Millimeter wave radar detection performance evaluation method under rainfall condition

Abstract

The invention discloses a millimeter wave radar detection performance evaluation method under a rainfall condition. The invention can be used. According to the method, the attenuation effect and the back scattering effect of millimeter wave signals under the rainfall condition are analyzed based on the scattering principle, a propagation path in the millimeter wave radar main lobe width under the rainfall condition is regarded as a spherical cone by adopting a finite element method, and the spherical cone is divided into spherical cone shell elements according to the distance R; compared with existing methods such as actual measurement data fitting, the method has the advantages that the method is more rigorous, and the calculation result is more accurate; finally, the signal-to-clutter ratio is adopted to evaluate the detection performance of the millimeter-wave radar, the influence of the rainfall backscattering power on the detection performance of the millimeter-wave radar is fully considered, and the evaluation result is more reliable and closer to the real situation compared with the evaluation result which only considers the echo signal power.

Description

Technical Field

[0001] The present invention relates to the technical field of millimeter-wave radar, and particularly relates to a method for evaluating the detection performance of a millimeter-wave radar under rainfall conditions. Background Technique

[0002] A millimeter-wave radar emits electromagnetic waves in the millimeter-wave band. When these electromagnetic waves encounter a target object, they will be reflected. The radar receives the reflected echo signal and analyzes it to obtain information related to the target object. In this process, many factors will affect the detection performance of the millimeter-wave radar, causing the maximum working distance of the millimeter-wave radar to decrease. By calculating the maximum working distance of the millimeter-wave radar, the detection performance of the millimeter-wave radar can be evaluated.

[0003] The radar equation is a mathematical equation for radar accuracy analysis, working distance calculation, and anti-interference ability analysis, as shown in Equation (1):

[0004]

[0005] Among them, P r is the received power of the radar, R is the radar detection distance, P t is the transmitted power of the radar, G is the radar antenna gain coefficient, λ is the radar operating wavelength, σ is the backscattering cross-sectional area, k is the Boltzmann constant, T e is the effective noise temperature, B is the operating bandwidth, and L is the propagation loss.

[0006] Generally, there is a minimum requirement for the received power P r of the radar; the transmitted power P t of the radar, the radar antenna gain coefficient G, the radar operating wavelength λ, the backscattering cross-sectional area σ, the operating bandwidth B, etc. are the inherent parameters of the radar. The propagation loss L of the radar is generally obtained by fitting the measured data or by the method of propagation path modeling; substituting the above parameters into the radar equation can solve the maximum detection distance R of the radar.

[0007] Therefore, the commonly used method for evaluating the detection performance of a millimeter-wave radar is mainly to obtain the propagation loss L of the radar by fitting the measured data or by the method of propagation path modeling, and then combine the radar equation to solve for the maximum detection distance R of the radar, so as to evaluate the detection performance of the millimeter-wave radar. Among them, the measured data fitting method is a method of fitting the measured data. After obtaining the propagation loss at different detection distances through measurement, the propagation loss is fitted into a function of the detection distance through some mathematical methods. For example, the commonly used free space propagation loss formula is:

[0008] L fs (dB) = 32.45 + 20log 10 (f) + 20log 10(R)(1.2)

[0009] Where f is the radar operating frequency and R is the radar detection range.

[0010] The propagation path modeling rule calculates the propagation loss by establishing an electromagnetic model for different propagation paths. For example, the propagation loss of the millimeter-wave communication link in the air-ground propagation is calculated by modeling with parameters such as the ground scene type, the coordinates of the air and ground nodes, and the communication frequency.

[0011] Existing methods for evaluating the detection performance of millimeter-wave radars are all for the detection performance evaluation of millimeter-wave radars under general conditions. For the special case of rainfall, existing methods usually calculate by fitting the measured data. Since the propagation loss of millimeter-wave radars under rainfall conditions is related to various environmental factors, such as terrain, altitude, temperature, etc., the results obtained by data fitting using existing methods are only applicable to the environmental factors at the time of data collection, resulting in a large error from the actual situation, thus affecting the evaluation results of the detection performance of millimeter-wave radars. Summary of the Invention

[0012] In view of this, the present invention provides a method for evaluating the detection performance of millimeter-wave radars under rainfall conditions, which is objective, effective, and highly accurate.

