A method and apparatus for real-time calibration of a micro displacement radar

Abstract

The present application belongs to the field of radar signal, and relates to a kind of micro displacement radar real-time calibration method and device, comprising: step one, the received radar echo signal is carried out fast fourier transform, and the target echo signal spectrum and coupling echo signal spectrum are obtained;Step two, the signal frequency of target echo signal spectrum and coupling echo signal spectrum is determined respectively, and the target echo frequency and coupling echo frequency are obtained, and target distance and coupling distance are calculated;Step three, target echo phase and coupling echo phase are calculated;Step four, step one to step three are carried out at initial time and detection time respectively, and the target echo phase and coupling echo phase at initial time and detection time are obtained respectively;Step five, the target echo phase difference and coupling echo phase difference from initial time to detection time are obtained;Step six, target displacement change amount is calculated;With real-time displacement error compensation to radar, the effect of accurate displacement measurement is achieved.

Description

Technical Field

[0001] This invention relates to the field of radar signals, and specifically discloses a method and apparatus for real-time calibration of micro-displacement radar. Background Technology

[0002] Millimeter-wave radars of 60GHz or 80GHz are used for detecting minute displacements, featuring low cost, high resolution, high sensitivity, and strong environmental adaptability, making them suitable for large-scale deployment. However, due to their high frequency and short wavelength (e.g., 3.7mm for 80GHz millimeter-wave radar), they require high long-term hardware stability. Otherwise, in practical applications, displacement detection errors can easily occur due to the non-ideal nature of the radar components, affecting the accuracy of the detected object's displacement and causing false alarms. Existing millimeter-wave radar displacement detection technology often employs low-cost MIMO radar schemes. Since the detected target is usually close to the radar, linear frequency modulated continuous wave radar systems are commonly used. The radar transmits the signal to be transmitted through different transmitting antennas, which often operate in a time-division switching mode. Multiple receiving antennas simultaneously receive the echo signal reflected from the target. The received signal is mixed to obtain a baseband signal, which is then converted from analog to digital to a digital signal. The signal processing unit detects the target and measures its distance and movement information.

[0003] Taking a frequency-modulated continuous wave radar with a single transmitting and receiving antenna as an example, for a radar signal with a carrier frequency of 80 GHz and a wavelength of 3.7 mm, when the detected target moves by 0.1 mm, the phase shift is 19.459°. Existing derivations assume that the carrier frequency and sampling rate of the radar transmission remain constant at different times. However, in actual radar systems, the carrier frequency and sampling rate of the transmitted signal have slight differences at different time intervals. For example, if the ADC sampling rate is fixed at 20 MHz, and the radar transmission carrier frequency is 80 GHz and 80.001 GHz at two different times, assuming a target distance of 50 meters, the phase difference between the target echoes from the two transmissions is 120°. At this point, the calculated target movement is 0.6 mm, while in reality, the target has not moved, resulting in a significant measurement error in the detection result.

[0004] In view of this, the present invention proposes a real-time calibration method and device for micro-displacement radar. In view of the non-ideal nature of the radar itself, a real-time automatic calibration scheme is proposed to compensate for the displacement error of the radar in real time, so as to achieve the effect of accurate displacement measurement. Summary of the Invention

[0005] The purpose of this invention is to provide a real-time calibration method and apparatus for micro-displacement radar, solving the problem of real-time displacement error compensation for radar to achieve accurate displacement measurement; the specific solution is as follows:

[0006] A real-time calibration method for a small displacement radar includes: Step 1, performing a Fast Fourier Transform on the received radar echo signal to obtain the target echo signal spectrum and the coupled echo signal spectrum; Step 2, determining the signal frequencies of the target echo signal spectrum and the coupled echo signal spectrum respectively to obtain the target echo frequency and the coupled echo frequency, and calculating the target distance and the coupled distance; Step 3, calculating the target echo phase and the coupled echo phase based on the target echo signal spectrum and the coupled echo signal spectrum respectively; Step 4, executing Step 1 to Step 3 at the initial time and the detection time respectively to obtain the target echo phase and the coupled echo phase at the initial time and the detection time respectively; Step 5, subtracting the target echo phase and the coupled echo phase at the initial time and the detection time respectively to obtain the target echo phase difference and the coupled echo phase difference from the initial time to the detection time; Step 6, calculating the target displacement change using the target echo phase difference and the coupled echo phase difference.

