CN105223553A - A kind of half frequency range matched filtering realizes shift-frequency jamming recognition methods - Google Patents

Abstract

A half-bandwidth matching filter to realize frequency shift interference identification method, which has four major steps: 1. Preprocess the signal received by the radar, and divide it into three channels before matching filter; 2. Pass the three channels of signal through the complete matched filter, and extract the peak value of each matched filter output voltage; 3. Set the threshold; 4. According to the ratio of the matching output peak value of the target under different matched filters and combined with the set threshold to determine whether the target is a false target for frequency shift interference . The present invention overcomes the drawbacks of the frequency-shift measurement method, where the jammer controls the center frequency of the jamming signal, resulting in failure to recognize the frequency-shift jamming, and can realize the detection and recognition of the active pilot false target jamming; the present invention has fewer implementation steps and a small amount of calculation, It can satisfy the radar's real-time recognition of multiple targets, and has no additional requirements on the hardware system, and is easy to implement in engineering.

Description

A Half-bandwidth Matched Filter Realization Method for Frequency-Shifting Interference Identification

technical field

The invention belongs to the field of radar anti-jamming, relates to radar jamming false target recognition technology, and more specifically provides a half-band width matching filter to realize frequency-shifting jamming recognition method for linear frequency modulation radar.

Background technique

Linear frequency modulation signal (also known as chirp signal abroad) is a kind of pulse compression signal which is the earliest researched and most widely used. However, the chirp radar, which has many advantages such as large operating distance and high resolution, is extremely vulnerable to frequency shift interference. Immediately after detecting the signal, the frequency-shifting jamming technology will be used to generate long-distance realistic false targets in front of and behind itself, making it difficult for the radar to identify the real target. The target group will greatly consume radar resources. The major survival challenge faced by LFM radar makes it of great military application value to seek real-time and effective frequency shift jamming false target identification method.

There are two main methods for identifying false targets of frequency-shifted jamming in existing radars: frequency-shift measurement method and fractional Fourier transform method (FRFT). The frequency shift measurement method uses the digital receiver processing technology to calculate the center frequency of the echo signal, and calculates the frequency shift amount of the interference signal from the center frequency, so as to judge whether the target is a false target of frequency shift interference. The disadvantage of this method is that it assumes that the frequency-shifted interference signal has the same time width and bandwidth as the real target echo, and the jammer can completely change the time width and bandwidth of the forwarded interference signal by using DRFM technology, and control the center of the interference signal. Frequency, to ensure that it is the same as the target echo signal, so that the frequency shift measurement method is invalid. The fractional Fourier transform method combines the fractional Fourier transform with the matching results in the radar receiver, and uses the target speed information estimated by the fractional Fourier transform and the distance information obtained by pulse compression to identify the frequency-shifted jamming false target launched by the jammer . However, in practical applications, this method requires a lot of searching work for the optimal FRFT rotation angle, which affects the timeliness of false target recognition. In summary, the current frequency-shifting jamming false target recognition methods have their own shortcomings and shortcomings, and there is no effective frequency-shifting jamming false target recognition method applied to chirp radar.

Contents of the invention

The purpose of the present invention is to enable the radar to effectively identify false targets generated by frequency-shifting interference, and provide support for subsequent anti-jamming means, which is also an important key point (false target recognition) in radar anti-frequency-shifting interference. The technical problem to be solved by the present invention is: using the difference in frequency characteristics between the target echo signal, the frequency-shifted interference signal and the matched filter, using the method of combining half-bandwidth matching and full matching, comparing the received signal of the radar through half-frequency The ratio of the output peak of the wide matched filter to the fully matched filter, under ideal conditions, the ratio will guarantee a strict For frequency shift interference, the ratio will be greater or less than According to this difference, the rapid identification of false targets in the distance of frequency shift interference can be realized.

The technical solution of the present invention is: a half-bandwidth matched filter realizes a frequency-shifting interference identification method, which comprises the following steps:

Step 1: Preprocess the signal received by the radar, and divide it into three paths before matching filtering.