[0013] The method for evaluating the detection performance of millimeter-wave radars under rainfall conditions of the present invention includes:

[0014] S1, calculating the attenuation power and the backscattering power of the millimeter-wave radar signal by raindrop particles per unit volume based on the scattering theory and the backscattering power

[0015] S2, using the finite element method to model the propagation path of the millimeter-wave radar signal under rainfall conditions, and calculating the attenuation power P and the backscattering power P ext and the backscattering power P b ;

[0016] Wherein, the transmitting end antenna of the millimeter-wave radar is regarded as a point source, the propagation path within the main lobe width of the millimeter-wave radar is regarded as a spherical cone, and the spherical cone is divided into spherical cone shell elements according to the distance R. The thickness of each spherical cone shell element is dR, and the volume dV of the spherical cone shell element is the difference between the volumes of two spherical cones with heights of R and R + dR;

[0017] Then the attenuation power and the backscattering power generated by the millimeter-wave radar signal passing through a spherical cone shell element are respectively: the and the backscattering power per unit volume are respectively multiplied by the volume dV of the spherical cone shell element and the power density S of the millimeter-wave radar signal IThe product of;

[0018] The attenuation power P on the propagation path of the millimeter-wave radar signal ext And the backscattering power P b Is: Integrating the attenuation power of the spherical conical shell element on the propagation path of the millimeter-wave radar signal And the backscattering power With respect to the distance R;

[0019] S3. Based on the attenuation power P on the propagation path of the millimeter-wave radar signal ext And the backscattering power P b , Calculate the SINR of the millimeter-wave radar echo signal, and evaluate the detection performance of the millimeter-wave radar under rainfall conditions based on the SINR.

[0020] Further, in S1, the Rayleigh scattering theory, the geometric optics approximation theory, the discrete dipole approximation theory or the T-matrix method is adopted.

[0021] Further, in S1, first use the Mie scattering theory to solve the extinction coefficient Q of a single scatterer particle ext And the backscattering coefficient Q b ; Then, based on the spectral distribution model of raindrop particles, obtain the attenuation power of raindrop particles per unit volume on the millimeter-wave radar signal at a certain rainfall rate Rate And the backscattering power

[0022] Further, the extinction coefficient Q of a single scatterer particle ext And the backscattering coefficient Q b Are:

[0023]

[0024] Where, m represents the complex refractive index of water, λ represents the incident wavelength, r represents the radius of the spherical raindrop particle, a n And b n Are the coefficients of the Mie scattering theory, Re represents the real part, x is the size parameter, and satisfies the formula

[0025]

[0026] Further, m is calculated using the Ray empirical formula.

[0027] Further, the spectral distribution model of raindrop particles adopts the Marshall-Palmer model, the Gamma distribution model, the log-normal distribution model, the Weibull distribution model or the generalized Gamma distribution model.

[0028] Furthermore, at a certain rainfall rate Rate, the attenuation power and backscattering power of raindrop particles per unit volume on the millimeter-wave radar signal are as follows:

[0029]

[0030] Among them, S I represents the power density of the millimeter-wave radar signal, r max and r min respectively represent the maximum and minimum radii of spherical raindrop particles per unit volume, and N(r) is the spectral distribution function of the radii of spherical raindrop particles.

[0031] Furthermore, the attenuation power P ext and backscattering power P b of the millimeter-wave radar signal passing through a spherical conical shell element are calculated as follows

[0032]

[0033] The volume dV of the spherical conical shell element is:

[0034]

[0035] The power density S I of the millimeter-wave radar signal is:

[0036]

[0037] Among them, P t represents the incident power corresponding to this spherical conical shell element; θ bw represents the main lobe width of the transmitting end antenna of the millimeter-wave radar.

