CN111896924B - Simulation method and simulation model for radar sea surface low-altitude detection performance - Google Patents
Simulation method and simulation model for radar sea surface low-altitude detection performance Download PDFInfo
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Abstract
The invention discloses a radar sea surface low-altitude detection performance simulation method and a simulation model, wherein the model comprises the following steps: the free space maximum acting distance calculation module is used for calculating the free space maximum acting distance of the radar to target detection by utilizing a radar equation; the vision distance and interference area far-range calculation module is used for solving the interference area far-range distance; the interference zone and diffraction zone propagation factor calculation module is used for calculating interference zone propagation factors and diffraction zone propagation factors; the navigation path signal-to-noise ratio calculation module is used for calculating the signal-to-noise ratio and the free space signal-to-noise ratio of echo signals of each point of the sea surface low-altitude target navigation path in an interference area and a diffraction area; and the low-altitude detection performance graph drawing module is used for drawing a low-altitude detection performance graph according to the calculated echo signal to noise ratio and free space signal to noise ratio of each point of the target airway. Compared with the simulation results of other conventional models, the simulation model built by the method is more real and accurate, and has stronger application scene adaptability.
Description
Technical Field
The invention belongs to a ship-borne radar detection simulation technology, and particularly relates to a radar sea surface low-altitude detection performance simulation method and a simulation model.
Background
Due to the multipath effect formed by reflection of electromagnetic wave signals by the sea surface and the shielding diffraction effect of the curvature of the earth on the electromagnetic wave signals, the detection dead zone and the detection power of the microwave radar on the detection of the sea surface ultra-low altitude small targets (such as anti-ship missiles and airplanes) are reduced.
By constructing a radar sea surface low-altitude detection performance simulation model and utilizing an MATLAB simulation calculation tool, radar sea surface ultra-low-altitude detection performance parameters such as blind area positions and ranges, blind compensation performance, low-altitude maximum acting distance, line-of-sight reduction coefficient and the like can be obtained through analysis, technical support can be provided for carrier-based radar development, test and reaction time analysis of a reverse weapon system, and the existing sea surface low-altitude detection simulation model mainly has the following three defects:
1) The model is only suitable for an interference area, the far-range of the interference area cannot be determined, and the simulation error outside the interference area is obviously increased;
2) The model does not consider the relevance of sea surface reflection coefficient and environmental parameters (sea water temperature, sea water salinity, sea conditions and the like);
3) The model cannot be applied to a radar of a transceiver antenna split system.
Disclosure of Invention
The invention aims to provide a radar sea surface low-altitude detection performance simulation method, which can construct a radar sea surface low-altitude detection performance simulation model according to input parameters such as radar working parameters, target parameters, environment parameters and the like, and realize simulation analysis of radar sea surface low-altitude detection performance such as blind area positions and ranges, blind compensation performance, low-altitude maximum acting distance, line-of-sight reduction coefficients and the like.
The technical solution for realizing the purpose of the invention is as follows: a radar sea surface low-altitude detection performance simulation method comprises the following specific steps:
step 1: according to specific radar working parameters and target parameters, calculating the maximum acting distance of the radar to the target detection by utilizing a radar equation;
step 2: solving the observation sight distance of the radar to the target by utilizing the geometric relation between the radar antenna and the target position; according to the working frequency of the radar and the equivalent radius of the earth, the remote ground wiping angle of the interference area is solved, and according to the antenna stand height of the radar, the target flying height and the geometric relationship of the radar and the target flying height, the remote distance of the interference area is solved;
step 3: calculating interference region propagation factors and diffraction region propagation factors;
step 4: according to the target course position, the line-of-sight parameter, the interference zone far-range parameter, the interference zone propagation factor and the diffraction zone propagation factor, calculating the echo signal to noise ratio and the free space signal to noise ratio of each point of the sea surface low-altitude target course in the interference zone and the diffraction zone;
step 5: and drawing a low-altitude detection performance curve graph according to the calculated echo signal to noise ratio and free space signal to noise ratio of each point of the target airway.
Preferably, a specific formula for calculating the maximum free space acting distance of the radar to target detection by using a radar equation is as follows:
wherein ,R0 Is the maximum action distance of free space; p (P) t For transmitting pulse power; τ is the transmit pulse width; n (N) p Accumulating the number for the pulses; g t Pointing the gain for the transmit antenna beam; g r Pointing the gain for the receive antenna beam; lambda is the working wavelength; t (T) s To receive system noise temperature; sigma is the radar cross-sectional area of the target; SNR of min Is the minimum detectable signal to noise ratio; k is Boltzmann constant; l (L) s Is a system loss.
Preferably, the radar's viewing line of sight of the target is:
in the formula ,ha For raising the antenna, h t For target fly height, r e Is the equivalent radius of the earth.
Preferably, the interference zone is at a far-range ground wiping angle of:
in the formula ,re Is the earth equivalent radius, lambda is the operating wavelength.
