Phase and amplitude consistency field calibration method and system for large low-frequency phased array radar

Abstract

The present application relates to the field of radar technology, especially relates to a kind of large low frequency phased array radar amplitude and phase consistency field calibration method and system, wherein field calibration method is deployed by probe antenna in the position of near-field region in front of array but meeting the single-array far-field condition, high-resolution time-domain data are obtained using wideband frequency step scanning, and by applying the gating processing based on direct wave arrival time to time-domain impulse response, ground reflection and other multipath components are filtered out in digital domain, and "virtual microwave darkroom" is equivalently constructed.Further, combined with accurate Fries voltage transmission model and pre-stored antenna pattern database, the inherent amplitude and phase characteristics of each array element channel are inverted, and finally high-precision consistency calibration is completed.The problems of multipath interference during near-field test and insufficient time-domain resolution in multipath separation are solved.

Description

Technical Field

[0001] This invention relates to the field of radar technology, and in particular to a method and system for on-site calibration of amplitude and phase consistency of a large low-frequency phased array radar. Background Technology

[0002] Large-scale low-frequency phased array wind profiler radars are key equipment in meteorological detection and ionospheric monitoring. They typically have a large physical aperture and a long operating wavelength, generally exceeding 10 meters × 10 meters, with an operating wavelength of approximately 0.5-1 meter. To ensure beam pointing accuracy, low sidelobe performance, and the reliability of the detection data, high-precision amplitude and phase (referred to as "amplitude and phase") consistency calibration must be performed on hundreds or thousands of T / R array elements.

[0003] However, field calibration of such radars faces significant challenges, as traditional methods all have inherent limitations:

[0004] First, the stringent far-field testing conditions cannot be achieved in the field. According to 2D antenna theory... 2 The / λ far-field criterion, where D is the antenna aperture and λ is the wavelength; for a typical radar with a 10-meter aperture and a 0.67-meter wavelength, the required minimum far-field distance exceeds 300 meters, resulting in an excessively large Fresnel zone. Deploying such a large-scale test site and a signal source tower hundreds of meters high in the field would be extremely costly and generally not feasible.

[0005] Secondly, when measurements are performed at achievable close range, such as in the near-field or mid-field radiation regions, strong multipath interference causes severe distortion of the measurement data. Due to the strong diffraction capability and wide antenna beam of low-frequency electromagnetic waves, reflected signals from the ground interfere with the direct signals between the probe antenna and the radar array. This interference results in amplitude fluctuations of up to 3-6 dB and phase deviations exceeding 20° for the composite signals received by array elements at different spatial locations, rendering conventional calibration methods based on single-frequency measurements completely ineffective.

[0006] Although existing technologies attempt to utilize the radar's own operating bandwidth (e.g., 20MHz) for time-domain analysis, aiming to separate multipath signals through "time-domain gating," the inherent time-domain resolution of narrowband signals is severely insufficient due to physical limitations. A 20MHz bandwidth corresponds to a range resolution of approximately 15 meters, while in field tests, the path difference between direct waves and ground-reflected waves is typically only about 1 meter. Therefore, the two waves completely overlap in the time domain, making effective separation impossible, and rendering "time-domain gating" ineffective in practical applications.

[0007] Therefore, there is an urgent need for a method and system for on-site calibration of amplitude and phase consistency of large low-frequency phased array radar. Summary of the Invention

[0008] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a method and system for on-site calibration of amplitude and phase consistency of a large low-frequency phased array radar, which solves the problems of multipath interference and insufficient time domain resolution in multipath separation during near-field testing.

[0009] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0010] In a first aspect, the present invention provides a field calibration method for the amplitude and phase consistency of a large low-frequency phased array radar. The method is based on a probe antenna arranged in the near-field region in front of the phased array wind profile radar array. The distance between the probe antenna and any T / R array element in the radar satisfies the far-field condition of a single array element. The method includes: obtaining the phase center coordinates of the probe antenna and each array element of the radar.

[0011] Each array element is activated sequentially, with only one array element activated at a time. For each activated array element, a frequency step scan covering a preset calibration bandwidth is performed through the probe antenna to obtain the complex frequency response dataset of the array element. The temporal spatial resolution corresponding to the calibration bandwidth is smaller than the path difference between the direct wave and the ground reflected wave between the probe antenna and the radar array.

[0012] For each array element, an inverse discrete Fourier transform is performed on the complex frequency response dataset to obtain the time-domain impulse response. Based on the phase center coordinates of the probe antenna and the array element, the arrival time of the direct wave is determined. A time-domain gated window function is applied to the time-domain impulse response based on the arrival time of the direct wave to extract the direct wave component of the time-domain impulse response. The direct wave component is then transformed into the frequency domain to obtain the effective transmission coefficient of the array element. Based on the Fries voltage transmission model and combined with the pre-established radiation pattern databases of each array element and the probe antenna, the complex intrinsic excitation of the array element is determined by inversion based on the effective transmission coefficient of the array element. Based on the complex intrinsic excitation of all array elements, the amplitude and phase of all radar array elements are calibrated.

[0013] Optionally, the calibration bandwidth is at least 200MHz.

