Compact range double-station RCS plane scanning test method and system

Abstract

The invention relates to the technical field of target scattering characteristic testing, in particular to a compact range double-station RCS plane scanning testing method and system. The system comprises a transmitting antenna, a double-cylindrical-surface reflecting surface module, a plane scanning frame, a receiving antenna, radio frequency receiving and transmitting equipment and a test computer. According to the method, a mode of combining single compact range plane wave irradiation and plane scanning near field receiving is adopted. The transmitting end forms a plane wave in a quiet zone through the double-cylinder compact range to irradiate a to-be-measured target; the receiving antenna is driven by the plane scanning frame to scan in a two-dimensional plane and acquire a target near-field bistatic scattering signal; and the test computer processes the signal based on a near-far field transformation algorithm, and performs inversion to obtain the far-field double-station RCS of the target. According to the method, a receiving end compact range is replaced by plane scanning, the system cost, complexity and site requirements are remarkably reduced, and the prominent problems that a traditional indoor double-station RCS test technology is difficult to implement and high in cost are solved.

Description

Technical Field

[0001] This invention relates to the field of target scattering characteristic testing technology, and in particular to a compact field bistatic RCS plane scanning test method and system. Background Technology

[0002] The radar cross-section (RCS) of a target is a key parameter characterizing its electromagnetic scattering properties. Ideal RCS measurements are based on far-field conditions, where both the incident and scattered waves are plane waves. Compact field techniques utilize reflecting surfaces to convert spherical waves generated by point sources into plane waves, thereby simulating far-field conditions within a limited indoor space. This technique has been widely applied to monostation RCS (transmitter-receiver co-location) measurements.

[0003] However, existing technologies have significant shortcomings in applications requiring bistatic RCS (transmit-receive-distributed) measurements. If a compacted field system is desired for indoor use, both the transmitter and receiver need a separate, high-precision compacted field system. Furthermore, to acquire RCS data at different bistatic angles, the receiver's compacted field system must be mobile. This approach suffers from the following drawbacks: First, it drastically increases system complexity and cost. The fabrication and calibration of high-precision reflectors are already very expensive; setting up two systems, with one mobile, is prohibitively costly. Second, achieving stable and precise movement of a large, precision reflector system presents significant engineering challenges. Finally, this approach places extremely stringent requirements on the spatial dimensions of the testing site, limiting its application scope.

[0004] Therefore, there is an urgent need for a solution that can be implemented in a conventional laboratory, is cost-effective, and can effectively complete bi-station RCS testing. Summary of the Invention

[0005] The purpose of this invention is to provide a compact field bistation RCS planar scanning test method and system, which solves the technical problems of complex system, high cost, difficult engineering implementation and high site requirements when using a dual compact field system for indoor bistation RCS testing in the prior art.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a compact field bistatic RCS planar scanning test method, which is implemented using a bistatic test system. The bistatic test system includes a transmitting antenna, a dual cylindrical reflector module, a planar scanning frame, a receiving antenna, radio frequency transceiver equipment, and a test computer. The method includes the following steps: Step S1: Place the target to be tested within the quiet zone of the dual cylindrical reflector module; Step S2: The radio frequency transceiver generates a radio frequency signal, which is radiated by the transmitting antenna to produce a spherical wave signal. After being reflected by the dual cylindrical reflector module, the spherical wave signal forms a plane wave in the quiet zone to illuminate the target under test. Step S3: Fix the receiving antenna on the planar scanning frame, and control the planar scanning frame to drive the receiving antenna to move in two dimensions within a predetermined planar area, so as to collect the near-field bistatic scattering signal of the target under test at different locations; Step S4: The near-field bistatic scattering signal is transmitted back to the test computer through the radio frequency transceiver. The test computer processes the near-field bistatic scattering signal based on the near-field-far-field transformation algorithm to obtain far-field bistatic scattering information, and then calculates the bistatic RCS of the target under test.

