CN109818681B - MIMO radar detection method and device based on double optical frequency combs and difference frequency multiplexing - Google Patents
MIMO radar detection method and device based on double optical frequency combs and difference frequency multiplexing Download PDFInfo
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Abstract
The invention discloses a MIMO radar detection method based on double optical frequency combs and difference frequency multiplexing. The method of the invention generates M paths of modulation optical signals of a transmitting end by improving the prior MIMO radar detection technology based on microwave photon orthogonal difference frequency multiplexing and adopting the following method: firstly, dividing an optical carrier into an upper path and a lower path; modulating an upper optical carrier by using a local oscillator signal to generate a first optical frequency comb signal, and modulating a lower optical carrier by using an intermediate frequency signal and an intermediate frequency linear frequency modulation signal to generate a second optical frequency comb signal; after the first optical frequency comb signal and the second optical frequency comb signal are coupled into one path, the first optical frequency comb signal and the second optical frequency comb signal are divided into M paths of modulated optical signals respectively consisting of a single intermediate frequency linear frequency modulation spectral line and a single local oscillator signal spectral line through wave beam shaping filtering. The invention also discloses an MIMO radar detection device based on the double optical frequency comb and the difference frequency multiplexing. The invention can greatly simplify the structure of the transmitter, reduce the system implementation cost and effectively ensure the coherence among all paths of signals.
Description
Technical Field
The present invention relates to a microwave photonic radar detection method, and in particular, to a difference frequency multiplexing microwave photonic MIMO (Multiple-Input Multiple-Output) radar detection method and a microwave photonic MIMO radar apparatus.
Background
The Modern Radar has highly diversified uses, including air traffic control, vehicle collision avoidance, meteorological precipitation detection and the like, high-precision, high-resolution and real-time multi-target detection are always the development directions of the Radar, and in order to realize real-time multi-target detection tracking and high-resolution imaging, a large-bandwidth transmitting signal, an MIMO technology and the support of a high-speed sampling system are required (see [ Pan Timlong, Zhudan, Zhang Fang. Microwave Photonics for model radio Systems [ J ]. Transactionsof Nanjing University of Aeronautitics and Astronautics,2014,31(03):219 and 240. ]).
A Multiple Input Multiple Output (MIMO) radar is a radar with a new system which is generated by introducing Multiple input and Multiple output technologies in a wireless communication system into the field of radars and combining the technologies with a digital array technology. The Panlongtong subject group applies the microwave photon technology to the MIMO radar, utilizes the characteristics of large bandwidth, low loss, electromagnetic interference resistance and the like of an optical device, provides a radar signal with large bandwidth for the MIMO radar, and improves the resolution of the radar. In addition, the MIMO radar has virtual aperture expansion capability and more flexible power distribution capability, improves the performance of the system, such as energy utilization rate, angle measurement accuracy, clutter suppression, low interception capability and the like, in order to separate signal paths, mutual orthogonality among transmission signals is needed, common methods include frequency division multiplexing, time division multiplexing and wavelength division multiplexing, the frequency band utilization rates of the modes are not high, the sampling rate requirement of a digital signal processing system is high, by using a difference frequency multiplexing method, the radar can simultaneously transmit multiple signals, deskew processing of the received signals is completed in a receiving device, the received signals of different channels are separated, and the time signals are mutually orthogonal at a receiving end.
In order to improve the frequency band utilization rate of the microwave photon MIMO radar, the Panshilong subject group in a Chinese invention patent CN107222263A provides a method and a device for detecting the MIMO radar based on the microwave photon orthogonal difference frequency multiplexing. The technical idea is that M modulators are utilized at a radar transmitting end to carry out frequency mixing on M paths of completely same linear frequency modulation signals and M paths of local oscillator signals with frequencies increasing in a difference frequency mode, and M paths of orthogonal up-conversion linear frequency modulation signals are obtained after photoelectric conversion and are sent out; and performing deskew and digital domain frequency mixing processing on the echo signals by using the M reference light signals at the radar receiving end, and obtaining target detection information after signal processing. Through such a structure, the frequency band utilization rate of the MIMO system can be improved, data channels far more than the actual receiving and transmitting array elements and the system degree of freedom are obtained, high radar azimuth resolution can be realized in a short measuring time under the same condition, and the requirement on the sampling rate is reduced. However, the method needs to generate M local oscillator signals with different frequencies, and M modulators are needed, so that the structure is complex and the cost is high, and meanwhile, the system coherence cannot be ensured, so that the subsequent signal processing is limited.
Disclosure of Invention
The technical problem to be solved by the invention is to overcome the defects of the existing MIMO radar detection technology based on microwave photon orthogonal difference frequency multiplexing, and provide a MIMO radar detection method based on double optical frequency combs and difference frequency multiplexing, which can greatly simplify the structure of a transmitter, reduce the implementation cost of a system and effectively ensure the coherence among signals of all paths.
