CN102998672A - Step frequency inverse synthetic aperture radar (ISAR) imaging method based on coherent processing - Google Patents

Abstract

The invention is a step-frequency ISAR imaging method based on coherent processing. It mainly solves the problem that the operation efficiency of the traditional parameter estimation method is low, and the phase error after envelope compensation has a great influence on the frequency synthesis. The implementation steps are: establish a step-frequency ISAR echo signal model; estimate motion parameters according to the echo signal model; construct a compensation function to compensate the sub-pulse envelope of the echo signal; Frequency synthesis for chemical processing; perform IFFT transformation on the synthesized echo signal spectrum to obtain high-resolution one-dimensional range images; use RD algorithm or RID algorithm for azimuth imaging to obtain azimuth high-resolution images. Experiments prove that the invention has the advantages of high phase error compensation precision and high operation efficiency, and can be used to realize two-dimensional high-resolution ISAR imaging of a target.

Description

Step frequency ISAR formation method based on the phase drying and other treatment

Technical field

The invention belongs to the Radar Technology field, particularly inverse synthetic aperture radar (ISAR) high-resolution imaging technology can be used for the high-resolution two-dimensional imaging of realize target.

Background technology

High-resolution ISAR imaging radar is conducive to identification and the classification of target, thereby is widely used in the modern radar system because two-dimensional imaging that can realize target obtains more abundant target scattering information.Target is carried out the vertical and horizontal resolution that high-resolution ISAR imaging need to improve radar.Lateral resolution is to realize relative to rotating of radar by target, and longitudinal frame to be large-signal bandwidth by radar emission realize.

Linearly modulated stepped frequency is owing to the longitudinal frame that can synthesize large signal bandwidth raising radar is widely used in the high-resolution imaging radar system.Linearly modulated stepped frequency is synthetic generally to have three kinds of methods apart from high resolution processing: synthetic apart from envelope method, time domain synthetic method and frequency domain synthetic method.High owing to frequency domain synthetic method operation efficiency, can not produce false pseudo-peak and be subject to more paying attention to and using.

The kinematic parameter that focuses on moving target of step frequency high-resolution ISAR imaging algorithm is estimated and kinematic error compensates, and for the synthesis of High Range Resolution, and finally obtains the high-resolution two dimensional image of target.Utilize Minimum entropy method that moving target is carried out parameter estimation, and the kinematic error in the arteries and veins group in the compensation echo data.Come the kinematic parameter of match target by the amount of movement of echo envelope.But this several method has a lot of deficiencies in practical application:

1. Minimum entropy method need to utilize the method for search that kinematic parameter is estimated, its search stepping amount size is difficult to control, and operation efficiency is lower.

2. come the kinematic parameter of match target by the amount of movement of echo envelope, its evaluated error is larger, and residual phase error is also large, has a strong impact on the coherence between each subpulse in the arteries and veins group, makes target after synthetic look like to occur the phenomenon of main lobe broadening and secondary lobe variation.

Summary of the invention

The object of the invention is to the deficiency for above-mentioned prior art, a kind of step frequency ISAR formation method based on the phase drying and other treatment has been proposed, efficiently, accurately to compensate in the step frequency signal relative envelope and the phase error between each subpulse in the arteries and veins group, obtain better the synthetic high-resolution one-dimensional range profile of target.

Realize that the object of the invention technical thought is: by the neighboring and correlative method echo data is carried out dimension-reduction treatment, utilize the correlation energy peak value of Fourier pair echo data to accumulate; Utilize after the accumulation peak value distance to the orientation to projected position, estimate rapidly speed and the acceleration of moving target, the interpulse envelope migration of structure penalty function syndrome; Utilize the phase drying technique that the orientation phase error of each subpulse in the arteries and veins group is proofreaied and correct, obtain the high-resolution one-dimensional range profile of target by the frequency domain synthetic method; Utilize RD algorithm or RID algorithm to carry out the orientation imaging, obtain the full resolution pricture of target azimuth.Implementation step comprises as follows:

(1) sets up step frequency ISAR echo signal model;

(2) carrying out kinematic parameter according to echo signal model estimates:

2a) first subpulse data of different arteries and veins groups are taken out respectively, obtain echoed signal neighboring and correlative expression formula and be:

$R(\mathrm{\τ},m{T}_a)={\mathrm{\σ}}_P\sin c\left(A(\mathrm{\τ}+\frac{2M}{c})\right)\×\exp \left(j\frac{4\mathrm{\π}}{\mathrm{\λ}}{M}_1\right)\×\exp \left(j\frac{4\mathrm{\π}}{\mathrm{\λ}}{M}_2\right)$

