Multi-band signal fusion microwave photon radar system and implementation method thereof

Abstract

The invention discloses a multi-frequency-band signal fusion microwave photon radar system and an implementation method thereof, and relates to the technical field of optical signal processing, and the system comprises a multi-frequency-band signal transmitting module which is used for generating a multi-frequency-band bandwidth radar signal; the m microwave photon dechirp receiving modules are used for receiving echo signals of three or more multi-band bandwidth radar signals in an optical domain; the multi-frequency-band signal fusion processing module is used for carrying out interpolation and filling of spectrum gaps on missing frequency bands among multiple frequency bands through a coherent fusion technology so as to realize fusion splicing of multi-frequency-band signals; m is the number of multi-band channels; according to the method, the broadband characteristic of the photon technology can be fully utilized, and the distance resolution of target detection is effectively improved under the condition that the bandwidth requirement of the radar waveform electrical generator is not increased through fusion processing of multi-band bandwidth radar signals.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical signal processing and the technical field of modern radar, and particularly relates to a microwave photonic radar system for multi-band signal fusion and an implementation method thereof. BACKGROUND

[0002] Radar is an important means for high-precision applications such as target detection and identification, distance measurement, and is widely used in aerospace, military, traffic monitoring and other fields. In a linear frequency modulation signal radar system, the bandwidth of the radar signal is inversely proportional to the resolution, and increasing the bandwidth is an effective means to improve the resolution. Since it is difficult for traditional electrical methods to generate a wideband radar signal across an octave with a single signal generator, and it is technically easier to generate multiple narrowband signals in different frequency bands by frequency division, a multi-band signal can be fused into an equivalent wideband signal by coherent fusion technology, thereby improving the resolution of radar detection. However, since multiple independent microwave sources are needed as multi-frequency carriers, the complexity of the system is greatly increased. Microwave photonics technology uses the wideband characteristics of photonic technology to generate wideband signals and multi-carrier signals covering a wide frequency range, and through the fusion processing of multi-band received signals, an equivalent wideband signal is obtained, breaking the limitations of traditional electrical methods in wideband signal generation, and thereby achieving the improvement of radar resolution.

[0003] In recent years, multiple microwave photonic radar schemes based on multi-band signal fusion have been proposed, which can be divided into two categories according to their principles. The first category is to construct multiple sets of microwave photonic radars with different frequency bands, and then use multi-band signal fusion technology to improve the bandwidth of the radar signal. Each set of radar generates high-order optical modulation sidebands of narrow-band radar signals through a dual-parallel Mach-Zehnder modulator (DPMZM), and then uses the beating of two high-order modulation sidebands in a photodetector to achieve frequency and bandwidth multiplication of the radar signal. When receiving, the optical modulation sidebands generated by the DPMZM are used as optical carriers for optical deskew processing in the optical domain, reducing the bandwidth required for detection and signal processing (Xin Zhu, Fangzheng Zhang, et al. "High-resolution Detection by Multiband Fusion of Photonics-based Radars." Photonics and Electromagnetics Research Symposium, 794-800 (2021).). However, this method still requires multiple sets of transmitting and receiving systems to implement multi-band signal transmission and reception, and does not fully utilize the wideband characteristics of photonic technology to reduce system complexity. In addition, the frequencies of adjacent frequency bands in this system are connected at both ends, which on the one hand is susceptible to interference from adjacent frequency bands, affecting the quality of the signal and the accuracy of the measurement, and on the other hand, the bandwidth multiplication obtained by multi-band signal fusion is limited by the number of frequency bands, and cannot be further improved by increasing the blank frequency between frequency bands. The second category of methods generates dual-band microwave photonic radar signals using a single set of transmitting and receiving devices, and performs time-domain interpolation and spectral gap filling on the dual-band deskewed signals through coherent fusion technology to achieve large-bandwidth signal target detection. For example, Shaowen Peng et al. used a 4-bit photonic digital-to-analog converter (PDAC) to generate a dual-frequency optical carrier linear frequency modulation signal, which was then double-sideband modulated by a microwave source-driven MZM to achieve spectral replication and shifting. Then, through photodetector beating, a multi-band radar signal was generated, which was then transmitted through the corresponding frequency band filter and amplifier through the antenna. At the receiving end, a polarization multiplexing double-drive Mach-Zehnder modulator (PM-DMZM) was used to demodulate the dual-band signal synchronously to complete the optical deskew processing (Shaowen Peng, Shangyuan Li, et al. "A Photonics-Based Coherent Dual-Band Radar for Super-Resolution Range Profile." Photonics Journal, 11(4), 1-8, (2019).). However, the number of frequency bands of the multi-band radar signal generated by the double-sideband modulation of the MZM is limited.In addition, since the receiving mode adopts a PM-DMZM as an optical domain deskewing demodulator, it is unable to simultaneously receive and process signals of three or more frequency bands. SUMMARY

[0004] In order to solve the above problems, the application provides a microwave photon radar system for multi-band signal fusion and an implementation method thereof.

[0005] A multi-band signal transmitting module is configured to generate a multi-band bandwidth radar signal.

[0006] m microwave photon deskewing receiving modules are configured to receive three or more multi-band echo signals in an optical domain.

