Dual-channel three-dimensional radar low-altitude multipath detection and elevation dynamic measurement method

Abstract

The application discloses a kind of three-dimensional radar low altitude multipath detection and elevation dynamic measurement method of double channel, and the adaptive decision threshold of multipath decision model is constructed in combination with real-time signal-to-noise ratio, so that the judgment of target echo complex signal can be accurately identified the occurrence and end of multipath interference like " switch ", when target echo is interfered by multipath, start the elevation measurement method for multipath interference, significantly improve the environmental adaptability and robustness of radar;The imaginary part characteristics of complex single pulse ratio are used in combination with the adaptive threshold of signal-to-noise ratio, which is more accurate than the simple distance threshold in identifying the multipath state, with higher detection accuracy.The application uses the characteristics that phase information is distorted but still maintains segmented monotonicity under multipath environment, first locks the subdivided monotonic interval where the target is located, and then uses high-sensitivity amplitude information to perform table lookup inversion in the interval, without changing the 1T2R hardware architecture, the problem of angle measurement error caused by multipath interference is solved.

Description

Technical Field

[0001] This invention belongs to the field of radar signal processing technology, specifically relating to a dual-channel three-coordinate radar method for low-altitude multipath detection and dynamic elevation angle measurement. Background Technology

[0002] In recent years, with the booming development of the low-altitude economy, the demand for detection and surveillance of "low, slow, and small" targets such as drones and various low-altitude aircraft has become increasingly urgent. To build a comprehensive, distributed low-altitude safety network, radar systems face the dual challenges of "high-performance detection" and "low-cost deployment." How to achieve precise three-dimensional positioning of low-altitude targets with relatively low hardware costs is an important research direction in the current radar technology field.

[0003] In existing radar systems, while all-digital phased array radars offer high angle measurement accuracy and flexible beam control, their large number of channels, complex hardware architecture, and high cost make them difficult to meet the cost control requirements for large-scale civilian low-altitude surveillance. In contrast, three-coordinate radars with a single transmitter and dual receiver architecture have become the preferred low-cost radar solution due to their simplified architecture. Currently, elevation angle measurement methods for three-coordinate radars are mainly divided into all-digital phased array systems (Multiple-Input Multiple-Output) and single-pulse / interferometer systems (Single-Input Multiple-Output). Among them, the multiple-transmitter multiple-receiver system utilizes orthogonal waveforms and digital beamforming (DBF) technology to form multiple beams simultaneously at the receiver. Although it offers high angle measurement accuracy and strong anti-interference capabilities, the system requires a large number of radio frequency transceiver channels and high-performance processing units, resulting in a large size, high power consumption, and high cost, making it difficult to meet the requirements for low-cost large-scale deployment. The one-transmit-two-receive (single transmit, dual-channel receive) system has a simple hardware structure and low cost. The elevation angle estimation depends entirely on the amplitude difference or phase difference on a single vertical baseline.