Wherein, τ is correlation time, and m is arteries and veins group number, 0≤m≤M-1, mT _aBe the discrete representation of orientation time, σ _PBe the target echo backscattering coefficient, A is the relevant matches amount, and c is the light velocity, and λ is signal wavelength, M=M ₁+ M ₂, ${\mathrm{<figure-callout\; id="1"\; label="M"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">M</figure-callout>}}_1=(v_r-x_P\mathrm{\&omega;})T_a+\frac{1}{2}{a}_r{T}_a^2,$ M ₂＝T _aa _rmT _a

Wherein, v _rThe radial velocity of the relative radar motion of target, x _PBe the lateral attitude information of scattering point, ω is the rotational angular velocity of the relative radar motion of target, T _aBe the repetition period between the arteries and veins group, a _rIt is the radial acceleration of the relative radar motion of target.

2b) to echoed signal neighboring and correlative expression formula along the orientation to doing the FFT accumulation, obtaining orientation frequency domain echo signal neighboring and correlative expression formula be:

$R(\mathrm{\&tau;},f_a)={\mathrm{\&sigma;}}_P\sin c\left(A(\mathrm{\&tau;}+\frac{2M}{c})\right)\&times;\sin c\left(\mathrm{\&pi;}{T}_m(f_a-\frac{2T_a}{\mathrm{\&lambda;}}{a}_r)\right)\&times;\exp \left(j\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}{M}_1\right)$

Wherein, T _mBe subpulse repetition period, f _aFor the orientation to frequency,

It is the correlation peak location of echoed signal neighboring and correlative expression formula;

Ignore the envelope variation that adjacent twice return ω causes among the M, then correlation peak location can be expressed as again

2c) with correlation peak location the distance to the orientation to coordinate be made as respectively

With

Calculate the radial acceleration a of target _rAnd speed v _r:

$\left\{\begin{array}{cc}{a}_r=\frac{\mathrm{\&lambda;prf}[\tilde{n}-(\frac{\tilde{N}}{2}+1)]}{2N{T}_a}& \tilde{n}=1,.....,\tilde{N}\\ v_r=-\frac{c[\tilde{m}-(\frac{\tilde{M}}{2}+1)]}{2f_s{T}_a}-\frac{\mathrm{\&lambda;}[\tilde{n}-(\frac{\tilde{n}}{2}+1)]}{4\tilde{N}{T}_a}& \tilde{m}=1,.....,\tilde{M}\end{array}\right.$

Wherein,

With Be respectively the distance to the orientation to discrete counting, prf be the orientation to sample frequency, f _sFor the distance to sample frequency, T _rBe the pulse repetition time;

(3) according to radial acceleration a _rAnd speed v _r, utilize the phase compensation function s of following envelope cancellation _SrefSubpulse envelope to echoed signal compensates,

$s_{\mathrm{sref}}=\exp (-j\frac{4\mathrm{\&pi;}}{c}(v_r{f}_r{t}_m+\frac{1}{2}{a}_r{f}_r{t}_m^2))$

Wherein, f _rFor the distance to frequency, t _mFor the orientation to the time;

(4) echoed signal of finishing the subpulse envelope cancellation is carried out frequency synthesis based on the phase drying and other treatment, obtain the echoed signal frequency spectrum s (f after synthetic _r, T _r);

(5) to the echoed signal frequency spectrum s (f after synthetic _r, T _r) carry out contrary Fourier IFFT conversion, obtain the high-resolution one-dimensional range profile;

(6) utilize RD algorithm or RID algorithm to carry out the orientation imaging to the high-resolution one-dimensional range profile, obtain the full resolution pricture of target azimuth.

The present invention compared with prior art has the following advantages

The first, the present invention adopts and constructs first the compression of wave filter realization range pulse, intercepts out the backward energy data, utilizes motion compensation and the phase coherence realization method synthetic apart from high-resolution, and the frequency domain synthetic method with respect to traditional reduces handled data volume;

The second, the present invention utilizes the neighboring and correlative of adjacent twice return, obtains the position of main peak value energy accumulation along orientation accumulation, estimates the value of speed and acceleration, so that estimated accuracy, estimated efficiency are higher.Even than also using in the situation, little on the estimated accuracy impact at low signal;

The 3rd, because the precision of the required compensation of phase place will be higher than the precision of envelope cancellation, the parameters of target motion precision that the methods such as conventional minimum entropy and data envelopment fitting are estimated is not high enough again, and often synthetic effect is not obvious.The present invention adopts the method for phase drying and other treatment to compensate phase error between subpulse, and synthetic effect is obvious.