[0007] A multi-band signal fusion processing module is configured to perform interpolation on missing frequency bands and fill spectral gaps between the multi-band signals by using a coherent fusion technology, so as to realize fusion and splicing of the multi-band signals.

[0008] m is the number of multi-band channels.

[0009] The multi-band signal transmitting module comprises, in sequence, a continuous wave laser, an optical pulse modulation and compression module, a second intensity modulator, a 1x(m+1) optical coupler, a first photodetector, a second electric amplifier and a transmitting antenna.

[0010] Each microwave photon deskewing receiving module comprises, in sequence, a receiving antenna, an electric band-pass filter, a 90° electric bridge, a double-drive intensity modulator, a second photodetector, an electric low-pass filter and an ADC.

[0011] The microwave photon radar system in the application utilizes the generation of a multi-band bandwidth radar signal, optical domain wideband signal deskewing receiving and multi-band signal fusion processing technology, effectively improves the equivalent bandwidth of the system and optimizes the distance detection resolution of the system.

[0012] Further, the multi-band signal transmitting module further comprises an erbium-doped fiber amplifier and an adjustable optical filter connected in sequence, the erbium-doped fiber amplifier is connected with the second intensity modulator, and the adjustable optical filter is connected with the 1x(m+1) optical coupler.

[0013] Preferably, the first intensity modulator and the second intensity modulator both adopt Mach-Zehnder modulators (MZMs), and the double-drive intensity modulator adopts a double-drive Mach-Zehnder modulator (DDMZM).

[0014] Preferably, the arbitrary waveform generator linear frequency modulation signal f LFM The center frequency is 1 / 4f LO , and the wide bandwidth is 1 / 3f LO . Too small bandwidth will result in too large white spectrum between the multi-bands, so that the multi-band splicing cannot be realized (maximum white space 67%), and too large bandwidth will result in spectrum aliasing, and the bandwidth cannot exceed half of the frequency of the microwave source. The center wavelength of the continuous wave laser is 900-1700nm, and the output frequency of the local oscillator signal of the microwave source with the frequency f LO is 1-40GHz.

[0015] Meanwhile, the application further discloses an implementation method of the microwave photon radar system for multi-band signal fusion, which is based on the microwave photon radar system for multi-band signal fusion and comprises the following steps.

[0016] The multi-band signal transmitting step: the light frequency comb with narrow pulse width characteristics is generated by using the light pulse modulation and compression module, the linear frequency modulation microwave signal is loaded on the light frequency comb through electro-optical modulation, the multi-band bandwidth radar signal is generated through photoelectric conversion and is transmitted.

[0017] The multi-band signal transmitting step: the light frequency comb with narrow pulse width characteristics is generated by using the light pulse modulation and compression module, the linear frequency modulation microwave signal is loaded on the light frequency comb through electro-optical modulation, the multi-band bandwidth radar signal is generated through photoelectric conversion and is transmitted.

[0018] The microwave photon desquamation receiving step: the echo signals of the multi-band bandwidth radar signals are respectively subjected to desquamation processing in the optical domain, and the desquamation intermediate frequency signals corresponding to different frequency bands are obtained.

[0019] The multi-band signal fusion processing step: through the coherent fusion technology of the full pole point model, the missing frequency bands between the different frequency band corresponding dechirp intermediate frequency signals are time domain extrapolation interpolated, so as to fill the spectral gap, realize the fusion splicing of the multi-band signals, and obtain the target detection result of the equivalent large bandwidth signal.

[0020] Further, the multi-band signal transmitting step specifically comprises:

[0021] The continuous wave laser generates an optical carrier with a frequency f0, which is injected into a first intensity modulator of the optical pulse modulation and compression module to form an initial optical pulse sequence; a power divider in the microwave driving module divides a sinusoidal local oscillator signal with a frequency f LO generated by a microwave source into two paths, one of which drives the first intensity modulator of the optical pulse modulation and compression module, and the other of which is amplified by a first electric amplifier and phase-shifted by an electric phase shifter before being connected to a phase modulator of the optical pulse modulation and compression module; the phase shift by the electric phase shifter causes the peaks or valleys of the amplified sinusoidal local oscillator signal waveform to align with the peaks of the initial optical pulse sequence; the initial optical pulse sequence passes through the phase modulator to form a linearly chirped optical pulse sequence, which is compressed in time domain by a dispersive medium to obtain a compressed linearly chirped optical pulse sequence, the spectrum of which is an optical frequency comb with a spacing f LO ;

[0022] The linear frequency modulation microwave signal generated by the arbitrary waveform generator is double sideband modulated on the compressed linearly chirped optical pulse sequence by a second intensity modulator, and the generated optical carrier linear frequency modulation microwave signal is sequentially amplified by an erbium-doped fiber amplifier and filtered to remove the spontaneous emission noise from the erbium-doped fiber amplifier by an adjustable optical filter, and then the optical signal is divided into m+1 outputs by a 1×(m+1) optical coupler, one of which is used as an upper branch and converted into a multi-band bandwidth radar signal by a first photodetector, and the multi-band bandwidth radar signal is sequentially amplified by a second electric amplifier and transmitted by a transmitting antenna; the remaining m outputs are used as lower branches and are used as receiving reference optical signals for optical dechirp of m microwave photon dechirp receiving modules and are injected into double-drive intensity modulators.

