CN102033227B - Weak target detection method for passive radar taking global positioning system (GPS) navigation satellite as external radiation source - Google Patents

Abstract

The invention provides a weak target detection method for a passive radar taking a global positioning system (GPS) navigation satellite as an external radiation source. A standard GPS receiver is adopted in a reference channel and a received signal is taken as a reference signal and purified. The method comprises the following steps of: in a radar target echo channel, amplifying and filtering the signal, performing down conversion to a medium frequency for processing, removing navigation information carried in a GPS signal, suppressing direct waves and flooding waves by using a least square (LS)-CLEAN method, performing matched filtering on suppressed signal and the reference signal and performing Doppler effect correction at the output end of a matched filter; suppressing the shielding effect of a strong target side lobe on the weak target; and performing coherent integration and constant false alarm processing. Direct wave interference, multipath interference, flooding wave interference and shielding interference of a strong target echo side lobe can be suppressed effectively, so that weak target echo is detected.

Description

Passive radar Weak target detecting method take the GPS navigation satellite as the external radiation source

Technical field

What the present invention relates to is a kind of passive radar technical field, relates in particular to utilize the GPS navigation satellite as the Weak target detecting method in the passive radar field in external radiation source.

Background technology

Passive radar refers to radar itself not electromagnetic signals and the radar of only using target emanation electromagnetic wave signal (external radiation source) to carry out target detection and tracking, and it has good " four resistance energy " and has low, disguised strong, the maneuverability advantages of higher of cost.The electromagnetic signal of target emanation may be the signal of target self emission, or the electromagnetic signal of third party's electromagnetic wave signal after the target reflection.Therefore, type according to the target emanation signal source, passive radar can be divided into two classes: the one, utilize the passive radar of target self radiation source, and comprise the radiation source that target to be observed is self-contained, such as electronic equipments such as radar, communication, answering machine, active interference and navigation; The 2nd, utilize the third party to transmit through the passive radar of the signal of target reflection, this class emissive source comprises terrestrial broadcasting radio station, TV station, communication station, live telecast satellite and satellite navigation and location system etc.From radar system, its receiver is the strange land configuration with the transmitter that sends the external radiation source, so it also belongs to two (many) Ji Leida.

Have the advantage that a lot of traditional monostatic radars do not have based on gps signal as external radiation signal passive radar: (1) passive radar receiver is not owing to there is powerful device, and the impact that not leaked by transmitter power, thereby has higher sensitivity; (2) a plurality of operation of receiver can carry out passive location to interference source; (3) because sending and receiving split, and receiver is mourned in silence, also can be motor-driven, so system has the ability of anti-electronics investigation, the destruction of anti-interference and anti-antiradiation missile; (4) when receiver is preposition, can utilize irradiation source aerial, the space, can detect the following and deck-level target in far field of sight line of transmitter, anti-ultra-low altitude penetration ability is strong; (5) has anti-stealthy effect, because Stealthy Target only has minimum radar cross section (RCS) in ° scope of nose cone ± 30, and side direction and top scattering and diffraction do not reduce, and is also very strong, so that passive radar has good effect to the detection of Stealthy Target; (6) because self emitting electromagnetic wave not, Passive Radar System has disguise and emergentness, and system survivability is strong.

Core technology based on the passive radar of gps signal is passive relevant location technology, its basic thought be beyond radiation source emission direct-path signal as a reference, detect the signal energy of evaluating objects reflected radiation source emission, estimate the parameters such as arrival direction, time of arrival and Doppler shift of target echo, thereby realize location and tracking to target.Because gps satellite signal belongs to omnidirectional's continuous-wave radiation, direct-path signal is very strong, there is multipath effect so that clutter is stronger, and the echo of strong target also can disturb the detection of weak target echo greatly, need to carry out to the non-co-operation signal that receives therefore that clutter suppresses and the signal processing just can detect target.