[0007] Optionally, the radio frequency transceiver includes a 4-port vector network analyzer, a power amplifier, a directional coupler, a reference frequency conversion module, a photoelectric conversion module, and a radio frequency module; In step S2, generating the radio frequency signal specifically involves: The vector network analyzer transmits a signal through port 1, which is then radiated out sequentially through the power amplifier and the transmitting antenna. Simultaneously, a portion of the transmitted signal is coupled through the directional coupler, processed by the reference frequency conversion module, and then transmitted back to the vector network analyzer as a reference signal; The vector network analyzer transmits a signal through port 3. This signal is split into two paths by a power divider. One path serves as the local oscillator signal of the reference frequency conversion module, and the other path is transmitted through the photoelectric conversion module to the radio frequency module at the receiving antenna end, serving as the local oscillator signal of the radio frequency module.

[0008] Optionally, in step S3, the acquisition of the near-field bistatic scattering signal specifically involves: The horizontally polarized scattering signal is received through port 2 of the vector network analyzer as a measurement link; The vertically polarized scattering signal is received by using port 4 of the vector network analyzer as the measurement link.

[0009] Optionally, the b4 / a1 parameter of the vector network analyzer can be used as the measurement value of VV polarization, and the b2 / a1 parameter of the vector network analyzer can be used as the measurement value of HH polarization.

[0010] Optionally, in step S4, processing the near-field bistatic scattering signal based on the near-field-far-field transformation algorithm specifically includes: The received near-field bistatic scattering signal is represented as: (1) in: The one-way spherical wave factor; For wave number, , It is the wavelength of electromagnetic waves; These are the plane coordinates of the receiving antenna; The coordinates of the target scattering point; The target scattering coefficient distribution; Let be the distance from the scattering point to the receiving antenna, and its expression is as follows: The x-coordinate of the equivalent phase center of the transmitting antenna; In a three-dimensional rectangular coordinate system, equation (1) is written as equation (2): (2) in, Location of the transmit and receive antennas; Location of the scattering point; The Green's function in free space is as follows: (3) Equation (3) is expressed using the fundamental wave function in a rectangular coordinate system and substituted into the source point under the condition of an infinitely large uniform space. After integrating the scalar Helmholtz equation and simplifying, we get: (4) Substituting equation (4) into equation (1), we obtain the near-field and far-field transformation relationship: (5) According to equation (5) The far-field RCS is obtained by interpolating the mapping relationship; Transforming equation (5), the far-field RCS is expressed as: (6) Wherein, the transfer function is: .

[0011] In a second aspect, the present invention also provides a compact field bistationary RCS plane scanning test system for implementing the method described in any one of the first aspects, the system comprising: Transmitting antenna, used to radiate spherical wave signals; A dual-cylindrical reflector module is disposed in the radiation direction of the transmitting antenna to convert the spherical wave signal into a plane wave signal and form a quiet zone; A planar scanning frame, the scanning plane of which faces the quiet zone; A receiving antenna, fixed on the planar scanning frame, is used to move within the scanning plane under the drive of the planar scanning frame and to collect the near-field bistatic scattering signal of the target under test. A radio frequency transceiver, connected to the transmitting antenna and the receiving antenna, is used to generate a transmitted signal and receive the near-field bistatic scattered signal; A test computer is communicatively connected to the radio frequency transceiver equipment, used to control the planar scanning frame and the radio frequency transceiver equipment, and to process the near-field bistatic scattering signal to obtain the bistatic RCS.

[0012] Optionally, the dual-cylindrical reflector module includes a secondary reflector and a primary reflector arranged at a certain angle, used to convert the spherical wave signal into a plane wave signal and form a quiet zone after being reflected sequentially by the secondary reflector and the primary reflector.

[0013] Optionally, the receiving antenna is mounted on a liftable antenna tower, which is movably mounted on a horizontal track via a movable base or trolley.

[0014] Optionally, the radio frequency transceiver includes a 4-port vector network analyzer, a power amplifier, a directional coupler, a reference frequency converter module, a photoelectric conversion module, a radio frequency module, and a power divider; Port 1 of the vector network analyzer is connected in sequence to the power amplifier and the transmitting antenna; The directional coupler is used to couple the transmitted signal of port 1 to the reference frequency conversion module, and the output signal of the reference frequency conversion module is transmitted back to the vector network analyzer as a reference signal; Port 3 of the vector network analyzer is connected to the input of the power divider. One output of the power divider is connected to the reference frequency conversion module to provide a local oscillator signal, and the other output is connected to the radio frequency module of the receiving antenna through the photoelectric conversion module to provide a local oscillator signal. Ports 2 and 4 of the vector network analyzer are connected to the radio frequency module and are used to receive horizontally polarized scattering signals and vertically polarized scattering signals, respectively.