[0023] The first intensity modulator and the second intensity modulator both work at a linear bias point.

[0024] Further, the dechirp step of each microwave photon dechirp receiving module in the microwave photon dechirp receiving step is the same, specifically comprising:

[0025] The echo signal of the multi-band bandwidth radar signal is collected by the receiving antenna, amplified by a low noise amplifier, and then selected in frequency and filtered to remove out-of-band clutter by an electric band-pass filter.

[0026] The signal after filtering out the out-of-band spurs is divided into two phase quadrature paths by a 90° bridge, which respectively drive the two RF ports of the dual-drive intensity modulator; at the same time, the optical input port of the dual-drive intensity modulator is injected with a reference light signal to realize single sideband modulation.

[0027] The modulated signal enters the second photodetector for photoelectric conversion, and outputs a despread intermediate frequency signal, realizing optical domain despread processing of the chirp signal.

[0028] After the despread intermediate frequency signal enters the electric low-pass filter to filter out high-frequency components, the time-domain waveform of the despread intermediate frequency signal is sampled by the ADC to obtain a sampling signal.

[0029] The dual-drive intensity modulator works at a linear bias point.

[0030] Further, the multi-band intermediate frequency signal fusion processing step specifically comprises:

[0031] Let the sampling signal of the i-th frequency band be s i (n), i=1, 2, 3…m, wherein i is the frequency band number, and n is the signal sampling point number.

[0032] Step one: determine whether the sampling signal is a positive chirp signal; if it is not a positive chirp signal, flip the time domain of the sampling signal, and if it is, keep the original signal unchanged.

[0033] Step two: construct the Hankel matrix H i of the i-th frequency band signal

[0034]

[0035] wherein N i represents the maximum sampling point number of the i-th frequency band, L i represents the window length, L i =N i / 3, then singular value decomposition is performed on H i respectively.

[0036] H i =U i S i V i H

[0037] wherein H represents conjugate transpose, U i and V i are left singular vector matrix and right singular vector matrix respectively, and S i represents singular value matrix.

[0038] Step three: let the matrix S iThe matrix is M x N dimensional, the values of AIC(k) and MDL(k) are obtained by AIC criterion and MDL criterion, and the k at the minimum of AIC(k) and MDL(k) is taken as the order of the all-pole model of the frequency band, wherein the formulas of AIC and MDL criterion are,

[0039]

[0040] wherein k=0, 1, …, M-1, and k is the model order;

[0041] Step four: singular value decomposition of the right singular value vector matrix V i According to the model order k, it is divided into signal subspace V i sn and noise subspace V i n , the two subspaces are orthogonal to each other,

[0042] V i = [V i sn V i n ]

[0043] wherein the signal subspace matrix V i sn has k columns, and the noise subspace matrix V i n has L i -k columns; the noise subspace generating matrix A i is generated:

[0044] A i = V i n V i nH

[0045] wherein H represents conjugate transpose, the first row of A i is d ij , j represents j elements of the first row, and constitutes a polynomial,

[0046]

[0047] The root of A i (z) is solved by root-MUSIC, and the root result is the pole value of the subband; k points closest to the unit circle are selected as the poles of the subband, and the pole value p ik of the i-th frequency band is obtained. k

[0048] Step five: the pole value p ik ​= [p1, p2,... pN k ] constructs a Vandermonde matrix P,

[0049]

[0050] According to the least square formula, the amplitude and phase coefficients a ik = [a1, a2,... aN i1 ] i2 ik T ,

[0051]

[0052] Where [s i (0), s i (1),... s i (Ni-1)] T is a signal vector constructed by the sampling signal s i (n);

[0053] Step six: obtain the pole values p ik and the amplitude and phase coefficients a ik of each sub-band all-pole model, then fit the signal of the i-th frequency band, and the fitting formula is,

[0054]

[0055] Where k represents the model order;

[0056] Step seven: based on the all-pole model, extrapolate and interpolate the i-th sub-band signal to expand the signal length from N i to N i +N ex ,

[0057]

[0058] Where N ex is the length of the extrapolated and interpolated signal;

[0059] Step eight: to achieve the phase consistency between sub-bands, construct the coherence function C,

[0060]

[0061] Where Δθ i is the difference in rotation angle between two sub-bands, and ΔA i is the difference in amplitude coefficient between two sub-bands;

[0062] Through the optimization algorithm, the optimal rotation angle Δθ i and the amplitude coefficient deviation ΔA i ​​The coherent function C=C min The coherent function C=C

[0063]

[0064] The above steps 1 to 8 are repeated with a certain sub-band as a reference to realize extrapolation interpolation and mutual coherence among all sub-bands. The spectrum among the sub-bands is effectively spliced and fused, and finally an equivalent wide-band signal is synthesized, thereby significantly improving the detection resolution and target recognition capability of the system.

