CN106646472A - Method for restraining SAR radio-frequency interference based on space-frequency cascading filtering - Google Patents

Abstract

The invention provides a method for restraining a SAR radio-frequency interference based on space-frequency cascading filtering. According to the technical scheme, the method comprises the following steps of: 1) estimating DOA of RFI (Radio Frequency Interference), namely utilizing a MUSIC algorithm to estimate the DOA of the RFI in a received signal and then confirming all the RFI space guiding vectors according to the DOA; 2) filtering a frequency domain, namely performing FFT (Fast Fourier Transform) on the received signal and transforming to the frequency domain, and then utilizing a 3 delta judging method to separate a frequency spectrum support zone of the RFI from the received signal; and 3) filtering a space domain: calculating the radio-frequency interference and filtering the interference through the space filtering. According to the method provided by the invention, the loss of the useful signal can be effectively reduced and the interference restraining effect is better.

Description

SAR Radio frequency interference suppressing methods based on null tone cascade filtering

Technical field

The invention belongs to the interleaving techniques field of space flight and microwave remote sensing, more particularly to a kind of SAR (Synthetic Aperture Radar, synthetic aperture radar) RFI (Radio Frequency Interference, Radio frequency interference) in data Suppressing method.

Background technology

The SAR (Synthetic Aperture Radar, synthetic aperture radar) for being operated in low band is easily subject to same The interference of the television network, communication network and other civil equipment institute transmission of electromagnetic signals of frequency range, i.e., so-called RFI (Radio Frequency Interference, Radio frequency interference).The presence of RFI has a strong impact on the quality of image and interpretation and interpretation.Mesh Front airspace filter method, and the document that sees reference " Zhu Feng, Zhang Youyi. the Study of Interference [J] to adaptive spatial filtering. modern electricity Sub- technology, 2013,36 (11):67～74 ".For Whole frequency band filtering, it is totally constrained with RFI directions identical useful signal, While suppressing RFI, useful signal is also suppressed.

For this present situation, the high power, narrow-band characteristic according to Radio frequency interference, it is proposed that one kind is based on null tone cascade filter The Radio frequency interference suppressing method of ripple.Before airspace filter, the docking collection of letters number carries out frequency domain filtering, isolates the frequency at RFI places Band, then for RFI be located frequency band carry out airspace filter.Compared to existing airspace filter method, this paper institutes extracting method will be damaged The useful signal of mistake is limited in the narrow-band at RFI places, effectively reduces the loss of useful signal.

The content of the invention

The purpose of the present invention is：A kind of Radio frequency interference suppressing method based on null tone cascade filtering is proposed, can be effective Ground reduces the loss of useful signal, with more preferable interference suppressioning effect.

The thinking of technical solution of the present invention is：First with MUSIC (Multiple Signal Classification, Multiple signal classification) algorithm estimates the DOA (Direction of Arrival, direction of arrival) of RFI, then built according to DOA The steric direction vector of RFI.Next signal will be received by FFT to frequency domain, the high power, narrow frequency according to Radio frequency interference Band characteristic, the docking collection of letters number carries out frequency domain filtering, isolates the frequency band at RFI places.Finally, using the steric direction vector of RFI Spatial filter is built, for the band signal that RFI is located, realizes filtering using spatial filter.

The technical scheme is that：A kind of SAR Radio frequency interference suppressing methods based on null tone cascade filtering, it is assumed that x (t, η_L) represent SAR in slow moment η_LReception signal, wherein t represents the fast time, it is characterised in that comprise the steps：

The first step：The DOA of RFI estimates：

Estimate to receive signal x (t, η using MUSIC algorithms_L) in RFI DOA, determine that the space of all RFI is led according to DOA To vector, the steric direction vector for remembering i-th RFI is d (θ_i), i=1,2 ..., N, N represents the number of RFI.

