CN103532656A - Broadband linear frequency-modulated (LFM) signal multi-decoy interference method based on fractional Fourier domain channelization - Google Patents
Broadband linear frequency-modulated (LFM) signal multi-decoy interference method based on fractional Fourier domain channelization Download PDFInfo
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Abstract
The invention relates to a broadband linear frequency-modulated (LFM) signal multi-decoy interference method based on fractional Fourier domain channelization, in particular to an interference method for performing multi-decoy deception on a broadband LFM signal in a pulse on the basis of fractional Fourier domain channelization, and belongs to the technical field of electronic interference. According to the broadband LFM signal multi-decoy interference method based on fractional Fourier domain channelization, all broadband LFM signals can be focused into one channel for outputting by using the energy focusing property of fractional Fourier transform on instable signals, so that the completeness of the signals is ensured, and the problems of reduction of signal energy and distortion of waveforms since the energy of the broadband LFM signals overflow into two or more channels in the conventional Fourier domain channelization are solved; meanwhile, the requirement on the instant bandwidth of a DRFM (Digital Radio Frequency Memory) system is lowered.
Description
Technical Field
The invention relates to a broadband linear frequency modulation signal multi-decoy interference method based on fractional Fourier domain channelization, in particular to an interference method for carrying out multi-decoy deception on a broadband linear frequency modulation signal in a pulse based on fractional Fourier domain channelization, and belongs to the technical field of electronic interference.
Background
In modern Electronic Warfare (EW), radar countermeasure is an important means and guarantee to gain military advantages. Radar countermeasure includes radar reconnaissance and radar interference, which is an important component of radar countermeasure. For an early radar system, the radar waveform is simple, the working frequency range is relatively fixed, and the main interference patterns include aiming type interference, blocking type interference and noise suppression interference. With the rapid development of signal and information processing technology, the new system radar widely adopts various anti-interference technologies, for example, a Linear Frequency Modulation (LFM) signal with a large time-bandwidth product is adopted as a radar transmitting signal, and a pulse compression (matched filtering) technology is adopted at a receiving end, so that the problems of working distance and distance resolution can be well solved, noise interference signals irrelevant to radar signals can be inhibited, and the anti-interference capability of the radar is greatly improved. Therefore, in order to effectively interfere with the chirp signal, a strong coherent interference function is required for the jammer. With the development and maturity of Digital Radio Frequency Memory (DRFM) technology and Direct Digital Synthesis (DDS) technology, reliable technical support is provided for coherent interference. Common coherent interference techniques are delayed interference and frequency shifted interference. The time delay interference is to store the intercepted radar emission signal and forward the signal after a certain time interval. This interference pattern is relatively simple and easy to implement, but produces false targets that all fall behind true targets. The frequency shift interference modulates a Doppler interference signal on the intercepted radar signal by using the special range-Doppler coupling characteristic of the LFM signal, and then the Doppler interference signal is forwarded out. This interference pattern can produce both early and late decoys, but it requires the jammer to operate in the receive-while-transmit state, which puts high demands on the isolation of the jammer's transmit-receive antennas.
In recent years, a new interference pattern, namely intermittent sampling forwarding interference, appears, which is to sample and store a small section of a received LFM signal and then forward the signal immediately, sample and store the next section after the forwarding is finished, and sample, store and forward the signal in a time-sharing and alternative mode until the signal is finished. Intermittent sampling can well solve the problem that a false target lags too much when full pulse storage and forwarding interference occurs, high isolation of a transmitting antenna and a receiving antenna can be guaranteed, and DRFM is required to have a large frequency coverage range for LFM signals with wide bandwidth. To reduce the storage requirements of DRFM, interference systems employ digital channelization techniques that band divide the input full-band signal into multiple sub-band signals and then process each sub-band. But conventional fourier-domain channelization can spill the energy of the wideband LFM signal over multiple channels and even lose a portion of the interfering signal. How to solve the interference problem of the broadband linear frequency modulation signal, ensure the rapid generation of the interference signal and obtain the effective interference effect is the key point of the research at the present stage.