[0065] The present application has the following advantages: a multi-band microwave radar signal is generated by optical frequency comb modulation and photoelectric detection, a single set of transmission system can simultaneously generate radar signals of multiple frequency bands (the number of frequency bands is greater than or equal to 3), the structure of the transmission system is simplified, and the frequency coverage range is wide; the frequency band spacing is flexible and tunable, and the phase is synchronized, the optical carrier multi-band signal divided from the transmission link is used as a reference optical carrier, the receiving is completed in the optical domain, a photoelectric-electric-optical conversion link is saved, the signal loss is greatly reduced, and the receiving efficiency is improved. The multi-band fusion processing fills the frequency spectrum gap between frequency bands by full pole model coherent interpolation, breaks through the limitation of single frequency band bandwidth, and significantly improves the equivalent bandwidth. BRIEF DESCRIPTION OF DRAWINGS

[0066] Figure 1 The figure is a schematic diagram of the system structure of the present application;

[0067] Figure 2 The figure is an output time domain waveform diagram of the dispersion module of the embodiment;

[0068] Figure 3 The figure is an output spectrum diagram of the dispersion module of the embodiment;

[0069] Figure 4 The figure is an output spectrum diagram of the second MZM of the embodiment;

[0070] Figure 5 The figure is an output spectrum diagram of the first photoelectric detector of the embodiment;

[0071] Figure 6 The figure is a time domain diagram after the first channel (4-6GHz) is dechirped;

[0072] Figure 7 The figure is a range image of the first channel (4-6GHz) of the embodiment;

[0073] Figure 8 The figure is a time domain diagram after the first, second and third channels are dechirped;

[0074] Figure 9 The figure is a time domain diagram of bandwidth extrapolation interpolation of the embodiment;

[0075] Figure 10Time domain image after phase correlation for the embodiment;

[0076] Figure 11 Distance image after three-channel phase correlation fusion for the embodiment;

[0077] 1-continuous wave laser, 2-optical pulse modulation and compression module, 3-microwave driving module, 4-second MZM, 5-arbitrary waveform generator, 6-doped fiber amplifier, 7-adjustable optical filter, 8-1x(m+1) optical coupler, 9-first photodetector, 10-second electric amplifier, 11-transmitting antenna, 12-receiving antenna, 13-low noise amplifier, 14-electric band-pass filter, 15-90° electric bridge, 16-DDMZM, 17-second photodetector, 18-electric low-pass filter, 19-ADC, 20-multiband signal fusion processing module. DETAILED DESCRIPTION

[0078] The application will be described in detail below with reference to the accompanying drawings and embodiments, taking a microwave photon radar with three multiband signal fusions as an example. Figures 1-11 As shown in the figure, the microwave photon radar system with multiband signal fusion of the application comprises:

[0079] Figure 1 A multiband signal transmitting module for generating multiband bandwidth radar signals;

[0080] m microwave photon de-skewing receiving modules for receiving three or more multiband echo signals in the optical domain;

[0081] A multiband signal fusion processing module for interpolating the missing frequency bands and filling the spectral gaps between the multiband signals through phase correlation fusion technology, so as to realize the fusion and splicing of the multiband signals;

[0082] m is the number of multiband channels;

[0083] The multiband signal transmitting module comprises a continuous wave laser, an optical pulse modulation and compression module, a second intensity modulator, a 1x(m+1) optical coupler, a first photodetector, a second electric amplifier and a transmitting antenna connected in sequence; wherein the optical pulse modulation and compression module and the second intensity modulator are respectively driven by a microwave driving module and an arbitrary waveform generator; the optical pulse modulation and compression module is cascaded by a first intensity modulator, a phase modulator and a dispersion medium; in the microwave driving module, a microwave source output is connected to a power divider, one output of the power divider is connected to the first intensity modulator, and the other output is connected to the phase modulator after being cascaded with a first electric amplifier and an electric phase shifter;

[0084] The multiband signal transmitting module comprises a continuous wave laser, an optical pulse modulation and compression module, a second intensity modulator, a 1x(m+1) optical coupler, a first photodetector, a second electric amplifier and a transmitting antenna connected in sequence; wherein the optical pulse modulation and compression module and the second intensity modulator are respectively driven by a microwave driving module and an arbitrary waveform generator; the optical pulse modulation and compression module is cascaded by a first intensity modulator, a phase modulator and a dispersion medium; in the microwave driving module, a microwave source output is connected to a power divider, one output of the power divider is connected to the first intensity modulator, and the other output is connected to the phase modulator after being cascaded with a first electric amplifier and an electric phase shifter;

[0085] ​Each microwave photon deskewing receiving module comprises a receiving antenna, an electrical band-pass filter, a 90-degree electrical bridge, a double-drive intensity modulator, a second photoelectric detector, an electrical low-pass filter and an ADC connected in sequence; m output ports of the optical coupler are connected with m double-drive intensity modulators in the microwave photon deskewing receiving modules respectively; m ADC outputs are connected with the multi-band signal fusion processing module.

[0086] The multi-band signal transmitting module further comprises an erbium-doped fiber amplifier and an adjustable optical filter connected in sequence, the erbium-doped fiber amplifier is connected with the second intensity modulator, and the adjustable optical filter is connected with the 1*(m+1) optical coupler; in each microwave photon deskewing receiving module, a low-noise amplifier is arranged between the receiving antenna and the electrical band-pass filter.