[0014] Optionally, the frequency interval of the frequency step scan is less than or equal to 1 MHz.

[0015] Optionally, the center of the time-domain gated window function is aligned with the peak time of the direct wave component in the time-domain impulse response, and the time-domain width of the time-domain gated window function is smaller than the time delay difference between the ground reflected wave and the direct wave; the time-domain gated window function is either the Tukey window function or the Kaiser window function.

[0016] Alternatively, the Frisian voltage transfer model can be expressed as:

[0017] ;

[0018] in:

[0019] For radar number Each element at the center frequency The inherent excitation of complex numbers at a given location;

[0020] For the first After time-domain gating, the effective transmission coefficients containing only the direct wave component are extracted from each array element.

[0021] The radar's operating center frequency;

[0022] For the first The straight-line Euclidean distance between the phase center of each array element and the phase center of the probe antenna;

[0023] Center frequency The corresponding free space wavelength;

[0024] It is the inverse factor of free space voltage transmission loss;

[0025] For the probe antenna pointing to the first Complex gain in the direction of each array element With the phase center of the probe antenna as the origin, pointing towards the first The local spherical coordinate system angle of each array element;

[0026] For the first The complex pattern gain of each array element in an embedded cell under a mutually coupled array environment. Therefore, the first The phase center of each array element is the origin, pointing to the local spherical coordinate system angle of the probe antenna;

[0027] Center frequency The corresponding wave number is calculated using the following formula: ;

[0028] This is the compensation factor for spatial phase delay.

[0029] Optionally, the pre-established array element radiation pattern database is obtained by performing full-wave electromagnetic simulation on the array elements in the phased array wind profiler radar. For any target array element, the corresponding simulation calculation model includes the metal base plate of the radar array, the radome, the target array element, and at least two other array elements adjacent to the target array element in the array, so as to obtain target array element radiation pattern data that accurately simulates the array mutual coupling effect and edge truncation effect. Based on the simulation results of all array elements, a database containing non-uniform radiation pattern data of array elements at different positions in the array is established.

[0030] Optionally, the amplitude and phase of all array elements of the radar are calibrated according to the complex intrinsic excitation of all array elements, including: selecting an array element as a reference array element; for each array element to be calibrated other than the reference array element, determining the compensation coefficient of the array element to be calibrated according to the complex intrinsic excitation of the array element to be calibrated and the complex intrinsic excitation of the reference array element; the compensation coefficient of the array element to be calibrated includes the amplitude compensation coefficient and the phase compensation coefficient; and calibrating the corresponding array element according to the compensation coefficient of the array element to be calibrated.

[0031] Optionally, the amplitude and phase of all radar elements are calibrated based on the complex intrinsic excitation of all elements, including: determining the standard deviation of the intrinsic amplitude and the standard deviation of the intrinsic phase based on the complex intrinsic excitation of all elements; comparing the standard deviation of the intrinsic amplitude with a preset first threshold to determine whether the amplitude consistency of all radar elements meets the standard; comparing the standard deviation of the intrinsic phase with a preset second threshold to determine whether the phase consistency of all radar elements meets the standard; and selectively performing consistency calibration on the amplitude and phase of all radar elements based on the comparison results.

[0032] Secondly, the present invention provides an amplitude and phase consistency field calibration system for a large low-frequency phased array radar, comprising:

[0033] The probe antenna is used to be deployed in the near field area in front of the radar array, and the distance between the probe antenna and any T / R element in the phased array wind profiler radar satisfies the far field condition of a single element.

[0034] A broadband transceiver, connected to the beam control unit and probe antenna of a phased array wind profiler radar, is configured to generate frequency step-scan signals and receive and measure response signals from each active array element to obtain a complex frequency response dataset.

[0035] The positioning device is configured to measure and output the three-dimensional coordinates of the phase center of the probe antenna and the phase centers of each array element;

[0036] The signal processing and control unit, which is communicatively connected to the broadband transceiver and positioning unit, performs the following operations: controlling the sequential activation of array elements and the scanning process of the probe antenna; determining the arrival time of the direct wave based on the three-dimensional coordinates of the phase center of the probe antenna and the phase center of each array element; performing inverse discrete Fourier transform, time-domain gating, and frequency-domain transform on the complex frequency response dataset to obtain the effective transmission coefficients; performing parameter inversion based on the Fries voltage transmission model and the pre-established array element radiation pattern database and probe antenna radiation pattern database to obtain the complex intrinsic excitation; generating amplitude and phase compensation coefficients based on the complex intrinsic excitations of all array elements; and calibrating the amplitude and phase of all radar array elements.

[0037] Optionally, the broadband transceiver integrates a vector network analysis module for performing complex parameter measurements at stepped frequency points.

