A method for measuring and calibrating an airborne bistatic radar in an external field

Abstract

The present application relates to bistatic radar measurement calibration technical field, especially to a kind of outfield airborne bistatic radar measurement calibration method, the method is by selecting active calibration equipment for receiving radar transmitting antenna signal and after amplification is forwarded to radar receiving antenna, first aircraft with radar transmitting antenna and second aircraft with radar receiving antenna are respectively flown according to measurement calibration work scene, and corresponding index is measured.The correspondence between the specific index of active calibration equipment and the link gain and the RCS value of passive standard body is clarified, the background clutter during calibration can be suppressed, the problem of significant change of passive standard body RCS value caused by bistatic angle error of double flight platforms in airborne bistatic measurement is solved.The precision of airborne bistatic radar measurement data is improved, and the same active calibration equipment can replace multiple specifications of passive standard body, outfield application is light and flexible, and has important engineering application value.

Description

Technical Field

[0001] This invention relates to the field of bistatic radar measurement and calibration technology, and in particular to a method for field airborne bistatic radar measurement and calibration. Background Technology

[0002] Airborne bistatic radar measurement systems, capable of acquiring electromagnetic scattering characteristics data of ground and sea targets under different bistatic angles, are attracting increasing attention. The widespread application of precision-guided ground and sea strike weapons has made the role of airborne bistatic radar measurement in the study of the characteristics of ground and sea targets increasingly prominent. Furthermore, because the transmitter and receiver are located on separate flight platforms, different flight trajectories result in different flight configurations, enabling the acquisition of scattering information from ground objects illuminated and received at different angles. This has significant research value for studying the scattering characteristics of targets.

[0003] Calibration is an essential step in airborne bistatic radar measurement, and its accuracy directly affects the accuracy of airborne bistatic measurement data.

[0004] Currently, most airborne bistatic radar calibration methods rely on simulation, resulting in relatively poor calibration accuracy. As technology advances, the accuracy requirements for airborne bistatic radar calibration become increasingly stringent, rendering simulation calibration insufficient. However, due to the need for coordinated airspace and the high level of technical expertise required, research on field calibration is limited.

[0005] Chinese patent application CN117647784A discloses a bistatic ground-to-air dynamic RCS calibration method. Based on a rotary-wing UAV platform, it calibrates the coefficients of both the bistatic transmitting and receiving radars separately, obtaining the bistatic radar K-value coefficients to provide a standard basis for calculating the bistatic RCS data of a target. This calibration method is not limited by the bistatic baseline distance, has strong operability, and good adaptability to natural environments. The invention calibrates the bistatic transmitting and receiving radars separately, with the standard metal spheres at a relatively close distance and a high elevation angle, effectively avoiding the influence of ground clutter and resulting in high calibration quality. It solves the technical problem that current methods require the bistatic angle to be less than a certain angle, have high limitations on baseline distance, making it difficult to meet the requirements of pre- and post-calibration, thus greatly limiting practicality. However, the following technical problems exist with using this method for airborne bistatic radar calibration:

[0006] 1) This method uses optical sights to guide and capture standard metal spheres for both the receiving and transmitting radars, rather than performing calibration specific to the measurement scenario. Furthermore, the so-called calibration refers to calibrating the systematic errors of the bistatic radar during the measurement process. Therefore, calibration and measurement should be completed within the entire measurement period, not in separate time slots, as the systematic errors of the radar system may differ at different times, making precise calibration impossible. Additionally, the receiving radar in a bistatic radar system only receives signals and does not transmit; therefore, the obtained K2 is not the actual calibration coefficient K2 of the receiving radar within the bistatic radar system. Moreover, the combination of the transmitting and receiving radars in a bistatic radar system introduces new calibration coefficients that cannot be determined solely by the individual calibration coefficient formulas for the transmitting and receiving radars.

[0007] 2) Metal spheres cannot be measured from below because the size of the metal sphere itself is small and may be submerged in clutter. In addition, there is no theoretical value for the bi-station angle of the metal sphere.

[0008] Therefore, the above-mentioned dual-station ground-to-air dynamic RCS calibration method cannot effectively solve the problem of accurate calibration of airborne dual-station radar.

