A method for simulating pulse doppler echo of a rotor unmanned aerial vehicle

Abstract

The application particularly relates to a pulse Doppler echo simulation method of a rotor unmanned aerial vehicle, which comprises the following steps: equivalent to a machine body as an isotropic scattering point, simulating a radar echo signal of the machine body based on an RCS of the machine body scattering point and a distance between the radar and a machine body gravity center; equivalent to rotor blades as a group of uniformly distributed isotropic scattering points on straight lines, simulating a radar echo signal of the rotor scattering points based on an RCS of the rotor scattering points and a distance between the rotor scattering points and the machine body gravity center; simulating a radar echo signal of a single blade based on the radar echo signal of the rotor scattering points, simulating a radar echo signal of a single rotor based on the radar echo signal of the single blade, simulating a radar echo signal of all rotors based on the radar echo signal of the single rotor; and simulating a pulse Doppler echo signal of the rotor unmanned aerial vehicle based on the radar echo signal of all rotors, the radar echo signal of the machine body and an echo signal noise. The method more truly simulates a radar echo characteristic of the rotor unmanned aerial vehicle.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of echo modeling simulation, and particularly relates to a pulse Doppler echo simulation method for a rotor unmanned aerial vehicle. BACKGROUND

[0002] There are three main modeling methods for the rotor echo model, which are an integral model, an equivalent radar cross section (RCS) model and a scattering point model.

[0003] The integral model regards the rotor blade as a rigid line with the same scattering coefficient, and then integrates it to finally obtain an analytical expression of the corresponding radar echo model.

[0004] The equivalent RCS model calculates the RCS of the rotor blade by using a physical optics method, an equivalent electromagnetic current method, a quasi-static method and the like, and analyzes the time-frequency domain characteristics of the blade based on a time-frequency transformation method, so as to obtain a rotor target echo model.

[0005] The scattering point model equivalently regards the blade as a plurality of strong scattering points, and models the motion state of the scattering points.

[0006] The integral model and the equivalent RCS model pay more attention to the change of echo amplitude, and the scattering point model pays more attention to the change of echo phase.

[0007] However, the rotor blade is simplified in the existing radar echo modeling of the rotor unmanned aerial vehicle, which will cause a significant deviation between the simulation result and the actual echo.

[0008] It should be noted that the information disclosed in the above background section is only used to strengthen the understanding of the background of the present application, and therefore can include information that does not constitute prior art known to those of ordinary skill in the art. SUMMARY

[0009] The present application provides a pulse Doppler echo simulation method for a rotor unmanned aerial vehicle, which equivalently regards the rotor blade as a series of scattering points, not only considers the reflection characteristics of a single blade, but also comprehensively analyzes the dynamic changes of the rotor blade under different flight states, so as to more truly simulate the radar echo characteristics of the rotor unmanned aerial vehicle.

[0010] Other characteristics and advantages of the present application will become apparent from the following detailed description, or will be learned by practice of the present application.

[0011] According to a first aspect of the present application, a pulse Doppler echo simulation method for a rotor unmanned aerial vehicle is provided, and the method comprises:

[0012] equivalently regarding the fuselage as an isotropic scattering point, simulating the radar echo signal of the fuselage based on the RCS of the fuselage scattering point and the distance between the radar and the gravity center of the fuselage;

[0013] The rotor blade is equivalent to a set of uniformly distributed isotropic scattering points on a straight line, and the radar echo signal of the rotor scattering point is simulated based on the RCS of the rotor scattering point and the distance from the rotor scattering point to the center of gravity of the fuselage;

[0014] The radar echo signal of a single blade is simulated based on the radar echo signal of the rotor scattering point, the radar echo signal of a single rotor is simulated based on the radar echo signal of a single blade, and the radar echo signal of all rotors is simulated based on the radar echo signal of a single rotor;

[0015] The pulse Doppler echo signal of the rotor unmanned aerial vehicle is simulated based on the radar echo signal of all rotors, the radar echo signal of the fuselage and the echo signal noise.

[0016] In some example embodiments, the rotation directions of two adjacent rotors of the rotor unmanned aerial vehicle are opposite.

