An angle measurement method based on frequency diversity technology
By optimizing the frequency interval and number of frequency points through frequency diversity technology, transmitting signals in time division, and calculating and fusing measurement values, the problem of large radar angle measurement error in low-altitude multipath environments is solved, and stability and accuracy are improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- XIAN HUANGHE MECHANICAL & ELECTRICAL CO LTD
- Filing Date
- 2026-04-27
- Publication Date
- 2026-07-14
AI Technical Summary
In low-altitude or sea environments, the coherent superposition of multipath reflected radar echoes and direct radar signals leads to serious errors in angle measurement methods. Existing technologies such as low-elevation tracking technology sacrifice data rate and search capability, while complex model compensation methods have poor robustness.
By employing frequency diversity technology, the frequency interval constraint set is calculated, the frequency interval and the number of frequency points are selected, signals at each frequency point are transmitted in time division, the target elevation single pulse ratio and noise variance are calculated, an objective function model is constructed, the optimal weight vector is solved, and the measurement values are weighted and fused.
It effectively reduces environmental interference in single-frequency angle measurement, improves angle measurement stability and accuracy, meets high update rate requirements, requires no additional hardware cost, and is suitable for low elevation angle multipath scenarios.
Smart Images
Figure CN122386259A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of radar technology, and in particular to an angle measurement method based on frequency diversity technology. Background Technology
[0002] In low-altitude or sea environments, radar echoes from targets are often accompanied by strong multipath reflection signals. The multipath signals and direct signals coherently superimpose at the receiver, causing wavefront distortion of the composite signal. This leads to serious errors in angle measurement methods based on amplitude-to-amplitude or single-frequency phase interferometry, and may even result in angular scintillation and tracking loss.
[0003] In tracking angle measurement technology, monopulse angle measurement is widely used due to its high data rate and relatively simple structure. However, in low-altitude multipath environments, direct waves and ground-reflected waves interfere at the receiver, causing severe distortion in the amplitude and phase relationship of the sum and difference beams. This leads to systematic errors in monopulse angle measurement results based on sum and difference amplitude (phase) comparison, and even angular flicker, seriously threatening guidance accuracy. Existing technologies, such as low-elevation tracking techniques (e.g., off-axis scanning), sacrifice data rate and search capability; complex ground reflection multipath model compensation methods rely on prior knowledge and have poor robustness. Frequency diversity techniques, by transmitting signals at multiple different carrier frequencies, cause the multipath reflection coefficient to vary with frequency, thus showing potential in multipath suppression and angle estimation.
[0004] Therefore, it is necessary to provide a new technical solution to improve one or more of the problems existing in the above solutions.
[0005] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention
[0006] The purpose of this application is to provide an angle measurement method based on frequency diversity technology, thereby overcoming, to at least to some extent, one or more problems caused by the limitations and defects of related technologies.
[0007] An angle measurement method based on frequency diversity technology is provided according to an embodiment of this application. The method includes: The frequency spacing constraint set is obtained based on the radar antenna height, the distance between the target and the radar, and the target's flight altitude; Select a frequency interval based on the set of frequency interval constraints, and determine the number of frequency points based on the frequency interval and the total system width; The radar uses a time-division multiplexing method to sequentially transmit signals at each frequency point and receive target echo signals at each frequency point. The target pitch single pulse ratio is calculated based on the target echo signal, and the target pitch angle measurement value vector at all frequencies is calculated based on the target pitch single pulse ratio. Based on the real-time signal-to-noise ratio, the target noise variance of each frequency point is calculated, and the target noise covariance matrix of all frequency points is obtained based on the target noise variance of each frequency point. Calculate the target sample residual for each frequency point, and obtain the target multipath deviation covariance matrix for all frequency points based on the target sample residual for each frequency point; Construct an objective function model for the target pitch angle; Based on the relationship between the target pitch angle measurement value and the noise vector and multipath deviation vector, and combining the noise covariance matrix and the multipath deviation covariance matrix, the objective function model is solved to obtain the optimal weight vector for each frequency point; The target elevation angle measurements at various frequencies are weighted and fused to obtain the optimal estimate of the target elevation angle.
