CN110806576B - Microwave photon large-range automatic focusing radar imaging system and method - Google Patents

Microwave photon large-range automatic focusing radar imaging system and method Download PDF

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CN110806576B
CN110806576B CN201911182685.5A CN201911182685A CN110806576B CN 110806576 B CN110806576 B CN 110806576B CN 201911182685 A CN201911182685 A CN 201911182685A CN 110806576 B CN110806576 B CN 110806576B
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radar
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CN110806576A (en
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郑小平
肖雪迪
李尚远
薛晓晓
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Tsinghua University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging

Abstract

The invention discloses a microwave photon large-range automatic focusing radar imaging system and a method, wherein the system comprises: the microwave source is connected with the reconfigurable microwave photon radar transmitter and the reconfigurable microwave photon radar receiver; the radar transmitter is connected with the radio frequency front end of the transmitter and the radar receiver; the radio frequency front end of the transmitter is connected with a transmitting antenna; the receiving antenna is connected with the radio frequency front end of the receiver; the radio frequency front end of the receiver is connected with the radar receiver; the receiver is connected with the control and processing module; the control and processing module is connected with the radar transmitter. The method comprises the steps of obtaining the distance between a target and a radar system through matched filtering in a narrow-band ranging mode, adjusting the time sequence relation of a trigger signal of a transmitter according to the target distance in a wide-band imaging mode, controlling signal time delay to enable the target distance to fall in a distance window of a deskew receiver, achieving automatic focusing of the target, and then carrying out digital signal processing on the deskew signal to carry out high-resolution imaging on the target.

Description

Microwave photon large-range automatic focusing radar imaging system and method
Technical Field
The invention relates to the technical field of radar imaging, in particular to a microwave photon large-range automatic focusing radar imaging system and method.
Background
Due to the all-time and all-weather observation capability, the radar system is very critical to target detection, tracking and identification. By radar imaging, the spatial distribution of scattering points of the target can be obtained, thereby identifying and classifying the target. As targets become more complex and diverse, the need for radars with higher resolving power is more and more urgent. Higher time jitter is introduced when higher frequency and larger bandwidth signals are generated and processed based on conventional electronics methods, so that it is difficult to continue to increase the bandwidth and frequency of the radar system.
The radar imaging system is a feasible approach constructed by a microwave photonics method, and the current common microwave photon radar system has a structure as shown in fig. 1, and comprises a microwave photon radar transmitter, a transmitter radio frequency front end, a transmitting antenna, a receiving antenna, a receiver radio frequency front end, a microwave photon radar deskew receiver, a dimmable delay module and a signal processing module. At the transmitting end, the microwave photon radar transmitter generates a broadband radar signal and divides the broadband radar signal into two paths, one path is output from the transmitter and sent to the radio frequency front end of the transmitter, and the other path is used as a reference signal and sent to the dimmable time delay module to adjust time delay. And the output end of the adjustable light time delay module is sent to the reference signal input end of the microwave photon radar deskew receiver. The output end of the radio frequency front end of the transmitter is connected with the input end of the transmitting antenna. At a receiving end, the output end of a receiving antenna is connected with the input end of the radio frequency front end of a receiver, and the output end of the radio frequency front end of the receiver is connected with the receiving signal input end of a microwave photon radar deskew receiver; the microwave photon radar deskew receiver utilizes the broadband radar signal received from the microwave photon radar transmitter as a reference signal for deskew processing, and performs deskew processing on an echo signal received at the radio frequency front end of the receiver to generate a deskew signal and sends the deskew signal to the signal processing module. By adopting the deskew processing, the linear frequency modulation echo signal of the high-frequency broadband can be converted into the single-frequency signal of the low-frequency narrowband, and the high-resolution range image of the target can be obtained by FFT processing on the deskew signal. But the distance window for the deskew process is limited: when the target distance is far away, the delay of the echo signal is larger than that of the reference signal, so that the frequency of the signal subjected to deskew processing is higher, and the signal may fall outside the bandwidth of a microwave photon radar deskew receiver; under more extreme conditions, the delay of the echo signal is very large, so that the echo signal and the reference signal are not overlapped in time, the deskew processing cannot be completed, and the focusing on the target cannot be realized. Therefore, in order to achieve focusing on the target, it is necessary to ensure a large overlap time between the echo signal and the reference signal. Although the echo signal and the reference signal can have larger overlapping time by adjusting the time delay of the reference signal through the adjustable light time delay module, the focusing of targets with different distances cannot be realized due to the limited time delay adjusting range of the adjustable light time delay module. In addition, in an actual scene, an external system is required to provide an approximate distance of the target, and then the delay amount of the adjustable optical delay module is adjusted according to the distance. The focusing of the target cannot be realized based on a single radar system, and a high-resolution image of the target cannot be acquired. Therefore, current microwave photonic radar systems still have problems in achieving high resolution imaging of targets.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art.
Therefore, an object of the present invention is to provide a microwave photon large-range automatic focusing radar imaging system, which can realize large-range automatic focusing and high-resolution imaging of targets with different distances. The microwave photon large-range automatic focusing radar imaging system provided by the invention has important significance for detection, tracking and identification of targets.
The invention also aims to provide a microwave photon large-range automatic focusing radar imaging method.
In order to achieve the above object, an embodiment of the present invention provides a microwave photon wide-range auto-focusing radar imaging system, including: the reconfigurable microwave photon radar system comprises a reconfigurable microwave photon radar transmitter, a transmitter radio frequency front end, a transmitting antenna, a receiving antenna, a receiver radio frequency front end, a reconfigurable microwave photon radar receiver, a microwave source and a control and processing module;
the microwave source is connected with the reconfigurable microwave photon radar transmitter and the reconfigurable microwave photon radar receiver and is used for generating local oscillation signals and sending the local oscillation signals to the reconfigurable microwave photon radar transmitter and the reconfigurable microwave photon radar receiver;
the reconfigurable microwave photon radar transmitter is connected with the transmitter radio frequency front end and the reconfigurable microwave photon radar receiver and is used for generating a transmitting signal and a reference signal, sending the transmitting signal to the transmitter radio frequency front end and sending the reference signal to the reconfigurable microwave photon radar receiver;
the transmitter radio frequency front end is connected with the transmitting antenna and used for amplifying the transmitting signal and transmitting the amplified transmitting signal to the transmitting antenna;
the transmitting antenna is used for radiating the amplified transmitting signal to the air;
the receiving antenna is connected with the radio frequency front end of the receiver and used for receiving an echo signal radiated to a target by the transmitting signal and sending the echo signal to the radio frequency front end of the receiver;
the receiver radio-frequency front end is connected with the reconfigurable microwave photon radar receiver and is used for amplifying the echo signal and sending the amplified echo signal to the reconfigurable microwave photon radar receiver;
the reconfigurable microwave photon radar receiver is connected with the control and processing module and is used for performing down-conversion processing on the amplified echo signals and the local oscillator signals to generate down-conversion signals and/or performing deskew processing on the amplified echo signals and the reference signals to generate deskew signals;
the control and processing module is connected with the reconfigurable microwave photon radar transmitter and is used for carrying out digital signal processing on the down-conversion signal and/or the deskew signal to obtain an imaging result of a target, generating a transmitter trigger signal and further controlling time delay between the transmitting signal and the reference signal.