[0009] However, using passive standard bodies for calibration is subject to severe background clutter interference. Furthermore, passive standard bodies that meet the calibration conditions have a large area and are heavy. In addition, the bistatic error formed by the two flight platforms will cause significant changes in the RCS value of the standard body, which cannot meet the accuracy requirements of airborne bistatic radar measurement for calibration data.

[0010] Therefore, there is an urgent need for a method and device for field-based airborne bistatic radar measurement and calibration. Summary of the Invention

[0011] The purpose of this invention is to provide a method for field airborne bistatic radar measurement and calibration, which solves the problem that the passive standard body is significantly affected by background clutter interference and bistatic angle error of dual flight platforms in airborne bistatic radar measurement, and achieves accurate field calibration of airborne bistatic radar.

[0012] To achieve the above objectives, the present invention provides a method for field airborne bistatic radar measurement calibration, comprising the following steps:

[0013] An active calibration device is selected to receive the signal from the radar transmitting antenna and amplify it before forwarding it to the radar receiving antenna;

[0014] The first aircraft equipped with a radar transmitting antenna and the second aircraft equipped with a radar receiving antenna flew according to the measurement calibration working scenario and measured the following indicators:

[0015] The respective flight altitude and speed of the first and second aircraft, the beamwidth of the radar transmitting antenna, the angle between the radar transmitting antenna beam pointing and the ground, the operating parameters of the radar transmitting antenna, the transmitting power, the antenna gain, and the main lobe-to-side lobe ratio of the antenna, the beamwidth of the radar receiving antenna, the angle between the radar receiving antenna beam pointing and the ground, the operating parameters of the radar receiving antenna, the receiving power, the antenna gain, and the main lobe-to-side lobe ratio of the antenna.

[0016] Determine the receive power range, link gain, and device delay time of the active calibration equipment;

[0017] The conversion relationship between the link gain of the active calibration device and the RCS value of the equivalent passive standard body is determined based on the radar equation.

[0018] Based on the radar equations, the RCS of the airborne bistationary measurement data is determined using the relative comparison method.

[0019] Optionally, the selected active calibration equipment meets the following conditions:

[0020] The azimuth and elevation beamwidths of the transmitting and receiving antennas of the active calibration equipment are both greater than 40° in both directions.

[0021] Optionally, the azimuth and elevation angles of the transmitting and receiving antennas of the selected active calibration device can be adjusted and detected.

[0022] Optionally, an active calibration device may be selected that meets the following conditions:

[0023] (a) Coherent with bistatic radar signals, the relayed signals maintain phase and waveform consistency;

[0024] (b) Amplify the received signal with a fixed gain to make the device equivalent to a constant RCS target.

[0025] Optionally, determining the received power range, link gain, and device delay time of the active calibration device includes the following steps:

[0026] Based on the working scenario of airborne bistatic radar measurement and calibration, the farthest and closest distances from the radar transmitting antenna to the main lobe of the active calibration equipment are calculated, thereby calculating the receiving power range of the active calibration equipment.

[0027] The link gain of the active calibration equipment is determined based on the received power index and the equivalent passive standard size of the equipment.

[0028] The delay time is determined based on the length of the clutter echo within the main lobe of the transmitting antenna in the radar calibration scenario.

[0029] Optionally, the conversion relationship between the link gain of the active calibration device and the RCS value of the equivalent passive standard body is determined according to the radar equation, including the following steps:

[0030] The transmit power measured by the airborne bistatic radar is P. t The transmit antenna gain is G t The effective receiving area of ​​the receiving antenna is A. e Assuming the equivalent passive standard body RCS is σ, and the distance from the radar transmitting antenna to the target is R. t The distance from the target to the radar receiving antenna is R. r When the signal transmitted by the bistatic radar is reflected off a passive standard object and then back to the bistatic radar receiving antenna, the radar received power P is... r1 for

[0031]

[0032] The passive standard is replaced with an active calibration device. The dual-station measurement radar wavelength is λ, and the receiving antenna gain of the active calibration device is G. dr The effective receiving area is A d :

[0033]

[0034] The actual overall link gain is G n The radar signal is reflected back onto the active calibration equipment. The gain of the active calibration equipment's transmitting antenna is G. dt Then the radar received power P r2 for:

[0035]

[0036] Let P r1 =P r2 Then we have:

[0037]

[0038] Therefore, we get:

[0039]

[0040] Perform logarithmic operations:

[0041] (σ) dBsm =(G n ) dB +(G dr ) dB -(G dt ) dB +20log(λ)-10log(4π) (6).