[0038] The beneficial effects of this invention are:

[0039] This invention provides a method and system for on-site calibration of amplitude and phase consistency for large-scale low-frequency phased array wind profiler radar. By deploying the probe antenna in the near-field region of the array that meets the far-field conditions of a single array element, and using ultra-wideband frequency step scanning to acquire high-resolution time-domain data, a "virtual microwave anechoic chamber" is constructed in the digital domain using time-domain gating technology to filter out multipath interference. Then, a precise inversion is performed using a model that integrates the element radiation pattern and a modified Fries voltage transfer model. Finally, selective amplitude and phase compensation is performed based on the inherent excitation of each array channel obtained from the inversion. This method systematically solves the on-site calibration problems caused by insufficient test distance, severe multipath interference, and the limited operating bandwidth of the radar itself. This invention achieves high-precision and high-efficiency consistency calibration of the amplitude and phase characteristics of all T / R array element channels of a large-scale low-frequency phased array wind profiler radar under ordinary field conditions without relying on a far-field range of hundreds of meters or constructing a microwave anechoic chamber. This significantly improves the radar's beamforming quality and detection performance, and has significant engineering practical value. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the geometric layout and multipath propagation of the probe antenna and radar array in a field calibration scenario according to a specific implementation method.

[0041] Figure 2 This is a flowchart illustrating the on-site calibration method for amplitude and phase consistency of a large-scale low-frequency phased array wind profiler radar according to a specific implementation method.

[0042] Figure 3 This is a schematic diagram of the radar channel time-domain impulse response obtained based on broadband frequency step scanning according to a specific implementation method;

[0043] Figure 4This is a schematic diagram illustrating the effect of applying a time-domain gated window function for extracting direct wave components according to a specific implementation method.

[0044] Figure 5 This is a schematic diagram comparing the radiation patterns of the radar array synthetic antenna before and after calibration according to a specific implementation method.

[0045] Explanation of reference numerals in the attached figures

[0046] 1: Radar array; 2: Probe antenna; 3: T / R array element. Detailed Implementation

[0047] To better explain and facilitate understanding of the present invention, it is described in detail below with reference to the accompanying drawings and specific embodiments. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a clearer and more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0048] This invention provides a field calibration method for amplitude and phase consistency of a large low-frequency phased array wind profiler radar, such as... Figure 1 As shown, the field calibration method is based on the probe antenna 2 arranged in the near field area in front of the radar array 1, and the distance between the probe antenna and any T / R array element 3 in the phased array wind profiler radar satisfies the far field condition of a single array element.

[0049] The deployment conditions of the probe antenna 2 described above ensure that the incident wavefront of the electromagnetic wave can be approximated as a plane wave for each individually measured array element, fully satisfying the far-field testing conditions for that element. This deployment strategy is one of the key prerequisites for the success of this method. It ensures that the signal characteristics measured from a single array element primarily reflect the performance of that element itself and the propagation path loss, while avoiding additional complex phase errors introduced by wavefront curvature. This lays a reliable physical foundation for subsequent high-precision parameter inversion.

[0050] Furthermore, the beamwidth of probe antenna 2 is sufficient to cover the entire array aperture of the phased array wind profiler radar to be calibrated. Because probe antenna 2 has a wide beamwidth covering the entire array aperture, during testing, the probe can be fixed in one position without any mechanical movement or scanning; full array measurement can be completed simply by electronically switching between different array elements. This avoids positioning errors, instability, and time consumption introduced by mechanical movement.

[0051] Specifically, probe antenna 2 is a biconical antenna or a log-periodic antenna.

[0052] As an example, a typical array element size d is approximately 0.34 meters, the operating wavelength λ is 0.67 meters, and the far-field distance of a single element is calculated according to the far-field criterion R=2d. 2 / λ is calculated to be only about 0.35 meters.

[0053] like Figure 2 As shown, the on-site calibration method for amplitude and phase consistency of a large low-frequency band phased array wind profiler radar provided by the present invention includes the following steps:

[0054] Step 11: Obtain the phase center coordinates of the probe antenna and each array element of the radar.

[0055] Step 12: Activate each array element in sequence, and activate only one array element at a time; for each activated array element, perform a frequency step scan covering the preset calibration bandwidth through the probe antenna to obtain the complex frequency response dataset of the array element.

[0056] Specifically, the beam control unit of the phased array wind profiler radar activates each array element in sequence, while the remaining array elements are connected to the matching load.

[0057] Specifically, frequency step scanning refers to the process of sequentially transmitting and receiving signals at discrete, equally spaced frequency points within a relatively wide frequency range (i.e., a preset calibration bandwidth). As an example, frequency step scanning is typically performed by a broadband transceiver with vector network analysis capabilities, which generates a starting frequency f. start The termination frequency is f stop A sequence of frequency points with a frequency interval of Δf; for each frequency point f in the sequence k The broadband transceiver transmits a continuous wave signal through probe antenna 2, while the currently active single array element receives this signal. The broadband transceiver accurately measures and records the complex transmission coefficient from the probe to the active array element at that frequency point. After completing the measurement at this frequency point, the system automatically steps to the next frequency point f. k+1 Repeat the above process until the content from f is covered. start to f stop The entire calibration bandwidth B cal =f stop -f start Ultimately, for a single array element, a set of coverage bandwidths B will be obtained. cal The discrete complex transmission coefficients, arranged in frequency order, are equivalent to obtaining the system frequency response of the channel within that bandwidth.