Disclosure of Invention
The invention provides a broadband linear frequency modulation signal multi-decoy interference method based on fractional Fourier domain channelization aiming at interference of a broadband linear frequency modulation signal in a dense signal environment on the basis of intermittent sampling and forwarding interference.
The purpose of the invention is realized by the following technical scheme.
The invention discloses a broadband linear frequency modulation signal multi-decoy interference method based on fractional Fourier domain channelization, which comprises the steps of firstly selecting a fractional Fourier domain channelized transformation order p (p = -2arccot (2 pi mu)/pi) according to a frequency modulation rate mu of a linear frequency modulation radar signal (if the mu is known, directly determining the transformation order; if the mu is unknown, estimating the mu in advance by adopting a mature algorithm) and a counterclockwise rotation angle alpha (alpha = pi/2) of a fractional Fourier domain relative to the Fourier domain, establishing a fractional Fourier domain channelized structure, and determining the number of channelsK (in order to use a Fast Fourier Transform (FFT) algorithm, the channel number K is a power of 2, the number of decoys is related to K, K takes a small number of decoys, and takes a large number of decoys, so that the value of K depends on the interference requirement), a factor M (K = FM, F is a scaling factor, and F takes a value of 1 or 2; an efficient structure of complex signal channelization is performed under the condition of critical sampling, usually F =1, and then K = M), and a high-speed analog-to-digital converter (ADC) at the receiving end of the radar jammer samples the radar transmission signal at a frequency FsSampling interval of Δ t =1/fs；
The method comprises the following steps:
step one, according to the frequency modulation rate mu of an LFM signal x (n) transmitted by a radar, selecting the transformation order p of a fractional Fourier domain and the anticlockwise rotation angle alpha (alpha = p pi/2) of the fractional Fourier domain relative to the Fourier domain, and constructing a fractional Fourier domain filter bank { h } hk,p(n)}k=0,1,…K-1；
WhereinIs a conventional band-pass filter bank in the fourier domain,
k is the number of channels, and K is the power of 2; n is the number of points of the filter; Δ t is the sampling interval, Δ t =1/fs，fsIs the sampling frequency;
p = -2arccot (2 pi mu)/pi; if mu is known, directly determining the transformation order; if mu is unknown, mu can be estimated in advance by adopting a mature algorithm;
step two, starting a receiving module of the jammer, and intermittently sampling the intercepted radar signal x (n), wherein a sampling gate function is p (n), and the method comprises the following steps:
and closing the receiving module after sampling is completed. The sampled signal is s (n)
Wherein k is' is discrete number of points, and takes values from 0 to N1Natural number in (1); p (N) is of width N1Repetition interval of N2Periodic square wave sequence (to get multiple realistic decoy interference, N)2The value range of (1/B) to (T/2) fsB is the bandwidth of the radar pulse signal, T is the repetition period of the radar pulse signal), and the duty ratio of the periodic sequence isp (N) width N1The larger the value is, the number of false targets formed by the interference signal after pulse compression is less; n is a radical of1The processing gain obtained after the interference signal is subjected to pulse compression is small, and N is selected in a compromise mode1Is usually taken as N 21/4, 1/6, 1/8; r is the number of cycles of p (n);
step three, using the fractional order Fourier domain filter bank { h) obtained in the step onek,p(n)}k=0,1,…K-1Performing fractional Fourier domain filtering on the signal s (n) obtained by intermittent sampling in the second step, and performing extraction on the output of each subchannel by M times to obtain the output signal of each subchannel channelized in the fractional Fourier domain
Wherein,
representing a convolution over the p-order fractional fourier domain,
represents a convolution over the fourier domain;
k = FM, F is a scale factor, and F takes the value of 1 or 2; f =1 is usually taken, then K = M;
fourthly, performing channel detection on the output signals of the K channels in the third step by utilizing an autocorrelation accumulation algorithm, wherein the method comprises the following steps: output signal for each channelRespectively selecting N points for autocorrelation accumulation (the value range of N is generally 16-128), and obtaining a signal zk,p(m)|k=0,1...K-1
Wherein i is a natural number from 0 to N-1;
then according to the selected threshold TH, making threshold decision for K channels, if the self-correlation accumulation z of the K channelk,p(m) if the module value has continuous D points which are larger than the threshold TH (D is about 50 generally), judging that the channel has signal output, and recording a channel number k; otherwise, the channel is considered to have no signal output.
