Low-altitude unmanned aerial vehicle electromagnetic countermeasure signal processing method and system based on wide-angle search and threat locking linkage

Abstract

The application relates to a low-altitude unmanned aerial vehicle electromagnetic countermeasure signal processing method and system based on wide-angle search and threat locking linkage, and relates to the technical field of communication, which comprises the following steps: scanning a preset airspace with a wide beam, detecting and extracting the distance gate and azimuth angle of a suspicious target, and generating a suspicious target list; screening a priority target, taking the azimuth angle of the target as a beam pointing parameter, and calculating a receiving time sequence delay; transmitting an inquiry signal with the wide beam and receiving a return wave, and judging whether the target is an enemy target; if the target is an enemy target, accurate positioning and track prediction are carried out; a narrow beam is maintained, the transmission pulse repetition frequency is modulated, and a directional electromagnetic wave is transmitted along a predicted track; a return wave is received during a transmission gap to evaluate the interference effect; if the interference effect does not reach a threshold value, the transmission parameters are adjusted and re-evaluated until the interference effect reaches a preset threshold value or the target return wave disappears and the system is reset; the problems that the search efficiency and tracking accuracy of an existing anti-unmanned aerial vehicle system cannot be considered simultaneously, the interference is open-loop, and the energy and target physical characteristics lack coupling are solved.

Description

Technical Field

[0001] This invention relates to the field of communication technology, and specifically to a method and system for electromagnetic countermeasures signal processing of low-altitude unmanned aerial vehicles based on the linkage of wide-angle search and threat locking. Background Technology

[0002] In recent years, with the rapid development of the civilian drone industry and the widespread adoption of low-altitude, slow-moving, and small drones, incidents of unauthorized and excessive drone flights have become increasingly frequent, posing a growing threat to public safety, military facilities, and important locations. Currently, anti-drone systems typically consist of two parts: a drone detection system and a drone countermeasure system. The detection system includes radar, photoelectric, and spectrum detection equipment, while the countermeasure system usually employs electronic jamming, lasers, and other methods, becoming an important technological means in the field of low-altitude security protection.

[0003] However, existing anti-drone signal processing technologies have significant technical deficiencies in both the detection and countermeasure phases. In the detection phase, existing radar detection systems generally use phased array antennas with fixed beamwidths for electronic scanning. Due to the physical constraint that the gain × beamwidth is approximately constant, the system struggles to balance "wide visibility" and "accurate measurement." Although some existing technologies have proposed strategies that combine wide beam search with narrow beam tracking, the switching between wide and narrow beams usually relies on two independent antenna systems or a fixed beamforming network. This lacks the ability to dynamically reconstruct the antenna aperture structure, and once the beam shape is determined, it cannot be adaptively adjusted on the same hardware platform according to the mission phase.

[0004] Meanwhile, among existing detection methods, radar struggles to detect low, slow, and small targets; radio detection relies on communication signals actively transmitted by UAVs and is ineffective against electromagnetically silent targets; and photoelectric detection is severely affected by weather and lighting conditions. Each single detection method has inherent limitations. In the countermeasure phase, existing electromagnetic countermeasure technologies mainly employ full-band suppression, protocol deception, or navigation signal jamming. The jamming and detection phases are disconnected, and the system lacks real-time perception of the jamming effect after jamming is transmitted. It cannot dynamically adjust jamming parameters based on the target's actual response, resulting in an "open-loop blind attack" situation. Furthermore, the jamming energy is dispersed across a wide frequency band, with a low effective energy percentage, easily causing collateral interference to nearby legitimate communication equipment.

[0005] Chinese patent CN109358322A discloses a forward-looking target detection radar. It uses wide-beam and narrow-beam transmitting antennas to scan different areas. The receiving antenna array receives two types of echo signals, which are then processed by an information processing module to locate the target. A secondary clustering algorithm fuses the wide-beam and narrow-beam target location information to determine the target information. While this method balances detection range and positioning accuracy to some extent, the wide and narrow beams are implemented by two separate transmitting antennas, resulting in high hardware redundancy and low system integration. It cannot dynamically reconstruct the beam pattern based on mission phases on a single hardware platform. Furthermore, the division of labor between the wide and narrow beams is spatially segmented (wide beams cover the near-field area at large angles, narrow beams cover the far-field area at small angles), failing to form a complete processing chain from search to confirmation to engagement.

[0006] To this end, we propose a method that can balance search efficiency and tracking accuracy during the detection phase, adaptively adjust the open-loop operation of detection and interference based on the target response, and couple interference energy with the target's physical characteristics. Summary of the Invention

[0007] The purpose of this invention is to provide a method and system for electromagnetic countermeasures signal processing of low-altitude unmanned aerial vehicles (UAVs) based on wide-angle search and threat locking linkage. This method addresses the technical problems in existing anti-UAV systems, such as the inability to simultaneously achieve search efficiency and tracking accuracy during the detection phase, the inability of the open-loop operation of detection and jamming during the countermeasures phase to adaptively adjust according to the target response, and the lack of coupling between jamming energy and target physical characteristics.

[0008] This invention is achieved through the following technical solution: A low-altitude UAV electromagnetic countermeasure signal processing method based on wide-angle search and threat locking linkage includes: S1. Scan the preset airspace with a wide beam, receive and detect echo signals, extract the range gate and azimuth of suspicious targets, and generate a list of suspicious targets; S2. Select priority targets from the list of suspected targets, use their azimuth angle as the beam pointing parameter, and calculate the reception timing delay based on their range gate; S3. Based on the beam pointing parameters, transmit the interrogation signal with a wide beam and receive the echo with a narrow beam, set the receiving window according to the receiving timing delay, obtain the target echo characteristics, and determine whether it is a hostile target; S4. If the target is identified as a hostile target, switch to narrow beam to accurately locate and predict its trajectory. S5. Maintain a high-gain narrow beam, modulate the repetition frequency of the transmitted pulse according to the echo characteristics, and transmit directional electromagnetic waves along the predicted trajectory; S6. During the transmission interval, switch to wide beam echo reception, evaluate the interference effect based on the echo characteristics before transmission, and if the threshold is not reached, adjust the transmission parameters and re-evaluate until the interference effect reaches the preset threshold or the target echo disappears, and then reset to S1.

[0009] Furthermore, both the wide-beam transmission and narrow-beam reception adopt an asynchronous heterogeneous mode, specifically: The transmit beam and receive beam are formed simultaneously by different subarrays of the same array. The ratio of transmit beamwidth to receive beamwidth is ≥10:1. The transmit signal duration is ≤0.5ms. A guard interval is set after the transmission ends. The duration of the protection interval is dynamically calculated based on the target distance gate.

