High sensitivity target detection method and system based on microwave optical receiver

Abstract

The application discloses a high-sensitivity target detection method and system based on a microwave optical receiver, which is improved and integrated and optimized for the detection requirement of low-speed weak targets, introduces an optical injection locking local oscillator technology in a millimeter wave frequency band, generates a low-phase-noise and high-stability optical local oscillator signal for heterodyne down-conversion, and significantly improves the frequency stability and detection sensitivity of the system; a focal plane is also introduced to adopt a surface array detector for large-space-beam receiving, and a multi-pulse accumulation trajectory tracking algorithm is adopted in a signal processing module to realize long-time accumulation detection of weak target echo signals, effectively extract low signal-to-noise ratio target signals, and suppress clutter and single-frequency interference, and the system is endowed with high-precision and high-sensitivity detection capability for multiple targets.

Description

Technical Field

[0001] This application belongs to the field of microwave photonics technology and radar detection technology, and in particular relates to a target detection system based on a microwave optical receiver. Background Technology

[0002] As an all-weather, all-day target detection device, radar plays an irreplaceable role in civilian surveillance (such as low-altitude UAV monitoring and traffic flow monitoring) and military reconnaissance (such as weak-reflection target identification and battlefield environment monitoring). With the development of target technology, detection targets are gradually evolving towards miniaturization, low speed, and low radar cross-section, placing higher demands on the detection sensitivity, accuracy, stability, and anti-interference capabilities of radar systems. Among these, the millimeter-wave band, due to its short wavelength, narrow beam, and high resolution, has become the preferred frequency band for high-precision detection. However, this band suffers from significant signal transmission loss, and traditional radar electronic links struggle to balance the demands of high resolution and high sensitivity. These technological bottlenecks are becoming increasingly prominent, necessitating breakthroughs through cross-domain technological integration.

[0003] To address the aforementioned issues, several microwave photonics-based radar receiving schemes have been proposed. For example, Chinese Patent Publication No. CN107947864A discloses a photonic microwave down-conversion device that up-converts radio frequency signals to the optical domain via electro-optic modulation. It then uses a single-sideband light-injection-locked distributed feedback laser to generate a low-phase-noise optical local oscillator signal, which coherently beats with the signal light carrying target information in a photodetector, achieving a single optical domain down-conversion reception and demodulation, thereby improving system frequency stability and weak signal reception sensitivity. Another example is Chinese Patent Application Publication No. CN113193916A, which proposes a microwave multi-beam optical receiving and demodulation system. This system uses the simulated beamforming capability of optical lenses to up-convert microwave signals from different directions and frequencies to the optical domain, converging them at corresponding positions in a photodetector array. Simultaneously, it utilizes the coherent beat of the optical local oscillator and the signal light to complete the down-conversion reception of the radio frequency signal. This scheme can handle multiple beams using simple optical components, greatly simplifying the multi-target receiving structure. It also offers stronger anti-interference capabilities compared to traditional electronic multi-beam receivers and better system compatibility. In addition, Japanese Patent Application Publication No. JP2013026944A and US Patent Application Publication No. US2019319355A1 have also explored new methods for using photonics technology in radar transceivers, aiming to improve radar signal frequency stability and detection sensitivity while achieving high-resolution detection of multiple targets and enhancing anti-jamming performance.

[0004] In particular, CN113193916A employs a coherent demodulation scheme with optical down-conversion at the receiver end. It utilizes a photodetector array to simultaneously receive multi-channel signals, but can only receive signals in one dimension, making it unable to process multi-beam signals over large spatial domains. CN113193916A primarily focuses on the implementation of a multi-beam optical receiver architecture. Although it mentions obtaining a stable local oscillator light source through methods such as injection locking, its scheme fails to organically combine improved sensitivity to weak targets in the millimeter-wave band with a multi-pulse accumulation detection algorithm. Therefore, it still falls short in its ability to detect low-speed, weakly reflective targets in cluttered environments.

