A ris-assisted radar non-line-of-sight and difference beam angle measurement method

Abstract

The application discloses a RIS-assisted radar non-line-of-sight and difference beam angle measurement method, and belongs to the technical field of radars, which comprises the following steps: transmitting a signal to a target to be measured in a line of sight through a transmitting station of a radar, and converting the transmitted signal into a scattered signal after scattering by the target to be measured; receiving the scattered signal of the target to be measured through a pre-set sum subarray and difference subarray of a RIS, corresponding to form echo signals in two modes of sum beam and difference beam, and guiding the echo signals in the two modes to different receiving stations respectively; the target to be measured is a non-line-of-sight target of the two receiving stations of the radar; receiving the corresponding echo signals through the two receiving stations of the radar respectively, and calculating a ratio of the echo signals; substituting the ratio of the echo signals into a pre-designed and saved angle judgment curve to solve the target angle to be measured, and the target angle to be measured is the azimuth angle of the target to be measured relative to the RIS. The application can solve the problem that a single pulse cannot be used to realize angle measurement of a RIS-assisted radar in a non-line-of-sight state.

Description

Technical Field

[0001] This invention relates to the field of radar technology, and in particular to a non-line-of-sight sum-difference beam angle measurement method for RIS-assisted radar. Background Technology

[0002] In non-line-of-sight (N-LoS) radar detection scenarios, obstructions exist between the radar and the target, and there is no direct propagation path between the transceiver antenna and the target, making it difficult for traditional radars to effectively detect targets and measure angles. Therefore, achieving high-precision angle estimation under non-line-of-sight conditions is a crucial problem that urgently needs to be solved in the field of radar detection. For non-line-of-sight detection, existing radar systems can employ a multi-station network approach, using multiple spatially distributed transceiver stations to work collaboratively for joint target localization. However, multi-station radar systems have high deployment costs, require precise synchronization and data transmission between stations, and often face difficult-to-meet deployment conditions in practical applications, resulting in significant system complexity.

[0003] Reconfigurable smart surfaces (RIS), as a two-dimensional planar array composed of a large number of passive electromagnetic units, can dynamically reconfigure wireless propagation channels to achieve directional control of electromagnetic beams with low energy consumption. Deploying RIS in radar detection scenarios allows them to bypass obstructions and reach targets by reflecting radar signals, providing a new technical approach for single radars to achieve non-line-of-sight detection.

[0004] However, in non-line-of-sight detection using RIS-assisted radar, the unknown target azimuth makes it difficult to obtain channel information from the RIS to the target, thus hindering the optimization of the RIS reflection phase configuration. This presents a dilemma: target angle information is needed to optimize the RIS phase shift so that the reflected beam is aligned with the target, while the optimized phase shift is also required to estimate the target angle.

[0005] In existing solutions, the accuracy of codebook search methods is limited by codebook resolution, while direction-of-arrival (DOA) estimation methods require multiple pulses to obtain stable results. Single-pulse sum-difference beamforming, a mature instantaneous angle measurement technology in phased array radar, calculates the target angle within a single pulse by comparing the amplitude ratio of the received sum and difference beam signals and combining it with the angle discrimination curve, offering advantages such as high accuracy and fast response. However, due to the lack of signal storage and digital processing capabilities in the RIS (Radio Frequency Identification) system, the RIS can only configure one phase distribution instantaneously and can only generate a single-mode reflected beam at any given moment, unable to simultaneously generate sum and difference beams. If the sum and difference beams are generated sequentially through time-division scanning, at least two pulses are required, losing the instantaneous advantage of single-pulse sum-difference beamforming. Therefore, the sum-difference beamforming method of phased array radar cannot be directly applied. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a sum-difference beam angle measurement method for non-line-of-sight radar using RIS-assisted radar, thereby solving the problem that angle measurement under non-line-of-sight conditions using RIS-assisted radar cannot be achieved using a single pulse.

[0007] To solve the above-mentioned technical problems, the present invention is implemented using the following technical solution:

[0008] This invention provides a non-line-of-sight sum-difference beam angle measurement method for RIS-assisted radar, comprising:

[0009] The radar transmits a signal to the target within line of sight through its transmitting station. The transmitted signal is then scattered by the target and converted into a scattered signal.

[0010] The radar receives the scattered signal from the target by using a pre-set sum and difference subarray of the RIS, which forms echo signals in two modes: sum beam and difference beam. The echo signals of the two modes are then directed to different receiving stations. The target is a non-line-of-sight target of the two receiving stations of the radar.

[0011] The radar receives the corresponding echo signals from two receiving stations and calculates the echo signal ratio.

[0012] The echo signal ratio is substituted into a pre-designed and saved angle discrimination curve to calculate the target angle to be measured, which is the azimuth angle of the target to be measured relative to the RIS.

[0013] The aforementioned RIS-assisted radar non-line-of-sight sum and difference beam angle measurement method pre-sets the sum and difference subarrays of the RIS, including:

[0014] Construct the sum and difference subarrays of RIS;

[0015] The system receives the scattered signal in the preset wavefront direction by using a sum subarray and a difference subarray, and performs null design on the sum subarray and difference subarray based on the scattered signal in the preset wavefront direction to obtain the optimal reflection phase of each subarray in the preset wavefront direction; the null design is used to suppress mutual interference between the two subarrays.

