Background technology
Along with modern radar system is day by day complicated, function is constantly perfect, simulation of Radar System has caused increasing attention.The today particularly developing rapidly in capacity and the speed of computing machine, for meticulous simulation of Radar System provides material base.By Computer Simulation, verify rationality, the realizability of radar system overall design philosophy.SAR needs to carry out population parameter design and demonstration according to technical indicator before development and design, and current traditional radar population parameter design is based on theoretical formula model, and this technical method exists deficiency below:
(1) model is inaccurate: theoretical formula model, obtain, yet actual system behavior index is subject to the impact of multiple error, can not represent by desirable analytic formula through approximate processing.
(2) do not consider various systematic error impacts: in interference SAR system, exist the various error sources such as channel noise, thermonoise, kinematic error, the existence of these errors finally affects interference performance.
(3) do not carry out overall synthetic design: current carrying out population parameter when design, for some or several parameters, design separately respectively, do not carry out overall synthetic design, the error that whole interference SAR echo data is obtained, produced in imaging processing and interference handle link process does not have system demonstration.
Summary of the invention
The present invention overcomes the defect of prior art, for overcoming the deficiency of current interference SAR system population parameter design and demonstration, propose a kind of high precision interference SAR system performance synthesis analytical approach, by emulation and the processing procedure of whole closed loop, totally verify interference system performance.
A method for high precision interference SAR system performance evaluation, comprises the steps:
Step 1, according to user's index demand, adopt conventional theoretical formula to calculate interference SAR system parameter, parameter comprises podium level, beam center visual angle, beam angle, pulse repetition rate, data sampling frequency, antenna parameter, transmitter power, noise figure, system loss, fuzzy ratio, quantizes signal to noise ratio (S/N ratio), thereby obtains interference SAR initial parameter value;
Step 2, the interference SAR system parameter obtaining according to step 1, carry out the simulation of interference SAR echoed signal; Set up interference SAR hyperchannel original echoed signals realistic model, and error source is incorporated in original echo data; Interference SAR echoed signal is based upon on model space geometric basis, and according to SAR data acquisition principle, in orientation, each PRF place obtains original echo data;
Step 3, the echo data of emulation in step 2 is carried out to the compensation of imaging processing and kinematic error, obtain coherence's complex pattern; Imaging processing is carried out azimuth-range compression to original echo data, makes focusing on a synthetic aperture self-energy of each pixel;
Step 4, the complex pattern obtaining in step 3 is interfered to processing, realize same atural object corresponding same pixel on image, phase filtering filtering phase noise, phase unwrapping reverts to original phase by the phase place of winding, according to interference SAR ultimate principle, by launching phase place, resolve landform value, and carry out inverting elevation by the original phase after launching;
Step 5, according to the elevation inversion result obtaining in the imaging results of obtaining in step 3 and step 4, system performance index is analyzed, whether verification system can reach the demand of design.
Since then, completed a kind of high precision interference SAR system performance synthesis analytical approach.
Error source described in step 2 comprises, channel noise, hyperchannel imbalance, thermonoise, coherent speckle noise, fuzzy noise, quantizing noise;
In step 5, design requirement index comprises: vertical accuracy, resolution, mapping bandwidth, operating distance, signal to noise ratio (S/N ratio), peak sidelobe ratio, integration secondary lobe ratio, fuzzy ratio.
The present invention compared with prior art advantage is: the present invention has introduced interference SAR real system error source, and comparing with current method is a kind of analytical approach that more approaches real system; From original echo, getting elevation inverting, the whole active link of interference SAR system is simulated, is a kind of interference SAR system analytical approach.
Embodiment
As shown in Figure 1, a kind of high precision interference SAR system method for analyzing performance, comprises step below:
Step 1, according to user's index demand, adopt conventional theoretical formula to calculate interference SAR system parameter.The parameter of design comprises podium level, beam center visual angle, beam angle, pulse repetition rate, data sampling frequency, antenna parameter, transmitter power, noise figure, system loss, fuzzy ratio, quantize signal to noise ratio (S/N ratio), thereby obtain interference SAR initial parameter value.