According to the microwave photon large-range automatic focusing radar imaging system, a transmitter and a receiver can be reconstructed by utilizing microwave photons, and the distance between a target and a radar is obtained through matched filtering processing and measurement; according to the distance, the generation time of the transmitting signal and the reference signal is controlled, so that the deskew frequency of the echo signal and the reference signal falls within the bandwidth of the deskew receiver, and the target distance falls within a distance window of the deskew receiver, namely, the automatic focusing of the target is realized; by further digital signal processing, a high resolution image of the target can be obtained. The radar imaging system is used for generating and processing radar signals based on a microwave photonics method by utilizing a microwave photon large-range automatic focusing radar imaging system, and the advantages of microwave photon broadband and reconfigurability can be fully exerted, so that a high-resolution image of a target can be obtained. Compared with the current system for adjusting the time delay of the reference signal by using the adjustable light time delay module, the system has a larger time delay adjusting range, can realize large-range automatic focusing and high-resolution imaging of targets with different distances, and has important significance on detection, tracking and identification of the targets.
In addition, the microwave photon wide-range automatic focusing radar imaging system according to the above embodiment of the present invention may further have the following additional technical features:
further, in an embodiment of the present invention, at a transmitting end, an output end of the microwave source is connected to a local oscillator signal input end of the reconfigurable microwave photonic radar transmitter, a transmitting signal output end of the reconfigurable microwave photonic radar transmitter is connected to an input end of a radio frequency front end of the transmitter, an output end of the radio frequency front end of the transmitter is connected to an input end of the transmitting antenna, and a reference signal output end of the reconfigurable microwave photonic radar transmitter is connected to a reference signal input end of the reconfigurable microwave photonic radar receiver;
at a receiving end, the output end of the receiving antenna is connected with the input end of the radio frequency front end of the receiver, the output end of the radio frequency front end of the receiver is connected with the receiving signal input end of the reconfigurable microwave photon radar receiver, the other output end of the microwave source is connected with the local oscillation signal input end of the reconfigurable microwave photon radar receiver, and the output end of the reconfigurable microwave photon radar receiver is connected with the input end of the control and processing module;
and the output end of the control and processing module is connected with the reconfigurable microwave photon radar transmitter.
Further, in one embodiment of the present invention, the reconfigurable microwave photonic radar transmitter includes: the device comprises a trigger signal generator, a photon digital-to-analog converter, an optical up-conversion module, an optical switch, two photoelectric detectors and two filters;
one output port of the trigger signal generator is connected with the photon digital-to-analog converter, the other output port of the trigger signal generator is connected with the optical switch, the output end of the photon digital-to-analog converter is connected with the input end of the optical up-conversion module, the output end of the optical up-conversion module is connected with the input end of the optical switch, the two output ends of the optical switch are respectively connected with the input ends of the two photoelectric detectors, the output ends of the two photoelectric detectors are respectively connected with the input ends of the two filters, the output end of one filter is used as a transmitting signal output end and connected with the input end of the radio frequency front end of the transmitter, and the output end of the other filter is used as a reference signal output end and connected with the reference signal input end of the reconfigurable microwave photon radar receiver.
Further, in one embodiment of the present invention, the reconfigurable microwave photonic radar transmitter includes: the device comprises a photon digital-to-analog converter, an optical up-conversion module, a photoelectric detector, a filter and a microwave switch;
one output port of the trigger signal generator is connected with the photon digital-to-analog converter, the other output port of the trigger signal generator is connected with the microwave switch, the output end of the photon digital-to-analog converter is connected with the input end of the optical up-conversion module, the output end of the optical up-conversion module is connected with the input end of the photoelectric detector, the output end of the photoelectric detector is connected with the input end of the filter, the output end of the filter is connected with the input end of the microwave switch, one output end of the microwave switch serves as a transmitting signal output end and is connected with the input end of the radio frequency front end of the transmitter, and the other output end of the microwave switch serves as a reference signal output end and is connected with the reference signal input end of the reconfigurable microwave photon radar receiver.
Further, in one embodiment of the present invention, the optical up-conversion module is used for optically up-converting the baseband signal, and comprises a microwave source and an electro-optical intensity modulator;
the microwave source output end is connected with the radio frequency input end of the electro-optical intensity modulator, the optical input end of the electro-optical intensity modulator is connected with the output end of the photon digital-to-analog converter, and the output end of the electro-optical intensity modulator is connected with the input end of the optical switch or the photoelectric detector.
Further, in one embodiment of the present invention, the reconfigurable microwave photonic radar receiver includes: the device comprises a laser, an optical receiving module, a microwave switch and an analog-to-digital converter;
wherein, the output end of the laser is connected with the input end of the optical receiving module, one input end of the microwave switch is used as the local oscillator signal input end of the reconfigurable microwave photon radar receiver to be connected with the local oscillator signal output by the microwave source, the other input end is used as the reference signal input end of the reconfigurable microwave photon radar receiver to be connected with the reference signal output by the reconfigurable microwave photon radar transmitter, the output end of the microwave switch is connected with one radio frequency input port of the optical receiving module, the other radio frequency input port of the optical receiving module is used as a receiving signal input end of the reconfigurable microwave photon radar receiver and is connected with the output end of the radio frequency front end of the receiver, the output end of the optical receiving module is connected with the input end of the analog-to-digital converter, and the output end of the analog-to-digital converter is connected with the input end of the control and processing module.
Further, in an embodiment of the present invention, the optical receiving module includes: a double parallel modulator, a photodetector and a low pass filter;
the input ports of the double parallel modulators are connected with the output end of the laser, the two radio frequency input ports of the double parallel modulators correspond to the two radio frequency input ports of the optical receiving module, the output ends of the double parallel modulators are connected with the input end of the photoelectric detector, the output end of the photoelectric detector is connected with the input end of the low-pass filter, and the output end of the low-pass filter is connected with the input end of the analog-to-digital converter.
In order to achieve the above object, another embodiment of the present invention provides a microwave photon wide-range auto-focusing radar imaging method, including:
s1, generating radio frequency narrowband chirp waves according to the narrowband radar signals and the local oscillator signals, and radiating the radio frequency narrowband chirp waves to the air;
s2, generating a first echo signal after the radio frequency narrow-band linear frequency modulation wave is radiated to a target, and performing down-conversion processing according to the first echo signal and the local oscillator signal to generate a low-frequency narrow-band signal after echo down-conversion;
s3, processing the low-frequency narrow-band signal after the echo down-conversion to obtain target echo delay;
s4, generating a broadband radar signal and a reference signal according to the target echo delay, generating a radio frequency broadband linear frequency modulation wave according to the broadband radar signal and the local oscillator signal, and radiating the radio frequency broadband linear frequency modulation wave to the air;
s5, radiating the radio frequency broadband linear frequency modulation wave to a target to generate a second echo signal, and performing deskew processing according to the second echo signal and the reference signal to generate a low-frequency narrow-band signal after deskew of the echo;
and S6, processing the low-frequency narrow-band signal after the echo is deskewed to obtain high-resolution imaging of the target.
According to the microwave photon large-range automatic focusing radar imaging method, the first echo signal is obtained by emitting the radio frequency narrow-band linear frequency modulation wave, and the distance between the target and the radar is obtained according to the first echo signal and the local oscillator signal. And controlling the time for generating the transmitting signal and the reference signal according to the distance, generating a second echo signal by transmitting a radio frequency broadband linear frequency modulation wave, enabling the deskew frequency of the echo signal and the reference signal to fall within the bandwidth of the deskew receiver, and enabling the target distance to fall within a distance window of the deskew receiver, namely realizing automatic focusing on the target. The deskewed signals are further processed to achieve high resolution imaging of the target. The method has a larger time delay adjusting range, can realize large-range automatic focusing and high-resolution imaging of targets with different distances, and has important significance for detection, tracking and identification of the targets.