[0017] In some example embodiments, the radar echo signal of the fuselage is simulated based on the RCS of the fuselage scattering point and the distance from the radar to the center of gravity of the fuselage, and the formula used is as follows:

[0018]

[0019] Where σ b is the RCS of the fuselage scattering point, c represents the speed of light, t f represents the fast time, f c represents the signal carrier frequency, and R b represents the distance from the radar to the center of gravity of the fuselage.

[0020] In some example embodiments, the radar echo signal of the rotor scattering point is simulated based on the RCS of the rotor scattering point and the distance from the rotor scattering point to the center of gravity of the fuselage, and the formula used is as follows:

[0021]

[0022] Where σ P is the RCS of the rotor scattering point, and R P is the distance from the rotor scattering point to the center of gravity of the fuselage.

[0023] In some example embodiments, the radar echo signal of a single blade is simulated based on the radar echo signal of the rotor scattering point, and the formula used is as follows:

[0024]

[0025] Where n s is the number of rotor scattering points of a single blade.

[0026] In some example embodiments, the radar echo signal of a single blade is used to simulate the radar echo signal of a single rotor, and the formula used is as follows:

[0027]

[0028] wherein n j is the number of blades of a single rotor.

[0029] In some example embodiments, the radar echo signal of a single blade is used to simulate the radar echo signal of all rotors, and the formula used is as follows:

[0030]

[0031] wherein n k is the number of rotors with different angular velocities and initial phases.

[0032] According to a second aspect of the present application, a storage medium is provided, which stores a computer program, and the computer program, when executed by a processor, implements the pulse Doppler echo simulation method of the rotor unmanned aerial vehicle according to the first aspect.

[0033] According to a third aspect of the present application, a computer program product is provided, which stores a computer program, and the computer program, when executed by a processor, implements the pulse Doppler echo simulation method of the rotor unmanned aerial vehicle according to the first aspect.

[0034] According to a fourth aspect of the present application, an electronic device is provided, which comprises:

[0035] a processor; and

[0036] a memory for storing executable instructions of the processor;

[0037] wherein the processor is configured to implement the pulse Doppler echo simulation method of the rotor unmanned aerial vehicle according to the first aspect by executing the executable instructions.

[0038] The pulse Doppler echo simulation method of the rotor unmanned aerial vehicle provided by the embodiments of the present application represents the rotor blades with uniformly distributed isotropic scattering points on a set of straight lines, and represents the fuselage with an isotropic scattering point; the model considers the reflection characteristics of a single rotor blade and the dynamic changes of multiple blades in different flight states; in order to offset the counter torque caused by the rotation of the rotor and maintain the stability of the fuselage, the rotation directions of adjacent two rotors are opposite. Whether it is a spike formed by the overall motion of the unmanned aerial vehicle or a spectrum broadening caused by the micro-motion of the rotor, the simulated echo is very close to the actually measured echo.

[0039] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the application, as claimed. BRIEF DESCRIPTION OF DRAWINGS

[0040] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the application and serve to explain the principles of the application. It is readily apparent to one skilled in the art that the following description is merely exemplary and explanatory of the application and that various embodiments of the application can be readily made without departing from the spirit and scope of the application.

[0041] Figure 1 Flow chart of the pulse Doppler echo simulation method for the rotor unmanned aerial vehicle of the embodiments of the application;

[0042] Figure 2 Radar and unmanned aerial vehicle position relationship of the embodiments of the application;

[0043] Figure 3 Radar and rotor single-scattering point position relationship of the embodiments of the application;

[0044] Figure 4 Single-blade model of the embodiments of the application;

[0045] Figure 5 Unmanned aerial vehicle echo simulation result of the embodiments of the application;

[0046] Figure 6 Unmanned aerial vehicle hovering echo actual measurement result of the embodiments of the application;

[0047] Figure 7 Unmanned aerial vehicle flying echo actual measurement result of the embodiments of the application;

[0048] Figure 8 Extracting the distance unit where the target is located in the MTD plane of the embodiments of the application. DETAILED DESCRIPTION

[0049] Example implementations will now be described more fully with reference to the accompanying drawings. Example implementations may, however, be implemented in many different forms and should not be construed as limited to the examples set forth herein; rather, these implementations are provided so that this disclosure will be thorough and complete, and will fully convey the scope of example implementations to those skilled in the art. Features described in the description, structures, or characteristics may be combined in any suitable manner in one or more implementations.