Description of drawings

Fig. 1 is realization flow figure of the present invention;

Fig. 2 is the sub-process figure that the parameters of target motion are estimated among the present invention;

Fig. 3 is the synoptic diagram of adjacent subpulse frequency spectrum shift among the present invention;

Fig. 4 is simulation objectives high-resolution ISAR imaging results figure of the present invention;

Fig. 5 is that the present invention surveys Ship Target step frequency high-resolution ISAR imaging results figure.

Embodiment

The present invention will be further described below in conjunction with accompanying drawing.

With reference to Fig. 1, implementation step of the present invention is as follows:

Step 1. is set up step frequency ISAR echo signal model.

The waveform of supposing the radar emission linearly modulated stepped frequency is:

U(t)＝u ₁(t)exp(j2π(f ₀+nΔf)t) 0≤n≤N-1

In the formula, u ₁(t)=rect (t/T ₁) exp (j π γ t ²) be the linear frequency modulation subpulse, exp is the exponential function truth of a matter, j is imaginary number, f ₀Be fundamental frequency, n is frequency modulation stepping subpulse number, and Δ f is number of frequency steps, f ₀+ n Δ f is the carrier frequency of n frequency modulation stepping subpulse, and t is the time, and N is the stepping frequency modulation number of subpulse in each arteries and veins group, T ₁Be the subpulse width, γ is subpulse frequency modulation rate;

The distance table that moving target is taken up an official post between meaning one scattering point P and radar during with radar emission n sub-pulse signal is shown:

$R_P\left(t_m\right)\&ap;(R_0+y_P)+(v_r-\mathrm{\&omega;}{x}_P)t_m+\frac{1}{2}{a}_{\mathrm{<figure-callout\; id="2"\; label="r\; t\; m"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">r</figure-callout>}}{t}_m^{}{}_2^{}$

In the formula, t _mBe orientation time, R ₀Be the initial action distance of target to radar, x _PAnd y _PRespectively the horizontal and vertical positional information of scattering point P, v _rBe the radial velocity of the relative radar motion of target, ω is the rotational angular velocity of the relative radar motion of target, a _rIt is the radial acceleration of the relative radar motion of target;

Utilize U (t) and R _P(t _m), the echoed signal that obtains scattering point P is:

$s_n\left(t\right)={\mathrm{\&sigma;}}_P\mathrm{rect}\left(\frac{t-2R_P\left(t_m\right)/c}{T_1}\right)\exp \left(\mathrm{j\&pi;\&gamma;}{(t-\frac{2R_P\left(t_m\right)}{c})}^2\right)\exp (-j4\mathrm{\&pi;}({\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">f</figure-callout>}}_0+\mathrm{n\&Delta;f})\frac{R_P\left(t_m\right)}{c})$

In the formula, rect is rectangular function, and c is the light velocity, σ _PBe the target echo backscattering coefficient;

Step 2. is carried out kinematic parameter according to echo signal model and is estimated.

With reference to Fig. 2, being implemented as follows of this step:

2a) to echoed signal s _n(t) carry out pulse compression apart from matched filtering, the echoed signal that obtains after the pulse compression is:

$s_n^{\&prime;}\left(t\right)={\mathrm{\&sigma;}}_P\sin c\left(B(t-\frac{2R_P\left(t_m\right)}{c})\right)\exp (-j\frac{4\mathrm{\&pi;}{R}_P\left(t_m\right)}{c}({\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">f</figure-callout>}}_0+\mathrm{n\&Delta;f}))$

In the formula, B is emission subpulse signal bandwidth;

2b) take out respectively that first subpulse echoed signal of different arteries and veins groups is after the pulse compression:

$s_{f_0}\left(t\right)={\mathrm{\&sigma;}}_P\sin c\left(B(t-\frac{2R_P\left(t_m\right)}{c})\right)\exp (-j\frac{4\mathrm{\&pi;}{f}_0}{c}{R}_P\left(t_m\right))$

The neighboring and correlative expression formula that obtains echoed signal is:

$R(\mathrm{\&tau;},m{T}_a)={\mathrm{\&sigma;}}_P\sin c\left(A(\mathrm{\&tau;}+\frac{2M}{c})\right)\&times;\exp \left(j\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}{M}_1\right)\&times;\exp \left(j\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}{M}_2\right)$