[0007] Furthermore, the radar echo signal includes a target echo signal and a coupled echo signal, which are respectively:

[0008] ;

[0009] ;

[0010] in, This refers to the target echo signal, including the target echo signal at the initial moment. and the target echo signal at the time of detection ; exp represents the exponential function; j represents the imaginary unit; R represents pi; R represents the target distance, including the target distance at the initial moment. Distance to the target at the time of detection c represents the speed of electromagnetic wave propagation; This represents the radar carrier frequency, including the radar carrier frequency at the initial moment. and radar carrier frequency at the detection time ; The slope represents the modulation rate of the frequency modulation signal; t represents the time variable. This represents the coupled echo signal, including the coupled echo signal at the initial moment. Coupled echo signal at the detection time ; Indicates the coupling distance;

[0011] The target echo signal spectrum and the coupled echo signal spectrum are respectively:

[0012] ;

[0013] ;

[0014] Where FFT stands for Fast Fourier Transform; This represents the target echo signal spectrum, including the initial target echo signal spectrum at the initial moment. The spectrum of the target echo signal at the detection time ; This represents the spectrum of the coupled echo signal, including the initial coupled echo signal spectrum at the initial moment. Spectrum of the detection coupling echo signal at the detection time .

[0015] Furthermore, the target distance and the coupling distance are respectively:

[0016] ;

[0017] ;

[0018] Where R represents the target distance, including the target distance at the initial moment. Distance to the target at the time of detection ; This indicates the target echo frequency, including the target echo frequency at the initial moment. and the target echo frequency at the detection time c represents the speed of electromagnetic wave propagation; This represents the coupling distance, including the coupling distance at the initial moment. Coupling distance at the detection time ; This represents the coupled echo frequency, including the coupled echo frequency at the initial moment. Coupled echo frequency at the detection time ; This represents the modulation slope of the frequency modulation signal.

[0019] Furthermore, the target echo phase and the coupled echo phase are respectively:

[0020] ;

[0021] ;

[0022] in, This represents the target echo phase, including the target echo phase at the initial moment. and the target echo phase at the detection time ; Represents the arctangent function; Im represents the imaginary part of the complex number; Re represents the real part of the complex number; This represents the target echo signal spectrum, including the initial target echo signal spectrum at the initial moment. The spectrum of the target echo signal at the detection time ; This represents the coupled echo phase, including the coupled echo phase at the initial moment. Coupled echo phase at the detection time ; This represents the spectrum of the coupled echo signal, including the initial coupled echo signal spectrum at the initial moment. Spectrum of the detection coupling echo signal at the detection time .

[0023] Furthermore, the target echo phase difference and the coupled echo phase difference are respectively:

[0024] ;

[0025] ;

[0026] in, Indicates the phase difference of the target echo; Indicates the target echo phase at the initial moment; Indicates the phase of the target echo at the moment of detection; Indicates the phase difference of the coupled echo; This indicates the phase of the coupled echo at the initial moment; This indicates the phase of the coupled echo at the detection moment.

[0027] Furthermore, the target displacement change is:

[0028] ;

[0029] in, Indicates the change in target displacement; Indicates the phase difference of the target echo; Indicates the target distance at the initial moment; Indicates the coupling distance; The phase difference of the coupled echo is represented by c; the propagation speed of the electromagnetic wave is represented by c. Represents pi; This represents the radar carrier frequency at the initial moment.

[0030] A real-time calibration device for micro-displacement radar using the above-mentioned real-time calibration method for micro-displacement radar includes a signal transmitting device and a signal receiving device. The signal transmitting device includes multiple transmitting ports, and the signal receiving device includes multiple receiving ports. The transmitting ports include a signal transmitting port connected to a transmitting antenna and a transmitting coupling port connected to the receiving ports. The receiving ports include a signal receiving port connected to a receiving antenna and a receiving coupling port connected to the transmitting ports.

