Calibration method suitable for mechanical linear scanning SAR imaging system
By converting the two ports of the vector network analyzer into a single-port model and using time-domain gating technology, and calibrating with a large-size metal plate, the systematic error problem of the mechanical linear scanning SAR imaging system was solved, achieving high-precision data calibration and subsequent imaging testing.
Patent Information
- Application Number
- CN202610305774.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-13
- Publication Date
- 2026-05-15
AI Technical Summary
The systematic errors of mechanical linear scanning SAR imaging systems severely restrict measurement accuracy. Traditional methods are cumbersome and conflict with the working mode of scanning motion, making them impossible to implement during the scanning process and thus failing to guarantee measurement accuracy.
By converting the two ports of a vector network analyzer into a single-port model and incorporating time-domain gating technology, only free space and a large metal plate are needed as calibration loads to accurately solve and compensate for system errors.
Efficient data acquisition was achieved, and a new technology was established to apply the scan data, while attention was paid to the calibration methods implemented during the scanning process.
Smart Images
Figure CN122043387A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of image processing technology, and more specifically to a calibration method suitable for mechanical linear scanning SAR imaging systems. Background Technology
[0002] SAR imaging systems employing linear scanning achieve synthetic aperture through linear translation of the antenna and are widely used for near-field target scattering measurement and imaging. In a typical configuration, the transmit (Tx) antenna and receive (Rx) antenna are placed adjacent to each other and share a single fixture. The transmission parameter S is measured using a vector network analyzer (VNA). 21 To obtain target information.
[0003] However, the inherent errors of SAR imaging systems in line-scan mode severely limit measurement accuracy.
[0004] First, the system errors are complex and directly coupled into the measurement signal, mainly including: (1) spatial mutual coupling between the Tx and Rx antennas, forming a constant background signal independent of the target; (2) non-ideal frequency response of the RF link (cable, connector, antenna); and (3) antenna port impedance mismatch leading to multiple signal reflections. These error vectors are superimposed on the target echo, causing the original S... 21 Data distortion.
[0005] Secondly, traditional vector network analyzer calibration methods (such as SOLT) face fundamental challenges in this scenario. This method requires sequentially connecting multiple precision calibration components (open circuit, short circuit, load) to each test port, a cumbersome process that relies on precise mechanical connections and resets. This completely conflicts with the continuous or stepped movement required by mechanically scanned SAR antennas, making it impossible to implement during scanning. This forces actual testing to often be performed without system-level calibration, compromising measurement accuracy.
[0006] Finally, even when attempting partial calibration under static conditions, commonly used short-circuit calibration components (such as small metal plates) exhibit significant edge diffraction due to their limited size. This diffraction signal is recorded by the system as an error, making the calibration itself inaccurate and introducing secondary errors.
[0007] Therefore, there is an urgent need for a dedicated calibration method that can adapt to the dynamic working characteristics of mechanical scanning, is easy to operate, and can accurately isolate the above-mentioned systematic errors. Summary of the Invention
[0008] In view of the above problems, this invention is proposed to provide a calibration method suitable for mechanically linear scanning SAR imaging systems that overcomes or at least partially solves the above problems. This method is performed before testing. By equating the two-port measurement system to a single-port model and incorporating time-domain gating technology, it only requires free space and a large-size metal plate as the calibration load to accurately solve and compensate for the core system errors, providing a clean data foundation for subsequent high-precision imaging tests.
[0009] To achieve the above objectives, the present invention adopts the following technical solution:
[0010] In a first aspect, embodiments of the present invention provide a calibration method suitable for a mechanically linear scanning SAR imaging system, comprising the following steps: The transmission parameters between the two ports of the vector network analyzer are equivalent to the reflection measurement parameters of a single port, denoted as the equivalent reflection measurement parameters. A mathematical model including directional error, reflection tracking error and source matching error is established to determine the true equivalent reflection coefficient after eliminating systematic errors. Equivalent reflection measurement parameters are collected by the vector network analyzer in a free space region without reflection interference and under a large-size metal plate, respectively. The values of directional error, reflection tracking error and source matching error are determined by time-domain gating based on the two obtained equivalent reflection measurement parameters. The large-size metal plate is a metal plate that can cover the entire preset mechanical scanning angle and stroke range. By substituting the determined values of directional error, reflection tracking error, and source matching error into the mathematical model, the true equivalent reflection coefficient after eliminating systematic errors is obtained, thereby achieving the calibration of the mechanical linear scanning SAR imaging system.
