Frequency-modulated continuous wave radar and speckle removal method

Abstract

The embodiment of the invention discloses a frequency-modulated continuous wave radar and a speckle removal method. The frequency-modulated continuous wave radar comprises a frequency-modulated continuous light source, a transmitting unit, a receiving unit, an IQ optical mixer, a first photoelectric detector, a second photoelectric detector and a processing unit. The frequency modulation continuous light source outputs a local oscillator beam and a signal beam; the transmitting unit transmits the signal light beam to a to-be-measured target, and a frequency shift signal light beam reflected by the to-be-measured target is received by the receiving unit and then is transmitted to a second input end of the IQ optical mixer; the first photoelectric detector receives an in-phase signal, the second photoelectric detector receives an orthogonal signal, and the processing unit removes the influence of speckles according to the in-phase signal and the orthogonal signal. According to the technical scheme provided by the embodiment of the invention, a speckle removing algorithm is provided based on the IQ optical mixer, so that the intensity fluctuation caused by the speckle problem is removed, after the intensity fluctuation is removed, the frequency peak splitting phenomenon in the frequency domain also disappears naturally, and the measurement accuracy of the frequency-modulated continuous wave radar is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of frequency modulated continuous wave radar, and in particular to a frequency modulated continuous wave radar and a speckle removal method. Background Art

[0002] Frequency modulated continuous wave (FMCW) radar systems are often used for distance measurement. By analyzing the frequency of the signal, the distance of the target can be calculated. As a coherent detection system, FMCW requires the laser source to have the characteristics of narrow linewidth. The high coherence of narrow linewidth lasers will bring about speckle problems. The cause of speckle comes from the light spot of the laser hitting the target surface. Due to the uneven surface of the diffuse reflection object, the light reflected from different positions is focused by the lens and interferes with each other in the fiber core. The roughness of the surface determines the phase of the reflected light, which in turn affects the intensity of the light after interference. Therefore, during the continuous scanning process, due to the change in the scanning position, the collected waveform is affected by the change in light intensity and will show the phenomenon of amplitude changing with time.

[0003] From the waveform performance, the effect of speckle is equivalent to adding an intensity modulation to the original signal. Under this influence, the signal shows the characteristics of frequency splitting in the frequency domain. Frequency splitting will cause frequency misjudgment and affect the accuracy of distance calculation. Since the generation of two split frequencies is always accompanied by the movement of the main frequency of the signal, this intensity modulation is difficult to remove by a simple filtering solution. Summary of the invention

[0004] The embodiment of the present invention provides a frequency modulated continuous wave radar and a speckle removal method. The frequency modulated continuous wave radar proposes a speckle removal algorithm based on an IQ optical mixer, aiming to remove the intensity fluctuation caused by the speckle problem. After the intensity fluctuation is removed, the phenomenon of frequency peak splitting will naturally disappear in the frequency domain, which is beneficial to improving the measurement accuracy of the frequency modulated continuous wave radar.

[0005] According to one aspect of the present invention, there is provided a frequency modulated continuous wave radar, comprising a frequency modulated continuous wave light source, a transmitting unit, a receiving unit, an IQ optical mixer, a first photodetector, a second photodetector and a processing unit;

[0006] The frequency modulated continuous light source is used to output a local oscillator light beam and a signal light beam, the local oscillator light beam is transmitted to the first input end of the IQ optical mixer, and the signal light beam is transmitted to the transmitting unit;

[0007] The transmitting unit is used to transmit the signal light beam to the target to be measured, and the frequency-shifted signal light beam reflected by the target to be measured is received by the receiving unit and then transmitted to the second input end of the IQ optical mixer;

[0008] The first output terminal and the second output terminal of the IQ optical mixer are both connected to the first photodetector, the third output terminal and the fourth output terminal of the IQ optical mixer are both connected to the second photodetector, the first photodetector and the second photodetector are both connected to the processing unit, the first photodetector receives an in-phase signal output by the IQ optical mixer, the second photodetector receives an orthogonal signal output by the IQ optical mixer, and the processing unit removes the influence of speckle according to the in-phase signal and the orthogonal signal;

[0009] The in-phase signal and the quadrature signal have a fixed phase difference of 90°.