The invention specifically adopts the following technical scheme to solve the technical problems:
the MIMO radar detection method based on double optical frequency combs and difference frequency multiplexing comprises the steps that at a transmitting end, M paths of modulation optical signals are generated firstly, a beam splitting modulation optical signal of one path of modulation optical signal is divided into N paths of reference optical signals, then M paths of modulation optical signals are subjected to photoelectric conversion respectively to obtain M paths of mutually orthogonal linear frequency modulation signals, and the M paths of mutually orthogonal linear frequency modulation signals are transmitted through M transmitting antennas respectively; at a receiving end, respectively receiving M paths of reflected signals of a target by using N receiving antennas, respectively performing optical domain deskew processing on the reflected signals received by the N receiving antennas based on the N paths of reference optical signals, then performing digital domain mixing processing to obtain M multiplied by N paths of digital signals carrying target information, and processing the digital signals to obtain a target detection result; m, N are positive integers, and the sum of the positive integers is more than or equal to 4; the M paths of modulated optical signals are generated by the following method: firstly, dividing an optical carrier into an upper path and a lower path; with frequency fLOThe local oscillator signal of (2) modulates the optical carrier of the upper path to generate a first optical frequency comb signal with a frequency of (f)dOf intermediate frequency signal of f0The intermediate frequency linear frequency modulation signal of + kt modulates the optical carrier of the next path to generate a second optical frequency comb signal; after the first optical frequency comb signal and the second optical frequency comb signal are coupled into one path, the first optical frequency comb signal and the second optical frequency comb signal are divided into M paths of modulated optical signals respectively consisting of a single intermediate frequency linear frequency modulation spectral line and a single local oscillator signal spectral line through wave beam shaping filtering, and the difference frequency of the M paths of modulated optical signals after being subjected to beat frequency respectively is fd-fLOAnd sequentially increasing.
Preferably, the frequency is fLOThe local oscillator signal is used for modulating the optical carrier wave on the upper path, and specifically, the local oscillator signal is used for modulating the optical carrier wave on the upper pathLine phase modulation to generate a first optical frequency comb signal; said frequency of use is fdOf intermediate frequency signal of f0The + kt intermediate frequency linear frequency modulation signal modulates the optical carrier of the next path, specifically: firstly, carrying out phase modulation on a downlink optical carrier by using the intermediate frequency signal to generate a phase modulation signal; and then modulating the intermediate frequency linear frequency modulation signal on the phase modulation signal through a double parallel Mach-Zehnder modulator working in a mode of inhibiting a carrier single sideband to generate a second optical frequency comb signal.
As a second preferred embodiment, the frequency is fLOThe local oscillator signal of (2) modulates the optical carrier of the upper path, specifically: modulating the local oscillator signal on an upper optical carrier through a partial division multiplexing double Mach-Zehnder modulator, and then analyzing the generated modulation signal to generate a first optical frequency comb signal; said frequency of use is fdOf intermediate frequency signal of f0The + kt intermediate frequency linear frequency modulation signal modulates the optical carrier of the next path, specifically: the intermediate frequency signal is modulated on a down-path optical carrier through a partial division multiplexing double Mach-Zehnder modulator, then the generated modulation signal is subjected to polarization detection, and finally the intermediate frequency linear frequency modulation signal is modulated on the modulated signal subjected to polarization detection through a double parallel Mach-Zehnder modulator working in a carrier single-sideband suppression mode to generate a second optical frequency comb signal.
Preferably, the frequency is fLOThe local oscillator signal of (2) modulates the optical carrier of the upper path, specifically: dividing the local oscillator signals into two paths; firstly, modulating a local oscillator signal on an upper path optical carrier through a polarization modulator, wherein a main shaft of the polarization modulator forms an angle of 45 degrees with the upper path optical carrier; then, the generated polarization modulation signal is analyzed; finally, the other path of local oscillation signal is modulated on the polarization modulation signal after polarization detection through a phase modulator after phase shifting to generate a first optical frequency comb signal; said frequency of use is fdOf intermediate frequency signal of f0The + kt intermediate frequency linear frequency modulation signal modulates the optical carrier of the next path, specifically: dividing the intermediate frequency signal into two paths; first pass polarization modulatorModulating one path of intermediate frequency signals on a downlink optical carrier, wherein a main shaft of the polarization modulator forms an angle of 45 degrees with the downlink optical carrier; then, the generated polarization modulation signal is analyzed; then, the other path of intermediate frequency signal is modulated on the polarization modulation signal after polarization detection through a phase modulator after phase shifting; and finally, modulating the intermediate frequency linear frequency modulation signal on the generated phase modulation signal through a double parallel Mach-Zehnder modulator working in a mode of inhibiting a carrier single sideband to generate a second optical frequency comb signal.
Further preferably, the initial frequency of the intermediate frequency linear frequency modulation signal component in any path of modulated optical signal is greater than the local oscillator signal component frequency in the modulated optical signal;RMAXand the maximum detection distance of the radar is, c is the light speed, and k is the chirp rate of the intermediate frequency linear frequency modulation signal.