[0010] Furthermore, the specific steps for acquiring target echo characteristics and determining whether it is a hostile target are as follows: Extracting the micro-Doppler frequency sequence from the echo signal; Calculate the modulation period stability coefficient of the sequence; If the coefficient is less than the preset threshold, it is determined that there is a stable rotor modulation feature; Cepstral analysis was performed on the frequency sequence to extract the number of rotor blades and the rotation frequency; The extracted rotor blade count, rotation frequency, and stability coefficient are compared with the feature database, and the comparison results are used to determine whether it is a hostile target. If the coefficient is greater than or equal to the preset threshold, the target is determined to lack stable rotor modulation characteristics and is marked as a non-hostile target.

[0011] Furthermore, the trajectory prediction employs adaptive filtering, specifically as follows: The noise covariance of the adaptive filter is dynamically adjusted according to the modulation period stability coefficient of the echo signal; When the stability coefficient increases, the filter's confidence weight for the current measurement value is increased. When the stability coefficient decreases, the filter's trust weight for historical predictions is increased.

[0012] Furthermore, the specific steps for modulating the repetition rate of the transmitted pulse based on the echo characteristics are as follows: Extract the micro-Doppler fundamental frequency and its dominant harmonics from the target echo, and calculate the electromagnetic-mechanical coupling efficiency factor for each frequency. The frequency with the largest efficiency factor is selected as the injection frequency, the repetition frequency of the transmitted pulse is set to be equal to the value of the injection frequency, and an amplitude modulation envelope with the same frequency as the injection frequency is superimposed on the transmitted pulse train. During the transmission process, the echo amplitude at the injection frequency is continuously monitored. If the attenuation is insufficient, each harmonic frequency is tried in turn.

[0013] Furthermore, the step of switching to wide-beam echo reception during the transmission gap and evaluating the interference effect based on the echo characteristics before transmission is as follows: Before launch, establish a baseline spectrum template for the target echo and record the baseline energy distribution entropy of the template; After transmission, the current echo spectrum is acquired, its correlation coefficient with the baseline spectrum template is calculated, the main peak frequency of the current echo spectrum is extracted and its offset relative to the baseline main peak frequency is calculated, and the change in energy distribution entropy of the current echo spectrum is calculated based on the baseline energy distribution entropy. The interference effect index is calculated by combining the correlation coefficient, the change in energy distribution entropy, and the shift of the main peak of the spectrum. If the indicator is lower than the preset threshold, the interference is determined to be invalid, and the optimal injection frequency is searched by step-by-step frequency sweep with the current injection frequency as the center. If the indicator is greater than or equal to the preset threshold, the interference is deemed valid.

[0014] Furthermore, when the target echo disappears, the narrow beam is kept pointing towards the last position of the target, and a detection pulse is emitted with a low duty cycle and the echo is listened to for a preset duration. If no echo is detected within this time period, the process resets to S1; if an echo is detected again, the process jumps to S4.

[0015] A low-altitude UAV electromagnetic countermeasure signal processing system based on wide-angle search and threat locking linkage includes a signal processing chip, TR components and a reconfigurable antenna array; The signal processing chip is used to execute a low-altitude UAV electromagnetic countermeasure signal processing method based on wide-angle search and threat locking linkage, and to send directional electromagnetic waves, interrogation signals and switching control signals to the TR component, as well as to receive the target echo signal output by the TR component. The TR component is used to send directional electromagnetic waves, interrogation signals and switching control signals to the reconfigurable antenna array, and to receive the target echo signal output by the reconfigurable antenna array. The reconfigurable antenna array consists of multiple radiating elements, each of which integrates a radio frequency switch. By receiving a switching control signal, the multiple radio frequency switches are controlled to start or stop, enabling the antenna array to switch between wide beam mode and narrow beam mode. It also emits directional electromagnetic waves or interrogation signals through multiple radiating units and receives target echo signals.

[0016] Furthermore, the reconfigurable antenna array operates in frequency bands covering 15 GHz and 17 GHz; The radio frequency switch is a single-pole double-throw switch with a switching time ≤1μs; The single transmit channel of the TR component has an output power of 0.5W, and the noise figure of the receive channel is ≤3dB.

[0017] Furthermore, the TR component and the reconfigurable antenna array are located on the front and back sides of the same multilayer board, respectively, and are connected by a vertical transition hole between the boards.

[0018] The technical solution of the present invention has at least the following advantages and beneficial effects: This invention discloses a method and system for electromagnetic countermeasures signal processing of low-altitude UAVs based on wide-angle search and threat locking linkage. By switching the same reconfigurable antenna array to different beamforms at different mission stages, the antenna gain and beamwidth are no longer limited by the physical constraint that "gain × beam coverage" is approximately constant. This enables dynamic adjustment of the search field of view and directional gain across orders of magnitude. It meets the dual requirements of wide coverage and high-precision processing on a single hardware platform. Moreover, the switching of beamforms is precisely matched with the mission objectives at each stage, significantly improving the mission processing efficiency under limited hardware resources.

[0019] Through the closed-loop logic from S1 to S6, detection and countermeasures are constructed into an integrated process with real-time closed loop. This prevents the jamming energy from being emitted blindly, but rather dynamically adjusted based on real-time feedback of the target echo characteristics, significantly improving the utilization efficiency of jamming energy. At the same time, S6 completes evaluation and adjustment during the transmission interval, ensuring that the countermeasures process always maintains the ability to respond instantly to changes in the target's state.

[0020] Furthermore, by enabling the antenna beam to undergo a progressive convergence process of "coarse scan → pointing transmission → discrimination → fine determination" from wide-angle search to narrow-beam locking, and by using the predicted trajectory as the tracking basis for directional electromagnetic wave transmission, real-time matching of beam pointing with target motion state is achieved, avoiding beam miss due to target maneuvering, and effectively improving the continuity and reliability of countermeasures in dynamic scenarios. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the electromagnetic countermeasure signal processing method for low-altitude UAVs based on wide-angle search and threat locking linkage of the present invention. Figure 2 This is a schematic diagram of the electromagnetic countermeasure signal processing system for low-altitude unmanned aerial vehicles based on the linkage of wide-angle search and threat locking according to the present invention. Figure 3 This is a schematic diagram of the multilayer board lamination process of the present invention.

[0022] In the diagram, 1 is the signal processing chip; 2 is the TR component; 3 is the reconfigurable antenna array; 4 is the multilayer board; and 5 is the vertical transition hole. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0024] Example 1 This embodiment provides a method for processing electromagnetic countermeasure signals for low-altitude unmanned aerial vehicles (UAVs) based on the linkage of wide-angle search and threat locking. See also... Figure 1 This is a flowchart illustrating the signal processing method in this embodiment. For ease of explanation, only the parts relevant to this embodiment are shown.

[0025] The signal processing method includes: S1. Scan the preset airspace with a wide beam, receive and detect echo signals, extract the range gate and azimuth of suspicious targets, and generate a list of suspicious targets; In S1, the system actively detects a preset airspace sector using a wide beam. The beamwidth is typically set to 30°–60° to cover as large an airspace area as possible in a single scan. After the system transmits a millimeter-wave modulated signal (preferably a linear frequency modulated continuous wave signal in this embodiment), the echo signal reflected by the target is acquired by the receiving antenna array. Since the antenna gain of the wide beam is relatively low but the coverage area is wide, the core task of this stage is to quickly complete the initial search of a large airspace while sacrificing some angle measurement accuracy, so as to detect any potential intrusion targets as early as possible.