[0010] Optionally, the processing unit removes the influence of speckle using the following algorithm:

[0011] Assume that the frequency difference caused by the distance difference is f1, the frequency of the intensity modulation caused by the speckle is f2, the signal amplitude is A, and the intensity of the in-phase signal is X I The strength of the orthogonal signal X Q They are expressed as:

[0012]

[0013] Dividing the in-phase signal and the quadrature signal, we can get:

[0014]

[0015] Where X is the expression of the difference frequency signal between the local oscillator beam and the frequency-shifted signal beam with the effect of speckle removed.

[0016] Optionally, the frequency modulated continuous light source includes a frequency modulated signal source and a laser, wherein the frequency modulated signal source is connected to the laser, and the frequency modulated signal source applies a frequency modulated signal to the laser to control the laser to output a frequency modulated continuous light beam.

[0017] Optionally, the laser includes a first output end and a second output end, the first output end outputs the local oscillator light beam, and the second output end outputs the signal light beam.

[0018] Optionally, the frequency modulated continuous light source further includes a beam splitter, the output end of the laser is connected to the input end of the beam splitter, and the beam splitter is used to split the output beam of the laser into the local oscillator beam and the signal beam.

[0019] Optionally, the transmitting unit includes a transmitting lens group, and the transmitting lens group is used to collimate the local oscillator light beam and output it to the target to be measured;

[0020] The receiving unit includes a receiving lens group, and the receiving lens group is used to converge the frequency-shifted signal light beam to the second input end of the IQ optical mixer.

[0021] Optionally, both the first photodetector and the second photodetector are balanced photodetectors.

[0022] According to another aspect of the present invention, a speckle removal method for a frequency modulated continuous wave radar is provided, which is applicable to the above-mentioned frequency modulated continuous wave radar, and the speckle removal method comprises:

[0023] The frequency modulated continuous light source outputs a local oscillator beam and a signal beam, the local oscillator beam is transmitted to the first input end of the IQ optical mixer, and the signal beam is transmitted to the transmitting unit;

[0024] The transmitting unit transmits the signal light beam to the target to be measured, and the frequency-shifted signal light beam reflected by the target to be measured is received by the receiving unit and then transmitted to the second input end of the IQ optical mixer;

[0025] The first photodetector receives the in-phase signal output by the IQ optical mixer, the second photodetector receives the quadrature signal output by the IQ optical mixer, and the processing unit removes the influence of speckle according to the in-phase signal and the quadrature signal;

[0026] The in-phase signal and the quadrature signal have a fixed phase difference of 90°.

[0027] Optionally, the processing unit removes the influence of speckle according to the in-phase signal and the orthogonal signal, including:

[0028] Assume that the frequency difference caused by the distance difference is f1, the frequency of the intensity modulation caused by the speckle is f2, the signal amplitude is A, and the intensity of the in-phase signal is X I The strength of the orthogonal signal X Q They are expressed as:

[0029]

[0030] Dividing the in-phase signal and the quadrature signal, we can get:

[0031]

[0032] Where X is the expression of the difference frequency signal between the local oscillator beam and the frequency-shifted signal beam with the effect of speckle removed.

[0033] Optionally, after the processing unit removes the influence of speckle according to the in-phase signal and the orthogonal signal, the method further includes:

[0034] Perform frequency spectrum analysis on X to determine the distance of the target to be measured.