Preferably, the method for determining the far distance of the interference area is as follows: according to the geometrical relationship among the radar antenna position, the target position, the reflection point and the earth center, a triangle sine theorem and a triangle cosine theorem are applied, a linear distance calculation formula of the target relative to the radar antenna is deduced, and an interference area far-range ground wiping angle is brought into the formula to obtain the interference area far-range distance:
wherein , is a floor wiping angle
The invention also provides a radar sea surface low-altitude detection performance simulation model, which comprises the following steps:
the free space maximum acting distance calculation module is used for calculating the free space maximum acting distance of the radar on target detection by utilizing a radar equation according to specific radar working parameters and target parameters;
the sight distance and interference zone far-range calculation module is used for solving the observation sight distance of the radar to the target by utilizing the geometric relationship between the radar antenna and the target position; according to the working frequency of the radar and the equivalent radius of the earth, the remote ground wiping angle of the interference area is solved, and according to the antenna stand height of the radar, the target flying height and the geometric relationship of the radar and the target flying height, the remote distance of the interference area is solved;
the interference zone and diffraction zone propagation factor calculation module is used for calculating interference zone propagation factors and diffraction zone propagation factors;
the navigation path signal-to-noise ratio calculation module is used for calculating the echo signal-to-noise ratio and the free space signal-to-noise ratio of each point of the sea surface low-altitude target navigation path in the interference area and the diffraction area according to the target navigation path position, the line-of-sight parameter, the interference area far-distance parameter, the interference area propagation factor and the diffraction area propagation factor;
and the low-altitude detection performance graph drawing module is used for drawing a low-altitude detection performance graph according to the calculated echo signal to noise ratio and free space signal to noise ratio of each point of the target airway.
Compared with the prior art, the invention has the remarkable advantages that: the invention has the advantages that the environment factors are complete and close to the actual environment, the spherical reflection and diffusion model is adopted, the limitation of the interference area far-range to the application range of the multipath effect is considered, the transmission factor model of electromagnetic wave signals in the interference area and the diffraction area is established in sections, the influence of the sea water temperature, salinity, sea conditions and other environment factors on the sea surface reflection coefficient is considered, and the low-altitude detection performance calculation model which is suitable for the receiving and transmitting antenna shared radar and the receiving and transmitting antenna separated radar is established, so that the simulation result established by the invention is more real and accurate than the simulation result of other conventional models, and the application scene adaptability is stronger.
The present invention will be described in further detail with reference to the accompanying drawings.
Drawings
Figure 1 is a block diagram of the composition and calculation flow of a radar sea surface low altitude detection performance simulation model,
fig. 2 is a schematic view of a line-of-sight calculation geometry.
Fig. 3 is a schematic diagram of the spherical multipath phenomenon geometry.
Fig. 4 is a schematic diagram of planar and spherical diffusion phenomena.
Fig. 5 is a schematic diagram of a multi-path geometry of a split transceiver antenna.
FIG. 6 is a graphical illustration of the results of a low-altitude detection performance simulation.
Fig. 7 is a schematic diagram of a simulation result of dual-band blind-supplement performance.
Fig. 8 is a schematic diagram of simulation results of low-altitude detection performance of the receiving and transmitting antenna split radar.
Detailed Description
A radar sea surface low-altitude detection performance simulation model construction method specifically comprises the following steps:
step 1: according to specific radar working parameters and target parameters, calculating the maximum free space acting distance of the radar to target detection by using a radar equation, wherein the specific calculation formula is as follows:
wherein ,R0 Is the maximum action distance of free space;
radar operating parameters:
P t for transmitting pulse power;
τ is the transmit pulse width;
N p accumulating the number for the pulses;
G t pointing the gain for the transmit antenna beam;
G r for receiving antenna beam directional gain, if radar is a transmitting and receiving shared antenna, G r ＝G t ；
Lambda is the operating wavelength of the light,f is the radar working frequency, C is the speed of light;
T s to receive the system noise temperature, T s ＝T e +T a ＝T 0 (F n -1)+T a ≈T 0 ·F n ，F n For the noise figure of the receiver, T 0 At a standard temperature T 0 ＝290 0 K；
L s Is a system loss including antenna loss, feeder loss, bandwidth loss, beam shape loss,Signal processing loss, etc.;
target parameters: sigma is the radar cross-sectional area of the target (RCS)
SNR min The minimum detectable signal-to-noise ratio, which is related to the false alarm probability, the detection probability and the target fluctuation characteristic of the system, can be obtained through table look-up (RADAR TARGET DETECTION Handbook of Theory and Practice) DANIEL P.MEYER or calculation.
Constant: k is boltzmann constant k=1.38x10 -23
If the maximum free space range of the radar to the target is known, it can be set directly in the program without calculation according to the above formula.
Step 2: according to parameters such as the equivalent radius of the earth, the stand height of a radar antenna, the flying height of a target and the like, the geometrical relationship between the radar antenna and the position of the target is utilized to solve the observation sight distance of the radar to the target; and solving the far-range ground wiping angle of the interference area according to the radar working frequency and the equivalent radius of the earth, and solving the far-range of the interference area by utilizing the geometric relationship of the radar antenna stand height and the target flying height.
As shown in fig. 2, the viewing distance:
wherein ,ha If the radar antenna is arranged separately for antenna elevation, the antenna is arranged separatelyh at and har Respectively a transmitting antenna stand and a receiving antenna stand, h t For target fly height, r e Is equivalent to the earth radius>For the antenna receiving and transmitting split radar, h in the calculation a ＝min(h at ,h ar )，h at and har The transmit antenna mount and the receive antenna mount, respectively.