The following technical scheme can be obtained according to the same invention concept:
the MIMO radar detection device based on the double optical frequency comb and the difference frequency multiplexing comprises a transmitting end and a receiving end;
the transmitting end includes:
the M-path optical signal generating module is used for generating M-path modulation optical signals;
the M photoelectric detectors are used for respectively carrying out photoelectric conversion on the M paths of modulated optical signals to obtain M paths of mutually orthogonal linear frequency modulation signals;
m transmitting antennas for respectively transmitting M paths of mutually orthogonal linear frequency modulation signals;
the reference optical module is used for dividing the beam-splitting modulated optical signal of one path of modulated optical signal into N paths of reference optical signals;
the receiving end includes:
n receiving antennas for receiving M paths of reflected signals of a target;
the N optical domain deskew modules are used for respectively carrying out optical domain deskew processing on the reflection signals received by the N receiving antennas based on the N paths of reference optical signals and carrying out digital domain frequency mixing processing on the obtained signals to obtain M multiplied by N paths of digital signals carrying target information;
the signal acquisition and processing unit is used for processing the digital signal to obtain a target detection result;
m, N are positive integers, and the sum of the positive integers is more than or equal to 4;
the M-path optical signal generation module comprises:
the optical carrier unit is used for dividing an optical carrier into an upper path and a lower path;
a first optical frequency comb unit for using a frequency fLOThe local oscillator signal of the optical frequency comb modulates the optical carrier of the upper path to generate a first optical frequency comb signal;
a second optical frequency comb unit for using a frequency fdOf intermediate frequency signal of f0The intermediate frequency linear frequency modulation signal of + kt modulates the optical carrier of the next path to generate a second optical frequency comb signal;
a wave beam shaping and filtering unit for dividing the signal formed by coupling the first optical frequency comb signal and the second optical frequency comb signal into M paths of modulated optical signals respectively formed by a single intermediate frequency linear frequency modulation spectral line and a single local oscillator signal spectral line, wherein the difference frequency of the M paths of modulated optical signals after being respectively subjected to beat frequency is fd-fLOAnd sequentially increasing.
As one of the preferable schemes, the first optical frequency comb unit includes a phase modulator, configured to perform phase modulation on an upper optical carrier by using the local oscillator signal, and generate a first optical frequency comb signal; the second optical frequency comb unit comprises a cascaded phase modulator and a double-parallel Mach-Zehnder modulator, and the phase modulator is used for carrying out phase modulation on a downlink optical carrier by using the intermediate frequency signal to generate a phase modulation signal; the double parallel Mach-Zehnder modulator works in a carrier-rejection single-sideband mode and is used for modulating the intermediate frequency linear frequency modulation signal on the phase modulation signal to generate a second optical frequency comb signal.
As a second preferred scheme, the first optical frequency comb unit includes a polarization division multiplexing dual mach-zehnder modulator and a polarization analyzer, the polarization division multiplexing dual mach-zehnder modulator is configured to modulate the local oscillator signal on an upper optical carrier, and the polarization analyzer is configured to analyze the generated modulated signal to generate a first optical frequency comb signal; the second optical frequency comb unit comprises a partial division multiplexing double Mach-Zehnder modulator, a polarization detector and a double parallel Mach-Zehnder modulator which are sequentially cascaded, wherein the partial division multiplexing double Mach-Zehnder modulator is used for modulating the intermediate frequency signal on a downlink optical carrier, the polarization detector is used for detecting the generated modulation signal, and the double parallel Mach-Zehnder modulator works in a mode of inhibiting a single side band of the carrier and is used for modulating the intermediate frequency linear frequency modulation signal on the detected modulation signal to generate a second optical frequency comb signal.
As a third preferred scheme, the first optical frequency comb unit includes a polarization modulator, an analyzer, a phase shifter, and a phase modulator, where a main axis of the polarization modulator forms an angle of 45 ° with an upper optical carrier, and is configured to modulate one of the local oscillator signals on the upper optical carrier, the analyzer is configured to analyze the generated polarization modulation signal, the phase shifter is configured to shift the phase of the other local oscillator signal, and the phase modulator is configured to modulate the other local oscillator signal after phase shift on the polarization modulation signal after polarization detection, so as to generate a first optical frequency comb signal; the second optical frequency comb unit comprises a polarization modulator, an analyzer, a phase shifter, a phase modulator and a double-parallel Mach-Zehnder modulator, wherein a main shaft of the polarization modulator forms an angle of 45 degrees with a downlink optical carrier and is used for modulating one path of intermediate frequency signals on the downlink optical carrier, the analyzer is used for analyzing the generated polarization modulation signals, the phase shifter is used for shifting the phase of the other path of intermediate frequency signals, the phase modulator is used for modulating the other path of intermediate frequency signals after phase shifting on the polarization modulation signals after phase shifting, and the double-parallel Mach-Zehnder modulator works in a carrier single-sideband restraining mode and is used for modulating the intermediate frequency linear frequency modulation signals on the phase modulation signals output by the phase modulator to generate second optical frequency comb signals.
Further preferably, the initial frequency of the intermediate frequency chirp signal component in any one of the modulated optical signals is greater than the local oscillator signal component frequency in the modulated optical signalRate;RMAXand the maximum detection distance of the radar is, c is the light speed, and k is the chirp rate of the intermediate frequency linear frequency modulation signal.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
1) the invention utilizes a signal generation scheme based on the double optical frequency combs and a deskew scheme based on difference frequency multiplexing to realize MIMO radar detection, wherein compared with the prior art, the scheme of generating difference frequency signals by the double optical frequency combs greatly simplifies the structure of a transmitter, reduces the system cost, ensures the coherence among all paths of signals, greatly improves the frequency band utilization rate and the azimuth resolution of a radar system by the difference frequency multiplexing technology, and reduces the requirement on the sampling rate.