[0050] The echo model involved in the application is based on the following assumptions:

[0051] 1. The echo model is based on a pulse Doppler (PD) radar;

[0052] 2. The radar's range resolution is much greater than that of the UAV;

[0053] 3. The frequency resolution of radar is much smaller than the linear velocity of the rotor.

[0054] 4. The distance between the radar and the UAV meets the far-field condition;

[0055] 5. The reception time of radar transmitted signals is much longer than the transmission time;

[0056] 6. The echo model is interested in the echo phase rather than the echo amplitude, so it ignores the spatial attenuation of the radar signal.

[0057] Based on the above assumptions, the echo model adopts the "stationary-moving" method, that is, the distance between the scattering point and the radar remains unchanged when the signal is reflected; the echo model does not consider multipath, diffraction or structural reflection, and ignores the distance between the rotor center point and the fuselage; therefore, the reflected signal of the entire UAV is regarded as the vector superposition of the echo signals of all scattering points.

[0058] The positional relationship between radar and UAV is as follows: Figure 2 As shown, right-handed coordinate systems are established at the radar and UAV locations respectively. The radar coordinates are represented by (x... r ,y r ,z r ) indicates that the origin O of the coordinate system r At the geometric center of the radar array, x r For the horizontal direction of the array, y r This represents the direction of the array surface normal. The UAV coordinates are represented by (x...). u ,y u ,z u ) indicates that the origin O of the coordinate system u For the fuselage center of gravity, (x u ,y u ,z u ) direction and (x r ,y r ,z r The directions are consistent. u To O r The initial distance is R0, O u In (x r ,y r ,z r The azimuth and elevation angles of the coordinate system are α and β, respectively.

[0059] Assume the radar transmission signal is a linear frequency modulated signal:

[0060]

[0061] Among them, t ffast time, which denotes the sampling data of the received time in a pulse repetition integration (PRI), T p signal time width, K = B / T p chirp slope, B denotes the bandwidth of the transmitted signal, and f c denotes the carrier frequency of the signal.

[0062] Suppose that the UAV flies at a constant speed v on the x r axis, then the distance between a certain time O u and O r is:

[0063] R b = R0 + vt s

[0064] where t s denotes the slow time, and its expression is t s = mPRI, m denotes the mth PRI in a coherent pulse integration (CPI).

[0065] The fuselage echo signal received by the radar is

[0066]

[0067] where c denotes the speed of light, and σ b denotes the amplitude of the echo signal, which is proportional to the RCS of the scattering point.

[0068] Here, the propagation attenuation of the electromagnetic wave in space is ignored, so σ b can be equivalent to the RCS of the scattering point. The model assumes that the angle between the fuselage and the radar is constant, so the RCS of the fuselage scattering point is considered to be constant.

[0069] Suppose that the radar moving target detection (MTD) accumulation point number is m max , the slow time sampling rate is the pulse repetition frequency (PRF), and the frequency spectrum after the slow time dimension FFT is distributed in (-PRF / 2, +PRF / 2). The relationship between the velocity and the frequency is PRF / 2 = 2v / λ, so the maximum unambiguous velocity (positive and negative unambiguous) is v max = PRFλ / 4, and the velocity resolution is where λ = c / f denotes the carrier wavelength.

[0070] The relationship between the linear velocity v of the rotor and the angular velocity ω is v = ω · d, where d is the distance from the scattering point to the center of rotation. When the blade is equivalent to a series of scattering points, the maximum distance between each scattering point is The number of scattering points of a single blade is where L represents the total length of the blade, and the distance from each scattering point to the center of rotation is represented as d i = i · l.

[0071] To simplify the analysis, first consider a model with only a single rotor scattering point P, and set α and β to 0. The simplified model of the radar and the scattering point P is shown in Figure 3 .