[0011] Furthermore, the transmission parameters between the two ports of the vector network analyzer are obtained through the following steps: Connect the transmitting antenna to port 1 of the vector network analyzer, connect the receiving antenna to port 2 of the vector network analyzer, and firmly fix the transmitting end of the transmitting antenna and the receiving end of the receiving antenna together. The transmission parameters between port 2 and port 1 were measured using a vector network analyzer.
[0012] Furthermore, a mathematical model is established that includes directional error, reflection tracking error, and source matching error, specifically including the following mathematical model:
[0013] In the formula, S 11_M S represents the equivalent reflection measurement parameter. 11_A The true equivalent reflection coefficient after eliminating systematic errors; E _DTo characterize the directivity error of fixed mutual coupling between antennas and system leakage; E _R The reflection tracking error characterizes the system's frequency response; E _S The source matching error is used to characterize the mismatch of the equivalent port.
[0014] Furthermore, the large-size metal plate is made of a highly conductive material, including aluminum, copper, or brass.
[0015] Furthermore, based on the two obtained equivalent reflection measurement parameters, the values of the directivity error, reflection tracking error, and source matching error are determined through time-domain gating, specifically including: The two equivalent reflection measurement parameters obtained are converted into time-domain response signals respectively; Based on the time-domain response signal converted from the equivalent reflection measurement parameters under the large-size metal plate, the main signal and the expected time for the main signal to arrive at the receiving antenna are determined. The gating time of the time domain gate is determined based on the expected time, and the time domain response signals obtained from the two equivalent reflection measurement parameters are gated based on the gating time. The time-domain response signal after time-domain gating is converted into frequency-domain parameters to obtain the first gating frequency-domain parameters in the free space region and the second gating frequency-domain parameters in the large-size metal plate. Using the first gating frequency domain parameter as the equivalent reflection measurement parameter, the source matching error after time-domain gating is equivalent to 0, and the true equivalent reflection coefficient after eliminating system errors is set to 0 based on the matched load calibration condition. The directional error is obtained according to the mathematical model including directional error, reflection tracking error and source matching error: E _D = S 11_free_gated ; Among them, S 11_free_gated Indicates the frequency domain parameters of the first strobe; Using the second gating frequency domain parameter as the equivalent reflection measurement parameter, the source matching error after time-domain gating is equivalent to 0, and the true equivalent reflection coefficient after eliminating system errors is set to -1 based on the short-circuit load calibration condition. The relationship between the directivity error and the reflection tracking error is obtained from the mathematical model including the directivity error, reflection tracking error, and source matching error: ; Among them, S 11_metal_gated This represents the second strobe frequency domain parameter; The reflection tracking error is obtained based on the relationship between directional error and reflection tracking error.
[0016] Furthermore, the expected time for the main signal to arrive at the receiving antenna is obtained using the following formula: t _load = 2 d _load / c Where t _load This represents the expected time for the main signal to reach the receiving antenna, where c is the speed of light, and d is the speed of light. _load This indicates the vertical distance between the large metal plate and the receiving end of the receiving antenna.
[0017] Furthermore, the gating time of the time-domain gate is determined based on the obtained expected time, specifically including the following steps: The time-domain width of the main signal is determined by converting the time-domain response signal from the equivalent reflection measurement parameters under a large-size metal plate. ; Based on the expected arrival time of the main signal at the receiving antenna and the time domain width Determine the start and end times of the gating of the time-domain gate: ; ; in, Indicates the start time of the gating process. Indicates the gating deadline. This indicates the expected time for the main signal to reach the receiving antenna. The coefficient is between 0.5 and 1.