[0008] In the embodiments of this application, obtaining the frequency spacing constraint set based on the radar antenna height, the distance between the target and the radar, and the target flight altitude includes: The slant range difference between the target signal and the multi-aperture signal is calculated based on the radar antenna height, the distance between the target and the radar, and the target's flight altitude; wherein the formula for calculating the slant range difference is as follows: (1) In the formula, Indicates the difference in slope distance. Indicates the radar antenna height. Indicates the target flight altitude. Indicates the distance between the target and the radar. Indicates the target's pitch angle; The time delay between the target signal and the multi-aperture signal is calculated based on the slant range difference; wherein the formula for calculating the time delay is as follows: (2) In the formula, This represents time delay, and c represents the speed of light. ; The power fluctuation period of the received signal is calculated based on the time delay; wherein the formula for calculating the power fluctuation period is as follows: (3) In the formula, Indicates the period of power fluctuation; The lower bound of the frequency interval constraint set is calculated based on the power fluctuation period; wherein the lower bound of the frequency interval constraint set is as follows: (4) In the formula, This represents the lower bound of the set of frequency interval constraints; The upper limit of the frequency interval constraint set is calculated based on the total system width; wherein the upper limit of the frequency interval constraint set is as follows: (5) In the formula, This represents the upper limit of the set of frequency interval constraints. Indicates the total system bandwidth; The frequency interval constraint set is obtained based on the lower limit and the upper limit of the frequency interval constraint set; wherein, the expression of the frequency interval constraint set is as follows: (6) In the formula, This represents the set of frequency interval constraints.
[0009] In the embodiments of this application, the expression for the number of frequency points is as follows: (7) In the formula, Indicates the number of frequency points. Indicates frequency interval, This represents the total system bandwidth.
[0010] In the embodiments of this application, the calculation of the target's pitch single-pulse ratio and the calculation of the target pitch angle measurement vector at all frequency points based on the target's pitch single-pulse ratio include: The expression for the target's pitch single-pulse ratio is as follows: (8) In the formula, , This represents the target's pitch single-pulse ratio. Indicates taking the real part, Indicates the first Difference signal at each frequency point Indicates the first The complex conjugate of the sum of the frequencies, Indicates the first Array channels at each frequency point Received target echo signal, , This represents the number of array channels of the radar. The target pitch angle error at each frequency point is calculated based on the ratio of the target's pitch single pulse ratio to the target's single pulse slope; the expression for the target pitch angle error at each frequency point is as follows; (9) In the formula, Indicates the first Target elevation angle error at each frequency point Indicates the first The single-pulse slope of a target at a specific frequency point; The target pitch angle error vector for all frequency points is obtained based on the target pitch angle error at each frequency point; the expression for the target pitch angle error vector for all frequency points is as follows: (10) In the formula, This represents the target elevation angle error vector for all frequency points.
[0011] In the embodiments of this application, the step of calculating the target noise variance of each frequency point based on the real-time signal-to-noise ratio, and obtaining the target noise covariance matrix of all frequency points based on the target noise variance of each frequency point, includes: The expression for the target noise variance at each frequency point is as follows: (11) In the formula, This represents the target noise variance at each frequency point. Represents system constants. The signal-to-noise ratio of the target is represented by [symbol missing]. Indicates the gain when the beam is pointing upwards; The expression for the target noise covariance matrix at all frequency points is as follows: (12) In the formula, This represents the target noise covariance matrix for all frequency points.
[0012] In the embodiments of this application, the step of calculating the target sample residual for each frequency point to obtain the target sample residual covariance matrix for all frequency points, and then obtaining the target multipath deviation covariance matrix for all frequency points, includes: The expression for the target sample residual at each frequency point is as follows: (13) In the formula, This represents the target sample residual at each frequency point. Indicates the first Each frequency point The target pitch angle measurement value at that moment. express Filter the predicted pitch angle of the current target from the previous moment; The expression for the residual covariance matrix of the target samples at all frequency points is as follows: (14) The expression for the target multipath deviation covariance matrix for all frequency points is as follows: (15) In the formula, This represents the target multipath deviation covariance matrix for all frequency points. This represents the forgetting factor, which ranges from 0.9 to 0.99. Represents the target residual sample covariance matrix. This represents the initial multipath deviation covariance matrix of the target.
[0013] In the embodiments of this application, the expression of the objective function model is as follows; (16) In the formula, Represents the objective function model. This represents the target elevation angle measurements at all frequencies. Indicates the target The weight vector corresponding to each frequency point Indicates the first The weight of each frequency point.