2) The invention adopts MIMO radar multi-input multi-output structure, can transmit and receive multi-channel signals at the same time, increases the diversity and dimension of the acquired information, simultaneously each channel of received signals comprises a plurality of channels of transmitted signals, can observe the target in multiple angles, and improves the azimuth resolution of the radar.
3) In the digital signal processing part, the electric signal after deskew can be sampled only by using a low-speed analog-to-digital conversion module without specific digital matched filtering, so that the sampling rate and quality of the signal are increased, the requirement on data storage is lowered, and the real-time signal processing can be realized.
Drawings
FIG. 1 is a schematic diagram of a basic structure of a MIMO radar detection device based on dual optical frequency comb and difference frequency multiplexing;
FIG. 2 is a schematic diagram of optical signals generated by the M-channel optical signal generating module;
fig. 3 is a schematic structural diagram of an M-channel optical signal generating module;
fig. 4 is a schematic diagram of another specific structure of the M-channel optical signal generating module;
fig. 5 is a schematic diagram of another specific structure of the M-channel optical signal generating module.
Detailed Description
Aiming at the defects of the existing MIMO radar detection technology based on microwave photon orthogonal difference frequency multiplexing, the invention improves the transmitting end, utilizes a double-optical frequency comb scheme to generate difference frequency signals, improves the utilization rate of frequency bands, improves the azimuth resolution of the radar, reduces the requirement on the sampling rate, greatly simplifies the structure of a transmitter, reduces the realization cost of a system and effectively ensures the coherence among all paths of signals.
The invention provides a MIMO radar detection method based on double optical frequency combs and difference frequency multiplexing, which comprises the following steps:
at a transmitting end, firstly generating M paths of modulated optical signals, dividing the beam-splitting modulated optical signal of one path of modulated optical signal into N paths of reference optical signals, then respectively carrying out photoelectric conversion on the M paths of modulated optical signals to obtain M paths of mutually orthogonal linear frequency modulation signals, and respectively transmitting the M paths of mutually orthogonal linear frequency modulation signals through M transmitting antennas; at a receiving end, respectively receiving M paths of reflected signals of a target by using N receiving antennas, respectively performing optical domain deskew processing on the reflected signals received by the N receiving antennas based on the N paths of reference optical signals, then performing digital domain mixing processing to obtain M multiplied by N paths of digital signals carrying target information, and processing the digital signals to obtain a target detection result; m, N are positive integers, and the sum of the positive integers is more than or equal to 4; the M paths of modulated optical signals are generated by the following method: firstly, dividing an optical carrier into an upper path and a lower path; with frequency fLOThe local oscillator signal of (2) modulates the optical carrier of the upper path to generate a first optical frequency comb signal with a frequency of (f)dOf intermediate frequency signal of f0The intermediate frequency linear frequency modulation signal of + kt modulates the optical carrier of the next path to generate a second optical frequency comb signal; after the first optical frequency comb signal and the second optical frequency comb signal are coupled into one path, the first optical frequency comb signal and the second optical frequency comb signal are divided into M paths of modulated optical signals respectively consisting of a single intermediate frequency linear frequency modulation spectral line and a single local oscillator signal spectral line through wave beam shaping filtering, and the difference frequency of the M paths of modulated optical signals after being subjected to beat frequency respectively is fd-fLOAnd sequentially increasing.
For the public to understand, the technical scheme of the invention is explained in detail in the following with the attached drawings:
as shown in fig. 1, at a transmitting end, an optical carrier generated by a light source passes through M paths of optical signal generating modules to generate M paths of modulated optical signals, one path of the modulated optical signals is divided into two paths, and one path of the modulated optical signals is further divided into N paths of reference optical signals and sent to a receiving end; the M paths of modulated optical signals are respectively subjected to photoelectric conversion by using M photoelectric detectors to obtain M paths of mutually orthogonal linear frequency modulation signals, and the M paths of mutually orthogonal linear frequency modulation signals are respectively amplified by using amplifiers (PA) and finally reflected out through M transmitting antennas (Tr). At a receiving end, respectively receiving M paths of reflected signals of a target by using N receiving antennas (Re), respectively performing optical domain deskew processing on the reflected signals received by the N receiving antennas based on the N paths of reference optical signals, then performing digital domain mixing processing to obtain M multiplied by N paths of digital signals carrying target information, and processing the digital signals to obtain a target detection result; m, N are positive integers, and the sum of the positive integers is more than or equal to 4.