[0038] Beneficial effects:

[0039] Based on the scattering principle, the present invention analyzes the attenuation effect and backscattering effect of millimeter-wave signals under rainfall conditions, and uses the finite element method to regard the propagation path within the main lobe width of the millimeter-wave radar under rainfall conditions as a spherical cone, and divides the spherical cone into spherical conical shell elements according to the distance R, and then calculates the propagation path loss of the millimeter-wave radar under rainfall conditions. Compared with existing methods such as measured data fitting, it is more rigorous and the calculation results are more accurate; the signal-to-noise ratio is used to evaluate the detection performance of the millimeter-wave radar, fully considering the influence of the rainfall backscattering power on the detection performance of the millimeter-wave radar. The evaluation results are more reliable and closer to the real situation than only considering the echo signal power.

[0040] The present invention uses Mie scattering theory to model and analyze a single raindrop particle, and then uses the spectral distribution model of raindrop particles to analyze the collective effect of raindrops in a unit volume. Mie scattering theory is a rigorous mathematical solution for the interaction between electromagnetic waves and particles, with the advantages of a wide range of applicability and high accuracy, and is irreplaceable especially when dealing with medium-sized particles.

[0041] The present invention uses the Marshall-Palmer model to describe the spectral distribution of raindrop particles. The Marshall-Palmer model is a classic model in the study of raindrop spectra, with the advantages of few parameters, high computational efficiency, and clear physical meaning, and is particularly suitable for rapid estimation and standardized application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a flowchart of the evaluation method of the present invention.

[0043] Figure 2 It is a spherical cone propagation path model.

[0044] Figure 3 It is the variation of the received signal SNR / SINR with the rainfall rate at different distances. DETAILED DESCRIPTION OF THE INVENTION

[0045] The following combines the drawings and gives embodiments to describe the present invention in detail.

[0046] The present invention provides a method for evaluating the detection performance of a millimeter-wave radar under rainfall conditions.

[0047] The present invention uses the signal-to-interference-plus-noise ratio (SINR) to measure the detection performance of a millimeter-wave radar under rainfall conditions, and uses the SINR to evaluate the detection performance of the millimeter-wave radar, fully considering the influence of the rainfall backscattering power on the detection performance of the millimeter-wave radar.

[0048] The signal-to-noise ratio SNR and the signal-to-interference-plus-noise ratio SINR of the echo signal can be expressed as

[0049]

[0050] Where P r represents the received signal power at the receiving end, P b represents the backscattering signal power at the receiving end, and N represents the noise power at the receiver.

[0051] Affected by the rainfall attenuation effect, the received signal power P r and the noise power N at the receiver can be expressed as

[0052]

[0053] Where P tRepresents the signal transmission power, P ext Represents the rainfall attenuation power, G represents the antenna gain, λ represents the signal wavelength, σ represents the RCS of the target, R represents the distance between the radar and the target, F n Represents the receiver noise figure, k represents the Boltzmann constant, T e Represents the effective noise temperature, B represents the signal bandwidth, L represents the environmental clutter power except for the influence of rainfall.

[0054] In the Mie scattering theory, the attenuation effect and the backscattering effect of raindrop particles are jointly generated. The rainfall attenuation P ext and the backscattering signal power P b are mainly determined by the rainfall rate and the distance R. Scattering theories such as the Rayleigh scattering theory, the geometric optics approximation theory, the discrete dipole approximation (DDA) theory, or the T-matrix method can be used to calculate the rainfall attenuation P ext and the backscattering signal power P b in the environment of raindrop particles per unit volume. Then, the finite element method is used to establish the millimeter-wave radar signal propagation path model under rainfall conditions, and further obtain the attenuation power P ext and the backscattering power P b on the entire propagation path of the millimeter-wave radar under rainfall conditions, so as to obtain the signal-to-clutter ratio at the receiving end of the millimeter-wave radar under rainfall conditions and realize the evaluation of the detection performance of the millimeter-wave radar. As Figure 1 shown.

[0055] This embodiment adopts the Mie scattering theory. When using the scattering theory to analyze rainfall, raindrops are simplified as spherical scatterers. A part of the incident energy is absorbed and scattered by the scatterers. The scattering power P sca and the absorption power P abs The ratio to the incident power density S I is the scattering cross-section σ sca and the absorption cross-section σ abs The ratio of the scattering cross-section and the absorption cross-section to the physical cross-sectional area of the scatterer is called the scattering coefficient Q sca and the absorption coefficient Q abs . The extinction coefficient Q ext is the sum of the scattering coefficient and the absorption coefficient, which describes the attenuation effect of the scatterer on the incident energy.

