CN100472223C - Anti-RF interference method for high frequency radar - Google Patents

Abstract

The invention relates to a high frequency radar anti-radio frequency interference method, which detects the interference signal on the radar collected far distance element accumulating Doppler spectrum by the setting signal-to-noise ratio gate and adopts different scan frequency impulse phase modulating modes to reduce the bad effect of the detecting result by the radio frequency interference distribution received by the high frequency radar.

Description

Anti-RF interference method for high frequency radar

Technical field

The present invention relates to the method for the anti-Radio frequency interference (RFI) of a kind of higher-frequency radar.

Background technology

High frequency (3-30MHz) radars are because of its unique over the horizon and round-the-clock detectivity, and obtained broad research and be successfully applied to during the ocean surface kinetic parameter measures, but and moving targets such as real-time detection naval vessel, aircraft and guided missile.The Radio frequency interference (RFI) of generations such as intensive short wave communication and broadcasting station can have a strong impact on the detection performance of radar in the high band, and this is the operating subject matter of higher-frequency radar.In existing higher-frequency radar anti-interference method, the adaptive beam that adopts forms anti-interference method and depends on large phased-array usually, and system is comparatively complicated, and is not suitable for small-bore widebeam radar; And from the time domain of signal or the anti-interference method of frequency domain character, as based on detection-amputation-interpolation method of disturbing instantaneous feature with based on the undesired signal subspace orthographic projection of interference distance distribution characteristics etc., all need the received signal that contains Radio frequency interference (RFI) is carried out Filtering Processing, thereby inevitably can to useful signal cause to a certain degree loss and distortion (as signal spectrum main lobe broadening, secondary lobe raises), and when having a plurality of interference, this influence is then even more serious.

Summary of the invention

The purpose of this invention is to provide a kind of anti-RF interference method for high frequency radar, avoid the interference of existing filter processing method to suppress not exclusively to reach to adverse effects such as signal generation distortion, obtain interfere information more accurately, recover disturbance spectrum fully, make the useful signal randomization, reduce to disturb and the influencing each other of useful signal, realize the independent analysis of the two, for higher-frequency radar provides a kind of simple and direct effective and cheap radio frequency interference resistant method, to improve the especially detection performance of portable high frequency radar system of higher-frequency radar.

Technical scheme of the present invention is: a kind of anti-RF interference method for high frequency radar is characterized in that:

On the remote unit accumulation doppler spectral of radar collection, detect undesired signal by default signal-noise ratio threshold;

Different scanning frequency pulse phase modulation methods is adopted in the distribution of the Radio frequency interference (RFI) that receives according to higher-frequency radar, realizes anti-interference:

When disturbing when frequency domain be intensive distribution, adopt at random pm mode with in disturbance spectrum albefaction to the average substrate;

When disturbing when frequency domain is sparse distribution, adopt linear pm mode that disturbance spectrum is moved outside the interested spectrum district, recover concealed signal;

When disturb do not exist or its influence little during to admissible degree, adopt the constant phase mode, signal is not made any extra process.

Aforesaid method is characterized in that: modulation phase sequence is compensated, recover disturbance spectrum fully, make the useful signal randomization, reduce to disturb and the influencing each other of useful signal, realize the independent analysis of the two.

In interference distance-doppler spectral that higher-frequency radar receives, the formation of interference stripes is actually owing to the chirp waveform of radar emission in the relevant processing time is in full accord, thereby the formation of disturbance spectrum is similar to a kind of process of Radio Frequency Interfere being carried out extraction with radar pulse repetition frequency, disturbs to have obtained coherent accumulation.Based on this, the present invention considers the radar anti-interference problem along another kind of thinking, and promptly the chirp to radar emission carries out phase modulation (PM), with the spectrum form of change interference, thereby realizes anti-interference.Concentrated Radio frequency interference (RFI) at facing usually in the higher-frequency radar can adopt linear pm mode, and disturbance spectrum is moved to interested frequency range (as wave single order and second order spectrum district); And at expansion profile Radio frequency interference (RFI), then can adopt the mode of phase modulation at random, with disturbance spectrum randomization (albefaction) on a uniform substrate level.Because radar adopts coherent demodulation, local oscillation signal with transmit consistent, therefore phase modulation without any influence, but for radar provides convenient, antijamming measure cheaply, is particularly useful for being used for the portable high frequency groundwave radar of extra large attitude monitoring to useful echoed signal.Especially, adopt another benefit of pulse-phase modulation method to be, if carry out phase compensation to received signal, then can the former disturbance spectrum of reconstruct, and with useful echo spectrum randomization, thereby can obtain more accurate interference parameter estimation.Useful signal and undesired signal can separate processes, and influencing each other to each other reaches minimum.And do not exist or its intensity is lower than when allowing level when disturbing, can adopt constant initial phase frequency modulation on pulse again, signal is not made extra process.The present invention can be effectively applied in the anti-interference process of higher-frequency radar flexibly, thereby has improved the work efficiency and the detection performance of radar greatly.