[0016] Based on the scattering signal with a preset wave position direction, and the optimal reflection coefficients of the sum and difference subarrays with preset wave position directions, the amplitude distribution of the sum and difference subarrays is designed to obtain the final reflection coefficients of each subarray with a preset wave position direction.

[0017] The aforementioned RIS-assisted radar non-line-of-sight sum and difference beam angle measurement method, wherein constructing the sum and difference subarrays of the RIS includes:

[0018] Each element of the RIS linear array is numbered sequentially to obtain odd and even elements;

[0019] The odd and even elements of the RIS linear array are divided into sum subarrays and difference subarrays, with the RIS center serving as the geometric and phase center of the sum and difference subarrays.

[0020] The aforementioned RIS-assisted radar non-line-of-sight sum and difference beam angle measurement method and the null design objective of the subarray are: to obtain unity gain in the direction of the sum beam receiving station and to generate a deep null in the direction of the difference beam receiving station;

[0021] The null design goal of the difference subarray is to achieve unity gain in the direction of the difference beam receiver and generate a deep null in the direction of the sum beam receiver.

[0022] The process of obtaining the optimal reflection phase of the subarray's preset wavefront direction includes:

[0023] Based on the scattering signal in the preset wavefront direction and the null design target of the subarray, the reflection coefficient of the subarray is... The optimization problem is set as follows:

[0024] ,

[0025] In the formula, This represents the value of the variable that makes the function reach its minimum. Indicates constraints; Represents the reflection coefficient of the subarray. yes A dimensional vector; The number of elements in the summation array; The preset weighting factors, ; This represents the conjugate transpose operation; and These are the joint steering vector of the desired main lobe direction of the reflected beam and the joint steering vector of the desired null direction, respectively, where the main lobe direction is the direction for obtaining unity gain; The square operation for the L2 norm; Indicates the transpose operation; For the first and second formation The amplitude of the reflection coefficient corresponding to each array element Indicates the index of the array element in the subarray;

[0026] The joint steering vector of the reflected beam and the desired main lobe direction. And the joint steering vector of the beam's reflected beam and the desired null direction. The calculation formula is as follows:

[0027] ,

[0028] In the formula, The direction of departure angle from the subarray to the beam receiving station The guiding vector; This indicates the element-wise conjugate operation; For Hadamard product operations; To receive the preset wave position direction of the subarray The guiding vector; The departure angle direction from the subarray to the difference beam receiving station The guiding vector; express and yes A dimensional vector;

[0029] Solve for the reflection coefficient of the subarray. The optimization problem is solved to obtain the optimal reflection coefficient of the subarray in the preset wave position direction. .

[0030] The aforementioned RIS-assisted radar non-line-of-sight sum-difference beam angle measurement method, the process of obtaining the final reflection coefficient of each subarray corresponding to the preset wavefront direction, includes:

[0031] The optimal reflection coefficients of the subarray in the preset wave position direction are weighted by using a Taylor window function to obtain the final reflection coefficients of the subarray in the preset wave position direction.

[0032] The optimal reflection coefficients of the subarray in the preset wave position direction are weighted by using a Bayesian window function to obtain the final reflection coefficients of the subarray in the preset wave position direction.

[0033] The aforementioned RIS-assisted radar non-line-of-sight sum and difference beam angle measurement method, wherein the receiver receives the scattered signal of the target under test through the pre-set sum and difference subarrays of the RIS, correspondingly forming echo signals in two modes: sum beam and difference beam, and directing the echo signals of the two modes to different receiving stations, includes:

[0034] The scattered signal of the target under test received by the subarray is processed by the final reflection coefficient of the subarray in the preset wave position direction to generate the sum beam signal of the target under test and guide it to the sum beam receiving station.

[0035] The scattered signal of the target under test received by the difference subarray is processed by the final reflection coefficient of the preset wave position direction of the difference subarray to generate the difference beam signal of the target under test and guide it to the difference beam receiving station.

[0036] The aforementioned RIS-assisted radar non-line-of-sight sum-difference beam angle measurement method, including the design process of the angle discrimination curve, comprises:

[0037] Based on the geometry of the sum subarray, the final reflection coefficient of the preset wave position direction of the sum subarray, and the radar operating wavelength, determine the sum beam pattern function of the preset wave position direction; based on the geometry of the difference subarray, the final reflection coefficient of the preset wave position direction of the difference subarray, and the radar operating wavelength, determine the difference beam pattern function of the preset wave position direction.

[0038] Multiple target offset angles are selected by scanning within the preset beam position direction and half-power beamwidth range, and the corresponding target angles are calculated; the target offset angle is the offset angle of the target angle relative to the preset beam position direction; the target angle is the azimuth angle of the target relative to the RIS; the target offset angle... Corresponding target angle The calculation formula is:

[0039] In the formula, Preset wave position direction;

[0040] Substitute each target angle into the sum beam pattern function and the difference beam pattern function respectively to obtain the corresponding sum beam pattern function amplitude and difference beam pattern function amplitude;

[0041] Calculate the difference and amplitude ratio corresponding to each target angle based on the sum beam pattern function amplitude and the difference beam pattern function amplitude;

[0042] Based on the target angle, the difference between the target angles and the amplitude ratio, and the sign of the target offset angle, the fitted angle identification curve is obtained; the sign of the target offset angle is the offset direction of the target angle relative to the preset wave position direction.