[0072] Figure 3 In θ represents the angle between the scattering point P and the x u axis, x t and y t represent the projection distances of the scattering point P on the x u and y u axes, ω represents the rotational angular velocity of the rotor, and d P represents the distance from the scattering point P to the center of rotation.

[0073] O u In the (x r , y r , z r ) coordinate system, the coordinates are (R b , 0, 0), and in the (x r , y r , z r ) coordinate system, the coordinates of the scattering point P are (d P cosθ t , d P sinθ t , 0). Therefore, in the (x r , y r , z r ) coordinate system, the coordinates of point P are (R b +d P cosθ t , d P sinθ t , 0). The distance R u from the scattering point P to O P at a certain moment is

[0074]

[0075] where θ t = θ0+ ωt a , t a = t d + t s + t f , td is the time interval from the take-off time t0to the beginning time of the simulation echo.

[0076] The radar echo signal of the rotor scattering point is

[0077]

[0078] where σ P is the RCS of the scattering point P, which varies with the fast time.

[0079] Here σ P is the RCS of the scattering point P, which varies with the fast time. Figure 4

[0080] Figure 4 where h represents the height of the rectangular blade, because the model satisfies the far-field condition, n s scattering points on the same blade have the same angle with x r , so it is considered that all the scattering points of the same blade have the same σ P , σ P =hl|sinθ t |.

[0081] Then, the radar echo signal of a single blade can be expressed as

[0082] For the rotor with n j blades, considering that the initial phase of each blade is different, the radar echo signal of a single rotor is

[0083] Considering that n k rotors have different angular velocities ω k and initial phases θ k , the radar echo signal of all the rotors is where θ t =θ k +(j-1)2π / n j +ω k t a .

[0084] The radar echo signal of the entire rotor unmanned aerial vehicle is s(t s ,t a ) = s b (t s ) + s total (t a ) + s n , where s n represents the noise in the echo signal.

[0085] ​To illustrate the simulation effect of the present application, three scenarios of hovering, slow flight and fast flight are designed, and the detailed simulation experiment parameters are given in the following table.

[0086]

[0087] In order to offset the counter torque caused by the rotation of the rotor, keep the stability of the fuselage, the adjacent two rotors rotate in opposite directions, and the flight speed of the unmanned aerial vehicle does not exceed the radar blurring speed;

[0088] The simulation results of the unmanned aerial vehicle in the hovering, slow flight and fast flight states are shown in Figure 5 .

[0089] From Figure 5 (a, c, e), it can be seen that the simulation echo shows obvious "flickering" effect in time domain. From Figure 5 (b, d, f), it can be seen that the simulation echo forms a sharp peak on the MTD plane, the rotor micro-motion causes the target sharp peak to spread on both sides of the Doppler V, and the spread degree increases with the increase of the rotor speed, when the unmanned aerial vehicle hovers, the echo sharp peak will fall in the clutter channel;

[0090] Figure 6 and Figure 7 respectively give the results of the rotor unmanned aerial vehicle hovering and fast flight state echo measured by a certain ground armored platform radar after pulse compression and MTD processing;

[0091] From Figure 6 and Figure 7 , it can be seen that the measured echo forms a sharp peak on the MTD plane, and the sharp peak appears spectrum spread on both sides of the Doppler V;

[0092] When the unmanned aerial vehicle hovers, the echo sharp peak falls in the clutter channel. In addition, the measured echo also contains ground clutter and cloud rain clutter;

[0093] In order to further verify the effectiveness of the pulse Doppler echo simulation method of the rotor unmanned aerial vehicle, all Doppler channels of the target in the distance unit in the MTD plane are extracted for analysis, as shown in Figure 8 .

[0094] From Figure 8 , it can be seen that the simulation echo and the measured echo show similar spectrum distribution on the MTD plane;

[0095] Whether it is the sharp peak formed by the overall motion of the unmanned aerial vehicle, or the spectrum spread caused by the rotor micro-motion, the simulation echo and the measured echo are very close.