[0018] Furthermore, by substituting the determined values of directional error, reflection tracking error, and source matching error into the mathematical model, the steps to obtain the true equivalent reflection coefficient after eliminating systematic errors include: The source matching error after time-domain gating is equivalent to 0. Then, the reflection tracking error and source matching error determined by time-domain gating are substituted into a mathematical model containing directional error, reflection tracking error, and source matching error to obtain the true equivalent reflection coefficient after eliminating system errors.
[0019] Among them, S 11_A The true equivalent reflection coefficient after eliminating systematic errors; S 11_M E represents the equivalent reflection measurement parameter. _D To characterize the directivity error of fixed mutual coupling between antennas and system leakage; E _R The reflection tracking error is used to characterize the frequency response of the system.
[0020] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a calibration method suitable for mechanical linear scanning SAR imaging systems, which has the following beneficial effects: 1. The entire calibration process of this invention is completed in one go before the target test, without interfering with the continuous data acquisition of subsequent mechanical scanning, fundamentally solving the problem of incompatibility between traditional calibration and scanning motion.
[0021] 2. By equating the two-port system to a single-port system, the error model is significantly simplified. The application of time-domain gating technology is the core key, as it physically separates and suppresses the source matching error E_, which is difficult to solve directly. S This allows for a high-precision solution of the directional error E_ using only two load measurements. D and reflection tracking error E_ R The process is extremely simplified.
[0022] 3. By specifying that the size of the metal plate used for short-circuit calibration must cover the entire preset scanning range, it is ensured that the interaction state between the antenna beam and the metal plate is consistent and ideal during calibration acquisition and subsequent use of the compensation model. This avoids calibration conditions from failing or introducing additional errors due to scanning changes, and significantly improves the reliability and robustness of calibration.
[0023] 4. The directional error E_ obtained by the method of this invention D and reflection tracking error E_ R The established compensation coefficient model can accurately deduct the inherent background error of the system from the raw data of subsequent target testing to obtain high-fidelity target scattering data, which is a necessary prerequisite for obtaining high-resolution, low-clutter SAR images. Attached Figure Description
[0024] 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.
[0025] Figure 1 This is a schematic diagram for short-circuit load calibration, showing the length of the metal plate covering the antenna's linear scan path.
[0026] Figure 2 This is an overall flowchart of the calibration method of the present invention.
[0027] Figure 3 This is a schematic diagram of the time-domain gating technique, illustrating the separation of the main signal time window t_load calculated based on the load distance d_load from the early reflected signal. Detailed Implementation
[0028] The following will be based on embodiments of the present invention. Figures 1-3The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0029] The calibration method for mechanically linear scanning SAR imaging systems disclosed in this invention includes the following steps: Step 1: System Initialization and Single-Port Model Establishment The transmitting and receiving antennas of the mechanically scanned SAR are fixed adjacent to each other and connected to a vector network analyzer. Specifically, the transmitting antenna can be fixedly connected to Port 1 of the vector network analyzer, and the receiving antenna can be fixedly connected to Port 2 to ensure that the forward transmission coefficient S is being measured. 21 .
[0030] The operating frequency band, number of frequency points, and power of the vector network analyzer are set, and these parameter settings must be consistent with the subsequent target test parameters. Based on the characteristics of the adjacent arrangement of the transmitting and receiving antennas and the high beam overlap, the transmission parameters S measured by the vector network analyzer are... 21 In data processing, it is equivalent to a single-port reflection measurement parameter, denoted as S. 11_M .
[0031] For this equivalent single-port measurement, a mathematical model is established that includes three main systematic errors:
[0032] In the formula, S 11_A E represents the true equivalent reflection coefficient after eliminating systematic errors. _D Directional error, characterizing fixed mutual coupling between antennas and system leakage; E _R E represents the reflection tracking error, characterizing the system's frequency response. _S The source matching error characterizes the mismatch at the equivalent ports.
[0033] Step 2: Calibration Data Acquisition (1) Matching load calibration: Control the mechanical scanning system to align the transceiver antenna with a free space region free from reflection interference. The free space is used as the ideal matching load, and its true reflection coefficient S 11_A ≈ 0. In this state, the equivalent reflection parameters measured by the vector network analyzer are collected and recorded, denoted as S. 11_free .