[0043] In the aforementioned RIS-assisted radar non-line-of-sight sum-difference beam angle measurement method, the difference and amplitude ratio corresponding to the target angle are: the amplitude of the difference and signal ratio corresponding to the target angle;

[0044] The target angle described by the angle curve Corresponding difference and signal ratio The calculation formula is:

[0045] ,

[0046] In the formula, It's from the perspective of the target; It is the difference beam pattern function; It is the beam pattern function; It is the imaginary unit; It is the propagation phase with the beam receiving station; It is the radar operating wavelength; It is the propagation phase of the differential beam receiving station; It is the distance from the RIS center to the beam receiving station; It is the distance from the RIS center to the differential beam receiving station.

[0047] The aforementioned RIS-assisted radar non-line-of-sight sum-difference beam angle measurement method determines the effective angle measurement range of the radar based on the fitting range of the angle discrimination curve: the effective angle measurement range of the sum-difference beam half-power beamwidth range in the preset beam position direction is the effective angle measurement range of the radar.

[0048] The aforementioned RIS-assisted radar non-line-of-sight sum-difference beam angle measurement method, wherein the target to be measured is within the effective angle measurement range of the radar; the step of substituting the echo signal ratio into a pre-designed and stored angle discrimination curve to calculate the target angle includes:

[0049] The echo signal ratio is the complex ratio of the received signals from the two receiving stations measured in practice. The amplitude and phase sign of the echo signal ratio are substituted into the pre-designed and saved angle discrimination curve to obtain the corresponding target offset angle. The target offset angle is added to the preset wave position direction, and the result is the measured target angle. The measured target angle is the azimuth angle estimate of the target under test relative to RIS.

[0050] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0051] The non-line-of-sight (LOS) sum and difference beam angle measurement method of the RIS-assisted radar in this embodiment enables the RIS to generate sum and difference beams simultaneously by pre-setting sum and difference subarrays on the RIS. This allows for instantaneous single-pulse angle measurement under non-line-of-sight conditions, solving the problem that single-pulse angle measurement cannot be achieved using the RIS-assisted radar under non-line-of-sight conditions.

[0052] This invention pre-sets the sum and difference subarrays of the RIS array; by dividing the RIS array into cross-distributed sum and difference subarrays, after the geometric structure is determined, null designs are performed on the sum and difference subarrays to suppress mutual interference between them, and the sum and difference beam amplitude distribution is designed to obtain the final reflection coefficients of the sum and difference subarrays in the preset wave position direction, thereby improving the accuracy of angle measurement of the target within the effective angle measurement range of the radar.

[0053] In addition, considering that RIS itself is low in cost, low in power consumption, and flexible in deployment, the RIS-assisted single-radar angle measurement method of the present invention reduces system complexity and deployment cost compared with multi-station radar networking schemes. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the process of non-line-of-sight sum-difference beam angle measurement of a RIS-assisted radar according to Embodiment 1 of the present invention;

[0055] Figure 2 This is a schematic diagram of an angle measurement scenario under non-line-of-sight conditions using a RIS-assisted radar according to Embodiment 2 of the present invention;

[0056] Figure 3 This is a schematic diagram of signal reception and reflection angles in a non-line-of-sight angle measurement scenario using a RIS-assisted radar according to Embodiment 2 of the present invention.

[0057] Figure 4 This is the amplitude pattern of the RIS receiving beam in Embodiment 2 of the present invention;

[0058] Figure 5 This is the amplitude pattern of the RIS reflected beam in Embodiment 2 of the present invention;

[0059] Figure 6 This is a schematic diagram of the angle discrimination curve obtained by the non-line-of-sight sum-difference beam angle measurement method of the RIS-assisted radar in Embodiment 2 of the present invention;

[0060] Figure 7 This is a schematic diagram of the change of the prediction residual with the target offset angle in Embodiment 2 of the present invention;

[0061] Figure 8 This is a schematic diagram illustrating the change of the overall absolute error of the target as a function of SNR in Embodiment 2 of the present invention;

[0062] Figure 9 This is a schematic diagram illustrating the change of the overall absolute error of the target as a function of the beam scanning angle in Embodiment 2 of the present invention;

[0063] Figure 10 This is a schematic diagram illustrating the change of absolute error with SNR when the number of elements in both subarrays increases in Embodiment 2 of the present invention.

[0064] Figure 11 This is a schematic diagram illustrating the change of absolute error with SNR when only the number of subarray elements is increased in Embodiment 2 of the present invention. Detailed Implementation

[0065] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments and specific features in the embodiments are detailed descriptions of the technical solution of the present application, rather than limitations thereof. In the absence of conflict, the embodiments and technical features in the embodiments can be combined with each other.

[0066] In this article, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0067] Example 1:

[0068] This invention provides a non-line-of-sight sum-difference beam angle measurement method for RIS-assisted radar, such as... Figure 1 As shown, it includes:

[0069] S1: The radar transmitter transmits a signal to the target within line of sight. The transmitted signal is then scattered by the target and converted into a scattered signal.

[0070] S2: The scattered signal of the target under test is received by the sum and difference subarrays pre-set by the RIS, and correspondingly the echo signals of the sum beam and the difference beam are formed. The echo signals of the two modes are directed to different receiving stations respectively. The target under test is a non-line-of-sight target of the two receiving stations of the radar.