[0087] In the embodiment, the first intensity modulator and the second intensity modulator are both Mach-Zehnder modulators (MZM), and the double-drive intensity modulator is a double-drive Mach-Zehnder modulator (DDMZM). In the application, the Mach-Zehnder modulator (MZM) is the simplest structure for realizing double-sideband modulation, and other intensity modulators capable of realizing double-sideband modulation can also be selected; the double-drive Mach-Zehnder modulator (DDMZM) is the simplest structure for realizing single-sideband modulation, and other double-drive intensity modulators capable of realizing single-sideband modulation can also be selected. In the embodiment, the first intensity modulator and the second intensity modulator are both Mach-Zehnder modulators (MZM), and the double-drive intensity modulator is a double-drive Mach-Zehnder modulator (DDMZM). In the embodiment, the Mach-Zehnder modulator (MZM) is the simplest structure for realizing double-sideband modulation, and other intensity modulators capable of realizing double-sideband modulation can also be selected; the double-drive Mach-Zehnder modulator (DDMZM) is the simplest structure for realizing single-sideband modulation, and other double-drive intensity modulators capable of realizing single-sideband modulation can also be selected.

[0088] The application realizes the fusion splicing of multi-band signals by interpolating the missing frequency bands between the multi-bands and filling the spectral gaps through the coherent fusion technology, and effectively improves the radar range resolution. In addition, a part of the signal from the optical coupler is directly injected into the DDMZM as the echo reference light signal, which can avoid the energy conversion loss caused by the photoelectric-electric conversion and simplify the system structure. At the same time, since the echo reference signal and the transmitting signal come from the same light source, it ensures that they have high phase consistency, avoids the potential error caused by the phase asynchronization between multiple lasers, and significantly improves the stability and quality of the signal.

[0089] Specifically, assuming m takes 3, a multi-band signal fusion microwave photon radar system of the embodiment includes 1 continuous wave laser, 1 optical pulse modulation and compression module, 1 microwave drive module, 1 Mach-Zehnder modulator (MZM), 1 arbitrary waveform generator, 1 erbium-doped fiber amplifier, 1 adjustable optical filter, 1 1x4 optical coupler, 4 photodetectors, 1 electrical amplifier, 1 transmitting antenna, 3 receiving antennas, 3 low noise amplifiers, 3 electrical bandpass filters, 3 90° electrical bridges, 3 double drive Mach-Zehnder modulators (DDMZM), 3 electrical lowpass filters, 3 ADCs and 1 multi-band signal fusion processing module. The optical pulse modulation and compression module is a cascade of MZM, phase modulator (PM) and dispersion medium. The microwave drive module is a microwave source connected to a power divider, one output of which is connected to the first MZM, and the other output is connected to the PM through a first electrical amplifier and an electrical phase shifter.

[0090] The continuous wave laser has a center wavelength of 1550 nm, and the microwave source outputs a 7 GHz sinusoidal local oscillator signal. The sinusoidal local oscillator signal is divided into two outputs by an electrical power divider, one output drives the first MZM, and the other output is connected to the PM after being amplified in power by an electrical amplifier and being phase-shifted by an electrical phase shifter. The first MZM adopts a push-pull structure and is provided with a direct current bias voltage V1=V π1-MZM / 2, V π1-MZM being the half-wave voltage of the MZM. The driving voltage of the PM is set to V PM =3V π-PM , V π-PM being the half-wave voltage of the PM. The output optical signal of the continuous wave laser forms an initial optical pulse through the first MZM. The initial optical pulse is phase-modulated by the PM to output a linearly chirped optical pulse sequence. Then, the optical signal is subjected to optical pulse time-domain compression by a dispersion medium with a group velocity dispersion of -71300 ps 2 . The time-domain waveform and the optical spectrum of the output of the dispersion medium are shown in Figure 2 and Figure 3 respectively. As can be seen from the figures, the repetition frequency f LO of the ultra-short optical pulse sequence is 7 GHz, and the spectrum exhibits an optical comb. The arbitrary waveform generator generates a linear frequency modulation signal f LFM with a duration of 10 ms, a center frequency of 2 GHz and a bandwidth of 2 GHz. The signal is modulated on the envelope of the ultra-short optical pulse through the second MZM, which is a push-pull structure and is provided with a direct current bias voltage V b2 =V π2-MZM / 2, V π2-MZM being the half-wave voltage of the second MZM. The output spectrum of the second MZM is shown in Figure 4As shown in the diagram. The optical signal output from the second MZM is sequentially passed through an erbium-doped fiber amplifier and a tunable optical filter to improve optical power and suppress spontaneous emission noise of the erbium-doped fiber amplifier, respectively. Then, a 1×4 optical coupler splits the optical signal into four outputs, with output port 1-1 serving as the upper branch and output ports 2-1, 2-2, and 2-3 serving as lower branches. The lower branch output signals are injected as receiving reference light into the corresponding receiver module's DDMZM for optical domain deskewing. The upper branch output signal undergoes photoelectric conversion by a first photodetector with a 3dB bandwidth of 40GHz to generate a multi-band bandwidth radar signal, which is then amplified by a second amplifier. Finally, the signal is transmitted to a free-space target for detection via a transmitting antenna. The transmitted signal spectrum is shown in the diagram. Figure 5 As shown, the generated multi-band radar signal includes a center frequency of mf LO ±f LFM (m=1,2,3…) Multi-band up-conversion RF-LFM signal and center frequency mf LO The local oscillator frequency multiplier signal. By appropriately adjusting the frequencies and bandwidths of the local oscillator signal and the linear frequency modulated signal, multi-band signal tuning can be achieved. The arbitrary waveform generator's linear frequency modulated signal f LFM The center frequency is 1 / 4f LO The bandwidth is 1 / 3f LO Insufficient bandwidth will result in excessively large gaps in the spectrum between multiple frequency bands, making multi-band splicing impossible (maximum gap 67%). Excessive bandwidth will cause spectral aliasing; the bandwidth cannot exceed half the microwave source frequency. The center wavelength of the continuous wave laser is 900–1700 nm, and the microwave source generates a frequency of f. LO The output frequency of the local oscillator signal is 1–40 GHz.