Advantage of the present invention is: need not to be provided with any auxiliary antenna, make anti-interference more cheap; Do not have complicated signal processing, calculated amount is very little, and disposal route is very convenient; Disturbing number more after a little while, by linear phase modulation can move out disturbance spectrum fully and to useful signal without any loss, thereby avoided the interference of existing filter processing method to suppress to produce adverse effects such as distortion not exclusively and to signal; On the accumulation doppler spectral in the remote unit, detect and disturb, can obtain interfere information more accurately; Modulation phase sequence is compensated, can recover disturbance spectrum fully, and make the useful signal randomization, reduce influencing each other of interference and useful signal, realize the independent analysis of the two, and the accurate analysis of disturbing helps further optimizing the detection performance of radar system.

Description of drawings

Fig. 1, the higher-frequency radar fundamental diagram of the embodiment of the invention.Wherein, 1 receiving antenna, 2 local oscillation signals, 3 separate range conversion, 4 Doppler-shifts

Fig. 2, the accumulation doppler spectral of concentrating profile to disturb.

Fig. 3, the accumulation doppler spectral that the expansion profile disturbs.

Fig. 4, means for anti-jamming principle of work block diagram.Wherein, 11 transmit, 12 local oscillation signals, and 13 received signals, 14 target analysis of spectrum modules, 15 disturbance spectrum analysis modules, 16 pm modes are selected module, 17 follow-up signal processing modules, * represents conjugation.

Embodiment

Below in conjunction with drawings and Examples, the present invention is done more detailed explanation.

The principle of work of linear frequency modulation system higher-frequency radar and the feature of disturbance spectrum simply are described below:

The principle of work block diagram of high-frequency ground wave radar as shown in Figure 1.Radar adopts the linear frequency modulation system, in each frequency sweep cycle to demodulation after the signal discrete Fourier transform (DFT) of carrying out low-pass filtering, sampling and fast time domain obtain the distance spectrum of this frequency sweep cycle, wherein each spectrum is o'clock corresponding to a spectrum value sample on the distance element, in time a plurality of distance spectrum sequences are carried out slow time domain discrete Fourier transform at the coherent accumulation of being made up of a plurality of frequency sweep cycles and obtain distance-Doppler's two-dimensional spectrum (as shown in Figure 1, wherein 1 is receiving antenna, 2 is local oscillation signal, 3 for separating range conversion, and 4 is Doppler-shift).Distance-doppler spectral by signal on a plurality of receiving antenna passages just can extract extra large attitude information and moving target information.

Linear FM radar transmit and local oscillation signal can be expressed as

$g\left(t\right)=e^{j2\mathrm{\&pi;}(f_{0}t+\frac{1}{2}{\mathrm{kt}}^2)},-T/2\&le;t<T/2---\left(1\right)$

F wherein ₀, k and T be respectively radar center frequency, chirp slope and frequency sweep cycle, t is fast time variable.

The spectrum form that amplitude modulation (AM) the type communication that following analysis of high frequency radar faces is usually disturbed.N (n=0 ..., N-1) in the individual frequency sweep cycle, interference can be expressed as

S wherein _c(t ') and s _m(t ') is respectively carrier signal and modulation signal, a, f _lWith

Be respectively amplitude, frequency and the first phase of carrier wave.T '=nT+t is common time variable.