[0034] (2) Short-circuit load calibration: A metal plate is placed directly in front of the spatial region corresponding to the antenna scanning trajectory. The size of the metal plate must be large enough to ensure that the main lobe of the beam of the transmitting antenna and the receiving antenna is always completely covered by the metal plate within the entire preset mechanical scanning angle range, so that the metal plate is regarded as an ideal short-circuit load and its true reflection coefficient S 11_A ≈ -1. In this state, the equivalent reflection parameters measured by the vector network analyzer are collected and recorded, denoted as S. 11_metal .
[0035] In this invention, the metal plate must meet the following requirements to ensure that its electrical performance is close to the ideal short-circuit condition (true reflection coefficient S11_A ≈ -1∠0°): a) Material requirements: High conductivity materials should be used, preferably aluminum, copper, or brass. High conductivity materials can minimize the resistive loss of electromagnetic waves on their surface, ensuring total reflection of the signal, thus approximating an ideal short-circuit state.
[0036] b) Thickness requirements: The thickness of the metal plate should be much greater than the skin depth of the electromagnetic waves in the operating frequency band. For microwave frequency bands (such as 1-40 GHz), a thickness of not less than 1-2 mm is usually sufficient to meet the electrical performance requirements. However, more importantly, the thickness must ensure that the plate has sufficient mechanical strength and rigidity to remain flat and free from deformation during calibration, installation, and use.
[0037] c) Surface flatness requirements: The flatness of the metal plate surface is one of the core factors affecting calibration accuracy. The surface undulation should be much smaller than the wavelength λ_min corresponding to the highest operating frequency, preferably better than λ_min / 10 (for example, at a center frequency of 10 GHz and a wavelength of 30 mm, the surface undulation should be less than 3 mm). An uneven surface will cause diffuse reflection or phase distortion of the incoming wave, destroying its phase consistency as an ideal "short-circuit" surface, thus introducing calibration error.
[0038] d) Size requirements: The metal plate must be large enough to ensure that the main lobe of the beam of the transmitting and receiving antenna is always completely covered by the metal plate throughout the entire preset mechanical scanning angle and travel range. This is to avoid diffraction caused by the antenna beam hitting the edge of the plate, or clutter interference caused by hitting other objects behind the plate, and to ensure the purity and consistency of the calibration conditions.
[0039] Step 3: Time-domain gating and error term solution (1) The frequency domain data S collected in step two 11_free and S 11_metal Perform inverse Fourier transforms on each signal to obtain the corresponding time-domain response signals.
[0040] (2) Analyze the time-domain response: The signals are arranged in the time domain according to their time delays. The early-arriving portion of the signal (usually within a few nanoseconds) mainly originates from impedance mismatch reflections in near-field areas such as antenna ports and connectors. This portion of the signal is related to the error term E. _S Strong correlation. The later-arriving, significantly amplituded main signal peak originates from reflections from free space (corresponding to matched load) or a metal plate (corresponding to short-circuit load), with an arrival time (t...). _load The physical distance (d) of the calibration load _load The decision is made using the following formula: t _load = 2 d _load / c, where c is the speed of light.
[0041] The expected arrival time t_load of the main signal can be calculated based on the physical distance d_load of the short-circuit calibration load (metal plate). A significant peak should appear near time t_load in the time-domain response plot, representing the main signal reflected by the metal plate. For free-space measurement data, the temporal location of the effective main signal (which may originate from distant background or noise) can be determined and gated based on t_load.
[0042] In one specific implementation, the purpose of free-space measurement is to obtain the system's "directional error". The main causes are fixed mutual coupling and leakage between antennas, and these signals appear in the time domain at very early moments (much smaller than 10 ... By also setting the time domain gate for free space data... Nearby, it can be ensured that the gate does not contain any signals brought by external reflections, thus obtaining a "clean" time window with only system floor noise, consistent with the time window of short-circuit data.
