302 is filtered by the comb filter 303, the frequency interval becomes twice that of the original optical frequency comb; the signal of the first optical frequency comb 302 after passing through the comb filter 303 is input into the electro-optical modulator 304 in the transmitting subsystem 10 as an optical carrier signal, and the optical carrier signal is modulated by the linear frequency modulation signal in the electro-optical modulator. The modulated optical carrier signal is divided into two paths, one of which is input to the receiving subsystem 20 as a reference light, and the other is input to one of the input ports of the optical coupler 306 in the transmitting subsystem 10; the optical frequency comb signal generated by the second optical frequency comb 302 is also divided into two paths after being filtered by the comb filter 303, one of which is input to the receiving subsystem 20 as an optical carrier signal, and the other is coupled with the modulated signal in the electro-optical modulator 304 in the transmitting subsystem 10 through the optical coupler 306 in the transmitting subsystem 10, and then amplified by the amplifier 307 in the transmitting subsystem 10, and then input to the arrayed waveguide grating 308 in the transmitting subsystem 10. Different channels of the arrayed waveguide grating 308 in the transmitting subsystem 10 select M-path modulation signals and optical frequency comb signals, and after photoelectric conversion by the M-path detectors 309 in the transmitting subsystem 10, M-path frequency orthogonal linear frequency modulation microwave signals are obtained, and the M-path orthogonal linear frequency modulation signals are filtered and amplified and radiated into free space as the transmitting signals of the radar transmitting subsystem 10.

As shown in Fig. 5, the comb filter 303 is composed of a plurality of passbands and stopbands arranged periodically at certain frequency intervals. The comb filter 303 is used to filter the low repetition frequency optical frequency comb, suppress some frequency spectrum components in the original optical frequency comb, and allow the spectrum of a specific frequency to pass, thereby realizing the conversion of the low repetition frequency optical frequency comb to the high repetition frequency optical frequency comb. By performing spectrum filtering on the optical frequency comb 302 through the comb filter 303, the repetition frequency of the optical frequency comb 302 signal is doubled, solving the problem that it is difficult to generate a high repetition frequency optical frequency comb signal.

The electro-optic modulator 304 operates at the minimum bias point, suppresses the optical carrier signal, and only retains the modulated optical frequency comb signal of the positive and negative first-order optical sidebands. The linear frequency modulation signal is generated by a digital frequency synthesizer.

2. Receiving: The echo signal is collected by N receiving antennas, filtered and amplified by the receiving front end 311, and then input into the input end of N electro-optical modulators 304 in the receiving subsystem 20. The N echo signals are modulated onto the optical carriers branched by the second optical frequency comb 302 after filtering, and then input into the N arrayed waveguide gratings 308 in the receiving subsystem 20. Each echo and reference optical signal is divided into M different channels for output, and input into the detector 309 in the receiving subsystem 20 for de-skewing operation, and M×N de-skewing intermediate frequency signals are obtained. After analog-to-digital conversion, digital signal processing is performed to obtain the target information carried in the echo signal. The M and N are both positive integers, and the sum of M and N is greater than 2. The de-skewing operation is to modulate the radar echo signal onto the optical carrier, and input it into the arrayed waveguide grating together with the reference light. The corresponding optical sidebands of the echo signal and the reference optical signal are processed in the photoelectric detector to obtain the difference frequency signal of the echo and the reference signal. The reference signal at the receiving end is not modulated by the echo signal, and no new high-order modulation components are added to the reference signal. Finally, the spurious signal of the de-skewed intermediate frequency signal in the receiver can be effectively suppressed.

The present invention proposes a microwave photon MIMO radar transceiver system. Two optical frequency comb signals with different repetition frequencies are generated in the transmitter, one of which is used as a local oscillator optical frequency comb, and the other optical frequency comb is modulated by a baseband linear frequency modulation signal as an optical carrier. The modulated optical frequency comb is divided into two paths, one of which beats with the local oscillator optical frequency comb to obtain an up-converted M-path radar transmission waveform, and the other is transmitted to the receiving end as a reference optical signal; the N-path receiving antenna at the receiving end receives the radar echo signal and modulates it to the optical frequency comb coupled from the transmitting end, and after coupling with the reference optical signal, it is input into a photoelectric detector for beat frequency processing to obtain a de-slanted intermediate frequency signal of the radar echo signal. Finally, after sampling by an analog-to-digital converter, M×N digital signals are obtained, and subsequent digital signal processing is performed to obtain the target information carried in the radar echo.