[0014] In the embodiments of this application, the step of solving the objective function model based on the relationship between the target pitch angle measurement value and the noise vector and multipath deviation vector, combined with the noise covariance matrix and the multipath deviation covariance matrix, to obtain the optimal weight vector for all frequency points includes: The expressions for the target elevation angle measurements at all frequencies are as follows: (17) In the formula, This represents the target elevation angle measurements at all frequencies. , This represents the true vector of the target pitch angle. Indicates the first The true value of the target pitch angle at each frequency point Represents the multipath deviation vector. Indicates the first Multipath bias at each frequency point Represents the noise vector. Indicates the first Noise at each frequency point; The expression for the optimal weight vector for all frequency points is as follows: (18) In the formula, This represents the optimal weight vector for all frequency points. This represents the target noise covariance matrix for all frequency points.
[0015] In the embodiments of this application, the expression for the optimal estimate of the target pitch angle is as follows; (19) In the formula, This represents the optimal estimate of the target pitch angle.
[0016] The technical solutions provided by the embodiments of this application may include the following beneficial effects: In one embodiment of this application, the frequency interval is optimized and the number of frequency points is determined by the above method through a set of frequency interval constraints. Combined with the frequency diversity characteristics of time-division frequency point transmission and reception, environmental interference of single-frequency point angle measurement is effectively reduced, the drawback of single-frequency point angle measurement being susceptible to interference is effectively avoided, and the stability of angle measurement is improved. Time-division transmission ensures that target elevation angle measurement can be completed quickly at each frequency point, and the entire frequency diversity cycle time is short, which can meet the requirements of high update rate. By quantizing and modeling noise and multipath bias, the optimal weight vector of each frequency point is solved and weighted fusion is performed, which significantly improves the accuracy and robustness of elevation angle measurement. This application does not significantly increase hardware costs, has strong engineering practicality, and can effectively improve radar angle measurement performance in low elevation angle multipath scenarios.
[0017] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description
[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.
[0019] Figure 1 This schematically illustrates a flowchart of the steps of an angle measurement method based on frequency diversity technology in an exemplary embodiment of this application. Figure 2 This schematic diagram illustrates the geometric relationship between the target signal and the multipath signal in an exemplary embodiment of this application. Figure 3 This schematic diagram illustrates a comparison of pitch angle measurement results in an exemplary embodiment of this application. Detailed Implementation
[0020] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided to make this application more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
[0021] Furthermore, the accompanying drawings are merely illustrative of this application and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.
[0022] This example implementation provides a method for angle measurement based on frequency diversity technology, referencing... Figure 1 As shown, the method may include steps S101 to S109.
[0023] In step S101, the frequency interval constraint set is obtained based on the radar antenna height, the distance between the target and the radar, and the target flight altitude.
[0024] Step S102: Select the frequency interval according to the frequency interval constraint set, and determine the number of frequency points according to the frequency interval and the total system width.
[0025] Step S103: The radar sequentially transmits signals at each frequency point using a time-division multiplexing method and receives target echo signals at each frequency point.
[0026] Step S104: Calculate the target's pitch single pulse ratio based on the target echo signal, and calculate the target pitch angle measurement vector for all frequency points based on the target's pitch single pulse ratio.
[0027] Step S105: Calculate the target noise variance for each frequency point based on the real-time signal-to-noise ratio, and obtain the target noise covariance matrix for all frequency points based on the target noise variance for each frequency point.
[0028] Step S106: Calculate the target sample residual for each frequency point, and obtain the target multipath deviation covariance matrix for all frequency points based on the target sample residual for each frequency point.
[0029] Step S107: Construct the objective function model for the target pitch angle.
[0030] Step S108: Based on the relationship between the target pitch angle measurement value and the noise vector and multipath deviation vector, and combining the noise covariance matrix and the multipath deviation covariance matrix, solve the objective function model to obtain the optimal weight vector for each frequency point.
[0031] Step S109: Weighted fusion of target pitch angle measurements at various frequencies to obtain the optimal estimate of the target pitch angle.
