A device for measuring blind zone distance of coherent wind finding radar

Abstract

The utility model discloses a kind of device for measuring coherent wind-radar blind area distance, comprising: narrow linewidth laser, optical isolator, first beam splitter, signal generator, driver;External modulation optical device, frequency shift chopper modulation is carried out, and periodic pulsed light is formed;Second beam splitter, first photoelectric detector, coupler, second photoelectric detector and oscilloscope;Compared with prior art, through the comparison of electric drive signal, pulsed light waveform, beat frequency signal in time domain, it is realized in device level, characterized with the response time of "electric-optical", accurately characterized device "leakage light" duration, turn-off performance;At radar level, accurately calculate radar actual blind area distance.

Description

Technical Field

[0001] This utility model relates to the field of coherent wind-measuring radar technology, specifically to a device for measuring the blind zone distance of coherent wind-measuring radar. Background Technology

[0002] Coherent wind lidar is a non-contact telemetry lidar system based on the principle of coherent Doppler velocimetry. Existing coherent wind lidars cannot detect wind speed and direction within a distance d from the optical antenna output end. This area is the blind zone of the coherent wind lidar, and d is defined as the blind zone distance.

[0003] The blind zone distance of a wind-measuring lidar is one of the core indicators for evaluating its short-range detection capability, directly impacting data completeness and adaptability to application scenarios. Accurately measuring the blind zone distance is crucial to ensuring the integrity and accuracy of wind field data. Furthermore, different application scenarios have varying requirements for blind zone distance; precise blind zone distance measurement helps engineers select appropriate wind-measuring lidar equipment, ensuring the safety of engineering structures under wind loads. If the blind zone distance is too large, it indicates deficiencies in short-range detection, requiring optimization and improvement of the lidar's optical system and signal processing algorithms. Accurate blind zone distance measurements also provide important data for equipment calibration and standardization, ensuring that the wind-measuring lidar provides accurate and reliable measurement data under various environmental conditions.

[0004] If the speed of light in the atmosphere is c, and the pulse time-domain width is τ, then theoretically, the blind zone distance d (or range resolution) of the radar is determined by the following formula: However, in radar use, it is often found that the actual blind zone distance is greater than the theoretical blind zone distance. This is because the external modulation optical device requires a response time when it is turned off by chopping, which causes residual light to leak (leaked light) to the optical antenna within the theoretical optical pulse interval, and forms reflected light (leaked reflected light) at the output end face. At the same time, since the backscattered light signal intensity of atmospheric aerosol is very small, it will be overwhelmed by the leaked reflected light, making it impossible to distinguish wind speed and wind direction information, thus effectively causing the actual blind zone distance of the radar to be larger than the theoretical value.

[0005] There are two existing solutions:

[0006] 1. Using a high-speed photodetector and a high-speed oscilloscope, the pulse waveform of the radar is directly measured to obtain the duration of the "leakage light" and estimate the blind zone distance. High-speed photodetectors offer high sensitivity, low noise, and fast response time. When used with a high-bandwidth, high-sampling-rate oscilloscope, they can effectively detect and observe weak light signals, accurately detecting the arrival time and duration of the pulse light. Furthermore, within a certain optical power range, there is a good linear relationship between the output electrical signal and the input optical signal. The advantage of this method is its simplicity; however, high-speed photodetectors and oscilloscopes are expensive. In addition, because the "leakage light" is located at the tail of the pulse waveform, its power is significantly lower than the peak value of the pulse light by 1-2 orders of magnitude. Its amplitude on the oscilloscope is close to the bottom noise, making it impossible to clearly read the amplitude and duration of the pulse waveform tail. Therefore, the accurate duration of the "leakage light" cannot be confirmed, and the blind zone distance cannot be accurately quantified.

