CN112558497B

CN112558497B - Anti-interference digital simulation method and system for radar altimeter

Info

Publication number: CN112558497B
Application number: CN202011385284.2A
Authority: CN
Inventors: 沈晓卫; 左东广; 潘嶙; 何川; 朱晓菲; 樊天锁; 李国梁
Original assignee: Rocket Force University of Engineering of PLA
Current assignee: Rocket Force University of Engineering of PLA
Priority date: 2020-12-01
Filing date: 2020-12-01
Publication date: 2022-06-10
Anticipated expiration: 2040-12-01
Also published as: CN112558497A

Abstract

The invention relates to an anti-interference digital simulation method and system for a radar altimeter. The method comprises the steps of obtaining operation data sent by a scene controller; acquiring a baseband emission signal of the radar altimeter according to the starting signal; performing echo simulation by adopting a method combining a grid method and a statistical model method according to the terrain data, the ground electromagnetic characteristic data, the carrier position, the attitude, the antenna directional pattern data and the baseband transmitting signal to determine a baseband echo signal; generating an interference signal according to the control signal, the baseband transmission signal and an interference strategy; determining the electromagnetic transmission characteristic from the antenna end to the antenna end according to the position and the posture of the carrier and the antenna data; and determining a height signal of the radar altimeter according to the baseband echo signal, the interference signal and the electromagnetic transmission characteristic from the antenna end to the antenna end. The invention improves the flexibility, accuracy and high efficiency of the anti-interference digital simulation of the radar altimeter.

Description

Anti-interference digital simulation method and system for radar altimeter

Technical Field

The invention relates to the field of radar altimeter simulation, in particular to an anti-interference digital simulation method and system for a radar altimeter.

Background

The radar altimeter is used as an important component of an airborne platform, and the anti-interference performance of the radar altimeter directly influences the working performance of the platform. With the rapid development of foreign electronic warfare technologies, the anti-interference performance of a radar altimeter under complex electromagnetic environments and high-confrontation conditions needs to be inspected and evaluated urgently.

For anti-interference evaluation, the method mainly depends on an external field test and an internal field semi-physical test, but the external field test is often high in cost and limited in times, and the simulation details of the semi-physical test operation process and the reality of clutter simulation are inferior to those of a real test environment. And (3) establishing a mathematical model under an internal field condition by digital simulation, replacing all links and test-participating equipment in the interference test system by the mathematical model, changing the mathematical model into a simulation model, and carrying out an anti-interference simulation test on a simulation computer. At present, most simulation researches on radar altimeters only establish radar altimeters and echo mathematical models of various systems, and the whole simulation process is not established systematically, so that the accuracy of the detection and evaluation of the anti-interference performance of the radar altimeters in complex electromagnetic environments and high-confrontation conditions needs to be improved.

Disclosure of Invention

The invention aims to provide an anti-interference digital simulation method and system for a radar altimeter, and the flexibility, accuracy and high efficiency of the anti-interference digital simulation of the radar altimeter are improved.

In order to achieve the purpose, the invention provides the following scheme:

an anti-interference digital simulation method for a radar altimeter comprises the following steps:

acquiring operation data sent by a scene controller; the operational data includes: scene data, starting signals, terrain data, ground electromagnetic characteristic data, antenna directional pattern data, control signals and antenna data; the scene data includes: the method comprises the following steps of (1) carrying position, attitude, carrying speed vector, carrying rotation vector, radar altimeter antenna installation attitude, radar altimeter antenna directional diagram, jammer deployment position, jammer antenna installation attitude, jammer antenna directional diagram, radiation source deployment position, radiation source antenna installation attitude, radiation source antenna directional diagram, radar altimeter antenna gain and jammer antenna gain, jammer and radiation source line-of-sight and line-of-sight change rate, jammer antenna gain and radiation source antenna gain, radar altimeter antenna gain and radiation source antenna gain;

acquiring a baseband emission signal of the radar altimeter according to the starting signal;

performing echo simulation by adopting a method combining a grid method and a statistical model method according to the terrain data, the ground electromagnetic characteristic data, the carrier position, the attitude, the antenna directional pattern data and the baseband transmitting signal to determine a baseband echo signal;

generating an interference signal according to the control signal, the baseband transmission signal and an interference strategy; the interference signal includes: spoof interference and noise interference;

determining the electromagnetic transmission characteristic from the antenna end to the antenna end according to the position and the posture of the carrier and the antenna data; the electromagnetic transmission characteristics include: energy attenuation, delay, and doppler characteristics;

and determining a height signal of the radar altimeter according to the baseband echo signal, the interference signal and the electromagnetic transmission characteristic from the antenna end to the antenna end.