Wherein, τ is correlation time, and m is arteries and veins group number, 0≤m≤M-1, mT _aBe the discrete representation of orientation time, A is the relevant matches amount, and λ is signal wavelength, M=M ₁+ M ₂,

M ₂=T _aa _rMT _a, in the formula, T _aBe the repetition period between the arteries and veins group;

2c) to echoed signal neighboring and correlative expression formula along the orientation to doing Fourier transform FFT accumulation, obtaining orientation frequency domain echo signal neighboring and correlative expression formula be:

$R(\mathrm{\&tau;},f_a)={\mathrm{\&sigma;}}_P\sin c\left(A(\mathrm{\&tau;}+\frac{2M}{c})\right)\&times;\sin c\left(\mathrm{\&pi;}{T}_m(f_a-\frac{2T_a}{\mathrm{\&lambda;}}{a}_r)\right)\&times;\exp \left(j\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}{M}_1\right)$

Wherein, T _mBe subpulse repetition period, f _aFor the orientation to frequency,

It is the correlation peak location of echoed signal neighboring and correlative expression formula;

Ignore the envelope variation that adjacent twice return ω causes among the M, then correlation peak location can be expressed as again:

2d) with correlation peak location the distance to the orientation to coordinate be made as respectively With

, the radial acceleration a of calculating target _rAnd speed v _r:

$\left\{\begin{array}{cc}{a}_r=\frac{\mathrm{\&lambda;prf}[\tilde{n}-(\frac{\tilde{N}}{2}+1)]}{2N{T}_a}& \tilde{n}=1,.....,\tilde{N}\\ v_r=-\frac{c[\tilde{m}-(\frac{\tilde{M}}{2}+1)]}{2f_s{T}_a}-\frac{\mathrm{\&lambda;}[\tilde{n}-(\frac{\tilde{n}}{2}+1)]}{4\tilde{N}{T}_a}& \tilde{m}=1,.....,\tilde{M}\end{array}\right.$

Wherein,

With

Be respectively the distance to the orientation to discrete counting, prf be the orientation to sample frequency, f _sFor the distance to sample frequency, T _rBe the pulse repetition time.

Step 3. is configured to the phase compensation function of envelope cancellation.

According to radial acceleration a _rAnd speed v _r, utilize the phase compensation function s of following envelope cancellation _SrefSubpulse envelope to echoed signal compensates,

$s_{\mathrm{sref}}=\exp (-j\frac{4\mathrm{\&pi;}}{c}(v_r{f}_r{t}_m+\frac{1}{2}{a}_r{f}_r{t}_m^2)),$

Wherein, f _rFor the distance to frequency, t _mFor the orientation to the time.

Step 4. is carried out the frequency synthesis based on the phase drying and other treatment.

4a) utilize the phase compensation function that the envelope of subpulse is proofreaied and correct, obtain the echoed signal after envelope is proofreaied and correct:

$s_n^{\&prime;\&prime;}\left(t\right)={\mathrm{\&sigma;}}_P\sin c\left(B(t-\frac{2({\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">R</figure-callout>}}_0+y_P)}{c})\right)\exp (-j\frac{4\mathrm{\&pi;}({\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">f</figure-callout>}}_0+\mathrm{n\&Delta;f})}{c}({(\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">R</figure-callout>}}_0+y_P)+(v_r-\mathrm{\&omega;}{x}_P)t_m+\frac{1}{2}{a}_r{t}_m^2))$

The echoed signal s after the envelope correction " _n(t) transform to apart from frequency domain s _n(f _r, nT _r)

$s_n(f_r,n{T}_r)=\widetilde{\mathrm{\&sigma;}}\mathrm{rect}\left(\frac{f_r}{B}\right)\&times;\exp (-j\frac{4\mathrm{\&pi;}{f}_0}{c}({\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">R</figure-callout>}}_0+y_P))\&times;\exp (-j\frac{4\mathrm{\&pi;}(f_r+\mathrm{n\&Delta;f})}{c}({\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">R</figure-callout>}}_0+y_P))$

$\&times;\exp (-j\frac{4\mathrm{\&pi;}({\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">f</figure-callout>}}_0+\mathrm{n\&Delta;f})(v_r-\mathrm{\&omega;}{x}_P)n{T}_r+2\mathrm{\&pi;}({\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">f</figure-callout>}}_0+\mathrm{n\&Delta;f})a_r{\left(n{T}_r\right)}^2}{c})$

Wherein, f _rFor the distance to frequency, nT _rThe expression orientation time,