[0007] 2. For finished or semi-finished radar units, a data acquisition card is used to acquire the radar beat frequency signal (obtained from atmospheric backscattered light and local oscillator beat frequency) in the time domain. The acquired data is then processed to obtain the corresponding blind zone distance for the radar. However, this method generally cannot effectively control the intensity of the reflected light from the end face, as this intensity frequently fluctuates. High intensity can cause saturation distortion in the radar detector, affecting the measurement results. Furthermore, it is inconvenient to add an optical attenuator to adjust the light intensity in finished or semi-finished radar units. In addition, in finished or semi-finished radar units, the external modulation optical device is already installed and fixed. If the blind zone distance measured using the above method does not meet the requirements, it is necessary to disassemble and replace the external modulation optical device and even other connected optoelectronic devices, resulting in additional rework time. Therefore, this method cannot be used for incoming material inspection of the external modulation optical device. Utility Model Content

[0008] The purpose of this invention is to address the shortcomings of existing coherent wind-measuring lidar blind zone distance measurement, such as the high cost of high-speed photodetectors and high-speed oscilloscopes; the inability to stably control the intensity of reflected light from the end face, which easily leads to detector saturation distortion; and the tendency for finished or semi-finished lidar units to require additional rework for blind zone distance measurement, thus resulting in inaccurate measurement of blind zone distance. Therefore, this invention proposes a device that measures the "electro-optical" response time of the external modulation optical device used to obtain the blind zone distance of the coherent wind-measuring lidar.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] An apparatus for measuring the blind zone distance of a coherent wind-measuring radar, comprising:

[0011] Narrow linewidth lasers are used to emit continuous light;

[0012] Optical isolators are used to transmit forward-propagating light and isolate reverse-propagating light; they prevent potential backlighting in the optical path from damaging narrow-linewidth lasers.

[0013] The first beam splitter is used to split continuous light into local oscillator light and light to be modulated;

[0014] A signal generator controls the driver to turn on and off via electrical signals;

[0015] The driver is used to generate an electrical drive signal with a carrier wave; this signal is used to drive an external modulation optical device to perform frequency shift chopping modulation of the light to be modulated, and is simultaneously connected to an oscilloscope via a signal line for observation.

[0016] An external modulation optical device, electrically connected to a driver, receives an electrical drive signal generated by the driver; used to perform frequency shifting and chopping modulation on the light to be modulated to form periodic pulsed light;

[0017] The second beam splitter is used to split the periodic pulse light into two beams, one of which enters the coupler and the other enters the first photodetector.

[0018] The first photodetector is used to send the detected electrical signal to the oscilloscope;

[0019] The coupler is used to receive the local oscillator light and a modulated beam after beam splitting, and transmits it to the second photodetector after frequency beat;

[0020] The second photodetector is used to send the detected electrical signal to the oscilloscope;

[0021] An oscilloscope is used to observe the electrical drive signal generated by the driver and the electrical signals detected by the first and second photodetectors.

[0022] In this process, a narrow-linewidth laser emits continuous light, which passes through an optical isolator and enters the first beam splitter. The first beam splitter splits the continuous light into a local oscillator beam and a beam to be modulated. The local oscillator beam enters a coupler, while the beam to be modulated enters an external modulation device. Through the frequency-shifting chopping principle, periodic pulses are generated and sent to the second beam splitter. The second beam splitter splits the light into two beams. One beam enters the first photodetector, which detects the corresponding electrical signal and sends it to an oscilloscope for observation. The other beam enters the coupler, beats the local oscillator beam, and is then sent to the second photodetector. The second photodetector detects the corresponding electrical signal and sends it to an oscilloscope for observation.

[0023] As a further preferred embodiment of this invention, the external modulation optical device is one of an acousto-optic modulator (AOM), an electro-optic modulator (EOM), a thermo-optic modulator, or an on-chip integrated optical modulator.

[0024] As a further preferred embodiment of this invention, optical attenuators are respectively provided between the first beam splitter and the coupler, and between the second beam splitter and the coupler.

[0025] As a further preferred embodiment of this invention, the optical attenuator is an optical attenuator with adjustable attenuation.

[0026] As a further preferred embodiment of this invention, the first photodetector is configured as a photodiode or an avalanche diode; the second photodetector is a photodiode, an avalanche diode, or a balanced photodetector.