The threshold TH is according to TH = μ1+ξσ1Calculated where ξ is the given constant false alarm probability PfaA determined threshold coefficient, wherein <math><mrow>
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</mrow></math> N is the number of points of autocorrelation accumulation, σ2The noise power is determined by the bandwidth of the receiving end of the radar jammer;
step five, according to the channel number k determined in the step four, outputting the signal for the fractional Fourier domain channelizing
Performing M times zero value interpolation to obtain a signal yk,p(m)：
Step six, the signal y after the interpolation in the step five is finishedk,p(m) amplitude modulation is performed, the modulation coefficient is C, and an interference signal J (m):
J(m)=C·yk,p(m) （7）
because the amplitude of the signal spectrum obtained by performing extraction under the condition of M times in the third step is reduced to 1/M times before extraction, C is required to be larger than or equal to M to form effective deceptive interference. The larger interference signal obtained by C is easy to identify, the smaller interference signal can not achieve good interference effect, and the compromise selection C generally adopts 1.2-1.5M;
step seven, converting the signal J (m) modulated in the step six into an analog interference signal after passing through a high-speed digital-to-analog converter (DAC), starting an interference machine sending module, and increasing the transmitting power of the interference machine to forward the interference signal out through a transmitting antenna;
and step eight, closing the sending module and simultaneously opening the receiving module after the forwarding is finished, immediately turning to step two, and carrying out subsequent step processing on the next radar transmission pulse signal until the radar pulse signal is not received any more.
Advantageous effects
The broadband LFM signal multi-decoy interference method based on fractional Fourier domain channelization provided by the invention utilizes the energy focusing property of fractional Fourier transform on non-stationary signals, can focus broadband linear frequency modulation signals into one channel for output, ensures the integrity of the signals, and well solves the problems that the energy of the broadband LFM signals overflows into two or more channels in the traditional Fourier domain channelization, so that the energy of the signals is weakened and the waveform is distorted; meanwhile, the instantaneous bandwidth requirement of the DRFM system is reduced;
the broadband LFM signal multi-decoy interference method based on fractional Fourier domain channelization provided by the invention attacks the radar by utilizing intra-pulse coherence of a sub-band signal, so that the radar is subjected to a plurality of highly realistic decoy interferences; meanwhile, the intermittent sampling technology adopted by the interference method well solves the problems of short-distance interference of large-time wide signals and receiving and transmitting isolation of an interference machine, and effectively shortens the response time of the interference machine;
the broadband LFM signal multi-decoy interference method based on fractional Fourier domain channelization provided by the invention can interfere the signal with the highest threat level in a plurality of simultaneously arriving linear frequency modulation signals in a dense signal environment, and the pertinence of the interference is strong.
Fractional Fourier domain channelization is based on the focusing performance of fractional Fourier transform on non-stationary signals, can focus broadband linear frequency modulation signals into one channel for output, well solves the problem of energy overflow caused by spanning multiple channels in the traditional Fourier domain channelization, and ensures the integrity of interference signals and the pertinence of interference. Because of the conversion of the sampling rate, the output signal contains a plurality of sub-band signals, the sub-band signals well keep partial correlation characteristics with radar transmission signals, and certain processing gain can be obtained after matched filtering. And performing zero value interpolation on the output signal subjected to the fractional Fourier domain channelization, and introducing image frequency shift to obtain a leading decoy and a lagging decoy. The intermittent sampling technology better solves the problems of too much lag of a false target and poor coherence when the front edge is copied and interfered during full-pulse store-and-forward interference, effectively shortens the response time of an interference machine, and simultaneously solves the problem of insufficient isolation of a receiving and transmitting antenna. The interference method not only can cover a large frequency range, but also can form a plurality of false targets with higher fidelity.