[0032] In one embodiment of this application, the frequency interval is optimized and the number of frequency points is determined by the above method through a set of frequency interval constraints. Combined with the frequency diversity characteristics of time-division frequency point transmission and reception, environmental interference of single-frequency point angle measurement is effectively reduced, the drawback of single-frequency point angle measurement being susceptible to interference is effectively avoided, and the stability of angle measurement is improved. Time-division transmission ensures that target elevation angle measurement can be completed quickly at each frequency point, and the entire frequency diversity cycle time is short, which can meet the requirements of high update rate. By quantizing and modeling noise and multipath bias, the optimal weight vector of each frequency point is solved and weighted fusion is performed, which significantly improves the accuracy and robustness of elevation angle measurement. This application does not significantly increase hardware costs, has strong engineering practicality, and can effectively improve radar angle measurement performance in low elevation angle multipath scenarios.
[0033] Below, we will refer to Figures 1 to 2 The steps of the method described above in this example embodiment will be explained in more detail.
[0034] In step S101, refer to Figure 2 The geometric relationship between the target signal and the multipath signal includes the radar antenna height, the target flight altitude, and the distance between the target and the radar. Using the radar antenna height, the distance between the target and the radar, and the target flight altitude, a frequency spacing constraint set employing frequency diversity technology can be obtained. This set of frequency spacing constraints can adapt to different real-world detection scenarios, such as low-altitude / high-altitude and short-range / long-range detection, effectively suppressing measurement errors caused by multipath interference, range ambiguity, and high coupling.
[0035] In one embodiment, step S101 includes the following: The slant range difference between the target signal and the multi-aperture signal is calculated based on the radar antenna height, the distance between the target and the radar, and the target's flight altitude. The formula for calculating the slant range difference is as follows: (1) In the formula, Indicates the difference in slope distance. Indicates the radar antenna height. Indicates the target flight altitude. Indicates the distance between the target and the radar. Indicates the target's pitch angle; The time delay between the target signal and the multi-aperture signal is calculated based on the slant range difference; the formula for calculating the time delay is as follows: (2) In the formula, This represents time delay, and c represents the speed of light. ; The power fluctuation period of the received signal is calculated based on the time delay; the formula for calculating the power fluctuation period is as follows: (3) In the formula, Indicates the period of power fluctuation; The lower bound of the frequency interval constraint set is calculated based on the power fluctuation period; the lower bound of the frequency interval constraint set is as follows: (4) In the formula, This represents the lower bound of the set of frequency interval constraints; The upper limit of the frequency interval constraint set is calculated based on the total system width; the upper limit of the frequency interval constraint set is as follows: (5) In the formula, This represents the upper limit of the set of frequency interval constraints. Indicates the total system bandwidth; The frequency interval constraint set is obtained by defining the lower bound and the upper bound of the frequency interval constraint set; the expression for the frequency interval constraint set is as follows: (6) In the formula, This represents the set of frequency interval constraints.
[0036] It is understandable that the slant range difference between the target signal and the multiaperture signal can be calculated using the radar antenna height, the distance between the target and the radar, and the target's flight altitude. This can be calculated using formula (1). The slant range difference is used to calculate the time delay between the target signal and the multiaperture signal, which can be calculated using formula (2). The power fluctuation period of the received signal can be calculated using the time delay, which can be calculated using formula (3). The lower limit of the frequency spacing constraint set can be calculated using the power fluctuation period, which can be calculated using formula (4). The upper limit of the frequency spacing constraint set can be calculated using the total system width, which can be calculated using formula (5). The frequency spacing constraint set can be obtained using the lower limit and the upper limit of the frequency spacing constraint set, which can be obtained using formula (6). The frequency spacing constraint set is used for subsequent optimization of the frequency spacing and determination of the number of frequency points.
[0037] In step S102, a suitable frequency interval is selected from the frequency interval constraint set according to the required number of frequency points, thereby determining a set of uniformly distributed frequencies. , Describe the frequency of the Nth frequency point, satisfying = , Indicates frequency interval.
[0038] After selecting a suitable frequency interval, determine the number of frequency points based on the frequency interval and the total system bandwidth.
[0039] Furthermore, the expression for the number of frequency points is as follows: (7) In the formula, Indicates the number of frequency points. Indicates frequency interval, This represents the total system bandwidth.
[0040] It is understandable that the number of frequency points can be obtained through the frequency interval and the total system width, and the specific number of frequency points can be obtained according to formula (7).
[0041] In step S103, the radar sequentially transmits signals at each frequency point in a time-division manner and receives target echoes at each frequency point.