[0015] The above-described technical solution of the present invention has the following advantages: The compacted-field bistatic RCS planar scanning test method provided by this invention achieves synergy between plane wave illumination formed by a single compacted field and near-field signal acquisition by planar scanning, followed by far-field RCS acquisition through near-far-field transformation. Specifically, by replacing the second set of compacted fields required at the receiver end in traditional bistatic testing with a simpler planar scanning method, the system complexity and construction cost are significantly reduced. Simultaneously, since planar scanning requires far less longitudinal depth than far-field testing or movable compacted-field schemes, this method enables bistatic testing within the limited space of a conventional microwave anechoic chamber, greatly improving the method's site adaptability and engineering feasibility. More importantly, by employing a rigorous near-far-field transformation algorithm to invert the far-field RCS from the acquired near-field data, this fundamentally ensures that while achieving space compactness and cost control, the method still maintains the high accuracy necessary for metrology testing, effectively solving the prominent problem of existing technologies being difficult to widely apply due to system complexity, high cost, and demanding site requirements.

[0016] The compact-field bistatic RCS planar scanning test system provided by this invention mainly consists of a transmitting antenna, a dual-cylindrical reflector module, a planar scanning frame, a receiving antenna, RF transceiver equipment, and a test computer. The innovation of this system lies in its hybrid architecture of single compact-field transmission and planar scanning reception. By using a low-cost, precisely controlled planar scanning frame at the receiving end to replace the expensive and bulky movable receiving compact field in traditional solutions, it not only significantly reduces the system's hardware cost and complexity but also fundamentally solves the core engineering challenge of achieving stable and precise movement of large precision reflectors, greatly enhancing the system's reliability and engineering feasibility. Furthermore, this compact architecture significantly reduces the requirements for the longitudinal dimensions of the test site, making it better adaptable to existing standard microwave anechoic chambers and broadening the system's application range. Ultimately, this highly integrated system provides users with a complete, functional, easy-to-operate, and cost-effective indoor bistatic RCS test platform solution. Attached Figure Description

[0017] The accompanying drawings are provided for illustrative purposes only, and the proportions and quantities of the components in the drawings may not be consistent with the actual product.

[0018] Figure 1 This is a schematic diagram of a dual-cylinder compact field dual-station RCS planar scanning field in an embodiment of the present invention; Figure 2 This is a schematic diagram of the radio frequency transceiver link connection in an embodiment of the present invention.

[0019] In the picture: 10: Transmitting antenna; 20: Dual-cylindrical reflector module; 201: Primary reflector; 202: Secondary reflector; 30: Receiving antenna; 40: Retractable antenna tower; 50: Portable seat; 60: Horizontal guide rail; 100: The target being tested. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0021] like Figure 1 As shown in the embodiment of the present invention, a compact field bistatic RCS planar scanning test system is provided. The system includes a transmitting antenna 10, a dual cylindrical reflector module 20, a planar scanning frame, a receiving antenna 30, radio frequency transceivers, and a test computer.

[0022] The transmitting antenna 10 is used to radiate spherical wave signals. The dual cylindrical reflector module 20 is arranged in the radiation direction of the transmitting antenna 10 to convert the spherical wave signal into a plane wave signal and to form a quiet zone with uniform electromagnetic wave characteristics in front of it.

[0023] The planar scanning frame has its scanning plane facing the quiet zone. A receiving antenna 30 is fixed to the planar scanning frame and moves within the scanning plane under the movement of the frame to acquire the near-field bistatic scattering signal of the target under test. An RF transceiver is connected to the transmitting antenna 10 and the receiving antenna 30 to generate a transmitted signal and receive the near-field bistatic scattering signal. A test computer is communicatively connected to the RF transceiver and controls the planar scanning frame and the transceiver, and processes the near-field bistatic scattering signal to obtain the bistatic RCS.

[0024] In one specific implementation of this embodiment, the dual-cylindrical reflector module 20 includes a main reflector 201 and a sub-reflector 202 arranged at a certain angle. The signal emitted by the transmitting antenna 10 is first reflected by the sub-reflector 202 and then by the main reflector 201, forming a quiet zone with uniform electromagnetic wave characteristics in front of it.