The interference zone far zone calculation is derived according to the formula:
as shown in fig. 3, in the radar antenna-target-geocentric triangle, the target-to-radar antenna linear distance is:
wherein , is a floor wiping angle
In the radar antenna-ground-wiping-angle-geocentric triangle and the ground-wiping-angle-target-geocentric triangle, according to the sine theorem, there are:
when reflected wave is used for wiping floor angle(radian) while the target is in the diffraction zone; when reflected wave is wiped the earth angle->(radians) the target is in the interference zone.
Thus, the ground wiping angle at the far-end of the interference zone:
bringing formula (6) into the target-to-radar antenna linear distance R calculated in formulas (3), (4), (5) d I.e. the interference zone far distance r gm 。
For the antenna receiving and transmitting split radar, h in the calculation a ＝min(h at ,h ar )，h at and har The transmit antenna mount and the receive antenna mount, respectively.
For the multi-frequency blind-complement radar, lambda in the above calculation takes the maximum wavelength.
Step 3: according to parameters such as radar antenna elevation, relative positions of receiving and transmitting antennas, radar working frequency, polarization mode, beam shape, beam direction and width, target height and distance position, earth equivalent radius, sea state seawater temperature, free space dielectric constant and the like, interference region propagation factors and diffraction region propagation factors are calculated in sequence.
The interference region propagation factor and diffraction region propagation factor calculation includes: the method comprises the following steps of interference zone reflection point position calculation, direct path and reflection path length calculation, ground wiping angle calculation, direct view angle and reflection view angle calculation, spherical diffusion factor calculation, roughness factor calculation, sea water complex dielectric constant calculation, smooth plane sea water reflection coefficient calculation, rough spherical sea water reflection coefficient calculation, reflection line and direct ray pattern amplitude coefficient calculation and pattern propagation factor calculation.
1) Calculation of the reflection point position of an interference zone
When the radar antenna stand is lower and the target elevation angle is higher, the method is applicable to calculating the reflecting point position and the direct wave and reflected wave path difference by adopting a plane surface reflecting model, but in the ultra-low-altitude target detection scene, the condition is generally not satisfied, so that the spherical surface reflecting model is required to calculate the reflecting point position and the direct wave and reflected wave path difference.
As shown in fig. 3, in the radar antenna-target-geocentric triangle, it is available from the cosine law:
thus, the earth surface distance from the radar antenna ground projection point to the target ground projection point is:
according to Kerr, D.E., propgation of Short Radio Waves, MIT Radiation Laboratory Series, vol.13, mcGraw-Hill, book Company, new York,1951, reference at page 113, the reflection point position can be obtained by solving the following cubic equation:
solving to obtain the reflection point position G by using the following two intermediate parameters 1 、G 2 ：
G 2 ＝G-G 1
in the formula ,
2) Direct path and reflected path length calculation
Referring to fig. 3, the direct path length is the linear distance of the radar antenna to the target. For the receiving and transmitting antenna split radar, setting the linear distance from one antenna to the target as the target path distance, and calculating the linear distance from the other antenna to the target according to the formula (3).
In the sum of the radar antenna-geocentric-reflection point triangle and the geocentric-reflection point-target triangle, the reflection path length R can be obtained according to the cosine law r ：
R r ＝R 1 +R 2
in the formula ,
3) Calculation of floor wiping angle
The ground wiping angle is also called the sweep angle or the incidence complementary angle.
See fig. 3, in the sum of the radar antenna-geocentric-reflection point triangle and geocentric-reflection point-target triangle, there are according to the cosine law:
thus, the floor wiping angle
4) Reflection viewing angle and direct viewing angle calculation
The reflection view angle and the direct view angle are calculated for the direction diagram value calculation.
See fig. 3, reflection view angle of reflection line at radar antenna with respect to horizontal:
in the radar antenna-geocentric-reflection point triangle, there are according to the cosine law:
thus, the reflection view angle
In the radar antenna-target-reflection point triangle, there are, according to the cosine law:
thus, the direct view angle of the direct ray at the radar antenna with respect to the horizontal is:
5) Sphere diffusivity factor calculation
Sea surface reflectance is also affected by the spherical diffusivity factor D of the earth.
Referring to fig. 4, when an electromagnetic wave is incident on the surface of the spherical earth, the reflected wave diverges due to the influence of the curvature of the earth, and the divergence phenomenon causes the reflected energy to diverge, thereby reducing the spatial power density.
According to the formula (8.34) of "radar system analysis and design (MATLAB edition) (second edition)", P245: sphere diffusivity factor
in the formula ,G、G1 、G 2 Is the surface distance;is a floor wiping angle;
6) Seawater surface roughness factor calculation
According to the formula (8.36) of "radar system analysis and design (MATLAB edition) (second edition)," P247: sea water surface roughness factor
The formulas more consistent with the test results are as follows:
S r ＝e -z I 0 (z)， (14)
in the formula ,
I 0 (z) zero-order Bessel function value
The floor wiping angle calculated for the 3 rd section
σ h Is the standard deviation of wave height (root mean square of wave heave height relative to calm sea surface), H 1/3 for effective wave height or called three-one wave height, see "handbook of radars (second edition)" P48.