Step 2, the interference SAR parameter obtaining according to step 1, carry out the simulation of interference SAR echoed signal.Set up interference SAR hyperchannel original echoed signals realistic model, and error is incorporated in original echo data.Error source comprises, channel noise, hyperchannel imbalance, thermonoise, coherent speckle noise, fuzzy noise, quantizing noise.Interference SAR echoed signal is based upon on model space geometric basis, and according to SAR data acquisition principle, in orientation, each PRF place obtains original echo data.The flow process of binary channels interference SAR analogue echoes as shown in Figure 3, model model space geometric, interference SAR model space geometric as shown in Figure 2.X is platform speed direction, y be distance to, z is vertical ground direction, H is podium level, h is impact point height value, A1, A2 is two slave antenna positions, B is base length, α is baseline inclination angle.Radar every one pulse-recurrence time emission wavelength be λ, pulsewidth is T
r, the linear FM signal that frequency modulation rate is K:
ω wherein
0be carrier frequency, rect () is rectangular window function, and after coherent demodulation, radar any point (t, τ) in t receives its irradiation area is constantly located base band echo 2D signal and can be expressed as:
T wherein, τ is respectively the fast time of slow time of orientation and distance, and λ is the wavelength that transmits, and c is the light velocity, and σ is target backscattering coefficient, w
a(t) w
r(τ) be respectively orientation to distance to antenna radiation pattern, R is the instantaneous oblique distance of point target and radar.
Step 3, artificial echo data are carried out to the compensation of imaging processing and kinematic error, obtain coherence's complex pattern.Imaging processing is carried out azimuth-range compression to original echo data, makes focusing on a synthetic aperture self-energy of each pixel.
As shown in Figure 4, motion compensation is embedded in imaging processing, comprises step:
1), for airborne interference SAR system, before data are processed, can first utilize phase function to carry out elementary motion compensation.
2) by orientation FFT, data are transformed to range-Dopler domain from signal space.
3) be multiplied by first-phase bit function and carry out linear perturbation for a certain reference distance.
4) by data being transformed to two-dimentional frequency field (being wave number space) from range-Dopler domain apart from FFT
5) being multiplied by second-phase bit function completes band secondary range and compresses and complete range migration correction.
6) by data transformation being returned to range-Dopler domain apart from IFFT.
7) be multiplied by the slow variable-azimuth residual phase that the compensation of third phase bit function is introduced by linear perturbation function.
8) for airborne interference SAR system, by orientation IFFT, data are converted back apart from bearing signal territory from range-Dopler domain, utilize phase function to complete collateral motion compensation, then by orientation FFT layback Doppler domain.
9) be multiplied by the 4th phase function and complete Azimuth Compression, finally by orientation IFFT, obtain SAR complex pattern.
Step 4, complex pattern is interfered to processing.As shown in Figure 5, binary channels complex pattern is interfered and processed acquisition elevation information.First Channel Image is carried out to sub-pixel accuracy registration, make the same plot of a pair of pixel corresponding ground in two sub-pictures.Then interferometric phase is carried out to filtering, owing to there is the noises such as thermonoise, registration error, quantization error in the actual interferometric phase obtaining, these noises bring error to the measurement of higher degree, also to interferometric phase solution tape wrap, come difficult.Then carry out phase unwrapping processing, what obtain due to conjugate multiplication after two sub-picture registrations is interferometric phase winding value, need to carry out two-dimensional phase unwrapping and recover true phase place corresponding to original wave path-difference.
Step 5, system performance analysis and demonstration.According to imaging results and elevation inversion result, system performance index is analyzed, whether verification system can reach the demand of design.These indexs comprise: vertical accuracy, resolution, mapping bandwidth, operating distance, signal to noise ratio (S/N ratio), peak sidelobe ratio, integration secondary lobe ratio, fuzzy ratio.
In sum, these are only preferred embodiment of the present invention, be not intended to limit protection scope of the present invention.Within the spirit and principles in the present invention all, any modification of doing, be equal to replacement, improvement etc., within all should being included in protection scope of the present invention.