Drawings
FIG. 1 is a block diagram of a fractional Fourier domain channelized prototype architecture;
FIG. 2-schematic diagram of the intermittent sampling process;
FIG. 3-a schematic diagram of fractional Fourier domain filtering;
FIG. 4-image frequency shift interference schematic;
FIG. 5 is a flow chart of an intra-pulse multi-decoy interference method based on fractional Fourier domain channelization;
FIG. 6 is a system diagram of an intra-pulse multi-decoy interference method based on fractional Fourier domain channelization;
fig. 7 — (a) a conventional channelized output signal time-domain waveform (b) a fractional fourier-domain channelized output signal time-domain waveform;
FIG. 8-short-time spectrogram of a fractional Fourier domain channelized output signal;
FIG. 9- (a) p1Time domain waveform (b) p of order output signal2Outputting a signal time domain waveform in an order;
figure 10- (a) B =200MHz interference effect graph (B) B =400MHz interference effect graph;
fig. 11- (a) 8-channel channelization interference effect diagram (b) 16-channel channelization interference effect diagram.
Detailed Description
The invention is further illustrated with reference to the following figures and examples.
Examples
As shown in fig. 1, a flowchart of an intra-pulse multi-decoy interference method based on fractional fourier domain channelization according to an embodiment of the present invention is shown in fig. 5, and a system block diagram thereof is shown in fig. 6. Firstly, determining a fractional Fourier domain channelized transformation order p and a counterclockwise rotation angle alpha of a fractional Fourier domain where the fractional Fourier domain is located relative to a Fourier domain according to a frequency modulation rate mu of a radar pulse signal x (n), establishing a fractional Fourier domain channelized structure, wherein the channel number is K, an extraction factor is M, and a traditional low-pass filter h with a passband cut-off frequency of pi/K and a transition band cut-off frequency of 2 pi/K is selected0(n) a fractional fourier domain channelized low-pass prototype filter; secondly, determining the width N of the sampling wave gate function according to the interference requirement1And repetition interval N of intermittent sampling2Intermittently sampling the intercepted radar pulse signals; as shown in fig. 2, the intermittently sampled signals are channelized in the fractional fourier domain by extracting M times the number of K channels, the output of each channel is autocorrelation-accumulated after the channelization is completed, the channel number K with signal output is determined, andstoring the output signal of the kth channel as a radar sample signal; then, performing M-time zero value interpolation on the stored radar sample signal, and performing interference modulation (namely amplitude modulation) after the interpolation is completed so as to obtain a better interference effect; and finally, converting the modulated signal into an analog interference signal through a high-speed DAC, improving the transmitting power of the radar jammer and forwarding the interference signal.
On the basis, the method comprises the following specific implementation steps:
determining the transformation order p of a fractional Fourier domain and the anticlockwise rotation angle alpha of the fractional Fourier domain in which the fractional Fourier domain is positioned relative to the Fourier domain according to the frequency modulation rate mu of an intercepted radar pulse signal x (n), and constructing a fractional filter bank { h shown in a formula (1)k,p(n)}k=0,1,…K-1；
(II) according to a sampling gate function p (n) shown in a formula (2), intermittently sampling the intercepted radar pulse signal x (n) to obtain an output signal s (n) shown in a formula (3), and closing a receiving module after sampling is completed;
(III) using the fractional order domain filter bank { h) obtained in the step (I)k,p(n)}k=0,1,…K-1Fractional order domain filtering is carried out on the signal s (n) obtained in the step (II), and the filtering result of each sub-channel is extracted under M times, so that the output signal of each sub-channel after fractional order Fourier domain channelization is obtained
(IV) output of each channel in the step (III)
Selecting N points to perform autocorrelation accumulation for channel detection to obtain output z shown as formula (5)k,p(m)|k=0,1...K-1If z isk,p(m)|k=0,1...K-1If D continuous modulus values exceed the threshold value, the signal in the channel is judgedOutputting signals, otherwise, outputting no signals;
fifthly, according to the channel judgment in the step four, carrying out M-time zero value interpolation on the output signal after the fractional Fourier domain channelization to obtain an output signal y shown in the formula (6)k,p(m)；
Sixthly, the signal y obtained in the step (five) is subjected tok,p(m) carrying out interference modulation (namely amplitude modulation), and obtaining an output signal J (m) shown as a formula (7) after modulation is finished;
seventhly, converting the signals J (m) obtained in the step six into analog interference signals after passing through a high-speed DAC, starting a sending module, increasing the transmitting power of the radar jammer, forwarding the analog interference signals, closing the sending module after the forwarding is finished, and simultaneously starting a receiving module;
and (eighthly), turning to the step (II), and carrying out the step processing on the next radar pulse signal until the radar pulse signal is not received any more.