[0091] Two targets were positioned at distances of 1.00m and 1.02m from the radar, respectively. The echo signals reflected from the targets were collected by the receiving antenna, amplified by a low-noise amplifier, and then frequency-selected and filtered for out-of-band clutter by an electrical bandpass filter. Bandpass filters with center frequencies of 5GHz, 9GHz, and 12GHz, each with a bandwidth of 2GHz, were used. The filtered signals were split into two orthogonal paths by a 90° bridge to drive the two RF ports of the DDMZM. ​​The bias voltage of the DDMZM was set at the linear transmission point to achieve single-sideband modulation. The modulated signal underwent photoelectric conversion by a second photodetector, outputting a de-skewed intermediate frequency (IF) signal, achieving optical domain de-skew processing of the linear frequency modulated signal. Finally, after being filtered by a low-pass filter to remove high-frequency components, the signal entered a low-speed ADC for sampling. A multi-band signal fusion module fused the multi-band signals. The ADC sampling rate was 10kS / s. Taking a microwave photonic de-skew receiving module with an electrical bandpass filter center frequency of 5GHz and a bandwidth of 2GHz as an example, the time-domain waveform of the de-skewed IF signal is as follows: Figure 6Theoretical calculation shows that the dechirped intermediate frequency signal frequencies of target 1 and target 2 are 1.334 kHz and 1.36 kHz, respectively. Through Fourier transform, the frequency information is converted into distance information. As shown in FIG. 3, only one target is observed in the result. According to the distance resolution ΔR = c / 2B, the distance resolution of the 2 GHz bandwidth linear frequency modulation signal is 7.5 cm, so two targets with a distance of 2 cm cannot be distinguished. Figure 7 As shown in FIG. 4, only one target is observed in the result. According to the distance resolution ΔR = c / 2B, the distance resolution of the 2 GHz bandwidth linear frequency modulation signal is 7.5 cm, so two targets with a distance of 2 cm cannot be distinguished.

[0092] The coherent fusion technology based on the full pole model is adopted to fit each sub-band signal, and the time-domain waveform is as shown in FIG. 5. Figure 8 As shown in FIG. 5, frequency band 1, frequency band 2 and frequency band 3 represent signals passing through a 2 GHz bandwidth band-pass filter with center frequencies of 5 GHz, 9 GHz and 12 GHz, respectively. Since frequency band 1 and frequency band 3 use negative chirp signals, the sampling signals need to be reversed. The three frequency band signals are extrapolated and interpolated to obtain extrapolated and interpolated frequency band 1, extrapolated and interpolated frequency band 2 and extrapolated and interpolated frequency band 3, as shown in FIG. 6. Figure 9 As shown in FIG. 6, the results show that there is a phase difference between the overlapping parts of adjacent sub-bands, and directly splicing these sub-bands will cause obvious jumps or distortion at the connection. After the coherent function is constructed to coherently process different sub-bands, the time-domain waveform is as shown in FIG. 7. Figure 10 As shown in FIG. 7, the results show that the processed sub-bands maintain good continuity in phase. Then, the Fourier transform is performed on the fused signal to map the frequency information into distance information. As shown in FIG. 8, two separate peaks are clearly visible in the figure, corresponding to targets at 1.00 m and 1.02 m, respectively. The distance resolution of the 2 GHz bandwidth linear frequency modulation signal is 7.5 cm, and two targets with a distance of 2 cm cannot be distinguished. In order to improve the resolution, the fusion technology based on the full pole model is used to perform frequency band interpolation and fusion on three 2 GHz bandwidth sub-band signals of 5 GHz, 9 GHz and 12 GHz, to equivalently generate a 9 GHz bandwidth linear frequency modulation signal. The distance resolution of the fusion signal is 1.67 cm, and the 2 cm interval target is successfully distinguished. Figure 11 As can be seen from the specific examples, in the application, a microwave photon radar can generate multi-frequency band bandwidth radar signals through a single set of transmission system, and multiple receiving modules can simultaneously receive three or more multi-frequency band echo signals in the optical domain. Through the coherent fusion technology, the missing frequency bands between the multi-frequency bands are interpolated to fill the spectral gaps, the multi-frequency band signals are fused and spliced, and the radar distance resolution is effectively improved.