The basic implementation structure and principle of the receiving end are substantially the same as those in CN107222263A, and for the sake of brevity, the description is omitted here. Different from the prior art, the M-path optical signal generation module of the present invention adopts a dual optical frequency comb scheme, as shown in fig. 1, firstly, an optical carrier unit is used to divide an optical carrier into an upper path and a lower path; the first optical frequency comb unit has a frequency fLOThe local oscillator signal of (2) modulates the optical carrier of the upper path to generate a first optical frequency comb signal, and the frequency of the second optical frequency comb unit is fdOf intermediate frequency signal of f0The intermediate frequency linear frequency modulation signal of + kt modulates the optical carrier of the next path to generate a second optical frequency comb signal; the wave beam shaping filter unit is used for shaping a first optical frequency comb signal (local oscillator optical frequency comb, OFC)1) And a second optical frequency comb signal (chirped optical frequency comb, OFC)2) The coupled signal is split into M modulated optical signals. The frequency domain representation of the M optical signals is shown in FIG. 2, wherein the M optical signals are obtained by generating a double optical frequency comb with M + n groups of comb teeth at equal intervals, wherein M and n are positive integers, and the local oscillator optical frequency combStarting frequency of fLOCutoff frequency of (m + n) fLOThe spacing between adjacent comb teeth is fLOThe initial frequency of the optical frequency comb of the linear frequency modulation signal is fd+f0+ kt, cut-off frequency (m + n) fd+f0+ kt, spacing between adjacent comb teeth of fdAnd need to satisfy fd>fLOThe ith path of modulated optical signal is respectively divided into a single frequency ifd+f0+ kt IF chirp line and single frequency ifLOThe local oscillator signal spectral line is formed (i is more than or equal to 1 and less than or equal to m + n), and the beat frequency is i (f)d-fLO)+f0The beat frequency of the (i + 1) th path intermediate frequency linear frequency modulation spectral line and the local oscillation signal spectral line is f greater than that of the ith pathd-fLOThat is, the beat frequency difference of two adjacent paths of M optical signals is expressed by fd-fLOAnd (4) increasing.
The above-mentioned M-path optical signal generating module can be implemented by using various structures, and for the convenience of understanding, the following detailed description is made by using three specific examples.
Fig. 3 shows the basic structure of the first embodiment of the M-path optical signal generation module. The module comprises: one laser, two Phase Modulators (PM), one double parallel mach-zehnder modulator (DPMZM), three Phase Controllers (PC), two Optical Couplers (OC), one programmable optical processor (waveshape). As shown in FIG. 3, the laser generates a frequency fsigRespectively enters two Phase Modulators (PM) through the coupler to be modulated at a frequency fLOThe local oscillator signal LO of (a) drives a PM, and the resulting optical frequency comb can be expressed as:
with frequency fdThe intermediate frequency signal Fd drives a PM, the optical signal output by the PM is passed to the DPMZM, and the DPMZM is driven by the intermediate frequency chirp signal LFM, the DPMZM operates in a carrier-suppressed single sideband mode, and the generated optical frequency comb can be expressed as:
wherein A ismIs the corresponding amplitude, f, of each frequency pointsigIs the frequency of the optical carrier, fdAt intermediate frequency, f0Is the starting frequency of the intermediate frequency chirp signal, and k is its chirp rate.
Synthesizing two paths of optical signals output by the two PMs into one path of optical signal through an optical coupler and performing beam shaping filtering through a programmable optical processor to obtain M paths of optical signals formed by a single intermediate frequency linear frequency modulation spectral line and a single local oscillator signal spectral line, wherein the difference frequency between the intermediate frequency linear frequency modulation signal and the local oscillator signal is increased to fd-fLO(ii) a The optical signals are respectively input into the photoelectric detectors, so that M paths of mutually orthogonal linear frequency modulation electrical signals are obtained and are transmitted out through M antennas, wherein the mth path of transmission signals can be expressed as:
fTm(t)∝AmBmexp{j2π[m(fd-fLO)+fLO+f0+kt]t}。
fig. 4 shows the basic structure of a second embodiment of the M-path optical signal generating module. As shown in fig. 4, the module includes: one laser, two polarization division multiplexing dual Mach-Zehnder modulators (PM-DMZM), one dual parallel Mach-Zehnder modulator (DPMZM), two analyzers (Pol), and one programmable optical processor (Waveshape). Laser generating frequency fsigThe direct current light is divided into two paths through a coupler and respectively enters two polarization division multiplexing double Mach-Zehnder modulators (PM-DMZM) to be modulated; with frequency fLOThe output optical signal enters an analyzer (Pol) to be analyzed, and the generated optical frequency comb can be expressed as:
wherein A ismIs the corresponding amplitude, f, of each frequency pointsigIs the frequency of the optical carrier.
In the other path, the frequency f is generated by a phase-locked loopdIs generated by a direct digital frequency synthesizerAn intermediate frequency chirp signal; driving the downstream PM-DMZM by the intermediate frequency signal, enabling the output optical signal to enter an analyzer (Pol) for analyzing, enabling the optical signal output by the Pol to enter a downstream DPMZM, driving the DPMZM by the intermediate frequency linear frequency modulation signal, enabling the DPMZM to work in a carrier single sideband suppression mode, and generating an optical frequency comb which can be expressed as:
wherein B ismIs the corresponding amplitude, f, of each frequency pointsigIs the frequency of the optical carrier, fdAt intermediate frequency, f0Is the starting frequency of the intermediate frequency chirp signal, and k is its chirp rate.