[0058] Preferably, the frequency interval Δf of the frequency step scan is less than or equal to 1MHz.

[0059] Set calibration bandwidth B calThe fundamental goal is to achieve sufficiently high resolution in the time domain to separate direct waves from ground-reflected waves. The relationship between the time-domain resolution ΔR and the signal bandwidth B is: ΔR = c / B, where c is the speed of light. To ensure the ability to distinguish between direct and reflected waves with a path difference of ΔL, ΔR < ΔL, i.e., B < ΔL. cal >c / ΔL. That is, B cal The corresponding temporal spatial resolution is less than the path difference between the direct wave and the ground reflected wave between the probe antenna 2 and the radar array 1.

[0060] Preferably, the calibration bandwidth is at least 200MHz.

[0061] As an example, in a typical deployment scenario, assume that the geometry of the probe and radar array 1 results in a path difference ΔL ≈ 1.2 meters between the direct wave and the ground-reflected wave. To achieve sufficient temporal resolution to distinguish between the two, a bandwidth of at least B is required. cal >3×10 8 / 1.2≈250 MHz. Therefore, in practice, the calibration bandwidth can be preset to 300MHz, at which point the theoretical time-domain resolution ΔR≈1.0 meter can effectively ensure the separation of multipath signals with a path difference of about 1.2 meters.

[0062] For each activated array element and each scan frequency point, a complex transmission coefficient is measured, denoted as . In the formula, For transmission coefficient, For scanning frequency points, For the imaginary part, For amplitude;

[0063] For phase, the complex form (containing amplitude and phase information) must be obtained in order to obtain the time-domain impulse response containing accurate time delay information through the inverse Fourier transform.

[0064] Step 13: For each array element, perform an inverse discrete Fourier transform on the complex frequency response dataset to obtain the time-domain impulse response. Determine the arrival time of the direct wave based on the phase center coordinates of the probe antenna and the phase center coordinates of the array element. Apply a time-domain gated window function to the time-domain impulse response based on the arrival time of the direct wave to extract the direct wave component of the time-domain impulse response.

[0065] The time-domain impulse response (TVR) can intuitively show all the propagation paths of the signal from probe antenna 2 to the measured array element, as well as their corresponding time delays and intensities. In environments with multipath propagation, the TVR will exhibit multiple peaks, with the first and usually strongest peak corresponding to the direct path, and subsequent peaks corresponding to ground reflections and other environmental scattering paths.

[0066] Specifically, based on the phase center coordinates of probe antenna 2 and the phase center coordinates of the array element, the straight-line distance between probe antenna 2 and the array element is determined. The arrival time of the direct wave is then determined by the ratio of this straight-line distance to the speed of light. This calculated value provides a precise time reference for subsequent time-domain gating.

[0067] To separate the pure direct wave signal from the multipath-containing time-domain impulse response, time-domain gating is required. This involves selecting a window function with smooth edges, such as the Tukey or Kaiser window, aligning its center with the peak moment of the direct wave component in the time-domain impulse response, and setting the window's time width to be less than the time delay difference between the direct wave and the ground reflection wave (L / c). This ensures the window completely captures the direct wave pulse while effectively excluding subsequent reflected wave components. Specifically, the time-domain impulse response is multiplied point-by-point in the time domain by the window function. This operation is equivalent to applying a "time filter" in the time domain, retaining only the direct wave while forcing signals other than the direct wave to zero or significantly attenuating them.

[0068] Through the above steps, the effect of a "virtual microwave anechoic chamber" is achieved at the digital signal processing level. From the raw measurement data that is severely contaminated by multipath propagation, a pure time-domain response containing only the propagation path information of the direct wave is extracted, laying a key data foundation for the subsequent accurate inversion of the inherent characteristics of the array element channels.

[0069] Step 14: For each array element, transform the direct wave component into the frequency domain to obtain the effective transmission coefficient of the array element. Based on the Frisian voltage transmission model, and combined with the pre-established array element radiation pattern database and probe antenna radiation pattern database, determine the complex intrinsic excitation of the array element by inversion according to the effective transmission coefficient of the array element.

[0070] Among them, the direct wave component is transformed into the frequency domain, and the obtained array element effective transmission coefficient is the effective transmission coefficient after removing multipath interference. It characterizes the transmission response of the signal from probe antenna 2 to the specific array element in an ideal non-reflection environment.

[0071] To accurately reconstruct the inherent excitation of the array element channel from the effective transmission coefficients, i.e., to eliminate the influence of probe performance, spatial propagation loss, and antenna pattern, this invention employs a modified Friesian voltage transmission model for inversion. Compared to the traditional power transmission formula, this model, tailored to the characteristics of broadband measurements, clarifies the free space loss variation with frequency (wavelength), i.e., the 1 / λ effect, and introduces the complex antenna pattern to accurately characterize phase information.

[0072] For the Each array element, at the center frequency At this point, its complex intrinsic excitation is obtained by inversion using the following modified Frisian voltage transfer model:

[0073] ;

[0074] in:

[0075] For radar number Each element at the center frequency The inherent excitation of complex numbers at a given location;

[0076] For the first After time-domain gating, the effective transmission coefficients of the array elements are extracted, which contain only the direct wave component.