It is the guardian technique problem that Passive Radar System faces in signal is processed that undesired signal suppresses, the Restrainable algorithms of taking at present mainly contains: (a) based on the interference nulling of the capable one-tenth of adaptive beam: ultimate principle is amplitude and the phase place of regulating automatically the bay weighting coefficient according to acceptance criteria, make cost function value minimum, make system reach optimum reception under this criterion, wherein to form be two kinds of optimal beam forming devices that adaptive beam forms for least mean-square error (MMSE) and linear restriction minimum variance (LCMV) criterion wave beam; (b) adopt adaptive filter algorithm to disturb inhibition; (c) the direct wave Restrainable algorithms of subspace-based projection: this algorithm need not the required interference radiating way information of traditional Adaptive interference nulling technology, also need not the reference channel in the sidelobe cancellation technology, but utilize the receiving end equivalent signal to construct the orthogonal intersection cast shadow matrix of direct wave subspace, carry out to received signal projection, thereby suppress direct-wave jamming.

Summary of the invention

The object of the present invention is to provide a kind of direct-wave jamming, multipath interference, noise jamming and strong target echo secondary lobe of effectively suppressing to cover interference, thereby detect the passive radar Weak target detecting method take the GPS navigation satellite as the external radiation source of weak target echo.

The object of the present invention is achieved like this:

Adopt the GPS receiver of standard in reference channel, the signal that receives carries out purification processes as the reference signal to it; In the radar target passage, the signal that receives comprises by force, the echoed signal of weak target, direct-wave jamming, multipath disturbs, noise jamming and noise, at first it is amplified and filtering, then being down-converted to intermediate frequency processes, remove the navigation information that carries in the gps signal, utilize the LS-CLEAN method to carry out direct wave and clutter inhibition, signal and reference signal after suppressing are carried out matched filtering, output terminal at matched filter at first carries out Doppler effect correction, bridging effect to weak target suppresses to strong target secondary lobe again, carries out at last coherent accumulation, CFAR is processed.

The process that the described LS-CLEAN of utilization method is carried out direct wave and clutter inhibition is as follows:

(1) the time delay battle array S of structure reference signal _{Ref_d}

(2) time delay of structure reference signal-Doppler's battle array S _{Ref_df}

(3) construction data battle array A consists of interference space with its column vector;

(4) structure projection matrix P projects to subspace with the interference space quadrature with the target echo channel signal, reaches the purpose of carrying out direct wave, multipath, clutter and interferer suppression;

(5) matrix at this moment is assigned to processing array S as initial value, initialization iterations j=0;

(6) j=j+1 upgrades processing array S _J+1=S _j-m _jC _A

(7) target that detects is s _Wtj(i)=s _Wtj-1(i)+m _jδ (i-delay _i);

(8) energy of residual signal is judged, if it is higher than noise level, then proceeded to step (6), otherwise the circulation end detects all weak targets this moment.

Of the present invention in based on the passive radar detection system of GPS navigation satellite as the external radiation source, the method of utilizing the LS-CLEAN algorithm to carry out the weak target detection has following good effect and advantage: adopt the method can effectively suppress direct-wave jamming, multipath interference and noise jamming, can also effectively eliminate strong target echo secondary lobe to the capture-effect of weak target echo, calculated amount is easy simultaneously, is fit to process in real time.

Description of drawings

Fig. 1 is based on the GPS navigation satellite as the Passive Radar System synoptic diagram in external radiation source;

Fig. 2 is based on the GPS navigation satellite as the passive radar signal processing in external radiation source;

Fig. 3 is the enforcement block diagram that the LS-CLEAN method is carried out the weak target testing process.

Embodiment

By reference to the accompanying drawings the present invention is further elaborated.

As shown in Figure 1, belong to many bases passive radar detection system based on the GPS navigation satellite as the passive radar detection system in external radiation source, receive the radiofrequency signal of 4 GPS navigation satellite launchs at the passive radar receiver end, receiving system is divided into reference channel and radar target passage, is used for respectively receiving direct-path signal and through the echoed signal of target reflection.