[0042] Optionally, based on the radar equations, the RCS of the measured data is determined using a relative comparison method, including the following steps:

[0043] According to the radar equations, the radar-received target echo power can be expressed as a function of several parameters, including the target RCS, the transmitting system, the receiving system, and the propagation path. In airborne bistatic measurements, the bistatic RCS is defined as:

[0044]

[0045] Where, p r It is the received radar target echo power; p t It is the radar transmit power; G t It is the transmit antenna gain; G r λ is the receiver antenna gain; L is the radar wavelength; t It is the loss factor of the transmission system; L r It is the receiving system loss factor; L p It is the polarization loss factor; L m It is the loss factor along the propagation path; R t R is the distance from the radar transmitting antenna to the target. r It is the distance from the target to the radar receiving antenna; let:

[0046]

[0047] Then we can obtain:

[0048]

[0049] Apply RCS as (σ) dBsm The active calibration equipment calibrates the airborne bistatic radar measurements, letting (σ) dBsm =σ0, then:

[0050]

[0051] In the formula, k0 is the constant k of the active calibration device; p r0 To receive the echo power from the active calibration equipment; R t0 R is the distance from the radar transmitting antenna to the active calibration equipment. r0 It is the distance from the active calibration equipment to the radar receiving antenna; L m0 This represents the loss factor along the propagation path at that time.

[0052] During the measurement period, the airborne bistatic radar system operated smoothly, atmospheric propagation was stable, and the constants k = k0 and L were constant. m =L m0 The RCS of the target being measured is calculated using the following formula:

[0053]

[0054] Expressed in terms of receiver output voltage:

[0055]

[0056] Optionally, a minimum input threshold signal and a delay time can be set for the active calibration device. When the signal received by the active calibration device is greater than the minimum input threshold signal, it is considered a valid signal. The valid signal is amplified and then forwarded after a delay of the set delay time.

[0057] Optionally, the minimum input threshold signal of the active calibration device is determined based on the transmit power of the airborne bistatic radar transmitting antenna, the transmit antenna gain, and the farthest distance from the transmit antenna to the active calibration device.

[0058] Optionally, based on the maximum coverage length and width of the transmitting antenna beam during bistatic radar calibration, the clutter broadening time within the main lobe of the bistatic measurement radar transmitting antenna is calculated, and the delay time of the active calibration equipment is greater than the sum of the bistatic measurement radar transmitting pulse width and the clutter broadening.

[0059] The above-described technical solution of the present invention has the following advantages:

[0060] The present invention provides a method for calibration of airborne bistatic radar measurements in the field. This method utilizes an active calibration device to receive signals from the radar transmitting antenna, amplify them, and then transmit them to the radar receiving antenna. A first aircraft equipped with a radar transmitting antenna and a second aircraft equipped with a radar receiving antenna fly according to the calibration scenario, measuring corresponding parameters. The method clarifies the specific parameters of the active calibration device and the correspondence between its link gain and the RCS value of the passive standard, suppressing background clutter during calibration and resolving the problem of significant changes in the RCS value of the passive standard caused by bistatic angle errors of the two flight platforms in airborne bistatic measurements. This improves the accuracy of airborne bistatic radar measurement data, and the same active calibration device can replace passive standards of various specifications, making it lightweight, flexible, and of significant engineering application value. Attached Figure Description

[0061] The accompanying drawings are provided for illustrative purposes only, and the proportions and quantities of the components in the drawings may not be consistent with the actual product.