Optionally, the determining the baseband echo signal by performing echo simulation by using a method combining a mesh method and a statistical model method according to the terrain data, the ground electromagnetic property data, the carrier position, the attitude, the antenna directional diagram data, and the baseband transmission signal specifically includes:

determining echo signals in a first set range under the carrier by adopting a grid method according to the terrain data, the ground electromagnetic characteristic data, the carrier position, the attitude, the antenna directional pattern data and the baseband transmitting signals;

determining echo signals in a second set range under the carrier by using a statistical model method according to the terrain data, the ground electromagnetic characteristic data, the carrier position, the attitude, the antenna directional pattern data and the baseband transmitting signals;

and determining the baseband echo signal according to the echo signal within a first set range under the carrier and the echo signal within a second set range away from the carrier.

Optionally, the determining, according to the position and the posture of the carrier and the antenna data, the electromagnetic transmission characteristic from the antenna end to the antenna end specifically includes:

determining the channel transmission characteristics from the radar altimeter antenna to the jammer antenna according to the carrier position, the attitude and the antenna data;

and determining the channel transmission characteristics from the interference antenna to the radar altimeter antenna according to the position and the attitude of the carrier and the antenna data.

Optionally, the acquiring the operation data sent by the scene controller specifically includes:

the running data sent by the camera controller was acquired with a simulated step size of 0.02 seconds.

An anti-interference digital simulation system of a radar altimeter, comprising:

the operation data acquisition module is used for acquiring the operation data sent by the scene controller; the operational data includes: scene data, a starting signal, topographic data, ground electromagnetic characteristic data, antenna directional pattern data, a control signal and antenna data; the scene data includes: the method comprises the following steps of (1) carrying position, attitude, carrying speed vector, carrying rotation vector, radar altimeter antenna installation attitude, radar altimeter antenna directional diagram, jammer deployment position, jammer antenna installation attitude, jammer antenna directional diagram, radiation source deployment position, radiation source antenna installation attitude, radiation source antenna directional diagram, radar altimeter antenna gain and jammer antenna gain, jammer and radiation source line-of-sight and line-of-sight change rate, jammer antenna gain and radiation source antenna gain, radar altimeter antenna gain and radiation source antenna gain;

the base band emission signal acquisition module is used for acquiring a base band emission signal of the radar altimeter according to the starting signal;

a baseband echo signal determining module, configured to perform echo simulation by using a method combining a mesh method and a statistical model method according to the terrain data, the ground electromagnetic characteristic data, the carrier position, the attitude, the antenna directional pattern data, and the baseband transmit signal, and determine a baseband echo signal;

an interference signal generating module, configured to generate an interference signal according to the control signal, the baseband transmission signal, and an interference policy; the interference signal includes: spoof interference and noise interference;

the electromagnetic transmission characteristic determining module is used for determining the electromagnetic transmission characteristic from the antenna end to the antenna end according to the position and the posture of the carrier and the antenna data; the electromagnetic transmission characteristics include: energy attenuation, delay, and doppler characteristics;

and the height signal determining module is used for determining a height signal of the radar altimeter according to the baseband echo signal, the interference signal and the electromagnetic transmission characteristic from the antenna end to the antenna end.

Optionally, the baseband echo signal determining module specifically includes:

the echo signal first determining unit is used for determining echo signals in a first set range under the carrier by adopting a grid method according to the terrain data, the ground electromagnetic property data, the carrier position, the attitude, the antenna directional pattern data and the baseband transmitting signals;

the second echo signal determining unit is used for determining echo signals in a second set range from the position under the carrier by using a statistical model method according to the terrain data, the ground electromagnetic property data, the carrier position, the attitude, the antenna directional pattern data and the baseband transmitting signals;

and the baseband echo signal determining unit is used for determining the baseband echo signal according to the echo signal in a first set range under the carrier and the echo signal in a second set range away from the carrier.

Optionally, the electromagnetic transmission characteristic determining module specifically includes:

the first channel transmission characteristic determining module is used for determining the channel transmission characteristic from the radar altimeter antenna to the jammer antenna according to the carrier position, the attitude and the antenna data;

and the second channel transmission characteristic determining module is used for determining the channel transmission characteristics from the interference antenna to the radar altimeter antenna according to the carrier position, the attitude and the antenna data.

Optionally, the operation data obtaining module specifically includes:

According to the specific embodiment provided by the invention, the invention discloses the following technical effects:

according to the anti-interference digital simulation method and system for the radar altimeter, provided by the invention, echo simulation is carried out by adopting a method combining a grid method and a statistical model method according to the terrain data, the ground electromagnetic characteristic data, the carrier position, the attitude, the antenna directional pattern data and the baseband transmission signal, so that a baseband echo signal is determined, the algorithm operation amount can be reduced, the main components of the echo can be vividly simulated, and the echo is more practical compared with the traditional point target echo. The invention can construct different confrontation scenes by establishing radar altimeter models and interference signals of different systems; the method integrates and simulates the echoes, interferences and clutters of the radar altimeter, and has the characteristics of rich test scenes, simple method, high efficiency and the like.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.