[0056] In the scattering power P sca There is a part that is the backscattering power P b , and its ratio to the incident power density S I is the backscattering cross-section σ b , and the ratio of the backscattering cross-section to the physical cross-sectional area of the scatterer is called the backscattering coefficient Q b , which describes the backscattering effect of the scatterer on the incident energy.

[0057] According to Mie scattering theory, when the radius r of the scatterer and the incident wavelength λ are fixed, the extinction coefficient Q of a single scatterer particle is solved ext and the backscattering coefficient Q b The expression is

[0058]

[0059] where m represents the complex refractive index of water, which can be calculated using Ray's empirical formula, r represents the radius of the spherical scatterer particle, a n and b n are the coefficients of Mie scattering theory, x is the size parameter, satisfying the formula

[0060]

[0061] To analyze the collective effect of scatterers in a unit volume, the spectral distribution of the scatterer particle radius is required. The spectral distribution N(r) of the particle radius describes the distribution of particles with different radii in a unit volume under certain conditions. The Marshall-Palmer model, Gamma distribution model, lognormal distribution model, Weibull distribution model, generalized Gamma distribution model, etc. can be used to describe the spectral distribution of raindrop particles. In this embodiment, the Marshall-Palmer model is adopted. Under this model, the spectral distribution of raindrop particles during rainfall is close to the Γ distribution

[0062] N(r) = N0exp(-2Λr) (6)

[0063] where N0 and Λ are parameters, and the calculation methods are as follows:

[0064]

[0065] where r (mm) represents the radius of the raindrop particle, Rate (mm / h) represents the rainfall rate, and N(r)dr represents the number of raindrop particles with a radius in the range of r~r+dr (mm) in the unit volume of rain medium.

[0066] Based on the extinction coefficient Q ext and the backscattering coefficient Q b of a single raindrop particle, the collective effect of raindrop particles in a unit volume is analyzed. The rainfall rate is regarded as uniform, that is, the particle size distribution of raindrops is uniform in space.

[0067] At a certain rainfall rate Rate, the attenuation power of the incident signal by raindrop particles in a unit volume and the backscattering power

[0068]

[0069] Among them, r max and r min respectively represent the maximum and minimum radii of the group particles, and N(r) is the spectral distribution function of the particle radius.

[0070] On the propagation path of the millimeter-wave radar signal, the distance R is dynamically changing. The present invention uses the finite element method to model the propagation path of the millimeter-wave radar signal under rainfall conditions.

[0071] Regarding the transmitting end antenna of the millimeter-wave radar as a point source, the propagation path within its main lobe width is regarded as a spherical cone, which is composed of a cone and a spherical segment. The spherical cone is divided into spherical cone shell elements according to the distance R. The distance R from the points on one spherical cone shell element to the transmitting end antenna of the millimeter-wave radar is regarded as the same, and the thickness of each spherical cone shell element is dR, as Figure 2 shown.

[0072] The volume formula of the spherical cone is

[0073]

[0074] Among them, H represents the height of the conical part in the spherical cone, and θ bw represents the main lobe width of the transmitting end antenna of the millimeter-wave radar.

[0075] Then the volume of the spherical cone shell element is the difference between the volumes of two spherical cones with heights of R and R + dR

[0076]

[0077] Then the attenuation power P ext and the backscattering power P b generated when the millimeter-wave radar signal passes through a spherical cone shell element are calculated as

[0078]

[0079] Among them, the power density S I of the millimeter-wave radar signal is also related to the distance R:

[0080]

[0081] Among them, P t represents the incident power corresponding to this spherical cone shell element.

[0082] Integrating the distance R over the entire propagation path of the millimeter-wave radar signal can obtain the overall attenuation power P ext and the backscattering power P b .

[0083]

[0084] Combined with the calculation formula of SINR, the SINR of the millimeter-wave radar echo signal can be obtained. Keeping the SINR of the millimeter-wave radar echo signal above a certain threshold can be considered that the detection process is reliable under the corresponding detection probability. Selecting the rainfall rate as a variable and substituting relevant parameters for calculation, the variation of the maximum reliable detection distance of the millimeter-wave radar with the rainfall rate can be obtained, and the detection performance of the millimeter-wave radar can be evaluated.