[0062] Figure 1 This is a schematic diagram of airborne bistatic radar measurement and calibration in an embodiment of the present invention;

[0063] Figure 2 This is a schematic diagram of the process for airborne bistatic radar measurement and calibration in an embodiment of the present invention. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0065] In airborne bistatic radar measurements, the bistatic angle is affected by factors such as wind speed and flight errors, resulting in errors between the actual and designed bistatic angles. These bistatic angle errors cause drastic changes in the RCS of traditional passive calibration bodies. This invention uses an active calibration device to amplify the received radar signal before transmitting it to the bistatic radar receiving antenna. This solves the problem of drastic RCS changes in traditional passive calibration bodies caused by bistatic angle errors, provided the receiving and transmitting antennas of the active calibration device have sufficiently wide beams. Simultaneously, it suppresses background clutter during calibration, improving the accuracy of airborne bistatic radar measurement data. Furthermore, the same active calibration device can replace various specifications of passive standard bodies, making it lightweight and flexible for field applications and possessing significant engineering application value.

[0066] The present invention will be further illustrated by the following examples:

[0067] like Figure 1 and Figure 2 As shown, an embodiment of the present invention for field airborne bistatic radar measurement calibration using active calibration equipment includes the following steps:

[0068] S1: Select an active calibration device to receive the signal from the radar transmitting antenna and amplify it before forwarding it to the radar receiving antenna;

[0069] S2: The first aircraft equipped with a radar transmitting antenna and the second aircraft equipped with a radar receiving antenna fly according to the measurement calibration working scenario and measure the following indicators:

[0070] The respective flight altitude and speed of the first and second aircraft, the beamwidth of the radar transmitting antenna, the angle between the radar transmitting antenna beam pointing and the ground, the operating parameters of the radar transmitting antenna, the transmitting power, the antenna gain, and the main lobe-to-side lobe ratio of the antenna, the beamwidth of the radar receiving antenna, the angle between the radar receiving antenna beam pointing and the ground, the operating parameters of the radar receiving antenna, the receiving power, the antenna gain, and the main lobe-to-side lobe ratio of the antenna.

[0071] S3: Determine the receive power range, link gain, and device delay time of the active calibration device;

[0072] S4: Determine the conversion relationship between the link gain of the active calibration device and the RCS value of the equivalent passive standard body based on the radar equation;

[0073] S5: Based on the radar equations, the RCS of the airborne bistationary measurement data is determined using the relative comparison method.

[0074] In this embodiment, an active calibration device is used for field airborne bistatic radar measurement calibration. This ensures that the active calibration device reflects the echo within the main lobe of the airborne bistatic radar transmitting antenna, preventing the sidelobes of the transmitting antenna from detecting targets and causing measurement errors. It also allows for effective differentiation between the echo and clutter within the main lobe of the bistatic radar transmitting antenna in terms of range and power, thereby suppressing clutter and improving calibration accuracy. This addresses the problem of significant changes in the RCS value of passive standard bodies caused by bistatic angle errors from two flight platforms in airborne bistatic measurements. It improves the accuracy of airborne bistatic radar measurement data, and the same active calibration device can replace passive standard bodies of various specifications, making it lightweight, flexible, and of significant engineering application value.

[0075] In one example, the selected active calibration device meets the following conditions:

[0076] The azimuth and elevation 3dB beamwidths of the transmitting and receiving antennas of the active calibration equipment are both greater than 40°. The sufficiently wide 3dB beamwidth can better solve the problem of significant changes in the RCS value of passive standard objects caused by the bistatic angle error of the dual flight platform in airborne bistatic measurements. Generally, a bistatic angle error of about 10° can still avoid significant changes in the RCS value of passive standard objects.

[0077] In one example, the azimuth and elevation angles of the transmitting and receiving antennas of the selected active calibration equipment can be adjusted and detected (the adjusted angles can be known), which can meet the calibration requirements under different bistatic angles. It is worth noting that the adjustment of the azimuth and elevation angles of the transmitting and receiving antennas of the active calibration equipment can be achieved using existing structures, and will not be elaborated further here. Active calibration equipment generally includes a transmitting antenna, a receiving antenna, and a fixed magnified diagram; its structure is existing technology and will not be described in detail here.

[0078] In one example, the active calibration device is selected to meet the following conditions:

[0079] (a) Coherent with bistatic radar signals, the relayed signals maintain phase and waveform consistency;

[0080] (b) Amplify the received signal with a fixed gain to make the device equivalent to a constant RCS target.