[0027] As a further preferred embodiment of this invention, the splitting ratio of the first beam splitter is adjustable, while the splitting ratio of the second beam splitter is a fixed ratio.

[0028] As a further preferred embodiment of this invention, the beam splitting ratio of the second beam splitter is 1:1.

[0029] The device for measuring the blind zone distance of coherent wind-measuring radar proposed in this utility model has the following advantages compared with the prior art:

[0030] 1. This utility model achieves the following: at the device level, it characterizes the "electro-optic" response time and accurately characterizes the duration of "leakage light" and the turn-off performance of the device by comparing the electric drive signal, pulsed light waveform, and beat frequency signal in the time domain; at the radar level, it accurately calculates the actual blind zone distance of the radar.

[0031] 2. By setting up an optical attenuator, this utility model can attenuate the light intensity, effectively avoiding the problem of waveform saturation distortion when measuring the blind zone distance of finished or semi-finished radar units;

[0032] 3. This utility model supports component screening and incoming material inspection before radar assembly. It selects qualified external modulation optical components based on the "leakage light" performance, avoiding the problem of rework if the blind zone distance test fails after the radar is installed in a semi-finished or finished product state. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a coherent wind-measuring lidar.

[0034] Figure 2 This is a schematic diagram of the structure of a device for measuring the blind zone distance of a coherent wind-measuring radar, which relates to this utility model.

[0035] Figure 3 This is a schematic diagram of another device for measuring the blind zone distance of a coherent wind-measuring radar, which relates to this utility model.

[0036] Figure 4It is the electrical signal waveform generated by the signal generator to control the opening and closing of the driver;

[0037] Figure 5 It is the waveform of the electrical drive signal output by the driver as measured by an oscilloscope (carrier frequency is 40MHz);

[0038] Figure 6 It is the pulsed light waveform measured by the first photodetector;

[0039] Figure 7 It is the beat frequency signal waveform measured by the second photodetector (carrier frequency is 40MHz).

[0040] This is a schematic diagram of the structure of the present invention.

[0041] The meanings of the labels in the figure are as follows: 1. Narrow linewidth laser, 2. Optical isolator, 3. First beam splitter, 4. External modulation optical device, 5. Second beam splitter, 6. First photodetector, 7. Coupler, 8. Second photodetector, 9. Oscilloscope, 10. Driver, 11. Signal generator, 12. Optical attenuator. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0043] The working principle of coherent wind lidar: Pulsed light generated by a laser is emitted into the air being measured through an optical antenna. It interacts with aerosols in the air, generating a backscattered light signal containing atmospheric information. This backscattered light signal contains information about the velocity of the aerosols along the radial direction of the laser beam. After being received by the optical antenna and detected and processed by the signal processing unit, the wind speed and direction information of the scanned area in the atmosphere can be retrieved. Figure 1 As shown. Pulsed light is typically generated by externally modulated optical devices (such as acousto-optic modulators (AOM), electro-optic modulators (EOM), thermo-optic modulators, on-chip integrated optical modulators, etc.) through the principle of frequency shifting and chopping. These devices chop continuous light into pulsed light and simultaneously load a carrier wave with a certain frequency shift (e.g., 40MHz) onto the pulsed light to satisfy the heterodyne detection principle of coherent wind lidar. If the speed of light in the atmosphere is c and the pulse time-domain width is τ, then theoretically, the blind zone distance d (or range resolution) of the radar is determined by the following formula: In other words, within a distance *d* from the emitting end of the optical antenna, there is a radar blind zone, during which the radar cannot detect wind speed and direction. In actual use, due to the response time required when the external modulation optical device is turned off by chopping, optical signals leak to the optical antenna beyond the pulse width *τ* (hereinafter referred to as "leaked light") and form reflected light at the emitting end face (hereinafter referred to as "leaked reflected light"). At the same time, the backscattered light signal intensity of atmospheric aerosols is very small, with an average power usually only on the order of pW. Therefore, it will be overwhelmed by the "leaked reflected light," making it impossible to distinguish wind speed and direction information. This effectively increases the radar blind zone distance compared to the theoretical value mentioned above.