[0026] The received echo signal is first amplified with low noise and down-converted to a baseband signal. The baseband signal is then converted to a digital signal via analog-to-digital conversion and enters the signal processing chip. The chip performs a range-fast Fourier transform (Range-FFT) on the echo signal for each frame period, transforming the time-domain signal to the frequency domain. In linear frequency modulated continuous wave radar, the beat frequency between the transmitted signal and the echo signal... Distance from target The relationship between them is: , in, For frequency modulation slope, It is the speed of light. From this, the distance to the target can be deduced. : , The above relationship shows that the beat frequency is proportional to the target distance. Therefore, the frequency domain index (i.e., the range gate) after the range-dimensional FFT is proportional to the target distance. There is a one-to-one mapping relationship between them—each distance gate index corresponds to a specific distance value.

[0027] Based on this, the system employs a constant false alarm rate (CFAR) detection algorithm in the range-Doppler domain to extract target points. CFAR detection estimates background noise and clutter power levels by statistically averaging reference cells around each target cell in the range-Doppler plane, and adaptively adjusts the detection threshold accordingly, ensuring the system operates at a constant false alarm rate (in this embodiment, the false alarm rate is preset to a certain value). Under the premise of maximizing the target detection probability, each point extracted by CFAR detection contains three basic pieces of information: range gate, Doppler frequency (reflecting the radial velocity of the target), and signal-to-noise ratio.

[0028] However, not all points detected by CFAR are valid targets. A large number of these points may originate from stationary ground clutter (such as tunnel walls, buildings, trees, etc.), slow-moving objects (such as vehicles, people), fast-moving objects (such as birds), and noise false alarms. If all CFAR points are classified as "suspicious targets," the computational burden in subsequent processing stages will increase dramatically, and processing a large number of invalid targets will reduce the response time to truly threatening targets.

[0029] Therefore, the system applies pre-screening logic to CFAR traces, and only traces that meet the following conditions are included in the list of suspicious targets: Condition 1: Speed ​​rationality screening. Based on the Doppler frequency of the CFAR point trace. Calculate the target's radial velocity: , in, The wavelength of the transmitted signal is denoted as λ. The typical flight speed range for civilian drones is 0–30 m / s (hovering to high-speed cruising). If the radial velocity corresponding to the point of interest exceeds this range (e.g., greater than 50 m / s or less than 0.1 m / s of stationary clutter), it is determined to be a non-drone target and is eliminated. The upper limit of the speed threshold can be adjusted according to the actual application scenario. For example, it can be widened to 40 m / s around airports to cover high-speed drones, and narrowed to 20 m / s in core no-fly zones to improve screening sensitivity. In this embodiment, the preset lower speed limit is 0.2 m / s (eliminating stationary clutter), and the upper speed limit is 45 m / s (eliminating high-speed non-drone targets).

[0030] Condition 2: Signal-to-Noise Ratio (SNR) Threshold Screening. The SNR of the CFAR detection output reflects the reliability of the target echo signal. If the SNR is too low (below a preset threshold), the signal-to-noise ratio will be insufficient. The dots may be caused by random fluctuations in noise or clutter, and are considered high-probability false alarm sources. The system only retains those with a signal-to-noise ratio greater than or equal to... The dots. The value of is related to the preset constant false alarm rate (CFAR), and is usually set to be 3 dB higher than the CFAR detection threshold to ensure that traces entering the suspicious target list have a high degree of confidence. In this embodiment, The value is 15dB.

[0031] Condition 3: Continuous Confirmation and Screening. Isolated points appearing within a single frame period may be caused by transient clutter or intermittent interference. The system performs trajectory association confirmation on points appearing within similar range gates and azimuth angles over multiple consecutive frame periods—only points that meet the inter-frame association consistency are considered persistent targets and retained. In this embodiment, the system retains points appearing within a range of no more than 2 range gate fluctuations and no more than ±3° azimuth angle fluctuations over 3 consecutive frame periods. This screening effectively eliminates intermittent clutter caused by leaf swaying, vehicle instantaneous reflections, etc.

[0032] Condition 4: Pre-screening for micro-motion signs. For targets that meet the above three conditions, quickly detect whether there are periodically modulated micro-Doppler sidebands in their echo signals—because the rotation of the UAV rotor will produce periodic phase modulation on the echo, this modulation will appear as sideband components distributed on both sides of the main frequency in the amplitude or phase spectrum of the echo. If such periodic modulation signs are detected, the target is marked as a "high-confidence suspicious target" and given higher priority.

[0033] After the above four-stage screening, the remaining points are listed as suspicious targets. Due to the limited azimuth resolution of wide-beam spectral density, this stage can only extract the coarse azimuth angle of the suspicious targets using phase comparison angle measurement (with an accuracy typically ±3° to ±5°). The aforementioned range gate and coarse azimuth angle, as the basic position parameters of the target, are recorded together with the timestamp of the detection time, forming an entry in the suspicious target list. By performing the above screening and extraction processes on all detected points within the preset airspace sector, the system finally generates a suspicious target list containing the position information of all suspicious targets.

[0034] By employing a rapid search method combining wide-beam scanning, CFAR detection, and multi-condition pre-screening, the system can complete the initial screening of all moving targets within a preset sector (e.g., 120°) within a single frame period. Simultaneously, a large number of invalid targets are removed before entering subsequent processing, keeping the number of entries in the suspicious target list within the system's efficient processing capacity. Compared to traditional narrow-beam step scanning, the search speed is increased by 3 to 5 times, while effectively avoiding the waste of computational resources in the subsequent hostility determination stage.

[0035] S2. Select priority targets from the list of suspected targets, use their azimuth angle as the beam pointing parameter, and calculate the reception timing delay based on their range gate.

[0036] After generating a list of suspicious targets, the system needs to prioritize those from among the multiple suspicious targets. The selection criterion is a comprehensive priority score: the system calculates a priority score for each suspicious target in the list. : , in, The current target distance, For reference distance (200m in this embodiment), The signal-to-noise ratio of the current target. For reference signal-to-noise ratio (15dB in this embodiment), The label value for pre-screening micro-movement signs in S1 (1 for high-confidence targets, 0 for ordinary targets). , , The weighting coefficients are 0.4, 0.3, and 0.3 respectively in this embodiment, with a sum of 1. This scoring mechanism comprehensively reflects the target's distance urgency, signal reliability, and UAV confidence level. The target with the highest score is identified as the priority target.

[0037] After the screening is completed, the coarse azimuth of the priority target is extracted and used as the initial control parameter for beam pointing in the subsequent S3 and S4 stages.