[0081] In one example, determining the received power range, link gain, and device delay time of an active calibration device includes the following steps:

[0082] Based on the working scenario of airborne bistatic radar measurement and calibration, the farthest and closest distances from the radar transmitting antenna to the main lobe of the active calibration equipment are calculated, thereby calculating the receiving power range of the active calibration equipment.

[0083] The link gain of the active calibration equipment is determined based on the received power index and the equivalent passive standard size of the equipment.

[0084] The delay time is determined based on the length of the clutter echo within the main lobe of the transmitting antenna in the radar calibration scenario.

[0085] In this embodiment, a minimum input threshold signal and a delay time are set for the active calibration device. When the signal received by the active calibration device is greater than the minimum input threshold signal, it is considered a valid signal. The valid signal is amplified and then forwarded after a delay of the set delay time.

[0086] Specifically, the minimum input threshold signal of the active calibration device is determined based on the transmit power of the airborne bistatic radar transmitting antenna, the transmit antenna gain, and the farthest distance from the transmit antenna to the active calibration device.

[0087] Specifically, based on the maximum coverage length and width of the transmitting antenna beam during bistatic radar calibration, the clutter broadening time within the main lobe of the bistatic measurement radar transmitting antenna is calculated. The delay time of the active calibration equipment is greater than the sum of the bistatic measurement radar transmitting pulse width and the clutter broadening.

[0088] The received power of the active calibration equipment and the transmitted power p of the airborne bistatic measurement radar t Transmit antenna gain G t It is related to spatial transmission loss (LoS).

[0089] Los=32.44+20*log(D)+20*log(F);

[0090] Where: D is the transmission distance in meters (m); F is the operating frequency in GHz; based on the airborne bistatic radar measurement and calibration scenario, the farthest and closest distances D to the main lobe of the bistatic measurement radar transmitting antenna reaching the active calibration equipment are calculated, thereby calculating the range of the active calibration equipment's received power Pin: Pin = P t +G t -Los. The link gain of the active calibration equipment is determined based on its received power specifications and the equivalent passive standard RCS value. The signal delay time is determined based on the clutter echo length within the main lobe in the airborne bistatic radar measurement and calibration scenario.

[0091] In one example, determining the conversion relationship between the link gain of an active calibration device and the RCS value of an equivalent passive standard body based on radar equations includes the following steps:

[0092] The transmit power measured by the airborne bistatic radar is P. t The transmit antenna gain is G t The effective receiving area of ​​the receiving antenna is A. e Assuming the equivalent passive standard body RCS is σ, and the distance from the radar transmitting antenna to the target is R. t The distance from the target to the radar receiving antenna is R. r When the signal transmitted by the bistatic radar is reflected off a passive standard object and then back to the bistatic radar receiving antenna, the radar received power P is... r1 for

[0093]

[0094] The passive standard is replaced with an active calibration device. The dual-station measurement radar wavelength is λ, and the receiving antenna gain of the active calibration device is G. dr The effective receiving area is A d :

[0095]

[0096] The actual overall link gain is G n The radar signal is reflected back onto the active calibration equipment. The gain of the active calibration equipment's transmitting antenna is G. dt Then the radar received power P r2 for:

[0097]

[0098] Let P r1＝ P r2 Then we have:

[0099]

[0100] Therefore, we get:

[0101]

[0102] Perform logarithmic operations:

[0103] (σ) dBsm =(G n ) dB +(G dr ) dB -(G dt ) dB +20log(λ)-10log(4π) (6).

[0104] Thus, the technical specifications of the active calibration equipment were determined. Since the active calibration equipment and the passive standard operate in the same environment, the reflected echo power of the airborne bistatic radar signal illuminating the passive standard can be made the same as the reflected echo power illuminating the active calibration equipment. Therefore, the RCS value (σ) of the active calibration equipment can be calculated. dBsm and active calibration device link gain (G n ) dB Receiver antenna gain (G) dr ) dB Transmit antenna gain (G) dt ) dB And the relationship between wavelength λ.