Some theoretical explanations are made below for the intra-pulse multi-decoy interference method based on fractional fourier domain channelization.
Suppose that two wideband LFM signals x are received simultaneously by jammers1(n) and x2(n)，
μ1、μ2To the frequency modulation, f1、f2Is the starting frequency. To ensure the pertinence of interference, first, mixed signal x (n) = x1(n)+x2(n) fractional-domain filtering is performed, the principle of which is shown in fig. 3. If it is desired to pair signal x1(n) interfering with each other, selecting x1(n) corresponding focusing order p1Establishing a fractional Fourier domain channelized structure wherein
The mixed signal x (n) passing through p1Fractional order Fourier domain M channel filter bank of order, output in mth filterFrom fractional convolution one can obtain:
will cot alpha1=-2πμ1Andcan be substituted by the formula (9):
hm(n) is an ideal band-pass filter with amplitude-frequency response of Hm(ejω) And is and
if f1At hmIn the frequency band of (n) and f2Otherwise, the band characteristic of the filter is known
Suppose that
Is a Discrete Time Fourier Transform (DTFT) of U (e)jω) Is known to
Has a DTFT of delta (omega-2 pi f)1) From the properties of DTFT, it can be seen that:
conversion into the time domain yields:
from the formula (14), in p1Order, x1(n) is focused to the output in the mth channel, and x2(n) no focusing at this order. Thus, x2(n) output in other channels and may span multiple channels, as shown in fig. 3 (a). Similarly, if the signal x is to be compared2(n) interference, selectionFractional Fourier domain channelized focal order of p2That is, the filtering result is shown in fig. 3 (b).
Extracting the filtered output signal by M times to obtain
Namely, it is
as can be seen from equation (16), after M-fold decimation, the spectrum of the resulting signal is equivalent to that of signal x1And (n) performing M-fold expansion on the frequency spectrum, performing frequency shift of 2 pi l/M (l =0,1.. times.M-1) on an omega axis, and then performing superposition output.
Let the sampling rate of the ADC be fsAfter M times of extraction, the sampling rate of the output signal of each channel is reduced to fsWhere the bandwidth of LFM signal transmitted by radar is B, 2B usually appears>fsand/M, does not satisfy the Nyquist bandpass sampling theorem. Thus, the wideband LFM signal is focused into one channel output after fractional fourier domain channelization, and the output signal is undersampled with its spectrum aliased. Since the filter bank is uniformly divided over the entire monitoring band, the maximum bandwidth of the output signal per channel is fsand/M, thereby enabling a reduction in the instantaneous bandwidth requirements of the storage system.
After the fractional Fourier domain channelization, the output signal of the mth channel is
To pairPerform zero value interpolation, assuming
Is obtained by M times interpolationNamely:
as can be seen from the formula (18),spectrum ofM spectral samples are contained in (0 · 2 π), one of which is
The spectral samples are compressed by a factor of M along the frequency axis, and the remaining M-1 are the mirror images of the compressed spectrum. Thus, pair
After the zero value interpolation of M times, the frequency spectrum is firstly compressed by M times, and the frequency range of the mth channel after compression is (M-1) fs/M～mfs(ii)/M as shown in FIG. 4(a), and fswhere/M is the period extension to both sides of the period, as shown in FIG. 4 (b).