[0043] (3) Implement time-domain gating: Based on the time-domain analysis in step (2), set a time-domain gating gate. The start time of the gating gate (t) _gate_start The time is set to be slightly earlier than the theoretical arrival time t calculated from the load distance. _load To fully capture the main reflected signal; the cutoff time of the gate (t) _gate_stop ) Set at t _load This is followed by coverage of the main signal pulse width; simultaneously ensuring that the gating gate completely filters out early-arriving time-domain signal components related to port near-field mismatch (typically located at t). _gate_start (Previously). The gated time-domain signal is converted back to the frequency domain to obtain the purified parameter S. 11_free_gated and S 11_metal_gated The deadline t of the gate. _gate_stop Set at t _loadThen, the pulse width of the main signal is covered; at the same time, it is ensured that the gating gate completely filters out signals located at t. _gate_start The previous time-domain signal components. This process effectively suppressed the source matching error E. _S The effect can be approximated as E _S ≈0.
[0044] In one specific implementation, the start time and end time are obtained through the following steps: First, the time domain width of the main signal is determined by the time domain response waveform of the short-circuit load. (For example, the pulse width is the width at the point where the peak value drops by -10dB).
[0045] Then, according to the expected time and Set a gating gate: Start time: : Deadline: : in The coefficient is between 0.5 and 1, typically 0.75. This allows for complete capture of the main signal while filtering out near-field interference.
[0046] The above process can be summarized as follows: Step A: Generate the gating window function. In the time domain, create a window function. Within the interval from t_gate_start to t_gate_stop, the value of the window function is 1 (or varies depending on the window function type); outside this interval, the value of the window function is 0. The specific window function can be a rectangular window, or, to reduce spectral leakage, a Hamming window, a Gaussian window, etc., can be used.
[0047] Step B: Windowing. Multiply the original time-domain response signal point by point with this gating window function. The result of the multiplication is the "gated time-domain signal", which retains only the signal inside the gate, while the signals outside the gate (including the near-field error and far-field noise that we want to filter out) are set to zero.
[0048] Step C: Fourier Transform. Perform a Fourier transform on the gated time-domain signal to convert it back to the frequency domain. The resulting frequency-domain data is the purified parameter S. 11_free_gated and S 11_metal_gated .
[0049] In this step, time-domain gating physically separates and suppresses... The near-field reflected signal represented. After gating, we obtain the data ( and Source matching error The impact has been significantly reduced, at which point the source matching error can be reasonably approximated. .
[0050] (4) Solve for the key error term: the source matching error E _S Substituting ≈ 0 into the mathematical model and combining it with two ideal load conditions, the calculation is performed: Based on the matching load conditions: S 11_A = 0, from the model we get:
[0051] According to the short-circuit load condition: S 11_A = -1, from the model we get:
[0052] Therefore, the reflection tracking error can be obtained:
[0053] In the above steps, the raw data S containing all errors was first collected. 11_free and S 11_metal .
[0054] Then, by using time-domain gating, the source matching error E_ was filtered out. S The corresponding near-field reflection yielded "clean" data S containing only the response of the calibration load (free space / metal plate). 11_free_gated and S 11_metal_gated .
[0055] Finally, assume E_ S ≈ 0, and set these two "pure" data (which represent S in the error model after gating) to 0. 11_M Only by substituting into the mathematical model could E be solved. _D and E_ R .
[0056] Step 4: Establish an error compensation model to obtain the true equivalent reflection coefficient after eliminating systematic errors.
[0057] The error term E obtained in step three _D E _R and E _S Substituting the state ≈0 into the mathematical model, we obtain a simplified model for subsequent target test data compensation:
[0058] This model is the final established error compensation model. Wherein, S 11_M S is the original equivalent reflection parameter directly measured when scanning any target. 11_AThese are parameters that reflect the true scattering characteristics of the target after the system error compensation.