[0071] S3: Receive the corresponding echo signals through the two receiving stations of the radar and calculate the echo signal ratio;

[0072] S4: Substitute the echo signal ratio into the pre-designed and saved angle discrimination curve to calculate the target angle to be measured, wherein the target angle to be measured is the azimuth angle of the target to be measured relative to RIS.

[0073] The non-line-of-sight angle measurement method of RIS-assisted radar in this embodiment enables the RIS to generate both sum and difference beams simultaneously by pre-setting sum and difference subarrays on the RIS, thus solving the problem that angle measurement under non-line-of-sight conditions using RIS-assisted radar cannot be achieved using a single pulse.

[0074] Example 2:

[0075] This embodiment is based on the same inventive concept as Embodiment 1, and describes the specific implementation of each step in Embodiment 1.

[0076] Before performing step S1, the following steps are included:

[0077] A Receiving Target (RIS) is set up within the common line-of-sight of the two receiving stations of the radar and their non-line-of-sight targets. The receiving channel from the non-line-of-sight target to the receiving station is constructed through the RIS. The radar includes one transmitting station and two separately arranged receiving stations. The non-line-of-sight target of the receiving station refers to the target to which there is no direct line-of-sight link.

[0078] The non-line-of-sight target to receiving station receiving channel refers to a system where two radar receiving stations are separately located and there is no direct line-of-sight link between the target and the receiving stations. The signal transmitted by the radar transmitting station is scattered by the target and received by the RIS, and then reflected by the RIS back to the two radar receiving stations.

[0079] like Figure 2The RIS-assisted radar non-line-of-sight angle measurement scenario shown is constructed using one transmitting station and two receiving stations of the radar, along with a RIS auxiliary device. It assumes the target is within the line-of-sight (LoS) range of the radar transmitting station, but outside the LoS range of the two receiving stations, i.e., a non-line-of-sight target for the radar receiving stations. The signal emitted by the radar transmitting station is scattered by the target, received by the RIS, and then directed to the two receiving stations respectively. Indicates the distance between the radar transmitting station and the target. Indicates the array element from the target to the RIS distance, , These represent the array elements from the two radar receiving stations to the RIS. distance, It is the number of an array element in the RIS. An array element refers to a reflection unit in the linear array of the RIS. All array elements are arranged in numerical order to form the linear array of the RIS.

[0080] In step S2, the sum and difference subarrays of the RIS are pre-set, including: constructing the sum and difference subarrays of the RIS, and setting the final reflection coefficient of each subarray corresponding to the preset wave position direction, as shown in steps SZ1 to SZ3:

[0081] SZ1: Construct the sum and difference subarrays of RIS;

[0082] Each element of the RIS linear array is numbered sequentially to obtain odd and even elements;

[0083] The odd and even elements of the RIS linear array are divided into sum subarrays and difference subarrays, with the RIS center serving as the geometric and phase center of the sum and difference subarrays. Odd and even elements refer to odd-numbered elements and even-numbered elements. In this embodiment, odd-numbered elements form the difference subarray, and even-numbered elements form the sum subarray, so that the two subarrays are spatially intersected and the RIS center serves as the geometric center of the sum and difference subarrays, as well as their phase center.

[0084] SZ2: It receives the target scattering signal in the preset wavefront direction through the sum subarray and the difference subarray, and performs null design on the sum subarray and the difference subarray based on the scattering signal in the preset wavefront direction to obtain the optimal reflection phase of each subarray in the preset wavefront direction; the null design is used to suppress the mutual interference between the two subarrays.

[0085] The null design goal of the sum-beam receiver is to achieve unity gain in the direction of the sum-beam receiver and generate a deep null in the direction of the difference-beam receiver.

[0086] The null design goal of the difference subarray is to achieve unity gain in the direction of the difference beam receiver and generate a deep null in the direction of the sum beam receiver.

[0087] Take the sum formation as an example:

[0088] LX1: Based on the scattering signal in the preset wavefront direction and the null design target of the subarray, the reflection coefficient of the subarray is... The optimization problem is set as follows:

[0089] ,

[0090] In the formula, This represents the value of the variable that makes the function reach its minimum. Indicates constraints; Represents the reflection coefficient of the subarray. yes A dimensional vector; The number of elements in the summation array; The preset weighting factors, ; This represents the conjugate transpose operation; and These are the joint steering vector of the desired main lobe direction of the reflected beam and the joint steering vector of the desired null direction, respectively, where the main lobe direction is the direction for obtaining unity gain; The square operation for the L2 norm; Indicates the transpose operation; For the first and second formation The amplitude of the reflection coefficient corresponding to each array element Indicates the index of the array element in the subarray;

[0091] The joint steering vector of the reflected beam and the desired main lobe direction. And the joint steering vector of the beam's reflected beam and the desired null direction. The calculation formula is as follows:

[0092] ,

[0093] In the formula, The direction of departure angle from the subarray to the beam receiving station The guiding vector, such as Figure 3 As shown, the departure angle direction of the beam receiving station. The angle between the line connecting the beam receiving station to the center of the RIS and the normal at the center of the RIS; This indicates the element-wise conjugate operation; For Hadamard product operations; To receive the preset wave position direction of the subarray The guiding vector, such as Figure 3 As shown, The angle between the preset wave position direction and the normal at the center of the RIS; The departure angle direction from the subarray to the difference beam receiving station The guiding vector, such as Figure 3 As shown, the direction of the difference beam receiving station The angle between the line connecting the differential beam receiving station to the center of the RIS and the normal at the center of the RIS is defined as 0 degrees. In this embodiment, the angle within 90 degrees clockwise is considered negative, and the angle within 90 degrees counterclockwise is considered positive.

