CN103901419A - Outer transmitter-based radar range migration compensation method based on frequency domain phase correction - Google Patents

Abstract

The invention relates to an outer transmitter-based radar range migration compensation method based on frequency domain phase correction and belongs to the technical field of radar target acquisition. The method comprises the steps that segment treatment is conducted on echo signals firstly; then echoes are converted to the frequency domain; phase correction is conducted on the echoes in the frequency domain to enable in-phase superposition of the signals to be achieved within the bandwidth and eliminate the influence of range migration; finally, the phase-corrected echoes are converted to the time domain through Fourier inversion, mutual ambiguity function calculation is conducted between the echoes and direct wave signals, and then a mutual ambiguity function diagram is obtained. According to the method, under the condition of a tracking mode (target speed is known) or that rough target speed is known, the accumulation gain of the method is similar to that of Keystone conversion, while the amount of calculation is far smaller.

Description

A kind of external radiation source distance by radar migration compensation method based on frequency domain phase correction

Technical field

The present invention relates to a kind of external radiation source distance by radar migration compensation method based on frequency domain phase correction, belong to radar target acquisition technical field.

Background technology

External radiation source radar is a kind of two (many) bases radars, and it utilizes existing non-cooperation radiation source (as broadcast, TV signal etc.), by the echoed signal of passive receiving target scattering, realizes the detection to target, and it configures as shown in Figure 1.Because target echo is conventionally fainter, therefore need to carry out long-time coherent accumulation to improve signal to noise ratio (S/N ratio).For guaranteeing accumulate augment, require within coherent integration time, the range migration of target can not exceed a range unit.But because external radiation source radar target is very faint, the integration time needing is longer.Within longer integration time, target travel exceedes multiple range units apart from meeting, range migration phenomenon occurs, as shown in Figure 2.Range migration can cause the dispersion of target peak energy and signal to noise ratio (S/N ratio) to decline, and then affects systemic effect distance, therefore needs finding method to solve.

For pulse radar, Keystone conversion is a kind of effective ways that solve range migration.Mentioned the principle of pulsed radar Keystone conversion at " a kind of broad sense Keystone mapping algorithm for Testing of Feeble Signals " literary composition of Zhao Yongbo.Take point target as example, the base band echoed signal of target is expressed as:

$s\left(t\right)=s(\hat{t},t_m)=\mathrm{AP}(\hat{t},t_m)\exp (-\mathrm{<figure-callout\; id="4"\; label="j"\; filenames="HDA0000494403820000031.png,HDA0000494403820000032.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{{4\mathrm{\&pi;f}}_c}{c}R\left(t_m\right))---\left(1\right)$

Wherein

t _m=mT represents respectively fast time and slow time, and T is the pulse repetition time, and A is the amplitude of echo target, R (t _m) be t _mthe distance of moment target,

for normalized echo envelope, f _cfor carrier frequency.

(1) formula is carried out to Fourier transform at fast time dimension can be obtained:

$S(f,t_m)=\mathrm{AP}\left(f\right)\exp (-\mathrm{<figure-callout\; id="4"\; label="j"\; filenames="HDA0000494403820000031.png,HDA0000494403820000032.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{4\mathrm{\&pi;}}{c}(f+f_c)R\left(t_m\right))---\left(2\right)$

Through distance to pulse pressure after obtain:

$S(f,t_m)=A{\left|P\left(f\right)\right|}^2\exp (-\mathrm{<figure-callout\; id="4"\; label="j"\; filenames="HDA0000494403820000031.png,HDA0000494403820000032.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{4\mathrm{\&pi;}}{c}(f+f_c)R\left(t_m\right))---\left(3\right)$

Hypothetical target is at t _min uniform motion, speed v remains unchanged,

$S(f,t_m)=A{\left|P\left(f\right)\right|}^2\exp (-\mathrm{<figure-callout\; id="4"\; label="j"\; filenames="HDA0000494403820000031.png,HDA0000494403820000032.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{4\mathrm{\&pi;}}{c}\left({f+f}_c\right)R_0)\exp (-\mathrm{<figure-callout\; id="4"\; label="j"\; filenames="HDA0000494403820000031.png,HDA0000494403820000032.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{4\mathrm{\&pi;}}{c}\left({f+f}_c\right){\mathrm{vt}}_m)---\left(4\right)$

In above formula, first exponential term represents the target position in 0 moment, and second exponential term represents phase place t in time _mvariation, due to the existence of f, the rate of change of phase place is different.

