A precise RCS measurement method for small angles using a single-transmitter, multi-receiver cylindrical wave circular sparse array for local scanning

Abstract

The present invention provides a precise, small-angle RCS measurement method using a single-transmitter, multiple-receiver cylindrical wave circular sparse array for local scanning. This method addresses the RCS testing requirements of large-scale stealth aircraft. These targets are large, with their lateral dimensions much greater than their height, easily meeting far-field conditions in the height direction. Cylindrical wave circular scanning is used to conduct RCS testing in the near field, and then near-to-far-field conversion is used to obtain the target's far-field RCS. Compared to outdoor and compact field measurements, this method does not require plane wave simulation, is not restricted by target size, and has low site requirements. It also achieves comparable accuracy to compact field measurement systems, making it suitable for testing full-scale targets.

Description

Technical Field

[0001] The present invention relates to the field of scatterometry technology, and more particularly to a method for accurately measuring small-angle RCS using a single-transmitter-multiple-receiver (SIMO) cylindrical wave circular sparse array local scanning. Background Art

[0002] With the development of fields such as communications, radar, and defense, the demand for measuring the scattering characteristics of large targets such as aircraft, satellites, and ships continues to grow. Traditional far-field and compact-field measurements struggle to meet the required test distances. Near-field measurement effectively overcomes this shortcoming and offers unique advantages such as high precision, high confidentiality, and all-weather operation. Therefore, the near-field RCS measurement methods, measurement accuracy, and the near-field to far-field transformation for large targets are currently important research topics.

[0003] Radar Cross Section (RCS) is an important characteristic parameter reflecting the electromagnetic characteristics of a target and is also one of the important indicators for evaluating the stealth performance of a target. The methods for studying target RCS mainly include theoretical analysis and measurement technology. Among them, measurement technology is the most effective, fast and accurate means. Generally speaking, the minimum test distance for far-field measurement is R min =2D 2 / λ, where D is the maximum size of the target aperture and λ is the wavelength of the signal. As target size increases and operating frequencies rise, far-field measurement conditions become increasingly difficult to meet. The required test distance may reach several kilometers or even tens of kilometers. Furthermore, the complex electromagnetic environment of the test site significantly impacts measurement accuracy, making it difficult to guarantee test accuracy. Similarly, when measuring large targets, a compact field struggles to meet test environment requirements. Research on near-field measurement methods began abroad in the 1950s. Near-field measurements are often performed in microwave anechoic chambers, eliminating the need to meet far-field measurement conditions and overcoming the impact of the measurement site and external electromagnetic interference on measurement accuracy.

[0004] my country's RCS near-field measurement technology started slightly later than its international counterparts, beginning in the late 1980s. Research into indoor and outdoor measurement techniques for various targets, including antenna RCS, led to the emergence of near-field measurement methods such as planar scanning, circular scanning, and spherical scanning. Starting in the 1990s, my country independently conducted research on topics such as the relationship between near-field and far-field scattering, errors in RCS measurements under non-far-field conditions, and corrections for near-field measurements. The research methods employed differed from those used abroad. For example, Professor He Guoyu of the Beijing University of Aeronautics and Astronautics, in the field of electromagnetic scattering, drew on three-antenna theory to derive a chain relationship between near-field scattering and far-field RCS, reaching the same conclusion. This chain relationship indicates that the Multiple Transmitter, Multiple Receiver (MIMO) approach requires complete bistatic information to accurately predict far-field RCS, which is difficult to achieve in engineering practice. The Single Transmitter, Multiple Receiver (SIMO) approach, on the other hand, uses only partial bistatic information to obtain far-field RCS, meeting accuracy requirements while also ensuring engineering feasibility. Summary of the Invention

[0005] To address the technical problem of difficulty in accurately measuring the RCS of large-scale multi-scattering targets, the present invention provides a method for accurately measuring small-angle RCS using a single-shot, multiple-receiver cylindrical wave circular sparse array for local scanning. This method adopts a single-shot, multiple-receiver (SIMO) circular array near-field measurement method and a near-to-far-field transformation algorithm based on the Hankel function. Only partial dual-station information is used to obtain the far-field measured RCS, achieving both accuracy requirements and engineering feasibility.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for accurately measuring small-angle RCS using a single-transmitter, multiple-receiver cylindrical wave circular sparse array local scanning method includes the following steps:

[0008] Step 1: Design the receiving antenna array layout within the local angular range during measurement. One transmitting antenna emits a fixed-frequency signal, and the receiving antenna array receives the echo signal reflected by the object under test. The simulation frequency is f = 300 MHz. The object under test is placed on a turntable and rotated. The single measurement rotation angle is within 2°, that is, the local angular range is 2°. The distance between the object under test and the transmitting antenna and the receiving antenna array is R = 70m. The angular interval between the receiving antenna array and the turntable is 0.5λ / R = 0.4°. Where λ is the wavelength of the transmitted signal.