First, pre-process the signal received by the radar receiver, such as filtering and low-noise amplification, and then divide the received radar signal into three paths, so that matching filtering can be performed separately, and the peak value can be extracted and compared to identify whether the target is a fake. Target.

Step 2: Pass the three signals through the complete matched filter, and extract the peak value of the output voltage of each matched filter.

The left and right half-bandwidth matched filters are respectively close to the low and high frequency sides of the fully matched filter in the frequency domain, and the width is half of the fully matched filter. Assuming that the linear frequency modulation signal x(t), the bandwidth is B, and the pulse width is T, then the impulse response of its complete matched filter and left and right half-bandwidth matched filter is:

h ₀ (t)＝kx ^* (t ₀ -t),-T/2≤t＜T/2

h _L (t)＝kx ^* (t ₀ -t), -T/2≤t＜0 (Formula 1)

h _R (t)＝kx ^* (t ₀ -t), 0≤t＜T/2

Among them, "*" represents the conjugate, t ₀ is the peak moment of the matched filter output, and k is the normalization coefficient.

The frequency domain and time domain expressions of the chirp signal x(t) output through the three matched filters h ₀ (t), h _L (t), h _R (t) are:

Y ₀ (f)=X(f)H ₀ (f)

Y _L (f)=X(f)H _L (f) (Formula 2)

Y _R (f)=X(f)H _R (f)

And perform Fourier inverse transform on the result of formula 2 to calculate the signal matching output peak value:

(Formula 3)

Let the matching output peaks be y _{0max ,} y _{Lmax , and} y _Rmax respectively, where y _xmax =max(|y _x (t)|).

Step 3: Set the threshold.

Consider the mismatch caused by the Doppler frequency shift f _d =2v _max /λ=2v _max f ₀ /c brought by the target speed, and determine the threshold:

(Formula 4)

Among them, v _max is the maximum velocity of the radar-measurable target, λ is the wavelength of the radar transmission signal, f ₀ is the carrier frequency of the radar transmission signal, c is the speed of light, B is the frequency modulation signal bandwidth of the radar transmission, f _d is the Doppler frequency brought by the target speed Le frequency shift, n _cl and n _cr are the left and right thresholds.

Step 4: According to the matching output peak ratio of the target under different matched filters and combined with the set threshold, determine whether the target is a false target of frequency shift interference.

H ₀ : and The target is the true target;

H ₁ : or or or The target is a false target.

Beneficial effects of the present invention:

1. The start and end frequency characteristics of the frequency-shifting interference signal are skillfully used, and the process of identifying false targets is not affected by the center frequency of the frequency-shifting interference signal. The method effectively overcomes the drawbacks of the frequency shift measurement method, in which the jammer controls the center frequency of the jamming signal, resulting in failure to identify the frequency shift jamming.

2. It has a wide range of applications and can identify false targets of various jamming systems. The invention can identify false targets with multiple ranges generated by the range-Doppler coupling characteristics of linear frequency modulation signals such as intermittent sampling forwarding interference and frequency shifting interference.

Third, it makes up for the lack of radar frontier tracking and anti-jamming methods, and can realize the detection and identification of false target jamming with active guidance;

4. It can satisfy the real-time recognition of multiple targets by radar. The invention involves few realization steps, small amount of calculation, and is easy for engineering realization. Theoretically, a single signal echo can be used to determine the authenticity of the target, saving radar space-time resources, high efficiency and fast speed, and can meet the real-time recognition of multiple targets by radar.

Description of drawings

Fig. 1 is the overall flowchart of the false target recognition method that the present invention proposes;

Fig. 2 is a design block diagram of the frequency shift interference false target identification system proposed by the present invention;

Fig. 3 is each matched filter that the present invention proposes and the schematic diagram of radar received signal frequency spectrum; Among the figure, B is bandwidth, f is frequency, H ₀ (f), H _L (f), _HR (f) are complete Matched filter and the left and right half-bandwidth matched filter designed by the present invention;

Fig. 4 (a) is to utilize the present invention to carry out the comparative schematic diagram of the magnitude of the interference signal and the echo signal after the fully matched filter;

Fig. 4(b) is a schematic diagram of the amplitude comparison of the interference signal and the echo signal after passing through the left half-bandwidth matched filter in the simulation experiment performed by the present invention.

