Three-dimensional imaging method based on three-point auxiliary antenna positioning

Abstract

The invention discloses a three-dimensional imaging method based on three-point auxiliary antenna positioning, and the method comprises the following steps: confirming a plurality of reference positions, and constructing an auxiliary positioning system; detecting a first detection distance with the reference position through the transmitting-receiving antenna, and confirming the coordinates of the transmitting-receiving antenna according to the auxiliary positioning system; in a preset imaging area, calculating a second detection distance between the transceiving antenna and each pixel point, and calculating phase compensation for each pixel point; receiving echo signals, and performing coherent accumulation on the echo signals under phase compensation to obtain an imaging result; according to the method, three reference scattering points with known positions are adopted, the distance information between the antenna and the three points is extracted through the radar system, the current antenna position is reversely deduced through the three-ball intersection point principle, the cost is lower, the system integration degree is higher, deployment flexibility is higher, and the method is particularly suitable for a dynamic trajectory compensation task in a limited site.

Description

Technical Field

[0001] This invention relates to the field of three-dimensional imaging technology, and more specifically to a three-dimensional imaging method based on three-point auxiliary antenna positioning. Background Technology

[0002] Since its emergence in the 1970s, stealth technology has continuously developed and expanded in the modern military field, with stealth aircraft becoming a crucial "weapon" in air combat due to their low detectability. Regular stealth performance assessments of in-service fighter jets are essential for maintaining their combat readiness and effectiveness. Compared to expensive and time-consuming flight testing, near-field static field testing, due to its high efficiency and controllability, has gradually become the preferred method for stealth testing of in-service aircraft.

[0003] In actual outdoor static field tests, fighter jets are typically mounted on foam supports or their own landing gear for radar scattering measurements. However, the scattering from the supports themselves and the landing gear often masks or interferes with the scattering signals from the aircraft itself. While traditional two-dimensional imaging methods can suppress some of the scattering from the supports, they struggle to fully reproduce the three-dimensional scattering details of the aircraft, failing to meet the demands of high-precision diagnostics. Therefore, three-dimensional imaging technology, with its comprehensive depiction of the spatial distribution of target scattering sources, has become the mainstream method for stealth performance evaluation.

[0004] In 3D imaging systems, to ensure image quality, large guide rails or vertical lifting frames are typically used in conjunction with turntable movement to achieve controllable synthesis of scanning geometry. However, due to limitations in equipment manufacturing precision, structural vibration stability, and external wind load disturbances, the actual trajectory of the antenna often deviates from the ideal path. This positional offset accumulates phase errors in the propagation path of the echo signal, leading to inaccurate phase compensation. Consequently, reconstruction algorithms such as back projection may fail to focus properly, resulting in blurry images or even complete image loss.

[0005] To obtain high-precision antenna positions, common positioning methods include laser tracking, encoder feedback, or inertial navigation systems. For example, a target sphere can be installed near the antenna probe, and three non-collinear fixed reference spheres can be deployed at the test site. A laser tracker measures the relative positions of the spheres to construct a local rigid coordinate system, which is then converted to global or test site coordinates to calculate the antenna position. While this method can achieve millimeter-level positioning accuracy, the required laser tracker and high-precision sensor equipment are expensive, and the deployment and calibration process is cumbersome, making it unsuitable for rapid outdoor testing.

[0006] Therefore, how to reduce the phase error caused by antenna position offset and improve the accuracy of three-dimensional image reconstruction and scattering source localization is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] In view of this, the present invention provides a three-dimensional imaging method based on three-point assisted antenna positioning, which can compensate for the phase error caused by antenna position offset, and improve the accuracy of three-dimensional image reconstruction and scattering source positioning.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A three-dimensional imaging method based on three-point assisted antenna positioning includes the following steps:

[0010] Multiple reference locations are identified, and an auxiliary positioning system is constructed; a first detection distance between the reference locations is detected using a transceiver antenna, and the coordinates of the transceiver antenna are confirmed based on the auxiliary positioning system;

[0011] Within a preset imaging area, the second detection distance between the transceiver antenna and each pixel is calculated, and the phase compensation for each pixel is calculated.

[0012] The echo signal is received and coherently accumulated under the phase compensation to obtain the imaging result.