Mixing output undesired signal is s (t ')=s _i(t ') g (t).The interior distance spectrum of n frequency sweep cycle that forms by baseband low pass filters H (f) back is

$S^n\left(f\right)=F\left[s(t\&prime;)\right]H\left(f\right)=F\left[s_i(t\&prime;)g\left(t\right)\right]H\left(f\right)=F[s_c(t\&prime;)g\left(t\right)+s_m(t\&prime;)g\left(t\right)]H\left(f\right)$

(3)

$=F\left[s_c(t\&prime;)g\left(t\right)\right]H\left(f\right)+F\left[s_m(t\&prime;)g\left(t\right)\right]H\left(f\right)\stackrel{\mathrm{def}}{=}{S}_c^n\left(f\right)+S_m^n\left(f\right),$

F[wherein] Fourier transform of expression t when fast, subscript " expression frequency sweep cycle sequence number.Here disturbance spectrum is made up of definite carrier signal spectrum and Stochastic Modulation signal spectrum two parts.

Have by formula (2)

Therefore the interfering carrier spectrum is

$S_c^n\left(f\right)=F\left[s_c(t\&prime;)g\left(t\right)\right]H\left(f\right)=\left\{F\left[s_c\left(t\right)g\left(t\right)\right]H\left(f\right)\right\}{e}^{j2\mathrm{\&pi;}{f}_l\mathrm{nT}}=S_c^0\left(f\right)e^{j2\mathrm{\&pi;}{f}_l\mathrm{nT}}.---\left(5\right)$

This shows the characteristic of interfering carrier spectrum, it is a sinusoidal signal in slow time domain (is variable with n), thereby presents the line spectrum form in the Doppler territory, and this form and range-independence, and disturbance spectrum will appear on all distance elements.Definitely, interfering carrier is rendered as the bright wisp band that is parallel to distance axis on distance-doppler spectral, and its frequency location is

$f_D=\left\{\begin{array}{c}\mathrm{mod}(f_l,f_r),\mathrm{mod}(f_l,f_r)\&le;\frac{f_r}{2}\\ \mathrm{mod}(f_l,f_r)-f_r,\mathrm{mod}(f_l,f_r)>\frac{f_r}{2}\end{array}\right.,---\left(6\right)$

F wherein _r=1/T is the pulse repetition rate of radar.When disturbing phase place to exist fluctuation when (as owing to carry the ship motion or ionosphere changes), disturb then broadening and become strips to some extent of spectral line.

See the modulation signal part of interference again.Usually the modulation signal bandwidth is 5-10kHz, and its correlation time (inverse that is about bandwidth) is less than 1ms, and frequency sweep cycle is generally hundreds of ms, so can be considered the independent noise signal at different frequency sweep cycle modulation signals.After Doppler's processing, the power ratio of carrier wave and modulation signal will improve, and its gain equals scanning frequency pulse and counts N.Under this meaning, the modulation composition of interference only improves the generation contribution to the noise floor of echoed signal, and carrier wave then becomes the principal ingredient of disturbing the radar detection performance, therefore, and the work that the inhibition of interfering carrier composition is normally even more important.

As the above analysis, to present line spectrum be because obtained coherent accumulation in different frequency sweep cycles to interfering carrier.If each scanning frequency pulse parameter is all identical, will be equivalent to radar pulse repetition frequency the processing of interfering carrier so extraction will be carried out in interference, interfering frequency also will fold in the doppler analysis bandwidth on the corresponding position.Yet, if the parameter of scanning frequency pulse is time dependent, so just can carry out the transformation of certain mode to disturbance spectrum, avoid or reduce its interference echo spectrum interested district.As in extra large attitude is surveyed, interested is positive and negative single order Bragg spectrum of wave and second order spectrum district, and usually when extracting ocean current and unrestrained high information, generally only utilize the higher side spectrum district of signal to noise ratio (S/N ratio), thereby can consider disturbance spectrum moved outside this useful spectrum district and remove its adverse effect.Investigate the disturbance spectrum forming process, as can be known transponder pulse is carried out phase modulation, change the initial phase of each scanning frequency pulse, just can realize that disturbance spectrum moves.Suppose that the disturbance spectrum amount of moving is Δ f, then the respective phase modulation sequence is α (n)=2 π Δ fnT, and the transponder pulse behind the phase modulation is

g _m(t′)＝g(t)e ^ja(n)， (7)

Use g _m(t ') replaces g (t) substitution formula (3), and utilizes the character of Fourier transform, has

$S_m^n\left(f\right)=F\left[s_i(t\&prime;)g_m(t\&prime;)\right]H\left(f\right)=F\left[s_i(t\&prime;)g\left(t\right)e^{j2\mathrm{\&pi;f}\mathrm{nT}}\right]H\left(f\right)=S^n(f-\mathrm{\&Delta;f}).--\left(8\right)$