[0005] In summary, existing solutions only address single problems, such as local oscillator stability or spatial coverage, and cannot comprehensively solve multi-dimensional issues such as millimeter-wave loss, weak target extraction, and trajectory tracking. They also suffer from insufficient sensitivity, with the minimum detectable power in the millimeter-wave band typically exceeding -110dBm, making it impossible to detect weak targets with echo amplitudes below noise levels. Furthermore, they exhibit poor channel consistency, failing to fully leverage the multi-channel advantages of area array antennas, resulting in low multi-target resolution accuracy. Finally, they have limited anti-interference capabilities, relying solely on traditional electronic filtering techniques, which cannot filter out single-frequency interference in complex electromagnetic environments, and lack algorithmic suppression of background clutter, leading to a high false detection rate for target identification. Summary of the Invention

[0006] The purpose of this invention is to address at least one of the aforementioned drawbacks by providing an improved high-sensitivity target detection method and system based on a microwave optical receiver.

[0007] Some embodiments of this application provide a high-sensitivity target detection method based on a microwave optical receiver: it includes providing an intermediate frequency (IF) electrical signal with a preset value; and digitizing the IF electrical signal and extracting target distance and velocity parameters from it using a locked logarithmic time-domain cumulative tracking algorithm to achieve target detection; wherein, the formation of the IF electrical signal includes: providing a radio frequency (RF) detection signal, providing a low phase noise optical local oscillator (IOU) signal, the frequency difference between the IOU signal and the detection signal being the preset value; transmitting the detection signal and receiving the echo signal from the target to the detection signal; amplifying the echo signal... The system provides an echo optical signal, including providing an optical carrier, splitting the optical carrier into each modulator array; up-converting the amplified echo signal to an optical domain using the split optical carrier in each modulator array; collimating the echo optical signal with the optical local oscillator signal; extracting an upper sideband from the echo optical signal and a target sideband from the optical local oscillator signal; focusing the upper sideband onto the corresponding detector element of the photodetector array, such that the target sideband expands to cover the entire effective surface of the photodetector array to achieve coherent heterodyne beat frequency, and outputting the intermediate frequency electrical signal from the photodetector array.

[0008] Other embodiments of this application provide a high-sensitivity target detection system based on a microwave optical receiver: it includes a radio frequency source, including a first channel and a second channel, wherein the first channel is configured to output a detection signal, and the second channel is configured to output a local oscillator optical signal to drive a local oscillator optical module to generate a low-phase-noise optical local oscillator signal through optical injection locking; the frequency difference between the optical local oscillator signal and the detection signal is a preset value; an antenna array is configured to cover the millimeter-wave band to realize the transmission of the detection signal and the reception of the echo signal of the detection signal from the target; a low-noise amplifier array is configured to amplify the echo signal; a narrow-linewidth laser is configured to output an optical carrier; a beam splitter splits the optical carrier into various modulator arrays; and a modulator array is configured to utilize the... The beam-splittered optical carrier upconverts the amplified echo signal to the optical domain to form an echo optical signal; an optical antenna array collimates the echo optical signal and the optical local oscillator signal; an optical filter is configured to extract the upper sideband from the echo optical signal and the target sideband from the optical local oscillator signal; an optical lens and photodetector array are configured to focus the upper sideband onto the corresponding detector unit of the photodetector array, expand the target sideband to cover the entire effective surface of the photodetector array to achieve coherent heterodyne beat frequency, and output an intermediate frequency electrical signal corresponding to the preset value from the photodetector array; a signal acquisition and processing module is configured to digitize the intermediate frequency electrical signal and then extract the target distance and velocity parameters through a locked logarithmic time-domain cumulative tracking algorithm to achieve the detection of the target.

[0009] In some embodiments, the preset value is 1 GHz.

[0010] In some embodiments, the narrow-line laser outputs an optical carrier in the 1550nm~1551nm band, especially an optical carrier with a wavelength of 1550.770nm; the frequency of the detection signal output by the first channel of the radio frequency source is 35GHz; the frequency of the local oscillator signal output by the second channel is 34GHz; and the intermediate frequency signal is 1GHz.

[0011] In some embodiments, the intermediate frequency electrical signal is digitized by a high-speed analog-to-digital converter with a sampling rate of 4.8 GSa / s.

[0012] In some embodiments, the locked logarithmic time-domain cumulative tracking algorithm includes intra-frame CFAR detection, inter-frame M / N incoherent accumulation, and α-β trajectory tracking.

[0013] In some embodiments, the intra-frame CFAR detection includes Log-t / CFAR detection with an adjustable threshold of 12-18 dB; the inter-frame M / N incoherent accumulation includes M / N incoherent accumulation, where N=64 and M=32, and the parameters are adjustable; the α-β trajectory tracking includes α-β filtering, where α=0.15-0.25 and β=0.04-0.06, and extracts the angle of arrival information of the focal plane.