FIG. 1 is a schematic flow chart of an anti-interference digital simulation method for a radar altimeter provided by the invention;

FIG. 2 is a process of height signal simulation for a radar altimeter provided in the present invention;

FIG. 3 is a schematic diagram of an illuminated area of a radar altimeter based on meshing provided by the present invention;

FIG. 4 is a schematic view of scattering sites;

FIG. 5 is a Doppler diagram of a radar altimeter;

FIG. 6 is a schematic view of the region division right below the loader;

FIG. 7 is a schematic diagram of an echo simulation channel;

FIG. 8 is a block diagram of suppressing noise interference generation;

FIG. 9 is a schematic diagram of frequency sweep interference;

FIG. 10 is a schematic diagram of generation of dense decoys by IIR;

FIG. 11 is a schematic circuit diagram of an IIR-based multistage delay superposition method;

FIG. 12 is a block diagram of a range-speed-towed disturbance implementation;

FIG. 13 is a schematic diagram of a generation model of a lognormal distribution;

FIG. 14 is a schematic diagram of a generation model of a Webbing distribution;

FIG. 15 is a schematic diagram of a generation model of K distribution;

fig. 16 is a schematic diagram of radar altimeter signal modulation.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.

Fig. 1 is a schematic flow chart of an anti-interference digital simulation method for a radar altimeter provided by the present invention, fig. 2 is a schematic flow chart of an altitude signal simulation flow of a radar altimeter provided by the present invention, as shown in fig. 1 and fig. 2, the present invention provides an anti-interference digital simulation method for a radar altimeter, which includes:

s101, acquiring running data sent by a scene controller; the operational data includes: scene data, starting signals, terrain data, ground electromagnetic characteristic data, antenna directional pattern data, control signals and antenna data; the scene data includes: the method comprises the following steps of carrier position, attitude, carrier speed vector, carrier rotation vector, radar altimeter antenna installation attitude, radar altimeter antenna directional diagram, jammer deployment position, jammer antenna installation attitude, jammer antenna directional diagram, radiation source deployment position, radiation source antenna installation attitude, radiation source antenna directional diagram, radar altimeter antenna gain and jammer antenna gain, jammer and radiation source line-of-sight and line-of-sight change rate, jammer antenna gain and radiation source antenna gain, radar altimeter antenna gain and radiation source antenna gain. The scene controller is used for providing rendering, deduction and calculation services and controlling simulation time sequence.

And S102, acquiring a baseband emission signal of the radar altimeter according to the starting signal.

S103, performing echo simulation by adopting a method of combining a grid method and a statistical model method according to the terrain data, the ground electromagnetic characteristic data, the carrier position, the attitude, the antenna directional pattern data and the baseband emission signal, and determining a baseband echo signal.

S103 specifically comprises the following steps:

according to the terrain data, the ground electromagnetic characteristic data, the carrier position, the attitude, the antenna directional pattern data and the baseband transmission signal, determining an echo signal in a first set range under the carrier by adopting a grid method;

determining an echo signal within a second set range from the position under the aircraft by using a statistical model method according to the terrain data, the ground electromagnetic characteristic data, the carrier position, the attitude, the antenna directional pattern data and the baseband transmitting signal;

The echo simulation is to simulate the modulated signal to be transmitted to the radiation direction by using the digital circuit technology, and form an echo after reflection. Here, the echo of the electromagnetic wave emitted to the ground in a simulated manner is a surface target, not a point target, and the reflected echo may be distorted due to a path difference, and in addition to the influences of a terrain and a landform, a ground scattering coefficient, clutter interference and the like, the echo may be changed in amplitude and phase compared with the emitted signal, so as to form an echo signal.

The mesh division principle is as follows: during ground echo, a mesh segmentation method can be used for segmenting the surface target of a signal beam coverage area into square meshes, each mesh is regarded as an independent scattering element, echo signals of each scattering element are respectively calculated based on a radar equation, and the echo signals of the surface target in the whole signal illumination area are obtained by vector summation of all the scattering element echo signals.

Let the center of the antenna beam point to the nadir point, and the beam irradiation area be a, as shown in fig. 3. Firstly, a coordinate system is established, a nadir point is taken as an original point, the flight direction of the loader is taken in the positive direction of an X axis, and the right-hand coordinate system is taken in the positive direction of a Y axis and is perpendicular to the X direction. Carrying out grid division by the size of delta tau multiplied by delta v to obtain N grids A_i(i ═ 1.., N), then

For each grid, it is characterized by the coordinates of its center point. It is obvious that from the viewpoint of improving the simulation accuracy, the size of the mesh should be as small as possible. However, as the mesh division becomes finer, the simulation calculation amount becomes larger, and the requirement for the calculation speed becomes higher, so that the accuracy and the speed are in conflict with each other. In order to take account of both accuracy and operation speed, reasonable division is required.