As shown in Figure 2, adopt the GPS receiver of standard in reference channel, the signal that receives carries out purification processes as the reference signal to it; In the radar target passage, that the signal that receives comprises is strong, echoed signal, direct-wave jamming, multipath interference, noise jamming and the noise etc. of weak target.At first it is amplified and filtering, then being down-converted to intermediate frequency processes, remove the navigation information that carries in the gps signal, utilize the LS-CLEAN method to carry out direct wave and clutter inhibition, signal and reference signal after suppressing are carried out matched filtering, at first carry out Doppler effect correction at the output terminal of matched filter, the bridging effect to weak target suppresses to strong target secondary lobe again, carry out at last coherent accumulation, CFAR processing, reach the purpose that detects weak target.

In conjunction with Fig. 3, it is as follows that the present invention utilizes LS-CLEAN to carry out the process that weak target detects:

(1) the time delay battle array S of structure reference signal _{Ref_d}

(2) time delay of structure reference signal-Doppler's battle array S _{Ref_df}

(3) construction data battle array A consists of interference space with its column vector;

(4) structure projection matrix P projects to subspace with the interference space quadrature with the target echo channel signal, reaches the purpose of carrying out direct wave, multipath, clutter and interferer suppression;

(5) matrix at this moment is assigned to processing array S as initial value, initialization iterations j=0;

(6) j=j+1 upgrades processing array S _J+1=S _j-m _jC _A

(7) target that detects is s _Wtj(i)=s _Wtj-1(i)+m _jδ (i-delay _i);

(8) energy of residual signal is judged, if it is higher than noise level, then proceeded to step 6, otherwise the circulation end detects all weak targets this moment.

A kind of Weak target detecting method based on the LS-CLEAN algorithm of the present invention, radar echo signal is projected in the subspace with the interference space quadrature, establishment is carried out in direct-wave jamming, multipath interference, then echoed signal is carried out Doppler effect correction, further suppress iteratively each strong target secondary lobe to the bridging effect of weak target echo, thereby accurately detect weak target.

Receiving cable is divided into reference channel and target echo passage two parts in the system of the present invention, reference channel receives the direct signal of GPS navigation satellite as the reference signal, the signal that target echo passage reception gps signal arrives after reflecting through target also exists direct-wave jamming, multipath interference and strong target secondary lobe to the bridging effect of weak target this moment in the target echo passage.The thought of the LS-CLEAN algorithm that the present invention adopts is in the radar target passage, so that utilize the signal errors quadratic sum minimum after this method is disturbed inhibition, and namely so that following formula is minimum:

$\mathrm{\ξ}=\underset{i=i_1}{\overset{i_2}{\mathrm{\Σ}}}{|s_{\exp }\left(i\right)-s_{\mathrm{urv}\_c}\left(i\right)|}^2---\left(1\right)$

In the formula, ξ is for disturbing the signal errors quadratic sum after suppressing; || formula represents the signal delivery; s _ExpIt is the radar target channel signal of expectation; s _{Surv_c}It is the output signal of utilizing after the LS-CLEAN algorithm carries out preliminary direct wave and multipath interference inhibition; To t observing time ₁t ₂Sample, corresponding sampled point scope is i ₁i ₂, i is traversal sample range i ₁i ₂Sampled point.

In reference channel, (R is interested range points number for the simple crosscorrelation output that obtains target echo signal and reference signal on the front R range points, value in the light of actual conditions), reference signal is observed (R-1) individual sampled point more, be (N+R-1) individual sampled point (wherein N is the sampled point number of rear target echo signal of sampling) with reference to signal extension, reference that the signal that received by reference channel this moment consists of gust is:

s _ref＝[s _ref(-R+1)，…，s _ref(0)，…，s _ref(N-1)] ^T (2)

In the formula, s _RefExpression is with reference to battle array; s _Ref(i) be illustrated in the reference signal of i sampled point ,-R+1≤i≤N-1; [] ^TExpression is to transpose of a matrix.