[0077] This is the radar's operating center frequency;

[0078] For the first The straight-line Euclidean distance between the phase center of each array element and the phase center of probe antenna 2;

[0079] Center frequency The corresponding free space wavelength;

[0080] It is the inverse factor of free space voltage transmission loss;

[0081] For probe antenna 2 pointing to the first Complex gain in the direction of each array element With the phase center of probe antenna 2 as the origin, pointing towards the first The local spherical coordinate system angle of each array element;

[0082] For the first The complex pattern gain of each array element in an embedded cell under a mutually coupled array environment. Therefore, the first The phase center of each array element is the origin, pointing to the local spherical coordinate system angle of the probe antenna 2;

[0083] Center frequency The corresponding wave number is calculated using the following formula: ;

[0084] This is the compensation factor for spatial phase delay.

[0085] In the above Frith voltage transfer model, This is a precise compensation for the variation of free-space voltage transmission loss with frequency (wavelength). In broadband measurements, different frequency components correspond to different wavelengths (λ), and their spatial losses also differ. This correction ensures that the voltage loss derived from broadband measurement data is accurate. It is an accurate physical quantity that eliminates frequency-dependent propagation losses. This is achieved by substituting known geometric parameters. Antenna characteristics retrieved from the database and the measurements obtained The complex intrinsic excitation of each array element can then be solved. This parameter directly reflects the amplitude and phase characteristics of the three channels of the T / R array element, including the intrinsic amplitude and intrinsic phase, and serves as the benchmark for subsequent consistency calibration.

[0086] Preferably, the pre-established array element radiation pattern database is obtained through the following method: Full-wave electromagnetic simulation is performed on the array elements in the phased array wind profiler radar. For any target array element, the corresponding simulation model includes the metal base plate of radar array 1, the radome, the target array element, and at least two adjacent rings of other array elements in the array, to obtain target array element radiation pattern data that accurately simulates array mutual coupling and edge truncation effects. Based on the simulation results of all array elements, a database containing non-uniform radiation pattern data of array elements at different positions in the array is established. This better reflects the true radiation characteristics of array elements in the array than isolated element radiation patterns, improving the accuracy of the inversion.

[0087] Step 15: Based on the complex intrinsic excitation of all array elements, calibrate the amplitude and phase of all array elements of the radar.

[0088] Specifically, based on the complex intrinsic excitations of all array elements, the amplitude and phase of all radar array elements are calibrated, including: determining the standard deviation of the intrinsic amplitude and the standard deviation of the intrinsic phase based on the complex intrinsic excitations of all array elements; comparing the standard deviation of the intrinsic amplitude with a preset first threshold to determine whether the amplitude consistency of all radar array elements meets the standard; comparing the standard deviation of the intrinsic phase with a preset second threshold to determine whether the phase consistency of all radar array elements meets the standard; and selectively performing consistency calibration on the amplitude and phase of all radar array elements based on the comparison results. The consistency calibration process is as follows: selecting an array element as a reference array element; for each array element to be calibrated other than the reference array element, determining the compensation coefficient of the array element to be calibrated based on the complex intrinsic excitations of the array element to be calibrated and the complex intrinsic excitations of the reference array element; the compensation coefficient of the array element to be calibrated includes the amplitude compensation coefficient and / or the phase compensation coefficient; and calibrating the corresponding array element based on the compensation coefficient of the array element to be calibrated.

[0089] For consistency assessment results, perform calibration operations according to one of the following three scenarios: 1. Only amplitude consistency fails to meet the standard; in this case, only amplitude compensation is required. 2. Only phase consistency fails to meet the standard; in this case, only phase compensation is required. 3. Both amplitude and phase fail to meet the standard; in this case, a complete amplitude-phase joint calibration is required.

[0090] As an example, the first threshold is 0.5dB and the second threshold is 5°. If the standard deviation of the inherent amplitude is greater than 0.5dB, it is determined that the amplitude consistency of all radar elements is not up to standard. If the standard deviation of the inherent phase is greater than 5°, it is determined that the phase consistency of all radar elements is not up to standard.

[0091] Specifically, for each array element to be calibrated other than the reference element, its amplitude compensation coefficient is expressed by the formula:

[0092] ,

[0093] In the formula, This is the amplitude compensation coefficient; This is the inherent amplitude of the reference channel; The inherent amplitude of the channel to be calibrated;

[0094] The phase compensation coefficient is expressed by the formula:

[0095] ,

[0096] In the formula, This refers to the phase compensation coefficient; This is the inherent phase of the reference channel; This represents the inherent phase of the channel to be calibrated.

[0097] Through the above steps, the present invention completes the entire field calibration process from high-precision measurement and accurate inversion to final compensation, effectively improving the beamforming performance of large low-frequency phased array wind profiler radar in complex field environments.