[0031] Furthermore, the transmit coupling port is connected to the receive coupling port through a millimeter-wave delay line and an attenuator, so that the transmit signal from the transmit coupling port is directly coupled into the receive coupling port.

[0032] Furthermore, millimeter-wave delay lines convert millimeter-wave signals into surface acoustic waves by designing transducers and propagation paths on the surface of piezoelectric crystals. After being delayed by the surface acoustic wave delay line, the signals are then converted back into electromagnetic waves to delay the transmitted signals.

[0033] Furthermore, the attenuator is used to control the received power intensity when the transmitted signal returns directly to the receiving port without passing through the antenna.

[0034] The present invention has the following advantages and beneficial effects:

[0035] This invention primarily addresses the inherent non-idealities of radar by performing real-time displacement error compensation to achieve accurate displacement measurement. Attached Figure Description

[0036] Figure 1 This is a structural diagram of the self-calibrating micro-displacement radar real-time calibration device of the present invention;

[0037] Figure 2 This is a spectrum diagram of the radar received echo signal. Detailed Implementation

[0038] 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, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0039] To address the non-ideal nature of the device, this invention employs a real-time compensation method for the radar. The structure of the real-time calibration device for micro-displacement radar is as follows: Figure 1 As shown.

[0040] A real-time calibration device for micro-displacement radar includes a signal transmitting device and a signal receiving device. The signal transmitting device includes multiple transmitting ports, and the signal receiving device includes multiple receiving ports. Each transmitting port includes a signal transmitting port connected to a transmitting antenna and a transmitting coupling port connected to a receiving port. Similarly, each receiving port includes a signal receiving port connected to a receiving antenna and a receiving coupling port connected to a transmitting port. For example, in a millimeter-wave MIMO radar system with multiple transmitters and multiple receivers, a specific transmitted signal can be directly coupled into the receiving end via a series connection of a millimeter-wave delay line and an attenuator, instead of being directly connected to the transmitting antenna.

[0041] Millimeter-wave delay lines utilize surface acoustic wave (SAW) delay lines to convert millimeter-wave signals into SAW signals by designing appropriate transducers and propagation paths on the surface of piezoelectric crystals. After being delayed by a SAW delay line of length L, the signals are then converted back into electromagnetic waves, thus achieving the purpose of delaying the transmitted signal.

[0042] The attenuator controls the received power intensity when the transmitted signal returns directly to the receiver without passing through the antenna, preventing the receiver from experiencing excessive power.

[0043] The signal coupled back to the receiver from the transmitting end via a delay line and attenuator, although not passing through transmitting and receiving antennas, has the same signal form as conventional millimeter-wave radar. The frequency signal conforms to the form of a linearly frequency-modulated radar transmission signal, the received signal conforms to the form of a radar receiving radio frequency signal, and the signal conforms to the form of a mixed signal. The time delay of the coupled signal is a fixed delay between the transmitting and receiving ends, independent of external targets. Therefore, for the signal transmitted through the antenna, the baseband signal of the target echo at the initial moment is:

[0044] ;

[0045] Ignoring the higher-order terms, it can be written as:

[0046] ;

[0047] Similarly, the target echo at time T is:

[0048] ;

[0049] For the reference signal coupled to the receiver via the delay line, the baseband signal of the initial coupled echo is:

[0050] ;

[0051] in, This is the equivalent distance length of the delay line.

[0052] The reference signal after time T (the detection time) is:

[0053] ;

[0054] in, It is assumed that the carrier frequency of the transmitted signal undergoes a slight change after time T.

[0055] For the above equation, the echo of the reference signal at different times is a single-frequency signal with a different initial phase, where the echo frequency is:

[0056] ;

[0057] in, This indicates the echo frequency of the reference signal.

[0058] At time T (the detection time) and the initial time, the difference in the echo phase of the reference signal is:

[0059] ;

[0060] in, This indicates the phase difference of the coupled echo.

[0061] Due to the relative coupling (reference) distance of the reference signal Since the parameters are fixed, the echo phase difference of the reference signal is only related to the carrier frequency of the transmitted signal. Therefore, the magnitude of the change in the carrier frequency of the radar transmitted signal at time T relative to the initial time can be calculated as follows:

[0062] ;

[0063] in, This indicates the magnitude of the change in carrier frequency of the radar transmitted signal at time T relative to the initial time.