[0042] Specifically, the radar uses time-division multiplexing to transmit signals at different frequencies sequentially, which avoids frequency interference and signal aliasing caused by simultaneous transmission of multiple frequencies, thereby improving signal purity and echo signal-to-noise ratio.
[0043] In step S104, the target's pitch single-pulse ratio is calculated based on the target echo signal, and the target pitch angle measurement vector for all frequency points is calculated based on the target's pitch single-pulse ratio. Specifically, step S104 includes the following: The expression for the target's pitch single-pulse ratio is as follows: (8) In the formula, , This represents the target's pitch single-pulse ratio. Indicates taking the real part, Indicates the first Difference signal at each frequency point Indicates the first The complex conjugate of the sum of the frequencies, Indicates the first Array channels at each frequency point Received target echo signal, , This represents the number of array channels of the radar. The target pitch angle error at each frequency point is calculated based on the ratio of the target's pitch single pulse ratio to the target's single pulse slope; the expression for the target pitch angle error at each frequency point is as follows; (9) In the formula, Indicates the first Target elevation angle error at each frequency point Indicates the first The single-pulse slope of a target at a specific frequency point; The target pitch angle error vector for all frequency points is obtained based on the target pitch angle error at each frequency point; the expression for the target pitch angle error vector for all frequency points is as follows: (10) In the formula, This represents the target elevation angle error vector for all frequency points.
[0044] Understandably, for each frequency point, the target's pitch single-pulse ratio is obtained based on the sum signal and the pitch difference signal. Specifically, it can be calculated according to formula (8). Then, the target elevation angle error at each frequency point is obtained according to the ratio of the target's elevation single pulse ratio and the target's single pulse slope, which can be calculated according to formula (9). Finally, the target elevation angle error vector of all frequency points is obtained by comparing the target elevation angle error at each frequency point with the current beam pointing, which can be calculated according to formula (10); where, , Indicates the target's current beam direction.
[0045] In step S105, the target noise variance for each frequency point is calculated based on the real-time signal-to-noise ratio, and the target noise covariance matrix for all frequency points is obtained based on the target noise variance for each frequency point. Specifically, step S105 includes the following: The expression for the target noise variance at each frequency point is as follows: (11) In the formula, This represents the target noise variance at each frequency point. Represents system constants. The signal-to-noise ratio of the target is represented by [symbol missing]. Indicates the gain when the beam is pointing upwards; The expression for the target noise covariance matrix at all frequencies is as follows: (12) In the formula, This represents the target noise covariance matrix for all frequency points.
[0046] It is understandable that the target noise variance at each frequency point can be obtained through the real-time signal-to-noise ratio, which can be calculated according to formula (11). The target noise covariance matrix of all frequency points can be obtained through the target noise variance at each frequency point, which can be calculated according to formula (12).
[0047] In step S106, the target sample residual for each frequency point is calculated to obtain the target sample residual covariance matrix for all frequency points, and then the target multipath deviation covariance matrix for all frequency points is obtained. Specifically, step S106 includes the following: The expression for the target sample residual at each frequency point is as follows: (13) In the formula, Indicates the first Each frequency point The target pitch angle measurement value at that moment. express Filter the predicted pitch angle of the current target from the previous moment; The expression for the residual covariance matrix of the target samples at all frequency points is as follows: (14) The expression for the target multipath deviation covariance matrix for all frequency points is as follows: (15) In the formula, This represents the target multipath deviation covariance matrix for all frequency points. This represents the forgetting factor, which ranges from 0.9 to 0.99. Represents the target residual sample covariance matrix. This represents the initial multipath deviation covariance matrix of the target.
[0048] Understandable, Filtering is a filtering method; for details, please refer to existing technologies for understanding. and The target sample residuals at each frequency point can be obtained, and can be calculated according to formula (13). The target multipath deviation covariance matrix at each frequency point can be obtained by using the initial multipath deviation covariance matrix of the target, the target residual sample covariance matrix and the forgetting factor, and can be calculated according to formula (15).
[0049] It should be noted that by introducing the target noise covariance matrix and the target multipath deviation covariance matrix, it is possible to achieve quantitative modeling of noise and multipath error. Compared with traditional fixed-weight angle measurement, this is more in line with the actual radar working scenario and the error suppression is more accurate.