[0009] Step 2: Process the echo signal in step 1 using a near-field to far-field variation algorithm to obtain accurate far-field RCS results within a small angle range.

[0010] Step 3: Keep the receiving antenna array layout in step 1 unchanged and continue to rotate the object under test. Repeat steps 1 and 2 until the object under test is rotated 360°. The far-field RCS measurement results of the object under test are obtained by data splicing.

[0011] Furthermore, in step 1, the angle range of the receiving antenna array is between 2° and 3°, that is, the number of antennas in the receiving antenna array is 5 to 7. For a symmetrical target to be measured, the receiving antenna array is only arranged on one side of the transmitting antenna, and the echo data corresponding to the other side of the transmitting antenna is obtained by the data obtained by the receiving antenna array through diagonal symmetry; the data is a two-dimensional matrix obtained by circular scanning of a single-transmitter multi-receiver cylindrical wave, wherein the row data represents different transmitting angles for the same receiving angle, and the column data represents different receiving angles for the same transmitting angle, and the data of the two-dimensional matrix is ​​symmetrical about the diagonal.

[0012] Furthermore, in step 2, the accurate far-field RCS result within the 2° local angle range reaches 1.6° to 2°.

[0013] Beneficial effects:

[0014] The above technical solution demonstrates that, compared to existing technologies, the present invention utilizes only partial dual-station information to obtain far-field RCS in indoor near-field measurements, effectively meeting accuracy requirements while also ensuring project feasibility. Compared to multiple-transmit, multiple-receive (MIMO) measurement methods, this method effectively shortens measurement time. Using dihedral, cylindrical, and double-sphere targets as examples, simulations demonstrate the feasibility of this measurement method for precise small-angle RCS measurement. By selecting an appropriate receiving antenna array layout, measurement accuracy can reach 1 dB. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the small-angle RCS precision measurement method using a single-transmitter, multiple-receiver cylindrical wave circular sparse array for local scanning;

[0016] Figure 2 This is a schematic diagram of dihedral angle target measurement according to the present invention;

[0017] Figure 3 The scattered field amplitude diagram obtained by scanning the dihedral target with a single-transmitter multi-receiver cylindrical wave circular sparse array;

[0018] Figure 4 The type and size diagram of the target being measured;

[0019] Figure 5 Exploring the angular separation between the transmitter and the nearest receiver using the average error (left) and maximum error (right) for dihedral targets;

[0020] Figure 6For a cylindrical target, the angular separation between the transmitting point and the nearest receiving point is explored using the average error (left) and maximum error (right).

[0021] Figure 7 Exploration of the angular separation between the transmitting point and the closest receiving point using the average error (left) and maximum error (right) for a dual-sphere target. DETAILED DESCRIPTION

[0022] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0023] The present invention provides a small-angle RCS precise measurement method for local scanning of a single-shot, multiple-receiver cylindrical wave circular sparse array, which adopts a single-shot, multiple-receiver (SIMO) circular sparse array near-field measurement method and a near-far-field transformation algorithm based on the Hankel function. Only partial dual-station information is used to obtain the far-field measurement RCS, which can meet the accuracy requirements while taking into account the feasibility of the project.

[0024] like Figure 1 As shown in Figure 2, the near-field to far-field conversion algorithm for single-transmitter multiple-receiver (SIMO) near-field measurement of RCS is:

[0025] According to the chain relationship, the scattering relationship between the transmitting and receiving antennas and the target is obtained:

[0026]

[0027] in, is the angle between the transmitting antenna and the target, is the angle between the receiving antenna and the target, represents the far-field scattering coefficient, represents the near-field scattering coefficient, represents the kernel function of the transmitting antenna, Represents the kernel function of the receiving antenna.

[0028] In actual measurement, the cylindrical wave irradiation is approximated, and the kernel function of the transmitting antenna is finally solved according to the cylindrical wave function as follows:

[0029]

[0030]

[0031] Among them, r t is the maximum size of the target, n0 is much smaller than kr t, λ is the wavelength of the transmitted signal, is the second kind 0th order Hankel function, is the second kind n-order Hankel function.

[0032] Since the transmitting and receiving antennas in the measurement system are reciprocal,

[0033] like Figure 2 As shown, the small-angle RCS precise measurement method of the present invention using a single-transmitter and multiple-receiver cylindrical wave circular sparse array for local scanning does not need to meet the far-field conditions and can obtain accurate far-field RCS within the allowable error range.