In the traditional MIMO radar receiving scheme, the radar echo signal directly modulates the optical reference signal, and the modulated signal is input into the detector for de-slanting reception to obtain an intermediate frequency signal (the reference optical signal has been modulated once at the transmitting end, and is modulated again by the radar echo signal at the receiving end, which is prone to generate unnecessary high-order modulation components). In the radar echo signal receiving scheme proposed in the present invention, the radar echo signal is modulated onto an optical carrier signal, and then coupled to the reference optical signal through an optical coupler. The reference optical signal is not modulated twice, which reduces the high-order modulated optical sidebands generated by multiple modulations, thereby suppressing the spurious introduced by the high-order sidebands in the intermediate frequency signal.

The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (6)

1. A microwave photon MIMO radar transceiver system, comprising: a transmitting subsystem (10), a receiving subsystem (20); two paths of optical frequency comb signals with different repetition frequencies are generated in the transmitting subsystem (10), one path of optical frequency comb signals is used as a local oscillator optical frequency comb signal, the other path of optical frequency comb signals is used as an optical carrier wave of the transmitting subsystem (10) to be modulated by a baseband linear frequency modulation signal, the modulated optical frequency comb signals are divided into two paths, one path of optical frequency comb signals and the local oscillator optical frequency comb signals are subjected to beat frequency to obtain M paths of up-converted transmitting waveforms, and the other path of optical frequency comb signals are transmitted to the receiving subsystem (20) to be used as reference optical signals; n paths of receiving antennas of the receiving subsystem (20) receive echo signals, modulate the echo signals onto optical frequency comb signals coupled by the transmitting subsystem (10), couple the echo signals with reference optical signals, input the coupled signals into a photoelectric detector for beat frequency processing to obtain M multiplied by N paths of deskew intermediate frequency signals of the echo signals, and perform digital signal processing after analog-to-digital conversion to obtain target information carried in the echo signals;

The transmitting subsystem (10) comprises: a laser (301), 2 optical frequency combs (302), 2 comb filters (303), 1 electro-optic modulator (304), 2 beam splitters (305), 1 optical coupler (306), 1 amplifier (307), 1 arrayed waveguide grating (308), M detectors (309), and a transmit front end (310); the output ends of the lasers (301) are respectively connected with the input ends of 2 optical frequency combs (302), the output ends of the 2 optical frequency combs (302) are respectively connected with the input ends of 2 comb filters (303), the output ends of a first path of comb filters (303) are connected with the input ends of electro-optic modulators (304) of the transmitting subsystem (10), the output ends of the electro-optic modulators (304) of the transmitting subsystem (10) are connected with the input ends of a first path of beam splitters (305), the modulation wave input ends of the electro-optic modulators (304) of the transmitting subsystem (10) are input with baseband chirp signals, one output end of the first path of beam splitters (305) is connected with the first input end of an optical coupler (306) in the transmitting subsystem (10), the other output end of the first path of beam splitters (305) is connected with a receiving subsystem (20), the output end of the optical coupler (306) in the transmitting subsystem (10) is connected with the input end of an amplifier (307) in the transmitting subsystem (10), the output end of the amplifier (307) in the transmitting subsystem (10) is connected with the input end of a waveguide (308) in the transmitting subsystem (10) in the array (308) respectively connected with the output ends of the transmitting subsystem (308) in the transmitting subsystem (10), the output ends of the M detectors (309) in the transmitting subsystem (10) are connected with the transmitting front end (310); the output end of the second path comb filter (303) is connected with the input end of the second path beam splitter (305), one output end of the second path beam splitter (305) is connected with the second input end of the optical coupler (306) in the transmitting subsystem (10), and the other output end of the second path beam splitter (305) is connected with the receiving subsystem (20);

The receiving subsystem (20) comprises: n electro-optic modulators (304), N optical couplers (306), 1 amplifier (307), N arrayed waveguide gratings (308), M x N detectors (309), and a receiving front end (311); the output ends of the amplifiers (307) in the receiving subsystem (20) are respectively connected with the input ends of N electro-optical modulators (304) in the receiving subsystem (20), the second input ends of N optical couplers (306) in the receiving subsystem (20) are respectively connected with the output ends of N electro-optical modulators (304) in the receiving subsystem (20), the modulation wave input ports of N electro-optical modulators (304) in the receiving subsystem (20) are correspondingly connected with N output ends of the receiving front end (311), the output ends of N optical couplers (306) in the receiving subsystem (20) are respectively connected with the input ends of N array waveguide gratings (308) in the receiving subsystem (20), and the M output ends of each array waveguide grating (308) in the receiving subsystem (20) are respectively connected with the input ends of M detectors (309) in the receiving subsystem (20); the other output end of the first beam splitter (305) is respectively connected with the first input ends of N optical couplers (306) of the receiving subsystem (20); the other output end of the second path of beam splitter (305) is connected with the input end of an amplifier (307) in the receiving subsystem (20);