[0094] LX2: Solving for the reflection coefficients of the subarray. The optimization problem is solved to obtain the optimal reflection coefficient of the subarray in the preset wave position direction. ;

[0095] The optimal reflection coefficient for the preset wavefront direction of the subarray is obtained by referring to steps LX1 and LX2. The process is followed to obtain the optimal reflection coefficient of the subarray in the preset wave position direction. .

[0096] SZ3: Based on the scattered signal at the preset wavefront direction, and the optimal reflection coefficients of the sum and difference subarrays at the preset wavefront directions, the amplitude distribution of the sum and difference subarrays is designed respectively to obtain the final reflection coefficients of each subarray at the corresponding preset wavefront direction; as shown in steps SZ31 and SZ32:

[0097] SZ31: Obtain the final reflection coefficients of the subarray in the preset wavefront direction, including:

[0098] The optimal reflection coefficients of the subarray in the preset wavefront direction are weighted using a Taylor window function to obtain the final reflection coefficients of the subarray in the preset wavefront direction. The calculation formula is: ,

[0099] In the formula, Let be the weight vector of the Taylor window function of the submatrix. for A dimensional vector;

[0100] The weight vector of the Taylor window function of the subarray is composed of the weight coefficients of the Taylor window function of all elements of the subarray. ;

[0101] ,

[0102] In the formula, For the first and second formation The weight coefficients of the Taylor window function for each array element; The desired number of side lobes with equal amplitude is predefined. The number indicating the equal-amplitude sidelobe; For the first The coefficients of the cosine series expansion terms of each equal-amplitude sidelobe; The number of elements in the summation array; Indicates the sequence number of the subarray element;

[0103] SZ32: Obtains the final reflection coefficients for the preset wavefront directions of the subarray, including:

[0104] The optimal reflection coefficients of the subarray in the preset wavefront direction are weighted using a Bayesian window function to obtain the final reflection coefficients in that direction. The formula for calculating the final reflection coefficients in the preset wavefront direction is as follows: ,

[0105] In the formula, Let be the weight vector of the Bayesian window function of the difference submatrix. for A dimensional vector;

[0106] The weight vector of the Taylor window function of the difference submatrix is ​​formed by the weight coefficients of the Bayesian window functions of all elements of the difference submatrix. ;

[0107] ,

[0108] In the formula, For the difference of the first piece The weight coefficients of the Bayesian window function for each array element; For the first The coefficients of the sine series expansion terms of each equal-amplitude sidelobe; The number of array elements in the subarray; Indicates the sequence number of the subarray element;

[0109] When performing angle measurement, step S2 includes:

[0110] The scattered signal of the target under test received by the subarray is processed by the final reflection coefficient of the subarray in the preset wave position direction to generate the sum beam signal of the target under test and guide it to the sum beam receiving station.

[0111] The scattered signal of the target under test received by the difference subarray is processed by the final reflection coefficient of the preset wave position direction of the difference subarray to generate the difference beam signal of the target under test and guide it to the difference beam receiving station.

[0112] The sum beam receiver is used to receive the reflected signals from the sum subarray, while the difference beam receiver is responsible for receiving the reflected signals from the difference subarray.

[0113] Step S4, the design process of the angle curve, includes:

[0114] H1: Determine the beam pattern function of the preset beam pattern direction based on the geometry of the subarray, the final reflection coefficient of the preset beam pattern direction of the subarray, and the radar operating wavelength.

[0115] Based on the geometric structure of the difference subarray, the final reflection coefficient of the preset wave position direction of the difference subarray, and the radar operating wavelength, the difference beam pattern function of the preset wave position direction is determined.

[0116] H2: Select multiple target offset angles within the preset beam position direction and half-power beamwidth range, and calculate the corresponding target angles; the target offset angle is the offset angle of the target angle relative to the preset beam position direction; the target angle is the azimuth angle of the target relative to the RIS, that is, the angle between the line connecting the target to the center of the RIS and the normal at the center of the RIS; target offset angle Corresponding target angle The calculation formula is:

[0117] In the formula, Preset wave position direction;

[0118] like Figure 3 As shown, the range of half-power beamwidth for the preset beam position direction is: , For half-power beamwidth;

[0119] H3: Substitute each target angle into the sum beam pattern function and the difference beam pattern function respectively to obtain the corresponding sum beam pattern function amplitude and difference beam pattern function amplitude;

[0120] H4: Calculate the difference and amplitude ratio corresponding to each target angle based on the sum beam pattern function amplitude and the difference beam pattern function amplitude; the difference and amplitude ratio corresponding to the target angle is: the amplitude of the difference and signal ratio corresponding to the target angle;