[0004] To reduce hardware costs, existing low-cost three-coordinate radars typically employ a 1T2R architecture and utilize wide-spacing (long baseline) antennas to achieve high phase sensitivity. Due to phase ambiguity caused by long baselines, current technologies rely on coarse angle measurements provided by amplitude comparison to assist phase comparison in deambiguation. However, at low elevation angles, direct waves interfere with ground-reflected waves, generating multipath effects and causing severe distortion in the amplitude received by the antenna. Therefore, in areas with severe multipath interference, existing amplitude comparison methods cannot provide accurate coarse measurements, leading to incorrect periodic ambiguity number determination during phase deambiguation, ultimately resulting in significant jumps or even complete failure in angle measurement results. Furthermore, the intensity of actual multipath interference is greatly affected by factors such as ground roughness and terrain undulations (e.g., water surfaces, grasslands, concrete). Therefore, fixed thresholds cannot adapt to dynamically changing environments: in weak multipath environments (e.g., rough ground), fixed thresholds may force the system to use multipath smoothing algorithms, sacrificing response speed to moving targets; while in strong multipath environments, fixed thresholds may cause the system to fail to switch in time, outputting incorrect angles. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, this invention provides a dual-channel three-coordinate radar method for low-altitude multipath detection and dynamic elevation angle measurement. The technical problem to be solved by this invention is achieved through the following technical solution: This invention provides a dual-channel three-coordinate radar method for low-altitude multipath detection and dynamic elevation angle measurement, the method comprising: Confirm the complex-to-single pulse ratio of the target echo complex signal and extract the imaginary part of the complex-to-single pulse ratio; based on the pre-constructed multipath decision model, perform multipath detection and decision on the imaginary part of the complex-to-single pulse ratio to determine whether the target echo is affected by multipath interference; If the target echo is not affected by multipath interference, perform amplitude comparison angle measurement and phase comparison angle measurement on the target echo respectively. Use the result of amplitude comparison angle measurement to resolve the angle ambiguity caused by phase comparison angle measurement, and output the final target angle estimate as the elevation angle corresponding to the target echo. If the target echo is affected by multipath interference, the phase angle corresponding to the phase angle measurement is determined based on the phase difference of the complex signal of the target echo; the phase angle is matched in the pre-built index lookup table to determine the monotonic interval of the target echo; the elevation angle corresponding to the target echo is confirmed by looking up the measured normalized amplitude error corresponding to the complex signal of the target echo in the pre-built multipath correction error table. The multipath correction error table is constructed based on radar operating frequency, antenna installation height, and ground roughness parameters; the index lookup table is obtained from the multipath correction error table.

[0006] In one embodiment of the present invention, the expression for the complex-to-single-pulse ratio of the target echo complex signal is as follows: ; in, Indicates the ratio of complex to single pulse. Represents the imaginary unit. This represents the target echo complex signal acquired by the upper channel in a dual-channel configuration. This represents the target echo complex signal acquired by the lower channel in a dual-channel configuration.

[0007] In one embodiment of the present invention, based on a pre-constructed multipath decision model, multipath detection and decision are performed on the imaginary part of the complex single-pulse ratio to determine whether the target echo is affected by multipath interference, including: Determine the imaginary part of the complex single-pulse ratio and the size of the adaptive decision threshold of the pre-constructed multipath decision model; If the imaginary part of the complex single-pulse ratio is less than or equal to the adaptive decision threshold, it is determined that the current target echo is not affected by multipath interference. If the imaginary part of the complex single-pulse ratio is greater than the adaptive decision threshold, the current target echo is determined to be subject to multipath interference.

[0008] In one embodiment of the present invention, the expression for the adaptive decision threshold is as follows: ; in, The variance representing the imaginary part of the complex single-pulse ratio in the absence of multipath effects. This indicates the preset false alarm rate.

[0009] In one embodiment of the present invention, amplitude angle measurement and phase angle measurement are performed on the target echo, and the angular ambiguity caused by the phase angle measurement is resolved by the result of the amplitude angle measurement, so as to output the final target angle estimate as the elevation angle corresponding to the target echo, including: The first target angle estimate is obtained by comparing the amplitude and angle of the target echo; The ambiguity number is obtained based on the wavelength of the target echo and the estimated angle of the first target; The estimated angle of the second target is obtained by comparing the phase angle of the target echo; Based on the fuzzy number and the second target angle estimate, the final target angle estimate is confirmed as the elevation angle corresponding to the target echo.

[0010] In one embodiment of the present invention, the process of constructing the multipath correction error table and the index lookup table includes: Based on the radar operating frequency, antenna installation height, and ground roughness parameters, a theoretical normalized amplitude error signal curve incorporating multipath interference effects is constructed. The theoretically normalized amplitude error signal curve is divided into several monotonic intervals based on the peaks and troughs to form a multipath correction error table. Record the angle range corresponding to each monotonic interval and store it in a cell array to form an index lookup table.