[0064] The phase difference between the target's echo at time T and the initial time is:

[0065] ;

[0066] Combining the above equations, the change in the calibrated target displacement can be calculated as follows:

[0067] ;

[0068] Due to displacement change The difference is very small, and the frequency of radar transmission typically differs by no more than 1% between the initial moment and time T. For the calculation in the above formula, Can be adopted Therefore, the formula for calculating the target displacement in real-time compensation is:

[0069] .

[0070] Specific methods for real-time calibration of micro-displacement radar for real-time calibration of target displacement calculation include:

[0071] Step 1: Perform a Fast Fourier Transform (FFT) on the received radar echo signal, and record the results as the target echo signal spectrum. and the spectrum of the coupled echo signal The echo signal frequency is F.

[0072] For a signal transmitted through an antenna, the baseband signal of the target echo, ignoring higher-order terms, can be written as:

[0073] ;

[0074] The echo signal in the above equation is a single-frequency signal. After FFT processing, the time-domain signal is converted into a frequency-domain signal, and the echo spectrum of the target can be obtained. .in, This refers to the target echo signal, including the target echo signal at the initial moment. and the target echo signal at the time of detection ; exp represents the exponential function; j represents the imaginary unit; R represents pi; R represents the target distance, including the target distance at the initial moment. Distance to the target at the time of detection c represents the speed of electromagnetic wave propagation; This represents the radar carrier frequency, including the radar carrier frequency at the initial moment. and radar carrier frequency at the detection time ; The modulation slope of the frequency modulation signal is represented by t; the time variable is represented by t; and FFT represents the Fast Fourier Transform. This represents the target echo signal spectrum, including the initial target echo signal spectrum at the initial moment. The spectrum of the target echo signal at the detection time .like Figure 2 The image shows the spectrum of the radar echo signal.

[0075] Similarly, for the reference (coupled) signal coupled to the receiver via a delay line, the baseband signal of the coupled echo is...

[0076] ;

[0077] The coupled echo signal is also a single-frequency signal. After FFT processing, the time-domain signal is converted into a frequency-domain signal, and the echo spectrum of the target can be obtained. This represents the coupled echo signal, including the coupled echo signal at the initial moment. Coupled echo signal at the detection time ; Indicates the coupling distance; This represents the spectrum of the coupled echo signal, including the initial coupled echo signal spectrum at the initial moment. Spectrum of the detection coupling echo signal at the detection time .

[0078] Step 2: Determine the signal frequencies of the target echo signal spectrum and the coupled echo signal spectrum respectively to obtain the target echo frequency. and coupling echo frequency and according to Calculate the target distance R and coupling distance .

[0079] The target distance and the coupling distance are respectively:

[0080] ;

[0081] ;

[0082] Where R represents the target distance, including the target distance at the initial moment. Distance to the target at the time of detection ; This indicates the target echo frequency, including the target echo frequency at the initial moment. and the target echo frequency at the detection time c represents the speed of electromagnetic wave propagation; This represents the coupling distance, including the coupling distance at the initial moment. Coupling distance at the detection time ; This represents the coupled echo frequency, including the coupled echo frequency at the initial moment. Coupled echo frequency at the detection time ; This indicates the modulation slope of the frequency modulation signal. For example... Figure 2 As shown, the target peak is around 3MHz, then Figure 2 The target echo frequency shown It is 3MHz.

[0083] Step 3: Calculate the target echo phase based on the target echo signal spectrum and the coupled echo signal spectrum, respectively. and coupled echo phase .

[0084] The target echo phase and the coupled echo phase are respectively:

[0085] ;

[0086] ;

[0087] in, This represents the target echo phase, including the target echo phase at the initial moment. and the target echo phase at the detection time ; Represents the arctangent function; Im represents the imaginary part of the complex number; Re represents the real part of the complex number; This represents the target echo signal spectrum, including the initial target echo signal spectrum at the initial moment. The spectrum of the target echo signal at the detection time ; This represents the coupled echo phase, including the coupled echo phase at the initial moment. Coupled echo phase at the detection time ; This represents the spectrum of the coupled echo signal, including the initial coupled echo signal spectrum at the initial moment. Spectrum of the detection coupling echo signal at the detection time .