The working flow of the transmitting subsystem (10) comprises the following steps: the laser (301) generates continuous wave laser signals and is divided into two paths, the two paths are respectively injected and locked into 2 optical frequency combs (302), so that optical frequency comb signals generated by the 2 optical frequency combs (302) are phase-related, the frequency intervals of the optical signals generated by the 2 optical frequency combs (302) are FSR1 and FSR2 respectively, the signals generated by the 2 optical frequency combs are respectively input into 2 comb filters (303), the adjacent channel intervals of the comb filters (303) are twice the frequency intervals of the optical frequency combs (302), and therefore, after the optical signals generated by the optical frequency combs (302) are filtered by the comb filters (303), the frequency intervals are twice the frequency intervals of original optical frequency combs; the signal of the first path of optical frequency comb (302) after passing through the comb filter (303) is input into an electro-optic modulator (304) in the transmitting subsystem (10) as an optical carrier signal, and the optical carrier signal is modulated by a linear frequency modulation signal in the electro-optic modulator; the modulated optical carrier signal is divided into two paths, wherein one path is used as reference light to be input into a receiving subsystem (20), and the other path is input into one input port of an optical coupler (306) in a transmitting subsystem (10); the optical frequency comb signal generated by the second optical frequency comb (302) is divided into two paths after being filtered by a comb filter (303), one path is used as an optical carrier signal to be input into a receiving subsystem (20), the other path is coupled with a modulated signal in an electro-optical modulator (304) in a transmitting subsystem (10) through an optical coupler (306) in the transmitting subsystem (10), and the modulated signal is amplified by an amplifier (307) in the transmitting subsystem (10) and then is input into an array waveguide grating (308) in the transmitting subsystem (10); m paths of modulation signals and optical frequency comb signals are selected from different channels of an array waveguide grating (308) in the transmitting subsystem (10), after photoelectric conversion of M paths of detectors (309) in the transmitting subsystem (10), M paths of orthogonal frequency-modulated linear microwave signals are obtained, and the M paths of orthogonal linear frequency-modulated signals are used as transmitting signals of the radar transmitting subsystem (10) to radiate into free space after being filtered and amplified;

The workflow of the receiving subsystem (20): the echo signals are collected through N paths of receiving antennas, filtered and amplified by a receiving front end (311) and then respectively input into the input ends of N electro-optical modulators (304) in a receiving subsystem (20), the N paths of echo signals are respectively modulated onto optical carriers which are branched after being filtered by a second path of optical frequency comb (302), the N paths of echo signals are respectively input into N array waveguide gratings (308) in the receiving subsystem (20), each path of echo and a reference optical signal are respectively divided into M paths of different channels to be output, and the M paths of echo signals and the M paths of reference optical signals are input into a detector (309) in the receiving subsystem (20) to be subjected to declining operation to obtain M multiplied by N paths of declining intermediate frequency signals, and then are subjected to digital signal processing after analog-digital conversion to obtain target information carried in the echo signals; m, N are positive integers, and the sum of M and N is more than 2.

2. The microwave photon MIMO radar receiving and transmitting system according to claim 1, wherein the deskewing operation is to modulate a radar echo signal onto an optical carrier and input the radar echo signal and a reference light together into an arrayed waveguide grating, and the corresponding optical sidebands of the echo signal and the reference light signal are subjected to beat frequency processing in a photodetector to obtain a difference frequency signal of the echo signal and the reference signal.

3. A microwave photon MIMO radar transceiver system as in claim 1 wherein the laser (301) is configured to generate a continuous wave laser signal as an injection reference source for the optical frequency comb (302).

4. The microwave photon MIMO radar transceiver system of claim 1, wherein the comb filter (303) is composed of a plurality of pass bands and stop bands periodically arranged at certain frequency intervals, the comb filter (303) is used to filter the low repetition frequency optical frequency comb, specific frequency spectrum components in the original optical frequency comb are suppressed, and the spectrum of specific frequency is allowed to pass, so that the conversion from the low repetition frequency optical frequency comb to the high repetition frequency optical frequency comb is realized.

5. The microwave photon MIMO radar transceiver system of claim 1, wherein said electro-optical modulator (304) operates at a minimum bias point to suppress optical carrier signals and only retains modulated optical frequency comb signals of positive and negative first order optical sidebands.

6. A microwave-photonic MIMO radar transceiver system in accordance with claim 1, wherein the chirp signal is generated by a digital frequency synthesizer.