According to GJB4000-2000 (0) -p247 table 072-3, H 1/3 The corresponding relation with sea state grade (sea state) is as follows:
note that: h 1/3 The middle value of the range in GJB4000-2000 (0) -p247 table 072-3 is defaulted, and can be replaced according to the measured value of the actual sea condition.
7) Complex dielectric constant calculation of seawater
The complex dielectric constant of seawater is: epsilon s ＝ε I +ε Q ·i (15)
Wherein the real part
Imaginary part
in the formula ,ε0 ＝8.854×10 -12 Fm -1 Is the free space dielectric constant; f is radar operating frequency (Hz); epsilon sw0 Is the static dielectric constant of seawater and the salinity S of the seawater sw And sea water temperature T sw The relation of (2) is:
ε sw0 ＝ε sw0T0 ×a TS (18)
in the formula ,εsw0T0 The static dielectric constant of pure water was calculated as follows:
a TS for correction, the following formula is calculated:
τ sw for sea water relaxation time τ sw ＝τ swT0 ×b TS (19)
in the formula ,τswT0 For the relaxation time of pure water, the following formula is calculated:
b TS for correction, the following formula is calculated:
σ i for ion conductivity of sea water, sigma i ＝σ i25 e -φ (20)
in the formula ,σi25 The ionic conductivity of seawater at 25 ℃ is calculated according to the following formula:
phi is S sw And delta=25-T sw Is calculated as follows:
φ＝Δ[2.033×10 -2 +1.266×10 -4 Δ+2.464×10 -6 Δ 2
-S sw (1.849×10 -5 -2.551×10 -7 Δ+2.551×10 -8 Δ 2 )]
salinity S of sea water sw Defined as the salinity per kilogram of seawater, the average salinity of the ocean is 0.035, the highest 0.038 (red sea) and the lowest 0.007 (Porro sea).
8) Smooth plane seawater reflection coefficient calculation
The reflection coefficient of a smooth surface depends on frequency, surface dielectric constant and ground wiping angle, and the reflection coefficients of vertical polarization and horizontal polarization of the seawater smooth surface are as follows:
in the formula ,ρV0 、ρ H0 The complex reflection coefficient modulus values of the vertical polarization and the horizontal polarization of the smooth surface are respectively; psi phi type V 、ψ H The phase angles of the complex reflection coefficients of vertical polarization and horizontal polarization are respectively; epsilon s Is the complex dielectric constant of seawater;the calculated floor wiping angle is obtained;
9) Calculation of rough bending seawater reflection coefficient module value
Considering the diffusion scattering effect and the bending surface diffusion effect of the rough seawater surface, the reflection coefficient modulus of the rough bending seawater is as follows:
ρ V ＝ρ V0 ·D·S r (23)
ρ H ＝ρ H0 ·D·S r (24)
in the formula ,ρv0 、ρ H0 The calculated complex reflection coefficient modulus value of the smooth plane sea water in the 8 th section; d is the spherical diffusivity factor calculated in section 5); s is S r The sea water surface roughness factor calculated in the 6 th section;
10 Diffraction zone parameter values
In the diffraction region, the ground wiping angle is very small, the sea water reflection coefficient modulus value is close to 1, the phase angle is close to pi, and the reflection coefficient modulus value and the phase angle calculated according to the geometrical relation of the interference region have larger deviation, so that:
in the diffraction region, let: ρ in the formula (23) and the formula (24) V ＝ρ H ＝1
Psi in the formula (21) and the formula (22) V ＝ψ H ＝π
11 Direct and reflected ray pattern amplitude coefficient calculation
Obtaining values of the reflection line and the amplitude coefficient of the direct ray according to the pitching visual angles of the direct ray and the reflection line according to the radar beam shape function
Amplitude coefficient of direct ray A md ＝f(θ d )
Amplitude coefficient A of reflected line mr ＝f(θ r )
Wherein f (theta) is a radar beam pitch shape function;
θ d and θr The reflection viewing angle and the direct viewing angle calculated in the section 4);
12 Interference region and diffraction region pattern propagation factor calculation
The interference area pattern propagation factor and the diffraction area pattern propagation factor reflect the influence of sea surface multipath propagation interference effect and horizon blocking attenuation on radar detection performance.
The pattern propagation factor F is defined as:
wherein E is the actual field intensity at a certain point in the propagation direction of the electromagnetic wave; e (E) 0 Free space field strength for the point;
as shown in fig. 3, there are four paths from radar transmission to target and back to radar reception:
the field strength of the "antenna-target-antenna" path electromagnetic wave signal at the antenna is:
the field strength of the electromagnetic wave signal at the antenna of the antenna-target-reflection point-antenna path is:
the field strength of the electromagnetic wave signal at the antenna of the antenna-reflection point-target-antenna path is:
the field strength of the electromagnetic wave signal at the antenna of the antenna-reflection point-target-reflection point-antenna path is:
the resultant signal field strength at the radar receiving antenna is then:
the signal field strength of path 1 (i.e., the "antenna-target-antenna" path) is free space field strength, i.e., E, irrespective of atmospheric attenuation 0 ＝E 1
Thus, for a radar with a shared system of transmitting and receiving antennas, four propagation paths of electromagnetic waves are shown in fig. 3, and the propagation factors of the directivity pattern are as follows:
in the above, A md 、A mr Respectively the first11 A direct ray and reflection line pattern amplitude coefficient value obtained by calculation in the section;
ρ is the reflectance model calculated in section 9), ρ=ρ for horizontal polarization H For vertical polarization, ρ=ρ V ；
Psi is the reflection coefficient phase angle calculated in section 8), psi=psi for horizontal polarization H For vertical polarization, ψ=ψ V 。
Taking the module value of the propagation factor F of the formula (31) as the step 4 route signal to noise ratio calculation carry-in value.