[0013] Preferably, the steps of constructing the assisted positioning system include:

[0014] Construct antenna position constraints based on the first detection distance;

[0015] Under the antenna position constraints, the distance residuals between the transceiver antenna coordinates and each of the reference positions are calculated, and the transceiver antenna coordinates are confirmed by fitting the point with the minimum residual.

[0016] Preferably, the antenna position constraint is as follows:

[0017] M·p=b

[0018]

[0019] Where p represents the three-dimensional position coordinates of the antenna to be estimated in the global coordinate system, and the M matrix is ​​a 2×3 coefficient matrix composed of two sphere center difference vectors, used to construct the linearized distance relationship. b is the right-hand term vector, whose components are the combination of the sphere center norm difference and the squared difference of the measured distance.

[0020] Preferably, the point where the fitting residual is minimized is:

[0021]

[0022] Where p is the optimal coordinate of the transmit and receive antennas. Let i be the optimal value of the transmit / receive antenna coordinates, and let P be the variable representing the reference position. i Let d be the coordinates of the i-th reference position.i The first detection distance corresponds to the i-th reference position.

[0023] Preferably, the least squares method is used to fit the point with the minimum residual, and the optimal antenna coordinates are obtained as the transmit and receive antenna coordinates.

[0024] Preferably, the echo signal is coherently accumulated under the phase compensation, including:

[0025] s(x1,y1,z1)=∫∫∫E s (θ,f,z')e j2kd dθdfdz'

[0026] Where s(x1,y1,z1) is the scattering coefficient of the target pixel, E s (θ,f,z′) represents the echo signal, θ represents the relative angle between the transceiver antenna and the scanning target, f represents the step frequency, z′ represents the height of the transceiver antenna, k represents the wave number, d represents the second detection range, and e represents the wave number. j2kd This is the phase compensation factor.

[0027] Preferably, the second detection distance is:

[0028]

[0029] Where x1, y1, and z1 are the coordinates of the target point, and R is the horizontal distance between the transceiver antenna and the center of the target object.

[0030] A three-dimensional imaging system based on three-point assisted antenna positioning includes a vertical scanning guide rail, a transceiver antenna, a turntable, an imaging module, and multiple reference targets.

[0031] The reference target is located within the detection area of ​​the transceiver antenna; the turntable is used to place the target under test; the transceiver antenna is mounted on the vertical scanning guide rail; the transceiver antenna performs height scanning motion along the vertical scanning guide rail, so that the antenna collects backscattering data of the target at various angles on the cylindrical surface, thereby forming a multi-directional and multi-height data combination; the imaging module performs three-dimensional imaging based on the scanning data of the transceiver antenna on the reference target and the target under test.

[0032] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a three-dimensional imaging method based on three-point assisted antenna positioning. It uses three reference scattering points with known positions, extracts the distance information between the antenna and the three points through the radar system itself, and uses the principle of the intersection of three spheres to infer the current antenna position. It has lower cost, higher system integration and stronger deployment flexibility, and is particularly suitable for dynamic trajectory compensation tasks in restricted areas. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of a three-dimensional imaging method based on three-point auxiliary antenna positioning provided by the present invention.

[0035] Figure 2 This is a schematic diagram illustrating the principle of the auxiliary positioning model in this embodiment of the invention;

[0036] Figure 3 This is a schematic diagram of the equivalent model of the imaging model in an embodiment of the present invention;

[0037] Figure 4 This is an imaging effect diagram under error position compensation in an embodiment of the present invention;

[0038] Figure 5 This is an image showing the imaging effect under three-point positioning compensation in an embodiment of the present invention;

[0039] Figure 6 This is an image showing the imaging effect under correct position compensation in an embodiment of the present invention;

[0040] Figure 7 A schematic diagram of a three-dimensional imaging system based on three-point auxiliary antenna positioning provided by the present invention. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1

[0043] like Figure 1 This invention discloses a three-dimensional imaging method based on three-point assisted antenna positioning, comprising the following steps:

[0044] S1: Identify multiple reference locations and construct an auxiliary positioning system.

[0045] S2: Detect the first detection distance between the transmitting and receiving antennas and the reference position, and confirm the coordinates of the transmitting and receiving antennas based on the auxiliary positioning system.

