CN103969644B - A kind of hyperchannel Continuous Wave with frequency modulation SAR formation method - Google Patents

Abstract

The present invention provides a kind of hyperchannel Continuous Wave with frequency modulation SAR formation method. Technical scheme comprises the following steps: 1. utilizing a channel emission Continuous Wave with frequency modulation signal, other M passage receives simultaneously, obtains the two-dimentional Continuous Wave with frequency modulation SAR echo signal of orientation, M road to lack sampling; 2. above-mentioned obtained M road signal being carried out two-dimensional Fourier transform, carry out doppler's ambiguity solution in two-dimensional frequency, the orientation that is eliminated is to mixed folded equivalent single channel signal; 3. the equivalent single channel signal of two-dimensional frequency is carried out focusing process, obtain two dimension high resolving power Continuous Wave with frequency modulation SAR image. Compared with existing single passage Continuous Wave with frequency modulation SAR, when identical transmitted power, adopt method provided by the present invention, it is possible to be operated in the imaging resolution pattern of farther operating distance, wider mapping swath width and Geng Gao, thus expanded the application of Continuous Wave with frequency modulation SAR.

Description

A kind of hyperchannel Continuous Wave with frequency modulation SAR formation method

Technical field

The invention belongs to Radar Technology field, specifically, the present invention relates to a kind of hyperchannel Continuous Wave with frequency modulation SAR (Synthetic-apertureradar, synthetic-aperture radar) formation method.

Background technology

Synthetic-aperture radar is a kind of initiatively microwave remote sensing equipment, it is possible to round-the-clock, round-the-clock realize ground observation, and can through information under earth's surface and vegetation acquisition earth's surface, and the numerous areas in national economy and Military Application all plays an important role.

Continuous Wave with frequency modulation SAR is the high resolution radar imaging equipment that a kind of volume is little, weight is light, cost is low and immunity from interference is strong, is a current topmost class miniaturization SAR, is widely used in without man-machine grade on the very harsh flight platform of loading demands. At present, the Continuous Wave with frequency modulation SAR complete machine weight of U.S.'s development is less than 2.5kg, and maximum current consumption is only 35W, and operating distance the farthest away is less than 4km, and imaging resolution is 0.5m �� 0.5m. The Continuous Wave with frequency modulation SAR radio frequency component weight of Germany's development is less than 4kg, maximum effect distance 4km, and mapping swath width is 1km to the maximum, and imaging resolution is 0.5m �� 0.5m. The Continuous Wave with frequency modulation SAR radio frequency component weight of Holland's development is less than 3 kilograms, and complete machine power consumption is about 30W, and maximum functional distance is 5km, and imaging resolution is 0.3m �� 0.3m. The Continuous Wave with frequency modulation SAR radio frequency component weight of China's development is less than 3.5 kilograms, and maximum functional distance is 3km, and imaging resolution is 0.3m �� 0.3m. From the technical feature of existing Continuous Wave with frequency modulation SAR, the SAR of this kind of system compares conventional Pulsed SAR and truly has obviously advantage in the indexs such as weight, volume, power consumption. But existing Continuous Wave with frequency modulation SAR operating distance is all very short, 5km only the farthest away. And it is also very narrow to survey and draw band, generally at about 1km. These all limit Continuous Wave with frequency modulation SAR range of application.

In order to more miniaturized application demand, it is necessary to improve the system performance of Continuous Wave with frequency modulation SAR on the whole, make it the MODE of operation in farther operating distance, more wide swath width and higher imaging resolution. Usually, the way addressed this problem has three classes: the first improves transmitted power; Its two be increase antenna aperture; Its three be reduce PRF (pulserepetitionfrequency, pulse-repetition frequency). Improve operating distance and mapping swath width that transmitted power can increase radar, but so the requirement of device is greatly increased, and add the complexity of system. More seriously, under high-power state, transceiver insulation problem specific to frequency modulated continuous wave radar will be very outstanding, and this limits the most basic factor of frequency modulated continuous wave radar operating distance just. Increase antenna aperture and can improve the gain amplifier of antenna, but can limit so on the one hand orientation to resolving power, also can be constrained to the mapping swath width of picture in addition on the one hand. Reduce PRF can increase distance to the accumulation time, thus improve distance to processing gain, but easy like this cause the frequency spectrum in high azimuth resolution situation mixed folded.