[0014] In some embodiments, the Log-t / CFAR threshold is set to 15 dB; the α-β filter parameters are α=0.2 and β=0.05.

[0015] In some embodiments, the optical filter is either a fixed bandpass filter or a tunable bandpass filter with a tuning range of fc +34 GHz to fc +35 GHz.

[0016] In some embodiments, the antenna array is configured such that the spacing between antenna elements is less than or equal to half the center wavelength of the 35 GHz signal, for example, a spacing of ≤4.28 mm, and the amplitude deviation of each channel of the RF link is ≤0.5 dB and the phase deviation is ≤5°.

[0017] The modulator array is consistent with the optical carrier polarization state of the modulator built into the local oscillator optical module.

[0018] The beneficial effects of this application include:

[0019] Some embodiments construct a microwave-optical-electric domain coordinated detection system, which integrates functions through components including lasers, beam splitters, local oscillator modules, optical antenna arrays, radio frequency sources, optical filters, optical lenses, photodetector arrays, signal acquisition and processing modules, antenna arrays, low-noise amplifier arrays, and modulator arrays.

[0020] Some embodiments have been improved and optimized to address the detection needs of low-speed, weak targets. On one hand, millimeter-wave band optical injection-locked local oscillator technology is introduced to generate a low-phase-noise, high-stability optical local oscillator signal for heterodyne down-conversion, significantly improving the system's frequency stability and detection sensitivity. On the other hand, a focal plane array detector is used for large-area beam reception, and a multi-pulse accumulation trajectory tracking algorithm is employed in the signal processing module to achieve long-term accumulation detection of weak target echo signals. This effectively extracts low signal-to-noise ratio target signals and suppresses clutter and single-frequency interference, giving the system high-precision, high-sensitivity detection capabilities for multiple targets. Therefore, by supporting millimeter-wave band local oscillator locking and multi-pulse accumulation detection of weak targets, this invention further improves the sensitivity and anti-interference performance of multi-target detection, better meeting the detection needs of low-speed, weak targets in complex environments.

[0021] In some embodiments, the system adapts to the millimeter-wave band, reducing the minimum detectable power to -125 dBm and improving the sensitivity for detecting weak targets. In some embodiments, the system optimizes channel consistency and combines with a planar array antenna to achieve three-dimensional multi-target coverage, improving multi-target resolution. In some embodiments, the system integrates a locked logarithmic time-domain cumulative tracking algorithm to achieve clutter suppression and single-frequency interference filtering, reducing the false detection rate and making it suitable for real-time detection of low-speed, weakly reflective targets in complex electromagnetic environments. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a high-sensitivity target detection system based on a microwave optical receiver according to an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the focal plane detection principle of a high-sensitivity target detection system based on a microwave optical receiver according to an embodiment of the present invention.

[0024] Figure 3 This is a range-Doppler diagram of a high-sensitivity target detection system based on a microwave optical receiver according to an embodiment of the present invention.

[0025] Figure 4 This is a multi-beam target detection point map of a high-sensitivity target detection system based on a microwave optical receiver in a cluttered environment, according to an embodiment of the present invention.

[0026] Appendix Figure 1 The components are labeled as follows: 1 is the laser; 2 is the beam splitter; 3 is the local oscillator module; 4 is the optical antenna array; 5 is the radio frequency source; 6 is the optical filter; 7 is the optical lens; 8 is the photodetector array; 9 is the signal acquisition and processing module; 10 is the antenna array; 11 is the low-noise amplifier array; and 12 is the modulator array. Detailed Implementation

[0027] The specific embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0028] Some embodiments of this application provide a high-sensitivity target detection method based on a microwave optical receiver, which includes providing an intermediate frequency (IF) electrical signal with a preset value; and digitizing the IF electrical signal and extracting target distance and velocity parameters from it using a locked logarithmic time-domain cumulative tracking algorithm to achieve target detection. The formation of the IF electrical signal includes: providing a radio frequency (RF) detection signal; providing a low-phase-noise optical local oscillator (IOU) signal, the frequency difference between the IOU signal and the detection signal being the preset value; transmitting the detection signal and receiving the echo signal from the target to the detection signal; amplifying the echo signal; providing the echo optical signal, including providing an optical carrier and splitting the optical carrier into various modulator arrays; up-converting the amplified echo signal to an optical domain in each modulator array using the split optical carrier; collimating the echo optical signal and the IOU signal; extracting an upper sideband from the echo optical signal and a target sideband from the IOU signal; and focusing the upper sideband onto a corresponding detector unit of a photodetector array, such that the target sideband is expanded to cover the entire photodetector. Based on this method, this application also provides a specific system implementation, as well as system improvement schemes to enhance the system's performance.