[0038] Simultaneously, the system calculates the reception timing delay based on the range gate of the priority target. In radar detection, the time required for an electromagnetic wave to travel from emission to its reflection back to the receiving antenna is proportional to the target distance. The target distance corresponding to the range gate in S1... Receive timing delay The calculation method is as follows: , in, The target distance extracted in S1 (obtained by distance gate mapping) The speed of light. This delay value determines when the receiving window opens—the system needs to wait precisely after transmitting the interrogation signal. The receiving window is opened only after a certain time to ensure precise alignment with the arrival time of the target echo. If the receiving window opens too early, the received signal will mainly consist of transmitted leakage signals and near-field clutter; if it opens too late, the effective energy of the target echo will be lost. This step ensures that the echo signal received in the subsequent S3 stage has the highest signal-to-noise ratio, providing high-quality raw data for hostility identification.

[0039] S3. Based on the beam pointing parameters, transmit an interrogation signal with a wide beam and receive the echo with a narrow beam, set the receiving window according to the receiving timing delay, obtain the target echo characteristics, and determine whether it is a hostile target.

[0040] After determining the approximate azimuth and reception timing delay of the priority target, the system enters the hostility discrimination phase. The core of this phase is to transmit interrogation signals with a wide beam to cover the uncertainty range of the target, while receiving echoes with a narrow beam to ensure sufficient angular resolution for feature extraction.

[0041] The wide-beam transmission and narrow-beam reception employ an asynchronous heterogeneous mode, meaning the transmit and receive beams are simultaneously formed by different subarrays of the same array. Specifically, the reconfigurable antenna array is divided along its centerline into two sub-apertures of equal area—the first sub-aperture operates in a sparsely fed state to form a wide beam for transmission, and the second sub-aperture operates in a fully coherent fed state to form a narrow beam for reception. The ratio of transmit beamwidth to receive beamwidth is ≥10:1, and the transmit signal duration is ≤0.5ms. This asymmetric beam configuration of "wide transmit, narrow receive" allows for parallel operation of wide-coverage interrogation transmission and high-resolution echo reception within a single pulse repetition frequency, eliminating the need for time-division multiplexing of transmit and receive states and effectively reducing the time consumed in the hostile determination stage.

[0042] After launch, the system sets a protection interval, the duration of which is dynamically determined based on the target range gate calculated in S2. , in, The propagation delay of electromagnetic waves between the target and the radar. The guard interval is the transmit pulse width. Its purpose is to ensure that the transmitter has switched from transmit to receive mode before receiving the target echo, preventing transmitted leakage signals from entering the receive channel and causing saturation or false detections. Since the guard interval is dynamically calculated based on the target distance, shorter guard intervals correspond to closer targets, and longer guard intervals correspond to farther targets. This avoids unnecessary waiting (wasting time) at close range with a fixed guard interval, and also avoids transmit leakage contamination caused by insufficient guard intervals at long ranges.

[0043] The receiving window opens based on the receiving timing delay calculated by S2. Within the receiving window, the system receives echo signals from the direction of the priority target using a narrow beam. The high gain of the narrow beam (typically 15-20 dB higher than a wide beam) significantly improves the signal-to-noise ratio of the echo signal, allowing subsequent feature extraction to be performed on high-quality input data. From the received echo signal, the system extracts target echo features, mainly including a high-resolution one-dimensional range profile and a micro-Doppler spectrum. The high-resolution one-dimensional range profile reflects the distribution of scattering points of the target in the radar radial direction and can be used to initially determine the structural characteristics of the target; the micro-Doppler spectrum reflects the frequency modulation of the radar echo by moving parts on the target (such as rotors) and is a key basis for identifying UAV targets.

[0044] The specific steps for extracting the micro-Doppler frequency sequence from the echo signal and determining hostile targets are as follows: First, a Short-Time Fourier Transform (STFT) is performed on the received baseband signal to generate a time-spectrum graph. The STFT obtains the signal frequency's frequency history over time by sliding a finite-length time window along the time axis and performing a Fourier transform on the signal within each window position. The choice of time window length requires a trade-off between time resolution and frequency resolution—a shorter window provides higher time resolution but lower frequency resolution, and vice versa. In this embodiment, the time window length is adaptively set according to the target range gate and is equal to 1 / 10 of the time delay corresponding to that range gate. The micro-Doppler frequency sequence is obtained by extracting the periodically modulated frequency components along the time axis from the time-spectrum graph. .

[0045] Calculate the modulation period stability coefficient of the microDoppler frequency sequence: , in, The mean frequency is... This represents the standard deviation of the frequency. This coefficient reflects the regularity of the target's micro-Doppler frequency modulation. The rotation of a UAV rotor is highly periodic, and the resulting micro-Doppler frequency sequence exhibits stable periodic modulation characteristics; while non-rotor targets such as birds and balloons, or targets without stable rotating parts, show poor stability of the modulation period of their micro-Doppler frequency sequences. If so, the target is determined to have stable rotor modulation characteristics, and proceeds to subsequent detailed analysis; if If the target does not possess stable rotor modulation characteristics, it is directly marked as a non-hostile target, and the decision-making process is terminated. This pre-screening step effectively eliminates a large number of non-UAV targets, avoiding the waste of subsequent computing resources.

[0046] For targets that pass the stability screening, cepstral analysis is performed on the micro-Doppler frequency sequence to extract the number of rotor blades and the rotation frequency. The specific operation of cepstral analysis is as follows: after taking the logarithm of the power spectrum of the micro-Doppler frequency sequence, an inverse Fourier transform is performed to obtain the peak distribution in the cepstral domain. In the cepstral domain, the peak positions correspond to the rotor blade transit periods, and the number of rotor blades can be inferred from the peak positions. and rotation frequency This physical parameter extraction process enables the system to directly obtain the inherent characteristics of the UAV's power system from the echo signal. These characteristics are determined by the physical structure of the motor (number of pole pairs) and the geometric parameters of the rotor (number of blades), making them difficult to disguise using electronic deception.

[0047] Extract The triplet is compared with the aircraft feature vectors in the pre-set enemy aircraft feature database using Mahalanobis distance. Measured feature vectors. This refers to the triplet extracted above: , Each known drone model in the database corresponds to a mean vector. and a covariance matrix subscript Represents the first in the database Type of machine: , , Measured feature vectors With the The formula for calculating the Mahalanobis distance between similar models is: , Mahalanobis distance takes into account the correlation between various feature dimensions and is more suitable than Euclidean distance for measuring the similarity of multi-dimensional features. The system iterates through each model type in the database, calculates the Mahalanobis distance between the measured feature vector and each model type, and takes the minimum value. , like If the value is below a preset threshold, the target is identified as a hostile target and matched with the corresponding aircraft type; otherwise, it is marked as a non-hostile target. In this embodiment, the preset threshold is 5.0. This discrimination mechanism does not rely on easily spoofed information layer features such as the UAV's communication protocols or navigation signals, but rather on the inherent electromechanical and physical characteristics of its power system for identification, significantly improving the reliability and anti-deception capability of hostile identification.