Summary of the invention

It is an object of the invention to overcome the mutual constraint condition of the indexs such as existing Continuous Wave with frequency modulation SAR operating distance far away, wide swath width and high resolving power, improve the system performance of Continuous Wave with frequency modulation SAR on the whole so that it is meet the application demand of more miniaturizations. The present invention provides a kind of hyperchannel Continuous Wave with frequency modulation SAR formation method, utilize multiple reception channel, breach azimuth resolution to the restricted condition in radar receiving antenna aperture, make radar high-resolution can obtain high gain of antenna in maintenance simultaneously, and obtain bigger distance to processing gain.

For realizing described object, the technical solution of the present invention is: a kind of hyperchannel Continuous Wave with frequency modulation SAR formation method, the method comprises the following steps: establish hyperchannel Continuous Wave with frequency modulation SAR to have multiple passage, 1. a channel emission Continuous Wave with frequency modulation signal is utilized, other M passage receives simultaneously, obtains the two-dimentional Continuous Wave with frequency modulation SAR echo signal of orientation, M road to lack sampling; 2. above-mentioned obtained M road signal being carried out two-dimensional Fourier transform, carry out doppler's ambiguity solution in two-dimensional frequency, the orientation that is eliminated is to mixed folded equivalent single channel signal; 3. the equivalent single channel signal of two-dimensional frequency is carried out focusing process, obtain two dimension high resolving power Continuous Wave with frequency modulation SAR image.

The technique effect of the present invention is as follows: by adopting, multiple reception channel receives simultaneously in the present invention, digital signal processing mode is utilized to carry out orientation ambiguity solution, eliminate azimuth resolution to the constraint condition of antenna aperture, make Continuous Wave with frequency modulation SAR high-resolution can obtain high gain of antenna in maintenance simultaneously, and obtain bigger distance to processing gain, thus improve the overall performance of Continuous Wave with frequency modulation SAR. Compared with existing single passage Continuous Wave with frequency modulation SAR, when identical transmitted power, adopt method provided by the present invention, it is possible to be operated in the imaging resolution pattern of farther operating distance, wider mapping swath width and Geng Gao, thus expanded the application of Continuous Wave with frequency modulation SAR.

Accompanying drawing explanation

Fig. 1 is hyperchannel Continuous Wave with frequency modulation SAR formation method schema of the present invention;

Fig. 2 is that two-dimensional frequency orientation of the present invention is to ambiguity solution embodiment schema;

Fig. 3 is an embodiment schema of two-dimension focusing of the present invention;

Fig. 4 is the simulation parameter figure of one embodiment of the invention;

Fig. 5 is the point target emulation result figure of one embodiment of the invention.

Embodiment

Below in conjunction with the drawings and specific embodiments, a kind of hyperchannel Continuous Wave with frequency modulation SAR formation method provided by the invention is done explanation detailed further.

A kind of hyperchannel Continuous Wave with frequency modulation SAR formation method provided by the present invention, its implementing procedure as shown in Figure 1, specifically comprises following three steps:

Step is 1.: utilizing a channel emission Continuous Wave with frequency modulation signal, M passage receives simultaneously, obtains the two-dimentional Continuous Wave with frequency modulation SAR echo signal of orientation, M road to lack sampling.

If obtaining the two-dimentional Continuous Wave with frequency modulation SAR echo signal ss of orientation, M road to lack sampling_m(t_a, t_r;r₀) it is:

${\mathrm{ss}}_m(t_a,t_r;r_0)=A_0\exp (-j\frac{2\mathrm{\π}{f}_c}{c_0}\·R_{t,m})\·\exp [j\frac{\mathrm{\π}{k}_r}{c_0^2}\·{(R_{t,m}-2r_c)}^2]$

$\·\exp [-j\frac{2\mathrm{\π}{k}_r}{c_0}\·(R_{t,m}-2r_c)\·(t_r-\frac{{2r}_c}{c_0})]$

Wherein t_aFor orientation is to the time, t_rFor distance is to the time, r₀For target distance, A₀For echo signal amplitude, f_cFor launching signal center frequency, c₀For the light velocity, k_rFor chirp rate, r_cFor reference range, R_t,mIt is the distance of m passage, can represent and be:

$R_{t,m}(t_a,t_r;r_0)=\sqrt{r_0^2+V^2\·{(t_a+t_r)}^2}+\sqrt{r_0^2+{[V(t_a+t_r)-\mathrm{\Δ}{x}_m]}^2}$

Wherein V is the Platform movement speed at hyperchannel Continuous Wave with frequency modulation SAR place, �� x_mIt it is the distance between m receiving antenna and transmitting antenna.