[0029] Reference Figure 1 The system of this application consists of the following components: a laser 1 with narrow linewidth, outputting optical carriers in the 1550nm~1551nm band, such as optical carriers with a wavelength of 1550.770nm; a beam splitter 2 configured to divide the optical carriers into multiple paths, matching the number of channels in the modulator array; a local oscillator module 3 configured to generate a low phase noise optical local oscillator signal through optical injection locking (OIL); an optical antenna array 4 configured to collimate the echo optical signal and the optical local oscillator signal to ensure beam direction consistency; a radio frequency source 5 with dual-channel output capability: the first channel provides a 35GHz pulse signal as a detection signal, and the second channel provides a 34GHz pulse signal, with the two channels synchronized by a reference clock; and an optical filter 6, which can be used for bandpass filtering to extract the upper sideband (f) of the echo light. c + f RF1 ) and the target sideband of the optical local oscillator (f c +f RF2 ), f cThe optical carrier frequency is 7; optical lens 7 is configured to focus the echo light signal onto the corresponding unit of the photodetector array, while expanding the local oscillator signal to cover the effective surface of the detector, ensuring coherent beat frequency; photodetector array 8 is configured to output a 1GHz intermediate frequency electrical signal with bandwidth matching beat frequency requirements; signal acquisition and processing module 9 has a built-in 4.8GSa / s high-speed analog-to-digital converter and a locked logarithmic time-domain cumulative tracking algorithm module; antenna array 10 operates in the millimeter-wave band, with unit spacing ≤ 1 / 2 of the center wavelength of the operating frequency band. One unit transmits, and the rest receive; a low-noise amplifier array 11 is used to amplify the echo signal with a noise figure ≤2dB to avoid signal attenuation; a modulator array 12 is configured to upconvert the echo signal to the optical domain with a half-wave voltage ≤5V, a modulation bandwidth covering the millimeter-wave band, and coherence with the modulator built into the local oscillator module; the antenna array 10, low-noise amplifier array 11, modulator array 12, and RF source 5 can be connected by RF cables to ensure low-loss transmission of RF signals; optical domain components such as laser 1, beam splitter 2, local oscillator module 3, optical antenna array 4, optical filter 6, optical lens 7, and photodetector array 8 can be connected by polarization-maintaining fiber to suppress changes in the polarization state of the optical signal and ensure phase consistency.

[0030] To ensure uniform reception of the target signal in three-dimensional space, the antenna array 10 can be configured such that the element spacing is ≤ half the center wavelength of the 35GHz signal, for example, a spacing of ≤4.28mm, and the amplitude deviation and phase deviation of each channel of the RF link, such as antenna array 4-modulator array 12, are ≤0.5dB and ≤5°. To ensure phase matching during spatial light beats, the polarization state of the optical carrier in modulator array 12 is consistent with that in the local oscillator module 3. The center frequency difference between the first and second channels of the RF source 5, for example, is 1GHz, which must satisfy the bandwidth of photodetector array 8, for example, ≥1GHz, and the sampling rate of signal acquisition and processing module 9, for example, 4.8GSa / s, satisfying the Nyquist sampling theorem, i.e., the sampling rate ≥ 2 times the intermediate frequency.

[0031] Figure 2 This is a schematic diagram of the focal plane detection principle of a high-sensitivity target detection system based on a microwave optical receiver according to an embodiment of the present invention. The microwave array antenna receiving frequency is... The signal, provided by laser 1, has a frequency of The optical carrier signal is up-converted to the optical domain by phase modulator 12. By analyzing the lower sideband (LSB) after electro-optic modulation, the following relationship can be obtained:

[0032]

[0033] in The angle of the principal ray at the end of the optical fiber relative to the principal axis. It refers to the distance between the two microwave antennas. The frequency of the received radio frequency signal. The distance between the two optical fibers at the receiving end. The frequency of the lower sideband signal. The angle between the radio frequency signal and the antenna's main axis.

[0034] In summary, different frequencies and different incident angles After the radio frequency signal is converted into an optical signal through electro-optic modulation, the angle of the main ray at the end of the optical fiber relative to the main axis is also different. The target beam is distinguished by reaching different positions of the photodetector 8.