[0025] In one specific implementation of this embodiment, the planar scanning frame includes a horizontal guide rail 60 and a movable base 50 movably mounted thereon. A liftable antenna tower 40 is mounted on the movable base 50. The receiving antenna 30 is fixedly mounted on the liftable antenna tower 40. Through the horizontal movement of the movable base 50 on the horizontal guide rail 60 and the vertical lifting movement of the liftable antenna tower 40, the receiving antenna 30 can perform precise scanning within a predetermined two-dimensional planar area. In another embodiment, a trolley capable of moving along a track can be used instead of the movable base 50.

[0026] See Figure 2 The radio frequency transceiver equipment includes a 4-port vector network analyzer, a power amplifier, a directional coupler, a reference frequency converter module, an optoelectronic conversion module, a radio frequency module, and a power divider.

[0027] Its specific connections and signal flow are as follows: Transmission link: Port 1 of the vector network analyzer is connected in sequence to the power amplifier and the transmitting antenna 10.

[0028] Reference Link: The directional coupler is used to couple the transmit signal of port 1 to the reference frequency conversion module. The output signal of the reference frequency conversion module is transmitted back to the vector network analyzer as a reference signal for accurately measuring the amplitude and phase characteristics of the transmit channel.

[0029] Local Oscillator Distribution Link: Port 3 of the vector network analyzer is connected to the input of the power divider. One output of the power divider is connected to the reference frequency converter module, providing it with a local oscillator signal; the other output is connected to the RF module at the receiving antenna 30 via the optoelectronic conversion module, providing it with a local oscillator signal. This design utilizes the advantages of low transmission loss and good phase stability of optical fiber to ensure the quality of the local oscillator signal at the remote receiver.

[0030] Receiving Links: Ports 2 and 4 of the vector network analyzer are connected to the output of the RF module, serving as measurement links for the horizontally polarized (H) and vertically polarized (V) scattering signals, respectively. In this example, by introducing a reference channel and fiber optic transmission of the local oscillator, the dynamic range, amplitude and phase measurement accuracy, and stability of the system are effectively improved. It can simultaneously support dual-polarization measurements, providing crucial hardware support for obtaining a high-precision bistatic scattering matrix of the target.

[0031] The method for testing using the above system includes the following steps: Step S1: Place the target to be tested within the quiet zone of the dual cylindrical reflector module; Step S2: The radio frequency transceiver generates a radio frequency signal, which is radiated by the transmitting antenna to produce a spherical wave signal. After being reflected by the dual cylindrical reflector module, the spherical wave signal forms a plane wave in the quiet zone to illuminate the target under test. Step S3: Fix the receiving antenna on the planar scanning frame, and control the planar scanning frame to drive the receiving antenna to move in two dimensions within a predetermined planar area, so as to collect the near-field bistatic scattering signal of the target under test at different locations; Step S4: The near-field bistatic scattering signal is transmitted back to the test computer through the radio frequency transceiver. The test computer processes the near-field bistatic scattering signal based on the near-field-far-field transformation algorithm to obtain far-field bistatic scattering information, and then calculates the bistatic RCS of the target under test.

[0032] This embodiment requires only one transmitting end compact field, and the receiving end uses a simple planar scanning frame, eliminating the need for an expensive and complex movable receiving compact field. The precision motion control technology of the planar scanning frame is mature, making it easy to move and position large reflective surfaces. The reduced longitudinal depth requirement of the laboratory makes it possible to conduct bistatic RCS testing in more existing sites. Through a rigorous near-field to far-field transformation algorithm, the acquired near-field scattering data is accurately converted into far-field RCS, theoretically ensuring the accuracy and reliability of the measurement results. This method saves space and cost without sacrificing its core accuracy as a metrological testing tool.

[0033] In one example, generating the radio frequency signal in step S2 specifically involves: A test signal is transmitted from port 1 of the vector network analyzer.

[0034] The signal is amplified sequentially by the power amplifier and then radiated through the transmitting antenna 10. Simultaneously, a portion of the transmitted signal is coupled through the directional coupler, processed by the reference frequency conversion module, and then transmitted back to the vector network analyzer as a reference signal.