[0050] In step S107, constructing the objective function model for the target pitch angle includes the following: The expression for the objective function model is as follows; (16) In the formula, Represents the objective function model. This represents the target elevation angle measurements at all frequencies. Indicates the target The weight vector corresponding to each frequency point Indicates the first The weight of each frequency point.
[0051] Understandably, through the goal The objective function model can be obtained from the weight vector corresponding to each frequency point and the target pitch angle measurement values of all frequency points, which can be obtained according to formula (16). The objective function model is used to obtain the optimal weight vector of each frequency point in the subsequent process. That is, by solving the objective function model, the optimal weight vector of each frequency point can be obtained.
[0052] In step S108, based on the relationship between the target pitch angle measurement value and the noise vector and multipath deviation vector, and combining the noise covariance matrix and the multipath deviation covariance matrix, the objective function model is solved to obtain the optimal weight vector for each frequency point. Specifically, the optimal weight vector for each frequency point can be obtained from the target pitch angle measurement value vector, the noise vector, and the multipath deviation vector. .Will Substituting into formula (16), and combining the noise covariance matrix and the multipath deviation covariance matrix, the optimal linear unbiased estimation method is used to obtain the optimal weight vector for each frequency point.
[0053] Furthermore, step S108 includes the following: The expressions for the target elevation angle measurements at all frequencies are as follows: (17) In the formula, This represents the target elevation angle measurements at all frequencies. , This represents the true vector of the target pitch angle. Indicates the first The true value of the target pitch angle at each frequency point Represents the multipath deviation vector. Indicates the first Multipath bias at each frequency point Represents the noise vector. Indicates the first Noise at each frequency point; The expression for the optimal weight vector at each frequency point is as follows: (18) In the formula, This represents the optimal weight vector for each frequency point. This represents the target noise covariance matrix for all frequency points.
[0054] It should be noted that formula (17) is also the relationship between the target pitch angle measurement value and the noise vector and multipath deviation vector. Formula (17) can be used to obtain... Combining formula (15), the optimal weight vector for each frequency point is obtained by using the optimal linear unbiased estimation method.
[0055] In step S109, the target elevation angle measurements from each frequency point are weighted and fused to obtain the optimal estimate of the target elevation angle. Specifically, this is done based on the optimal weight vector of each frequency point and... Weighted fusion is performed to obtain the optimal estimate of the target pitch angle. Furthermore, the expression for the optimal estimate of the target pitch angle is as follows; (19) In the formula, This represents the optimal estimate of the target pitch angle.
[0056] Specifically, the optimal estimate of the target pitch angle can be obtained according to formula (19). This application is based on the target's... The weight vector corresponding to the i-th frequency point and the i-th frequency point The objective function model for the target elevation angle is constructed by weighting each frequency point. The optimal weight vector for each frequency point is solved and then weighted and fused. This maximizes the frequency diversity gain and fully integrates the angle measurement advantages of each frequency point, effectively offsetting the angle measurement errors caused by noise and multipath bias, and significantly improving the accuracy and robustness of target elevation angle measurement. This application relies on frequency domain signal processing and data fusion optimization, without the need to increase the antenna array size or add complex hardware equipment. While controlling hardware costs and system complexity, it improves angle measurement performance and has strong engineering practicality. It can be efficiently adapted to complex radar angle measurement scenarios such as low elevation angle multipath, solving the technical problems of low accuracy and poor stability of existing angle measurement methods in such scenarios.
[0057] While maintaining the high data rate advantage of monopulse angle measurement, frequency diversity technology is introduced to suppress random and systematic errors caused by multipath propagation, significantly improving radar tracking accuracy. Specifically, this application utilizes frequency diversity to smooth angle flicker and deviations caused by multipath propagation, improving angle measurement stability, with significant multipath suppression. Time-division transmission ensures rapid target elevation angle measurement at each frequency point, and the short overall frequency diversity cycle time meets the requirements for high update rates. Furthermore, this application boasts strong engineering practicality and compatibility, being compatible with existing monopulse hardware and processing procedures. Only modules related to multi-frequency waveform generation, time-division control, and data processing need to be added, resulting in low modification costs.
[0058] To verify the angle measurement method based on frequency diversity technology provided in this application, the following experiments are conducted.