[0098] This invention provides a field calibration method for amplitude and phase consistency of a large-scale low-frequency phased array wind profiler radar. The method involves deploying the probe antenna 2 in the near-field region of the array that meets the far-field conditions for a single array element, acquiring high-resolution time-domain data using ultra-wideband frequency step scanning, constructing a "virtual microwave anechoic chamber" in the digital domain using time-domain gating technology to filter out multipath interference, and then performing accurate inversion using a Fries voltage transfer model that integrates the element radiation pattern and a modified model. Finally, selective amplitude and phase compensation is performed based on the inherent excitation of each array channel obtained from the inversion. This method systematically solves the field calibration challenges caused by insufficient test distance, severe multipath interference, and the limited operating bandwidth of the radar itself. Under ordinary field conditions without relying on a far-field distance of several hundred meters or constructing a microwave anechoic chamber, this invention achieves high-precision and high-efficiency consistency calibration of the amplitude and phase characteristics of all three channels of the T / R array elements in a large-scale low-frequency phased array wind profiler radar, significantly improving the radar's beamforming quality and detection performance, and possessing significant engineering practical value.

[0099] Corresponding to the aforementioned field calibration method, this invention also provides a field calibration system for amplitude and phase consistency of a large-scale low-frequency phased array wind profiler radar. This system mainly includes: a probe antenna 2, a broadband transceiver, a positioning device, and a signal processing and control device.

[0100] The probe antenna 2 is deployed in the near-field radiation region in front of the radar array 1. Its deployment position must meet the following requirements: the distance between it and any T / R element 3 in the phased array wind profiler radar must satisfy the far-field conditions of a single element; and its beamwidth must be sufficient to cover the entire aperture of the radar array 1 to be calibrated. This design ensures that the probe can illuminate the entire array from a fixed position without requiring mechanical movement.

[0101] A broadband transceiver is connected to the beam control unit and probe antenna 2 of the phased array wind profiler radar. Its main functions are to generate frequency-stepped scanning signals and transmit them through probe antenna 2; simultaneously, it receives response signals from the currently activated individual array elements of the radar and accurately measures the complex transmission coefficients at each step frequency point, thereby acquiring a complex frequency response dataset. Preferably, this broadband transceiver integrates a vector network analysis (VNA) module, which can measure the amplitude and phase of the signal, i.e., complex parameters, with high precision to meet the requirements of high-precision calibration.

[0102] The positioning device is used to accurately measure and output the three-dimensional spatial coordinates between the phase center of probe antenna 2 and the phase centers of each element in the radar array. This device can be a high-precision surveying instrument such as a total station or laser tracker, and the accurate geometric relationship it provides is the basis for calculating the direct wave path, performing time-domain gating, and accurate inversion.

[0103] The signal processing and control unit, communicating with the broadband transceiver and positioning device, is the core of the calibration process's control and computation. This unit is programmed or configured to execute all steps of the aforementioned field calibration method. Specifically, it is used to: control the beam control unit to sequentially activate individual array elements; control the broadband transceiver to execute a frequency stepping scan process; receive coordinate data from the positioning device and measurement data from the broadband transceiver; perform inverse discrete Fourier transform and time-domain gating algorithms to extract the direct wave component; perform parameter inversion based on a modified Friesian voltage transfer model, combined with a pre-stored array element pattern database and the probe antenna pattern, to determine the complex intrinsic excitation of each array element; and finally, determine the amplitude and phase compensation coefficients based on the intrinsic excitations of all array elements and output them to the radar's beamforming controller to complete the calibration.

[0104] This calibration system, through hardware integration and software algorithm collaboration, constructs a complete field calibration solution, providing a fully automated physical device that can be deployed on-site. This system completely eliminates the reliance on 100-meter far-field or large anechoic chambers, enabling it to operate directly at actual radar deployment sites (such as field stations). Through automated processes, it efficiently completes high-precision amplitude and phase calibration for hundreds or thousands of channels, significantly improving the engineering maintenance efficiency and beam performance reliability of large low-frequency phased array wind profiler radars.

[0105] As a specific embodiment, the following describes the implementation and effects of the present invention in further detail using the field calibration process of a typical P-band wind profiler radar.

[0106] The object under test is a P-band wind profiler radar with 128 T / R elements, and its operating center frequency is... 445MHz, corresponding wavelength The distance is approximately 0.674 meters. The calibration system is deployed at the actual radar site. First, a high-precision total station is used to accurately measure the three-dimensional coordinates of the phase center of all elements in the radar array and the phase center of probe antenna 2. Probe antenna 2 is a broadband standard gain horn antenna, mounted approximately 3.5 meters in front of the radar array 1, satisfying the far-field conditions for a single element, at a height of 1.5 meters. Probe antenna 2 is connected to the transmit port of a vector network analyzer (VNA) via a cable, and the receive port of the VNA is connected to the radar's T / R component port via a multi-channel switch matrix. The radar's beam control unit, VNA, and switch matrix are all controlled by a single industrial computer.

[0107] Based on deployment geometry calculations, the direct wave path length is approximately 3.5 meters, and the estimated ground-reflected wave path length is approximately 4.8 meters, with a path difference ΔL of approximately 1.3 meters. To effectively separate this multipath signal in the time domain, the required calibration bandwidth B... cal The frequency must be greater than 230MHz. In this embodiment, a VNA is set to perform frequency step scanning, with a scanning frequency range of 300MHz to 600MHz, a bandwidth of 300MHz, and a scanning point count of 1601 points. The frequency point interval Δf is less than 1MHz. At this time, the theoretical time domain resolution ΔR ≈ 1.0 meter, which is less than the path difference of 1.3 meters, thus satisfying the separation condition.