In addition, the microwave photon large-range automatic focusing radar imaging method according to the above embodiment of the present invention may further have the following additional technical features:
further, in an embodiment of the present invention, the S1-S3 further includes:
acquiring an optical signal carrying a baseband narrowband chirp as the narrowband radar signal, wherein the baseband narrowband chirp is as follows:
Figure BDA0002291690220000051
wherein, TpnIs the pulse width, V, of the baseband narrow-band chirp wavebnIs the amplitude, f1nIs the starting frequency, knIs the chirp rate, t is time;
processing the narrow-band radar signal and the local oscillator signal to generate a radio frequency narrow-band chirp, wherein the radio frequency narrow-band chirp is as follows:
Figure BDA0002291690220000052
wherein, VTnIs the amplitude, f, of the radio frequency narrowband chirp waveLOIs the frequency of the local oscillator signal provided by the microwave source;
amplifying the radio frequency narrow-band chirp waves and radiating the radio frequency narrow-band chirp waves into the air, wherein the radio frequency narrow-band chirp waves generate a first echo signal after being radiated to a target, and the first echo signal is as follows:
Figure BDA0002291690220000053
where τ is the target echo delay;
amplifying and filtering the first echo signal, performing down-conversion processing on the amplified and filtered first echo signal and the local oscillator signal, and generating a low-frequency narrow-band signal after echo down-conversion, where the low-frequency narrow-band signal after echo down-conversion is:
sdown(t)∝cos[2πf1n(t-τ)+knπ(t-τ)2-2πfLOτ]
and processing the low-frequency narrow-band signal after the echo down-conversion to obtain the target echo delay.
Further, in an embodiment of the present invention, the S4-S6 further includes:
acquiring an optical signal carrying a baseband broadband chirp as the broadband radar signal, wherein the baseband broadband chirp is as follows:
Figure BDA0002291690220000061
wherein, TpwIs the pulse width, V, of a baseband broadband chirpbwIs the amplitude, f1wIs the starting frequency, kwIs the chirp rate, t is time;
processing the broadband radar signal and the local oscillator signal to generate a radio frequency broadband chirp, wherein the radio frequency broadband chirp is as follows:
Figure BDA0002291690220000062
wherein, VTwIs the amplitude, f, of the radio frequency broadband chirpLOIs the frequency of the local oscillator signal provided by the microwave source;
amplifying the radio frequency broadband linear frequency modulation wave and radiating the amplified radio frequency broadband linear frequency modulation wave to the air, and generating the reference signal after the broadband radar signal according to the target echo delay, wherein the reference signal is as follows:
Figure BDA0002291690220000063
wherein, Δ τ is a delay difference between the reference signal and the echo signal;
generating a second echo signal after the radio frequency broadband chirp is radiated to the target, wherein the second echo signal is:
Figure BDA0002291690220000064
where τ is the target echo delay;
amplifying and filtering the second echo signal, and deskewing the amplified and filtered second echo signal and the reference signal to generate a low-frequency narrowband signal after echo deskew, where the low-frequency narrowband signal after echo deskew is:
sdechirp(t)＝cos[2kwπΔτt+2π(f1w+fLO)Δτ-kwπΔτ2-2kwπΔτ·τ]
and processing the low-frequency narrow-band signal after the echo is deskewed to obtain high-resolution imaging of the target.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The foregoing and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic structural diagram of a conventional microwave photon radar system;
FIG. 2 is a schematic structural diagram of a microwave photon large-range auto-focus radar imaging system according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a reconfigurable microwave photonic radar transmitter architecture according to one embodiment of the present invention;
FIG. 4 is a schematic diagram of an optical upconversion module of a reconfigurable microwave photonic radar transmitter in accordance with an embodiment of the present invention;
FIG. 5 is a schematic diagram of a reconfigurable microwave photonic radar receiver architecture according to one embodiment of the present invention;
FIG. 6 is a schematic diagram of an optical receive block of a reconfigurable microwave photonic radar receiver according to one embodiment of the present invention;
FIG. 7 is a diagram illustrating range profile results according to one embodiment of the present invention;
FIG. 8 is a flowchart of a microwave photon wide-range autofocus radar imaging method according to an embodiment of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
The microwave photon large-range automatic focusing radar imaging system and method provided by the embodiment of the invention are described below with reference to the attached drawings.
First, a microwave photonic wide-range auto-focus radar imaging system proposed according to an embodiment of the present invention will be described with reference to the accompanying drawings.
Fig. 2 is a schematic structural diagram of a microwave photon large-range auto-focusing radar imaging system according to an embodiment of the present invention.
As shown in fig. 2, the microwave photon wide-range auto-focus radar imaging system includes: the system comprises 1 reconfigurable microwave photon radar transmitter, 1 transmitter radio frequency front end, 1 transmitting antenna, 1 receiving antenna, 1 receiver radio frequency front end, 1 reconfigurable microwave photon radar receiver, 1 microwave source and 1 control and processing module.
The microwave source is connected with the reconfigurable microwave photon radar transmitter and the reconfigurable microwave photon radar receiver and used for generating local oscillation signals and sending the local oscillation signals to the reconfigurable microwave photon radar transmitter and the reconfigurable microwave photon radar receiver;
the reconfigurable microwave photon radar transmitter is connected with the transmitter radio frequency front end and the reconfigurable microwave photon radar receiver and is used for generating a transmitting signal and a reference signal, transmitting the transmitting signal to the transmitter radio frequency front end and transmitting the reference signal to the reconfigurable microwave photon radar receiver;
the transmitter radio frequency front end is connected with the transmitting antenna and used for amplifying the transmitting signal and transmitting the signal to the transmitting antenna;
the transmitting antenna is used for radiating the amplified transmitting signal to the air;
the receiving antenna is connected with the radio frequency front end of the receiver and used for receiving an echo signal after the emission signal is radiated to a target and sending the echo signal to the radio frequency front end of the receiver;
the receiver radio frequency front end is connected with the reconfigurable microwave photon radar receiver and is used for amplifying the echo signal and sending the amplified echo signal to the reconfigurable microwave photon radar receiver;
the reconfigurable microwave photon radar receiver is connected with the control and processing module and is used for performing down-conversion processing on the amplified echo signals and local oscillation signals to generate down-conversion signals and/or performing deskew processing on the amplified echo signals and reference signals to generate deskew signals;
the control and processing module is connected with the reconfigurable microwave photon radar transmitter and is used for carrying out digital signal processing on the down-conversion signal and/or the deskew signal to obtain an imaging result of a target, generating a transmitter trigger signal and further controlling time delay between the transmitting signal and the reference signal.
At the transmitting end, the output end of the microwave source is connected with the local oscillator signal input end of the reconfigurable microwave photon radar transmitter, the transmitting signal output end of the reconfigurable microwave photon radar transmitter is connected with the input end of the radio frequency front end of the transmitter, the output end of the radio frequency front end of the transmitter is connected with the input end of the transmitting antenna, and the reference signal output end of the reconfigurable microwave photon radar transmitter is connected with the reference signal input end of the reconfigurable microwave photon radar receiver.