As is clear from the formulae (16) and (18),
is converted into a time domain representation of
As can be seen from the formula (20),
can be seen as pair x1And (n) performing frequency shift for multiple times and then performing superposition output. Assuming that the first frequency shift amount is fl(fl=lfs/M) according to the frequency-shift interference principle, when the frequency shift amount is larger than the bandwidth of the LFM signal, i.e. fl>B, the matched filter will not produce any output because of severe mismatch, so the range of l is
Since the mirror image has symmetry, the number of false targets generated is
Indicating a rounding down. When f islWhen =0, i.e. l =0, the pulse pressure output has a main peak at the end of the pulse, also called a main false target; when f islWhen not equal to 0, the first false target is generated. Because the frequency shift and the time delay of the linear frequency modulation signal have strong coupling, the time domain interval between the first-time false target and the main false target is tl：
The distance between the first-time false target and the main false target in the distance direction is (c is the speed of light):
the time domain interval between adjacent decoys is Δ t:
the distance between adjacent false targets in the distance direction is as follows:
the distance-wise resolution of the wideband LFM signal after pulse compression is assumed to be
If Δ R<Rho, the real target is submerged in the false target, and the pressing type interference can be formed; if Δ R>P, the inability to effectively distinguish between real and false objects, will formFraudulent interference. In addition, zero interpolation produces image frequency shift quantities that are positive or negative. Thus, the zero-valued interpolation technique may produce both secondary decoys that lead the primary decoys and secondary decoys that lag the primary decoys.
The following simulation division is carried out on the intra-pulse multi-decoy interference method based on fractional Fourier domain channelization
And (3) analysis:
(1) setting simulation parameters: time domain sampling frequency fs=1.2GHz, starting frequency f of the chirp signal0=120MHz, bandwidth B =400MHz, pulse width T =80 μ s. The signal is analyzed using conventional fourier domain channelization with 8 channels 8 extraction and fractional fourier domain channelization, respectively. After the signal is subjected to the conventional fourier domain channelization, the energy of the signal overflows into the 2 nd, 3 rd, 4 th and 5 th channels, and the output signal of each channel has different degrees of attenuation, as shown in fig. 7 (a). After the fractional Fourier domain channelization, the signal is focused to the 2 nd channel for output, so that the overflow of energy is well inhibited, and the integrity of an interference signal is ensured, as shown in FIG. 7 (b). The fractional fourier domain channelized output signal is time-frequency analyzed using a Short Time Fourier Transform (STFT), as shown in fig. 8. As can be seen from fig. 8, after the broadband chirp signal transmitted by the radar is channelized in the fractional fourier domain, the output signal includes a plurality of subband signals, and each subband signal well maintains coherence with the signal transmitted by the radar.
(2) Setting simulation parameters: time domain sampling frequency fs=1.2GHz, chirp signal x1(n)、x2(n) starting frequencies of f1=120MHz、f2=60 MHz. Bandwidth is respectively B1=400MHz、B2=160MHz, pulse width T1、T2All 80. mu.s. The fractional fourier domain channelization with 8 channels and 8 extractions was used for reception, and the simulation results are shown in fig. 9. As can be seen in FIG. 9, to perturb one of the LFM signals, the focusing order of the signal is selected to construct a fractional Fourier transformThe domain channelizes, the signal will be focused in one channel to ensure signal integrity and interference pertinence, while another LFM signal will be output across multiple channels, each with different degrees of attenuation.
(3) Setting simulation parameters: time domain sampling frequency fs=1.2GHz, starting frequency f of the chirp signal0The signal with bandwidth B =200MHz and bandwidth B =400MHz were simulated by receiving with 8 channels and 8 decimated fractional fourier domain channelization =120MHz and pulse width T =80 μ s, respectively, and the interference effect is shown in fig. 10.
(4) Setting simulation parameters: time domain sampling frequency fs=1.2GHz, starting frequency f of the chirp signal0=120MHz, bandwidth B =400MHz, pulse width T =80 μ s, and reception is performed by fractional fourier domain channelization using 8-channel 8 decimation and 16-channel 16 decimation, respectively, and the interference effect is shown in fig. 11.
As can be seen from fig. 10 and 11, the number of decoys generated by the interference technique is related to the bandwidth of the chirp signal transmitted by the radar and the number of channels channelized in the fractional fourier domain, and the wider the bandwidth of the signal, the more the number of channels channelized in the fractional fourier domain, the more the number of decoys generated, the smaller the interval between adjacent decoys and the closer the amplitude, and the better the interference effect of the spoofing. Therefore, the interference technique can not only cover a wide frequency band range, but also control the position and number of decoys by changing the number of channels.