The echo calculation principle is as follows: the description of the kth scattering element, as shown in fig. 4, includes the following parameters:

1) scattering unit anddistance r of radar_kOr a time delay.

2) Antenna gain G_k＝G(β_k) G (beta) is a function of the antenna gain direction, beta_kIs the angle between the antenna pointing direction and the beam direction.

And taking the nadir point as a coordinate origin, setting the height of the radar as H, the flight direction as X-axis forward direction, limiting a velocity vector V in an X-Z plane, setting the pitch angle as 0 and the roll angle as 0, and setting the beam center of the radar antenna and the nadir point Q as the same point. In the three-dimensional coordinate system, the position coordinate of the radar is (0,0, H), and the position coordinate of the kth scattering bin P is (x)_k,y_kAnd 0), the distance between the scattering element and the receiving antenna of the radar altimeter is as follows:

thereby, the delay time of the radar echo signal generated by the scattering element reaching the receiving antenna can be converted into

In order to obtain the radar echo time domain waveform, firstly, a radar equation is rewritten into a function of time. Considering the use of a transmit-receive shared antenna, the instantaneous power of radar reception is expressed as follows:

in the formula, τ is a target two-way delay time. Assuming a complex signal Ψ for a radar-transmitted signal_T(t) is used to represent the time period,

the power of the complex signal is:

P_T(t)＝|ψ_T(t)|²。

from fixed point targetsThe reflected signal will be Ψ_T(t) and its amplitude is multiplied by a scaling factor. Its complex signal expression is as follows:

where φ is a phase offset.

Assuming that the flying speed of the aircraft is v, the included angle between x below the altimeter and the nadir point is v

As shown in fig. 5, the doppler frequency at this point is:

when in use

When the ratio of the water to the oil is small,

the doppler frequency can be expressed as:

from the above equation, the point doppler frequency near the right lower side of the carrier has a linear relationship with x, and the lower side of the carrier can be divided into uniform doppler stripes.

Will Doppler to

The derivation can be:

f 'can be seen from the above formula'_dAnd

is inversely proportional to when

The smaller the Doppler change, the more severe (near linear) the change with

The slower the doppler change is.

The principle of echo simulation synthesis: the echo is simulated by adopting a grid method, the finer the grid division is, the more vivid the echo characteristic can be simulated, but the operation is complex, the calculation amount is too large, the resource consumption is large, and great requirements are put forward on the real-time simulation of hardware. If a statistical model method is adopted for simulation, the calculated amount is small, the operation is fast, but the simulation is not vivid enough. Considering that the echo energy right below the carrier is large, the Doppler stripe changes rapidly, and whether the altitude simulation is correct or not is directly influenced, and relatively fine simulation is needed; and position echo energy just below a far-away carrier is small, Doppler changes are gentle, the influence on height simulation is small, and a statistical model can be adopted for simulation. As shown in fig. 7, in the present project, a method combining a grid method and a statistical model method is used for echo simulation, a grid method is used for simulating echoes near under the aircraft, and a statistical model method is used for simulating echoes including sidelobe echoes at positions far away from under the aircraft, so that the algorithm computation amount can be reduced, and the main components of the echoes can be simulated realistically, wherein the area under the aircraft is divided as shown in fig. 6.

The echo simulation is divided into 32 channels, wherein 28 channels simulate the carrier waves near the position right below the altimeter carrier by adopting a grid method, and the other four channels simulate the echo of a far zone by utilizing a model statistical method. When the grid method is used for carrying out echo simulation, carrier Doppler strips are divided according to the speed, the posture and the like of the carrier, then the echo amplitude and the echo time delay are calculated according to the antenna gain and the height of the carrier, and the echo simulation is carried out on the data signal added with the time delay and the Doppler information. When the model statistical method is used, the echo simulation is carried out by selecting the relative statistical simulation according to the parameters of the ground, the sea surface, the incidence angle, the height of the carrier, the antenna gain and the like below the carrier. Echo signals of 32 channels are superposed, and echo of the whole irradiation area of the altimeter can be simulated.

S104, generating an interference signal according to the control signal, the baseband emission signal and an interference strategy; the interference signal includes: spoof interference and noise interference.

The implementation principle of S104 is as follows:

as shown in fig. 8, the narrow-band gaussian noise generation process is as follows:

step 1: two independent sets of random sequences are generated at a sampling rate, with intervals of [0, 1] being evenly distributed.

Step 2: the two sequences obtained are transformed into an independent, standard-distributed gaussian white noise sequence.

And step 3: and filtering in a time domain to form narrow-band noise.