At a receiving end, the output end of the receiving antenna is connected with the input end of the radio frequency front end of the receiver, the output end of the radio frequency front end of the receiver is connected with the receiving signal input end of the reconfigurable microwave photon radar receiver, the output end of the microwave source is connected with the local oscillation signal input end of the reconfigurable microwave photon radar receiver, and the output end of the reconfigurable microwave photon radar receiver is connected with the input end of the control and processing module.
It is to be understood that the microwave source is configured to provide local oscillator signals to the reconfigurable microwave photonic radar transmitter and the reconfigurable microwave photonic radar receiver, and conventional devices may be used.
The reconfigurable microwave photon radar transmitter is used for generating a transmitting signal to be sent to the radio frequency front end of the transmitter, generating a reference signal to be sent to the reconfigurable microwave photon radar receiver.
The transmitter radio frequency front end is used for amplifying radar signals received from the reconfigurable microwave photon radar transmitter, generating high-power radar signals and sending the radar signals to the transmitting antenna, and conventional components can be adopted.
The transmitting antenna is used for radiating radar signals received from the radio frequency front end of the transmitter to the air, the receiving antenna is used for receiving echo signals sent by the transmitting antenna and radiated to a target, and the echo signals are sent to the radio frequency front end of the receiver, and the transmitting antenna and the receiving antenna both adopt conventional components.
The receiver radio frequency front end is used for amplifying the echo signals received from the receiving antenna and sending the echo signals to the reconfigurable microwave photon radar receiver, and conventional components can be adopted.
The reconfigurable microwave photon radar receiver performs down-conversion processing or deskew processing on an echo signal received by a radio frequency front end of the receiver by using a local oscillator signal received from a microwave source or a reference signal received from a reconfigurable microwave photon radar transmitter, generates a down-conversion signal or a deskew signal and sends the down-conversion signal or the deskew signal to the control and processing module.
The control and processing module is used for carrying out digital signal processing on the received down-conversion or deskew signals to obtain imaging results; and is used for generating a transmitter trigger signal so as to control the generation time of the transmission signal and the reference signal; conventional components may be employed.
As shown in fig. 3, the reconfigurable microwave photonic radar transmitter may be divided into two structures, where the structure shown in fig. 3(a) includes 1 trigger signal generator, 1 photonic digital-to-analog converter, 1 optical up-conversion module, 1 optical switch, two photodetectors, and two filters.
The output port 1 of the trigger signal generator is connected with a photon digital-to-analog converter, the output port 2 is connected with an optical switch, the output end of the photon digital-to-analog converter is connected with the input end of an optical up-conversion module, the output end of the optical up-conversion module is connected with the input end of the optical switch, the two output ends of the optical switch are respectively connected with the input ends of two photoelectric detectors, the output ends of the two photoelectric detectors are respectively connected with the input ends of two filters, the output end (transmitting signal output end) of one filter is connected with the input end of the radio frequency front end of a transmitter, and the output end (reference signal output end) of the other filter is connected with the reference signal input end of a reconfigurable microwave photon radar receiver. The model requirement is as follows: the trigger signal generator has two output channels. The optical switch adopts a 1 multiplied by 2 optical switch, and the switching speed is less than or equal to ns magnitude. The bandwidth of the photodetector is greater than the highest signal frequency. The filter is a band-pass filter, and the bandwidth covers the target wave band. The rest parts adopt conventional parts.
The structure shown in fig. 3(b) includes 1 trigger signal generator, 1 photon digital-to-analog converter, 1 optical up-conversion module, 1 photodetector, 1 filter, and 1 microwave switch.
An output port 1 of the trigger signal generator is connected with a photon digital-to-analog converter, an output port 2 of the trigger signal generator is connected with a microwave switch, an output end of the photon digital-to-analog converter is connected with an input end of an optical up-conversion module, an output end of the optical up-conversion module is connected with an input end of a photoelectric detector, an output end of the photoelectric detector is connected with an input end of a filter, an output end of the filter is connected with an input end of the microwave switch, one output end (a transmitting signal output end) of the microwave switch is connected with an input end of a radio frequency front end of a transmitter, and the other output end (a reference signal output end) of the microwave switch is connected with a reference signal input end of a reconfigurable microwave photon radar receiver. The model requirement is as follows: the trigger signal generator has two output channels. The bandwidth of the photodetector is greater than the highest signal frequency. The filter is a band-pass filter, and the bandwidth covers the target wave band. The microwave switch adopts a 1 multiplied by 2 microwave switch, and the switching speed is less than or equal to ns magnitude. The rest parts adopt conventional parts.
The optical up-conversion module in the reconfigurable microwave photonic radar transmitter is used for performing optical up-conversion on a baseband signal, and has various implementation structures, wherein a typical structure is shown in fig. 4 and comprises a microwave source and 1 electro-optical intensity modulator.
The output end of the microwave source is connected with the radio frequency input end of the electro-optical intensity modulator, the optical input end of the electro-optical intensity modulator is connected with the output end of the photon digital-to-analog converter, and the output end of the electro-optical intensity modulator is connected with the optical switch (adopting the structure shown in fig. 3 (a)) or the input end of the photoelectric detector (adopting the structure shown in fig. 3 (b)).
The structure of the reconfigurable microwave photonic radar receiver is shown in fig. 5, and comprises 1 laser, 1 optical receiving module, 1 microwave switch, and 1 analog-to-digital converter.
The output end of the laser is connected with the input end of the optical receiving module and used for providing a light source required by the optical receiving module. Two input ends of the microwave switch are respectively connected with a local oscillator signal output by a microwave source and a reference signal provided by the reconfigurable microwave photon radar transmitter, an output end of the microwave switch is connected with a radio frequency input port 1 of the optical receiving module, and a radio frequency input port 2 of the optical receiving module, namely a receiving signal input end of the reconfigurable microwave photon radar receiver, is connected with an output end of a radio frequency front end of the receiver. The output end of the optical receiving module is connected with the input end of the analog-to-digital converter, and the output end of the analog-to-digital converter is connected with the input end of the control and processing module. The optical receiving module performs down-conversion or deskew processing on an echo signal received by the radio frequency front end of the receiver by using a local oscillator signal provided by a microwave source or a reference signal provided by a reconfigurable microwave photon radar transmitter to generate a down-conversion signal or deskew signal, and the down-conversion signal or deskew signal is acquired by the analog-to-digital converter and sent to the control and processing module. The model requirement is as follows: the microwave switch adopts a 1 multiplied by 2 microwave switch, and the switching speed is less than or equal to ns magnitude. The rest parts adopt conventional parts.
An optical receiving module in the reconfigurable microwave photonic radar receiver is shown in fig. 6, and includes 1 dual-parallel modulator (a dual-drive modulator may be used), 1 photodetector, and 1 low-pass filter. The input ports of the double parallel modulators are connected with the output end of a laser in the reconfigurable microwave photon radar receiver, the radio frequency input port 1 and the radio frequency input port 2 of the double parallel modulators correspond to the radio frequency input port 1 and the radio frequency input port 2 of the optical receiving module, the output ends of the double parallel modulators are connected with the input end of the photoelectric detector, the output end of the photoelectric detector is connected with the input end of the low-pass filter, and the output end of the low-pass filter is connected with the input end of the analog-to-digital converter.
The working principle of the microwave photon large-range automatic focusing radar imaging system is described below.