[0048] S4. If the target is identified as a hostile target, switch to narrow beam to accurately locate and predict its trajectory.

[0049] Once S3 determines the target to be hostile, the system enters the precise positioning and trajectory prediction phase. The core task of this phase is to switch the beam from the "wide transmit, narrow receive" mode in S3 to a high-gain narrow beam mode with full array coherence to obtain the target's precise angle information and predict the target's future trajectory based on continuous frame observation data.

[0050] After switching to a narrow beam, all radiating elements of the antenna array participate in coherent combining, forming a high-gain narrow beam with a beamwidth of 1°–3°. The antenna gain of the narrow beam is increased by 15–20 dB compared to the wide beam mode, significantly improving the angular resolution. The system uses the coarse azimuth angle obtained in S2 as the center and performs a micro-scan within a ±2° range using a single-pulse sum-difference angle measurement method. Single-pulse angle measurement simultaneously forms the sum and difference beams, utilizing the amplitude and phase information of the difference beam to quickly calculate the angular error of the target deviating from the beam center, achieving an angle measurement accuracy on the order of 0.1°. During the micro-scan, the system records the echo amplitude under different beam directions and determines the precise azimuth angle corresponding to the maximum echo amplitude through interpolation fitting.

[0051] After obtaining the target's precise angle, the system initiates the trajectory prediction module. Trajectory prediction employs an adaptive filtering algorithm. The core function of this filter is to recursively estimate the target's optimal state from target state observations containing measurement noise. The filter's state vector is defined as: , in, It is the azimuth angle. The pitch angle, For distance, Radial velocity, subscript Indicates the first Each frame period. The filter's prediction step extrapolates the target state based on the motion model: , in This is the state transition matrix. The update step then corrects the prediction results based on the actual measurements of the current frame: , in, This is the measurement vector for the current frame. For the observation matrix, This is the Kalman gain.

[0052] Noise covariance matrix of a traditional Kalman filter (Process noise covariance) and (Measurement noise covariance) is typically set to a fixed value. However, in UAV countermeasure scenarios, the target's motion pattern may change at any time—the uncertainty of the target's state varies significantly depending on the mode, such as hovering, constant speed cruising, accelerated escape, or violent maneuvering. This embodiment employs an adaptive filtering strategy to make... and Based on the micro-Doppler spectrum modulation period stability coefficient extracted from S3 Dynamic adjustment: , , in and The initial preset value, and The preset adjustment coefficient is, and In this embodiment, Take 1.5, Set to 0.8, the initial preset value. and Set according to the system calibration results. When the target rotor modulation stabilizes, indicating that the target is in a stable flight state, the process noise covariance increases. Increase the measurement noise covariance As the value decreases, the filter trusts the current measurement more and can respond quickly to changes in the target's motion state; when When the speed decreases (the target rotor modulation is unstable, and it may be in a maneuvering or disturbed state). Decrease By increasing the filter's size, it places greater trust in historical predictions, smoothing the output track to avoid track divergence caused by measurement anomalies. This adaptive mechanism enables the filter to directly respond to the target's physical motion state, improving the robustness and continuity of track prediction in dynamic scenarios.

[0053] Track prediction update cycle With the repetition frequency of the transmitted pulse It is irrelevant; it is set as follows: , in, Let be the time window length of the short-time Fourier transform in S3. In this embodiment, a preset reference stability coefficient is used. Take 0.08, where ceil is the floor function. When the target rotor modulation is stable ( When the target rotor modulation is relatively large, the micro-Doppler information is abundant, and the filter can use a shorter update cycle to maintain high-frequency tracking of the target motion; when the target rotor modulation is unstable ( When the data is relatively small, the reliability of micro-Doppler information decreases, and the filter automatically extends its update cycle to avoid making erroneous state estimates based on unreliable data. Through the above adaptive filtering, the system can output the predicted trajectory of the target within a time window of 0.5 to 1 second, providing beam tracking basis for the S5's targeted strikes.

[0054] S5. Maintain a high-gain narrow beam, modulate the repetition frequency of the transmitted pulse according to the echo characteristics, and transmit directional electromagnetic waves along the predicted trajectory.

[0055] After achieving precise target location and trajectory prediction, the system enters the directional electromagnetic countermeasure phase. The core of this phase lies in the fact that the repetition rate of the transmitted pulse is no longer a fixed parameter or a simple frequency sweep sequence, but is precisely modulated based on the target's micro-Doppler characteristics extracted in S3, so that the interference energy is coupled with the target's electromechanical and physical characteristics.

[0056] Extracting the micro-Doppler fundamental frequency from the target echo and its dominant harmonics , Fundamental frequency Corresponding to the rotational frequency of the drone's rotor, the dominant harmonics correspond to the passing frequency of the rotor blades and its harmonics. These frequencies are inherent physical parameters of the drone's power system, determined by the motor's speed and the number of rotor blades.

[0057] Calculate the fundamental frequency separately and its harmonics The corresponding electromagnetic-mechanical coupling efficiency factor is: , in, For the transmission system at frequency The equivalent radiative power spectral density at that location. The efficiency factor represents the amplitude of the target's mechanical vibration response at that frequency (characterized by the amplitude of the frequency component corresponding to the micro-Doppler spectrum in S3). This efficiency factor reflects the efficiency with which electromagnetic energy is converted into target mechanical vibration at a specific frequency—the energy conversion efficiency is highest when the frequency of the emitted electromagnetic wave matches the natural frequency of the target mechanical structure.

[0058] Select The highest frequency As the injection frequency, the transmit pulse repetition rate is set to be equal to this injection frequency value, and an amplitude modulation envelope with the same frequency as the injection frequency is superimposed on the transmit pulse train, so that the amplitude of the transmit pulse... Over time It changes according to the following pattern: , in, For amplitude modulation depth In this embodiment, m is taken as 0.8. This serves as the reference amplitude for the transmitted pulse. This amplitude modulation method ensures that the power spectrum of the transmitted electromagnetic wave is within the dominant frequency range. An energy concentration peak is formed at the target, precisely delivering electromagnetic energy to the frequency point where the electromechanical coupling efficiency is highest. The physical effect is that the emitted pulse train acts like a precisely tuned "electromagnetic hammer," striking the UAV in a rhythm synchronized with the target's rotor rotation. This efficiently converts electromagnetic energy into mechanical vibration energy, thereby interfering with the accuracy of its inertial measurement unit and causing instability in the flight control system.

[0059] During transmission, the system continuously monitors the echo amplitude at the injection frequency. If the amplitude attenuates beyond a preset threshold within N consecutive pulse repetition frequencies... (In this embodiment) If the attenuation is 3dB and N is 10, then resonant coupling is considered established, and the current PRF continues to be emitted; if the attenuation is insufficient, it indicates that there is a deviation between the current injection frequency and the target's actual electromechanical resonant frequency (possibly due to changes in rotor speed caused by target maneuvering), then try sequentially. , , The interference is tracked at various harmonic frequencies until an effective injection frequency is found. This adaptive frequency tracking mechanism ensures that the interference energy remains at the optimal coupling frequency even when the target electromechanical characteristics drift, thus maintaining the continuous effectiveness of the interference.