[0035] In one example, the acquisition of near-field bistatic scattering signals in step S3 specifically involves: The horizontally polarized scattering signal is received via port 2 of the vector network analyzer as a measurement link.

[0036] The vertically polarized scattering signal is received via port 4 of the vector network analyzer as a measurement link.

[0037] The b4 / a1 parameters of the vector network analyzer are used as the measured values ​​for VV polarization. The b2 / a1 parameters of the vector network analyzer are used as the measured values ​​for HH polarization. This example provides a high-precision, high-stability RF transceiver scheme, ensuring measurement accuracy through a reference channel and fiber optic transmission of the local oscillator, and achieving synchronous acquisition of dual-polarization scattering information.

[0038] One example details the core algorithm executed on the test computer. The specific steps of the near-field and far-field transformation algorithm are as follows: Near-field signal modeling: Received near-field bistatic scattered signal Represented as: (1) in: The one-way spherical wave factor; For wave number, , It is the wavelength of electromagnetic waves; These are the plane coordinates of the receiving antenna; The coordinates of the target scattering point; The target scattering coefficient distribution; Let be the distance from the scattering point to the receiving antenna, and its expression is as follows: The x-coordinate is the equivalent phase center of the transmitting antenna.

[0039] The kernel function in equation (1) can be written in the form of a free-space Green's function: (2) in, Location of the receiving antenna; Location of the scattering point; (3) Equation (3) is expressed using the fundamental wave function in a rectangular coordinate system and substituted into the source point under the condition of an infinitely large uniform space. After integrating the scalar Helmholtz equation and simplifying, we get: (4) in, , , For wavenumber vector components.

[0040] Substituting equation (4) into equation (1), we obtain the near-field and far-field transformation relationship: (5) in, This is the far-field scattering information obtained after transformation.

[0041] According to equation (5) By interpolating the mapping relationship, the far-field RCS can be obtained.

[0042] Transforming equation (5), the far-field RCS can be expressed as the convolution of the near-field signal and the transfer function: (6) Among them, the transfer function of near-field transformation The definition of is: .

[0043] Any aspects of this invention not described in detail are common knowledge or prior art in the field.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that not every embodiment contains only one independent technical solution, and in the absence of conflict between solutions, the various technical features mentioned in each embodiment can be combined in any way to form other implementation methods that can be understood by those skilled in the art.

[0045] Furthermore, without departing from the scope of the present invention, modifications to the technical solutions described in the foregoing embodiments, or equivalent substitutions of some of the technical features, shall not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A compact range bistatic RCS planform scanning test method, characterized in that: The double-station test system comprises a transmitting antenna, a double-cylinder reflecting surface module, a plane scanning frame, a receiving antenna, a radio frequency transceiver device and a test computer; The method comprises the following steps: Step S1: placing a target to be tested in a quiet zone of the double-cylinder reflecting surface module; Step S2: generating a radio frequency signal by the radio frequency transceiver device, radiating a spherical wave signal out of the transmitting antenna, and forming a plane wave in the quiet zone after the spherical wave signal is reflected by the double-cylinder reflecting surface module to irradiate the target to be tested; Step S3: fixing the receiving antenna on the plane scanning frame, controlling the plane scanning frame to drive the receiving antenna to move in two dimensions in a predetermined plane area to collect near-field double-station scattering signals of the target to be tested at different position points; Step S4: returning the near-field double-station scattering signals to the test computer through the radio frequency transceiver device, processing the near-field double-station scattering signals based on a near-far field transformation algorithm by the test computer to obtain far-field double-station scattering information, and then calculating the double-station RCS of the target to be tested.

2. The method of claim 1, wherein: The radio frequency transceiver device comprises a 4-port vector network analyzer, a power amplifier, a directional coupler, a reference frequency conversion module, an optoelectronic conversion module and a radio frequency module; In step S2, the radio frequency signal is generated in the following manner: Port 1 of the vector network analyzer transmits a signal, which is radiated out of the transmitting antenna through the power amplifier in sequence; Meanwhile, a part of the transmitted signal is coupled through the directional coupler and transmitted back to the vector network analyzer as a reference signal after being processed by the reference frequency conversion module; Port 3 of the vector network analyzer transmits a signal, which is divided into two paths through a power divider, one path serving as a local oscillator signal of the reference frequency conversion module, and the other path being transmitted to the radio frequency module at the receiving antenna end through the optoelectronic conversion module as a local oscillator signal of the radio frequency module.