Similarly, for a transmitting-receiving antenna split system radar, four propagation paths of electromagnetic waves are shown in fig. 5, and the field intensity of a synthesized signal at a radar receiving antenna is as follows:
thus, the pattern propagation factor of the transmitting-receiving antenna split system radar is:
in the above, A md1 、A md2 The direct ray pattern amplitude coefficient values for the "transmit antenna-target" and "receive antenna-target" paths, respectively; a is that mr1 、A mr2 Reflection line pattern amplitude coefficient values of "transmitting antenna-reflection point 1-target" and "receiving antenna-reflection point 2-target", respectively; ρ 1 、ρ 1 Reflection coefficient modulus values of "transmitting antenna-reflection point 1-target" and "receiving antenna-reflection point 2-target", respectively; psi phi type 1 、ψ 2 The reflection coefficient phase angles of the "transmitting antenna-reflection point 1-target" and the "receiving antenna-reflection point 2-target" respectively; r is R d1 、R d2 The linear distances from the transmitting antenna to the target and the receiving antenna to the target are respectively; r is R 11 、R 12 The distances from the transmitting antenna to the reflecting point 1 and the receiving antenna to the reflecting point 2 are respectively; r is R 21 、R 22 The distances from the reflection point 1 to the target and the reflection point 2 to the target, respectively
The above parameters can be calculated by referring to the 1) to 11) sections.
The propagation factor F of equation (33) is modulo-valued and the carry-in value is calculated as step 4 way signal to noise ratio.
The interference region propagation factor calculation model described by the invention is characterized in that: according to the multipath echo superposition principle, the superposition calculation is carried out on each path signal on the antenna according to the signal synthesis principle by calculating each path length, so that the propagation factor which is suitable for the receiving and transmitting shared antenna radar and the receiving and transmitting separated antenna radar is obtained. Whereas the conventional calculation model is based on the direct and reflected path differences and the total phase difference alpha by calculatingThe method is only suitable for calculating the propagation factors of the transmitting and receiving shared antenna radar, but is not suitable for calculating the propagation factors of the transmitting and receiving separated antenna radar.
Step 4: and (3) calculating the signal-to-noise ratio and the free space signal-to-noise ratio of echo signals of each point of the sea surface low-altitude target airway in the interference area and the diffraction area according to the target airway position, the sight distance parameter and the interference area far-distance parameter calculated in the step (2) and the interference area propagation factor and the diffraction area propagation factor calculated in the step (3). The specific method comprises the following steps:
let the maximum working distance of the free space (f=1) radar be R 0 The maximum working distance R of the radar in the actual environment max The method comprises the following steps:
for the receiving and transmitting shared antenna radar: r is R max ＝R 0 F (34)
Transmitting and receiving separated antenna radar:
according to the radar equation there are:
free space radar maximum range:
wherein ,
the relation between the free space target distance R and the signal to noise ratio is as follows:
from equations (36) and (37), the signal to noise ratio at distance R in the free space target course is:
expressed as logarithm:
considering the influence of low-altitude environment, for a sea surface low-altitude target at a distance radar antenna R, the relation between the distance R and the signal-to-noise ratio is as follows:
wherein F is the sea surface low altitude direction map propagation factor value obtained by the calculation of the third step low 12), SNR R Signal to noise ratio of sea surface low-altitude target at the distance radar antenna R;
from equations (36) and (39), the signal to noise ratio at distance R in the sea surface low altitude target course is obtained as:
expressed as logarithm: SNR of R (dB)＝40logF+10log(SNR 0R (dB)) (40)
The signal-to-noise ratio at the distance R in the free space target course is calculated according to equation (38) and a set of free space course signal-to-noise ratio curve values is formed.
And (3) calculating the signal-to-noise ratio of the distance R in the sea surface low-altitude target course according to the formula (40), and forming a group of sea surface low-altitude course signal-to-noise ratio curve values.
The target course is divided into two sections: interference zone course and diffraction zone course, the distance between them is the interference zone far distance r gm . The interference area channel signal-to-noise ratio calculated according to the interference area parameters is connected with the diffraction area channel signal-to-noise ratio calculated according to the diffraction area parameters at the far-distance position of the interference area:
let the difference between the signal-to-noise ratio of the interference region and the signal-to-noise ratio of the diffraction region at the far-end of the interference region be delta SN
The signal to noise ratio of the diffraction zone is added with delta based on the original SN And (5) completing the connection of the two.