[0044] Based on the accurate measurement of the duration of "leakage light" and the device turn-off time of externally modulated optical devices, this invention derives the principle of blind zone distance and proposes a device for measuring the blind zone distance of coherent wind-measuring radar. This device can also be used to evaluate the performance of externally modulated optical devices.

[0045] Example 1: Combining Figure 2 A device for measuring the blind zone distance of a coherent wind-measuring radar includes: a narrow-linewidth laser 1 for emitting continuous light; an optical isolator 2 for transmitting forward transmitted light and isolating reverse transmitted light to prevent potential backlighting in the optical path from damaging the narrow-linewidth laser; a first beam splitter 3 for splitting the continuous light into local oscillator light and light to be modulated, the splitting ratio of the first beam splitter 3 being adjustable; a signal generator 11 for controlling the opening and closing of a driver via an electrical signal; a driver 10 for generating an electrical drive signal; this signal is used to drive an external modulation optical device 4 to perform frequency-shift chopping modulation on the light to be modulated, and is simultaneously connected to an oscilloscope via a signal line for observation; the external modulation optical device 4 is electrically connected to the driver 10 and receives the electrical drive signal generated by the driver; it is used to perform frequency-shift chopping modulation on the light to be modulated, producing periodic pulsed light.

[0046] The external modulation optical device 4 is one of an acousto-optic modulator (AOM), an electro-optic modulator (EOM), a thermo-optic modulator, or an on-chip integrated optical modulator; the driver 10 is electrically connected to the signal generator 11; the signal generator 11 controls the driver 10 to turn on and off via an electrical signal, the waveform of which is as follows: Figure 4As shown; the electric drive signal generated by the driver controls the external modulation optical device 4 to form periodic pulsed light by frequency shifting and chopping principle of continuous light; the second beam splitter 5 is used to split the periodic pulsed light into two beams, one beam enters the coupler 7, and the other beam enters the first photodetector 6; the first photodetector 6 is used to send the detected electrical signal to the oscilloscope 9; the coupler 7 is used to receive the local oscillator light and the modulated light after the second beam splitter 5, perform frequency beat and transmit it to the second photodetector 8; the second photodetector 8 is used to send the detected electrical signal to the oscilloscope 9; the first photodetector 6 is a photodiode or an avalanche diode; the second photodetector 8 is a photodiode, an avalanche diode or a balanced photodetector; the oscilloscope 9 is used to observe the electric drive signal generated by the driver 10 and the electrical signals detected by the first photodetector 6 and the second photodetector 8.

[0047] In this system, a narrow-linewidth laser 1 emits continuous light, which passes through an optical isolator 2 and enters a first beam splitter 3. The first beam splitter 3 splits the continuous light into a local oscillator beam and a beam to be modulated. The local oscillator beam enters a coupler 7. The beam to be modulated enters an external modulation device 4, which, through the principle of frequency shifting and chopping, forms periodic pulses of light, which are then sent to a second beam splitter 5. The second beam splitter 5 splits the light into two beams. One beam enters a first photodetector 6, which detects the corresponding electrical signal and sends it to an oscilloscope 9 for observation. The other beam enters a coupler 7, beats the local oscillator beam, and is then sent to a second photodetector 8. The second photodetector 8 detects the corresponding electrical signal and sends it to an oscilloscope 9 for observation.