Second step：Frequency domain filtering：

Signal x (t, η will be received_L) FFT is carried out to frequency domain, obtain receiving frequency domain signal X (f, η_L)；

Frequency spectrum Support X (f ', η ' of RFI are isolated from reception signal using 3 δ diagnostic methods_L),

Wherein, 0≤η '_L≤ Δ η, 0≤f '≤B_S, Δ η is to receive signal x (t, η_L) in there is slow time of Radio frequency interference Width, B_STo receive signal x (t, η_L) in Radio frequency interference bandwidth；

3rd step：Airspace filter：

Radio frequency interference r (f ', η ' are calculated using following formula_L′)：

Wherein D^H(θ_i) it is that steric direction vector is d (θ_i) frequency domain complex conjugate vector；

Again from frequency domain signal X (f, η_L) in deduct Radio frequency interference r (f ', η '_L), obtain the reception letter of Jing Radio frequency interferences suppression Number.

Following technique effect can use to obtain using the present invention：

SAR Radio frequency interference suppressing methods based on null tone cascade filtering proposed by the present invention, make use of the frequency domain of RFI special Property, the docking collection of letters number first carries out frequency domain filtering, isolates the frequency band at RFI places.Then, using the steric direction vector of RFI Spatial filter is built, for the band signal that RFI is located, realizes filtering using spatial filter.The present invention will can lose Useful signal be limited to RFI place narrow-band in, be effectively reduced the loss of useful signal, improve the matter of image Amount.

Description of the drawings

The principle flow chart of the SAR Radio frequency interference suppressing methods that Fig. 1 is provided for the present invention；

Fig. 2 is the imaging results of the point target used in emulation experiment；

Fig. 3 is the imaging results for adding point target after Radio frequency interference to Fig. 2；

Fig. 4 is to carry out imaging results after AF panel to Fig. 3 using existing airspace filter method；

Fig. 5 is to carry out imaging results after AF panel to Fig. 3 using the method for inventing offer herein；

Fig. 6 is the imaging results of the measured data used in emulation experiment；

Fig. 7 is the imaging results for adding data after Radio frequency interference to Fig. 6；

Fig. 8 is that the imaging results after AF panel are carried out to Fig. 7 using existing airspace filter method；

Fig. 9 is that the method provided using the present invention carries out the imaging results after AF panel to Fig. 7.

Specific embodiment

The principle flow chart of the suppression method for satellite-borne SAR radio-frequency interference that Fig. 1 is provided for the present invention.For the original to the present invention Reason is described in detail, and is illustrated from theory deduction angle below：

Assume x (t, η_L) represent SAR in slow moment η_LReception signal, receive signal x (t, η_L) can be expressed as following shape Formula：

Wherein, s_k(t,η_L) fast time t antenna arrays are corresponded in slow moment η_LK-th useful signal for receiving, φ_k It is the DOA of k-th useful signal, d (φ_k) be k-th useful signal steric direction vector, K is the number of useful signal, this Variable is calculated to be needed, and is not required to estimate when being filtered below.r_i(t,η_L) fast time t antenna arrays are corresponded in slow moment η_LConnect I-th RFI, θ for receiving_iIt is the DOA of i-th RFI, d (θ_i) be i-th RFI steric direction vector, N is the number of RFI.

By x (t, η_L) FFT is carried out to frequency domain, such as following formula：

Wherein D^H(θ_i) it is that steric direction vector is d (θ_i) frequency domain complex conjugate vector.

According to the frequency spectrum characteristic of RFI, the frequency spectrum Support of RFI is isolated from reception signal using 3 δ diagnostic methods.RFI's Frequency spectrum Support is following form：

Wherein, 0≤η '_L≤ Δ η, 0≤f '≤B_S, Δ η is to receive the slow time width that there is Radio frequency interference in signal, B_S The bandwidth of Radio frequency interference in receive signal.

By the use of the frequency domain complex conjugate vector of RFI steric direction vectors as spatial filter, from RFI places frequency spectrum Support Extract RFI, such as following formula：

Further, the RFI forms for obtaining extracting are as follows：

Steric direction vector has following correlation：

Further, the RFI for obtaining is following form：

From above formula, work as φ_k≠θ_iWhen, without useful signal loss, work as φ_k=θ_iWhen, the useful signal of loss is S_k (f ', η '), but the useful signal of loss has been limited to 0≤f '≤B_SIn the range of, it is complete compared to existing airspace filter method Frequency band loses, and effectively improves the interference free performance of system.