Claims (5)
1. The broadband linear frequency modulation signal multi-decoy interference method based on fractional Fourier domain channelization is characterized by comprising the following steps of:
step one, selecting a transformation order p of a fractional Fourier domain and a counterclockwise rotation angle alpha, alpha = p pi/2 of the fractional Fourier domain relative to the Fourier domain according to a frequency modulation rate mu of a linear frequency modulation signal x (n) transmitted by a radar, and constructing a fractional Fourier domain filter bank { hk,p(n)}k=0,1,…K-1；
Wherein
Is a conventional band-pass filter bank in the fourier domain,
a high pass filter in the conventional fourier domain; h isk(n)=h0(n) is a low pass filter of the conventional fourier domain;
k is the number of channels, and K is the power of 2; Δ t is the sampling interval, Δ t =1/fs，fsIs the sampling frequency; p = -2arccot (2 pi mu)/pi;
step two, starting a receiving module of the jammer, and intermittently sampling the intercepted radar signal x (n), wherein a sampling gate function is p (n), and the method comprises the following steps:
closing the receiving module after sampling is completed; the sampled signal is s (n)
Wherein k' is discrete number of points and takes the value from 0 to N1Natural number in (1); p (N) is of width N1Repetition interval of N2Periodic square wave sequence of (2), N2Has a value range of (1/B-T/2) fsB is the bandwidth of the radar pulse signal, T is the repetition period of the radar pulse signal, and the duty ratio of the periodic sequence is
r is the number of cycles of p (n);
step three, using the fractional order Fourier domain filter bank { h) obtained in the step onek,p(n)}k=0,1,…K-1Performing fractional Fourier domain filtering on the signal s (n) obtained by intermittent sampling in the second step, and performing extraction on the output of each subchannel by M times to obtain the output signal of each subchannel channelized in the fractional Fourier domain
Wherein,
representing a convolution over the p-order fractional fourier domain,
represents a convolution over the fourier domain;
k = F.M, F is a scale factor, and F takes the value of 1 or 2;
fourthly, performing channel detection on the output signals of the K channels in the third step by utilizing an autocorrelation accumulation algorithm, wherein the method comprises the following steps: output signal for each channel
Respectively selecting N points to perform autocorrelation accumulation to obtain a signal zk,p(m)|k=0,1...K-1
Wherein i is a natural number from 0 to N-1;
then according to the selected threshold TH, making threshold decision for K channels, if the self-correlation accumulation z of the K channelk,p(m) if D continuous points of the module value are larger than the threshold TH, judging that the channel has signal output, and recording a channel number k; otherwise, the channel is considered to have no signal output;
the threshold TH is according to TH = μ1+ξσ1Calculated where ξ is the given constant false alarm probability PfaA determined threshold coefficient, wherein
N is the number of points of autocorrelation accumulation, σ2The noise power is determined by the bandwidth of the receiving end of the radar jammer;
step five, according to the channel number k determined in the step four, outputting the signal for the fractional Fourier domain channelizingPerforming M times zero value interpolation to obtain a signal yk,p(m)：
Step six, the signal y after the interpolation in the step five is finishedk,p(m) amplitude modulation is performed, the modulation coefficient is C, and an interference signal J (m):
J(m)=C·yk,p(m) （7）
c is greater than or equal to M;
step seven, converting the signal J (m) after modulation in the step six into an analog interference signal through a high-speed digital-to-analog converter, starting an interference machine sending module, and forwarding the interference signal out through a transmitting antenna by the sending module;
and step eight, closing the sending module and simultaneously opening the receiving module after the forwarding is finished, turning to step two, and carrying out subsequent step processing on the next radar transmission pulse signal until the radar pulse signal is not received any more.
2. The fractional fourier domain channelization based wideband chirp signal multi-decoy interference method of claim 1, wherein: n in step III1Is N21/4-, 1/6-or 1/8-fold.
3. The fractional fourier domain channelization based wideband chirp signal multi-decoy interference method of claim 1, wherein: and the value range of N in the fourth step is 16-128.
4. The fractional fourier domain channelization based wideband chirp signal multi-decoy interference method of claim 1, wherein: and taking 50 from D in the fourth step.
5. The fractional fourier domain channelization based wideband chirp signal multi-decoy interference method of claim 1, wherein: and step six, taking 1.2-1.5M.
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