In above-mentioned formula, the orientation of this signal is f to sample frequency_p, orientation is B to doppler bandwidth_a, and have f_p<B_a. Data in Azimuth Direction acquisition time is T_a, number of data points is N_a. Distance is T to data acquisition time_r, number of data points is N_r. The echo of each passage is a N_r��N_aTwo-dimentional matrix.

Step is 2.: above-mentioned obtained M road signal is carried out two-dimensional Fourier transform, carries out doppler's ambiguity solution in two-dimensional frequency, and the orientation that is eliminated, to mixed folded equivalent single channel signal, specifically comprises following sub-process:

(2a) the two-dimensional time-domain echo of each passage is carried out two-dimensional Fourier transform, its middle distance to fourier transformation namely complete Range compress, orientation to fourier transformation then convert the signal into Doppler domain, obtain two-dimensional frequency signal SS_m(f_a,f_r;r₀), wherein f_rFor distance is to frequency, f_aFor orientation is to frequency;

(2b) to each channel signal in orientation to carrying out channel phases compensation, like this by each passage with parameter, �� x_mRelevant stationary phase item eliminates, and is compensated the signal after passage stationary phase:

SS_CPC,m(f_a,f_r;r₀)=SS_m(f_a,f_r;r₀)��H_CPC(��x_m;r₀)

Wherein channel compensation phase location factor H_CPC(��x_m;r₀) it is:

$H_1\left(\mathrm{\&Delta;}{x}_m\right)=\exp [j\frac{2\mathrm{\&pi;}{f}_c}{c_0}\&CenterDot;\frac{\mathrm{\&Delta;}{x}_m^2}{4r_0}]$

(2c) frequency domain doppler's ambiguity solution wave filter that each passage is corresponding is designed. The ambiguity solution wave filter P that the m passage is corresponding_m(f_a) represent. The algorithm being designed with multiple maturation of doppler's ambiguity solution wave filter, such as the method based on universal sample theory, the method etc. based on space-time adaptive theory. The present embodiment adopts the method based on universal sample theory. In this kind of method, P_mCan regard as and be made up of multiple bandpass filter, solve by the mode of following matrix inversion:

$\left[\begin{array}{c}{P}_1\left(f_a\right)\\ P_2\left(f_a\right)\\ .\\ .\\ .\\ P_M\left(f_a\right)\end{array}\right]=\left[\begin{array}{cccc}{P}_{11}\left(f_a\right)& P_{12}(f_a+f_p)& ...& P_{1M}(f_a+(M-1)f_p)\\ P_{21}\left(f_a\right)& P_{22}(f_a+f_p)& ...& P_{2M}(f_a+(M-1)f_p)\\ .& .& .& .\\ .& .& .& .\\ .& .& .& .\\ P_{M1}\left(f_a\right)& P_{M2}(f_a+f_p)& ...& P_{\mathrm{MM}}(f_a+(M-1)f_p)\end{array}\right]$

$={\left[\begin{array}{ccc}\exp (-j\frac{\mathrm{\&pi;\&Delta;}{x}_1}{V}{f}_a)& ...& \exp (-j\frac{\mathrm{\&pi;\&Delta;}{x}_M}{V}{f}_a)\\ \exp (-j\frac{\mathrm{\&pi;\&Delta;}{x}_1}{V}(f_a+f_p))& ...& \exp (-j\frac{\mathrm{\&pi;\&Delta;}{x}_M}{V}(f_a+f_p))\\ .& .& .\\ .& .& .\\ .& .& .\\ \exp (-j\frac{\mathrm{\&pi;\&Delta;}{x}_1}{V}(f_a+(M-1)f_p))& ...& \exp (-j\frac{\mathrm{\&pi;\&Delta;}{x}_M}{V}(f_a+(M-1)f_p))\end{array}\right]}^{-1}$

(2d) corresponding ambiguity solution wave filter is passed through respectively to signal in the orientation of each passage, also namely it is that the orientation of each passage is multiplied with corresponding ambiguity solution wave filter to signal:

SS_AR,m(f_a,f_r;r₀)=SS_CPC,m(f_a,f_r;r₀)��P_m(f_a)

Wherein

P_m(f_a)=[P_m1(f_a)P_m2(f_a+f_p)��P_mM(f_a+(M-1)f_p)]

(2e) by the results added of each passage gained in step (2d), the orientation that is eliminated is to mixed folded two-dimensional frequency equivalence single channel signal SS (f_a,f_r;r₀) it is:

$\mathrm{SS}(f_a,f_r;r_0)=\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{\mathrm{SS}}_{\mathrm{AR},m}(f_a,f_r;r_0)$

Two-dimensional frequency doppler's ambiguity solution schema of above-described embodiment is as shown in Figure 2.