Firstly, the microwave photon large-range automatic focusing radar imaging system works in a narrow-band ranging mode, a microwave photon radar transmitter can be reconstructed to generate a narrow-band radar signal at a transmitting end, and the narrow-band radar signal is transmitted to the radio frequency front end of the transmitter through a transmitting signal output end under the control of an optical switch or a microwave switch.
Wherein the photonic digital-to-analog converter generates an optical signal carrying a baseband narrowband chirp, which can be expressed as:
Figure BDA0002291690220000101
wherein, TpnIs the pulse width, V, of the baseband narrow-band chirp wavebnIs the amplitude, f1nIs the starting frequency, knIs the chirp rate and t is time.
This light signal can produce the radio frequency narrowband chirp wave of light year behind the optics upconversion module, and the radio frequency narrowband chirp wave of light year then can produce the radio frequency narrowband chirp wave of electric domain after the photoelectric detector beat frequency, can obtain required radio frequency narrowband chirp wave through the filter filtering, and radio frequency narrowband chirp wave is:
Figure BDA0002291690220000102
wherein, VTnIs the amplitude, f, of a radio frequency narrow-band chirp waveLOIs the frequency of the local oscillator signal provided by the microwave source.
And further, radio frequency narrowband linear frequency modulation waves generated by the reconfigurable microwave photon radar transmitter are input to the radio frequency front end of the transmitter for amplification, and are radiated to the air through the transmitting antenna.
Generating an echo signal after the radio frequency narrowband linear frequency modulation wave is radiated to a target, receiving the echo by a receiving antenna at a receiving end and sending the echo to a radio frequency front end of a receiver, amplifying and filtering the echo by the radio frequency front end of the receiver, sending the echo to a receiving signal input end of a reconfigurable microwave photon radar receiver and sending the echo to a radio frequency input port 2 of an optical receiving module, and recording the echo signal as:
Figure BDA0002291690220000111
where τ is the target echo delay.
Meanwhile, under the control of a microwave switch in the reconfigurable microwave photon radar receiver, a local oscillation signal provided by a microwave source is sent to a radio frequency input port 1 of the optical receiving module. The laser sends laser and sends into the double parallel modulator in the optical receiving module, and double parallel modulator's output optical signal passes through photoelectric detector and low pass filter, can obtain the low frequency narrowband signal after the echo down-conversion at last, sends digital-to-analog converter collection, and sends control and processing module to handle, marks as:
sdown(t)∝cos[2πf1n(t-τ)+knπ(t-τ)2-2πfLOτ]
and matching and filtering the down-conversion waveform in a control and processing module, and calculating to obtain the target echo delay tau.
The control and processing module generates a transmitter trigger signal according to the target echo delay, thereby controlling the generation time of the transmitting signal and the reference signal.
Then, the system works in a 'broadband imaging' mode, at a transmitting end, under the control of a transmitter trigger signal, the reconfigurable microwave photon radar transmitter firstly generates a broadband radar signal, and the broadband radar signal is transmitted to the radio-frequency front end of the transmitter through a transmitting signal output end under the control of an optical switch (using a structure shown in fig. 3 (a)) or a microwave switch (using a structure shown in fig. 3 (b)).
Wherein the photonic digital-to-analog converter generates an optical signal carrying a baseband wideband chirp, which can be expressed as:
Figure BDA0002291690220000112
wherein, TpwIs the pulse width, V, of a baseband broadband chirpbwIs the amplitude, f1wIs the starting frequency, kwIs the chirp rate and t is time.
After the optical signal passes through the optical up-conversion module, a radio frequency broadband linear frequency modulation wave of an optical carrier can be generated, after the beat frequency of the photoelectric detector, the radio frequency broadband linear frequency modulation wave of an electric domain can be generated, and the required radio frequency broadband linear frequency modulation wave can be obtained through the filtering of a filter and is recorded as:
Figure BDA0002291690220000113
wherein, VTwIs the amplitude, f, of a radio frequency broadband chirpLOIs the frequency of the local oscillator signal provided by the microwave source.
The reconfigurable microwave photon radar transmitter generates radio frequency broadband linear frequency modulation waves, the radio frequency broadband linear frequency modulation waves are input to the radio frequency front end of the transmitter to be amplified, and then the radio frequency broadband linear frequency modulation waves are radiated to the air through the transmitting antenna. Under the control of a transmitter trigger signal, after a radio frequency broadband chirp wave generates tau + delta tau time, a reconfigurable microwave photon radar transmitter generates the same radio frequency broadband chirp wave (reference signal), and under the control of an optical switch (using a structure shown in fig. 3 (a)) or a microwave switch (using a structure shown in fig. 3 (b)), the reference signal is sent to a reference signal input end of a reconfigurable microwave photon radar receiver through a reference signal output end, and the reference signal is recorded as:
Figure BDA0002291690220000121
at a receiving end, after tau time, a receiving antenna receives an echo and sends the echo to a radio frequency front end of a receiver, the radio frequency front end of the receiver amplifies and filters the echo and sends the echo to a receiving signal input end of the reconfigurable microwave photon radar receiver and sends the echo to a radio frequency input port 2 of an optical receiving module, and echo signals are recorded as:
Figure BDA0002291690220000122
meanwhile, under the control of a microwave switch in the reconfigurable microwave photon radar receiver, a reference signal provided by the reconfigurable microwave photon radar transmitter is sent to a radio frequency input port 1 of the optical receiving module. The laser sends laser and sends into the double parallel modulator in the optical receiving module, and double parallel modulator's output optical signal passes through photoelectric detector and low pass filter, can obtain the low frequency narrowband signal after the echo declivity at last, sends digital-to-analog converter collection, and sends control and processing module to handle, marks as:
sdechirp(t)＝cos[2kwπΔτt+2π(f1w+fLO)Δτ-kwπΔτ2-2kwπΔτ·τ]
finally, FFT processing is carried out on the waveform of the deskew signal in a control and processing module, and the radio frequency broadband signal can be converted into a frequency kwThe frequency of the signal after deskew can fall within the bandwidth of the deskew receiver by adjusting the size of delta tau, so that the target distance falls within the distance window of the deskew receiver, and automatic focusing of the target is realized. And a high-resolution image of the target can be obtained through subsequent signal processing.
The reconfigurable microwave photonic radar system comprises a reconfigurable microwave photonic radar transmitter, a microwave source, a transmission signal output end, a radio frequency front end and a radio frequency front end, wherein the reconfigurable microwave photonic radar transmitter is used for transmitting a signal to be transmitted to the transmission signal output end; the output end of the radio frequency front end of the transmitter is connected with the input end of the transmitting antenna. At a receiving end, the output end of a receiving antenna is connected with the input end of the radio frequency front end of a receiver, the output end of the radio frequency front end of the receiver is connected with the receiving signal input end of the reconfigurable microwave photon radar receiver, and meanwhile, a local oscillation signal generated by a microwave source is sent to the local oscillation signal input end of the reconfigurable microwave photon radar receiver; the reconfigurable microwave photon radar receiver performs down-conversion processing on the received echo signals by using local oscillation signals, generates down-conversion signals and sends the down-conversion signals to the control and processing module; and the control and processing module processes the received signals to obtain the distance between the target and the radar system.