Synthesizing the two paths of optical signals output by the PM-DMZM into one path of optical signal through an optical coupler, and performing beam shaping filtering through a programmable optical processor to obtain M paths of optical signals consisting of a single intermediate frequency linear frequency modulation spectral line and a single local oscillator signal spectral line, wherein the difference frequency between the intermediate frequency linear frequency modulation signal and the local oscillator signal is increased to fd-fLO(ii) a Inputting the optical signals into a photoelectric detector, outputting to obtain M paths of mutually orthogonal linear frequency modulation electrical signals, and transmitting the M paths of mutually orthogonal linear frequency modulation electrical signals through M antennas, wherein the mth path of transmission signals can be expressed as:
fTm(t)∝AmBmexp{j2π[m(fd-fLO)+fLO+f0+kt]t}。
fig. 5 shows the basic structure of a third embodiment of the M-path optical signal generating module. As shown in fig. 5, the module includes: one laser, two polarization modulators (PolM), two Phase Modulators (PM), one double parallel mach-zehnder modulator (DPMZM), two Phase Shifters (PS), two polarization analyzers (Pol), six Phase Controllers (PC), two Optical Couplers (OC), and one programmable optical processor (waveshape).
Laser generating frequency fsigThe direct current light is divided into two paths through a coupler and respectively enters two polarization modulators (PolM) to be modulated, and the two paths of direct current light are respectively modulated through a polarization controller 1 and a polarization controller 4 (PC)1 and PC4) such that the linearly polarized incident light wave from the Laser (LD) makes an angle of 45 with one of the principal axes of PolM.
In the upper branch, a frequency f is generated by a phase-locked loopLOThe local oscillator signal of (2) divides the local oscillator signal into two paths. One PolM is driven by one local oscillator signal. Since the incident light wave makes a 45 angle with one of the principal axes of PolM, a pair of complementary phased signals are generated along both principal axes of PolM. The PolM output signal was input to PC2 and an optical signal containing two orthogonal polarization states was obtained by adjusting PC 2. The output optical signal is input to an analyzer (Pol) for analysis and input to a Phase Modulator (PM) via a PC 3. The other path of local oscillation signal drives PM through a Phase Shifter (PS) to modulate the output optical signal of PolM after polarization detection, and the generated optical frequency comb can be represented as:
wherein A ismIs the corresponding amplitude, f, of each frequency pointsigIs the frequency of the optical carrier, fdAt intermediate frequency, f0As the starting frequency, k is its chirp rate.
The other path generates a frequency f through a phase-locked loopdThe direct digital frequency synthesizer generates an intermediate frequency linear frequency modulation signal, and the intermediate frequency signal is divided into two paths. A PolM is driven by an intermediate frequency signal and the resulting modulated optical signal is input to the PM via Pol and PC. And the other path of intermediate frequency signal passes through a PS drive PM to modulate the output optical signal of the polM after the polarization detection. And introducing an optical signal output by the PM into a DPMZM, driving the DPMZM by using the intermediate frequency linear frequency modulation signal, wherein the DPMZM works in a carrier-rejection single-sideband mode, and the generated optical frequency comb can be expressed as:
wherein A ismIs the corresponding amplitude, f, of each frequency pointsigIs the frequency of the optical carrier, fdAt intermediate frequency, f0As the starting frequency, k is its chirp rate.
The two paths of optical frequency comb signals are synthesized into one path of optical signal by an optical coupler, and the optical signal is divided into M paths of modulated optical signals formed by single intermediate frequency linear frequency modulation spectral lines and single local oscillator signal spectral lines by a programmable optical processor through beam shaping filtering, wherein the difference frequency between the intermediate frequency linear frequency modulation signal and the local oscillator signal is increased to fd-fLO(ii) a Inputting the optical signals into a photoelectric detector, outputting to obtain M paths of mutually orthogonal linear frequency modulation electrical signals, and transmitting the M paths of mutually orthogonal linear frequency modulation electrical signals through M antennas, wherein the mth path of transmission signals can be expressed as:
fTm(t)∝AmBmexp{j2π[m(fd-fLO)+fLO+f0+kt]t}
note that, to further avoid frequency overlap, the start frequency of the intermediate frequency chirp signal component in any one of the modulated optical signals should be greater than the local oscillator signal component frequency in the modulated optical signal:
ifd+f0>ifLO(1≤i≤M)
in order to avoid the frequency overlapping between the echo signal of the mth path of transmission signal and the m +1 path of transmission signal, the following requirements are met:
wherein f isd-fLOFor frequency differences between the transmitted signals, RMAXAnd c is the maximum detection distance of the radar and the speed of light.