[0059] The relevant experimental parameters and conditions are as follows: The radar's center frequency is 10 GHz, wavelength is 0.03 m, and the radar antenna array is a uniform linear array with 16 channels. The radar antenna height is 3 m, the target's flight altitude relative to the radar array center is 40 m, the target is flying horizontally towards the radar, and the slant range of the target relative to the radar array center varies from 3500 m to 1350 m. Tests were conducted using four frequency points with a frequency spacing of 0.8 GHz: 8.4 GHz, 9.2 GHz, 10 GHz, and 10.8 GHz. The echo signal-to-noise ratio is 20 dB.
[0060] Please refer to the pitch angle measurement results (i.e., the target pitch angle measurement results). Figure 3 In the figure, the blue curve represents the target elevation angle measurement value at a frequency of 10 GHz, and the red curve represents the target elevation angle obtained by weighted fusion of the angle measurement results at four frequencies using the method proposed in this invention. The blue curve shows that the single-frequency angle measurement results are obviously affected by sinusoidal modulation caused by multipath signals, and the larger the slant range, the longer the modulation period. The red curve, on the other hand, is much flatter, indicating that after using frequency diversity technology, the influence of multipath effect on the angle measurement accuracy is significantly eliminated, and the angle measurement accuracy of the target elevation angle is greatly improved.
[0061] It should be noted that although the steps of the method in this application are described in a specific order in the accompanying drawings, this does not require or imply that these steps must be performed in that specific order, or that all the steps shown must be performed to achieve the desired result. Additional or alternative steps may be omitted, multiple steps may be combined into one step, and / or a step may be broken down into multiple steps. Furthermore, it is readily understood that these steps may be executed synchronously or asynchronously, for example, in multiple modules / processes / threads.
[0062] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.
Claims
1. A method for angle measurement based on frequency diversity technology, characterized in that, The method includes: The frequency spacing constraint set is obtained based on the radar antenna height, the distance between the target and the radar, and the target's flight altitude; Select a frequency interval based on the set of frequency interval constraints, and determine the number of frequency points based on the frequency interval and the total system width; The radar uses a time-division multiplexing method to sequentially transmit signals at each frequency point and receive target echo signals at each frequency point. The target pitch single pulse ratio is calculated based on the target echo signal, and the target pitch angle measurement value vector at all frequencies is calculated based on the target pitch single pulse ratio. Based on the real-time signal-to-noise ratio, the target noise variance of each frequency point is calculated, and the target noise covariance matrix of all frequency points is obtained based on the target noise variance of each frequency point. Calculate the target sample residual for each frequency point, and obtain the target multipath deviation covariance matrix for all frequency points based on the target sample residual for each frequency point; Construct an objective function model for the target pitch angle; Based on the relationship between the target pitch angle measurement value and the noise vector and multipath deviation vector, and combining the noise covariance matrix and the multipath deviation covariance matrix, the objective function model is solved to obtain the optimal weight vector for each frequency point; The target elevation angle measurements at various frequencies are weighted and fused to obtain the optimal estimate of the target elevation angle.
2. The angle measurement method based on frequency diversity technology according to claim 1, characterized in that, The frequency spacing constraint set obtained based on the radar antenna height, the distance between the target and the radar, and the target's flight altitude includes: The slant range difference between the target signal and the multi-aperture signal is calculated based on the radar antenna height, the distance between the target and the radar, and the target's flight altitude; wherein the formula for calculating the slant range difference is as follows: （1） In the formula, Indicates the difference in slope distance. Indicates the radar antenna height. Indicates the target flight altitude. Indicates the distance between the target and the radar. Indicates the target's pitch angle; The time delay between the target signal and the multi-aperture signal is calculated based on the slant range difference; wherein the formula for calculating the time delay is as follows: （2） In the formula, This represents time delay, and c represents the speed of light. ; The power fluctuation period of the received signal is calculated based on the time delay; wherein the formula for calculating the power fluctuation period is as follows: （3） In the formula, Indicates the period of power fluctuation; The lower bound of the frequency interval constraint set is calculated based on the power fluctuation period; wherein the lower bound of the frequency interval constraint set is as follows: （4） In the formula, This represents the lower bound of the set of frequency interval constraints. The upper limit of the frequency interval constraint set is calculated based on the total system width; wherein the upper limit of the frequency interval constraint set is as follows: （5） In the formula, This represents the upper limit of the set of frequency interval constraints. Indicates the total system bandwidth; The frequency interval constraint set is obtained based on the lower limit and the upper limit of the frequency interval constraint set; wherein, the expression of the frequency interval constraint set is as follows: （6） In the formula, This represents the set of frequency interval constraints.