[0035] The frequency modulated continuous wave radar provided by the embodiment of the present invention includes a frequency modulated continuous light source, a transmitting unit, a receiving unit, an IQ optical mixer, a first photodetector, a second photodetector and a processing unit. The frequency modulated continuous light source outputs a local oscillator beam and a signal beam, the local oscillator beam is transmitted to the first input end of the IQ optical mixer, and the signal beam is transmitted to the transmitting unit; the signal beam is transmitted to the target to be measured by the transmitting unit, and the frequency shifted signal beam reflected by the target to be measured is received by the receiving unit and transmitted to the second input end of the IQ optical mixer; the in-phase signal output by the IQ optical mixer is received by the first photodetector, and the orthogonal signal output by the IQ optical mixer is received by the second photodetector, and the influence of speckle is removed by the processing unit according to the in-phase signal and the orthogonal signal. The frequency modulated continuous wave radar provided by the embodiment of the present invention proposes a de-speckle algorithm based on the IQ optical mixer, aiming to remove the intensity fluctuation caused by the speckle problem. After the intensity fluctuation is removed, the phenomenon of frequency peak splitting will naturally disappear in the frequency domain, which is conducive to improving the measurement accuracy of the frequency modulated continuous wave radar.

[0036] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0038] Figure 1 It is a schematic diagram of the time domain waveform of a normal single-frequency signal;

[0039] Figure 2 It is a schematic diagram of the spectrum of a normal single-frequency signal;

[0040] Figure 3 is a schematic diagram of the time domain waveform of a signal affected by speckles;

[0041] Figure 4 is a schematic diagram of the spectrum of the signal affected by speckle;

[0042] Figure 5 A structural block diagram of a frequency modulated continuous wave radar provided by an embodiment of the present invention;

[0043] Figure 6 Schematic diagram of time domain waveforms of two groups of signals;

[0044] Figure 7 Schematic diagram of the time domain waveform and spectrum of the restored signal;

[0045] Figure 8 It is a schematic diagram of the time domain waveform with speckle influence;

[0046] Fig. 9 for Figure 8 Schematic diagram of the spectrum;

[0047] Fig.10 For Figure 8 Schematic diagram of the time domain waveform after waveform correction;

[0048] Fig.11 for Fig.10 Schematic diagram of the spectrum;

[0049] Fig.12 A structural block diagram of another frequency modulated continuous wave radar provided by an embodiment of the present invention;

[0050] Fig.13 A structural block diagram of another frequency modulated continuous wave radar provided by an embodiment of the present invention;

[0051] Fig.14 A structural block diagram of another frequency modulated continuous wave radar provided by an embodiment of the present invention;

[0052] Fig.15 A schematic flow chart of a method for removing speckle from a frequency modulated continuous wave radar provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0053] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0054] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0055] FMCW radar usually uses a single-frequency laser source with narrow linewidth characteristics. Figure 1 It is a schematic diagram of the time domain waveform of a normal single-frequency signal. Figure 2 This is a schematic diagram of the spectrum of a normal single-frequency signal. Figure 3 is a schematic diagram of the time domain waveform of the signal affected by speckle. Figure 4 is a schematic diagram of the spectrum of the signal affected by speckle, Figure 1 to Figure 4 It can be seen that the effect of speckle is equivalent to adding an intensity modulation to the original signal. Under this influence, the signal exhibits the characteristics of frequency splitting in the frequency domain, such as Figure 4 As shown in Figure 2, the frequency splitting will cause the frequency to be misjudged, affecting the accuracy of the distance solution. Since the generation of two split frequencies is always accompanied by the main frequency shift of the signal, the intensity modulation is difficult to remove by a simple filtering scheme.