[0088] Step 4: Execute steps 1 to 3 at the initial time and the detection time respectively to obtain the target echo phase and the coupled echo phase at the initial time and the detection time respectively.

[0089] At time T and the initial time, the difference in echo phase between the reference signal and the reference signal is:

[0090]

[0091] Due to the relative coupling distance of the reference signal Since the parameters are fixed, the echo phase difference of the reference signal is only related to the carrier frequency of the transmitted signal. Therefore, the magnitude of the change in the carrier frequency of the radar transmitted signal at time T relative to the initial time can be calculated as follows:

[0092] ;

[0093] The phase difference between the target's echo at time T and the initial time is:

[0094] ;

[0095] Due to displacement change The difference is very small, and the frequency of radar transmission usually does not differ by more than 1% between the initial moment and time T. Can be adopted Calculate the displacement change, and thus obtain the formula for calculating the target displacement for real-time compensation. The calibrated target displacement change can then be calculated as follows:

[0096] ;

[0097] in, Indicates the change in target displacement; Indicates the phase difference of the target echo; Indicates the target distance at the initial moment; Indicates the coupling distance; The phase difference of the coupled echo is represented by c; the propagation speed of the electromagnetic wave is represented by c. Represents pi; This represents the radar carrier frequency at the initial moment.

[0098] Step 5: Subtract the target echo phase and coupled echo phase at the initial time and the detection time respectively to obtain the target echo phase difference from the initial time to the detection time. and coupling echo phase difference .

[0099] Calculate the phase difference between the target and reference signals at time T and the initial time, where the target echo phase difference and the coupled echo phase difference are respectively:

[0100] ;

[0101] ;

[0102] in, Indicates the phase difference of the target echo; Indicates the target echo phase at the initial moment; Indicates the phase of the target echo at the moment of detection; Indicates the phase difference of the coupled echo; This indicates the phase of the coupled echo at the initial moment; This indicates the phase of the coupled echo at the detection moment.

[0103] Step 6: Calculate the change in target displacement using the target distance, coupling distance, target echo phase difference, and coupling echo phase difference at the initial moment.

[0104] Solve according to step four. The formula and the results obtained from the detection calculation , , and Solve for the actual change in the target displacement. The distance calculated for the target at the initial moment. The distance is the reference signal, due to the target displacement. Extremely small, on the order of millimeters, while the initial distance to the target. The distance is usually above 10 meters, so even at time T, the target distance at the initial time can be used. calculate.

[0105] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for real-time calibration of a micro-displacement radar, characterized in that, The method comprises the following steps: Step one, performing fast Fourier transform on the received radar echo signal to obtain target echo signal spectrum and coupling echo signal spectrum; the radar echo signal comprises target echo signal reflected by a target and coupling echo signal formed by the coupling of the transmitted signal to the receiving end through a delay line and an attenuator, and the coupling echo signal does not pass through the transmitting antenna and the receiving antenna, and the time delay is a fixed delay; Step two, determining the signal frequency of the target echo signal spectrum and the coupling echo signal spectrum respectively to obtain the target echo frequency and the coupling echo frequency, and calculating the target distance and the coupling distance; the target distance and the coupling distance are respectively: ； ； wherein R denotes the target distance, including the target distance at the initial time and the target distance at the detection time ; denotes the target echo frequency, including the target echo frequency at the initial time and the target echo frequency at the detection time ; c denotes the electromagnetic wave propagation speed; denotes the coupling distance, including the coupling distance at the initial time and the coupling distance at the detection time ; denotes the coupling echo frequency, including the coupling echo frequency at the initial time and the coupling echo frequency at the detection time ; denotes the modulation slope of the frequency modulation signal; Step three, calculating the target echo phase and the coupling echo phase based on the target echo signal spectrum and the coupling echo signal spectrum respectively; the target echo phase and the coupling echo phase are respectively: ； ； wherein represents a target echo phase, including an initial target echo phase and a target echo phase at a detection time ; represents an arctangent function; Im represents an imaginary part of a complex number; Re represents a real part of a complex number; represents a target echo signal spectrum, including an initial target echo signal spectrum and a detected target echo signal spectrum at a detection time ; represents a coupling echo phase, including an initial coupling echo phase and a coupling echo phase at a detection time ; represents a coupling echo signal spectrum, including an initial coupling echo signal spectrum and a detected coupling echo signal spectrum at a detection time ; Step four, performing steps one to three at the initial time and the detection time to obtain the target echo phase and the coupling echo phase at the initial time and the detection time respectively; Step five, subtracting the target echo phase and the coupling echo phase at the initial time and the detection time respectively to obtain the target echo phase difference and the coupling echo phase difference from the initial time to the detection time; the coupling echo phase difference only reflects the carrier frequency variation of the transmitted signal and is irrelevant to the target displacement; Step six, calculating the target displacement variation based on the target distance, the coupling distance, the target echo phase difference and the coupling echo phase difference at the initial time; the target displacement variation is: ； wherein denotes a target displacement change amount; denotes a target echo phase difference; denotes a target distance at an initial time; denotes a coupling distance; denotes a coupling echo phase difference; c denotes an electromagnetic wave propagation speed; denotes a circle constant; denotes a radar carrier frequency at an initial time.