[0035] The operation of the above system can be roughly divided into several functional parts. Of course, this division of functional parts is only for the convenience of understanding the present invention and is not a special limitation on the functional division of the system.

[0036] The radio frequency signal transmission section includes a first channel of the radio frequency source 5 and a transmitting unit of the antenna array 10. The first channel of the radio frequency source 5 outputs a pulse signal with a center frequency of 35 GHz, for example, a pulse width of 100 ns and a repetition frequency of 1 kHz. The signal is transmitted to the transmitting unit of the antenna array 10 through a radio frequency cable, and the transmitting unit radiates the signal into space.

[0037] The target echo receiving and amplification section includes a receiving unit of antenna array 10 and a low-noise amplifier array 11. The echo signal reflected by a spatial target is received by the receiving unit of antenna array 10. The echo signal contains target time delay information corresponding to the distance and Doppler frequency shift information corresponding to the velocity. The receiving unit can be any unit of antenna array 10 except for the transmitting unit. The echo signal is transmitted to the low-noise amplifier array 11 via an RF cable. Each channel amplifier amplifies the signal by 20dB (noise figure ≤ 2dB) to prevent noise overwhelming during subsequent modulation. The amplified signal is then transmitted to modulator array 12.

[0038] The optical carrier generation section includes a laser 1 and a beam splitter 2. The laser 1 is configured to output an optical carrier with a wavelength in the 1550nm~1551nm band, such as 1550.770nm, and a narrow linewidth optical carrier with a linewidth ≤10kHz to ensure the stability of the optical domain signal. The laser 1 is divided into N equal paths by the beam splitter 2, where N is the same as the number of channels of the modulator array 12. Each optical carrier is transmitted to the corresponding channel of the modulator array 12.

[0039] The optical domain up-conversion and optical local oscillator generation section includes a modulator array 12. The modulator array 12 includes multiple channels. In each modulation channel, the amplified echo signal from one array unit of the low-noise amplifier array 11 is loaded onto a split optical carrier from the beam splitter 2. Each modulation channel generates an optical carrier (f) through electro-optic modulation. c ), top band (f) c + f RF1 ), and the lower band (f) c -f RF1 The optical signal, i.e., the echo optical signal; where f RF1 =35GHz, which is the frequency of the echo signal and the detection signal.

[0040] The optical filtering and coherent beat frequency section includes the second channel of the RF source 5, the local oscillator module 3, and the optical antenna array 4. The second channel of the RF source 5 outputs a pulse signal with a center frequency of 34 GHz, synchronized with the reference clock of the first channel signal, with a synchronization error ≤ 1 ns. This signal is transmitted to the local oscillator module 3 via an RF cable. The local oscillator module 3 has a built-in laser submodule and an optical injection locking submodule. It uses the 34 GHz pulse signal to trigger the optical injection locking state, generating a frequency of f. c + f RF2 The optical local oscillator signal, where f RF2 =34GHz, which is the frequency of the output signal of the second channel. The phase noise of this optical local oscillator signal is ≤-100dBc / Hz (10kHz offset), and the frequency difference between it and the upper sideband of the echo optical signal is 1GHz to match the bandwidth of the photodetector. The echo optical signal from the modulator array 12 and the optical local oscillator signal from the local oscillator module 3 are respectively transmitted to the optical antenna array 4, which collimates the two signals into parallel beams, for example, with a collimation accuracy of 0.1mrad, to ensure the coherence of subsequent beat frequencies.

[0041] The filtering and photoelectric detection section includes an optical filter 6, an optical lens 7, and a photodetector array 8. The collimated two optical signals enter the optical filter 6, which has a bandwidth of 1 GHz and a center frequency f. c +34.5GHz, to filter out optical carrier f c , lower sideband f of echo light c Useless frequency components such as -35GHz are retained, only the upper sideband f of the echo light is preserved. c +35GHz and optical local oscillator signal f c+34GHz. Optical lens 7 focuses the upper sideband signal of the echo light onto the corresponding detection unit of the photodetector array 8, for example, each detection unit corresponds to a receiving channel, while simultaneously expanding the optical local oscillator signal to cover the entire effective detection surface of the photodetector array 8; each unit of the photodetector array 8 receives the focused echo light signal and the expanded optical local oscillator signal, generating a coherent heterodyne beat frequency, and outputting an intermediate frequency electrical signal with a frequency of 1GHz, i.e., (f c +35GHz)-(f c +34GHz) = 1GHz. Each channel has an output power of -10dBm and a signal-to-noise ratio of 30dB.