[0108] During measurement, the industrial control computer controls the radar beam control unit, activating only one T / R element 3 at a time, while the ports of the remaining elements are connected to matched loads. The VNA performs point-by-point scanning within a set 300MHz bandwidth, accurately measuring and recording the complex transmission coefficients from probe antenna 2 to the currently activated element at each frequency point, thereby obtaining the complex frequency response dataset for each element.

[0109] For the complex frequency response data measured for each array element, windowing is first applied. In this embodiment, a Kaiser window is used with parameter β=6 to suppress spectral sidelobes. Then, an inverse fast Fourier transform is performed to obtain its time-domain impulse response, such as... Figure 3 As shown. In the obtained time-domain waveform, two separate peaks can be clearly observed: the first main peak appears at approximately 11.7 nanoseconds, corresponding to a direct wave propagation time of 3.5 meters, and the second peak appears at approximately 16 nanoseconds, corresponding to a reflected wave propagation time of 4.8 meters. Based on the phase center coordinates of the array elements and probe antenna 2, the theoretical arrival time of the direct wave is determined to be approximately 11.7 nanoseconds. A time-domain gating window centered at this moment and with a width of 3 nanoseconds is set, and the data outside the window is set to zero, as shown. Figure 4 As shown. Subsequently, a Fast Fourier Transform is performed on the windowed data to obtain the clean frequency domain effective transmission coefficients, which have been freed from multipath interference.

[0110] The value at the center frequency of 445MHz is extracted from the effective transmission coefficients. This value is then substituted into the modified Friesian voltage transmission model for inversion, yielding the complex intrinsic excitation of each element at the center frequency.

[0111] The array element at the center is used as the reference for amplitude and phase. For each of the remaining elements to be calibrated, a complex compensation coefficient is determined relative to the reference element. The amplitude portion of this compensation coefficient is used to compensate for gain differences, and the phase portion is used to compensate for phase differences. The compensation coefficients for all elements are then written into the radar's beamforming controller, thus completing the calibration.

[0112] To verify the calibration effect, the antenna patterns of the radar before and after calibration were compared, such as... Figure 5 As shown, before calibration, due to the inconsistency in amplitude and phase between array elements and the influence of ground multipath interference, the measured array pattern sidelobe level was relatively high, approximately -18dB. After on-site calibration using the method of this invention, the sidelobe level of the pattern was significantly reduced to -26dB upon remeasurement, approaching the theoretical design value of the array. Simultaneously, the beam pointing accuracy was significantly improved, with a pointing error of less than 0.05°. This embodiment fully demonstrates that the method of this invention can effectively overcome multipath interference in actual deployment sites, achieving high-precision amplitude and phase consistency calibration for large low-frequency phased array wind profiler radars, and significantly improving their beam performance.

[0113] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0114] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0115] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first and second features are in direct contact, or that they are in indirect contact through an intermediate medium. Furthermore, "above," "over," or "on top" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," or "beneath" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0116] In the description of this specification, the terms "one embodiment," "some embodiments," "embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0117] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for on-site calibration of amplitude and phase consistency of a large low-frequency phased array radar, characterized in that, The method is based on a probe antenna arranged in the near-field region in front of the phased array wind profiler radar array. The distance between the probe antenna and any T / R array element in the radar satisfies the far-field condition of a single array element. The method includes: obtaining the phase center coordinates of the probe antenna and each array element of the radar. Each array element is activated sequentially, with only one array element activated at a time. For each activated array element, a frequency step scan covering a preset calibration bandwidth is performed through the probe antenna to obtain the complex frequency response dataset of the array element. The temporal spatial resolution corresponding to the calibration bandwidth is smaller than the path difference between the direct wave and the ground reflected wave between the probe antenna and the radar array. For each array element, an inverse discrete Fourier transform is performed on the complex frequency response dataset to obtain the time-domain impulse response. Based on the phase center coordinates of the probe antenna and the array element, the arrival time of the direct wave is determined. A time-domain gated window function is applied to the time-domain impulse response based on the arrival time of the direct wave to extract the direct wave component of the time-domain impulse response. The direct wave component is then transformed into the frequency domain to obtain the effective transmission coefficient of the array element. Based on the Fries voltage transmission model, combined with the pre-established radiation pattern databases of each array element and the probe antenna, the complex intrinsic excitation of the array element is determined by inversion based on the effective transmission coefficient of the array element. Based on the complex intrinsic excitation of all array elements, the amplitude and / or phase of all radar array elements are calibrated.

2. The method for on-site calibration of amplitude and phase consistency of a large low-frequency phased array radar according to claim 1, characterized in that, The calibration bandwidth is at least 200MHz.

3. The method for on-site calibration of amplitude and phase consistency of a large low-frequency phased array radar according to claim 1, characterized in that, The frequency interval of the frequency step scan is less than or equal to 1MHz.