[0121] In this embodiment, since the receiving stations for the two beams are placed separately, the propagation phase from the RIS to the two receiving stations needs to be considered, therefore the target angle... Corresponding difference and signal ratio The calculation formula is:

[0122] ,

[0123] In the formula, It's from the perspective of the target; It is the difference beam pattern function; It is the beam pattern function; It is the imaginary unit; It is the propagation phase with the beam receiving station; It is the radar operating wavelength; It is the propagation phase of the differential beam receiving station; It is the distance from the RIS center to the beam receiving station; It is the distance from the RIS center to the differential beam receiving station;

[0124] H5: Based on the target angle, the difference and amplitude ratio corresponding to the target angle, and the sign of the target offset angle, a fitted angle identification curve is obtained; the sign of the target offset angle is the offset direction of the target angle relative to the preset wave position direction; the horizontal axis of the obtained angle identification curve is the target angle, and the vertical axis is the weighted result of the sign of the target offset angle with respect to the difference and amplitude ratio. The obtained angle identification curve is a function of the relationship between the target angle and the difference and amplitude ratio. Within the half-power beamwidth range of the preset wave position direction, the obtained angle identification curve is approximately linear, and the range of approximately linearity of the angle identification curve is the fitting range of the angle identification curve.

[0125] Based on the fitting range of the angle detection curve, the effective angle measurement range of the radar can be determined:

[0126] The range of the preset beam position direction and the half-power beamwidth is the effective angle measurement range of the radar, that is, the effective angle measurement range of the radar is: The target to be measured needs to be within the radar's effective angle measurement range in order to execute the angle measurement methods in steps S1 to S4 and obtain a relatively accurate angle measurement result. Changing the preset beam direction and the half-power beamwidth can obtain other effective angle measurement ranges and angle measurement accuracies.

[0127] Within the effective angle measurement range of the radar, when performing non-line-of-sight sum-difference beam angle measurement of the target under test using RIS-assisted radar, steps S1 to S3 are executed to obtain the echo signal ratio, which is the complex ratio of the received signals from the two receiving stations measured in practice.

[0128] Step S4 includes: substituting the amplitude and phase sign of the echo signal ratio into the pre-designed and saved angle discrimination curve to obtain the corresponding target offset angle; adding the target offset angle to the preset wave position direction; and obtaining the result as the measured target angle. The measured target angle is the azimuth angle estimate of the target under test relative to the RIS, specifically referring to the angle between the line connecting the target under test to the center of the RIS and the normal at the center of the RIS.

[0129] To verify the non-line-of-sight sum-difference beam angle measurement method of the RIS-assisted radar of the present invention, the following experiment was conducted:

[0130] In this embodiment, the RIS center is set at the origin of the coordinate system. The radar transmitting station is located at The location, and the beam receiving station are located at The differential beam receiving station is located at... At this point, assume the radar cross section (RCS) of the target UAV is... From this, the departure angle direction of the beam receiving station can be calculated. The angle is 20.86°, meaning the angle between the line connecting the sum beam receiver station to the center of the RIS and the normal at the center of the RIS is 20.86°. The departure angle direction of the difference beam receiver station is... The angle is -21.55°, meaning the angle between the line connecting the differential beam receiving station to the center of the RIS and the normal at the center of the RIS is -21.55°.

[0131] Experiment 1: Feasibility Analysis of RIS-Assisted Sum-Difference Beam Angle Measurement

[0132] Set the number of elements in the subarray. The number of elements in the subarray is 16. The preset wave position is 15. Set to -15°, weighting factor Set to 0.5 to pre-configure the sum and difference subarrays of the RIS.

[0133] Figure 4 The RIS was demonstrated to receive a preset wave position direction using a pre-set sum and difference subarray. The received beam pattern generated from the scattered signal shows that the main lobe direction of the sum beam and the center null direction of the difference beam both point accurately to the preset -15°.

[0134] Figure 5 It shows the signal from the preset wave position direction After incident, the radiation pattern of the RIS reflected beam shows that the subarray will... The signals from the directional beam converge and point at 20.86° in the direction of the sum beam receiving station, while forming a clear null at -21.55° in the direction of the difference beam receiving station, which meets the null design target of the sum subarray; the null at the center of the difference beam reflected by the difference subarray points in the direction of the difference beam receiving station, and forms a deep null in the direction of the sum beam receiving station, which meets the null design target of the difference subarray.

[0135] Figure 6 The blue dashed line in the image represents the preset wave position direction. The angle curve obtained above, The value is 6.37°. The horizontal axis represents the target angle obtained by adding the target offset angle to the preset beam position direction. The red solid line represents its half-power beamwidth. The results of linear fitting within the range. It can be seen that the angle curve is within... The good linearity within the range proves that the RIS-assisted radar non-line-of-sight sum-difference beam angle measurement method is theoretically feasible for achieving high-precision single-pulse angle measurement.

[0136] Experiment 2: Simulation of Angle Measurement Error Performance

[0137] The parameter settings are the same as in Experiment 1. Within the effective angular measurement range of the radar, 100 targets are randomly generated, and the distance from the targets to the RIS is within... Interval random distribution. 10,000 Monte Carlo experiments are conducted for each target, and the prediction residual is recorded for each experiment. The prediction residual is the predicted angle minus the true angle.