Then, the system works in a broadband imaging mode, the control and processing module designs the time sequence relation of the trigger signal of the transmitter according to the distance between the target and the radar system, generates the trigger signal of the transmitter and sends the trigger signal to the reconfigurable microwave photon radar transmitter. The local oscillator signal generated by the microwave source is sent to a local oscillator signal input end of the reconfigurable microwave photon radar transmitter, and the reconfigurable microwave photon radar transmitter firstly generates a broadband signal to be output from a transmitting signal output end and sends the broadband signal to a radio frequency front end of the transmitter under the control of a transmitter trigger signal; the output end of the radio frequency front end of the transmitter is connected with the input end of the transmitting antenna and is transmitted out through the antenna. After a period of time, the reconfigurable microwave photon radar transmitter generates a broadband signal, outputs the broadband signal from a reference signal output end, sends the broadband signal to a reference signal input end of the reconfigurable microwave photon radar receiver, performs deskew processing on the broadband signal and a received echo signal, generates a deskew signal and sends the deskew signal to the control and processing module; the control and processing module processes the received signals to obtain a high-resolution image of the target.
In a 'broadband imaging' mode, the time sequence relation of a trigger signal of a transmitter is designed according to a target distance measured in a 'narrow-band ranging' mode, and the generation time of a transmitting signal and a reference signal can be controlled, so that the signal frequency obtained by deskewing an echo signal and the reference signal falls within the bandwidth range of a reconfigurable microwave photon radar receiver, the target distance falls within a distance window of the deskew receiver, and automatic focusing on a target is realized. The generation time of the reference signal can be adjusted in a large range, and large-range automatic focusing and high-resolution imaging of targets with different distances can be easily realized.
The microwave photon large-range automatic focusing radar imaging system of the embodiment of the invention is explained in detail through a specific embodiment.
The reconfigurable microwave photonic radar transmitter adopts a structure shown in fig. 3(a), the reconfigurable microwave photonic radar receiver adopts a structure shown in fig. 5, the modulator adopts a double-parallel modulator, and three bias points of the modulator are respectively arranged at a minimum point, a minimum point and a maximum point.
The metal plate is used as a detection target, in order to simulate different distances from the target to the radar, the metal plate is fixedly placed at a position 1m away from the antenna, and optical fibers with lengths of 1km, 5km and 10km are respectively added to an upper path output port of an optical switch of the reconfigurable microwave photon radar transmitter.
Taking the length of the optical fiber as an example, in a narrow-band ranging stage, the photonic digital-to-analog converter generates a baseband linear frequency modulation wave with the bandwidth of 50MHz (0-0.05GHz), the microwave source provides a local oscillator signal with the frequency of 18GHz, the baseband linear frequency modulation wave is up-converted to 18-18.05GHz and is transmitted out to detect the metal plate. As a result of the distance measurement, as shown in fig. 7(a), it can be seen that the echo delay of the target is 5.27us, and the equivalent distance of the target is 790 m.
Then, the system works in a broadband imaging stage, the photon digital-to-analog converter generates baseband linear frequency modulation waves with the bandwidth of 8GHz (0-8GHz), the pulse width is 4us, the pulse repetition period is 10us, the microwave source provides local oscillation signals of 18GHz, and the baseband linear frequency modulation waves are subjected to up-conversion to 18-26 GHz. Under the control of a trigger pulse of a transmitter, firstly, broadband chirp waves are generated and used as transmitting signals to be transmitted through a transmitting antenna, the broadband chirp waves generated after 5.28us are used as reference signals to be sent into a reconfigurable microwave photon radar receiver, and are subjected to deskew with echo signals returned to the receiver after 5.27us to obtain deskewed signals, and the deskewed signals are subjected to FFT (fast Fourier transform) processing, and the result is shown in fig. 7 (b). The 3dB main lobe width is 1.7cm, the peak side lobe ratio is 13.34dB, the theoretical value is approached, and the result also shows that the ranging resolution of the system is 1.7 cm.
In addition, when the length of the optical fiber is 10km, the equivalent distance of the target obtained in the "narrow-band ranging" stage is 8.11km, the result of FFT of the deskew signal obtained in the "broadband imaging" stage is shown in fig. 7(c), the 3dB main lobe width is also 1.7cm, and a high-resolution image of the target is obtained. The result shows that the system provided by the invention can realize automatic focusing and high-resolution imaging for targets with different distances.
According to the microwave photon large-range automatic focusing radar imaging system provided by the embodiment of the invention, a transmitter and a receiver are reconstructed by utilizing microwave photons, and the distance between a target and a radar is obtained by matching, filtering and measuring; according to the distance, the generation time of the transmitting signal and the reference signal is controlled, so that the deskew frequency of the echo signal and the reference signal falls within the bandwidth of the deskew receiver, and the target distance falls within a distance window of the deskew receiver, namely, the automatic focusing of the target is realized; by further digital signal processing, a high resolution image of the target can be obtained. The radar imaging system is used for generating and processing radar signals based on a microwave photonics method by utilizing a microwave photon large-range automatic focusing radar imaging system, and the advantages of microwave photon broadband and reconfigurability can be fully exerted, so that a high-resolution image of a target can be obtained. Compared with the current system for adjusting the time delay of the reference signal by using the adjustable light time delay module, the system has a larger time delay adjusting range, can realize large-range automatic focusing and high-resolution imaging of targets with different distances, and has important significance on detection, tracking and identification of the targets.
The microwave photon large-range automatic focusing radar imaging method provided by the embodiment of the invention is described next with reference to the attached drawings.
FIG. 8 is a flowchart of a microwave photon wide-range autofocus radar imaging method according to an embodiment of the present invention.
As shown in fig. 8, the microwave photon wide-range automatic focusing radar imaging method includes the following steps:
s1, generating radio frequency narrowband chirp waves according to the narrowband radar signals and the local oscillator signals, and radiating the radio frequency narrowband chirp waves to the air;
s2, generating a first echo signal after the radio frequency narrow-band linear frequency modulation wave is radiated to a target, and performing down-conversion processing according to the first echo signal and the local oscillator signal to generate a low-frequency narrow-band signal after the echo down-conversion;
s3, processing the low-frequency narrow-band signal after the echo down-conversion to obtain target echo delay;
s4, generating a broadband radar signal and a reference signal according to the target echo delay, generating a radio frequency broadband linear frequency modulation wave according to the broadband radar signal and the local oscillator signal, and radiating the radio frequency broadband linear frequency modulation wave to the air;
s5, radiating the radio frequency broadband linear frequency modulation wave to a target to generate a second echo signal, and performing deskew processing according to the second echo signal and a reference signal to generate a low-frequency narrow-band signal after the echo is deskewed;
and S6, processing the low-frequency narrow-band signal after the echo is deskewed to obtain high-resolution imaging of the target.
Further, in an embodiment of the present invention, S1-S3 further comprises:
acquiring an optical signal carrying a baseband narrowband chirp wave as a narrowband radar signal, wherein the baseband narrowband chirp wave is as follows:
Figure BDA0002291690220000141
wherein, TpnIs the pulse width, V, of the baseband narrow-band chirp wavebnIs the amplitude, f1nIs the starting frequency, knIs the chirp rate, t is time;
processing the narrow-band radar signal and the local oscillator signal to generate a radio frequency narrow-band linear frequency modulation wave, wherein the radio frequency narrow-band linear frequency modulation wave is as follows:
Figure BDA0002291690220000151
wherein, VTnIs the amplitude, f, of a radio frequency narrow-band chirp waveLOIs the frequency of the local oscillator signal provided by the microwave source;
amplifying the radio frequency narrow-band linear frequency modulation wave and radiating the amplified wave to the air, wherein the radio frequency narrow-band linear frequency modulation wave generates a first echo signal after being radiated to a target, and the first echo signal is as follows:
Figure BDA0002291690220000152
where τ is the target echo delay;
amplifying and filtering the first echo signal, performing down-conversion processing on the amplified and filtered first echo signal and the local oscillator signal, generating a low-frequency narrow-band signal after echo down-conversion, wherein the low-frequency narrow-band signal after echo down-conversion is:
sdown(t)∝cos[2πf1n(t-τ)+knπ(t-τ)2-2πfLOτ]
and processing the low-frequency narrow-band signal after the echo down-conversion to obtain the target echo delay.