Front K pending in reference channel time delay point processed (K is interested time delay point number, in the light of actual conditions value), and the time delay that structure has (K-1) individual time delay point with reference to battle array is:

S _{ref_d}＝[s _ref，Ds _ref，D ²s _ref，…，D _k-1s _ref] (3)

In the formula, S _{Ref_d}Expression has the time delay of (K-1) individual time delay point with reference to battle array; D is the time delay battle array, and its form is as follows:

In the formula, d _IjIt is capable to be positioned at i among the expression time delay battle array D, the element of j row.

The time delay reference signal is constructed each different Doppler shifts, and time delay-Doppler of this moment with reference to battle array is:

S _{ref_df}＝[F _-pS _{ref_d}，…，F _-1S _{ref_d}，F ₀S _{ref_d}，F ₁S _{ref_d}，…，F _pS _{ref_d}] (5)

In the formula, S _{Ref_df}For having (K-1) individual time delay point, (2p+1) time delay-Doppler of individual Doppler shift point is with reference to battle array; F _pBe the Doppler shift battle array (p is interested Doppler shift point number, in the light of actual conditions value) of p Doppler shift point, as follows:

For will prolong-Doppler associates with reference to the signal of battle array and target echo passage output, utilize incidence matrix B to will prolong-Doppler processes with reference to battle array and obtains data matrix A, be shown below:

A＝BS _{ref_df} (7)

In the formula, B is incidence matrix, is shown below:

In the formula, b _IjCapable for being positioned at i among the incidence matrix B, the element of j row.

The column vector of data matrix A is consisted of the interference space of (2p+1) K dimension, utilize projection operator P with the radar target signal projection to the subspace of interference space quadrature in, projection operator P is expressed as:

P＝I-A(A ^HA) ^-1A ^H (9)

In the formula, A is data matrix; A ^HHermitian matrix for A; () ^-1Be inverse matrix; I is and the unit matrix of A with dimension;

Reception signal S with the radar target passage _SurvProjection in the subspace of interference space quadrature in, played direct-wave jamming and multipath disturbed the purpose that suppresses.Be exactly so that the signal of itself and wanted signal error sum of squares minimum with radar target signal in the subspace of interference space quadrature, the radar target signal after tentatively suppressing is:

s _{surv_c}＝Ps _surv＝I-A(A ^HA) ^-1A ^Hs _surv (10)

s _{Surv_c}To target echo signal s _SurvDirect-wave jamming and multipath disturb signal after suppressing, at this moment, therefore the weak target echo will further remove the capture-effect of the strong target echo secondary lobe that has detected still because the bridging effect of strong target echo secondary lobe and not detectable.At first, to s _{Surv_c}Carry out Doppler shift compensation (compensation method is not done concrete research at this), iteration is carried out in the bridging effect of strong target peak secondary lobe of the matched filtering output terminal after the compensation suppress.

Signal after the signal in the radar target passage being carried out direct wave, multipath, clutter and interferer suppression and carrying out Doppler effect correction is output as C through matched filter _InterThe capture-effect of strong target echo secondary lobe finally detects the weak target echoed signal according to by suppressing successively to weak order by force.First when suppressing strong target echo capture-effect, the initialization process matrix S, at initial time so that processing array be:

S ₀＝C _inter (11)

In the formula, S is processing array, and lower footnote represents iterations, S ₀Initial value for processing array; C _InterBe matched filter output.

Carrying out the j time iteration when suppressing (iterations j should more than the target number), processing array S upgraded according to following principle:

S _j+1(i＝delay _j-N，…，delay _j+N)＝S _j(i＝delay _j-N，…，delay _j+N)-m _jC _A (12)

In the formula, C _ABe reference signal s _RefAutocorrelation matrix; m _j=max (| S _j|) be S _jMaximal value; Delay _j=arg{max (| S _j|) be time delay corresponding to maximal value.

Through iterative processing, this moment, detected target echo signal was:

s _wtj(i)＝s _wtj-1(i)+m _jδ(i-delay _i) (13)

In the formula, s _Wtj-1Detected target echo when (i) being front (j-1) inferior iteration; I is the time delay of this moment; δ is impulse response function.