3. The method according to claim 2, wherein: In step S3, the near-field double-station scattering signals are collected in the following manner: Port 2 of the vector network analyzer is used as a measurement link to receive a horizontally polarized scattering signal; Port 4 of the vector network analyzer is used as a measurement link to receive a vertically polarized scattering signal.

4. The method of claim 3, wherein: The b4 / a1 parameter of the vector network analyzer is measured as a measurement value of the VV polarization, and the b2 / a1 parameter of the vector network analyzer is measured as a measurement value of the HH polarization.

5. The method of claim 1, wherein: In step S4, the near-field double-station scattering signals are processed based on the near-far field transformation algorithm in the following manner: The received near-field double-station scattering signals are expressed as: （1） Wherein: is the single-pass spherical wave factor; is the wave number, , is the electromagnetic wave length; to receive antenna planar coordinates; Target scatter point coordinates; target scatter coefficient distribution; is the distance from the scattering point to the receiving antenna, whose expression is as follows: x coordinate of the equivalent phase center for the transmit antenna In a three-dimensional rectangular coordinate system, equation (1) is written as equation (2) below: （2） wherein is a receive antenna position; is a scatterer position; For the free-space Green's function, we have: （3） The formula (3) is expressed by the basic wave function in the rectangular coordinate system and is brought into the scalar Helmholtz equation of the source point under the condition of the infinite uniform space, and then is integrated to obtain the following formula after arrangement: （4） The near-far field transformation relationship is obtained by substituting equation (4) into equation (1): （5） The far-field RCS is obtained by interpolating the mapping relationship of formula (5) , Equation (5) is transformed, and the far-field RCS is expressed as: （6） Wherein, the transfer function: 。 6. A compact range bistatic RCS planform scanning test system characterized by: The system is used to implement the method according to any one of claims 1 to 5, and the system comprises: a transmitting antenna for radiating a spherical wave signal; A double-cylinder reflecting surface module is arranged in the radiation direction of the transmitting antenna, and is used to convert the spherical wave signal into a plane wave signal and form a quiet zone. A plane scanning frame, whose scanning plane faces the quiet zone; A receiving antenna is fixed on the plane scanning frame, and is used to move in the scanning plane under the drive of the plane scanning frame, and collect the near-field bistatic scattering signal of the target to be measured; A radio frequency transceiver device is connected with the transmitting antenna and the receiving antenna, and is used to generate a transmitting signal and receive the near-field bistatic scattering signal; A test computer is connected with the radio frequency transceiver device, and is used to control the plane scanning frame and the radio frequency transceiver device, and process the near-field bistatic scattering signal to obtain the bistatic RCS.

7. The system according to claim 6, wherein: The double-cylinder reflecting surface module comprises a sub-reflector and a main reflector arranged at an angle, and is used to convert the spherical wave signal into a plane wave signal through the sub-reflector and the main reflector in sequence and form a quiet zone.

8. The system according to claim 6 or 7, wherein: The receiving antenna is installed on a liftable antenna tower, and the liftable antenna tower is movably installed on a horizontal rail through a moving base or a trolley.

9. The system according to claim 6, wherein: The radio frequency transceiver device comprises a 4-port vector network analyzer, a power amplifier, a directional coupler, a reference frequency conversion module, an optoelectronic conversion module, a radio frequency module and a power divider; Port 1 of the vector network analyzer is connected with the power amplifier and the transmitting antenna in sequence; The directional coupler is used to couple the transmitting signal of port 1 to the reference frequency conversion module, and the output signal of the reference frequency conversion module is transmitted back to the vector network analyzer as a reference signal; Port 3 of the vector network analyzer is connected with the input end of the power divider, one output end of the power divider is connected with the reference frequency conversion module to provide a local oscillator signal, and the other output end is connected with the radio frequency module at the end of the receiving antenna through the optoelectronic conversion module to provide a local oscillator signal; Port 2 and port 4 of the vector network analyzer are connected with the radio frequency module, and are used to receive horizontal polarization scattering signals and vertical polarization scattering signals, respectively.

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