Step 5: drawing a low-altitude detection performance curve graph according to the echo signal to noise ratio and the free space signal to noise ratio of the positions of each point of the target airway calculated in the step 4
And (3) drawing a radar 'free space channel signal-to-noise ratio curve' and a radar 'sea surface low altitude channel signal-to-noise ratio curve' on the same graph respectively according to the free space channel signal-to-noise ratio curve value and the sea surface low altitude channel signal-to-noise ratio curve value obtained by calculation in the step (4) by using a MATLAB drawing tool.
Based on SNR min The value, a "minimum detectable signal to noise ratio" horizontal line is plotted in the same graph as above.
And drawing a vertical line of the interference zone far-end in the same graph according to the interference zone far-end value calculated in the step 2.
Finally, the characters such as the title, the coordinate attribute, the radar antenna stand height and the target height are marked in the same drawing, and the drawing of the low-altitude detection performance curve graph is completed.
Low-altitude detection performance graph example: see fig. 6.
The relevant performance parameters can be read from fig. 6:
the dashed curve is a free space signal-to-noise ratio curve, and the distance corresponding to the intersection point of the horizontal straight line of the minimum detectable signal-to-noise ratio SNmin is the maximum detection distance (21.4 km in the figure) of the radar to the target in free space;
the solid line curve is a low-altitude signal-to-noise ratio curve, and the distance corresponding to the furthest intersection point of the horizontal straight line of the minimum detectable signal-to-noise ratio SNmin is the low-altitude maximum detection distance (27.5 km in the figure) of the radar to the target;
the range of the low-altitude signal-to-noise ratio curve lower than the minimum detectable signal-to-noise ratio Snmin is the low-altitude detection blind zone (17.6 km-20.5 km and 12.3 km-13.2 km in the figure)
The vertical line in the figure is the far interference zone (26.8 km in this figure);
the maximum point distance on the abscissa is the line of sight (39 km in this figure);
ha is the elevation of the radar antenna relative to the sea surface (25 m in this figure);
ht is the target relative sea level fly height (20 m in this figure);
the maximum detection distance to line of sight ratio is the line of sight compression factor (calculated from this map reading as 0.7).
Dual band blind-supplement performance graph example: see FIG. 7
Fig. 7 is a graph of C-band and X-band blind-mate performance, with a real wavy line being a C-band low-altitude snr curve and a dashed wavy line being an X-band low-altitude snr curve.
Therefore, the blind areas of the two wave bands compensate each other, and no detection blind area exists in the low-altitude power range.
The transmit-receive antenna split radar low-altitude detection performance graph illustrates: see FIG. 8
It can be seen that after the receiving and transmitting antennas are separated in height, although the average heights of the receiving and transmitting antennas are unchanged (25 m), the signal-to-noise ratio curve of the air route is distorted, and the low-altitude detection power (21.8 km in the figure), the blind area position, the blind area width and other low-altitude detection performances are changed.
A radar sea surface low-altitude detection performance simulation model, comprising:
the free space maximum acting distance calculation module is used for calculating the free space maximum acting distance of the radar on target detection by utilizing a radar equation according to specific radar working parameters and target parameters;
the sight distance and interference zone far-range calculation module is used for solving the observation sight distance of the radar to the target by utilizing the geometric relationship between the radar antenna and the target position; according to the working frequency of the radar and the equivalent radius of the earth, the remote ground wiping angle of the interference area is solved, and according to the antenna stand height of the radar, the target flying height and the geometric relationship of the radar and the target flying height, the remote distance of the interference area is solved;
the interference zone and diffraction zone propagation factor calculation module is used for calculating interference zone propagation factors and diffraction zone propagation factors;
the navigation path signal-to-noise ratio calculation module is used for calculating the echo signal-to-noise ratio and the free space signal-to-noise ratio of each point of the sea surface low-altitude target navigation path in the interference area and the diffraction area according to the target navigation path position, the line-of-sight parameter, the interference area far-distance parameter, the interference area propagation factor and the diffraction area propagation factor;
and the low-altitude detection performance graph drawing module is used for drawing a low-altitude detection performance graph according to the calculated echo signal to noise ratio and free space signal to noise ratio of each point of the target airway.
The radar sea surface low-altitude detection performance simulation model disclosed by the invention contains more complete environmental factors and is closer to the actual environment, such as: the method adopts spherical reflection and diffusion models (instead of plane reflection and diffusion models), considers the limitation of the interference area far-range to the application range of multipath effect, establishes the transmission factor models of electromagnetic wave signals in the interference area and the diffraction area in a segmented manner, considers the influence of the environmental factors such as sea water temperature, salinity and sea conditions on sea surface reflection coefficients, and establishes a low-altitude detection performance calculation model which is suitable for the receiving and transmitting antenna sharing radar and the receiving and transmitting antenna split radar. Therefore, compared with the simulation results of other conventional models, the simulation model built by the method is more real and accurate, and has stronger application scene adaptability.