[0056] In order to solve the above problems, Figure 5 A structural block diagram of a frequency modulated continuous wave radar provided by an embodiment of the present invention, refer to Figure 5The frequency modulated structured light radar includes a frequency modulated continuous light source 10, a transmitting unit 20, a receiving unit 30, an IQ optical mixer 40, a first photodetector 50, a second photodetector 60 and a processing unit 70; the frequency modulated continuous light source 10 is used to output a local oscillator beam and a signal beam, the local oscillator beam is transmitted to the first input end of the IQ optical mixer 40, and the signal beam is transmitted to the transmitting unit 20; the transmitting unit 20 is used to transmit the signal beam to the target 80 to be measured, and the frequency shifted signal beam reflected by the target 80 to be measured is received by the receiving unit 30 and transmitted to the second input end of the IQ optical mixer 40; the IQ optical The first output terminal and the second output terminal of the mixer 40 are both connected to the first photodetector 50, the third output terminal and the fourth output terminal of the IQ optical mixer 40 are both connected to the second photodetector 60, the first photodetector 50 and the second photodetector 60 are both connected to the processing unit 70, the first photodetector 50 receives the in-phase signal output by the IQ optical mixer 40, the second photodetector 60 receives the orthogonal signal output by the IQ optical mixer 40, and the processing unit 70 removes the influence of speckle according to the in-phase signal and the orthogonal signal; wherein the in-phase signal and the orthogonal signal have a fixed phase difference of 90°.

[0057] IQ demodulation is a technology widely used in digital communication systems. It uses two orthogonal carrier signals to transmit two independent signals simultaneously. In IQ demodulation, one signal is called the I (in-phase) component and the other is called the Q (quadrature) component. This method can effectively utilize spectrum resources and plays an important role in many modern communication systems. The basic idea of ​​IQ demodulation is to divide the data into two paths, perform carrier modulation on each path, and then make the two carriers orthogonal to each other. In this way, two signals can be transmitted simultaneously at the same frequency, thereby improving the efficiency of spectrum utilization. In IQ demodulation, the I component is multiplied by a cosine wave, and the Q component is multiplied by a sine wave and inverted, and then the two results are added to obtain the final modulated signal. The technical solution of the embodiment of the present invention proposes a de-speckling algorithm based on an IQ optical mixer, which aims to remove the intensity fluctuations caused by the speckle problem. Figure 3 The waveform state in the Figure 1 waveform state. After the intensity fluctuation is removed, the frequency peak splitting phenomenon will naturally disappear in the frequency domain. IQ optical mixers are often used in coherent optical communications. Their structure is a two-input and four-output coupler, and the two input ends are connected to the signals of the local oscillator beam and the signal beam respectively. The four output signals can be divided into two groups, defined as I and Q. According to the phase principle of the coupler, there is a 90° phase difference between the I and Q signals. Using an IQ optical mixer to replace the coupler at the receiving end of the FMCW radar, an additional new signal with a phase difference of 90° from the original signal is obtained. Figure 6Figure 1 is a schematic diagram of the time domain waveforms of the two groups of signals, where (b) is an enlarged view of the red frame in (a), where the blue line represents the I signal and the red line represents the Q signal. Figure 6 It can be seen that while the I and Q paths maintain a phase difference of 90°, the envelopes of the two waveforms are the same, that is, the effect of speckle on the IQ signal is the same. Therefore, the effect of speckle can be eliminated by the IQ two-path signal. Optionally, the first photodetector 50 and the second photodetector 60 are both balanced photodetectors.

[0058] Optionally, the processing unit 70 uses the following algorithm to remove the influence of speckle:

[0059] Assume that the frequency difference caused by the distance difference is f1, the frequency of intensity modulation caused by the speckle is f2, the signal amplitude is A, and the intensity of the in-phase signal is X I The strength of the orthogonal signal X Q They are expressed as:

[0060]

[0061] f2 is affected by the roughness of the object surface, and the effect is random and will change as the scan progresses. Since IQ is collected simultaneously, the intensity modulation has the same effect on both IQ channels. Therefore, the effect of speckle can be eliminated by dividing the two IQ signals. Dividing the in-phase signal and the orthogonal signal, we can get:

[0062]

[0063] Where X is the expression of the difference frequency signal between the local oscillator beam and the frequency-shifted signal beam without the influence of speckle. The influence of intensity modulation is eliminated by using the IQ two-way characteristics, and the original signal is finally restored. Figure 7 The time domain waveform and spectrum diagram of the restored signal, where (a) is the time domain waveform and (b) is the spectrum. According to the above calculation process, Figure 6 The signal is processed to obtain the restored signal as Figure 7 As shown in Figure 2, the intensity modulation of the signal is eliminated and the signal peak splitting phenomenon in the spectrum also disappears.