Claims (10)
1. The MIMO radar detection method based on double optical frequency combs and difference frequency multiplexing comprises the steps that at a transmitting end, M paths of modulation optical signals are generated firstly, a beam splitting modulation optical signal of one path of modulation optical signal is divided into N paths of reference optical signals, then M paths of modulation optical signals are subjected to photoelectric conversion respectively to obtain M paths of mutually orthogonal linear frequency modulation signals, and the M paths of mutually orthogonal linear frequency modulation signals are transmitted through M transmitting antennas respectively; at a receiving end, N receiving antennas are utilized to respectively receive M paths of reflected signals of a target, and the N receiving antennas are used for receiving the received signals in an inverted manner based on the N paths of reference optical signalsRespectively carrying out optical domain deskew processing on the transmitted signals, then carrying out digital domain frequency mixing processing on the signals to obtain M multiplied by N paths of digital signals carrying target information, and processing the digital signals to obtain a target detection result; m, N are positive integers, and the sum of the positive integers is more than or equal to 4; wherein the M-path modulated optical signal is generated by: firstly, dividing an optical carrier into an upper path and a lower path; with frequency fLOThe local oscillator signal of (2) modulates the optical carrier of the upper path to generate a first optical frequency comb signal with a frequency of (f)dOf intermediate frequency signal of f0The intermediate frequency linear frequency modulation signal of + kt modulates the downlink optical carrier to generate a second optical frequency comb signal fLO、fdFrequency, f, of local oscillator signal, intermediate frequency signal, respectively0And k are respectively the initial frequency and the chirp rate of the intermediate frequency linear frequency modulation signal; after the first optical frequency comb signal and the second optical frequency comb signal are coupled into one path, the first optical frequency comb signal and the second optical frequency comb signal are divided into M paths of modulated optical signals respectively consisting of a single intermediate frequency linear frequency modulation spectral line and a single local oscillator signal spectral line through wave beam shaping filtering, and the difference frequency of the M paths of modulated optical signals after being subjected to beat frequency respectively is fd-fLOAnd sequentially increasing.
2. The MIMO radar detection method of claim 1, wherein the frequency of use is fLOThe local oscillator signal of (1) performs modulation processing on the optical carrier of the upper path, specifically, performs phase modulation on the optical carrier of the upper path by using the local oscillator signal to generate a first optical frequency comb signal; said frequency of use is fdOf intermediate frequency signal of f0The + kt intermediate frequency linear frequency modulation signal modulates the optical carrier of the next path, specifically: firstly, carrying out phase modulation on a downlink optical carrier by using the intermediate frequency signal to generate a phase modulation signal; and then modulating the intermediate frequency linear frequency modulation signal on the phase modulation signal through a double parallel Mach-Zehnder modulator working in a mode of inhibiting a carrier single sideband to generate a second optical frequency comb signal.
3. The MIMO radar detection method of claim 1, wherein the frequency of use is fLOThe local oscillator signal of (2) modulates the optical carrier of the upper path, specifically: modulating the local oscillator signal on an upper optical carrier through a partial division multiplexing double Mach-Zehnder modulator, and then analyzing the generated modulation signal to generate a first optical frequency comb signal; said frequency of use is fdOf intermediate frequency signal of f0The + kt intermediate frequency linear frequency modulation signal modulates the optical carrier of the next path, specifically: the intermediate frequency signal is modulated on a down-path optical carrier through a partial division multiplexing double Mach-Zehnder modulator, then the generated modulation signal is subjected to polarization detection, and finally the intermediate frequency linear frequency modulation signal is modulated on the modulated signal subjected to polarization detection through a double parallel Mach-Zehnder modulator working in a carrier single-sideband suppression mode to generate a second optical frequency comb signal.
4. The MIMO radar detection method of claim 1, wherein the frequency of use is fLOThe local oscillator signal of (2) modulates the optical carrier of the upper path, specifically: dividing the local oscillator signals into two paths; firstly, modulating a local oscillator signal on an upper path optical carrier through a polarization modulator, wherein a main shaft of the polarization modulator forms an angle of 45 degrees with the upper path optical carrier; then, the generated polarization modulation signal is analyzed; finally, the other path of local oscillation signal is modulated on the polarization modulation signal after polarization detection through a phase modulator after phase shifting to generate a first optical frequency comb signal; said frequency of use is fdOf intermediate frequency signal of f0The + kt intermediate frequency linear frequency modulation signal modulates the optical carrier of the next path, specifically: dividing the intermediate frequency signal into two paths; firstly, modulating a path of intermediate frequency signal on a downlink optical carrier through a polarization modulator, wherein a main shaft of the polarization modulator forms an angle of 45 degrees with the downlink optical carrier; then, the generated polarization modulation signal is analyzed; then, the other path of intermediate frequency signal is modulated on the polarization modulation signal after polarization detection through a phase modulator after phase shifting; and finally, modulating the intermediate frequency linear frequency modulation signal on the generated phase modulation signal through a double parallel Mach-Zehnder modulator working in a mode of inhibiting a carrier single sideband to generate a second optical frequency comb signal.
5. The MIMO radar detection method of claim 1, wherein a start frequency of an intermediate frequency chirp component in any one of the modulated optical signals is greater than a local oscillator signal component frequency in the modulated optical signal;RMAXand the maximum detection distance of the radar is, c is the light speed, and k is the chirp rate of the intermediate frequency linear frequency modulation signal.