Further, in an embodiment of the present invention, S4-S6 further comprises:
acquiring an optical signal carrying a baseband broadband chirp as a broadband radar signal, wherein the baseband broadband chirp is as follows:
Figure BDA0002291690220000153
wherein, TpwIs the pulse width, V, of a baseband broadband chirpbwIs the amplitude, f1wIs the starting frequency, kwIs the chirp rate, t is time;
processing the broadband radar signal and the local oscillator signal to generate a radio frequency broadband linear frequency modulation wave, wherein the radio frequency broadband linear frequency modulation wave is as follows:
Figure BDA0002291690220000154
wherein, VTwIs the amplitude, f, of a radio frequency broadband chirpLOIs the frequency of the local oscillator signal provided by the microwave source;
amplifying the radio frequency broadband linear frequency modulation wave and radiating the amplified wave to the air, and generating a reference signal after a broadband radar signal according to target echo delay, wherein the reference signal is as follows:
Figure BDA0002291690220000155
wherein, Δ τ is a delay difference between the reference signal and the echo signal;
generating a second echo signal after the radio frequency broadband chirp is radiated to the target, wherein the second echo signal is as follows:
Figure BDA0002291690220000156
where τ is the target echo delay;
amplifying and filtering the second echo signal, deskewing the amplified and filtered second echo signal and the reference signal, and generating a low-frequency narrow-band signal after the echo deskew, wherein the low-frequency narrow-band signal after the echo deskew is:
sdechirp(t)＝cos[2kwπΔτt+2π(f1w+fLO)Δτ-kwπΔτ2-2kwπΔτ·τ]
and processing the low-frequency narrow-band signal after the echo is deskewed to obtain high-resolution imaging of the target.
It should be noted that the foregoing explanation of the embodiment of the microwave photon wide-range auto-focusing radar imaging system is also applicable to the method of the embodiment, and is not repeated here.
According to the microwave photon large-range automatic focusing radar imaging method provided by the embodiment of the invention, a first echo signal is obtained by transmitting radio frequency narrow-band linear frequency modulation waves, and the distance between a target and a radar is obtained according to the first echo signal and a local oscillator signal. And controlling the time for generating the transmitting signal and the reference signal according to the distance, generating a second echo signal by transmitting a radio frequency broadband linear frequency modulation wave, enabling the deskew frequency of the echo signal and the reference signal to fall within the bandwidth of the deskew receiver, and enabling the target distance to fall within a distance window of the deskew receiver, namely realizing automatic focusing on the target. The deskewed signals are further processed to achieve high resolution imaging of the target. The method has a larger time delay adjusting range, can realize large-range automatic focusing and high-resolution imaging of targets with different distances, and has important significance for detection, tracking and identification of the targets.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims (10)

1. A microwave photon large-range automatic focusing radar imaging system is characterized by comprising:
the reconfigurable microwave photon radar system comprises a reconfigurable microwave photon radar transmitter, a transmitter radio frequency front end, a transmitting antenna, a receiving antenna, a receiver radio frequency front end, a reconfigurable microwave photon radar receiver, a microwave source and a control and processing module;
the microwave source is connected with the reconfigurable microwave photon radar transmitter and the reconfigurable microwave photon radar receiver and is used for generating local oscillation signals and sending the local oscillation signals to the reconfigurable microwave photon radar transmitter and the reconfigurable microwave photon radar receiver;
the reconfigurable microwave photon radar transmitter is connected with the transmitter radio frequency front end and the reconfigurable microwave photon radar receiver and is used for generating a transmitting signal and a reference signal, sending the transmitting signal to the transmitter radio frequency front end and sending the reference signal to the reconfigurable microwave photon radar receiver;
the transmitter radio frequency front end is connected with the transmitting antenna and used for amplifying the transmitting signal and transmitting the amplified transmitting signal to the transmitting antenna;
the transmitting antenna is used for radiating the amplified transmitting signal to the air;
the receiving antenna is connected with the radio frequency front end of the receiver and used for receiving an echo signal radiated to a target by the transmitting signal and sending the echo signal to the radio frequency front end of the receiver;
the receiver radio-frequency front end is connected with the reconfigurable microwave photon radar receiver and is used for amplifying the echo signal and sending the amplified echo signal to the reconfigurable microwave photon radar receiver;
the reconfigurable microwave photon radar receiver is connected with the control and processing module and is used for performing down-conversion processing on the amplified echo signals and the local oscillator signals to generate down-conversion signals and/or performing deskew processing on the amplified echo signals and the reference signals to generate deskew signals;
the control and processing module is connected with the reconfigurable microwave photon radar transmitter and is used for carrying out digital signal processing on the down-conversion signal and/or the deskew signal to obtain an imaging result of a target, generating a transmitter trigger signal and further controlling time delay between the transmitting signal and the reference signal.
2. The microwave photonic wide range autofocus radar imaging system of claim 1,
at a transmitting end, one output end of the microwave source is connected with a local oscillator signal input end of the reconfigurable microwave photon radar transmitter, a transmitting signal output end of the reconfigurable microwave photon radar transmitter is connected with an input end of a radio frequency front end of the transmitter, an output end of the radio frequency front end of the transmitter is connected with an input end of the transmitting antenna, and a reference signal output end of the reconfigurable microwave photon radar transmitter is connected with a reference signal input end of the reconfigurable microwave photon radar receiver;
at a receiving end, the output end of the receiving antenna is connected with the input end of the radio frequency front end of the receiver, the output end of the radio frequency front end of the receiver is connected with the receiving signal input end of the reconfigurable microwave photon radar receiver, the other output end of the microwave source is connected with the local oscillation signal input end of the reconfigurable microwave photon radar receiver, and the output end of the reconfigurable microwave photon radar receiver is connected with the input end of the control and processing module;
and the output end of the control and processing module is connected with the reconfigurable microwave photon radar transmitter.
3. The microwave photonic wide range autofocus radar imaging system of claim 1, wherein the reconfigurable microwave photonic radar transmitter comprises: the device comprises a trigger signal generator, a photon digital-to-analog converter, an optical up-conversion module, an optical switch, two photoelectric detectors and two filters;
one output port of the trigger signal generator is connected with the photon digital-to-analog converter, the other output port of the trigger signal generator is connected with the optical switch, the output end of the photon digital-to-analog converter is connected with the input end of the optical up-conversion module, the output end of the optical up-conversion module is connected with the input end of the optical switch, the two output ends of the optical switch are respectively connected with the input ends of the two photoelectric detectors, the output ends of the two photoelectric detectors are respectively connected with the input ends of the two filters, the output end of one filter is used as a transmitting signal output end and connected with the input end of the radio frequency front end of the transmitter, and the output end of the other filter is used as a reference signal output end and connected with the reference signal input end of the reconfigurable microwave photon radar receiver.