[0105] In one example, the RCS of the measured data is determined using the relative comparison method based on the radar equations, including the following steps:

[0106] According to the radar equations, the radar-received target echo power can be expressed as a function of several parameters, including the target RCS, the transmitting system, the receiving system, and the propagation path. In airborne bistatic measurements, the bistatic RCS is defined as:

[0107]

[0108] Where, p r It is the received radar target echo power; p t It is the radar transmit power; G t It is the transmit antenna gain; G r λ is the receiver antenna gain; L is the radar wavelength; t It is the loss factor of the transmission system; L r It is the receiving system loss factor; L p It is the polarization loss factor; L m It is the loss factor along the propagation path; R t R is the distance from the radar transmitting antenna to the target. r It is the distance from the target to the radar receiving antenna; let:

[0109]

[0110] Then we can obtain:

[0111]

[0112] Apply RCS as (σ) dBsm The active calibration equipment calibrates the airborne bistatic radar measurements, letting (σ) dBsm =σ0, then:

[0113]

[0114] In the formula, k0 is the constant k of the active calibration device; p r0 To receive the echo power from the active calibration equipment; R t0 R is the distance from the radar transmitting antenna to the active calibration equipment. r0 It is the distance from the active calibration equipment to the radar receiving antenna; L m0 This represents the loss factor along the propagation path at that time.

[0115] During the measurement period, the airborne bistatic radar system operated smoothly, atmospheric propagation was stable, and the constants k = k0 and L were constant. m =L m0 The RCS of the target being measured is calculated using the following formula:

[0116]

[0117] Expressed in terms of receiver output voltage:

[0118]

[0119] Thus, the calibration method for airborne bistatic radar measurements using active calibration equipment was determined.

[0120] Based on the radar equations, the relative comparison method is used to calculate the RCS of the target by measuring the receiver output voltage value when the airborne bistatic radar measures the target and the receiver output voltage value when measuring the active calibration equipment, as well as the distances between the airborne radar transmitting antenna and the target, the airborne radar transmitting antenna and the active calibration equipment, the target and the airborne radar receiving antenna, and the active calibration equipment and the airborne radar receiving antenna during the airborne bistatic radar measurement.

[0121] It is worth noting that the measurement and calibration working scenario in this invention, the determination of the received power range, link gain and device delay time of the active calibration device, and the conversion relationship between the link gain of the active calibration device and the equivalent passive standard RCS value determined according to the radar equation, and the application of the relative comparison method to determine the RCS of the bi-station measurement data, all use existing technologies and will not be described in detail here.

[0122] Any aspects not described in detail in this invention are common knowledge or existing technology in the field, and will not be elaborated upon here.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that not every embodiment contains only one independent technical solution, and in the absence of conflict between solutions, the various technical features mentioned in each embodiment can be combined in any way to form other implementation methods that can be understood by those skilled in the art.