Keystone conversion adopts the method for being carried out to change of scale the slow time:

$t_m^{\&prime;}=\frac{f_c+f}{f_c}{t}_m---\left(5\right)$

Formula (5) substitution formula (4) is obtained:

$S_r(f,t_m)=A{\left|P\left(f\right)\right|}^2\exp [-\mathrm{<figure-callout\; id="4"\; label="j"\; filenames="HDA0000494403820000031.png,HDA0000494403820000032.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{4\mathrm{\&pi;}}{c}\left({f+f}_c\right)R_0]\exp (-\mathrm{<figure-callout\; id="4"\; label="j"\; filenames="HDA0000494403820000031.png,HDA0000494403820000032.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{4\mathrm{\&pi;}}{c}{f}_c{\mathrm{vt}}_m^{\&prime;})---\left(6\right)$

From formula (6), with t ' _mfor the new time measures, the rate of change of phase place is constant, and the envelope between the target echo signal of different sections no longer includes translation, thereby has solved range migration problem.

The principle of Keystone conversion as shown in Figure 3.Data before conversion are as shown in Fig. 3 (a), and the hollow dots in Fig. 3 (b) represents the data point after conversion.Because the data after conversion need to be carried out IFFT operation transform and returned time domain, so need to adopt the sampling interval of the data after the method adjustment conversion of SINC interpolation, the data after interpolation are as shown in the solid dot in Fig. 3 (b).

Keystone conversion can solve the problem of range migration while being applied to external radiation source radar, but operand is very large, need to find computing method fast.

Summary of the invention

While the object of the invention is for the faint echo of solution detection target, carry out long time integration appearance distance migration, be unfavorable for the problem of target detection, a kind of external radiation source distance by radar migration compensation method based on frequency domain phase correction is proposed, in tracking situation, under (target velocity is known) or target approximate velocity known case, eliminate target range migration, improve objective accumulation gain by the long-time coherent accumulation of external radiation source radar.

The present invention, by target echo being carried out to phase correction at frequency domain, can carry out with superimposed signal in bandwidth, to reach the object that improves target detection performance, has meanwhile also reduced operand.

The object of the invention is to be achieved through the following technical solutions, specifically comprise the following steps:

Step 1, data sectional

Echoed signal is carried out to data sectional processing, echoed signal to be processed is divided into N pulse, the number of data points of each pulse is L, and data to be processed are always counted as NL.

Step 2, frequency domain conversion

Echoed signal after step 1 segmentation is carried out to Fast Fourier Transform (FFT), transforms to frequency domain:

E＝FFT{e(n)} （7）

Wherein e (n) is the echoed signal after segmentation, and E is the expression of echoed signal at frequency domain.

Step 3, phase correction

In order to carry out with superimposed signal, need to make phase-frequency response is straight line in signal bandwidth, and the echoed signal therefore step 2 being obtained is carried out phase correction at frequency domain, and between adjacent pulse, phase correction amount φ (k) is:

$\mathrm{\&phi;}\left(k\right)=-(m-1)\frac{\frac{k}{L}\&times;f_s}{f_c}{\mathrm{\&theta;}}_c---\left(8\right)$

${\mathrm{\&theta;}}_c=\frac{2\mathrm{\&pi;}{f}_{d}L}{f_s}---\left(9\right)$

Wherein $k=-\frac{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000494403820000022.png,HDA0000494403820000031.png"\; state="\{\{state\}\}">L</figure-callout>}}{2},-\frac{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000494403820000022.png,HDA0000494403820000031.png"\; state="\{\{state\}\}">L</figure-callout>}}{2}+1,...,\frac{L}{2}-2,\frac{L}{2}-1;$

In formula, each variable is defined as:

M: m pulse of echoed signal, m=1,2 ..., N;

L: the number of data points in a pulse;

F _s: the baseband sampling rate of echoed signal;

F _c: the carrier frequency of echoed signal;

θ _c: the phase changing capacity at respective signal centre frequency place between the adjacent pulse of echoed signal;

F _d: the Doppler frequency of target;

N: the pulse number of echoed signal.