4. The microwave photonic wide range autofocus radar imaging system of claim 1, wherein the reconfigurable microwave photonic radar transmitter comprises: the device comprises a photon digital-to-analog converter, an optical up-conversion module, a photoelectric detector, a filter and a microwave switch;
one output port of the trigger signal generator is connected with the photon digital-to-analog converter, the other output port of the trigger signal generator is connected with the microwave switch, the output end of the photon digital-to-analog converter is connected with the input end of the optical up-conversion module, the output end of the optical up-conversion module is connected with the input end of the photoelectric detector, the output end of the photoelectric detector is connected with the input end of the filter, the output end of the filter is connected with the input end of the microwave switch, one output end of the microwave switch serves as a transmitting signal output end and is connected with the input end of the radio frequency front end of the transmitter, and the other output end of the microwave switch serves as a reference signal output end and is connected with the reference signal input end of the reconfigurable microwave photon radar receiver.
5. The microwave photonic wide-range auto-focus radar imaging system according to claim 3 or 4, wherein the optical up-conversion module is configured to optically up-convert the baseband signal, and comprises a microwave source and an electro-optical intensity modulator;
the microwave source output end is connected with the radio frequency input end of the electro-optical intensity modulator, the optical input end of the electro-optical intensity modulator is connected with the output end of the photon digital-to-analog converter, and the output end of the electro-optical intensity modulator is connected with the input end of the optical switch or the photoelectric detector.
6. The microwave photonic wide range autofocus radar imaging system of claim 1, wherein the reconfigurable microwave photonic radar receiver comprises: the device comprises a laser, an optical receiving module, a microwave switch and an analog-to-digital converter;
wherein, the output end of the laser is connected with the input end of the optical receiving module, one input end of the microwave switch is used as the local oscillator signal input end of the reconfigurable microwave photon radar receiver to be connected with the local oscillator signal output by the microwave source, the other input end is used as the reference signal input end of the reconfigurable microwave photon radar receiver to be connected with the reference signal output by the reconfigurable microwave photon radar transmitter, the output end of the microwave switch is connected with one radio frequency input port of the optical receiving module, the other radio frequency input port of the optical receiving module is used as a receiving signal input end of the reconfigurable microwave photon radar receiver and is connected with the output end of the radio frequency front end of the receiver, the output end of the optical receiving module is connected with the input end of the analog-to-digital converter, and the output end of the analog-to-digital converter is connected with the input end of the control and processing module.
7. The microwave photonic wide-range autofocus radar imaging system of claim 6, wherein the optical receiving module comprises: a double parallel modulator, a photodetector and a low pass filter;
the input ports of the double parallel modulators are connected with the output end of the laser, the two radio frequency input ports of the double parallel modulators correspond to the two radio frequency input ports of the optical receiving module, the output ends of the double parallel modulators are connected with the input end of the photoelectric detector, the output end of the photoelectric detector is connected with the input end of the low-pass filter, and the output end of the low-pass filter is connected with the input end of the analog-to-digital converter.
8. A microwave photon large-range automatic focusing radar imaging method is characterized by comprising the following steps:
s1, generating radio frequency narrowband chirp waves according to the narrowband radar signals and the local oscillator signals, and radiating the radio frequency narrowband chirp waves to the air;
s2, generating a first echo signal after the radio frequency narrow-band linear frequency modulation wave is radiated to a target, and performing down-conversion processing according to the first echo signal and the local oscillator signal to generate a low-frequency narrow-band signal after echo down-conversion;
s3, processing the low-frequency narrow-band signal after the echo down-conversion to obtain target echo delay;
s4, generating a broadband radar signal and a reference signal according to the target echo delay, generating a radio frequency broadband linear frequency modulation wave according to the broadband radar signal and the local oscillator signal, and radiating the radio frequency broadband linear frequency modulation wave to the air;
s5, radiating the radio frequency broadband linear frequency modulation wave to a target to generate a second echo signal, and performing deskew processing according to the second echo signal and the reference signal to generate a low-frequency narrow-band signal after deskew of the echo;
and S6, processing the low-frequency narrow-band signal after the echo is deskewed to obtain high-resolution imaging of the target.
9. The microwave photonic wide-range autofocus radar imaging method of claim 8, wherein the S1-S3 further comprises:
acquiring an optical signal carrying a baseband narrowband chirp as the narrowband radar signal, wherein the baseband narrowband chirp is as follows:
Figure FDA0002291690210000031
wherein, TpnIs the pulse width, V, of the baseband narrow-band chirp wavebnIs the amplitude, f1nIs the starting frequency, knIs the chirp rate, t is time;
processing the narrow-band radar signal and the local oscillator signal to generate a radio frequency narrow-band chirp, wherein the radio frequency narrow-band chirp is as follows:
Figure FDA0002291690210000032
wherein, VTnIs the amplitude, f, of the radio frequency narrowband chirp waveLOIs the frequency of the local oscillator signal provided by the microwave source;
amplifying the radio frequency narrow-band chirp waves and radiating the radio frequency narrow-band chirp waves into the air, wherein the radio frequency narrow-band chirp waves generate a first echo signal after being radiated to a target, and the first echo signal is as follows:
Figure FDA0002291690210000041
where τ is the target echo delay;
amplifying and filtering the first echo signal, performing down-conversion processing on the amplified and filtered first echo signal and the local oscillator signal, and generating a low-frequency narrow-band signal after echo down-conversion, where the low-frequency narrow-band signal after echo down-conversion is:
sdown(t)∝cos[2πf1n(t-τ)+knπ(t-τ)2-2πfLOτ]
and processing the low-frequency narrow-band signal after the echo down-conversion to obtain the target echo delay.
10. The microwave photonic wide-range autofocus radar imaging method of claim 8, wherein the S4-S6 further comprises:
acquiring an optical signal carrying a baseband broadband chirp as the broadband radar signal, wherein the baseband broadband chirp is as follows:
Figure FDA0002291690210000042
wherein, TpwIs the pulse width, V, of a baseband broadband chirpbwIs the amplitude, f1wIs the starting frequency, kwIs the chirp rate, t is time;
processing the broadband radar signal and the local oscillator signal to generate a radio frequency broadband chirp, wherein the radio frequency broadband chirp is as follows:
Figure FDA0002291690210000043
wherein, VTwIs the amplitude, f, of the radio frequency broadband chirpLOIs the frequency of the local oscillator signal provided by the microwave source;
amplifying the radio frequency broadband linear frequency modulation wave and radiating the amplified radio frequency broadband linear frequency modulation wave to the air, and generating the reference signal after the broadband radar signal according to the target echo delay, wherein the reference signal is as follows:
Figure FDA0002291690210000044
wherein, Δ τ is the delay difference between the reference signal and the target echo signal;
generating a second echo signal after the radio frequency broadband chirp is radiated to the target, wherein the second echo signal is:
Figure FDA0002291690210000051
where τ is the target echo delay;
amplifying and filtering the second echo signal, and deskewing the amplified and filtered second echo signal and the reference signal to generate a low-frequency narrowband signal after echo deskew, where the low-frequency narrowband signal after echo deskew is:
sdechirp(t)＝cos[2kwπΔτt+2π(f1w+fLO)Δτ-kwπΔτ2-2kwπΔτ·τ]
and processing the low-frequency narrow-band signal after the echo is deskewed to obtain high-resolution imaging of the target.
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