[0011] In one embodiment of the present invention, the expression for the theoretically normalized amplitude error signal is as follows: ; in, Indicates the angle of elevation The corresponding theoretical normalized amplitude error signal, This represents the reflection coefficient calculated using roughness attenuation. , Indicates the wavelength of the target echo. This indicates the height of the upper channel relative to the ground in a dual-channel configuration. This indicates the height of the lower channel relative to the ground in a dual-channel configuration.

[0012] In one embodiment of the present invention, the expression for the reflection coefficient used in roughness attenuation calculation is as follows: ; in, This represents the reflectance of a smooth surface. The root mean square value representing the undulation of the ground. Indicates the angle of elevation. Indicates the wavelength of the target echo.

[0013] In one embodiment of the present invention, the expression for the measured normalized amplitude error is as follows: ; in, This indicates the measured normalized amplitude error. This represents the target echo complex signal acquired by the upper channel in a dual-channel configuration. This represents the target echo complex signal acquired by the lower channel in a dual-channel configuration.

[0014] The beneficial effects of this invention are: The solution provided by this invention utilizes the fact that the imaginary part of the complex single-pulse ratio is theoretically zero in free space, while the imaginary part oscillates violently under multipath interference. Combined with the real-time signal-to-noise ratio, an adaptive decision threshold for the multipath decision model is constructed. This allows the judgment of the complex signal of the target echo to accurately identify the occurrence and termination of multipath interference, much like a "switch." When the target echo is affected by multipath interference, an elevation angle measurement method targeting multipath interference is activated, significantly improving the radar's environmental adaptability and robustness. By combining the imaginary part characteristics of the complex single-pulse ratio with the adaptive signal-to-noise ratio threshold, the multipath state is identified more accurately than a simple range threshold, resulting in higher detection accuracy. This invention leverages the characteristic that phase information, although distorted under multipath conditions, still maintains piecewise monotonicity. It first locks the target's location within a subdivided monotonic interval by phase detection, and then uses highly sensitive amplitude information within the interval for table lookup and inversion. Without changing the 1T2R hardware architecture, this solves the angle measurement error problem caused by multipath interference. Attached Figure Description

[0015] Figure 1 A schematic diagram illustrating the steps of a dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method provided in an embodiment of the present invention; Figure 2 This is a flowchart illustrating a dual-channel, three-coordinate radar method for low-altitude multipath detection and dynamic elevation angle measurement, provided in an embodiment of the present invention. Figure 3 This is a schematic diagram of the receiver antenna placement in a dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method provided in an embodiment of the present invention. Figure 4 This is a geometrical diagram of the multipath effect in a dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method provided in an embodiment of the present invention. Figure 5 This is a schematic diagram of the overlapping radiation patterns of two antennas in a dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method provided in an embodiment of the present invention. Figure 6 This is a schematic diagram of the angle discrimination curve generated in a dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method provided in an embodiment of the present invention. Figure 7 The graph shows the relationship between the root mean square value of the angle measurement error and the target angle at different angles in a dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method provided in an embodiment of the present invention. Figure 8 This is a schematic diagram of the theoretical normalized amplitude error signal curve in a dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method provided in an embodiment of the present invention. Figure 9This is a schematic diagram of multipath detection decision in a dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method provided in an embodiment of the present invention; Figure 10 This is a schematic diagram comparing the full-range angle measurement results in a dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method provided in an embodiment of the present invention. Detailed Implementation

[0016] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0017] This invention provides a dual-channel three-coordinate radar method for low-altitude multipath detection and dynamic elevation angle measurement, such as... Figure 1 and Figure 2 As shown, it may include: S1, confirm the complex-to-single pulse ratio of the target echo complex signal and extract the imaginary part of the complex-to-single pulse ratio; based on the pre-constructed multipath decision model, perform multipath detection and decision on the imaginary part of the complex-to-single pulse ratio to determine whether the target echo is affected by multipath interference; S2, If the target echo is not affected by multipath interference, perform amplitude comparison angle measurement and phase comparison angle measurement on the target echo respectively. Use the result of amplitude comparison angle measurement to resolve the angle ambiguity caused by phase comparison angle measurement, and output the final target angle estimate as the elevation angle corresponding to the target echo. S3. If the target echo is affected by multipath interference, determine the phase angle corresponding to the phase angle measurement based on the phase difference of the complex signal of the target echo; use the phase angle to match in the pre-built index lookup table to determine the monotonic interval where the target echo is located; use the measured normalized amplitude error corresponding to the complex signal of the target echo to look up in the pre-built multipath correction error table to confirm the elevation angle corresponding to the target echo. The multipath correction error table is constructed based on radar operating frequency, antenna installation height, and ground roughness parameters; the index lookup table is obtained from the multipath correction error table.