[0060] S6. During the transmission interval, switch to wide beam echo reception, evaluate the interference effect based on the echo characteristics before transmission, and if the threshold is not reached, adjust the transmission parameters and re-evaluate until the interference effect reaches the preset threshold or the target echo disappears, and then reset to S1.

[0061] After the directional electromagnetic wave is transmitted, the system needs to sense in real time whether the interference is effective and to what extent. Therefore, in this embodiment, the antenna is switched from a narrow beam mode to a wide beam mode during the interval between transmitted pulses (approximately 1 ms) to receive the target echo with a wide beam. A wide beam is used instead of a narrow beam for effect evaluation because high angular resolution is not required during the evaluation phase—only macroscopic changes in the target's micro-motion characteristics (how much amplitude attenuation, how much frequency shift) are needed, without precise positioning. The wide beam has a large coverage area, so even if the target undergoes slight maneuvers due to interference, it remains within the wide beam's coverage area and will not be lost. A reception evaluation is performed after every 5 pulses transmitted.

[0062] The specific evaluation methods are as follows: Before launch (i.e., the last before S5 begins) Within a pulse repetition frequency, in this embodiment (Take 20), and perform cumulative averaging on the received micro-Doppler spectra to generate a baseline spectrum template. Simultaneously, the energy distribution entropy of the baseline spectrum is recorded: , in For the first The proportion of each frequency component in the total energy. Energy distribution entropy reflects the degree of concentration of spectral energy—the smaller the entropy value, the more concentrated the energy (corresponding to stable rotor rotation), and the larger the entropy value, the more dispersed the energy (corresponding to disordered rotor rotation).

[0063] During the evaluation window following each launch, the current micro-Doppler spectrum is acquired. Calculate its relationship with the baseline template Spectral correlation coefficient: , Correlation coefficient The value range is [-1, 1]. The closer it is to 1, the more similar the current spectrum is to the spectrum before transmission (interference is ineffective). The closer it is to 0 or a negative value, the more significant the change in the spectrum structure is (interference is effective).

[0064] At the same time, extract the main peak frequency of the current spectrum. Calculate its main peak frequency relative to the baseline. offset And based on the baseline energy distribution entropy Calculate the change in energy distribution entropy of the current spectrum. ,in This represents the energy distribution entropy of the current spectrum.

[0065] The interference effect index is calculated by combining the above three indicators: , in, , , To predetermine the weighting coefficients, in this embodiment, we use 0.4, 0.35, and 0.25 respectively, with a sum of 1. This comprehensive index quantifies the interference effect from three complementary physical dimensions: Reflecting the degree of change in the shape of the spectrum, It reflects the degree of dispersion of spectral energy (whether the rotor rotation is disordered). It reflects the degree of deviation in rotor speed. The three dimensions correspond to the impact of disturbances on the target's "shape," "state," and "velocity," respectively, and complement each other.

[0066] like (If the preset effect threshold is 0.6 in this embodiment), then the interference is deemed effective, and the current transmission parameters are maintained to continue countermeasures; if If the interference is deemed ineffective or insufficient, the system will switch to adaptive parameter adjustment. The adjustment method is as follows: based on the current injection frequency... Centered on, according to Perform bidirectional frequency sweep with a step size—first perform forward frequency sweep. Step (in this embodiment) Take 6), then perform a reverse frequency sweep. Step, pause at each step The pulse repetition frequency (M3 in this embodiment) is calculated. Value, record The frequency corresponding to the maximum value Switch the launch parameters to The evaluation is then re-executed. This "two-way frequency sweeping hill climbing method" can quickly converge to the optimal injection frequency even when the exact resonant frequency of the target is unknown, significantly shortening the search time during periods of ineffective interference.

[0067] When the interference effect reaches a preset threshold, the system continues to emit directional electromagnetic waves to maintain continuous suppression of the target. When the target echo disappears, the system does not immediately reset to S1, but enters the confirmation state maintenance phase: maintaining a narrow beam pointing towards the last known position of the target, emitting probe pulses with a low duty cycle (≤5%) and listening for echoes, for a duration of [duration missing]. ,in This is the extrapolated duration of the trajectory prediction in S4. This confirmation mechanism is designed because the disappearance of the target echo can be caused by various reasons—the target may have been successfully countered and fallen, the target may have temporarily maneuvered outside the beam coverage area, or the signal may have been briefly blocked. If in If no valid echo is detected, the target is determined to be disabled or has left the monitoring area, and the system resets to S1; if in If the echo is detected again, the system jumps to S4 to re-accurately locate and predict the trajectory, and continues to execute countermeasures. This mechanism avoids prematurely declaring a successful countermeasure due to the temporary disappearance of the target, and also avoids wasting system resources and missing opportunities to deal with other targets due to excessively long and ineffective waiting.

[0068] Through a complete closed loop from S1 to S6, the system realizes a complete response chain from "search → pointing transmission → hostility identification → precise location → targeted strike → effect evaluation → parameter adjustment". The mission objective of each stage determines the optimal beamform for that stage—a wide beam is used in the search and evaluation stages to cover a larger uncertainty range, while a narrow beam is used in the hostility identification, precise location, and targeted strike stages to obtain higher gain and resolution. The switching between wide and narrow beams is achieved by the same reconfigurable antenna array through an RF switching network, with the switching time completed in microseconds. This allows the system to complete on-demand beamform switching within a single pulse repetition frequency, realizing dynamic adjustment across orders of magnitude between the search field of view and the directional gain.

[0069] Example 2 This embodiment provides a low-altitude UAV electromagnetic countermeasure signal processing system based on wide-angle search and threat locking linkage. This system is used to execute the method described in Embodiment 1; see also Figures 2-3 This is a schematic diagram of the signal processing system in this embodiment, and for ease of explanation, Figure 2 Only the parts relevant to this embodiment are shown.

[0070] The signal processing system includes a signal processing chip 1, a TR component 2, and a reconfigurable antenna array 3.

[0071] The signal processing chip 1 is used to execute the signal processing steps of the method described in S1 to S6 of Embodiment 1, and to send directional electromagnetic waves, interrogation signals and switching control signals to the TR component 2, as well as to receive the target echo signal output by the TR component 2. The signal processing chip 1 adopts a heterogeneous architecture of FPGA and DSP. The FPGA is responsible for parallel computing-intensive tasks such as front-end data acquisition, range-dimensional fast Fourier transform, Doppler-dimensional fast Fourier transform and CFAR detection. The DSP is responsible for serial algorithm-intensive tasks such as target screening and priority ranking, micro-Doppler feature extraction and hostility discrimination, adaptive Kalman filter trajectory prediction, electromagnetic-mechanical coupling efficiency factor calculation, comprehensive evaluation of interference effect index and adaptive adjustment of closed-loop parameters. The FPGA and DSP are connected through a high-speed data bus. After the FPGA completes the front-end processing, it transmits the detected target point data to the DSP through the high-speed bus. After the DSP completes the calculation of each stage, it sends the beam pointing control parameters, transmitted waveform parameters and switching control commands back to the FPGA, which outputs them to the TR component 2 through the control interface. Signal processing chip 1 also has a built-in storage unit for a pre-set enemy aircraft feature database, which contains the mean feature vectors of various known UAV models. Covariance Matrix This is used for Mahalanobis distance comparison in the S3 phase.