Claims (8)
1. A radar sea surface low-altitude detection performance simulation method is characterized by comprising the following specific steps:
step 1: according to specific radar working parameters and target parameters, calculating the maximum acting distance of the radar to the target detection by utilizing a radar equation;
step 2: solving the observation sight distance of the radar to the target by utilizing the geometric relation between the radar antenna and the target position; according to the working frequency of the radar and the equivalent radius of the earth, the remote ground wiping angle of the interference area is solved, and according to the antenna stand height of the radar, the target flying height and the geometric relationship of the radar and the target flying height, the remote distance of the interference area is solved;
step 3: calculating interference region propagation factors and diffraction region propagation factors;
step 4: according to the target course position, the line-of-sight parameter, the interference zone far-range parameter, the interference zone propagation factor and the diffraction zone propagation factor, calculating the echo signal to noise ratio and the free space signal to noise ratio of each point of the sea surface low-altitude target course in the interference zone and the diffraction zone;
step 5: and drawing a low-altitude detection performance curve graph according to the calculated echo signal to noise ratio and free space signal to noise ratio of each point of the target airway.
2. The simulation method of radar sea surface low-altitude detection performance according to claim 1, wherein the specific formula for calculating the free space maximum acting distance of the radar on target detection by using a radar equation is as follows:
wherein ,R0 Is the maximum action distance of free space; p (P) t For transmitting pulse power; τ is the transmit pulse width; n (N) p Accumulating the number for the pulses; g t Pointing the gain for the transmit antenna beam; g r Pointing the gain for the receive antenna beam; lambda is the working wavelength; t (T) s To receive system noise temperature; sigma is the radar cross-sectional area of the target; SNR of min Is the minimum detectable signal to noise ratio; k is Boltzmann constant; l (L) s Is a system loss.
3. The radar sea surface low-altitude detection performance simulation method according to claim 1, wherein the observation line of sight of the radar to the target is:
in the formula ,ha For raising the antenna, h t For target fly height, r e Is the equivalent radius of the earth.
4. The radar sea surface low-altitude detection performance simulation method according to claim 1, wherein the interference area far-range ground wiping angle is:
in the formula ,re Is the earth equivalent radius, lambda is the operating wavelength.
5. The radar sea surface low-altitude detection performance simulation method according to claim 1, wherein the interference area far-distance determination method is as follows: according to the geometrical relationship among the radar antenna position, the target position, the reflection point and the earth center, a triangle sine theorem and a triangle cosine theorem are applied, a linear distance calculation formula of the target relative to the radar antenna is deduced, and an interference area far-range ground wiping angle is brought into the formula to obtain the interference area far-range distance:
wherein ,is a floor wiping angle
in the formula ,ha For raising the antenna, h t For target fly height, λ is the operating wavelength, r e Is the equivalent radius of the earth.
6. The radar sea surface low-altitude detection performance simulation method according to claim 1, wherein calculating the interference region propagation factor and the diffraction region propagation factor specifically comprises:
calculating the position of the reflection point of the interference area and the position G of the reflection point 1 、G 2 The method comprises the following steps of:
G 2 ＝G-G 1
in the formula , h a for raising the antenna, h t For target fly height, r e R is the equivalent radius of the earth d The linear distance between the target and the radar antenna is set;
calculating the direct path length and the reflection path length, wherein the direct path length is the linear distance between the radar antenna and the target, and the reflection path length R r The method comprises the following steps:
R r ＝R 1 +R 2
in the formula ,
calculating a floor wiping angle, which specifically comprises the following steps:
calculating a reflection viewing angle and a direct viewing angle, wherein the reflection viewing angle of a reflection line at the radar antenna relative to a horizontal line is specifically as follows:
the direct view angle of the direct ray at the radar antenna relative to the horizontal is:
the spherical diffusivity factor is calculated, specifically:
calculating the surface roughness factor of the seawater, which comprises the following steps:
S r ＝e -z I 0 (z)
in the formula ,I0 (z) is the zero-order Bessel function value, σ h Standard deviation of wave height;
calculating the complex dielectric constant of seawater;
calculating the reflection coefficient of the seawater on the smooth plane, wherein the reflection coefficient comprises the reflection coefficients of vertical polarization and horizontal polarization of the seawater smooth surface, and the reflection coefficients are respectively as follows:
in the formula ,ρV0 、ρ H0 The complex reflection coefficient modulus values of the vertical polarization and the horizontal polarization of the smooth surface are respectively; psi phi type V 、ψ H The phase angles of the complex reflection coefficients of vertical polarization and horizontal polarization are respectively;
calculating the module value of the reflection coefficient of the rough bending seawater
ρ V ＝ρ V0 ·D·S r
ρ H ＝ρ H0 ·D·S r
in the formula ,ρv0 、ρ H0 Is the complex reflection coefficient module value of the smooth plane sea water; d is a spherical diffusivity factor; s is S r Is the sea water surface roughness factor;
calculating diffraction zone parameters;
calculating the amplitude coefficient of the direct ray and reflection line directional diagram, specifically:
amplitude coefficient of direct ray A md ＝f(θ d )
Amplitude coefficient A of reflected line mr ＝f(θ r )
Wherein f (theta) is a radar beam pitch shape function; θ d and θr Is a reflection view angle and a direct view angle;
calculating directional diagram propagation factors of an interference area and a diffraction area, wherein the directional diagram propagation factors of a receiving and transmitting antenna sharing system radar are as follows:
in the above, A md 、A mr The direct ray of "antenna-target" and the reflected ray pattern amplitude coefficient value of "antenna-reflected point-target", respectively; ρ,Psi is the reflection coefficient module value and phase angle at the reflection point;
the directional pattern propagation factors of the transmitting-receiving antenna split system radar are as follows:
in the above, A md1 、A md2 The direct ray pattern amplitude coefficient values for the "transmit antenna-target" and "receive antenna-target" paths, respectively; a is that mr1 、A mr2 Reflection line pattern amplitude coefficient values of "transmitting antenna-reflection point 1-target" and "receiving antenna-reflection point 2-target", respectively; ρ 1 、ρ 2 Reflection coefficient modulus values of "transmitting antenna-reflection point 1-target" and "receiving antenna-reflection point 2-target", respectively; psi phi type 1 、ψ 2 The reflection coefficient phase angles of the "transmitting antenna-reflection point 1-target" and the "receiving antenna-reflection point 2-target" respectively; r is R d1 、R d2 The linear distances from the transmitting antenna to the target and the receiving antenna to the target are respectively; r is R 11 、R 12 The distances from the transmitting antenna to the reflecting point 1 and the receiving antenna to the reflecting point 2 are respectively; r is R 21 、R 22 The distances from the reflection point 1 to the target and the reflection point 2 to the target, respectively.