And 4, step 4: the noise power is set as required.

And 5: and mixing the baseband noise signal and the carrier signal to obtain an intermediate frequency noise signal.

Frequency-of-sight interference

According to the centre frequency f of the interfering signal_jSpectrum width delta f_jWith respect to the radar receiver center frequency f_sBandwidth Δ f_sThe relationship (2) of (c).

The targeted disturbance generally satisfies:

f_j≈f_s,Δf_j＝(2～5)Δf_r。

the radar signal frequency must be firstly measured by adopting the aiming type interference, and then the frequency of the interference machine is adjusted to the radar frequency to ensure the narrow delta f_jThis process of overlay is called frequency steering. The main advantage of the targeted interference is at Δ f_rThe internal interference power is strong, which is the preferred mode for covering the interference, and the disadvantage is that the requirement for frequency guidance is high.

Frequency sweep interference

The sweep frequency interference presents dynamic scanning characteristics in a partial frequency spectrum. The time domain expression is:

wherein beta is_iFor the sweep rate, w_iIn order to be able to measure the initial angular frequency,

for the initial phase, T is the sweep duration. The interference signal is characterized by an instantaneous frequency that varies continuously linearly with time. The main parameters influencing the performance of frequency sweeping interference are as follows: the signal amplitude, sweep range, step time, etc., and the sweep interference frequency are shown in fig. 9.

Dense decoy interference

The generation of dense decoys by the IIR method is simpler than the FIR method, and the first-level IIR generation decoys method is shown in fig. 10.

The output signal is a weighted sum of the output signal of the previous stage and the input signal of the current stage, which can be expressed as:

y(i)＝x(i)+ω·y(i-τ)。

conversion to Z-domain analysis, one can obtain:

a schematic diagram of dense decoy generation by the IIR method of multi-stage delay superposition is shown in fig. 11.

The output of the first stage delay superposition circuit is as follows:

y₁(i)＝x(i)+x(i-τ₁)i＝0,1,…

the output after n-stage delay superposition is:

distance and velocity drag interference

For the radar capable of measuring distance and speed simultaneously, distance (speed) deception jamming is singly implemented, and because the speed is the variation of the distance in unit time, the radar can identify jamming by measuring undisturbed speed (distance) information, and an expected jamming effect cannot be achieved. At the moment, the distance and speed combined deception jamming is needed to be used for simultaneously jamming distance and speed information, so that the jamming of the radar capable of measuring distance and speed simultaneously can be disturbed, and the jamming of the radar capable of measuring distance and speed only singly can be also effective.

The distance and speed deception jamming is mainly realized in a mode of gate dragging jamming, interference signals are added with time delay and frequency shift simultaneously to drag the distance and speed tracking gates of the radar, and the dragging process is as follows:

a wave gate capturing stage: after intercepting the radar emission signal, the jammer forwards the interference signal with the same time delay and Doppler frequency information as the target echo signal in the shortest time and continues for a period of time, so that the interference signal with the amplitude larger than that of the target echo signal can simultaneously capture the distance and speed wave gate of the radar.

And (3) a wave gate dragging stage: after the interference signal controls the distance and speed wave gate of the radar, the jammer simultaneously changes the forwarding time delay and Doppler frequency shift of the interference signal according to a certain rule, and induces the radar distance and speed wave gate to deviate from a target echo signal along with the movement of the interference signal. The synchronous towing speed takes account of the distance and speed change information, and must be less than the minimum value between the radar distance tracking maximum speed and the speed tracking maximum speed, and the towing acceleration is generally about 3 times of the gravity acceleration.

And (3) interference closing stage: the jammer turns off when the radar range and velocity gates are towed a sufficient distance from the target echo. At this time, no signal exists in the wave gate, and the wave gate enters a searching state. The above process is repeated periodically, so that the normal work of the radar target tracking system can be destroyed.

For the moment, without considering the noise factor, as shown in fig. 12, the range-velocity synchronization pulling interference signal is:

wherein, U_sFor interfering signal amplitudes, Δ ω (Δ ω ═ 2 pi Δ f)_dj) For disturbing the deviation of the angular frequency of the echo signal from the target, Δ f_djDoppler shift applied for interference, Δ t_jIs the time delay of the disturbance relative to the target echo. In order to enable the disturbance to closely simulate the motion state of a real target, the Doppler shift function Δ f_dj(t) and a delay function Δ t_j(t) a certain logical relationship needs to be satisfied, where t represents the pulling time of the interference. Time delay function Δ t_j(t) the corresponding distance function is Δ R_j(t), the dragging speed is v when the synchronous dragging interference of the distance speed is dragged at a uniform speed, the dragging acceleration is a when the uniform acceleration is dragged, and then the constant speed is dragged:

therefore, Δ f at constant towing speed_dj(t) and Δ t_jThe relationship of (t) is:

as can be seen from the above formula, when dragging at a constant speed, the Doppler frequency shift Deltaf added by interference_dj(t) is constant and the time delay of the interference Δ t_jThe (t) is increased along with the increase of time, which means that the radar distance tracking wave gate gradually moves slowly when dragging interference, but the speed tracking wave gate jumps and is easily identified by a radar system, so the distance and speed synchronous dragging interference is generally not realized by uniform dragging. Similarly, when the uniform acceleration towing is carried out, the following steps are carried out:

Δf_dj(t) and Δ t_jThe corresponding relation of (t) is as follows:

according to the formula, when the uniform acceleration towing is carried out, the Doppler frequency shift and the time delay of the interference both change slowly along with the towing time, the distance and the speed wave gate of the radar are gradually towed to deviate from a real target, the fidelity is higher, and the deception is stronger, so that the uniform acceleration towing is the most common towing mode for distance-speed synchronous towing interference. Combining the distance-speed synchronous towing interference process, delta f can be given_dj(t) and Δ t_j(t) expression:

in the actual simulation, the delay and the Doppler frequency are updated according to the set dragging parameters and pulse intervals, so that the distance dragging interference and the speed dragging interference are simulated. Only the echo signal can be delayed to complete the distance dragging interference; or only Doppler modulation is added to the echo signal to complete velocity interference, and simultaneously distance and velocity joint interference can be realized.

S105, determining the electromagnetic transmission characteristic from the antenna end to the antenna end according to the position and the posture of the carrier and the antenna data; the electromagnetic transmission characteristics include: energy attenuation, delay, and doppler characteristics;

s105 specifically comprises the following steps:

A clutter model in the road model simulates echo background clutter and is used for generating clutter signals of typical environments such as land, sea and the like. The model of the probability density function describing the clutter backscattering coefficient is called a clutter distribution model, and the commonly used probability density functions include rayleigh distribution, lognormal distribution, weber distribution, K distribution and the like.

For ground clutter, the distribution characteristics can be simulated by a log-normal distribution at low ground clearance angles (less than 6 °), and the standard deviation increases with decreasing ground clearance angle, and obeys a weber distribution at larger ground clearance angles. For sea clutter, the K distribution is considered a good description.

Lognormal distribution

When the discrimination of the radar is improved or in a high sea condition, the tail part of the clutter is longer, the backscattering characteristic deviates from Rayleigh distribution, and the amplitude distribution relatively conforms to the logarithmic normal.

Omega distribution obeys N (lnu)_c,σ_c ²) By means of a nonlinear effect z ═ exp (ω), a lognormal probability density function for z is generated which contains two variables:

wherein v is a shape coefficient and represents the gradient of distribution, and the variation range of v is 0.335-1.247; mu.s_cIs a scale parameter, representing the median of the distribution, μ_cThe variation range of (A) is 1.065-1.93; exp () is the residual error function.

The lognormal distribution sequence has a long tail, and is suitable for low-incidence angle clutter data of complex terrain or flat-area high-resolution sea clutter data.

FIG. 13 shows a log-normal distribution clutter generation model based on memoryless nonlinear transformation (ZmNL).

V_iIs an independent uncorrelated, Gaussian distributed random vector, U_iIs V_iThe correlation Gaussian distribution random vector obtained by linear frequency spectrum modulation H (omega) has a correlation coefficient of rho_ij，U_iThen obtaining Z through nonlinear amplitude modulation_iI.e. correlation coefficient of S_ijClutter sequences that follow a lognormal distribution.

The specific process of generating the relevant lognormal distribution clutter based on the memoryless nonlinear transformation is as follows:

step 1: power spectral density S to clutter_ijSampling M times to establish power spectrum density sequence S_nI.e. of

Step 2: obtaining clutter correlation function sequence S by inverse Fourier transform_ijThe correlation sequence rho needed to be obtained for linear transformation is obtained by using the relational expression_ij。

And step 3: utilizing the correlation sequence rho obtained by calculation in the step 2)_ijModulate the required related normal random sequence U_iGenerating independent Gaussian distributed random sequences V_iThe transfer function H (ω) of the filter is obtained.

And 4, step 4: thus, the required sequence can be obtained by designing the transfer function of the filter and the nonlinear transformation rule.

Weber distribution

In the case of short distance, i.e. severe clutter, weber distribution is most suitable. The asymmetry of the distribution is smaller than that of the log-normal distribution, so that the selection of the Weber distribution is more suitable for the condition that the amplitude fluctuation of the sea clutter is more uniform. Probability density function of weber distribution:

wherein ν is a shape coefficient and represents the gradient of distribution, and the value is usually 1.4-2; mu.s_mIs a scale parameter representing the median of the distribution, as measured by the back-scattering cross-sectional area σ of the clutter_cAnd a shape parameter v:

where Γ () is a Gamma (Gamma) function.