[0042] In addition to being a fixed bandpass filter, the optical filter 6 can also be a filter with a tuning range f. c +34GHz to f c A +35GHz tunable bandpass filter is used to improve the system's adaptability to different frequency targets.

[0043] The intermediate frequency signal digitization and target parameter extraction section includes a signal acquisition and processing module 9, which incorporates a high-speed analog-to-digital converter and a digital signal input processing module. The high-speed analog-to-digital converter has a sampling rate of 4.8 GSa / s and a resolution of 12 bits, configured to convert a 1 GHz intermediate frequency electrical signal into a digital signal. The digital signal input processing module is configured to perform three steps: First, intra-frame processing: matched filtering (filter coefficients matched to the 35 GHz pulse signal) is applied to the single-frame digital signal to generate a high-resolution range profile; then, a Log-t / CFAR detector is used, with a detection threshold set to 15 dB to filter out background noise and clutter, retaining candidate target units (such as range points with signal amplitudes higher than the threshold); Second, inter-frame processing: M / N incoherent accumulation (M=32, i.e., only those appearing in at least 32 frames) is retained from the candidate target units of N consecutive frames (N=64). The system includes: 1) enhancing the energy of weak targets (energy boost of 15dB) and suppressing transient interference; and 2) trajectory tracking: using an α-β filter (α=0.2, β=0.05) to fit the "radial distance-velocity-angle of arrival" of the screened target units, establishing continuous trajectories (if the distance difference between adjacent frame target units is ≤0.1m and the velocity difference is ≤0.05m / s, they are determined to be the same target), eliminating false clutter points, such as isolated single-frame target units, and finally outputting the distance of multiple targets, for example, with an accuracy of 0.025m, and the velocity, for example, with an accuracy of 0.2m / s.

[0044] It should be understood that, depending on the clutter intensity, the Log-t / CFAR threshold can be set to be adjustable within the range of 12-18 dB. The α-β filter parameters can be adjusted to α=0.15-0.25 and β=0.04-0.06 without affecting the trajectory tracking accuracy.

[0045] This invention has been verified through system-level experiments and simulations. A microwave photon-assisted pulsed coherent multi-target detection system based on optical injection locking (OIL) combined with the locked logarithmic time-domain cumulative tracking (LLTAT) algorithm has been built. All core performance indicators have met the requirements, and the feasibility of the scheme has been confirmed, as detailed below:

[0046] I. Basic Experimental Configuration: The experimental hardware is consistent with the invention scheme. Key components include: a tunable laser (TL, 1550.770nm, linewidth ≤10kHz); a dual-channel arbitrary wave generator (AWG) (16 / 36GHz LFM signal, 200MHz bandwidth; 14GHz OIL local oscillator signal); two MZM and SL units (phase noise ≤-100dBc / Hz after OIL locking); a 4.8GSa / s 16-bit ADC; a channel simulator (simulating target echo and interference); 64-pulse accumulation (9.6ms) and an LLTAT algorithm threshold of 15dB are used.

[0047] II. Core Experimental Results: 1. Signal Link Effectiveness: Spectrum measurements at key nodes showed that after OIL locking, the SL linewidth was compressed to <100kHz. The photodetector (PD) output a 2GHz intermediate frequency signal with a 3dB linewidth of only 30Hz, exhibiting no jitter, indicating normal link function. 2. Ranging and Velocity Measurement Accuracy: Ku / Ka band experiments showed RMS ranging error ≈ 0.025m (maximum ≤ 0.03m), and RMS velocity measurement error ≈ 0.2m / s (maximum ≤ 0.39m / s), meeting design specifications. 3. Strong Interference Multi-Target Detection: Injecting 10dBm single-frequency interference, three targets (5.996 / 6.745 / 7.495km, 22m / s) could be clearly distinguished. Figure 3 As shown, a continuous trajectory is generated within 0.5 seconds, clutter is eliminated, and the anti-interference capability meets the standard. Figure 4 As shown. 4. Weak target sensitivity: When the echo power attenuates to -125dBm, the signal-to-noise ratio (SNR) is still ≥15dB, and the detection success rate is 99%; the sensitivity is improved by 8dB compared with the no-OIL scheme, reaching the minimum detectable power of -125dBm.