[0138] Figure 7 The results show that the average prediction residual of each target changes with the target offset angle when the signal-to-noise ratio (SNR) is 15dB: the closer the target is to the preset wave position direction of -15°, the smaller the residual; the greater the deviation, the larger the residual. This trend is mainly caused by the systematic error introduced by the linear fitting of the angle discrimination curve.

[0139] Figure 8 The curves showing the variation of mean absolute error (MAE) with SNR are presented. MAE refers to the result of averaging the absolute values ​​of the residuals. As SNR increases from -15dB to 20dB, the overall MAE of the target, represented by the red solid line, shows a monotonically decreasing trend, indicating that a high signal-to-noise ratio can effectively improve the accuracy of target angle measurement.

[0140] Figure 9 The average absolute error (AAR) is shown when the receiving beam scanning angle ranges from -45° to 45°. The AAR is smallest (approximately 1.03°) when the receiving beam is near 0°; the error increases to approximately 1.47° when scanning to ±45°, because the beamwidth widens at larger scanning angles. Therefore, changing the preset beam position will cause changes in the half-power beamwidth, primarily manifested as a wider beamwidth as the receiving beam deviates further from the center (0°), and a decrease in angle measurement accuracy.

[0141] Experiment 3: The Influence of RIS Array Element Size on Angle Measurement Error

[0142] Figure 10 The diagram illustrates the change in absolute error with SNR when the sizes of the sum and difference subarrays vary simultaneously: from -15dB to 20dB, all curves show a monotonically decreasing trend; for any given SNR, the larger the total number of array elements N, the lower the absolute error. For example, at SNR=0dB, the error corresponding to N=127 is approximately 1.8°, while the error corresponding to N=31 is higher than 7°. This intuitively demonstrates the positive effect of increasing the total number of array elements, i.e., increasing the array aperture size, on noise suppression and improved angle measurement accuracy.

[0143] Figure 11This study demonstrates the change in absolute error when only the number of difference subarray elements is increased, while the sum subarray remains fixed at 16 elements. The results show that simply increasing the size of the difference subarray effectively reduces the absolute error, and its performance in the high SNR region is close to that of the scheme that simultaneously increases two subarray elements. Notably, when the difference subarray size increases to more than 45 elements, the error rebounds. This is because the difference beamwidth is too narrow, smaller than the half-power beamwidth of the sum beam, causing the angle detection curve to no longer exhibit an approximately linear change within the main lobe range of the sum beam, thus increasing the prediction error. This finding indicates that by appropriately increasing the size of the difference subarray, excellent angle measurement performance can be achieved while controlling system complexity.

[0144] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0145] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0146] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0147] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0148] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A non-line-of-sight sum-difference beam angle measurement method for RIS-assisted radar, characterized in that, include: The radar transmits a signal to the target within line of sight through its transmitting station. The transmitted signal is then scattered by the target and converted into a scattered signal. The radar receives the scattered signal from the target by using a pre-set sum and difference subarray of the RIS, which forms echo signals in two modes: sum beam and difference beam. The echo signals of the two modes are then directed to different receiving stations. The target is a non-line-of-sight target of the two receiving stations of the radar. The radar receives the corresponding echo signals from two receiving stations and calculates the echo signal ratio. The echo signal ratio is substituted into a pre-designed and saved angle discrimination curve to calculate the target angle to be measured, which is the azimuth angle of the target to be measured relative to the RIS.

2. The RIS-assisted radar non-line-of-sight sum-difference beam angle measurement method according to claim 1, characterized in that, The sum and difference subarrays of the RIS are pre-defined, including: Construct the sum and difference subarrays of RIS; The system receives the scattered signal in the preset wavefront direction by using a sum subarray and a difference subarray, and performs null design on the sum subarray and difference subarray based on the scattered signal in the preset wavefront direction to obtain the optimal reflection phase of each subarray in the preset wavefront direction; the null design is used to suppress mutual interference between the two subarrays. Based on the scattering signal with a preset wave position direction, and the optimal reflection coefficients of the sum and difference subarrays with preset wave position directions, the amplitude distribution of the sum and difference subarrays is designed to obtain the final reflection coefficients of each subarray with a preset wave position direction.

3. The RIS-assisted radar non-line-of-sight sum-difference beam angle measurement method according to claim 2, characterized in that, The construction of the sum and difference subarrays of the RIS includes: Each element of the RIS linear array is numbered sequentially to obtain odd and even elements; The odd and even elements of the RIS linear array are divided into sum subarrays and difference subarrays, with the RIS center serving as the geometric and phase center of the sum and difference subarrays.