Be range coefficient, B is emission subpulse signal bandwidth;

4b) adjacent subpulse frequency domain echo signal location and phase place are changed, variable quantity is Δ f/2,

A n pulse frequency domain echoed signal such as Fig. 3 (a) before position and phase place change,

A n+1 pulse frequency domain echoed signal such as Fig. 3 (b) before position and phase place change,

$s_n(f_r+\mathrm{\&Delta;f}/2,n{T}_r)=\widetilde{\mathrm{\&sigma;}}\mathrm{rect}\left(\frac{f_r+\mathrm{\&Delta;f}/2}{B}\right)\&times;\exp (-j\frac{4\mathrm{\&pi;}{f}_0}{c}({\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">R</figure-callout>}}_0+y_P))$

$\&times;\exp (-j\frac{4\mathrm{\&pi;}(f_r+\mathrm{n\&Delta;f}+\mathrm{\&Delta;f}/2)}{c}({\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">R</figure-callout>}}_0+y_P))$

$\&times;\exp (-j\frac{4\mathrm{\&pi;}({\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">f</figure-callout>}}_0+\mathrm{n\&Delta;f})(v_r-\mathrm{\&omega;}{x}_P)n{T}_r+2\mathrm{\&pi;}({\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">f</figure-callout>}}_0+\mathrm{n\&Delta;f})a_r{\left(n{T}_r\right)}^2}{c})$

$s_{n+1}(f_r-\mathrm{\&Delta;f}/2,(n+1)T_r)=\widetilde{\mathrm{\&sigma;}}\mathrm{rect}\left(\frac{f_r-\mathrm{\&Delta;f}/2}{B}\right)\&times;\exp (-j\frac{4\mathrm{\&pi;}{f}_0}{c}({\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">R</figure-callout>}}_0+y_P))$

$\&times;\exp (-j\frac{4\mathrm{\&pi;}(f_r+\mathrm{n\&Delta;f}+\mathrm{\&Delta;f}/2)}{c}({\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">R</figure-callout>}}_0+y_P))$

$\&times;\exp (-j\frac{4\mathrm{\&pi;}({\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">f</figure-callout>}}_0+(n+1)\mathrm{\&Delta;f})(v_r-\mathrm{\&omega;}{x}_P)(n+1)T_r+2\mathrm{\&pi;}({\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">f</figure-callout>}}_0+(n+1)\mathrm{\&Delta;f})a_r{\left((n+1)T_r\right)}^2}{c})$

Wherein, s _n(f _r+ Δ f/2, nT _r) be the subpulse frequency domain echo signal after n position and phase place change, s _N+1(f _r-Δ f/2, (n+1) T _r) be the subpulse frequency domain echo signal after n+1 position and phase place change, f _rScope be [B _c/ 2～B _c/ 2], B _cBe the signal bandwidth that shares, nT _rThe expression orientation time, the adjacent subpulse frequency domain echo signal after position and phase place change such as Fig. 3 (c);

4c) obtain the poor ΔΦ of conjugate phase that changes frequency domain echo signal between rear adjacent subpulse _n:

$\mathrm{\&Delta;}{\mathrm{\&Phi;}}_n=\frac{4\mathrm{\&pi;}{T}_r({\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">f</figure-callout>}}_0+\mathrm{n\&Delta;f})(v_r-\mathrm{\&omega;}{x}_P)+\mathrm{\&Delta;f}(v_r-\mathrm{\&omega;}{x}_P)(n+1)T_r+2\mathrm{\&pi;}({\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">f</figure-callout>}}_0+(n+1)\mathrm{\&Delta;f})a_r(2n+1)T_r^2}{c};$

4d) in the echoed signal arteries and veins group phase place of first subpulse as reference, the poor ΔΦ of antithetical phrase impulse compensation conjugate phase successively _n, obtain the echoed signal frequency spectrum s (f after the frequency synthesis _r, T _r):

$s_n(f_r,T_r)=\widetilde{\mathrm{\&sigma;}}\mathrm{rect}\left(\frac{f_r}{B_{\mathrm{\&Delta;}}}\right)\&times;\exp (-j\frac{4\mathrm{\&pi;}{f}_0}{c}({\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">R</figure-callout>}}_0+y_P))\&times;\exp (-j\frac{4\mathrm{\&pi;}(f_r+\mathrm{\&Delta;f}/2)}{c}({\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="HDA00002477120200031.png"\; state="\{\{state\}\}">R</figure-callout>}}_0+y_P))$

$\&times;\exp (-j\frac{4\mathrm{\&pi;}{f}_0(v_r-\mathrm{\&omega;}{x}_P)T_r+2\mathrm{\&pi;}{f}_0{a}_r{\left(T_r\right)}^2}{c}),$

Wherein, B _Δ=N Δ f is the signal bandwidth after synthetic.