[0048] III. Simulation and Conclusion: MATLAB simulation verifies the effectiveness of the algorithm, achieving a 98% success rate in detecting weak targets under complex electromagnetic environments with an error of <5%. In summary, both experiments and simulations demonstrate the feasibility of this invention, with core performance indicators superior to traditional systems, meeting the requirements of weak target and strong interference scenarios.

[0049] Therefore, it can be seen that each embodiment of this application has its own technical advantages over the prior art. In some embodiments, the system sensitivity proposed in this application is significantly improved. By combining optical injection locking local oscillator with M / N incoherent accumulation, the minimum detectable power of the system reaches -125dBm (64 pulses accumulated), which is 15dB higher than the prior art (≥-110dBm). It can detect weak targets with echo amplitude lower than the noise level.

[0050] In some embodiments, the system proposed in this application has higher accuracy: within a distance range of 6.7km, the ranging accuracy is 0.025m and the velocity accuracy is 0.2m / s, which is a significant improvement over existing microwave photonic radars, due to the synergistic effect of low phase noise optical local oscillator and weak signal processing algorithm.

[0051] In some embodiments, the system integration and consistency proposed in this application are superior: the design of using a single local oscillator module combined with a multi-channel shared optical carrier results in a smaller system volume compared to independent local oscillator schemes, and at the same time, the multi-target resolution capability is stronger through the amplitude / phase deviation constraint of the RF link.

[0052] The system proposed in this application has stronger anti-interference capabilities: it integrates optical filters to filter out useless sidebands and uses Log-t / CFAR detection to filter out clutter. The suppression of single-frequency interference is significantly improved compared with traditional electronic filtering, and the false detection rate of targets in complex electromagnetic environments is significantly improved.

[0053] The system proposed in this application has better band adaptability: in some embodiments, such as the low-noise amplifier with a noise figure ≤2dB and the modulator bandwidth covering 34-35GHz, the millimeter-wave band characteristics are optimized in a targeted manner, solving the problems of high loss and insufficient sensitivity in the existing millimeter-wave band, and expanding the application scenarios of radar such as short-range high-precision detection.

[0054] In addition to detecting low-speed, weak-reflection targets in complex electromagnetic environments, this invention can be extended to the following scenarios: for example, monitoring low-altitude, low-speed unmanned aerial vehicles (UAVs), enabling the identification of micro-UAVs and other civilian surveillance applications; identifying weak-reflection targets, such as stealth aircraft and small vessels, particularly suitable for military reconnaissance in close-range battlefield environments; and high-precision monitoring of close-range (≤10km) aircraft, assisting in distance / speed measurement during takeoff and landing for air traffic control.

[0055] It should be understood that although the intermediate frequency (IF) signal in the embodiments given in this application is 1 GHz, this frequency is not mandatory, and the frequency of the IF signal can be arbitrarily set. This solution can achieve down-conversion of any IF signal. Considering the carrying bandwidth capacity, the phase noise of the IF signal, and the application scenarios, suitable frequency bands can be selected during the experiment.

[0056] It should be understood that although the wavelength of the laser used in the experiment of this application is 1550.770nm, the wavelength of the optical carrier output by the narrow linewidth laser does not necessarily have to be this wavelength. In fact, the wavelength can be extended to the 1550nm~1551nm band, and the mainstream microwave photonic devices are designed mainly for the 1550nm~1551nm band.

[0057] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A high-sensitivity target detection method based on a microwave optical receiver: characterized by: Including the following steps: Provides an intermediate frequency electrical signal with preset values; as well as The intermediate frequency electrical signal is digitized and the target distance and velocity parameters are extracted using a locked logarithmic time-domain cumulative tracking algorithm to achieve the detection of the target; The formation of the intermediate frequency electrical signal includes: A radio frequency detection signal is provided, and a low phase noise optical local oscillator signal is provided, wherein the frequency difference between the optical local oscillator signal and the detection signal is the preset value; Transmit the detection signal and receive the echo signal from the target; amplify the echo signal; Providing an echo optical signal includes providing an optical carrier, splitting the optical carrier into individual modulator arrays, and upconverting the amplified echo signal to an optical domain using the split optical carrier in each modulator array. Collimate the echo optical signal and the optical local oscillator signal; Extract the upper sideband from the echo optical signal and extract the target sideband from the optical local oscillator signal; The upper sideband is focused onto the corresponding detector unit of the photodetector array (7), so that the target sideband beam expander covers the entire effective surface of the photodetector array (7) to achieve coherent heterodyne beat frequency, and the intermediate frequency electrical signal is output by the photodetector array (8).