4. The RIS-assisted radar non-line-of-sight sum-difference beam angle measurement method according to claim 2, characterized in that, The null design goal of the sum-beam receiver is to achieve unity gain in the direction of the sum-beam receiver and generate a deep null in the direction of the difference-beam receiver. The null design goal of the difference subarray is to achieve unity gain in the direction of the difference beam receiver and generate a deep null in the direction of the sum beam receiver. The process of obtaining the optimal reflection phase of the subarray's preset wavefront direction includes: Based on the scattering signal in the preset wavefront direction and the null design target of the subarray, the reflection coefficient of the subarray is... The optimization problem is set as follows: ， In the formula, This represents the value of the variable that makes the function reach its minimum. Indicates constraints; Represents the reflection coefficient of the subarray. yes A dimensional vector; The number of elements in the summation array; The preset weighting factors, ; This represents the conjugate transpose operation; and These are the joint steering vector of the desired main lobe direction of the reflected beam and the joint steering vector of the desired null direction, respectively, where the main lobe direction is the direction for obtaining unity gain; Represents the square operation of the L2 norm; Indicates the transpose operation; For the first and second formation The amplitude of the reflection coefficient corresponding to each array element Indicates the index of the array element in the subarray; The joint steering vector of the reflected beam and the desired main lobe direction. And the joint steering vector of the beam's reflected beam and the desired null direction. The calculation formula is as follows: ， In the formula, The direction of departure angle from the subarray to the beam receiving station The guiding vector; This indicates the element-wise conjugate operation; For Hadamard product operations; To receive the preset wave position direction of the subarray The guiding vector; The departure angle direction from the subarray to the difference beam receiving station The guiding vector; express and yes A dimensional vector; Solve for the reflection coefficient of the subarray. The optimization problem is solved to obtain the optimal reflection coefficient of the subarray in the preset wave position direction. .

5. The RIS-assisted radar non-line-of-sight sum-difference beam angle measurement method according to claim 2, characterized in that, The process of obtaining the final reflection coefficients of each subarray corresponding to the preset wavefront direction includes: The optimal reflection coefficients of the subarray in the preset wave position direction are weighted by using a Taylor window function to obtain the final reflection coefficients of the subarray in the preset wave position direction. The optimal reflection coefficients of the subarray in the preset wave position direction are weighted by using a Bayesian window function to obtain the final reflection coefficients of the subarray in the preset wave position direction.

6. The RIS-assisted radar non-line-of-sight sum-difference beam angle measurement method according to claim 2, characterized in that, The method involves receiving the scattered signal from the target under test through a pre-set sum and difference subarray via a RIS, corresponding to the formation of echo signals in two modes: sum beam and difference beam. The echo signals of these two modes are then directed to different receiving stations, including: The scattered signal of the target under test received by the subarray is processed by the final reflection coefficient of the subarray in the preset wave position direction to generate the sum beam signal of the target under test and guide it to the sum beam receiving station. The scattered signal of the target under test received by the difference subarray is processed by the final reflection coefficient of the preset wave position direction of the difference subarray to generate the difference beam signal of the target under test and guide it to the difference beam receiving station.

7. The RIS-assisted radar non-line-of-sight sum-difference beam angle measurement method according to claim 2, characterized in that, The design process of the angle curve includes: Based on the geometry of the sum subarray, the final reflection coefficient of the preset wave position direction of the sum subarray, and the radar operating wavelength, determine the sum beam pattern function of the preset wave position direction; based on the geometry of the difference subarray, the final reflection coefficient of the preset wave position direction of the difference subarray, and the radar operating wavelength, determine the difference beam pattern function of the preset wave position direction. Multiple target offset angles are selected by scanning within the preset beam position direction and half-power beamwidth range, and the corresponding target angles are calculated; the target offset angle is the offset angle of the target angle relative to the preset beam position direction; the target angle is the azimuth angle of the target relative to the RIS; the target offset angle... Corresponding target angle The calculation formula is: In the formula, Preset wave position direction; Substitute each target angle into the sum beam pattern function and the difference beam pattern function respectively to obtain the corresponding sum beam pattern function amplitude and difference beam pattern function amplitude; Calculate the difference and amplitude ratio corresponding to each target angle based on the sum beam pattern function amplitude and the difference beam pattern function amplitude; Based on the target angle, the difference between the target angles and the amplitude ratio, and the sign of the target offset angle, the fitted angle identification curve is obtained; the sign of the target offset angle is the offset direction of the target angle relative to the preset wave position direction.

8. The RIS-assisted radar non-line-of-sight sum-difference beam angle measurement method according to claim 7, characterized in that, The difference and amplitude ratio corresponding to the target angle is: the amplitude of the difference and signal ratio corresponding to the target angle; Target Angle Corresponding difference and signal ratio The calculation formula is: ， In the formula, It's from the perspective of the target; It is the difference beam pattern function; It is the beam pattern function; It is the imaginary unit; It is the propagation phase with the beam receiving station; It is the radar operating wavelength; It is the propagation phase of the differential beam receiving station; It is the distance from the RIS center to the beam receiving station; It is the distance from the RIS center to the differential beam receiving station.

9. The RIS-assisted radar non-line-of-sight sum-difference beam angle measurement method according to claim 7, characterized in that, Based on the fitting range of the angle detection curve, the effective angle measurement range of the radar is determined: the range of the half-power beamwidth of the preset beam position direction is the effective angle measurement range of the radar.

10. The RIS-assisted radar non-line-of-sight sum-difference beam angle measurement method according to claim 9, characterized in that, The target to be measured is within the effective angle measurement range of the radar; the step of substituting the echo signal ratio into a pre-designed and stored angle discrimination curve to calculate the angle of the target to be measured includes: The echo signal ratio is the complex ratio of the received signals from the two receiving stations measured in practice. The amplitude and phase sign of the echo signal ratio are substituted into the pre-designed and saved angle discrimination curve to obtain the corresponding target offset angle. The target offset angle is added to the preset wave position direction, and the result is the measured target angle. The measured target angle is the azimuth angle estimate of the target under test relative to RIS.

Images