At frequency domain, echo is carried out to phase correction, concrete formula is:

E'＝E·exp(jφ(k)) （10）

Wherein E' carries out the echoed signal after phase correction compensation at frequency domain.

Step 4, frequency domain transforms to time domain

By inverse fast Fourier transform, the frequency domain echo signal that step 3 is carried out after phase correction transforms to time domain:

e'(n)＝IFFT{E'} （11）

Wherein e'(n) be the echoed signal after phase correction.

Beneficial effect

Compared with carrying out range migration compensation with traditional Keystone method, the calculated amount of method for correcting phase is little.Concrete operation amount is: what Keystone method was total answer, and to take advantage of number of times be 3N (Llog ₂(L)/2)+N (N+1) L, total number of times 3N (Llog that is added with ₂(L))+N (N-1) L.And total the answering of phase correction algorithm to take advantage of number of times be 2N (Llog ₂(L)/2), total number of times that is added with is 2N (Llog ₂(L)).Method for correcting phase of the present invention is obviously much smaller than the operand of Keystone method.

Accompanying drawing explanation

Fig. 1 is background technology China and foreign countries radiation source radar configuration schematic diagram;

Fig. 2 is long time integration range migration phenomenon in background technology;

Fig. 3 is Keystone shift theory schematic diagram in background technology, and wherein (a) is the data before Keystone conversion, is (b) data of Keystone after converting;

Fig. 4 is in the situation that in embodiment, be 1.0s integration time, ambiguity function side view mutually, and wherein (a) is frequency domain phase correction algorithm, (b) is Keystone algorithm;

Fig. 5 is in embodiment under different integration times, the comparison of frequency domain phase correction algorithm and Keystone algorithm operation quantity.

Embodiment

Below in conjunction with accompanying drawing and specific implementation method, the invention will be further described.

An external radiation source distance by radar migration compensation method based on frequency domain phase correction, is integrated in the Radar Signal Processing module of external radiation source.External radiation source radar generally has two slave antennas, and reference antenna receives direct-path signal, the TV signal of echo antenna reception target reflection, and the target of surveying is aircarrier aircraft, as shown in Figure 1.

The means of the present embodiment utilization experiment are verified validity of the present invention.

Experiment parameter: central television broadcast towers transmitted signal bandwidth is 7.56MHz, carrier frequency is 674MHz, baseband sampling rate f _s=10MHz, detection target is aircarrier aircraft, its Doppler frequency f _d=-483Hz.

Concrete implementation step is:

1) echoed signal is carried out to data sectional processing.If be T integration time _i, the data of echo are always counted as T _if _s, the number of data points L=5000 of each pulse, is divided into N=T echo _if _s/ 5000 pulses.Can be 1.0s proper integration time thus time, echo is always counted as 10M, and each pulse data L=5000 that counts, is divided into N=2000 pulse echo.

2) echoed signal is carried out to Fast Fourier Transform (FFT) to frequency domain.Every section of echoed signal is carried out to the FFT computing of 5000, obtain the frequency domain representation E=FFT{e (n) of echoed signal }.

3) phase correction.In the time that be 1.0s integration time, the Doppler frequency f of target _d=-483Hz, the phase changing capacity θ at respective signal centre frequency place between adjacent pulse _c=-0.483 π.Between adjacent pulse, phase correction amount is φ (k)=-(m-1) k/337000 (0.483 π), wherein k=-2500, and-2499 ..., 2498,2499, m=1,2 ..., 2000.Try to achieve θ _crear frequency domain carries out phase correction compensation to echoed signal, i.e. E'=Eexp[-(m-1) k/337000 (0.483 π)].