Step is 3.: the equivalent single channel signal of two-dimensional frequency is carried out focusing process, obtains two dimension high resolving power Continuous Wave with frequency modulation SAR image, specifically comprises following sub-step:

(3a) to the two-dimensional frequency equivalence single channel signal SS (f of gained_a,f_r;r₀) carry out distance to inverse Fourier transform, obtain distance-Doppler signal S_s(f_a,t_r;r₀);

(3b) to the distance-Doppler domain signal Ss (f of gained in step (3a)_a,t_r;r₀) carry out the correction that antenna moves continuously, obtain Ss_DFC(f_a,t_r;r₀):

The wherein continuous motion compensation factor H of antenna_DFC(f_a,t_r) it is:

H_DFC(f_a,t_r)=exp(-j2��f_a�¡�t_r)

Wherein $\mathrm{\&beta;}=\sqrt{1-{(f_a\mathrm{\&lambda;}/2V)}^2};$

(3c) to compensating the distance-Doppler domain signal Ss after antenna moves continuously_DFC(f_a,t_r;r₀) carry out range migration correction; Range migration correction has the algorithm of multiple maturation, such as RDA (RangeDopplerAlgorithm, range-doppler algorithm), FSA (FrequencyScalingAlgorithm, frequency scaling algorithm), RMA (RangeMigrationAlgorithm, range migration algorithm) etc. In the present embodiment, adopting FSA, because this kind of algorithm is without the need to interpolation arithmetic, efficiency is higher, and is easy to integrated motion compensation and frequency sweep nonlinear calibration. Specifically, FSA also comprises following sub-step:

(3c-1) apart from-Doppler domain signal times with the dimensions in frequency factor, will obtain:

Wherein dimensions in frequency factor H_FS(f_a,t_r) it is:

$H_{\mathrm{FS}}(f_a,t_r)=\exp \left[\mathrm{j\&pi;}{k}_r(1-\mathrm{\&beta;})t_r^2\right]$

(3c-2) signal of step (3c-1) gained is carried out distance to fourier transformation, obtain SS_FS(f_a,f_r;r₀);

(3c-3) it is multiplied by RVP correction factor in two-dimensional frequency, obtains:

SS_RVPC(f_a,f_r;r₀)=SS_FS(f_a,t_r;r₀)��H_RVPC(f_a,f_r)

Wherein RVP correction factor H_RVPC(f_a,f_r) it is:

$H_{\mathrm{RVPC}}(f_a,f_r)=\exp (-j\frac{\mathrm{\&pi;}{f}_r^2}{k_r\mathrm{\&beta;}})$

(3c-4) by SS_RVPC(f_a,f_r;r₀) carry out distance to inverse Fourier transform, obtain Ss_RVPC(f_a,t_r;r₀);

(3c-5) by Ss_RVPC(f_a,t_r;r₀) it is multiplied by frequency inverse yardstick transformation factor, obtain:

Wherein frequency inverse yardstick transformation factor H_IFS(f_a,t_r) it is:

$H_{\mathrm{IFS}}(f_a,t_r)=\exp \left[\mathrm{j\&pi;}{k}_r({\mathrm{\&beta;}}^2-\mathrm{\&beta;})t_r^2\right]$

(3c-6) by Ss_IFS(f_a,t_r;r₀) it is multiplied by the secondary range compression factor, obtain:

Wherein secondary range compression factor H_SRC(f_a,t_r;r_c) it is:

$H_{\mathrm{SRC}}(f_a,t_r;r_c)=\exp [+j\frac{2\mathrm{\&pi;}{r}_c{k}_r^2\mathrm{\&lambda;}}{c_0^2}\frac{({\mathrm{\&beta;}}^2-1)}{{\mathrm{\&beta;}}^3}{(\mathrm{\&beta;}{t}_r-\frac{{2r}_c}{c_0})}^2]$