Step 5. is obtained target high-resolution one-dimensional range profile.

To the echoed signal frequency spectrum s (f after the frequency synthesis _r, T _r) carry out contrary Fourier IFFT conversion, obtain the high-resolution one-dimensional range profile.

Step 6. is obtained the target azimuth full resolution pricture.

Utilize RD algorithm or RID algorithm to carry out the orientation imaging to the high-resolution one-dimensional range profile, obtain the full resolution pricture of target azimuth.

Effect of the present invention can be illustrated by following emulation experiment:

1. emulated data

Aircraft Targets data to emulation are carried out imaging, and its simulation parameter is as shown in table 1.

The work of table 1 radar and the parameters of target motion

Radar horizon	30km	Sample frequency	250MHz
				Arteries and veins group number	128	Pulse width	10us
The subpulse number	5	Signal bandwidth	200MHz
				Pulse repetition rate	1000Hz	The target radial acceleration	6m/s
Initial carrier frequency	10GHz	Target radial speed	120m/s
				Step frequency	180MHz	The target rotational angular velocity	0.07rad/s

2. to the emulated data imaging

Emulation Aircraft Targets, Aircraft Targets are comprised of 59 effective scattering points altogether, obtain the original image of Aircraft Targets, such as Fig. 4 (a);

In conjunction with radar work and the parameters of target motion, the Aircraft Targets of emulation is carried out the ISAR imaging, obtain ISAR image before the frequency synthesis of emulation Aircraft Targets, such as Fig. 4 (b);

In conjunction with radar work and the parameters of target motion, to the synthetic method ISAR imaging of Aircraft Targets employing step frequency of the present invention of emulation, obtain the ISAR image of emulation Aircraft Targets, such as Fig. 4 (c).

3. to the measured data imaging

Each arteries and veins group of known actual measurement Ship Target data is comprised of the subpulse of 31 frequency step;

The optical imagery of known Ship Target is such as Fig. 5 (a);

Utilize actual measurement Ship Target data to carry out the ISAR imaging, obtain the front ISAR image of frequency synthesis of Ship Target, such as Fig. 5 (b);

With the method that step frequency of the present invention is synthetic actual measurement Ship Target data are carried out the ISAR imaging, obtain surveying the frequency synthesis ISAR image of Ship Target, such as Fig. 5 (c);

As seen adopt the synthetic method of step frequency of the present invention to carry out the ISAR imaging than directly by Fig. 5 (b), 5 (c), can obtain more high-resolution target ISAR image, further proved high efficiency and the validity of method proposed by the invention.

Claims (3)

1. the step frequency ISAR formation method based on the phase drying and other treatment comprises the steps:

(1) sets up step frequency ISAR echo signal model;

(2) carrying out kinematic parameter according to echo signal model estimates:

2a) first subpulse data of different arteries and veins groups are taken out respectively, obtain echoed signal neighboring and correlative expression formula and be:

$R(\mathrm{\&tau;},{\mathrm{mT}}_a)={\mathrm{\&sigma;}}_P\sin c\left(A(\mathrm{\&tau;}+\frac{2M}{c})\right)\&times;\exp \left(j\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}{M}_1\right)\&times;\exp \left(j\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}{M}_2\right)$

Wherein, τ is correlation time, and m is arteries and veins group number, 0≤m≤M-1, mT _aBe the discrete representation of orientation time, σ _PBe the target echo backscattering coefficient, A is the relevant matches amount, and c is the light velocity, and λ is signal wavelength, M=M ₁+ M ₂, $M_1=\left(v_r{x}_P\mathrm{\&omega;}\right)T_a+\frac{1}{2}{a}_r{T}_a^2,$ M ₂=T _aa _rmT _a

Wherein, v _rThe radial velocity of the relative radar motion of target, x _PBe the lateral attitude information of scattering point, ω is the rotational angular velocity of the relative radar motion of target, T _aBe the repetition period between the arteries and veins group, a _rIt is the radial acceleration of the relative radar motion of target.