2. The real-time calibration method for a micro displacement radar according to claim 1, wherein The radar echo signal comprises target echo signal and coupling echo signal, and the target echo signal and the coupling echo signal are respectively: ； ； wherein represents the target echo signal, including the target echo signal at an initial time and the target echo signal at a detection time ; exp represents the exponential function; j represents the imaginary unit; represents the circle ratio; R represents the target distance, including the target distance at an initial time and the target distance at a detection time ; c represents the electromagnetic wave propagation speed; represents the radar carrier frequency, including the radar carrier frequency at an initial time and the radar carrier frequency at a detection time ; represents the modulation slope of the frequency modulation signal; t represents the time variable; represents the coupled echo signal, including the coupled echo signal at an initial time and the coupled echo signal at a detection time ; represents the coupled distance; The target echo signal spectrum and the coupling echo signal spectrum are respectively: ； ； where FFT denotes a fast Fourier transform; denotes a target echo signal spectrum, including an initial target echo signal spectrum at an initial time and a detection target echo signal spectrum at a detection time ; denotes a coupling echo signal spectrum, including an initial coupling echo signal spectrum at an initial time and a detection coupling echo signal spectrum at a detection time .

3. The real-time calibration method for a micro displacement radar according to claim 1, wherein, The target echo phase difference and the coupling echo phase difference are respectively: ； ； wherein denotes the target echo phase difference; denotes the target echo phase at the initial time instant; denotes the target echo phase at the detection time instant; denotes the coupling echo phase difference; denotes the coupling echo phase at the initial time instant; denotes the coupling echo phase at the detection time instant.

4. A micro displacement radar real-time calibration device using the micro displacement radar real-time calibration method according to any one of claims 1 to 3, comprising a signal transmitting device and a signal receiving device, characterized in that, The signal transmitting device comprises a plurality of transmitting ports, and the signal receiving device comprises a plurality of receiving ports; the transmitting port comprises a signal transmitting port connected with the transmitting antenna and a transmitting coupling port connected with the receiving port; the receiving port comprises a signal receiving port connected with the receiving antenna and a receiving coupling port connected with the transmitting port.

5. The real-time calibration apparatus for micro displacement radar according to claim 4, wherein The transmitting coupling port is connected with the receiving coupling port through a millimeter wave delay line and an attenuator, so that the transmitted signal of the transmitting coupling port is directly coupled into the receiving coupling port.

6. The real-time calibration apparatus for a micro displacement radar according to claim 5, wherein The millimeter wave delay line converts the millimeter wave signal into a surface acoustic wave by designing a transducer and a propagation path on the surface of a piezoelectric crystal, delays the surface acoustic wave through a surface acoustic wave delay line, and then converts the electromagnetic wave signal back to an electromagnetic wave signal to time delay the transmitted signal.

7. The millimeter-wave radar real-time calibration device according to claim 5, wherein The attenuator is used to control the receiving power intensity when the transmitted signal does not pass through the antenna and is directly returned to the receiving port.

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