7. The radar sea surface low-altitude detection performance simulation method according to claim 1, wherein the specific method for calculating the signal-to-noise ratio and the free space signal-to-noise ratio of echo signals of each point of a sea surface low-altitude target course in an interference area and a diffraction area is as follows:
let the maximum working distance of the free space radar be R 0 The maximum working distance R of the radar in the actual environment max The method comprises the following steps:
for the receiving and transmitting shared antenna radar: r is R max ＝R 0 F
Transmitting and receiving separated antenna radar:
according to the radar equation there are:
free space radar maximum range:
wherein ,
in the formula ,Pt For the transmit pulse power, τ is the transmit pulse width, N p To accumulate the number of pulses G t For transmitting antenna beam pointing gain, G r For receiving antenna beam pointing gain, sigma is target radar scattering cross section area, lambda is working wavelength, T s To receive the system noise temperature, L s SNR for system loss min K is Boltzmann constant, which is the minimum detectable signal-to-noise ratio;
the relation between the free space target distance R and the signal to noise ratio is as follows:
the signal to noise ratio at distance R in the free space target course is:
expressed as logarithm:
for a sea surface low-altitude target at a distance radar antenna R, the relation between the distance R and the signal-to-noise ratio is as follows:
wherein F is a sea-surface low-altitude pattern propagation factor value, SNR R Signal to noise ratio of sea surface low-altitude target at the distance radar antenna R;
the signal to noise ratio at the distance R in the sea surface low-altitude target route can be obtained as follows:
expressed as logarithm: SNR of R (dB)＝40logF+10log(SNR 0R (dB))
Calculating the signal-to-noise ratio of the distance R in the free space target course according to a signal-to-noise ratio calculation formula of the distance R in the free space target course, and forming a group of free space course signal-to-noise ratio curve values;
calculating the signal-to-noise ratio of the distance R in the sea surface low altitude target course according to a signal-to-noise ratio calculation formula of the distance R in the sea surface low altitude target course, and forming a group of sea surface low altitude course signal-to-noise ratio curve values;
the target course is divided into two sections: interference zone course and diffraction zone course, the distance between them is the interference zone far distance r gm The method comprises the steps of carrying out a first treatment on the surface of the The interference area channel signal-to-noise ratio calculated according to the interference area parameters is connected with the diffraction area channel signal-to-noise ratio calculated according to the diffraction area parameters at the far-distance position of the interference area:
let the difference between the signal-to-noise ratio of the interference region and the signal-to-noise ratio of the diffraction region at the far-end of the interference region be delta SN ；
The signal-to-noise ratio of the diffraction zone is added with delta on the original basis SN And (5) completing the connection of the two.
8. A radar sea surface low-altitude detection performance simulation model, comprising:
the free space maximum acting distance calculation module is used for calculating the free space maximum acting distance of the radar on target detection by utilizing a radar equation according to specific radar working parameters and target parameters;
the sight distance and interference zone far-range calculation module is used for solving the observation sight distance of the radar to the target by utilizing the geometric relationship between the radar antenna and the target position; according to the working frequency of the radar and the equivalent radius of the earth, the remote ground wiping angle of the interference area is solved, and according to the antenna stand height of the radar, the target flying height and the geometric relationship of the radar and the target flying height, the remote distance of the interference area is solved;
the interference zone and diffraction zone propagation factor calculation module is used for calculating interference zone propagation factors and diffraction zone propagation factors;
the navigation path signal-to-noise ratio calculation module is used for calculating the echo signal-to-noise ratio and the free space signal-to-noise ratio of each point of the sea surface low-altitude target navigation path in the interference area and the diffraction area according to the target navigation path position, the line-of-sight parameter, the interference area far-distance parameter, the interference area propagation factor and the diffraction area propagation factor;
and the low-altitude detection performance graph drawing module is used for drawing a low-altitude detection performance graph according to the calculated echo signal to noise ratio and free space signal to noise ratio of each point of the target airway.
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