$\&CenterDot;\exp [-j\frac{2\mathrm{\&pi;}{r}_c{k}_r^3{\mathrm{\&lambda;}}^3}{c_0^3}\frac{({\mathrm{\&beta;}}^2-1)}{{\mathrm{\&beta;}}^5}{(\mathrm{\&beta;}{t}_r-\frac{{2r}_c}{c_0})}^3]$

(3c-7) by Ss_SRC(f_a,t_r;r₀) it is multiplied by block shift factor, obtain:

Wherein block shift factor H_BV(f_a,t_r;r_c) it is:

$H_{\mathrm{BV}}(f_a,t_r;r_c)=\exp \left[j\frac{4\mathrm{\&pi;}{k}_r{r}_c}{c_0}(\frac{1}{\mathrm{\&beta;}}-1)(\mathrm{\&beta;}{t}_r-\frac{{2r}_c}{c_0})\right]$

So far the correction of range migration is completed;

(3d) distance-Doppler domain signal Ss adjusting the distance and moving after normal moveout correction_RCMC(f_a,t_r;r₀) carry out distance to fourier transformation, complete Range compress;

(3e) step (3d) gained result is carried out azimuth match filtering, obtain the Continuous Wave with frequency modulation SAR image of two-dimension focusing.

The equivalent single channel signal two-dimension focusing treatment scheme of above-described embodiment is as shown in Figure 3.

Below by the method for emulation, the present invention is verified. Simulation parameter as shown in Figure 4, can calculate wavelength X corresponding to mid-frequency is 0.02m, chirp rate k_rIt is 8.75 �� 10¹⁰Hz/s, orientation is to bandwidth B_aFor 333.3Hz. Consider again in addition FFT count be generally 2 power side, obtain distance to sampling number N_rBeing 8192 points, orientation is to points N_aIt is 1024 points. In emulation, reception channel number M is 2, first distance, delta x between receiving antenna and transmitting antenna₁For 0.6m, the 2nd the distance, delta x between receiving antenna and transmitting antenna₂For 1.2m. In emulation, point target used is placed on r₀=15.5km place, and suppose echo amplitude A₀It is 1. Emulation middle distance is to time variable t_rWith orientation to time variable t_aValue be respectively:

$t_r=\frac{n_r}{f_s}=0.8\&times;{10}^{-6}\&times;n_r,n_r=\mathrm{0,1},...,8191$

$t_a=\frac{n_a-N_a/2}{f_p}=0.0057\&times;(n_a-512),n_a=\mathrm{0,1},...,1023$

Distance is to frequency variable f_rValue be:

$f_r=n_r\&CenterDot;\frac{f_s}{N_r}=152.59\&times;n_r,n_r=\mathrm{0,1},...,8191$

Before orientation ambiguity solution, orientation is to frequency variable f_aValue be:

$f_a=(n_a-N_a/2)\&CenterDot;\frac{f_p}{N_a}=0.17\&times;(n_a-512),n_a=\mathrm{0,1},...,1023$

After orientation ambiguity solution completes, orientation is to frequency variable f_aValue be:

$f_a=(n_{a2}-N_a)\&CenterDot;\frac{f_p}{N_a}=0.17\&times;(n_{a2}-1024),n_{a2}=\mathrm{0,1},...,2047$

Fig. 5 show the imaging results of embodiment of the present invention gained in emulation runs. Point target is obtained good focusing effect after the process of the present invention. Theoretical analysis all shows with emulation result, and Continuous Wave with frequency modulation SAR works in many reception channels pattern, breaks through azimuth resolution to the restricted condition of antenna aperture by the mode of digital signal processing, can carry out imaging with better properties.

Claims (1)

1. a hyperchannel Continuous Wave with frequency modulation SAR formation method, it is characterised in that, comprise the following steps: utilizing a channel emission Continuous Wave with frequency modulation signal, other M passage receives simultaneously, obtain the two-dimentional Continuous Wave with frequency modulation SAR echo signal of orientation, M road to lack sampling; Above-mentioned obtained M road signal being carried out two-dimensional Fourier transform, carries out doppler's ambiguity solution in two-dimensional frequency, the orientation that is eliminated is to mixed folded equivalent single channel signal; The equivalent single channel signal of two-dimensional frequency is carried out focusing process, obtains two dimension Continuous Wave with frequency modulation SAR image.