[0093]

[0094] ​The application is not limited to the above-mentioned embodiments, and can make several equivalent modifications and replacements. The local oscillator signal is not limited to 7 GHz, the linear frequency modulation signal is not limited to 1-3 GHz, the intensity modulator is not limited to the MZM, and the bandwidth fusion technology is not limited to the multi-band bandwidth fusion technology based on the full pole model. Various simplifications and modifications within the scope of the principles and methods of the application are all within the protection scope of the application.

Claims

1. A multi-band signal fusion microwave photonic radar system, characterized in that, include: A multi-band signal transmission module for generating multi-band bandwidth radar signals; m microwave photonic deskewing receiver modules are used to receive echo signals of three or more multi-band bandwidth radar signals in the optical domain. A multi-band signal fusion processing module is used to interpolate and fill the missing frequency bands and spectral gaps between multiple frequency bands through coherent fusion technology, so as to realize the fusion and splicing of multi-band signals; m represents the number of multi-band channels; The multi-band signal transmission module includes a continuous wave laser, an optical pulse modulation and compression module, a second intensity modulator, a 1×(m+1) optical coupler, a first photodetector, a second electrical amplifier, and a transmitting antenna connected in sequence. The optical pulse modulation and compression module and the second intensity modulator are driven by a microwave driving module and an arbitrary waveform generator, respectively. The optical pulse modulation and compression module is composed of a first intensity modulator, a phase modulator, and a dispersive medium cascaded together. In the microwave driving module, the microwave source output is connected to a power divider; one output of the power divider is connected to the first intensity modulator, and the other output is cascaded with the first electrical amplifier and an electrical phase shifter before being connected to the phase modulator. Each microwave photonic deskewing receiver module includes a receiving antenna, an electrical bandpass filter, a 90° bridge, a dual-drive intensity modulator, a second photodetector, an electrical low-pass filter, and an ADC connected in sequence; m output ports of the optical coupler are respectively connected to the optical input ports of the dual-drive intensity modulators in the m microwave photonic deskewing receiver modules; the outputs of the m ADCs are all connected to the multi-band signal fusion processing module.

2. The multi-band signal fusion microwave photonic radar system of claim 1, wherein, The multi-band signal transmission module further includes an erbium-doped fiber amplifier and a tunable optical filter connected in sequence. The erbium-doped fiber amplifier is connected to the second intensity modulator, and the tunable optical filter is connected to the 1×(m+1) optical coupler. In each microwave photon deskewing receiving module, a low-noise amplifier is located between the receiving antenna and the electrical bandpass filter.

3. The multi-band signal fusion microwave photonic radar system of claim 1, wherein, Both the first intensity modulator and the second intensity modulator are Mach-Zehnder modulators, and the dual-drive intensity modulator is a dual-drive Mach-Zehnder modulator.

4. The multi-band signal fusion microwave photonic radar system of claim 1, wherein, The arbitrary waveform generator linear frequency modulation signal f LFM The center frequency is 1 / 4f LO The bandwidth is 1 / 3f LO The continuous wave laser center wavelength is 900-1700nm, and the microwave source generates a frequency of f LO The output frequency of the local signal is 1-40GHz.

5. An implementation method for a multi-band signal fusion microwave photonic radar system, characterized in that, The method is based on the microwave photonic radar system with multi-band signal fusion as described in any one of claims 1-4, and includes: Multi-band signal transmission steps: Use an optical pulse modulation and compression module to generate an optical frequency comb with narrow pulse width characteristics. Load the linear frequency modulated microwave signal onto the optical frequency comb through electro-optic modulation. After photoelectric conversion, generate a multi-band bandwidth radar signal and transmit it. Microwave photonic deskewing receiving steps: Deskewing is performed on the echo signals of multi-band bandwidth radar signals in the optical domain to obtain deskewing intermediate frequency signals corresponding to different frequency bands; Multi-band signal fusion processing steps: The missing frequency bands between the de-skewing intermediate frequency signals corresponding to different frequency bands are extrapolated in the time domain using the coherent fusion technology of the full pole model, thereby filling the spectral gaps, realizing the fusion and splicing of multi-band signals, and obtaining the target detection results of the equivalent large bandwidth signal.

6. The implementation method of claim 5, wherein, The multi-band signal transmission steps specifically include: The continuous wave laser generates an optical carrier with a frequency f0, which is injected into a first intensity modulator of an optical pulse modulation and compression module to form an initial optical pulse sequence; a power divider in a microwave driving module divides a sinusoidal local oscillator signal with a frequency f LO generated by a microwave source into two paths, one of which drives the first intensity modulator, and the other of which is amplified by a first electric amplifier and phase-shifted by an electric phase shifter before being connected to a phase modulator; the amplified sinusoidal local oscillator signal waveform is phase-shifted by the electric phase shifter so that the peaks or troughs of the waveform are aligned with the peaks of the initial optical pulse sequence; the initial optical pulse sequence passes through the phase modulator to form a linearly chirped optical pulse sequence, which is compressed in the time domain by passing through a dispersive medium to obtain a compressed linearly chirped optical pulse sequence, the spectrum of which is an optical frequency comb with a spacing f LO ​ The linear frequency modulation microwave signal generated by the arbitrary waveform generator is double sideband modulated to the compressed linear chirp optical pulse sequence by the second intensity modulator, and the generated optical carrier linear frequency modulation microwave signal is sequentially amplified by the erbium-doped fiber amplifier and filtered by the adjustable optical filter to remove the spontaneous emission noise from the erbium-doped fiber amplifier, and then the optical signal is divided into m+1 outputs by the 1×(m+1) optical coupler, one of which is used as the upper branch and is photoelectrically converted by the first photodetector to generate a multi-bandwidth radar signal, which is sequentially transmitted by the second electric amplifier and the transmitting antenna; the remaining m outputs are used as the lower branch and are used as the receiving reference light signals of the m microwave photon desquamation receiving modules, which are injected into the double-drive intensity modulator. The first intensity modulator and the second intensity modulator both work at a linear bias point.