2b) to echoed signal neighboring and correlative expression formula along the orientation to doing the FFT accumulation, obtaining orientation frequency domain echo signal neighboring and correlative expression formula be:

$R(\mathrm{\&tau;},f_a)={\mathrm{\&sigma;}}_P\sin c\left(A(\mathrm{\&tau;}+\frac{2M}{c})\right)\&times;\sin c\left({\mathrm{\&pi;T}}_m(f_a-\frac{{2T}_a}{\mathrm{\&lambda;}}{a}_r)\right)\&times;\exp \left(j\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}{M}_1\right)$

Wherein, T _mBe subpulse repetition period, f _aFor the orientation to frequency,

It is the correlation peak location of echoed signal neighboring and correlative expression formula;

Ignore the envelope variation that adjacent twice return ω causes among the M, then correlation peak location can be expressed as again

$(-\frac{{2v}_r{T}_a+a_r{T}_a^2}{c},\frac{{2T}_a{a}_r}{\mathrm{\&lambda;}});$

2c) with correlation peak location the distance to the orientation to coordinate be made as respectively

With

Calculate the radial acceleration a of target _rAnd speed v _r:

$\left\{\begin{array}{cc}{a}_r=\frac{\mathrm{\&lambda;prf}[\tilde{n}-(\frac{\tilde{N}}{2}+1)]}{{2\mathrm{NT}}_a}& \tilde{n}=1,.....,\tilde{N}\\ v_r=-\frac{c[\tilde{m}-(\frac{\tilde{M}}{2}+1)]}{{2f}_s{T}_a}-\frac{\mathrm{\&lambda;}[\tilde{n}-(\frac{\tilde{N}}{2}+1)]}{4\tilde{N}{T}_a}& \tilde{m}=1,.....,\tilde{M}\end{array}\right.$

Wherein, With

Be respectively the distance to the orientation to discrete counting, prf be the orientation to sample frequency, f _sFor the distance to sample frequency, T _rBe the pulse repetition time;

(3) according to radial acceleration a _rAnd speed v _r, utilize the phase compensation function s of following envelope cancellation _SrefSubpulse envelope to echoed signal compensates,

$s_{\mathrm{sref}}=\exp (-j\frac{4\mathrm{\&pi;}}{c}(v_r{f}_r{t}_m+\frac{1}{2}{a}_r{f}_r{t}_m^2))$

Wherein, f _rFor the distance to frequency, t _mFor the orientation to the time;

(4) echoed signal of finishing the subpulse envelope cancellation is carried out frequency synthesis based on the phase drying and other treatment, obtain the echoed signal frequency spectrum s (f after synthetic _r, T _r);

(5) to the echoed signal frequency spectrum s (f after synthetic _r, T _r) carry out contrary Fourier IFFT conversion, obtain the high-resolution one-dimensional range profile;

(6) utilize RD algorithm or RID algorithm to carry out the orientation imaging to the high-resolution one-dimensional range profile, obtain the full resolution pricture of target azimuth.

2. the step frequency ISAR formation method based on the phase drying and other treatment according to claim 1, wherein step (4) is described carries out frequency synthesis based on the phase drying and other treatment to the echoed signal of finishing the subpulse envelope cancellation, carries out as follows:

4a) echoed signal of finishing the subpulse envelope cancellation is transformed to apart from frequency domain s _n(f _r, nT _r);

$s_n(f_r,{\mathrm{nT}}_r)=\widetilde{\mathrm{\&sigma;}}\mathrm{rect}\left(\frac{f_r}{B}\right)\&times;\exp (-j\frac{{4\mathrm{\&pi;f}}_0}{c}(R_0+y_P))\&times;\exp (-j\frac{4\mathrm{\&pi;}(f_r+\mathrm{n\&Delta;f})}{c}(R_0+y_P))$

$\&times;\exp (-j\frac{4\mathrm{\&pi;}(f_0+\mathrm{n\&Delta;f})(v_r-{\mathrm{\&omega;x}}_P){\mathrm{nT}}_r+2\mathrm{\&pi;}(f_0+\mathrm{n\&Delta;f})a_r{\left({\mathrm{nT}}_r\right)}^2}{c})$

Wherein, f _rFor the distance to frequency, nT _rThe expression orientation time,

Be range coefficient, B is emission subpulse signal bandwidth, and c is the light velocity, R ₀Be the initial action distance of target to radar, y _PThe longitudinal position information of scattering point P, f ₀+ n Δ f is the carrier frequency of n frequency modulation stepping subpulse, and Δ f is number of frequency steps;

4b) adjacent subpulse frequency domain echo signal location and phase place are changed, variable quantity is Δ f/2, obtains the poor ΔΦ of conjugate phase that changes frequency domain echo signal between rear adjacent subpulse _n:

${\mathrm{\&Delta;\&Phi;}}_n=\frac{{4\mathrm{\&pi;T}}_r(f_0+\mathrm{n\&Delta;f})(v_r-{\mathrm{\&omega;x}}_P)+\mathrm{\&Delta;f}(v_r-{\mathrm{\&omega;x}}_P)(n+1)T_r+2\mathrm{\&pi;}(f_0+(n+1)\mathrm{\&Delta;f})a_r(2n+1)T_r^2}{c}$

Wherein, T _rBe the pulse repetition time, v _rBe the radial velocity of the relative radar motion of target, ω is the rotational angular velocity of the relative radar motion of target, x _PThe lateral attitude information of scattering point, a _rIt is the radial acceleration of the relative radar motion of target;

4c) in the echoed signal arteries and veins group phase place of first subpulse as reference, the poor ΔΦ of antithetical phrase impulse compensation conjugate phase successively _n, obtain the echoed signal frequency spectrum s (f after the frequency synthesis _r, T _r):

$s(f_r,T_r)=\widetilde{\mathrm{\&sigma;}}\mathrm{rect}\left(\frac{f_r}{B_{\mathrm{\&Delta;}}}\right)\&times;\exp (-j\frac{{4\mathrm{\&pi;f}}_0}{c}(R_0+y_P))\&times;\exp (-j\frac{4\mathrm{\&pi;}(f_r+\mathrm{\&Delta;f}/2)}{c}(R_0+y_P))$

$\&times;\exp (-j\frac{4\mathrm{\&pi;}{f}_0(v_r-{\mathrm{\&omega;x}}_P)T_r+2\mathrm{\&pi;}{f}_0{a}_r{\left(T_r\right)}^2}{c})$

Wherein, B _Δ=N Δ f is the signal bandwidth after synthetic.

3. the step frequency ISAR formation method based on the phase drying and other treatment according to claim 2, wherein step 4b) described adjacent subpulse frequency domain echo signal location and phase place are changed, undertaken by following formula:

$s_n(f_r+\mathrm{\&Delta;f}/2,{\mathrm{nT}}_r)=\widetilde{\mathrm{\&sigma;}}\mathrm{rect}\left(\frac{f_r+\mathrm{\&Delta;f}/2}{B}\right)\&times;\exp (-j\frac{4\mathrm{\&pi;}{f}_0}{c}(R_0+y_P))$

$\&times;\exp (-j\frac{4\mathrm{\&pi;}(f_r+\mathrm{n\&Delta;f}+\mathrm{\&Delta;f}/2)}{c}(R_0+y_P))$

$\&times;\exp (-j\frac{4\mathrm{\&pi;}(f_0+\mathrm{n\&Delta;f})(v_r-\mathrm{\&omega;}{x}_P){\mathrm{nT}}_r+2\mathrm{\&pi;}(f_0+\mathrm{n\&Delta;f})a_r{\left({\mathrm{nT}}_r\right)}^2}{c})$

$s_{n+1}(f_r-\mathrm{\&Delta;f}/2,(n+1)T_r)=\widetilde{\mathrm{\&sigma;}}\mathrm{rect}\left(\frac{f_r-\mathrm{\&Delta;f}/2}{B}\right)\&times;\exp (-j\frac{4\mathrm{\&pi;}{f}_0}{c}(R_0+y_P))$

$\&times;\exp (-j\frac{4\mathrm{\&pi;}(f_r+\mathrm{n\&Delta;f}+\mathrm{\&Delta;f}/2)}{c}(R_0+y_P))$

$\&times;\exp (-j\frac{4\mathrm{\&pi;}(f_0+(n+1)\mathrm{\&Delta;f})(v_r-\mathrm{\&omega;}{x}_P){(n+1)T}_r+2\mathrm{\&pi;}(f_0+(n+1)\mathrm{\&Delta;f})a_r{\left({(n+1)T}_r\right)}^2}{c})$

Wherein, s _n(f _r+ Δ f/2, nT _r) be the subpulse frequency domain echo signal after n position and phase place change, s _N+1(f _r-Δ f/2, (n+1) T _r) be the subpulse frequency domain echo signal after n+1 position and phase place change, f _rScope be [B _c/ 2～B _c/ 2], B _cBe the signal bandwidth that shares, nT _rThe expression orientation time, f ₀Be fundamental frequency, exp is the exponential function truth of a matter, and rect is rectangular function.

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