By selecting the suitable amount of moving, just can remove the influence of interference effectively, this linear phase modulation method can be effectively applied to disturb daytime the less situation about concentrating when distributing that is.Yet, at some more under the condition of severe, as between the lights or be intensive extended pattern disturbing evening and distribute, disturb the application of moving method then to be restricted, can adopt the method for random phase modulation this moment, with disturbance spectrum randomization (or albefaction), thus the inhibition that realization is disturbed.This moment, the phase modulation (PM) sequence α (n) in formula (7) elected any random series as, and in formula (8)

Also by correspondingly randomization, because the spread spectrum interfering carrier is attenuated N doubly, letter (number) do (disturbing) than corresponding acquisition gain N then.

If to adopting the received signal behind the phase-modulated pulse at random to carry out phase compensation, the signal times that is about to n frequency sweep cycle is with e ^{-ja (n)}, then can recover former disturbance spectrum, realize independent analysis to useful signal and undesired signal.Useful signal is because of being subjected to the random phase modulation by albefaction after phase compensation, and jam-to-signal obtains gain N, helps extracting more accurately interfere information, and this information can be used for subsequent treatment to obtain more excellent system's detection performance.

Key of the present invention is to detect undesired signal in the accumulation doppler spectral in remote unit, and it is anti-interference to realize to select for use suitable manner to carry out phase modulation according to the distribution characteristics of disturbing then.

In typically containing the echo distance-Doppler spectrogram of Radio frequency interference (RFI), useful signal is concentrated and is distributed in the nearer distance element section, intensity increases with distance and reduces, and Radio frequency interference (RFI) is the bright wisp zonal arrangement that is parallel to distance axis in distance-doppler spectral, its intensity is comparatively steady on different distance, therefore, and by rational radar parameter design, a larger distance section can be provided, make not contain useful signal on this distance segment and only contain undesired signal.

Selection obtains disturbance spectrum than carrying out the doppler spectral accumulation between far region.Typical concentrated profile disturbance spectrum wherein disturbs the unimodal form to separate to occur as shown in Figure 2.Typical expansion profile disturbance spectrum disturbs the spectrum district form that then distributes with expansion to occur as shown in Figure 3.By default signal-noise ratio threshold, can detect the existence and the frequency separation thereof of Radio frequency interference (RFI), and judge the distribution pattern of disturbing by interfering frequency length of an interval degree.

After judging the interference profile type, select corresponding pm mode to carry out the setting of scanning frequency pulse initial phase.For pm mode at random, with first phase α (n) (n=0 ... N-1) be made as random series arbitrarily, then it is made as α (n)=2 π Δ fnT for linear pm mode,, then establishes it and be arbitrarily normal value sequence if do not have interference or interference strength less than permissible range.

Modulation phase sequence is compensated, and the signal times that is about to n frequency sweep cycle is with e ^{-ja (n)}, recover disturbance spectrum fully, obtain the accurate information of interference, for follow-up further processing.

The anti-interference work block diagram of phase modulation as shown in Figure 4.Wherein 11 is to transmit, the 12nd, and local oscillation signal, the 13rd, received signal, the 14th, target analysis of spectrum module, the 15th, the disturbance spectrum analysis module, the 16th, pm mode is selected module, and the 17th, the follow-up signal processing module, * represents conjugation.

Claims (2)

1, a kind of anti-RF interference method for high frequency radar is characterized in that:

On the remote unit accumulation doppler spectral of radar collection, detect undesired signal by default signal-noise ratio threshold;

Different scanning frequency pulse phase modulation methods is adopted in the distribution of the Radio frequency interference (RFI) that receives according to higher-frequency radar, realizes anti-interference:

When disturbing when frequency domain be intensive distribution, adopt at random pm mode with in disturbance spectrum albefaction to the average substrate;

When disturbing when frequency domain is sparse distribution, adopt linear pm mode that disturbance spectrum is moved outside the interested spectrum district, recover concealed signal;

When disturb do not exist or its influence little during to admissible degree, adopt the constant phase mode, signal is not made any extra process.

2, the method for claim 1 is characterized in that: modulation phase sequence is compensated, recover disturbance spectrum fully, make the useful signal randomization, reduce to disturb and the influencing each other of useful signal, realize the independent analysis of the two.

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