[0072] TR component 2 is connected to reconfigurable antenna array 3; TR component 2 contains multiple TR channels with the same number of radiating elements as reconfigurable antenna array 3. Each TR channel contains a transmit branch and a receive branch. The transmit and receive branches are isolated by a circulator or transceiver switch. The transmit branch contains an adjustable gain amplifier and a phase shifter for power amplification and phase adjustment of the RF signal output by signal processing chip 1. The receive branch contains a low-noise amplifier and a phase shifter for low-noise amplification and phase adjustment of the weak echo signal received by reconfigurable antenna array 3 and output to signal processing chip 1. Each transmit channel has an output power of 0.5W.

[0073] TR component 2 supports time division duplex (TDD) mode and can switch between transmit and receive states in microseconds under the control of signal processing chip 1 to meet the precise timing requirements of S3 and S6 in embodiment 1. TR component 2 is also used to amplify and phase-configure the directional electromagnetic wave, interrogation signal and switching control signal sent by the signal processing chip and send them to the reconfigurable antenna array 3, and to receive the target echo signal output by the reconfigurable antenna array 3, amplify it with low noise and output it to the signal processing chip 1. In addition, a coupling calibration network is set between the TR component 2 and the reconfigurable antenna array 3, which can realize real-time online calibration of the system, compensate for the inconsistency of channel amplitude and phase caused by temperature changes and device aging, and ensure the accuracy of beamforming in both wide-beam and narrow-beam modes.

[0074] The reconfigurable antenna array 3 consists of multiple radiating elements, each integrating an RF switch. The reconfigurable antenna array 3 operates in the 15GHz and 17GHz frequency bands. The RF switches are single-pole double-throw switches with a switching time ≤1μs. By receiving switching control signals from the signal processing chip via the TR component, the multiple RF switches are controlled to start or stop, allowing the antenna array to switch between wide-beam and narrow-beam modes. Specifically: Wide-beam mode: When the system is in the S1 wide-angle search phase or the S6 interference effect evaluation phase, the signal processing chip sends switching control signals to the RF switches of each radiating element through the TR component, connecting the array elements to a sparse feed network (such as a Blass matrix feed network). In this network, the feed amplitude and phase of each radiating element are configured according to a pre-coded sparse distribution, making the array equivalent to a sparse array. This reduces the effective radiating aperture and results in a wide beamwidth of 30°–60°. Wide-beam antennas have relatively low gain but wide coverage, making them suitable for wide-coverage reception in uncertain target regions during rapid searches in large airspace and interference effect evaluations.

[0075] Narrow Beam Mode: During the narrow beam reception phase (S3 hostility discrimination), S4 precise positioning and trajectory prediction, and S5 directional strike phases, the signal processing chip sends switching control signals to the RF switches of each radiating element via the TR component, reconnecting all array elements to the fully coherent, equal-amplitude, in-phase feed network. In this network, all radiating elements participate in coherent synthesis, and the array is equivalent to a full-aperture dense array, achieving the physical limit of the effective radiating aperture. The synthesized beamwidth is a high-gain narrow beam with a width of 1°–3°. The antenna gain of the narrow beam is 15–20 dB higher than that of the wide beam mode, significantly improving angular resolution and making it suitable for high-precision angle measurement, precise positioning, and directional energy injection.

[0076] In the asynchronous heterogeneous transmit / receive mode of S3, the reconfigurable antenna array 3 is further configured to divide the array along the centerline into two sub-apertures of equal area—the first sub-aperture operates in a sparsely fed state to form a wide beam for transmitting interrogation signals, and the second sub-aperture operates in a fully coherent fed state to form a narrow beam for receiving echo signals. The RF switches of the two sub-apertures are independently controlled by the signal processing chip 1, enabling parallel operation of wide-coverage interrogation transmission and high-resolution echo reception within a single pulse repetition frequency, without the need for time-division switching.

[0077] The reconfigurable antenna array 3 transmits directional electromagnetic waves or interrogation signals through multiple radiating elements and receives target echo signals.

[0078] Furthermore, the TR component 2 and the reconfigurable antenna array 3 are located on the front and back sides of the same multilayer board 4, respectively, and are connected by a vertical transition hole 5 between the boards. Specifically, the multilayer board 4 is made of high-frequency dielectric material (such as Rogers RO3003 or RO4350B) laminated together, which has a stable dielectric constant and low loss tangent, and is suitable for high-frequency signal transmission in the 15GHz and 17GHz frequency bands. The radiating element and RF switch of the reconfigurable antenna array 3 are arranged on the front side (top layer) of the multilayer board, while the TR component 2 and its power supply circuit and control interface are arranged on the back side (bottom layer) of the multilayer board. The two are interconnected through a vertical transition hole 5 (i.e., a metallized via array) that penetrates the multilayer board to realize the interconnection of RF signals and DC control signals.

[0079] To achieve the above front and back layout, refer to Figure 3 The multilayer board 4 is completed using a two-stage lamination process. The first to third layers are laminated in the first lamination to form the front functional layer (containing the antenna radiating element and RF switch), while the third to the bottom layer are laminated in the second lamination to form the back functional layer (containing the TR component and its peripheral circuitry). The two layers are interconnected via a vertical transition via to achieve the interconnection of RF signals and low-frequency control signals. This two-stage lamination process ensures the consistency of the dielectric constant of the high-frequency dielectric layers on both sides, reducing phase errors introduced by dielectric inhomogeneity. Furthermore, the intermediate ground layer effectively isolates the RF signals from both sides, preventing interference coupling between the high-power signals emitted by the antenna and the receiving channel of the TR component 2.

[0080] This front-and-back layout compresses the RF transmission path between the antenna radiating element and the TR component to the thickness of the multilayer board (typically 2-4 mm), significantly shortening the transmission distance of the RF signal on the microstrip line and effectively reducing transmission loss and parasitic radiation. Simultaneously, placing the TR component 2 on the back of the antenna array avoids obstructing the antenna's radiating aperture, ensuring the radiation efficiency of the antenna array. Power and ground layers are also embedded within the multilayer board, providing stable DC power supply and low-impedance electrical reference ground for the TR component 2 and the RF switch, respectively.