[0048] Example 2: Combination Figure 3 A device for measuring the blind zone distance of a coherent wind-measuring radar includes: a narrow-linewidth laser 1 for emitting continuous light; an optical isolator 2 for transmitting forward-transmitting light and isolating reverse-transmitting light to prevent potential backlighting in the optical path from damaging the narrow-linewidth laser; a first beam splitter 3 for splitting the continuous light into local oscillator light and light to be modulated, the splitting ratio of the first beam splitter 3 being adjustable; a driver 10 for generating an electrical drive signal with a carrier wave; this signal is used to drive an external modulation optical device 4 to perform frequency-shift chopping modulation on the light to be modulated, and is simultaneously observed by connecting a signal line to an oscilloscope; the external modulation optical device 4 is electrically connected to the driver 10 and receives the electrical drive signal generated by the driver; it is used to perform frequency-shift chopping modulation on the light to be modulated to form periodic pulsed light; the external modulation optical device 4 is one of an acousto-optic modulator (AOM), an electro-optic modulator (EOM), a thermo-optic modulator, or an on-chip integrated optical modulator; the driver 10 is electrically connected to a signal generator 11; the signal generator 11 controls the opening and closing of the driver 10 through an electrical signal, the waveform of which is shown below. Figure 4As shown; the electric drive signal generated by the driver controls the external modulation optical device 4 to form periodic pulsed light by frequency shifting and chopping principle of continuous light; the second beam splitter 5 is used to split the periodic pulsed light into two beams, one beam enters the coupler 7, and the other beam enters the first photodetector; the first photodetector 6 is used to send the detected electrical signal to the oscilloscope 9; optical attenuators 12 are respectively set between the first beam splitter 3 and the coupler 7, and between the second beam splitter 5 and the coupler 7 to attenuate the light intensity; the coupler 7 is used to receive the attenuated local oscillator light and the modulated light beam split by the second beam splitter 5 and attenuated by the optical attenuator 12, and transmit it to the second photodetector 8 after frequency beat; the second photodetector 8 is used to send the detected electrical signal to the oscilloscope 9; the first photodetector 6 is a photodiode or avalanche diode; the second photodetector 8 is a photodiode, avalanche diode or balanced photodetector; the oscilloscope 9 is used to observe the electrical signals detected by the first photodetector 6 and the second photodetector 8.

[0049] In this system, a narrow-linewidth laser 1 emits continuous light, which passes through an optical isolator 2 and enters a first beam splitter 3. The first beam splitter 3 splits the continuous light into a local oscillator beam and a beam to be modulated. The local oscillator beam is attenuated by an optical attenuator 12 and then enters a coupler 7. The beam to be modulated enters an external modulation optical device 4, which forms periodic pulses through a frequency-shifting chopping principle and sends them to a second beam splitter 5. The second beam splitter 5 splits the light into two beams. One beam enters a first photodetector 6, which detects the corresponding electrical signal and sends it to an oscilloscope 9 for observation. The other beam is attenuated by an optical attenuator 12 and then enters a coupler 7. It beats the local oscillator beam and is then sent to a second photodetector 8, which detects the corresponding electrical signal and sends it to an oscilloscope 9 for observation.

[0050] Example 3: Method for measuring the blind zone distance of a coherent wind-measuring radar: S1. Construct the device according to Example 1 or Example 2; S2. Measure the waveform of the electrically driven signal used for modulation, and read out the signal time-domain width as t1, such as... Figure 5 As shown; S3, measure the modulated pulsed light waveform and read the pulse time-domain width as r0, as... Figure 6 As shown; S6, measure the waveform of the beat frequency signal after coupling, as shown. Figure 7 As shown; S5, use Hilbert transform to calculate the envelope of the observed beat frequency signal waveform, and the envelope width can be read as t2. Then, combine t0 and t1 to characterize the turn-off time of the external modulation device. S6, calculate the actual blind zone distance d of the radar based on the envelope width t2 of the beat frequency signal waveform.

[0051] The following characterizes the electro-optical response time of the external modulation device. The pulse time-domain width t0 is usually determined using a waveform inflection point estimation algorithm. Under normal circumstances, due to the time delay in the conversion of the electrical signal to the optical signal, r0 has become larger than r1; t0-t1 is used to characterize the photoelectric conversion delay of the external modulation optical device, that is, to characterize its electro-optical response time.