2. A high-sensitivity target detection system based on a microwave optical receiver: characterized in that: include The radio frequency source (5) includes a first channel and a second channel, wherein the first channel is configured to output a detection signal and the second channel is configured to output a local oscillator optical signal to drive the local oscillator optical module (3) to generate a low phase noise optical local oscillator signal through optical injection locking; the frequency difference between the optical local oscillator signal and the detection signal is a preset value; Antenna array (10) is configured to cover the millimeter wave band to enable the transmission of the detection signal and the reception of the echo signal of the detection signal from the target; A low-noise amplifier array (11) is configured to amplify the echo signal; A narrow linewidth laser (1) is configured to output an optical carrier; Beam splitter (2) splits the optical carrier into each modulator array; The modulator array (12) is configured to upconvert the amplified echo signal to the optical domain using the beam-splitting optical carrier to form an echo optical signal; Optical antenna array (4) collimates the echo optical signal and the optical local oscillator signal; The optical filter (6) is configured to extract the upper sideband from the echo optical signal and the target sideband from the optical local oscillator signal; The optical lens (7) and the photodetector array (8) are configured to focus the upper sideband onto the corresponding detector unit of the photodetector array (7), expand the target sideband to cover the entire effective surface of the photodetector array (7), so as to achieve coherent heterodyne beat frequency, and output the intermediate frequency electrical signal corresponding to the preset value by the photodetector array (8). The signal acquisition and processing module (9) is configured to digitize the intermediate frequency electrical signal and then extract the target distance and velocity parameters through a locked logarithmic time-domain cumulative tracking algorithm to realize the detection of the target.

3. The high-sensitivity target detection system based on a microwave optical receiver according to claim 2, characterized in that: The preset value is 1GHz.

4. The high-sensitivity target detection system based on a microwave optical receiver according to claim 2, characterized in that: The narrow-line laser outputs an optical carrier in the 1550nm~1551nm band, especially an optical carrier with a wavelength of 1550.770nm; the frequency of the detection signal output by the first channel of the radio frequency source is 35GHz; the frequency of the local oscillator optical signal output by the second channel is 34GHz; and the intermediate frequency signal is 1GHz.

5. The high-sensitivity target detection system based on a microwave optical receiver according to claim 2, characterized in that: The signal acquisition and processing module (9) includes a high-speed analog-to-digital converter, which is configured to digitize the intermediate frequency electrical signal, and the sampling rate of the high-speed analog-to-digital converter is 4.8 GSa / s.

6. The high-sensitivity target detection system based on a microwave optical receiver according to claim 2, characterized in that: The locked logarithmic time-domain cumulative tracking algorithm includes intra-frame CFAR detection, inter-frame M / N incoherent accumulation, and α-β trajectory tracking.

7. The high-sensitivity target detection system based on a microwave optical receiver according to claim 6, characterized in that: The intra-frame CFAR detection includes Log-t / CFAR detection, with an adjustable threshold of 12-18dB; the inter-frame M / N incoherent accumulation includes M / N incoherent accumulation, where N=64 and M=32, and the parameters are adjustable; the α-β trajectory tracking includes α-β filtering, where α=0.15-0.25 and β=0.04-0.06, and extracts the focal plane angle of arrival information.

8. The high-sensitivity target detection system based on a microwave optical receiver according to claim 7, characterized in that: The Log-t / CFAR threshold is set to 15 dB; the α-β filter parameters are α=0.2 and β=0.

05.

9. The high-sensitivity target detection system based on a microwave optical receiver according to claim 2, characterized in that: The optical filter (6) is either a fixed bandpass filter or a filter with a tuning range f. c +34GHz to f c A tunable bandpass filter for +35GHz.

10. The high-sensitivity target detection system based on a microwave optical receiver according to claim 2, characterized in that: The antenna array (10) is configured such that the spacing between antenna elements is less than or equal to 1 / 2 of the center wavelength of the 35GHz signal, for example, the spacing is ≤4.28mm, and the amplitude deviation of each channel of the RF link is ≤0.5dB and the phase deviation is ≤5°; the modulator array (12) is consistent with the optical carrier polarization state of the modulator built into the local oscillator module (3).

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