[0081] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for electromagnetic countermeasure signal processing of low-altitude unmanned aerial vehicles based on the linkage of wide-angle search and threat locking, characterized in that, include: S1. Scan the preset airspace with a wide beam, receive and detect echo signals, extract the range gate and azimuth of suspicious targets, and generate a list of suspicious targets; S2. Select priority targets from the list of suspected targets, use their azimuth angle as the beam pointing parameter, and calculate the reception timing delay based on their range gate; S3. Based on the beam pointing parameters, transmit the interrogation signal with a wide beam and receive the echo with a narrow beam, set the receiving window according to the receiving timing delay, obtain the target echo characteristics, and determine whether it is a hostile target; S4. If the target is identified as a hostile target, switch to narrow beam to accurately locate and predict its trajectory. S5. Maintain a high-gain narrow beam, modulate the repetition frequency of the transmitted pulse according to the echo characteristics, and transmit directional electromagnetic waves along the predicted trajectory; S6. During the transmission interval, switch to wide beam echo reception, evaluate the interference effect based on the echo characteristics before transmission, and if the threshold is not reached, adjust the transmission parameters and re-evaluate until the interference effect reaches the preset threshold or the target echo disappears, and then reset to S1.

2. The electromagnetic countermeasure signal processing method for low-altitude UAVs based on wide-angle search and threat locking linkage as described in claim 1, characterized in that, Both the wide-beam transmission and narrow-beam reception adopt an asynchronous heterogeneous mode, specifically: The transmit beam and receive beam are formed simultaneously by different subarrays of the same array. The ratio of transmit beamwidth to receive beamwidth is ≥10:

1. The transmit signal duration is ≤0.5ms. A guard interval is set after the transmission ends. The duration of the protection interval is dynamically calculated based on the target distance gate.

3. The electromagnetic countermeasure signal processing method for low-altitude UAVs based on wide-angle search and threat locking linkage as described in claim 1, characterized in that, The specific steps for acquiring target echo characteristics and determining whether it is a hostile target are as follows: Extracting the micro-Doppler frequency sequence from the echo signal; Calculate the modulation period stability coefficient of the sequence; If the coefficient is less than the preset threshold, it is determined that there is a stable rotor modulation feature; Cepstral analysis was performed on the frequency sequence to extract the number of rotor blades and the rotation frequency; The extracted rotor blade count, rotation frequency, and stability coefficient are compared with the feature database, and the comparison results are used to determine whether it is a hostile target. If the coefficient is greater than or equal to the preset threshold, the target is determined to lack stable rotor modulation characteristics and is marked as a non-hostile target.

4. The electromagnetic countermeasure signal processing method for low-altitude UAVs based on wide-angle search and threat locking linkage as described in claim 1, characterized in that, The trajectory prediction employs adaptive filtering, specifically: The noise covariance of the adaptive filter is dynamically adjusted according to the modulation period stability coefficient of the echo signal; When the stability coefficient increases, the filter's confidence weight for the current measurement value is increased. When the stability coefficient decreases, the filter's trust weight for historical predictions is increased.

5. The electromagnetic countermeasure signal processing method for low-altitude UAVs based on wide-angle search and threat locking linkage as described in claim 1, characterized in that, The specific steps for modulating the repetition rate of the transmitted pulse based on the echo characteristics are as follows: Extract the micro-Doppler fundamental frequency and its dominant harmonics from the target echo, and calculate the electromagnetic-mechanical coupling efficiency factor for each frequency. The frequency with the largest efficiency factor is selected as the injection frequency, the repetition frequency of the transmitted pulse is set to be equal to the value of the injection frequency, and an amplitude modulation envelope with the same frequency as the injection frequency is superimposed on the transmitted pulse train. During the transmission process, the echo amplitude at the injection frequency is continuously monitored. If the attenuation is insufficient, each harmonic frequency is tried in turn.

6. The electromagnetic countermeasure signal processing method for low-altitude UAVs based on wide-angle search and threat locking linkage as described in claim 5, characterized in that, The specific steps for switching to wide-beam echo reception during the transmission gap and evaluating the interference effect based on the echo characteristics before transmission are as follows: Before launch, establish a baseline spectrum template for the target echo and record the baseline energy distribution entropy of the template; After transmission, the current echo spectrum is acquired, its correlation coefficient with the baseline spectrum template is calculated, the main peak frequency of the current echo spectrum is extracted and its offset relative to the baseline main peak frequency is calculated, and the change in energy distribution entropy of the current echo spectrum is calculated based on the baseline energy distribution entropy. The interference effect index is calculated by combining the correlation coefficient, the change in energy distribution entropy, and the shift of the main peak of the spectrum. If the indicator is lower than the preset threshold, the interference is determined to be invalid, and the optimal injection frequency is searched by step-by-step frequency sweep with the current injection frequency as the center. If the indicator is greater than or equal to the preset threshold, the interference is deemed valid.

7. The electromagnetic countermeasure signal processing method for low-altitude UAVs based on wide-angle search and threat locking linkage as described in claim 1, characterized in that, When the target echo disappears, keep the narrow beam pointing to the last position of the target, emit a detection pulse with a low duty cycle and listen for the echo for a preset duration. If no echo is detected within this time period, the process resets to S1; if an echo is detected again, the process jumps to S4.

8. A low-altitude UAV electromagnetic countermeasure signal processing system based on wide-angle search and threat locking linkage, characterized in that, It includes a signal processing chip (1), a TR component (2), and a reconfigurable antenna array (3); The signal processing chip (1) is used to execute the low-altitude UAV electromagnetic countermeasure signal processing method based on wide-angle search and threat locking linkage as described in any of claims 1 to 7, and to send directional electromagnetic waves, interrogation signals and switching control signals to the TR component (2), and to receive the target echo signal output by the TR component (2); The TR component (2) is used to send directional electromagnetic waves, interrogation signals and switching control signals to the reconfigurable antenna array (3), and to receive the target echo signal output by the reconfigurable antenna array (3); The reconfigurable antenna array (3) consists of multiple radiating elements, each of which integrates a radio frequency switch. By receiving the switching control signal, the multiple radio frequency switches are controlled to start or stop, so that the antenna array switches between wide beam mode and narrow beam mode. It also emits directional electromagnetic waves or interrogation signals through multiple radiating units and receives target echo signals.

9. The low-altitude UAV electromagnetic countermeasure signal processing system based on wide-angle search and threat locking linkage as described in claim 8, characterized in that, The reconfigurable antenna array (3) operates in frequency bands covering 15 GHz and 17 GHz; The radio frequency switch is a single-pole double-throw switch with a switching time ≤1μs; The single transmit channel of the TR component has an output power of 0.5W, and the noise figure of the receive channel is ≤3dB.

10. The low-altitude UAV electromagnetic countermeasure signal processing system based on wide-angle search and threat locking linkage as described in claim 8, characterized in that, The TR component (2) and the reconfigurable antenna array (3) are located on the front and back sides of the same multilayer board (4), respectively, and are connected by a vertical transition hole (5) between the boards.

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