[0064] Furthermore, in order to verify the feasibility of the algorithm, the embodiment of the present invention also collects time domain data with speckle effect and verifies the above algorithm. Figure 8 is a schematic diagram of the time domain waveform with speckle influence. Fig. 9 for Figure 8 Schematic diagram of the spectrum, Fig.10 For Figure 8 Schematic diagram of the time domain waveform after waveform correction, Fig.11 for Fig.10After using this algorithm, the envelope of the original time domain signal disappears and becomes a sinusoidal signal with uniform amplitude, as shown in Fig.10 To further calculate its spectrum, see Fig. 9 and Fig.11 The signal frequency is corrected back to a single-frequency signal from the two peaks split by the speckle. This algorithm corrects the intensity modulation effect caused by the speckle, increases the accuracy of the FMCW radar peak search, and further increases the ranging accuracy.

[0065] The technical solution of the embodiment of the present invention is to output a local oscillator beam and a signal beam through a frequency modulated continuous light source, the local oscillator beam is transmitted to the first input end of the IQ optical mixer, and the signal beam is transmitted to the transmitting unit; the signal beam is transmitted to the target to be measured by the transmitting unit, and the frequency-shifted signal beam reflected by the target to be measured is received by the receiving unit and transmitted to the second input end of the IQ optical mixer; the in-phase signal output by the IQ optical mixer is received by the first photodetector, and the orthogonal signal output by the IQ optical mixer is received by the second photodetector, and the influence of speckle is removed by the processing unit according to the in-phase signal and the orthogonal signal. The frequency modulated continuous wave radar provided by the embodiment of the present invention proposes a de-speckle algorithm based on the IQ optical mixer, which aims to remove the intensity fluctuation caused by the speckle problem. After the intensity fluctuation is removed, the phenomenon of frequency peak splitting will naturally disappear in the frequency domain, which is conducive to improving the measurement accuracy of the frequency modulated continuous wave radar.

[0066] Fig.12 For a structural block diagram of another frequency modulated continuous wave radar provided in an embodiment of the present invention, refer to Fig.12 Optionally, the frequency modulated continuous light source 10 includes a frequency modulated signal source 11 and a laser 12, the frequency modulated signal source 11 is connected to the laser 12, and the frequency modulated signal source 11 applies a frequency modulated signal to the laser 12 to control the laser 12 to output a frequency modulated continuous light beam.

[0067] The FM signal source 11 may be a signal generator, and the FM signal may be a triangle wave.

[0068] Continue to refer Fig.12 Optionally, the laser 12 includes a first output end and a second output end, the first output end outputs a local oscillator beam, and the second output end outputs a signal beam.

[0069] In another embodiment, in order to improve the coherence of the local oscillator beam and the signal beam, the local oscillator beam and the signal beam may be split by the same beam. Fig.13 A structural block diagram of another frequency modulated continuous wave radar provided in an embodiment of the present invention is shown in FIG. Fig.13 Optionally, the frequency modulated continuous light source 10 further includes a beam splitter 13, the output end of the laser 12 is connected to the input end of the beam splitter 13, and the beam splitter 13 is used to split the output beam of the laser 12 into a local oscillator beam and a signal beam.

[0070] By arranging the beam splitter 13 to split the output beam of the laser 12 into two beams, it can be ensured that the local oscillator beam and the signal beam are completely identical, thereby improving the coherence of the local oscillator beam and the signal beam.