Fig. 4(c) is a schematic diagram of the amplitude comparison of the interference signal and the echo signal after passing through the right half-bandwidth matched filter in the simulation experiment performed by the present invention.

detailed description

Fig. 1, Fig. 2 are the overall flowchart of the false target identification method proposed by the present invention and the design block diagram of the false target identification system for radar chirp signal frequency shift interference.

The simulation experiment is based on a general-purpose computer and implemented on a Matlab simulation platform. The simulation parameters are set as follows: radar transmission signal pulse width T = 50us, bandwidth B = 10MHz, carrier frequency f ₀ = 3000MHz, interference frequency shift f _dj = -1Mhz, -3MHz , the leading distance of the false target generated at this time is 750m, 2250m.

A half-bandwidth matched filter of the present invention realizes a frequency shifting interference identification method, and the specific steps of the method are as follows:

Step 1: First, pre-process the signal received by the radar receiver, such as filtering and low-noise amplification, and then divide the received radar signal into three paths, so that matching filtering can be performed separately afterwards.

Here, the spectral relationship of the fully matched filter H ₀ (f) and the left and right half-bandwidth matched filters H _L (f) and _HR (f) is shown in Fig. 3 . Fig. 3 is each matched filter that the present invention proposes and involved radar received signal spectrum relation, can find out from this spectrum relation figure when target echo signal X (f) passes through H _L (f), _HR (f) The ratio of the peak value of the final output signal to the peak value of the output of X(f) through the complete matched filter will remain strictly (When the frequency shift caused by noise and target speed is not considered, it should be considered in practical applications), and the frequency shift interference signal X _J (f) passes through H _L (f) or _HR (f) and the output signal peak value is the same as X( f) The ratio of the output peaks passing through the complete matched filter H ₀ (f) will be greater or less than This is the basis for the present invention to identify false targets for frequency shift interference.

Step 2: Perform matched filter processing on the three signals respectively, and obtain the output peak value of the matched filter.

After the radar receiving signal is preprocessed, it passes through the complete matched filter H ₀ (f), the left half-frequency matched filter H _L (f), and the right half-frequency matched filter H _R (f), to obtain the matched output peak value y ₀ , y _L , y _R .

Step 3: Set the threshold.

Assuming that the maximum radial velocity _vmax of the target measured by the radar is 3400m/s (10 times the speed of sound), the Doppler frequency shift caused by the target velocity is _fd = 68kHz (it can be seen that the mismatch caused by the target velocity is very limited), considering Environmental factors such as noise can slightly relax the threshold, here the threshold is set to n _cl =49.0%, n _cr =51.0%.

Step 4: According to the matching output peak ratio of the target under different matched filters and combined with the set threshold to judge whether the target is true or false.

Will Compared with n _cl and n _cr , if H ₀ holds true, the target is determined to be a true target, otherwise it is a false target (as shown in Figure 2). In order to clearly clarify the false target recognition effect of the present invention, on the premise of not affecting the correctness of the simulation, it is assumed that the output peak values of the radar receiving signal through H ₀ (f), H _L (f) and H ₀ (f) are 1, see Figure 4(a), and use this peak value to normalize the corresponding target output peak values of H _L (f) and H ₀ (f). It can be seen from Figure 4(b) that the ratio of the target echo amplitude after passing through H _L (f) and H ₀ (f) is about However, the ratio of the frequency-shifted interference signal is no longer kept less than are about 44.4% and 28.6% respectively; similarly as shown in Figure 4(c), the ratios are about 55.6% and 72.4% after the frequency-shifting interference signal passes through _HR (f), which are far beyond the set thresholds n _cl and n _cr , it can be judged as a false target, and the identification of false targets for frequency shift interference is realized.