The end condition of iteration is as follows: the energy to residual signal calculates, if it approaches the noise level of expectation, then iteration finishes, the s of this moment _WtBe the weak target that has detected; Otherwise, if far above noise level, illustrating, the residual signal energy still have target echo to exist, then carry out weak target Check processing next time.

Claims (1)

1. passive radar Weak target detecting method take the GPS navigation satellite as the external radiation source is characterized in that: adopt the GPS receiver of standard in reference channel, the signal that receives carries out purification processes as the reference signal to it; In the radar target passage, the signal that receives comprises by force, the echoed signal of weak target, direct-wave jamming, multipath disturbs, noise jamming and noise, at first it is amplified and filtering, then being down-converted to intermediate frequency processes, remove the navigation information that carries in the gps signal, utilize the LS-CLEAN method to carry out direct wave and clutter inhibition, signal and reference signal after suppressing are carried out matched filtering, output terminal at matched filter at first carries out Doppler effect correction, bridging effect to weak target suppresses to strong target secondary lobe again, carries out at last coherent accumulation, CFAR is processed;

The process that the described LS-CLEAN of utilization method is carried out direct wave and clutter inhibition is as follows:

(1) the time delay battle array S of structure reference signal _{Ref_d}

S _{ref_d}＝[s _ref，Ds _ref，D ²s _ref，…，D ^k-1s _ref]

Wherein, S _{Ref_d}Expression has the time delay of K-1 time delay point with reference to battle array; K is interested time delay point number; D is the time delay battle array, and its form is as follows:

Wherein, d _IjIt is capable to be positioned at i among the expression time delay battle array D, the element of j row; R is interested range points number; N is the sampled point number of rear target echo signal of sampling;

(2) time delay of structure reference signal-Doppler's battle array S _{Ref_df}

S _{ref_df}＝[F _-pS _{ref_d}，…，F _-1S _{ref_d}，F ₀S _{ref_d}，F ₁S _{ref_d}，…，F _pS _{ref_d}]

Wherein, S _{Ref_df}For having K-1 time delay point, the time delay-Doppler of 2p+1 Doppler shift point is with reference to battle array; F _pBe the Doppler shift battle array of p Doppler shift point, p is interested Doppler shift point number, value in the light of actual conditions, and is as follows:

(3) construction data battle array A consists of interference space with its column vector;

A＝BS _{ref_df}

Wherein, B is incidence matrix, is shown below:

Wherein, b _IjCapable for being positioned at i among the incidence matrix B, the element of j row;

(4) structure projection matrix P projects to subspace with the interference space quadrature with the target echo channel signal, reaches the purpose of carrying out direct wave, multipath, clutter and interferer suppression;

The column vector of data matrix A is consisted of the interference space of (2p+1) K dimension, utilize projection matrix P with the radar target signal projection to the subspace of interference space quadrature in, projection matrix P is expressed as:

P＝I-A(A ^HA) ^-1A ^H

In the formula, A is data matrix; A ^HHermitian matrix for A; ()-1 is inverse matrix; I is and the unit matrix of A with dimension;

(5) matrix at this moment is assigned to processing array S as initial value, initialization iterations j=0;

S ₀＝C _inter

In the formula, S is processing array, and lower footnote represents iterations, S ₀Initial value for processing array; C _InterBe matched filter output;

(6) j=j+1 upgrades processing array S _J+1=S _j-m _jC _A

S _j+1(i＝delay _j-N，…，delay _j+N)＝S _j(i＝delay _j-N，…，delay _j+N)-m _jC _A

Wherein, C _ABe reference signal s _RefAutocorrelation matrix; m _j=max (| S _j|) be S _jMaximal value; Delay _j=arg{max (| S _j|) be time delay corresponding to maximal value;

(7) target that detects is s _Wtj(i)=s _Wtj-1(i)+m _jδ (i-delay _i);

Wherein, s _Wtj-1Detected target echo when (i) being front j-1 iteration; I is the time delay of this moment; δ is impulse response function;

(8) energy of residual signal is judged, if it is higher than noise level, then proceeded to step (6), otherwise the circulation end detects all weak targets this moment.

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