4) the frequency domain echo signal that carries out phase correction is transformed to time domain, every section of echoed signal of frequency domain is carried out to the time domain echoed signal after the IFFT of 5000 is proofreaied and correct: e'(n)=IFFT{E'}.

Do mutual ambiguity function and obtain mutual ambiguity function figure carrying out the echoed signal of phase correction and direct-path signal in time domain.In the time that be 1.0s integration time, ambiguity function figure as shown in Figure 4 mutually.Adopting the signal to noise ratio (S/N ratio) of frequency domain phase correction algorithm target is 17.1dB, and it is 1.2288 × 10 that number of times is taken advantage of in total answering ¹⁰, total number of times that is added with is 2.4575 × 10 ⁸; Adopting the signal to noise ratio (S/N ratio) of Keystone algorithm target is 16.9dB, and it is 2.0194 × 10 that number of times is taken advantage of in total answering ¹⁰, total number of times that is added with is 2.0359 × 10 ¹⁰.Under identical integration time, adopt frequency domain phase correction algorithm and adopt the detection performance of Keystone algorithm target suitable, but adopt frequency domain phase correction algorithm operation quantity to greatly reduce as can be seen here.

In the time that be 1.5s, 2.0s, 2.5s, 3.0s integration time, adopt frequency domain phase correction algorithm and adopt the detection performance of Keystone algorithm target suitable, but adopt frequency domain phase correction algorithm operation quantity to greatly reduce.Under different integration times, frequency domain phase correction algorithm and Keystone algorithm operation quantity more as shown in Figure 5.

The foregoing is only specific embodiments of the invention, the protection domain being not intended to limit the present invention, within the spirit and principles in the present invention all, any modification of making, be equal to replacement, improvement etc., within all should being included in protection scope of the present invention.

Claims (1)

1. the external radiation source distance by radar migration compensation method based on frequency domain phase correction, is characterized in that: specifically comprise the following steps:

Step 1, data sectional:

Echoed signal is carried out to data sectional processing, echoed signal to be processed is divided into N pulse, the number of data points of each pulse is L, and data to be processed are always counted as NL;

Step 2, frequency domain conversion:

Echoed signal after step 1 segmentation is carried out to Fast Fourier Transform (FFT), transforms to frequency domain:

E＝FFT{e(n)}

Wherein e (n) is the echoed signal after segmentation, and E is the expression of echoed signal at frequency domain;

Step 3, phase correction:

The echoed signal that step 2 is obtained is carried out phase correction at frequency domain, and make phase-frequency response is straight line in signal bandwidth, and between adjacent pulse, phase correction amount φ (k) is:

$\mathrm{\&phi;}\left(k\right)=-(m-1)\frac{\frac{k}{L}\&times;f_s}{f_c}{\mathrm{\&theta;}}_c$

${\mathrm{\&theta;}}_c=\frac{2\mathrm{\&pi;}{f}_{d}L}{f_s}$

Wherein $k=-\frac{L}{2},-\frac{L}{2}+1,...,\frac{L}{2}-2,\frac{L}{2}-1;$

In formula, each variable is defined as:

M: m pulse of echoed signal, m=1,2 ..., N;

L: the number of data points in a pulse;

F _s: the baseband sampling rate of echoed signal;

F _c: the carrier frequency of echoed signal;

θ _c: the phase changing capacity at respective signal centre frequency place between the adjacent pulse of echoed signal;

F _d: the Doppler frequency of target;

N: the pulse number of echoed signal;

At frequency domain, echo is carried out to phase correction, concrete formula is:

E'＝E·exp(jφ(k))

Wherein E' carries out the echoed signal after phase correction compensation at frequency domain;

Step 4, frequency domain transforms to time domain:

By inverse fast Fourier transform, the frequency domain echo signal that step 3 is carried out after phase correction transforms to time domain:

e'(n)＝IFFT{E'}

Wherein e'(n) be the echoed signal after phase correction.

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