[0059] Based on the above inventive concept, in a specific embodiment, taking the calibration of an X-band SAR system for linear scanning as an example, the calibration steps include: 1. Initialization: Mount a pair of horn antennas with a center frequency of 10 GHz adjacent to each other on the slide of the linear guide rail and connect them to the VNA. Set the VNA frequency to 8-12 GHz (401 points). The preset imaging scan is a linear trajectory with a travel length of L. _scan =1m.
[0060] 2. Matching load calibration: Control the slide to move to the midpoint of the guide rail and point the antenna into free space, measure and save S. 21 Data, as S 11_free .
[0061] 3. Short-circuit load calibration: A rectangular aluminum plate is vertically installed at a distance D = 1.5 m directly in front of the linear guide rail, parallel to the rail direction. The dimension of the aluminum plate along the guide rail direction (length direction) must be greater than (L... _scan +The coverage length of the antenna beam at distance D), ensuring that the main lobe of the beam is completely blocked at the start, end, and any other point in the travel path. Calculations show that an aluminum plate with a length of 2m and a height of 1.5m is selected. The slide is moved to the midpoint of the travel path for calibration measurement, and S is saved. 21 Data as S 11_metal .
[0062] 4. Time-domain gating and calculation: S 11_free With S 11_metal Data is converted to the time domain. The expected arrival time of the main signal is calculated: the distance from the metal plate is D = 1.5 m, the round-trip distance of the electromagnetic wave is 3 m, and the speed of light is c = 3e8 m / s. Therefore, the theoretical arrival time t of the main signal is... _load = 3 / 3e8 = 10 ns. In free space measurements, the effective reflection point is located in the far field, and its equivalent distance is usually much greater than that of near-field reflection. The main signal also appears at a similar or slightly later time delay position.
[0063] 5. Analyze the time-domain waveform: Observe the time-domain signal. Small early spikes can be observed at about 1-2 ns (corresponding to near-field reflections from antenna ports, connectors, etc.); obvious main signal peaks can be observed at about 10 ns.
[0064] 6. Setting a time-domain gate: To filter out near-field mismatch reflections and retain the main signal, set the start time t of the gating gate. _gate_start = 8 ns, deadline t _gate_stop = 15 ns. Converting the gated data back to the frequency domain yields S.11_free_gated and S 11_metal_gated .
[0065] 7. Calculate the error term: E _D = S 11_free_gated E _R = S 11_free_gated - S 11_metal_gated .
[0066] 8. Model Establishment: Calibration completed. Subsequently, during target line scanning, the raw data S measured at the displacement coordinate x is... 21 (x) (considered as S) 11_M (x) can all be obtained through S 11_A (x) = (S 11_M (x)-E _D ) / E _R Real-time compensation is performed to obtain calibrated target data S11_A(x) for imaging.
[0067] 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.
[0068] 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 calibration method suitable for mechanical linear scanning SAR imaging systems, characterized in that, Includes the following steps: The transmission parameters between the two ports of the vector network analyzer are equivalent to the reflection measurement parameters of a single port, denoted as the equivalent reflection measurement parameters. A mathematical model including directional error, reflection tracking error and source matching error is established to determine the true equivalent reflection coefficient after eliminating systematic errors. Equivalent reflection measurement parameters are collected by the vector network analyzer in a free space region without reflection interference and under a large-size metal plate, respectively. The values of directional error, reflection tracking error and source matching error are determined by time-domain gating based on the two obtained equivalent reflection measurement parameters. The large-size metal plate is a metal plate that can cover the entire preset mechanical scanning angle and stroke range. By substituting the determined values of directional error, reflection tracking error, and source matching error into the mathematical model, the true equivalent reflection coefficient after eliminating systematic errors is obtained, thereby achieving the calibration of the mechanical linear scanning SAR imaging system.
2. The calibration method as described in claim 1, characterized in that, The transmission parameters between the two ports of a vector network analyzer are obtained through the following steps: Connect the transmitting antenna to port 1 of the vector network analyzer, connect the receiving antenna to port 2 of the vector network analyzer, and firmly fix the transmitting end of the transmitting antenna and the receiving end of the receiving antenna together. The transmission parameters between port 2 and port 1 were measured using a vector network analyzer.