[0124] Furthermore, without departing from the scope of the present invention, modifications to the technical solutions described in the foregoing embodiments, or equivalent substitutions of some of the technical features, shall not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for field airborne bistatic radar measurement and calibration, characterized in that, Includes the following steps: An active calibration device is selected to receive the signal from the radar transmitting antenna and amplify it before forwarding it to the radar receiving antenna; The first aircraft equipped with a radar transmitting antenna and the second aircraft equipped with a radar receiving antenna flew according to the measurement calibration working scenario and measured the following indicators: The respective flight altitude and speed of the first and second aircraft, the beamwidth of the radar transmitting antenna, the angle between the radar transmitting antenna beam pointing and the ground, the operating parameters of the radar transmitting antenna, the transmitting power, the antenna gain, and the main lobe-to-side lobe ratio of the antenna, the beamwidth of the radar receiving antenna, the angle between the radar receiving antenna beam pointing and the ground, the operating parameters of the radar receiving antenna, the receiving power, the antenna gain, and the main lobe-to-side lobe ratio of the antenna. Determine the receive power range, link gain, and device delay time of the active calibration equipment; The conversion relationship between the link gain of the active calibration device and the RCS value of the equivalent passive standard body is determined based on the radar equation. Based on the radar equations, the RCS of the airborne bistatic measurement data is determined using the relative comparison method. The conversion relationship between the link gain of the active calibration device and the RCS value of the equivalent passive standard body is determined based on the radar equation, including the following steps: The transmit power measured by the airborne bistatic radar is The transmit antenna gain is The effective receiving area of ​​the receiving antenna is Assuming the equivalent passive standard body RCS is The distance from the radar transmitting antenna to the target is The distance from the target to the radar receiving antenna is When the signal transmitted by the bistatic radar is reflected off a passive standard object and then onto the bistatic radar receiving antenna, the radar received power... for: （1） The passive standard body was replaced with an active calibration device, and the dual-station measurement radar wavelength was [wavelength value missing]. The gain of the receiving antenna of the active calibration equipment is The effective receiving area is : （2） The actual overall link gain is The radar transmitted signal illuminates the active calibration equipment and reflects the echo. The gain of the active calibration equipment's transmitting antenna is... Then the radar receiving power for: （3） make Then we have: （4） Therefore, we get: （5） Perform logarithmic operations: （6）； Set the minimum input threshold signal and delay time for the active calibration device. When the signal received by the active calibration device is greater than the minimum input threshold signal, it is a valid signal. The valid signal is amplified and forwarded after a delay of the set delay time. Among them, the minimum input threshold signal of the active calibration equipment is determined based on the transmit power of the airborne bistatic radar transmitting antenna, the transmit antenna gain, and the farthest distance from the transmit antenna to the active calibration equipment; Based on the maximum coverage length and width of the transmitting antenna beam during bistatic radar calibration, the clutter broadening time within the main lobe of the bistatic measurement radar transmitting antenna is calculated. The delay time of the active calibration equipment is greater than the sum of the transmitting pulse width and the clutter broadening of the bistatic measurement radar.

2. The method according to claim 1, characterized in that: The selected active calibration equipment meets the following conditions: The azimuth and elevation beamwidths of the transmitting and receiving antennas of the active calibration equipment are both greater than 40° in both directions.

3. The method according to claim 1, characterized in that: The azimuth and elevation angles of the transmitting and receiving antennas of the selected active calibration equipment can be adjusted and detected.

4. The method according to claim 1, characterized in that: The following conditions must be met when selecting active calibration equipment: (a) Coherent with bistatic radar signals, the relayed signals maintain phase and waveform consistency; (b) Amplify the received signal with a fixed gain to make the device equivalent to a constant RCS target.

5. The method according to claim 1, characterized in that: Determine the received power range, link gain, and device delay time of the active calibration device, including the following steps: Based on the working scenario of airborne bistatic radar measurement and calibration, the farthest and closest distances from the radar transmitting antenna to the main lobe of the active calibration equipment are calculated, thereby calculating the receiving power range of the active calibration equipment. The link gain of the active calibration equipment is determined based on the received power index and the equivalent passive standard size of the equipment. The delay time is determined based on the length of the clutter echo within the main lobe of the transmitting antenna in the radar calibration scenario.

6. The method according to claim 1, characterized in that: Based on the radar equations, the RCS of the measured data is determined using the relative comparison method, including the following steps: According to the radar equations, the radar-received target echo power is expressed as a function of several parameters, including the target's RCS, the transmitting system, the receiving system, and the propagation path. In airborne bistatic measurements, the bistatic RCS is defined as: （7） in, It is the received radar target echo power; It is the radar transmission power; It is the transmit antenna gain; It is the receiving antenna gain; It is the radar wavelength; It is the loss factor of the transmission system; It is the loss factor of the receiving system; It is the polarization loss factor; It is the loss factor along the propagation path; It is the distance from the radar transmitting antenna to the target. It is the distance from the target to the radar receiving antenna; let: （8） Then we can obtain: （9） Apply RCS for Active calibration equipment calibrates airborne bistatic radar measurements, enabling... ,but: （10） In the formula, For active calibration equipment constants ; To receive the echo power from the active calibration equipment; It is the distance from the radar transmitting antenna to the active calibration equipment. It is the distance from the active calibration equipment to the radar receiving antenna; This represents the loss factor along the propagation path at that time. During the measurement period, the airborne bistatic radar system operated stably, atmospheric propagation was stable, and the constant was [unclear]. , The RCS of the target being measured is calculated using the following formula: （11） Expressed in terms of receiver output voltage: （12）。

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