[0085] Set the detection distances to 15m, 20m, and 30m respectively, and simulate the variation of the SNR and SINR at the receiving end of the millimeter-wave radar with the rainfall rate. The results are as Figure 3 shown. The results show that as the rainfall rate increases, the SINR at the receiving end of the millimeter-wave radar decreases, and the detection performance of the millimeter-wave radar decreases. Compared with SNR, its SINR decreases faster, indicating that compared with the attenuation effect of rain, the backscattering effect has a greater impact on the millimeter-wave radar.

[0086] In summary, the above is only the preferred embodiment of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for evaluating the detection performance of millimeter wave radar under rainfall conditions, characterized in that: include: S1, based on scattering theory, calculate the attenuation power of raindrop particles per unit volume on millimeter wave radar signals and backscatter power S2, the finite element method is used to model the propagation path of the millimeter-wave radar signal under rainfall conditions, and the attenuation power P of the millimeter-wave radar signal on the propagation path is calculated. ext and the backscatter power P b ; The transmitting antenna of the millimeter-wave radar is regarded as a point source, and the propagation path within the main lobe width of the millimeter-wave radar is regarded as a spherical cone. The spherical cone is divided into spherical cone shell elements according to the distance R. The thickness of each spherical cone shell element is dR, and the volume dV of the spherical cone shell element is the difference between the volumes of the two spherical cones with heights of R and R+dR. The attenuation power of the millimeter wave radar signal passing through a spherical cone shell element is and backscatter power They are: and backscatter power Respectively, the volume dV of the spherical cone shell and the power density S of the millimeter wave radar signal I The product of The attenuation power P of the millimeter wave radar signal on the propagation path ext and the backscatter power P b =The attenuation power of the spherical cone shell element on the propagation path of the millimeter wave radar signal and backscatter power Integrate the distance R to obtain; S3, based on the attenuation power P of the millimeter wave radar signal on the propagation path ext and the backscattered power P b , calculate the SINR of the millimeter-wave radar echo signal, and evaluate the millimeter-wave radar detection performance under rainfall conditions based on SINR.

2. The method according to claim 1, characterized in that In S1, Rayleigh scattering theory, geometric optics approximation theory, discrete dipole approximation theory or T-matrix method is adopted.

3. The method according to claim 1, characterized in that In S1, the Mie scattering theory is first used to solve the extinction coefficient Q of a single scatterer particle. ext and the backscatter coefficient Q b ; Then, based on the spectral distribution model of raindrop particles, the attenuation power of millimeter-wave radar signals per unit volume of raindrop particles at a certain rainfall rate is obtained. and backscatter power 4. The method according to claim 3, characterized in that Extinction coefficient Q of a single scatterer particle ext and the backscatter coefficient Q b for: Among them, m represents the complex refractive index of water, λ represents the incident wavelength, r represents the radius of the spherical raindrop particle, and a n and b n is the coefficient of Mie scattering theory, Re represents the real part, x is the scale parameter, and satisfies the formula 5. The method according to claim 4, characterized in that m is calculated using Ray's empirical formula.

6. The method according to claim 3, 4 or 5, characterized in that: The spectral distribution model of raindrop particles adopts the Marshall-Palmer model, the Gamma distribution model, the lognormal distribution model, the Weibull distribution model or the generalized Gamma distribution model.

7. The method according to claim 6, characterized in that At a certain rainfall rate, the attenuation power and backscattering power of the millimeter-wave radar signal per unit volume of raindrop particles are: Among them, S I represents the power density of the millimeter wave radar signal, r max With r min They represent the maximum and minimum radius of spherical raindrop particles within unit volume respectively, and N(r) is the spectral distribution function of the radius of spherical raindrop particles.

8. The method according to claim 7, characterized in that The attenuation power P generated by the millimeter wave radar signal passing through a spherical cone shell element ext and the backscatter power P b The calculation formula is The volume dV of the spherical cone shell element is: The power density S of the millimeter wave radar signal I for: Among them, P t represents the incident power corresponding to the spherical cone shell element; θ bw Indicates the main lobe width of the millimeter-wave radar transmitting antenna.

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