7. The implementation method of claim 5, wherein, In the microwave photon desquamation receiving step, the desquamation steps of each microwave photon desquamation receiving module are the same, and specifically include: After the echo signal of the multi-bandwidth radar signal is collected by the receiving antenna, it is amplified by the low-noise amplifier, and then is frequency-selected and filtered by the electric band-pass filter to remove the out-of-band clutter; The signal filtered to remove the out-of-band clutter is divided into two phase-orthogonal paths by the 90° electric bridge and drives the two radio frequency ports of the double-drive intensity modulator; at the same time, the optical input port of the double-drive intensity modulator is injected with the reference light signal to realize single sideband modulation; The modulated signal enters the second photodetector for photoelectric conversion to output the desquamation intermediate frequency signal, realizing the optical domain desquamation processing of the linear frequency modulation signal; After the desquamation intermediate frequency signal enters the electric low-pass filter to filter out the high-frequency components, the time-domain waveform of the desquamation intermediate frequency signal is sampled by the ADC to obtain a sampling signal. The double-drive intensity modulator works at a linear bias point.

8. The implementation method of claim 5, wherein, The multi-band intermediate frequency signal fusion processing step specifically includes: Let the sampling signal of the i-th frequency band be s i (n), i = 1, 2, 3…m, wherein i is the frequency band number, and n is the signal sampling point number; Step one: determine whether the sampling signal is a forward chirp signal; if it is not a forward chirp signal, flip the time domain of the sampling signal, and if it is, keep the original signal unchanged; Step two: Construct the Hankel matrix H of the i-th band signal i , wherein N i represents the maximum number of sampling points of the i-th frequency band, L i represents the window length, L i = N i / 3, and singular value decomposition is then performed on H i respectively, H i = U i S i V i H where H denotes the conjugate transpose, U i and V i are left and right singular vector matrices, respectively, and S i denotes the singular value matrix; Step three: Let S be the matrix obtained from singular value decomposition i The matrix is M x N dimensional, the values of AIC(k) and MDL(k) are obtained by AIC criterion and MDL criterion, and the order of the all-pole model of the frequency band is taken as the minimum of AIC(k) and MDL(k), where the formulas of AIC and MDL criteria are Wherein, k=0, 1, … M-1, k is the model order; Step four: the right singular vector matrix V of singular value decomposition i According to the model order k, the signal subspace V is divided i sn and the noise subspace V i n , the two subspaces are mutually orthogonal, V i = [V i sn V i n ] where the signal subspace matrix V i sn has k columns, the noise subspace matrix V i n has L i -k columns; the noise subspace generator matrix A i : A i = V i n V i nH where H denotes the conjugate transpose, A i the first row d ij of the first column, j denotes the jth element of the first row, and constitutes a polynomial, A i (z) is solved, and the result of the root is the pole value of the sub-band. The k points closest to the unit circle are selected as the poles of the sub-band, and the pole value p ik of the i frequency band is obtained. k ] Step five: Construct Vandermonde matrix P with pole values p ik = [p1, p2,..., p k ] of the i-th frequency band According to the least square method formula, the amplitude and phase coefficients a of the i frequency band are obtained ik = [a i1 , a i2 , …, a ik ] T , where [s i (0),s i (1), …, s i (Ni-1)] T is a signal vector constructed from the sampled signal s i (n). Step six: obtain the pole value p of each sub-band full pole model ik and amplitude-phase coefficient a ik Then, the signal of the i-th frequency band is fitted, and the fitting formula is Wherein, k represents the model order; Step seven: extrapolate and interpolate the i-th subband signal based on the all-pole model to extend the signal length from N i to N i +N ex , where N ex is the length of the extrapolated interpolated signal; Step eight: construct a coherence function C to realize the phase consistency between subbands, where Δθ i is the difference in the rotation angle between the two subbands, and ΔA i is the difference in the amplitude coefficient between the two subbands. Optimization algorithm is used to search the optimal rotation angle Δθ i and amplitude coefficient deviation ΔA i , so that the coherence function C=C min , and the sub-band after coherence Take one subband as a reference, repeat the above steps one to eight to realize the extrapolation interpolation and mutual coherence between all subbands, and the spectrum between each subband is spliced and fused to finally synthesize an equivalent large bandwidth signal.

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