Fig. 2～Fig. 5 is to carry out point target the simulation experiment result.Fig. 2 is original point target received signal imaging results, from figure As can be seen that point target focusing effect is good as in.Fig. 3 is to add the imaging results that Radio frequency interference is followed by the collection of letters number in fig. 2, Can see that point target fall into oblivion by disturbed signal.The original image of Fig. 2 and Fig. 3 is coloured image, and it is right after gray-scale map to be changed to Than unobvious.Fig. 4 is that the imaging results after AF panel are carried out to Fig. 3 using existing airspace filter method, can from image Go out, interference is focused on well, but detailed information is destroyed.Fig. 5 be using the present invention provide method carry out after AF panel into As result, it can be seen that point target is focused on well, and disturb residual less.

Fig. 6～Fig. 9 is the result for carrying out Area Objects emulation experiment.Emulation experiment have chosen a glitch-free airborne X ripple Section triple channel SAR measured data.

Fig. 6 is the imaging results of the initial data used in emulation experiment.It can be seen that image clearly, contrast Degree is high.Fig. 7 is the imaging results for adding data after Radio frequency interference to Fig. 6.It can be seen that due to the presence disturbed, figure As target information is capped, picture contrast declines.Fig. 8 is that existing airspace filter method carries out the imaging after AF panel to Fig. 7 As a result, after AF panel, picture quality gets a promotion, but the contrast of image declines, and light and shade region occurs, and detailed information is not Substantially.Fig. 9 is that the method provided using the present invention carries out the imaging results after AF panel, after AF panel, image matter to Fig. 7 Amount is obviously improved, and detailed information is recovered more substantially, and picture contrast is significantly improved.

Above emulation experiment illustrates that the inventive method can effectively make up existing method in terms of AF panel not Foot, effectively lifts the SAR image quality after AF panel.

Claims (1)

1. a kind of SAR Radio frequency interference suppressing methods based on null tone cascade filtering, SAR refers to synthetic aperture radar, it is assumed that x (t, η_L) represent SAR in slow moment η_LReception signal, wherein t represents the fast time, it is characterised in that comprise the steps：

The first step：The DOA of RFI estimates：

Estimate to receive signal x (t, η using MUSIC algorithms_L) in RFI DOA, according to DOA determine all RFI steric direction arrow Amount, the steric direction vector for remembering i-th RFI is d (θ_i), i=1,2 ..., N, N represents the number of RFI；Wherein, RFI is referred to and penetrated Frequency is disturbed, and DOA refers to direction of arrival；

Second step：Frequency domain filtering

Signal x (t, η will be received_L) Fast Fourier Transform (FFT) is carried out to frequency domain, obtain receiving frequency domain signal X (f, η_L)；

Frequency spectrum Support X (f ', η ' of RFI are isolated from reception signal using 3 δ diagnostic methods_L),

Wherein, 0≤η '_L≤ Δ η, 0≤f '≤B_S, Δ η is to receive signal x (t, η_L) in there is the slow time width of Radio frequency interference, B_STo receive signal x (t, η_L) in Radio frequency interference bandwidth.

3rd step：Airspace filter

Radio frequency interference r (f ', η ' are calculated using following formula_L)：

$r(f^{\′},{\mathrm{\η}}_L^{\′})=X(f^{\′},{\mathrm{\η}}_L^{\′})\underset{i=1}{\overset{N}{\Σ}}{D}^H\left({\mathrm{\θ}}_i\right)$

Wherein D^H(θ_i) it is that steric direction vector is d (θ_i) frequency domain complex conjugate vector；

Again from frequency domain signal X (f, η_L) in deduct Radio frequency interference r (f ', η '_L), obtain the reception signal of Jing Radio frequency interferences suppression.