[0034] Since the target to be measured is very large and its lateral size is much larger than its height size, the far-field condition is easily satisfied in the height direction. Therefore, during near-field circular scanning measurement, the spherical wave emitted by the transmitting antenna can be approximated as a cylindrical wave irradiating the target; similarly, the receiving antenna array can also be approximated as a cylindrical wave receiving wave. The near-far-field transformation algorithm based on the Hankel function can be used to perform convolution transformation on the scattered field of the multi-scattering target to obtain the far-field RCS.

[0035] In circular scanning measurements, the target is placed on a turntable and can be rotated 360° for measurement. Therefore, it is only necessary to use the single-transmitter, multiple-receiver (SIMO) measurement method to first obtain the accurate far-field RCS after transformation within a small angle range. Then, through rotational measurement, the data is spliced ​​to obtain the far-field RCS after transformation within a 360° range.

[0036] Therefore, the small-angle RCS precise measurement method of the present invention using a single-transmitter-multiple-receiver cylindrical wave circular sparse array local scanning mainly includes the following steps:

[0037] Step 1: Based on the prior knowledge of the scattering characteristics of the target to be measured, the receiving antenna array layout within the local angle range during measurement is designed. One transmitting antenna sends a fixed frequency signal, and the receiving antenna array receives the echo signal reflected by the object to be measured. The simulation frequency is f = 300MHz, the object to be measured is placed on a turntable for rotation, the single measurement rotation angle is within 2°, the distance between the object to be measured and the transmitting antenna and the receiving antenna array is R = 70m, and the angular interval between the receiving antenna array and the turntable is 0.5λ / R = 0.4°. To ensure engineering feasibility, the receiving antenna array angle range is between 2° and 3°, that is, the number of antennas in the receiving antenna array is 5 to 7. For a symmetrical target to be measured, the receiving antenna array only needs to be arranged on one side of the transmitting antenna. The echo data corresponding to the other side of the transmitting antenna can be obtained by diagonally symmetric the receiving antenna array data, such as Figure 3As shown, taking the dihedral angle as an example, the scattered field amplitude in the figure is symmetric about the diagonal; the data is a two-dimensional matrix obtained by circular scanning of a single-transmitter multi-receiver cylindrical wave, wherein the row data represents different transmission angles for the same reception angle, and the column data represents different reception angles for the same transmission angle, and the data of the two-dimensional matrix is ​​symmetric about the diagonal.

[0038] Step 2: Process the echo signals within the local angle range using a near-far field variation algorithm to obtain an accurate far-field radar cross section (RCS) result within a small angle range. The local angle range is the measurement rotation angle of 2°, and the small angle range is an angle range less than 2°. According to simulation results, the accurate far-field radar cross section (RCS) result within the local angle range can reach 1.6° to 2°, that is, more than 80% of the radar cross section (RCS) results within the local angle range meet engineering requirements.

[0039] Step 3: Keep the receiving antenna array layout unchanged in step 1 and continue to rotate the object under test. Repeat steps 1 and 2 until the object under test is rotated 360°. By splicing the RCS data within the above small angle range, the far-field RCS measurement results of the object under test can be obtained at all angles.

[0040] To ensure engineering feasibility, the minimum angular spacing between the transmitting antenna and the receiving antenna array is selected in the appropriate receiving antenna array layout; the minimum angular spacing is 0.5λ / R=0.4°. Taking a cylinder as an example, Figure 6 As shown in the figure, when the local angle range of measurement is 0-40°, the minimum angular separation between the transmitting antenna and the receiving antenna array of the cylindrical target is 0.4°. This is the first receiving antenna array layout. When the local angle range of measurement is 40°-140°, the minimum angular separation between the transmitting antenna and the receiving antenna array of the cylindrical target is approximately 6°. This is the second receiving antenna array layout. When the local angle range of measurement is 140°-180°, the minimum angular separation between the transmitting antenna and the receiving antenna array of the cylindrical target is approximately 0.4°, which is the same as the first receiving antenna array layout. In other words, both sparse receiving antenna array layouts can accurately measure cylindrical targets within the corresponding angle ranges.

[0041] In order to verify the feasibility of the present invention, the measurement method is used to simulate and calculate three targets with multi-scattering characteristics: dihedral angle, cylinder and double sphere. The sizes of the three targets are as follows: Figure 4As shown in the figure, the lateral distance is greater than the longitudinal height. The long side of the dihedral angle is 10m, the short side is 3m, the cylinder diameter is 1m, the length is 10m, the double sphere diameter is 3m, and the distance between the two sphere centers is 6m. The test distance R = 70m, so that the target meets the far-field condition in terms of height. Therefore, the spherical wave irradiation can be approximated as cylindrical wave irradiation, and the near-far-field transformation algorithm based on the Hankel function can be used.