[0046] S3: Within a preset imaging area, calculate the second detection distance between the transmitting and receiving antennas and each pixel, and calculate the phase compensation for each pixel. Within the preset imaging area, there is a set of pixels, which can be determined in advance through various physical parameters and is a known quantity.

[0047] S4: Receive the echo signal and coherently accumulate the echo signal under phase compensation to obtain the imaging result.

[0048] In this embodiment, the antenna position can be reversed based on the reference position and the auxiliary positioning system, thus significantly reducing the phase error caused by the antenna position offset, thereby improving the accuracy of three-dimensional image reconstruction and the accuracy of scattering source localization.

[0049] To further implement the above technical solution and construct an assisted positioning system, the steps include:

[0050] Construct an antenna position constraint based on the first detection distance; under the antenna position constraint, calculate the distance residual between the transceiver antenna coordinates and each reference position, and confirm the transceiver antenna coordinates by fitting the point with the minimum residual.

[0051] Specifically, taking three reference positions as an example, the principle of assisted positioning will be explained:

[0052] like Figure 2 The three reference positions are P A =(x A ,y A ,z A ), P B =(x B ,y B ,z B ) and P C =(x C ,y C ,z C The spatial coordinates are known a priori in the radar coordinate system. At each scanning moment, the antenna obtains its distances to three reference points at the current moment through range spectrum detection, denoted as dA, dB, and dC. At this time, each reference point can be regarded as a sphere center, and the distance value corresponds to the sphere radius, forming three spheres in three-dimensional space.

[0053] The three spheres can form the following system of equations:

[0054]

[0055] This set of equations describes the geometric constraints from the antenna point (x, y, z) to the boundary of the three spheres.

[0056] Simplifying the above system of equations, we get:

[0057] M·p=b

[0058] Where p represents the three-dimensional position coordinates of the antenna to be estimated in the global coordinate system. The M matrix is ​​a 2×3 coefficient matrix composed of two sphere center difference vectors, used to construct the linearized distance relationship. b is the right-hand side vector, whose components are a combination of the sphere center norm difference and the squared difference of the measured distance.

[0059] p = [x, y, z] T

[0060]

[0061] In theory, the intersection of the three spheres should uniquely determine the current location of the antenna, which can be solved by solving a system of linear equations. However, since this invention considers actual interference, the three spheres do not strictly intersect. In this case, the linear equations may have no real solutions, causing the analytical method to fail. Furthermore, it is extremely sensitive to errors and has poor robustness, therefore it cannot be solved directly.

[0062] To achieve assisted positioning, this invention proposes using a nonlinear least squares method as the positioning solution strategy. The position is estimated by fitting the point with the minimum distance residual between multiple antenna points and three reference points.

[0063]

[0064] Where p is the optimal transmit and receive antenna coordinates. Let i be the optimal value of the transmit and receive antenna coordinates, and let P be the variable representing the reference position. i Let d be the coordinates of the i-th reference position. i The first detection distance corresponds to the i-th reference position.

[0065] This method does not require analytical intersection points and always has a stable solution, which has stronger fault tolerance and engineering practical value. It is suitable for high-precision estimation of antenna trajectory in environments with certain errors in echo ranging and noisy environments.

[0066] To further implement the above technical solution, the imaging model is constructed as follows:

[0067] like Figure 3 The figure shows the equivalent model under cylindrical scanning. In the model, the target is stationary, and the antenna rotates around the target at various heights. The center of rotation is the center of the turntable where the target is located. The radius of the rotation number s(x,y,z) is the horizontal distance between the transmitting and receiving antenna and the turntable, which is represented by R in the figure.

[0068] Under this model, the change d in distance between the antenna and the target can be expressed as:

[0069]

[0070] The antenna performs a step scan along the vertical guide rail z′. At each scan point, the antenna emits an electromagnetic wave with a step frequency of f. Assuming the target position is (x1, y1, z1), the phase delay generated after the signal is reflected by the target is 2kd, where k is the wave number. The calculation formula is as follows, where c is the speed of light.

[0071]

[0072] Assuming the target's scattering coefficient is s(x,y,z), the signal received by the antenna on the scanning axis is:

[0073] E s (θ,f,z′)=∫∫∫s(x,y,z)e -j2kd dxdydz

[0074] With echo signal E s (θ,f,z′) is represented by a coherent cumulative imaging method. The corresponding echo signals are phase-compensated and then accumulated. Correct phase compensation aligns the echoes from each viewpoint from the true scattering point to the same imaging point (x1,y1,z1). Coherent accumulation produces high-brightness focusing, which can then represent the scattering coefficient of the target.

[0075] s(x1,y1,z1)=∫∫∫E s (θ,f,z')e j2kd dθdfdz'

[0076] The phase compensation factor for pixel (x1, y1, z1) in the coherent accumulation algorithm can be expressed as e j2kd d represents the geometric distance between the current antenna pose and the target point. This distance is confirmed through three-point positioning, thus representing the true position under jitter interference. The compensation factor based on this position ensures no phase compensation deviation during coherent accumulation, enabling multi-view echoes from the same scattering point to be completely in phase superimposed on three-dimensional pixels to achieve maximum focusing. Otherwise, if phase deviation exists, partial or complete cancellation will occur during accumulation, leading to decreased imaging brightness or the target becoming unfocused.

[0077] Next, experiments will be conducted to further demonstrate the effectiveness of this invention:

[0078] In the simulation verification process, a random perturbation term was introduced into the antenna's vertical position vector. Specifically, at each elevation point, a random jitter value of different amplitude was added to the three-dimensional position of the antenna coordinates. The perturbation distribution was Gaussian white noise with a mean of 0 and a standard deviation of 10 mm. The imaging dynamic range was set to 15 dB. The final imaging effects of three compensation methods were compared: compensation using an incorrect antenna position without jitter, compensation using a correctly positioned antenna after positioning, and compensation using a correctly positioned antenna with jitter. The results are shown below. Figure 4 , Figure 5 and Figure 6 As shown.

[0079] Comparing the imaging results under three methods—error compensation, three-point positioning compensation, and correct compensation—it can be observed that three-point positioning compensation is significantly better than the uncompensated scheme in terms of imaging quality, achieving near-ideal focusing capability and effectively restoring the target point source position and shape.

[0080] The target to be measured is placed on a turntable. Based on the maximum size D of the target space and the size of the measurement area, a suitable near-field measurement distance d is determined. Generally, the radiation near-field distance is considered to be... Where λ is the measurement wavelength. Three reference targets with known coordinates are placed outside the imaging area, and the distances between the three reference targets and the antenna must meet the following conditions:

[0081] The measurement equipment is configured with a single transmitter and receiver antenna, which is fixed in parallel at the same height on a vertical guide rail. The antenna is vertically raised and lowered along the guide rail to achieve sampling in the height direction. The sampling interval is determined by the frequency and imaging area range.

[0082] After the measuring equipment is configured, the transmitting antenna emits electromagnetic waves, and the receiving antenna receives electromagnetic waves. After the reception is completed, the turntable rotates at an angle interval and repeats the above electromagnetic wave transmission and reception process until the turntable completes the required azimuth angle measurement of the target.

[0083] This invention introduces three-point positioning during the imaging process, using the antenna coordinates derived from the intersection of the three spheres as the real-time position input. The propagation path length of the echo signal at each sampling position is recalculated, and the actual distance is used to replace the ideal distance for phase compensation. This eliminates the phase mismatch caused by trajectory deviation before coherent accumulation, thereby achieving high-precision focusing.

[0084] Compared with the traditional method of using a laser tracker in conjunction with multiple target spheres for spatial measurement, the three-point assisted positioning method proposed in this invention also utilizes the geometric principle of constructing coordinates from three spatial points. However, the difference lies in the following: laser measurement relies on high-precision external equipment to acquire the spatial coordinates of the reflecting spheres in real time and construct a rigid body coordinate system; while the method in this paper uses reference scattering points with known three-point positions, extracts the distance information between the antenna and the three points through the radar system itself, and uses the principle of the intersection of the three spheres to infer the current antenna position. This method has lower cost, higher system integration, and stronger deployment flexibility, and is particularly suitable for dynamic trajectory compensation tasks in confined spaces.

[0085] Example 2

[0086] like Figure 7 Based on the same inventive concept, this invention discloses a three-dimensional imaging system based on three-point auxiliary antenna positioning, including a vertical scanning guide rail, a transceiver antenna, a turntable, an imaging module, and multiple reference targets.