Claims (1)

1. A half-bandwidth matched filter realizes frequency-shifting interference identification method, is characterized in that: it comprises the following steps: Step 1: Preprocess the signal received by the radar, and divide it into three paths before matching filtering; Firstly, the signal received by the radar receiver is pre-processed by filtering and low-noise amplification, and then the received radar signal is divided into three paths, so that the matching filter is performed separately, and the peak value is extracted and compared to identify whether the target is a false target; Step 2: Pass the three-way signal through the complete matched filter, and extract the peak value of the output voltage of each matched filter; The left and right half-bandwidth matched filters are respectively perfectly matched filters in the frequency domain, which are close to the low and high frequency sides, and the width is half of the fully matched filter. Let the chirp signal x(t) have a bandwidth of B, and the pulse The width is T, then the impulse response of its fully matched filter and left and right half-bandwidth matched filter is: h ₀ (t)＝kx ^* (t ₀ -t),-T/2≤t＜T/2 h _L (t)＝kx ^* (t ₀ -t), -T/2≤t＜0 (Formula 1) h _R (t)＝kx ^* (t ₀ -t), 0≤t＜T/2 Among them, "*" represents the conjugate, t ₀ is the peak moment of the matched filter output, and k is the normalization coefficient; The frequency domain and time domain expressions of the chirp signal x(t) output through the three matched filters h ₀ (t), h _L (t), h _R (t) are: Y ₀ (f)=X(f)H ₀ (f) Y _L (f)=X(f)H _L (f) (Formula 2) Y _R (f)=X(f)H _R (f) And perform Fourier inverse transform on the result of formula 2 to calculate the signal matching output peak value: $<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>{<span\; class="notranslate">\; \&Integral;</span>}_{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&infin;</span>}}^{\mathrm{<span\; class="notranslate">\; \&infin;</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; |</span>$ $\left|{\mathrm{the\; y}}_L\left(t\right)\right|=\left|{\&Integral;}_{-\mathrm{\&infin;}}^{\mathrm{\&infin;}}{Y}_L\left(f\right)e^{j2\mathrm{\&pi;}ft}df\right|$ (Formula 3) $<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>{<span\; class="notranslate">\; \&Integral;</span>}_{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&infin;</span>}}^{\mathrm{<span\; class="notranslate">\; \&infin;</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; |</span>$ Let the matching output peaks be y _0max , y _Lmax , y _Rmax respectively, where y _xmax =max(|y _x (t)|); Step 3: Set the threshold; Consider the mismatch caused by the Doppler frequency shift f _d =2v _max /λ=2v _max f ₀ /c brought by the target speed, and determine the threshold: ${\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}{\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; )</span>}$ (Formula 4) ${\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; )</span>}$ Among them, v _max is the maximum velocity of the radar-measurable target, λ is the wavelength of the radar transmission signal, f ₀ is the carrier frequency of the radar transmission signal, c is the speed of light, B is the frequency modulation signal bandwidth of the radar transmission, f _d is the Doppler frequency brought by the target speed Le frequency shift, n _cl and n _cr are the left and right thresholds; Step 4: According to the matching output peak ratio of the target under different matched filters and combined with the set threshold to determine whether the target is a false target of frequency shift interference; H ₀ : ${\mathrm{no}}_{cl}\&le;\frac{\left|{\mathrm{the\; y}}_L\right|}{\left|{\mathrm{the\; y}}_0\right|}\&le;{\mathrm{no}}_{cr}$ and ${\mathrm{no}}_{cl}\&le;\frac{\left|{\mathrm{the\; y}}_R\right|}{\left|{\mathrm{the\; y}}_0\right|}\&le;{\mathrm{no}}_{cr}$ The target is the true target; H ₁ : $\frac{\left|{\mathrm{the\; y}}_L\right|}{\left|{\mathrm{the\; y}}_0\right|}\&le;{\mathrm{no}}_{cl}$ or $\frac{\left|{\mathrm{the\; y}}_R\right|}{\left|{\mathrm{the\; y}}_0\right|}\&le;{\mathrm{no}}_{cl}$ or $\frac{\left|{\mathrm{the\; y}}_R\right|}{\left|{\mathrm{the\; y}}_0\right|}\&Greater\; Equal;{\mathrm{no}}_{cr}$ or $\frac{\left|{\mathrm{the\; y}}_L\right|}{\left|{\mathrm{the\; y}}_0\right|}\&Greater\; Equal;{\mathrm{no}}_{cr}$ The target is a false target.