The estimation formula of the scale parameter can be simplified as follows:

the dynamic range of the weber distribution is between that of the lognormal distribution and the rayleigh distribution, so that the actual clutter distribution can be accurately represented in a wider range. Generally, sea clutter of general sea conditions can be accurately described by a webby distribution in the case of high-resolution radar and low incidence angle, and ground clutter can also be described by a webby distribution.

FIG. 14 shows a correlation Weber distribution clutter generation model based on a memoryless nonlinear transformation (ZmNL):

V_1,jand V_2,jIs an independent uncorrelated, Gaussian distributed random vector, U_1,j、U_2,jIs a V_1,j、V_2,jThe correlation coefficient of the random vector of the related Gaussian distribution obtained by linear spectrum modulation is rho_ij，U_1,jAnd U_2,jThen obtaining Z through nonlinear amplitude modulation_iI.e. the correlation coefficient is Z_iClutter sequences that follow a weber distribution.

Step 1: sampling a given power spectral density function S (f) to establish a power spectral density sequence S_nAnd i.e.:

step 2: for the sequence { S_nCarrying out inverse Fourier transform (IFFT) to obtain Z_iIs related to_ij。

And 3, step 3: by means of S_ijAnd rho_ijThe correlation sequence rho required to be obtained by linear transformation is obtained by the relational expression of (1)_ij。

And 4, step 4: utilizing the correlation sequence rho obtained by calculation in the step 2)_ijTo modulate the required related normal random sequence U_i。

And 5: generating independent Gaussian distributed random sequences V_iThe transfer function H (ω) of the filter is obtained.

Step 6: thus, the required sequence can be obtained by designing the transfer function of the filter and the nonlinear transformation rule.

K distribution

Rayleigh, lognormal, and Weber clutter models are based on single point statistics, and are therefore only suitable for single pulse detection. The main disadvantage is the lack of temporal and spatial correlation of the analog clutter. In recent years, the introduced K-distribution hybrid model is closer to the actual form when analyzing the physical characteristics of waves. This distribution model not only satisfies the observed amplitude measurement characteristics well, but also includes inter-pulse correlation properties. The occurrence of the K distribution concept and the application of the K distribution concept in a clutter model provide a basis for quantitative processing of relevant characteristics, and the K distribution is used as a newly constructed mixed model, is suitable for describing various ground clutter and sea clutter with high resolution and low ground friction angle, and is a model which is recognized to accurately reflect the clutter at present.

The probability density function of the K distribution is:

where ν is a shape parameter and a is a scale parameter. K is_v-1Is of order v-1 of a second type of correctionA bessel function.

The mixed model of the K-distribution contains two parts of clutter fluctuation, which have different correlation times. The first component is the fundamental amplitude modulation component, i.e. the slowly varying component, which is caused by the spatially varying average level of the scattered beam associated with the scatterer structure. The second component is the speckle component, i.e., the fast-varying component, which is generated by the multipath scattering properties of clutter in any range bin.

FIG. 15 shows a correlation K-distribution hybrid generation model based on a memoryless nonlinear transformation (ZmNL).

V_n,jIs independent uncorrelated Gaussian distribution random vector, and after the whole random sequence is processed, the first theta random variables generate Y_jThe remaining two random variables generate X_jSuch that K distributes the random sequence Z_iPDF of (A) is represented by X_iAnd Y_iThe square root of the product.

Step 1: sampling a given power spectral density function S (f) to establish a power spectral density sequence S_nI.e. that

And step 3: by means of S_ijAnd rho_ijThe correlation sequence rho required to be obtained by linear transformation is obtained by the relational expression of (1)_ij。

And 4, step 4: utilizing the correlation sequence rho obtained by calculation in the step 2)_ijModulate the required related normal random sequence U_iGenerating independent Gaussian distributed random sequences V_iThe transfer function H (ω) of the filter is obtained.

And 5: thus, the required sequence can be obtained by designing the transfer function of the filter and the nonlinear transformation rule.

And S106, determining a height signal of the radar altimeter according to the baseband echo signal, the interference signal and the electromagnetic transmission characteristic from the antenna end to the antenna end.

As a specific example, the system of the radar altimeter signal is a pulse doppler signal, and specific input parameters are shown in table 1, where table 1 is as follows:

TABLE 1

For pulse system radar signals, the key to signal generation includes two parts: firstly, performing baseband modulation on pulses by utilizing two-phase coding to generate a single pulse baseband signal; secondly, according to a set pulse repetition period, repeating the single pulse baseband signal to finish the final radar altimeter signal generation.