[0018] For step S1, the radar acquires the target echo complex signal using two vertically arranged receiving channels (upper channel and lower channel); the complex-to-mono pulse ratio is calculated based on the target echo complex signal, and the expression for the complex-to-mono pulse ratio of the target echo complex signal is as follows: ; in, Indicates the ratio of complex to single pulse. Represents the imaginary unit. This represents the target echo complex signal acquired by the upper channel in a dual-channel configuration. This represents the target echo complex signal acquired by the lower channel in a dual-channel configuration.

[0019] Extract the imaginary part of the above complex single-pulse ratio. In real-world multipath scenarios, when the target's flight elevation angle is large, the multipath signal is suppressed by the antenna sidelobes. At this time, the mean of the single-pulse ratio is a real number, and the angle measurement error is mainly affected by noise. When the target's flight altitude is low and the elevation angle is small, the multipath signal gradually enters from the antenna main lobe. The interference intensity exceeds the noise and becomes the decisive factor affecting the angle measurement error. At this time, the mean of the single-pulse ratio is a complex number, and the interference between the mirror target and the real target brings imaginary part fluctuations. The variance of the single-pulse ratio reflects the degree of fluctuation.

[0020] Constructing a multipath decision model: When multipath signals and direct signals simultaneously enter from the antenna main lobe, the single-pulse ratio still follows a complex Gaussian distribution. The statistical characteristics of the single-pulse ratio under multipath conditions, with its mean and variance, are as follows: ; ; in, The slope of a single pulse, when used in dual-channel phase angle measurement, can be specifically written as: , Indicates the synthesis angle under multipath effects. The signal-to-noise ratio of the channel is represented.

[0021] The statistical characteristics of the imaginary part of the single-pulse ratio under multipath conditions are analyzed, and a generalized likelihood ratio model is established: ; in, Assuming the case without multipath effects, Assuming the existence of multipath effects, This indicates that it follows a one-dimensional real Gaussian distribution. Representing the true target perspective, This represents the synthesis angle under multipath effects. The multipath decision region is defined based on the constant false alarm rate (CFAR) using the Newman-Pearson criterion.

[0022] exist Assume that its probability density function is: ; in, ,express Assuming The variance.

[0023] The system determines the current received signal-to-noise ratio (SNR) based on the signal-to-noise ratio (SNR). ) and preset false alarm rate The detection threshold is dynamically calculated.

[0024] Preset false alarm rate as follows: ; The multipath decision region is then: ; in, It must be less than 0.

[0025] The signal-to-noise ratio (SNR) of the multi-channel configuration is expressed as follows, and its relationship with the single-channel SNR is: , This indicates two channels and a direction pattern.

[0026] Therefore, based on a pre-built multipath decision model, multipath detection and decision are performed on the imaginary part of the complex single-pulse ratio to determine whether the target echo is affected by multipath interference. This can include: Determine the imaginary part of the complex single-pulse ratio and the size of the adaptive decision threshold of the pre-constructed multipath decision model; If the imaginary part of the complex single-pulse ratio is less than or equal to the adaptive decision threshold, it is determined that the current target echo is not affected by multipath interference. If the imaginary part of the complex single-pulse ratio is greater than the adaptive decision threshold, the current target echo is determined to be subject to multipath interference.

[0027] The expression for the adaptive decision threshold is as follows: ; in, The variance representing the imaginary part of the complex single-pulse ratio in the absence of multipath effects. This indicates the preset false alarm rate.

[0028] Understandable, if If it is determined that the current echo is not significantly affected by multipath propagation, select the amplitude-assisted phase-angle measurement mode in free space corresponding to step S2 to obtain the elevation angle corresponding to the target echo; if If the current echo is determined to be subject to severe multipath interference, select the multipath-based amplitude and phase joint angle measurement mode corresponding to step S3 to obtain the elevation angle corresponding to the target echo.

[0029] The receiver antenna in the three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method provided in this embodiment of the invention is as follows: Figure 3 As shown, the two receiving antennas are spaced a certain distance apart. This causes a phase difference in the target echo, allowing for phase comparison and angle measurement; simultaneously, the two receiving antennas tilt towards the center. x This generates overlapping elevation patterns, allowing for amplitude-to-angle comparison. The amplitude-to-angle comparison result can, to some extent, resolve the angular ambiguity caused by the phase-to-angle comparison method. Specifically, amplitude-to-angle and phase-to-angle comparisons are performed on the target echo separately. The amplitude-to-angle comparison result resolves the angular ambiguity caused by the phase-to-angle comparison, and the final target angle estimate is output as the elevation angle corresponding to the target echo. This can include: The first target angle estimate is obtained by amplitude comparison and angle measurement of the target echo. ; Based on the wavelength of the target echo and the estimated angle of the first target. , to obtain fuzzy numbers ; The second target angle estimate is obtained by comparing the phase angle of the target echo. ; Based on fuzzy numbers Second target angle estimate Confirm the final target angle estimate The elevation angle corresponding to the target echo.

[0030] in, , , , Indicates the wavelength of the echo signal. This indicates the distance between the two receiving antennas. The geometrical diagram of the multipath effect in the dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method provided in this embodiment of the invention is as follows: Figure 4 As shown, the first i The complex signal expression for each receiving channel is composed of the superposition of direct and reflected waves, and the synthesized signal model is: ; in, Indicates the angle of the direct wave. Indicates the angle of multipath reflected waves. The radiation pattern function of the antenna. Indicates the phase corresponding to the direct wave. This indicates the phase of the reflected wave.

[0031] When the target echo is determined to be affected by multipath interference, the method of "phase interval determination and amplitude precise angle determination" is adopted to confirm the elevation angle corresponding to the target echo in order to address the problems of "amplitude monotonicity failure" and "phase accuracy degradation".

[0032] The process of constructing the multipath correction error table and index lookup table may include: Based on the radar operating frequency, antenna installation height, and ground roughness parameters, a theoretical normalized amplitude error signal curve incorporating multipath interference effects is constructed. The theoretically normalized amplitude error signal curve is divided into several monotonic intervals based on the peaks and troughs to form a multipath correction error table. Record the angle range corresponding to each monotonic interval and store it in a cell array to form an index lookup table.

[0033] In complex environments, the reflection coefficient is calculated using roughness attenuation: ; in, This represents the reflectance of a smooth surface. The root mean square value representing the undulation of the ground. Indicates the angle of elevation. Indicates the wavelength of the target echo.

[0034] The theoretical normalized amplitude error signal is expressed as follows: ; in, Indicates the angle of elevation The corresponding theoretical normalized amplitude error signal, This represents the reflection coefficient calculated using roughness attenuation. , Indicates the wavelength of the target echo. This indicates the height of the upper channel relative to the ground in a dual-channel configuration. This indicates the height of the lower channel relative to the ground in a dual-channel configuration.

[0035] A dual-channel receiver (upper channel and lower channel) receives the target echo signal and acquires the target echo complex signal. (Upper passage) and (Lower channel) The phase difference is used to determine the phase angle corresponding to the phase angle measurement. The phase angle is then used to match the target echo in a pre-built index lookup table to determine the monotonic interval of the target echo.

[0036] Within the defined monotonic interval, the measured normalized amplitude error is used. The expression for the measured normalized amplitude error is obtained by looking up the pre-built multipath correction error table: ; in, This indicates the measured normalized amplitude error. This represents the target echo complex signal acquired by the upper channel in a dual-channel configuration. This represents the target echo complex signal acquired by the lower channel in a dual-channel configuration.

[0037] Because the amplitude error signal is extremely sensitive to angle changes within a single monotonic interval, a unique and highly accurate elevation angle value can be obtained. In step S3, this embodiment of the invention utilizes the highly sensitive amplitude information contained in the amplitude oscillation phenomenon generated by multipath propagation, achieving angle measurement accuracy that surpasses traditional methods. Even if the phase is blurred multiple times in the entire spatial domain (e.g., -10° to 10°), within this specific low elevation angle range triggered by multipath propagation, the phase is usually unambiguous (or the number of blurring events is extremely small and easily eliminated through simple logic).

[0038] Understandably, embodiments of the present invention pre-construct a theoretically normalized amplitude error signal curve containing multipath interference effects, and divide it into multiple monotonic intervals based on the peaks and troughs of the curve to form a multipath correction error table. Utilizing the physical characteristic that multipath effects mainly occur at low elevation angles, the calculation range of the target elevation angle is locked within a preset low elevation angle region (e.g., within the first ambiguity period), thereby eliminating high elevation angle phase ambiguity solutions caused by long baselines; using measured phase difference information, combined with the constraints of the low elevation angle region, the current monotonic interval in which the target is located is uniquely determined; using measured amplitude error information, a unique high-precision target elevation angle is obtained within the determined monotonic interval by looking up a table.

[0039] The following simulation experiments demonstrate the beneficial effects of the dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method provided in this embodiment of the invention.

[0040] In this embodiment of the invention, two receiving antennas are designed to be tilted 5° in different directions, with the distance between the two antennas set to 12 times the wavelength. The ambiguity range of the phase comparison method is [-2.38°, 2.38°]. The relationship between the root mean square value of the height measurement error and the target angle is simulated for different traditional angle measurement methods. Simulation conditions: 16.51 GHz frequency is selected, and the directions of the two antennas are... Figure 1 Therefore, each antenna is tilted 5° in a different direction. Antenna spacing The experiment was conducted independently and repeatedly 1000 times, with target angles ranging from -10° to 10°. The resulting diagram showing the overlap of the two antenna radiation patterns is shown below. Figure 5 As shown, the original angle identification curve and the fitted smoothed angle identification curve are as follows: Figure 6 As shown in the figure, the relationship between the root mean square value of the angle measurement error and the target angle for different angle measurement methods at different angles is as follows: Figure 7 As shown, it can be seen that the results of the amplitude comparison method can resolve the ambiguity of the phase comparison method to a certain extent, and the angle measurement effect of the amplitude-phase comparison method is better than that of the amplitude comparison method and the phase comparison method.

[0041] Setting the implementation conditions for embodiments of the present invention: Radar frequency: 16.51 GHz (Ku band); Antenna configuration: Vertical dual channels, spacing The lower passage is 2m high; Target scenario: Target height The flight distance is 500m to 5000m.

[0042] Environmental parameters: ground roughness .

[0043] False alarm probability: 10 -5 .

[0044] A schematic diagram of the pre-generated theoretical normalized amplitude error signal curve, as shown below. Figure 8 As shown, the curve is identified to have multiple oscillation periods, which are then divided into multiple monotonic intervals. The two endpoints of each interval are stored in a cell array.

[0045] The imaginary part of the complex single-pulse ratio is extracted for multipath existence detection and decision-making. A schematic diagram of the multipath detection and decision-making process is shown below. Figure 9 As shown. Based on the current signal-to-noise ratio (SNR) SNR ) and false alarm rate ( P fa The decision threshold Th is dynamically calculated. Before 1969m, the imaginary part of the complex-monopulsive ratio is less than the threshold, indicating a stable region (free space). After 1969m, the imaginary part of the complex-monopulsive ratio is greater than the threshold, indicating a multipath interference region. Multipath interference is strongly correlated with low elevation angles; high elevation angle targets (e.g., greater than 3 degrees) typically do not trigger the multipath detection threshold. Therefore, once the system detects "multipath presence," it means the target is located in the low elevation angle region, and there is no phase ambiguity.

[0046] Branch angle measurement strategy: Branch A (Stable Region): The standard phase-to-amplitude comparison method is used. The phase-to-amplitude comparison method is combined with the phase-to-amplitude comparison method to resolve ambiguity and obtain a high-precision elevation angle.

[0047] Branch B (multipath interference zone): Employs a multipath-based amplitude and phase joint angle measurement method.

[0048] The system first forces the angle search range to be limited to the first ambiguity period (e.g., -2.38° to 2.38°) based on the trigger signal of the multipath mode. It then calculates the measured phase difference between the two channels and uses this phase value to match against a pre-stored index table to determine which monotonic interval the target is currently in, thereby eliminating false matches at high elevation angles.

[0049] Calculate the measured normalized amplitude error of the two channels. : .

[0050] Within the previously determined monotonic intervals, using By performing interpolation and table lookup, a unique high-precision elevation angle can be obtained.

[0051] A schematic diagram comparing the full-range angle measurement results in the dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement methods, as shown below. Figure 10 As shown, it can be seen that the measurement method provided by the embodiments of the present invention closely follows the true value in the long-distance multipath region, while the amplitude and phase comparison method diverges in the low elevation angle region.

[0052] The dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method provided in this invention has the following advantages: Strong resistance to multipath interference: It treats the oscillations caused by multipath interference as useful information rather than noise, and can still work with high precision under severe multipath conditions. In the low elevation angle region, the root mean square error of the amplitude and phase comparison method is 5.126°, while the root mean square error of the amplitude and phase comparison method based on multipath is 0.401°.

[0053] High detection accuracy: By utilizing the imaginary part of the complex single-pulse ratio combined with the signal-to-noise ratio adaptive threshold, multipath states can be identified more accurately than a simple distance threshold.

[0054] High computational efficiency: The measurement method adopts offline table creation and online table lookup interpolation, avoiding complex real-time iterative searches, which is suitable for engineering implementation.

[0055] The measurement method provided in this invention utilizes the theoretical zero imaginary part of the complex single-pulse ratio in free space, and the physical characteristic of violent oscillation of the imaginary part under multipath interference. Combined with the real-time signal-to-noise ratio, an adaptive decision threshold for the multipath decision model is constructed. This allows the judgment of the complex signal of the target echo to accurately identify the occurrence and termination of multipath interference, much like a "switch." When the target echo is affected by multipath interference, an elevation angle measurement method targeting multipath interference is activated, significantly improving the radar's environmental adaptability and robustness. By utilizing the imaginary part characteristics of the complex single-pulse ratio combined with the adaptive signal-to-noise ratio threshold, multipath states are identified more accurately than a simple range threshold, resulting in higher detection accuracy. This invention leverages the characteristic that phase information, although distorted under multipath conditions, still maintains piecewise monotonicity. It first locks the target's location within a subdivided monotonic interval by phase detection, and then uses highly sensitive amplitude information within the interval for table lookup and inversion. Without changing the 1T2R hardware architecture, this solves the angle measurement error problem caused by multipath interference.

[0056] It should be noted that, in the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A dual-channel three-coordinate radar method for low-altitude multipath detection and dynamic elevation angle measurement, characterized in that, include: Confirm the complex-to-single pulse ratio of the target echo complex signal and extract the imaginary part of the complex-to-single pulse ratio; Based on a pre-built multipath decision model, multipath detection and decision are performed on the imaginary part of the complex single-pulse ratio to determine whether the target echo is affected by multipath interference. If the target echo is not affected by multipath interference, perform amplitude comparison angle measurement and phase comparison angle measurement on the target echo respectively. Use the result of amplitude comparison angle measurement to resolve the angle ambiguity caused by phase comparison angle measurement, and output the final target angle estimate as the elevation angle corresponding to the target echo. If the target echo is affected by multipath interference, the phase normal angle corresponding to the phase angle measurement is determined based on the phase difference of the complex signal of the target echo; the phase normal angle is used to match in the pre-built index lookup table to determine the monotonic interval of the target echo. The elevation angle corresponding to the target echo is confirmed by searching the pre-constructed multipath correction error table for the measured normalized amplitude error corresponding to the complex signal of the target echo. The multipath correction error table is constructed based on radar operating frequency, antenna installation height, and ground roughness parameters. The index lookup table is obtained from the multipath correction error table.