6. The MIMO radar detection device based on the double optical frequency comb and the difference frequency multiplexing comprises a transmitting end and a receiving end;
the transmitting end includes:
the M-path optical signal generating module is used for generating M-path modulation optical signals;
the M photoelectric detectors are used for respectively carrying out photoelectric conversion on the M paths of modulated optical signals to obtain M paths of mutually orthogonal linear frequency modulation signals;
m transmitting antennas for respectively transmitting M paths of mutually orthogonal linear frequency modulation signals;
the reference optical module is used for dividing the beam-splitting modulated optical signal of one path of modulated optical signal into N paths of reference optical signals;
the receiving end includes:
n receiving antennas for receiving M paths of reflected signals of a target;
the N optical domain deskew modules are used for respectively carrying out optical domain deskew processing on the reflection signals received by the N receiving antennas based on the N paths of reference optical signals and carrying out digital domain frequency mixing processing on the obtained signals to obtain M multiplied by N paths of digital signals carrying target information;
the signal acquisition and processing unit is used for processing the digital signal to obtain a target detection result;
m, N are positive integers, and the sum of the positive integers is more than or equal to 4;
wherein the M optical signal generating modules include:
the optical carrier unit is used for dividing an optical carrier into an upper path and a lower path;
a first optical frequency comb unit for using a frequency fLOThe local oscillator signal of (f) modulates the optical carrier of the upper path to generate a first optical frequency comb signalLOThe frequency of the local oscillation signal;
a second optical frequency comb unit for using a frequency fdOf intermediate frequency signal of f0The intermediate frequency linear frequency modulation signal of + kt modulates the downlink optical carrier to generate a second optical frequency comb signal fdIs the frequency of the intermediate frequency signal, f0And k are respectively the initial frequency and the chirp rate of the intermediate frequency linear frequency modulation signal;
a wave beam shaping and filtering unit for dividing the signal formed by coupling the first optical frequency comb signal and the second optical frequency comb signal into M paths of modulated optical signals respectively formed by a single intermediate frequency linear frequency modulation spectral line and a single local oscillator signal spectral line, wherein the difference frequency of the M paths of modulated optical signals after being respectively subjected to beat frequency is fd-fLOAnd sequentially increasing.
7. The MIMO radar detection apparatus of claim 6, wherein the first optical-frequency comb unit includes a phase modulator for performing phase modulation on an upper optical carrier by the local oscillator signal to generate a first optical-frequency comb signal; the second optical frequency comb unit comprises a cascaded phase modulator and a double-parallel Mach-Zehnder modulator, and the phase modulator is used for carrying out phase modulation on a downlink optical carrier by using the intermediate frequency signal to generate a phase modulation signal; the double parallel Mach-Zehnder modulator works in a carrier-rejection single-sideband mode and is used for modulating the intermediate frequency linear frequency modulation signal on the phase modulation signal to generate a second optical frequency comb signal.
8. The MIMO radar detection apparatus of claim 6, wherein the first optical-frequency comb unit includes a polarization-division multiplexing dual mach-zehnder modulator and an analyzer, the polarization-division multiplexing dual mach-zehnder modulator being configured to modulate the local oscillator signal onto an uplink optical carrier, the analyzer being configured to analyze the generated modulated signal to generate a first optical-frequency comb signal; the second optical frequency comb unit comprises a partial division multiplexing double Mach-Zehnder modulator, a polarization detector and a double parallel Mach-Zehnder modulator which are sequentially cascaded, wherein the partial division multiplexing double Mach-Zehnder modulator is used for modulating the intermediate frequency signal on a downlink optical carrier, the polarization detector is used for detecting the generated modulation signal, and the double parallel Mach-Zehnder modulator works in a mode of inhibiting a single side band of the carrier and is used for modulating the intermediate frequency linear frequency modulation signal on the detected modulation signal to generate a second optical frequency comb signal.
9. The MIMO radar detection apparatus as claimed in claim 6, wherein the first optical frequency comb unit includes a polarization modulator, an analyzer, a phase shifter, and a phase modulator, one principal axis of the polarization modulator forms an angle of 45 ° with an upstream optical carrier, and the polarization modulator is configured to modulate one of the local oscillator signals onto the upstream optical carrier, the analyzer is configured to analyze the generated polarization modulation signal, the phase shifter is configured to shift the phase of the other of the local oscillator signals, and the phase modulator is configured to modulate the other of the local oscillator signals after phase shift onto the polarization modulation signal after phase shift, and generate the first optical frequency comb signal; the second optical frequency comb unit comprises a polarization modulator, an analyzer, a phase shifter, a phase modulator and a double-parallel Mach-Zehnder modulator, wherein a main shaft of the polarization modulator forms an angle of 45 degrees with a downlink optical carrier and is used for modulating one path of intermediate frequency signals on the downlink optical carrier, the analyzer is used for analyzing the generated polarization modulation signals, the phase shifter is used for shifting the phase of the other path of intermediate frequency signals, the phase modulator is used for modulating the other path of intermediate frequency signals after phase shifting on the polarization modulation signals after phase shifting, and the double-parallel Mach-Zehnder modulator works in a carrier single-sideband restraining mode and is used for modulating the intermediate frequency linear frequency modulation signals on the phase modulation signals output by the phase modulator to generate second optical frequency comb signals.
10. The MIMO radar probe of claim 6, wherein any of the tones isThe initial frequency of the intermediate frequency linear frequency modulation signal component in the optical modulation signal is greater than the local oscillation signal component frequency in the optical modulation signal;RMAXand the maximum detection distance of the radar is, c is the light speed, and k is the chirp rate of the intermediate frequency linear frequency modulation signal.
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