[0096] It should be noted that, as another aspect, the present application also provides a storage medium, which can be included in an electronic device, or exist separately without being assembled into the electronic device. The storage medium carries one or more programs, which, when executed by an electronic device, cause the electronic device to implement the method described in the above embodiments. For example, the electronic device can implement each step of the method as shown in Figure 1

[0097] In one embodiment, the present application provides a computer program product, which includes a computer program that, when executed by a processor, implements the steps in the above method embodiments.

[0098] In addition, the above figures are only schematic illustrations of the processes included in the method according to the exemplary embodiments of the present application, and are not intended to be limiting. It is easy to understand that the processes shown in the above figures do not indicate or limit the time sequence of the processes. In addition, it is also easy to understand that the processes can be executed synchronously or asynchronously, for example, in multiple modules.

[0099] Other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The application is intended to cover any variations, uses or adaptations of the application following, in general, the principles of the application and including such steps that are apparent to those skilled in the art to which the application pertains. It is intended to include and invoke the doctrine of equivalents as it pertains to the scope of the application. The specification and examples are to be considered exemplary only, with the true scope and spirit of the application indicated by the following claims.

[0100] It should be understood that the present application is not limited to the precise construction that has been described above and illustrated in the accompanying drawings, and that various modifications and changes can be made by those skilled in the art without departing from the scope of the present application. The scope of the present application is limited only by the appended claims.​

Claims

1. A method of simulating pulsed Doppler returns for a rotorcraft unmanned aerial vehicle, comprising: The method comprises: equivalent to a fuselage body isotropic scattering point, based on the RCS of the fuselage body scattering point and the distance between the radar and the center of gravity of the fuselage body, simulating the radar echo signal of the fuselage body; equivalent to a group of uniformly distributed isotropic scattering points on a straight line, based on the RCS of the rotor scattering point and the distance from the rotor scattering point to the center of gravity of the fuselage body, simulating the radar echo signal of the rotor scattering point; based on the radar echo signal of the rotor scattering point, simulating the radar echo signal of a single blade, based on the radar echo signal of a single blade, simulating the radar echo signal of a single rotor, and based on the radar echo signal of a single rotor, simulating the radar echo signal of all rotors; based on the radar echo signal of all rotors, the radar echo signal of the fuselage body and the echo signal noise, simulating the pulse Doppler echo signal of the rotor unmanned aerial vehicle; The formula used in the simulation of the radar echo signal of the fuselage body based on the RCS of the fuselage body scattering point and the distance between the radar and the center of gravity of the fuselage body is as follows: wherein, RCS of the body scattering point, c denotes the speed of light, denotes the fast time, denotes the signal carrier frequency, denotes the distance of the radar from the body's center of gravity; The formula used in the simulation of the radar echo signal of the rotor scattering point based on the RCS of the rotor scattering point and the distance from the rotor scattering point to the center of gravity of the fuselage body is as follows: wherein, RCS is the RCS of the rotor scatter point, is the distance from the rotor scatter point to the center of gravity of the fuselage; The formula used in the simulation of the radar echo signal of a single blade based on the radar echo signal of the rotor scattering point is as follows: wherein, Np is the number of scattering points for a single blade of the rotor; The formula used in the simulation of the radar echo signal of a single rotor based on the radar echo signal of a single blade is as follows: wherein, is the number of blades of the single rotor; The formula used in the simulation of the radar echo signal of all rotors based on the radar echo signal of a single rotor is as follows: wherein is the number of rotors with different angular velocities and initial phases.

2. The method of claim 1, wherein, The adjacent two rotors of the rotor unmanned aerial vehicle rotate in opposite directions.

3. A storage medium having stored thereon a computer program, characterized in that The computer program is executed by the processor to realize the pulse Doppler echo simulation method of the rotor unmanned aerial vehicle according to any one of claims 1 to 2.

4. A computer program product comprising a computer program, characterized in that, The computer program is executed by the processor to realize the pulse Doppler echo simulation method of the rotor unmanned aerial vehicle according to any one of claims 1 to 2.

5. An electronic device, comprising: Comprise: a processor; and a memory for storing executable instructions of the processor; wherein the processor is configured to execute the pulse Doppler echo simulation method of the rotor unmanned aerial vehicle according to any one of claims 1 to 2 by executing the executable instructions.

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