2. The dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method according to claim 1, characterized in that, The expression for the complex-to-single pulse ratio of the target echo complex signal is as follows: ； in, Indicates the ratio of complex to single pulse. Represents the imaginary unit. This represents the target echo complex signal acquired by the upper channel in a dual-channel configuration. This represents the target echo complex signal acquired by the lower channel in a dual-channel configuration.

3. The dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method according to claim 1, characterized in that, The pre-constructed multipath decision model performs multipath detection and decision on the imaginary part of the complex single-pulse ratio to determine whether the target echo is affected by multipath interference, including: Determine the imaginary part of the complex single-pulse ratio and the size of the adaptive decision threshold of the pre-constructed multipath decision model; If the imaginary part of the complex single-pulse ratio is less than or equal to the adaptive decision threshold, it is determined that the current target echo is not affected by multipath interference. If the imaginary part of the complex single-pulse ratio is greater than the adaptive decision threshold, the current target echo is determined to be subject to multipath interference.

4. The dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method according to claim 3, characterized in that, The expression for the adaptive decision threshold is as follows: ； in, The variance representing the imaginary part of the complex single-pulse ratio in the absence of multipath effects. This indicates the preset false alarm rate.

5. The dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method according to claim 1, characterized in that, The process of performing amplitude and phase angle measurements on the target echo, resolving the angular ambiguity caused by the phase angle measurement using the amplitude angle measurement result, and outputting the final target angle estimate as the elevation angle corresponding to the target echo includes: The first target angle estimate is obtained by comparing the amplitude and angle of the target echo; The ambiguity number is obtained based on the wavelength of the target echo and the estimated angle of the first target; The estimated angle of the second target is obtained by comparing the phase angle of the target echo; Based on the fuzzy number and the second target angle estimate, the final target angle estimate is confirmed as the elevation angle corresponding to the target echo.

6. The dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method according to claim 1, characterized in that, The process of constructing the multipath correction error table and index lookup table includes: Based on the radar operating frequency, antenna installation height, and ground roughness parameters, a theoretical normalized amplitude error signal curve incorporating multipath interference effects is constructed. The theoretically normalized amplitude error signal curve is divided into several monotonic intervals based on the peaks and troughs to form a multipath correction error table. Record the angle range corresponding to each monotonic interval and store it in a cell array to form an index lookup table.

7. The dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method according to claim 6, characterized in that, The expression for the theoretically normalized amplitude error signal is as follows: ； in, Indicates the angle of elevation The corresponding theoretical normalized amplitude error signal, This represents the reflection coefficient calculated using roughness attenuation. , Indicates the wavelength of the target echo. This indicates the height of the upper channel relative to the ground in a dual-channel configuration. This indicates the height of the lower channel relative to the ground in a dual-channel configuration.

8. The dual-channel three-coordinate radar low-altitude multipath detection and elevation angle dynamic measurement method according to claim 7, characterized in that, The expression for the reflection coefficient, which incorporates roughness attenuation calculation, is as follows: ； in, This represents the reflectance of a smooth surface. The root mean square value representing the undulation of the ground. Indicates the angle of elevation. Indicates the wavelength of the target echo.

9. A dual-channel three-coordinate radar method for low-altitude multipath detection and dynamic elevation angle measurement according to claim 1, characterized in that, The expression for the measured normalized amplitude error is as follows: ； in, This indicates the measured normalized amplitude error. This represents the target echo complex signal acquired by the upper channel in a dual-channel configuration. This represents the target echo complex signal acquired by the lower channel in a dual-channel configuration.

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