[0052] The following characterizes the duration of the "leaking light" and the actual blind zone distance of the radar. Because the waveform inflection point estimation algorithm is used to determine t0, t0 cannot accurately reflect the duration of the "leaking light." This is because, regardless of how the inflection point of the pulse tail is defined mathematically, a small "leaking light" portion still exists after the inflection point. The amplitude of this portion is close to the noise floor level of the oscilloscope, and its duration is difficult to read on the oscilloscope. However, in this invention, by acquiring the corresponding beat frequency signal, it is easy to read the moment when its amplitude drops to zero. Performing a Hilbert transform on the beat frequency signal waveform yields the envelope of the waveform. Then, the envelope width t2 is calculated. t2-t0 represents the duration of the "leaking light," which is also used to characterize the turn-off time of the external modulation optical device. Furthermore, the actual blind zone distance of the radar can be calculated as follows:

[0053]

[0054] Where c is the speed of light in the atmosphere, and d is the minimum detection range (or range resolution) of the radar, which is the actual blind zone distance of the radar.

[0055] In the description of this utility model, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0056] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; 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; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0057] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is 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.

[0058] The foregoing has shown and described the basic principles, main features, and advantages of this utility model. Those skilled in the art should understand that the above embodiments do not limit this utility model in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of this utility model.

Claims

1. An apparatus for measuring a blind zone distance of a coherent wind finding radar, characterized in that include: Narrow linewidth lasers are used to emit continuous light; Optical isolators are used to transmit forward-propagating light and isolate reverse-propagating light. The first beam splitter is used to split continuous light into local oscillator light and light to be modulated; A signal generator controls the driver to turn on and off via electrical signals; A driver, used to generate electrical drive signals; An externally modulated optical device is electrically connected to the driver and receives the electrical drive signal generated by the driver. Used for frequency shifting and chopping modulation of the light to be modulated, forming periodic pulsed light; The second beam splitter is used to split the periodic pulse light into two beams, one of which enters the coupler and the other enters the first photodetector. The first photodetector is used to send the detected electrical signal to the oscilloscope; The coupler is used to receive the local oscillator light and a modulated beam after beam splitting, and transmits it to the second photodetector after frequency beat; The second photodetector is used to send the detected electrical signal to the oscilloscope; An oscilloscope is used to observe the electrical drive signal generated by the driver and the electrical signals detected by the first and second photodetectors. In this process, a narrow-linewidth laser emits continuous light, which passes through an optical isolator and enters the first beam splitter. The first beam splitter splits the continuous light into a local oscillator beam and a beam to be modulated. The local oscillator beam enters a coupler, while the beam to be modulated enters an external modulation device. Through the frequency-shifting chopping principle, periodic pulses are generated and sent to the second beam splitter. The second beam splitter splits the light into two beams. One beam enters the first photodetector, which detects the corresponding electrical signal and sends it to an oscilloscope for observation. The other beam enters the coupler, beats the local oscillator beam, and is then sent to the second photodetector. The second photodetector detects the corresponding electrical signal and sends it to an oscilloscope for observation.

2. The device for measuring the blind zone distance of a coherent wind finding radar according to claim 1, characterized in that The external modulation optical device is one of an acousto-optic modulator (AOM), an electro-optic modulator (EOM), a thermo-optic modulator, or an on-chip integrated optical modulator.

3. The device for measuring the blind zone distance of a coherent wind finding radar according to claim 1, characterized in that Optical attenuators are respectively installed between the first beam splitter and the coupler, and between the second beam splitter and the coupler.

4. The device for measuring the blind zone distance of a coherent wind finding radar according to claim 3, characterized in that The optical attenuator is an adjustable optical attenuator.

5. The device for measuring the blind zone distance of a coherent wind finding radar according to claim 1, characterized in that The first photodetector is configured as a photodiode or an avalanche diode; the second photodetector is a photodiode, an avalanche diode, or a balanced photodetector.

6. The device for measuring the blind zone distance of a coherent wind finding radar according to claim 1, characterized in that The splitting ratio of the first beam splitter is adjustable, while the splitting ratio of the second beam splitter is fixed.

7. The device for measuring the blind zone distance of a coherent wind-measuring radar according to claim 6, characterized in that, The splitting ratio of the second beam splitter is 1:1.

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