4. The method for on-site calibration of amplitude and phase consistency of a large low-frequency phased array radar according to claim 1, characterized in that, The center of the time-domain gated window function is aligned with the peak moment of the direct wave component in the time-domain impulse response, and the time-domain width of the time-domain gated window function is less than the time delay difference between the ground reflected wave and the direct wave; the time-domain gated window function is either the Tukey window function or the Kaiser window function.

5. The method for on-site calibration of amplitude and phase consistency of a large low-frequency phased array radar according to claim 1, characterized in that, The Frisian voltage transfer model is expressed as: ； in: For radar number Each element at the center frequency The inherent excitation of complex numbers at a given location; For the first After time-domain gating, the effective transmission coefficients containing only the direct wave component are extracted from each array element. This is the radar's operating center frequency; For the first The straight-line Euclidean distance between the phase center of each array element and the phase center of the probe antenna; Center frequency The corresponding free space wavelength; It is the inverse factor of free space voltage transmission loss; For the probe antenna pointing to the first Complex gain in the direction of each array element With the phase center of the probe antenna as the origin, pointing towards the first The local spherical coordinate system angle of each array element; For the first The complex pattern gain of each array element in an embedded cell under a mutually coupled array environment. Therefore, the first The phase center of each array element is the origin, pointing to the local spherical coordinate system angle of the probe antenna; Center frequency The corresponding wave number is calculated using the following formula: ; This is the compensation factor for spatial phase delay.

6. The method for on-site calibration of amplitude and phase consistency of a large low-frequency phased array radar according to claim 1, characterized in that, The pre-established array element orientation pattern database is obtained through the following methods: Full-wave electromagnetic simulation was performed on the array elements in a phased array wind profiler radar. For any target array element, the corresponding simulation calculation model included the metal base plate of the radar array, the radome, the target array element, and at least two other array elements adjacent to the target array element in the array, in order to obtain target array element radiation pattern data that accurately simulates the array mutual coupling effect and edge truncation effect. Based on the simulation results of all array elements, a database containing non-uniform radiation pattern data of array elements at different positions in the array was established.

7. The method for on-site calibration of amplitude and phase consistency of a large low-frequency phased array radar according to claim 1, characterized in that, Based on the complex intrinsic excitation of all array elements, the amplitude and / or phase of all radar array elements are calibrated, including: Select one array element as the reference array element; for each array element to be calibrated other than the reference array element, determine the compensation coefficient of the array element to be calibrated based on the complex intrinsic excitation of the array element to be calibrated and the complex intrinsic excitation of the reference array element; the compensation coefficient of the array element to be calibrated includes the amplitude compensation coefficient and / or the phase compensation coefficient; calibrate the corresponding array element according to the compensation coefficient of the array element to be calibrated.

8. The method for on-site calibration of amplitude and phase consistency of a large low-frequency phased array radar according to claim 1, characterized in that, Based on the complex intrinsic excitation of all array elements, the amplitude and / or phase of all radar array elements are calibrated, including: Based on the complex intrinsic excitation of all array elements, the standard deviation of the intrinsic amplitude and the standard deviation of the intrinsic phase are determined; the standard deviation of the intrinsic amplitude is compared with a preset first threshold to determine whether the amplitude consistency of all array elements of the radar meets the standard; the standard deviation of the intrinsic phase is compared with a preset second threshold to determine whether the phase consistency of all array elements of the radar meets the standard; based on the comparison results, the amplitude and phase of all array elements of the radar are selectively calibrated for consistency.

9. A field calibration system for amplitude and phase consistency of a large low-frequency phased array radar, characterized in that, include: The probe antenna is used to be deployed in the near field area in front of the radar array, and the distance between the probe antenna and any T / R element in the phased array wind profiler radar satisfies the far field condition of a single element. A broadband transceiver, connected to the beam control unit and probe antenna of a phased array wind profiler radar, is configured to generate frequency step-scan signals and receive and measure response signals from each active array element to obtain a complex frequency response dataset. The positioning device is configured to measure and output the three-dimensional coordinates of the phase center of the probe antenna and the phase centers of each array element; The signal processing and control device, which is communicatively connected to the broadband transceiver and positioning device, performs the following operations: controlling the sequential activation of array elements and the scanning process of the probe antenna; determining the arrival time of the direct wave based on the three-dimensional coordinates of the phase center of the probe antenna and the phase center of each array element; performing inverse discrete Fourier transform, time-domain gating, and frequency-domain transform on the complex frequency response dataset to obtain the effective transmission coefficients; performing parameter inversion based on the Fries voltage transmission model and the pre-established array element pattern database and probe antenna pattern database to obtain the complex intrinsic excitation; generating amplitude and phase compensation coefficients based on the complex intrinsic excitations of all array elements; and calibrating the amplitude and / or phase of all radar array elements.

10. The field calibration system for amplitude and phase consistency of a large low-frequency phased array radar according to claim 9, characterized in that, The broadband transceiver integrates a vector network analysis module for performing complex parameter measurements at stepped frequency points.

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