3. The angle measurement method based on frequency diversity technology according to claim 1, characterized in that, The expression for the number of frequency points is as follows: （7） In the formula, Indicates the number of frequency points. Indicates frequency interval, This represents the total system bandwidth.
4. The angle measurement method based on frequency diversity technology according to claim 3, characterized in that, The calculation involves determining the target's pitch single-pulse ratio and, based on this ratio, calculating a vector of target pitch angle measurements at all frequencies, including: The expression for the target's pitch single-pulse ratio is as follows: （8） In the formula, , This represents the target's pitch single-pulse ratio. Indicates taking the real part, Indicates the first Difference signal at each frequency point Indicates the first The complex conjugate of the sum of the frequencies, Indicates the first Array channels at each frequency point Received target echo signal, , This represents the number of array channels of the radar. The target pitch angle error at each frequency point is calculated based on the ratio of the target's pitch single pulse ratio to the target's single pulse slope; the expression for the target pitch angle error at each frequency point is as follows; （9） In the formula, Indicates the first Target elevation angle error at each frequency point Indicates the first The single-pulse slope of a target at a specific frequency point; The target pitch angle error vector for all frequency points is obtained based on the target pitch angle error at each frequency point; the expression for the target pitch angle error vector for all frequency points is as follows: （10） In the formula, This represents the target pitch angle error vector for all frequency points.
5. The angle measurement method based on frequency diversity technology according to claim 4, characterized in that, The step of calculating the target noise variance for each frequency point based on the real-time signal-to-noise ratio, and obtaining the target noise covariance matrix for all frequency points based on the target noise variance for each frequency point, includes: The expression for the target noise variance at each frequency point is as follows: （11） In the formula, This represents the target noise variance at each frequency point. Represents system constants. The signal-to-noise ratio of the target is represented by [symbol missing]. Indicates the gain when the beam is pointing upwards; The expression for the target noise covariance matrix at all frequency points is as follows: （12） In the formula, This represents the target noise covariance matrix for all frequency points.
6. The angle measurement method based on frequency diversity technology according to claim 5, characterized in that, The calculation of the target sample residual at each frequency point yields the target sample residual covariance matrix for all frequency points, and then the target multipath deviation covariance matrix for all frequency points is obtained, including: The expression for the target sample residual at each frequency point is as follows: （13） In the formula, Indicates the first The residual of the target sample at each frequency point Indicates the first Each frequency point The target pitch angle measurement value at that moment. express Filter the predicted pitch angle of the current target from the previous moment; The expression for the residual covariance matrix of the target samples at all frequency points is as follows: （14） The expression for the target multipath deviation covariance matrix for all frequency points is as follows: （15） In the formula, This represents the target multipath deviation covariance matrix for all frequency points. This represents the forgetting factor, which ranges from 0.9 to 0.
99. Represents the target residual sample covariance matrix. This represents the initial multipath deviation covariance matrix of the target.
7. The angle measurement method based on frequency diversity technology according to claim 6, characterized in that, The expression for the objective function model is as follows; （16） In the formula, Represents the objective function model. This represents the target elevation angle measurements at all frequencies. Indicates the target The weight vector corresponding to each frequency point Indicates the first The weight of each frequency point.
8. The angle measurement method based on frequency diversity technology according to claim 7, characterized in that, The objective function model is solved based on the relationship between the target pitch angle measurement value and the noise vector and multipath deviation vector, combined with the noise covariance matrix and the multipath deviation covariance matrix, to obtain the optimal weight vector for all frequency points, including: The expressions for the target elevation angle measurements at all frequencies are as follows: （17） In the formula, This represents the target elevation angle measurements at all frequencies. , This represents the true vector of the target pitch angle. Indicates the first The true value of the target pitch angle at each frequency point Represents the multipath deviation vector. Indicates the first Multipath bias at each frequency point Represents the noise vector. Indicates the first Noise at each frequency point; The expression for the optimal weight vector for all frequency points is as follows: （18） In the formula, This represents the optimal weight vector for all frequency points. This represents the target noise covariance matrix for all frequency points.
9. The angle measurement method based on frequency diversity technology according to claim 8, characterized in that, The expression for the optimal estimate of the target pitch angle is as follows; （19） In the formula, This represents the optimal estimate of the target pitch angle.