[0071] Fig.14 A structural block diagram of another frequency modulated continuous wave radar provided in an embodiment of the present invention is shown in FIG. Fig.14 Optionally, the transmitting unit 20 includes a transmitting lens group 21, which is used to collimate the local oscillator light beam and output it to the target 80 to be measured; the receiving unit 30 includes a receiving lens group 31, which is used to converge the frequency-shifted signal light beam to the second input end of the IQ optical mixer 40.

[0072] The transmitting lens group 21 and the receiving lens group 31 each include at least one converging lens, which is used to adjust the transmission direction of the signal and improve the performance of the frequency modulated continuous wave radar. The specific structures of the transmitting lens group 21 and the receiving lens group 31 can be designed according to actual conditions, and the embodiment of the present invention does not limit this.

[0073] Fig.15 FIG. 1 is a flow chart of a speckle removal method for a frequency modulated continuous wave radar provided in an embodiment of the present invention. The speckle removal method is applicable to any frequency modulated continuous wave radar provided in the above embodiments. Fig.15 , speckle removal methods include:

[0074] S110, the frequency modulated continuous light source outputs a local oscillator beam and a signal beam, the local oscillator beam is transmitted to the first input end of the IQ optical mixer, and the signal beam is transmitted to the transmitting unit.

[0075] S120, the transmitting unit transmits the signal light beam to the target to be measured, and the frequency-shifted signal light beam reflected by the target to be measured is received by the receiving unit and then transmitted to the second input end of the IQ optical mixer.

[0076] S130. The first photodetector receives the in-phase signal output by the IQ optical mixer, the second photodetector receives the quadrature signal output by the IQ optical mixer, and the processing unit removes the influence of speckle according to the in-phase signal and the quadrature signal.

[0077] The in-phase signal and the quadrature signal have a fixed phase difference of 90°.

[0078] Optionally, the processing unit removes the influence of speckle according to the in-phase signal and the orthogonal signal, including:

[0079] Assume that the frequency difference caused by the distance difference is f1, the frequency of intensity modulation caused by the speckle is f2, the signal amplitude is A, and the intensity of the in-phase signal is X I The strength of the orthogonal signal X QThey are expressed as:

[0080]

[0081] Dividing the in-phase signal and the quadrature signal, we get:

[0082]

[0083] Where X is the expression of the difference frequency signal between the local oscillator beam and the frequency-shifted signal beam with the effect of speckle removed.

[0084] The speckle removal method for a frequency modulated continuous wave radar provided in an embodiment of the present invention has the same or corresponding technical effect as that of the frequency modulated continuous wave radar, which will not be described in detail herein.

[0085] Optionally, after the processing unit removes the influence of speckle according to the in-phase signal and the orthogonal signal, the method further includes:

[0086] Perform spectrum analysis on X to determine the distance of the target to be measured.

[0087] The distance of the target to be measured can be calculated through spectrum analysis to achieve distance detection.

[0088] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A frequency modulated continuous wave radar, characterized in that: It includes a frequency modulated continuous light source, a transmitting unit, a receiving unit, an IQ optical mixer, a first photodetector, a second photodetector and a processing unit; The frequency modulated continuous light source is used to output a local oscillator light beam and a signal light beam, the local oscillator light beam is transmitted to the first input end of the IQ optical mixer, and the signal light beam is transmitted to the transmitting unit; The transmitting unit is used to transmit the signal light beam to the target to be measured, and the frequency-shifted signal light beam reflected by the target to be measured is received by the receiving unit and then transmitted to the second input end of the IQ optical mixer; The first output terminal and the second output terminal of the IQ optical mixer are both connected to the first photodetector, the third output terminal and the fourth output terminal of the IQ optical mixer are both connected to the second photodetector, the first photodetector and the second photodetector are both connected to the processing unit, the first photodetector receives an in-phase signal output by the IQ optical mixer, the second photodetector receives an orthogonal signal output by the IQ optical mixer, and the processing unit removes the influence of speckle according to the in-phase signal and the orthogonal signal; The in-phase signal and the quadrature signal have a fixed phase difference of 90°.