[0042] According to the present invention, first, a suitable sparse array layout range of receiving antennas is designed; according to engineering requirements, the length of the receiving array needs to be controlled between 2m and 3m, and the angular interval of the receiving antennas is 0.4°, thereby determining that the angular range of the receiving antenna array is approximately 2.4°.

[0043] After determining the receiving array layout, the array layout is kept unchanged, and the angular interval θ between the transmitting antenna and the nearest receiving antenna is varied between 0 and 90°, where the transmitting antenna scanning angle range is 0 to 180°. The average error and maximum error are used to evaluate the accuracy of the RCS obtained by the near-field and far-field transformation, respectively. The average error here refers to "for a scattering target, within a certain angle range (2°) and an angle interval θ, the average value of the error between the RCS simulated under far-field conditions and the far-field RCS transformed by the kernel function convolution under near-field conditions at the corresponding angle. The maximum error here refers to "for a scattering target, within a certain angle range (2°) and an angle interval θ, the maximum value of the error between the RCS simulated under far-field conditions and the far-field RCS transformed by the kernel function convolution under near-field conditions at the corresponding angle."

[0044] First, the single-transmitter, multiple-receiver (SIMO) circular array RCS near-field measurement method is used to explore the receiving array layout that minimizes the RCS error when the dihedral target is within the incident angle range of 0 to 180 degrees. The simulation results are as follows: Figure 5 As shown, the angular separation between the transmitting point and the nearest receiving point is explored using the average error (left) and maximum error (right) for dihedral targets.

[0045] Next, we explore the receiving array layout position that minimizes the RCS error when the cylindrical target is within the incident angle range of 0 to 180 degrees. The simulation results are as follows: Figure 6 As shown, the angular separation between the transmitting point and the nearest receiving point is explored using the average error (left) and maximum error (right) for a cylindrical target.

[0046] Finally, the receiving array layout position that minimizes the RCS error when the double-ball target is within the incident angle range of 0 to 180 degrees is explored. The simulation results are as follows Figure 7 As shown, the angular separation between the transmitting point and the nearest receiving point is explored using the average error (left) and maximum error (right) for a double-sphere target.

[0047] Figure 5 , Figure 6 , Figure 7 It can be seen that the minimum angular interval between the transmitting antenna and the receiving array of the dihedral target is approximately 4°, marked by an arrow; the minimum angular interval between the transmitting antenna and the receiving array of the cylindrical target is 0.4°, marked by an arrow; the minimum angular interval between the transmitting antenna and the receiving array of the double-sphere target is 0.4°, marked by an arrow.

[0048] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A small-angle RCS precision measurement method using a single-transmitter, multiple-receiver cylindrical wave circular sparse array local scanning, characterized in that: The steps include: Step 1: Design the receiving antenna array layout within the local angular range during measurement. One transmitting antenna emits a fixed-frequency signal, and the receiving antenna array receives the echo signal reflected by the object under test. The simulation frequency is f = 300 MHz. The object under test is placed on a turntable and rotated. The single measurement rotation angle is within 2°, that is, the local angular range is 2°. The distance between the object under test and the transmitting antenna and the receiving antenna array is R = 70m. The angular interval between the receiving antenna array and the turntable is 0.5λ / R = 0.4°. Where λ is the wavelength of the transmitted signal. Step 2: Process the echo signal in step 1 using a near-field to far-field variation algorithm to obtain accurate far-field RCS results within a small angle range. Step 3: Keep the receiving antenna array layout in step 1 unchanged and continue to rotate the object under test. Repeat steps 1 and 2 until the object under test is rotated 360°. The far-field RCS measurement results of the object under test are obtained by data splicing.

2. The small-angle RCS precision measurement method of a single-transmitter-multiple-receiver cylindrical wave circular sparse array local scanning according to claim 1 is characterized in that: In step 1, the angle range of the receiving antenna array is between 2° and 3°, that is, the number of antennas in the receiving antenna array is 5 to 7. For a symmetrical target to be measured, the receiving antenna array is only arranged on one side of the transmitting antenna, and the echo data corresponding to the other side of the transmitting antenna is obtained by the data obtained by the receiving antenna array through diagonal symmetry; the data is a two-dimensional matrix obtained by circular scanning of a single-transmitter multi-receiver cylindrical wave, wherein the row data represents different transmitting angles for the same receiving angle, and the column data represents different receiving angles for the same transmitting angle, and the data of the two-dimensional matrix is ​​symmetrical about the diagonal.

3. The small-angle RCS precision measurement method of a single-transmitter-multiple-receiver cylindrical wave circular sparse array local scanning according to claim 1 is characterized in that: In step 2, the accurate far-field RCS result within the 2° local angle range reaches 1.6° to 2°.

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