[0087] The reference target is within the detection area of ​​the transceiver antenna; the turntable is used to place the target under test; the transceiver antenna is mounted on a vertical scanning guide rail; the transceiver antenna moves along the vertical scanning guide rail to perform height scanning, so that the antenna collects backscatter data of the target at various angles on the cylindrical surface, thereby forming a multi-directional and multi-height data combination; the imaging module performs three-dimensional imaging based on the scanning data of the transceiver antenna on the reference target and the target under test.

[0088] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0089] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A three-dimensional imaging method based on three-point assisted antenna positioning, characterized in that, Includes the following steps: Multiple reference locations are identified, and an auxiliary positioning system is constructed; a first detection distance between the reference locations is detected using a transceiver antenna, and the coordinates of the transceiver antenna are confirmed based on the auxiliary positioning system; Within a preset imaging area, the second detection distance between the transceiver antenna and each pixel is calculated, and the phase compensation for each pixel is calculated. The echo signal is received and coherently accumulated under the phase compensation to obtain the imaging result.

2. The three-dimensional imaging method based on three-point assisted antenna positioning according to claim 1, characterized in that, The steps for constructing the assisted positioning system include: Construct antenna position constraints based on the first detection distance; Under the antenna position constraints, the distance residuals between the transceiver antenna coordinates and each of the reference positions are calculated, and the transceiver antenna coordinates are confirmed by fitting the point with the minimum residual.

3. The three-dimensional imaging method based on three-point assisted antenna positioning according to claim 2, characterized in that, The antenna position constraint is: M·p=b Where p represents the three-dimensional position coordinates of the antenna to be estimated in the global coordinate system, and the M matrix is ​​a 2×3 coefficient matrix composed of two sphere center difference vectors. A P B and P C Let be the coordinates of three different reference positions, used to construct a linearized distance relationship, and b be the right-hand term vector, whose components are the combination of the sphere center norm difference and the squared difference of the measured distance.

4. A three-dimensional imaging method based on three-point assisted antenna positioning according to claim 2 or 3, characterized in that, The point where the fitting residual is minimum is: Where p is the optimal coordinate of the transmit and receive antennas. Let i be the optimal value of the transmit / receive antenna coordinates, and let P be the variable representing the reference position. i Let d be the coordinates of the i-th reference position. i The first detection distance corresponds to the i-th reference position.

5. A three-dimensional imaging method based on point-assisted antenna positioning according to claim 4, characterized in that, The least squares method is used to fit the point with the minimum residual, and the optimal antenna coordinates are obtained as the transmit and receive antenna coordinates.

6. The three-dimensional imaging method based on three-point assisted antenna positioning according to claim 1, characterized in that, The echo signal is coherently accumulated under the phase compensation, including: s(x1,y1,z1)=∫∫∫E s (θ,f,z')ej 2kd dθdfdz' Where s(x1,y1,z1) is the scattering coefficient of the target pixel, E s (θ,f,z') represents the echo signal, θ represents the relative angle between the transceiver antenna and the scanning target, f represents the step frequency, z' represents the height of the transceiver antenna, k represents the wave number, d represents the second detection range, and e represents the wave number. j2kd This is the phase compensation factor.

7. A three-dimensional imaging method based on three-point assisted antenna positioning according to claim 6, characterized in that, The second detection distance is: Where x1, y1, and z1 are the coordinates of the target point, and R is the horizontal distance between the transceiver antenna and the center of the target object.

8. A three-dimensional imaging system based on three-point assisted antenna positioning, characterized in that, The three-dimensional imaging method described in any one of claims 1-7 is adopted, including a vertical scanning guide rail, a transceiver antenna, a turntable, an imaging module, and multiple reference targets; The reference target is located within the detection area of ​​the transceiver antenna; The turntable is used to place the target being measured. The transceiver antenna is mounted on the vertical scanning guide rail; the transceiver antenna performs height scanning motion along the vertical scanning guide rail, so that the antenna collects backscattered data of the target at various angles on the cylindrical surface, thereby forming a multi-directional and multi-height data combination; The imaging module performs three-dimensional imaging based on the scanning data of the reference target and the target under test from the transceiver antenna.

Images