2. The frequency modulated continuous wave radar according to claim 1, characterized in that: The processing unit uses the following algorithm to remove the influence of speckle: Assume that the frequency difference caused by the distance difference is f1, the frequency of the intensity modulation caused by the speckle is f2, the signal amplitude is A, and the intensity of the in-phase signal is X I The strength of the orthogonal signal X Q They are expressed as: Dividing the in-phase signal and the quadrature signal, we can get: Where X is the expression of the difference frequency signal between the local oscillator beam and the frequency-shifted signal beam with the effect of speckle removed.

3. The frequency modulated continuous wave radar according to claim 1, characterized in that: The frequency modulated continuous light source comprises a frequency modulated signal source and a laser. The frequency modulated signal source is connected to the laser. The frequency modulated signal source applies a frequency modulated signal to the laser to control the laser to output a frequency modulated continuous light beam.

4. The frequency modulated continuous wave radar according to claim 3, characterized in that: The laser comprises a first output end and a second output end, the first output end outputs the local oscillator light beam, and the second output end outputs the signal light beam.

5. The frequency modulated continuous wave radar according to claim 3, characterized in that: The frequency modulated continuous light source also includes a beam splitter, the output end of the laser is connected to the input end of the beam splitter, and the beam splitter is used to split the output beam of the laser into the local oscillator beam and the signal beam.

6. The frequency modulated continuous wave radar according to claim 1, characterized in that: The transmitting unit comprises a transmitting lens group, and the transmitting lens group is used to collimate the local oscillator light beam and then output it to the target to be measured; The receiving unit includes a receiving lens group, and the receiving lens group is used to converge the frequency-shifted signal light beam to the second input end of the IQ optical mixer.

7. The frequency modulated continuous wave radar according to claim 1, characterized in that: The first photodetector and the second photodetector are both balanced photodetectors.

8. A method for removing speckle from a frequency modulated continuous wave radar, characterized in that: Applicable to the frequency modulated continuous wave radar according to any one of claims 1 to 7, the speckle removal method comprises: The frequency modulated continuous light source outputs a local oscillator beam and a signal beam, the local oscillator beam is transmitted to the first input end of the IQ optical mixer, and the signal beam is transmitted to the transmitting unit; The transmitting unit transmits the signal light beam to the target to be measured, and the frequency-shifted signal light beam reflected by the target to be measured is received by the receiving unit and then transmitted to the second input end of the IQ optical mixer; The first photodetector receives the in-phase signal output by the IQ optical mixer, the second photodetector receives the orthogonal signal output by the IQ optical mixer, and the processing unit removes the influence of speckle according to the in-phase signal and the orthogonal signal; The in-phase signal and the quadrature signal have a fixed phase difference of 90°.

9. The speckle removal method of FMCW radar according to claim 8, characterized in that: The processing unit removes the influence of speckle according to the in-phase signal and the orthogonal signal, including: Assume that the frequency difference caused by the distance difference is f1, the frequency of the intensity modulation caused by the speckle is f2, the signal amplitude is A, and the intensity of the in-phase signal is X I The strength of the orthogonal signal X Q They are expressed as: Dividing the in-phase signal and the quadrature signal, we can get: Where X is the expression of the difference frequency signal between the local oscillator beam and the frequency-shifted signal beam with the effect of speckle removed.

10. The speckle removal method of FMCW radar according to claim 9, characterized in that: After the processing unit removes the influence of speckle according to the in-phase signal and the orthogonal signal, the method further includes: Perform frequency spectrum analysis on X to determine the distance of the target to be measured.

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