3. The calibration method as described in claim 1, characterized in that, A mathematical model is established that includes directional error, reflection tracking error, and source matching error, specifically including the following mathematical model: In the formula, S 11_M S represents the equivalent reflection measurement parameter. 11_A The true equivalent reflection coefficient after eliminating systematic errors; E _D To characterize the directivity error of fixed mutual coupling between antennas and system leakage; E _R The reflection tracking error characterizes the system's frequency response; E _S The source matching error is used to characterize the mismatch of the equivalent port.
4. The calibration method as described in claim 1, characterized in that, The large-size metal plate is made of a highly conductive material, including aluminum, copper, or brass.
5. The calibration method as described in claim 3, characterized in that, Based on the two equivalent reflection measurement parameters obtained, the values of directivity error, reflection tracking error, and source matching error are determined through time-domain gating, specifically including: The two equivalent reflection measurement parameters obtained are converted into time-domain response signals respectively; Based on the time-domain response signal converted from the equivalent reflection measurement parameters under the large-size metal plate, the main signal and the expected time for the main signal to arrive at the receiving antenna are determined. The gating time of the time domain gate is determined based on the expected time, and the time domain response signals obtained from the two equivalent reflection measurement parameters are gated based on the gating time. The time-domain response signal after time-domain gating is converted into frequency-domain parameters to obtain the first gating frequency-domain parameters in the free space region and the second gating frequency-domain parameters in the large-size metal plate. Using the first gating frequency domain parameter as the equivalent reflection measurement parameter, the source matching error after time-domain gating is equivalent to 0, and the true equivalent reflection coefficient after eliminating system errors is set to 0 based on the matched load calibration condition. The directional error is obtained according to the mathematical model including directional error, reflection tracking error and source matching error: E _D = S 11_free_gated ; Among them, S 11_free_gated Indicates the frequency domain parameters of the first strobe; Using the second gating frequency domain parameter as the equivalent reflection measurement parameter, the source matching error after time-domain gating is equivalent to 0, and the true equivalent reflection coefficient after eliminating system errors is set to -1 based on the short-circuit load calibration condition. The relationship between the directivity error and the reflection tracking error is obtained from the mathematical model including the directivity error, reflection tracking error, and source matching error: ； Among them, S 11_metal_gated This represents the second strobe frequency domain parameter; The reflection tracking error is obtained based on the relationship between directional error and reflection tracking error.
6. The calibration method as described in claim 5, characterized in that, The expected time for the main signal to arrive at the receiving antenna is obtained using the following formula: t _load = 2 d _load / c Where t _load This represents the expected time for the main signal to reach the receiving antenna, where c is the speed of light, and d is the speed of light. _load This indicates the vertical distance between the large metal plate and the receiving end of the receiving antenna.
7. The calibration method as described in claim 5, characterized in that, Determining the gating time of the time-domain gate based on the obtained expected time includes the following steps: The time-domain width of the main signal is determined by converting the time-domain response signal from the equivalent reflection measurement parameters under a large-size metal plate. ; Based on the expected arrival time of the main signal at the receiving antenna and the time domain width Determine the start and end times of the gating of the time-domain gate: ； ； in, Indicates the start time of the gating process. Indicates the gating deadline. This indicates the expected time for the main signal to reach the receiving antenna. The coefficient is between 0.5 and 1.
8. The calibration method as described in claim 1, characterized in that, The steps to obtain the true equivalent reflection coefficient after eliminating systematic errors by substituting the determined values of directional error, reflection tracking error, and source matching error into the mathematical model include: The source matching error after time-domain gating is equivalent to 0. Then, the reflection tracking error and source matching error determined by time-domain gating are substituted into a mathematical model containing directional error, reflection tracking error, and source matching error to obtain the true equivalent reflection coefficient after eliminating system errors. Among them, S 11_A The true equivalent reflection coefficient after eliminating systematic errors; S 11_M E represents the equivalent reflection measurement parameter. _D To characterize the directivity error of fixed mutual coupling between antennas and system leakage; E _R The reflection tracking error is used to characterize the frequency response of the system.