As shown in fig. 16, the pulse-modulated radar fuse signal generates a modulation code signal based on pulse modulation, the modulation code period is the same as the pulse repetition period, when the symbol is 0, the modulation code signal is 1, when the symbol is 1, the modulation code signal is-1, and the pulse signal is multiplied by the modulation code signal to complete pulse-to-pulse modulation. And performing amplitude modulation and carrier modulation on the adjusted signal to generate an inter-pulse coding radar fuze signal with corresponding frequency.

the operation data acquisition module is used for acquiring the operation data sent by the scene controller; the operational data includes: scene data, starting signals, terrain data, ground electromagnetic characteristic data, antenna directional pattern data, control signals and antenna data; the scene data includes: the method comprises the following steps of carrier position, attitude, carrier speed vector, carrier rotation vector, radar altimeter antenna installation attitude, radar altimeter antenna directional diagram, jammer deployment position, jammer antenna installation attitude, jammer antenna directional diagram, radiation source deployment position, radiation source antenna installation attitude, radiation source antenna directional diagram, radar altimeter antenna gain and jammer antenna gain, jammer and radiation source line-of-sight and line-of-sight change rate, jammer antenna gain and radiation source antenna gain, radar altimeter antenna gain and radiation source antenna gain.

And the baseband emission signal acquisition module is used for acquiring the baseband emission signal of the radar altimeter according to the starting signal.

And the baseband echo signal determining module is used for performing echo simulation by adopting a method of combining a grid method and a statistical model method according to the terrain data, the ground electromagnetic characteristic data, the carrier position, the attitude, the antenna directional pattern data and the baseband transmitting signal to determine a baseband echo signal.

An interference signal generating module, configured to generate an interference signal according to the control signal, the baseband transmission signal, and an interference policy; the interference signal includes: spoof interference and noise interference.

The electromagnetic transmission characteristic determining module is used for determining the electromagnetic transmission characteristic from the antenna end to the antenna end according to the position and the posture of the carrier and the antenna data; the electromagnetic transmission characteristics include: energy attenuation, time delay, and doppler characteristics.

The baseband echo signal determination module specifically includes:

and the echo signal first determining unit is used for determining the echo signal in a first set range under the carrier by adopting a grid method according to the terrain data, the ground electromagnetic property data, the carrier position, the attitude, the antenna directional pattern data and the baseband transmitting signal.

And the echo signal second determining unit is used for determining an echo signal within a second set range from the position just below the carrier by using a statistical model method according to the terrain data, the ground electromagnetic characteristic data, the carrier position, the attitude, the antenna directional pattern data and the baseband transmitting signal.

The electromagnetic transmission characteristic determination module specifically includes:

and the first channel transmission characteristic determining module is used for determining the channel transmission characteristic from the radar altimeter antenna to the jammer antenna according to the carrier position, the attitude and the antenna data.

The operation data acquisition module specifically comprises:

In the present specification, the embodiments are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.

The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims

1. An anti-interference digital simulation method for a radar altimeter is characterized by comprising the following steps:

acquiring operation data sent by a scene controller; the operational data includes: scene data, starting signals, terrain data, ground electromagnetic characteristic data, antenna directional pattern data, control signals and antenna data; the scene data includes: carrier position and attitude;

determining a height signal of a radar altimeter according to the baseband echo signal, the interference signal and the electromagnetic transmission characteristic from the antenna end to the antenna end;

the method for performing echo simulation according to the terrain data, the ground electromagnetic characteristic data, the carrier position, the attitude, the antenna directional pattern data and the baseband transmission signal by combining a grid method and a statistical model method to determine a baseband echo signal specifically comprises the following steps:

2. The anti-interference digital simulation method for the radar altimeter according to claim 1, wherein the determining the electromagnetic transmission characteristics from the antenna end to the antenna end according to the carrier position, the attitude, and the antenna data specifically comprises:

3. The anti-interference digital simulation method for the radar altimeter according to claim 1, wherein the acquiring of the operation data sent by the scene controller specifically comprises:

and acquiring the running data sent by the scene controller by a simulation step size of 0.02 second.

4. An anti-interference digital simulation system of a radar altimeter is characterized by comprising:

the operation data acquisition module is used for acquiring the operation data sent by the scene controller; the operational data includes: scene data, starting signals, terrain data, ground electromagnetic characteristic data, antenna directional pattern data, control signals and antenna data; the scene data includes: carrier position and attitude;

the height signal determining module is used for determining a height signal of the radar altimeter according to the baseband echo signal, the interference signal and the electromagnetic transmission characteristic from the antenna end to the antenna end;

the baseband echo signal determination module specifically includes:

5. The radar altimeter anti-interference digital simulation system according to claim 4, wherein the electromagnetic transmission characteristic determining module specifically comprises:

6. The radar altimeter anti-interference digital simulation system according to claim 4, wherein the operation data acquisition module specifically comprises: