CN110927691A - A Design Method of Low Intercept Radar Signal Based on Multi-time Coded Phase Modulation - Google Patents

Abstract

The invention discloses a low intercept radar signal design method based on multi-time code phase modulation, in particular a design method of radar waveform with excellent resolution performance, anti-interference performance and low intercept performance. Multi-time coding is approximated by a frequency modulated signal, the number of phase states can be controlled artificially and the duration of each phase state is different. The implementation steps of the invention are as follows: firstly, selecting a frequency modulation basic signal waveform; then approximating the frequency modulation signal according to the multi-time coding rule to obtain a multi-time coding phase; then performing frequency coding modulation on each phase; and finally obtaining a complex modulated low intercept radar signal waveform. The invention can obtain a variety of complex modulated low intercept radar signal waveforms by adopting different frequency modulation forms in the obtained multi-time coded phase sub-pulses. The obtained signal waveform has good resolution performance, anti-jamming performance and low interception performance, and can meet the requirements of low interception performance of radar signal waveform in complex electromagnetic environment of modern warfare.

Description

A Design Method of Low Intercept Radar Signal Based on Multi-time Coded Phase Modulation

technical field

The invention belongs to the field of radar signal processing, and further relates to a design method of a low intercept radar signal waveform in the field of electronic countermeasures. The designed low-acquisition radar waveform has excellent resolution performance, anti-jamming performance and low-acquisition performance.

Background technique

With the development of science and technology, the electromagnetic environment of modern warfare is becoming more and more complex, and the scenarios of radar applications are also becoming more and more complex. The rapid development of signal processing technology has brought new challenges to the stealth of radar signals. The radar signal waveform with low interception performance is in modern times. The status of electronic countermeasures is becoming more and more important. How to design a waveform with good low interception performance on the premise of ensuring the radar signal completes its work function is a hot spot in the field of signal waveform design. This is of great significance to improve the anti-interception performance and anti-jamming performance of the radar system.

Harbin Institute of Technology in the patent document "Radar LFM Composite Waveform Design Method" (application date: June 23, 2016, publication number: CN106019237A, publication date: October 12, 2016), a compound based on chirp signal is disclosed. Waveform Design Methods. On the conventional chirp signal, this method combines the low correlation sidelobe waveform design method and the chirp noise waveform design idea, and introduces the correlation sidelobe template vector to construct the corresponding objective function and then analyzes the constraints to construct the signal design algorithm frame. The advantage of this method is that the designed waveform has lower correlated side lobe characteristics. However, the disadvantage of this method is that the modulation form of the chirp signal is too simple, and it is easier to be sorted and identified by the intercepting receiver to obtain the parameters of the signal waveform.

Xidian University disclosed in the patent document "Signal Waveform Design Method of Low Intercept Radar Communication Integrated System" (application date: May 30, 2018, publication number: CN108768446A, publication date: November 6, 2018) A signal waveform design method of a low intercept radar communication integrated system. In the method, the communication information is encoded to establish the mapping relationship between the information chips and the signal phase, and then the radar communication integrated transmission signal is formed by the linear frequency modulation baseband signal. The advantage of this method is that the functions of radar detection and information transmission are combined in the same system, which increases the complexity of the transmitted signal of the integrated radar communication system and the accuracy of target detection. However, the disadvantage of this method is that the communication information is encoded and transmitted through a chirp baseband signal. Although it has a certain low intercept, the modulation form is still relatively simple, and the obtained signal waveform anti-interference performance and low intercept performance are limited.

SUMMARY OF THE INVENTION

The purpose of the present invention is to aim at the shortcomings of the above methods, in order to improve the radar signal waveform complexity, low intercept performance and anti-jamming performance, a low intercept radar signal design method based on multi-time coded phase modulation is proposed.

The present invention adopts the following technical solutions in order to achieve the above-mentioned goals, and the steps are:

(1) Select the frequency modulation basic signal waveform to be approximated. Different frequency modulated basic signal waveforms and multi-time coded signals obtained after approximate quantization coding are different. The basic waveforms on which the multi-time code generation depends are the frequency step waveform and the linear frequency modulation waveform.

The frequency step signal waveform is expressed as:

f_i∈f＝{f_n|f_n＝f₀+nΔf，n＝0，1，...，N-1}。in,

f _i ∈ f={f _n |f _n =f ₀ +nΔf, n=0, 1, . . . , N-1}.

In the formula, Tr is the pulse repetition period, τ is the pulse width, f ₀ is the signal carrier frequency, Δf is the step frequency interval, and f is the set of N frequencies whose frequency interval is Δf.

The chirp signal waveform is expressed as:

In the formula, f ₀ is the center frequency, μ is the frequency modulation slope, and τ is the pulse width.

(2) After the selected frequency modulated basic signal waveform is quantized into n phase state codes, a multi-time phase coded signal T(n) is obtained.

The expression of the multi-time code T1(n) code and T2(n) code folding phase relative to time obtained by the frequency step waveform approximation is:

In the formula, n is the number of phase states, j=0, 1, ..., k-1 is the segment number of the frequency step waveform. k is the segment number of multi-time encoding, and T is the entire encoding duration.

For the multi-time code T3(n) code approximated by the chirp waveform, the expression of the folding phase of the T4(n) code with respect to time is:

In the formula, n is the number of phase states, ΔF is the modulation bandwidth, and t _m is the modulation period.

(3) Select the frequency modulation form adopted in each sub-pulse and set the corresponding parameters. The frequency modulated signal is denoted as u(t).

(4) Obtain the complex modulation signal U(t):

U(t)=u(t)exp(jφ(t))

Compared with the prior art, the present invention has the following beneficial effects:

The present invention performs waveform design based on multi-time coding phase modulation waveform, adopts multi-time coding between pulses, and adopts frequency modulation signal with good performance in pulse to form complex modulation waveform. The number of phases and the duration of each phase of the multi-time encoding can be freely generated under a certain waveform complexity constraint, and it has the broadband characteristic of phase modulation in time. On the premise of ensuring the detection performance and resolution performance, the complexity of waveform modulation, anti-jamming performance and low interception performance are increased. Compared with the modulation form of the existing low intercept radar signal, on the premise of ensuring the working performance of the radar signal, the multi-time coded phase modulation form adopted by the present invention is more complex and flexible, and has better low intercept performance.

Description of drawings

1 is a flowchart of a method for designing a low intercept radar signal based on multi-time coded phase modulation according to the present invention;

Fig. 2 (a) is the multi-time coding T1 code folding phase diagram of the embodiment;

Fig. 2 (b) is the multi-time coding T3 code folding phase diagram of the embodiment;

Figure 3 (a) is a three-dimensional ambiguity function diagram of the T1-Costas radar signal of the embodiment;

Figure 3(b) is a three-dimensional ambiguity function diagram of the T3-Costas radar signal of the embodiment

Fig. 4 (a) is the ambiguity function distance section view of the T1-Costas radar signal of the embodiment;

FIG. 4(b) is a sectional view of the ambiguity function of the T3-Costas radar signal of the embodiment;

Fig. 5(a) is a sectional view of the ambiguity function velocity of the T1-Costas radar signal of the embodiment;

Fig. 5(b) is a sectional view of the ambiguity function velocity of the T3-Costas radar signal of the embodiment;

Figure 6(a) is a graph showing the anti-jamming performance of the T1-Costas radar signal of the embodiment;

Figure 6(b) is a graph showing the anti-jamming performance of the T3-Costas radar signal of the embodiment;

Detailed ways

The present invention will be further explained below in conjunction with the accompanying drawings.

Fig. 1 shows the flow chart of the low intercept radar signal design method based on multi-time coded phase modulation according to the present invention; including the following steps:

(1) Select the frequency step waveform as the basic signal waveform of frequency modulation to be approximated, and the time domain form of the frequency step waveform is expressed as:

f_i∈f＝{f_n|f_n＝f₀+nΔf，n＝0，1，...，N-1}。in,

f _i ∈ f={f _n |f _n =f ₀ +nΔf, n=0, 1, . . . , N-1}.

In the formula, T _r is the pulse repetition period, τ is the pulse width, f ₀ is the signal carrier frequency, Δf is the step frequency interval, and f is the set of N frequencies whose frequency interval is Δf.

The linear frequency modulation waveform is selected as the basic frequency modulation signal waveform to be approximated, and the time domain form of the frequency step waveform is expressed as:

In the formula, f ₀ is the center frequency, μ is the frequency modulation slope, and τ is the pulse width.

(2) Select two basic waveforms for approximation respectively, according to the T1(n) code and T3(n) encoding rules, quantize them into n phase states and encode them to obtain multi-time phase encoded signals T1(n), T3(n) .

The expression of the multi-time coding T1(n) code folding phase relative to time is:

In the formula, n is the number of phase states, j=0, 1, ..., k-1 is the segment number of the frequency step waveform. k is the segment number of multi-time encoding, and T is the entire encoding duration.

The expression of the folding phase of the T3(n) code with respect to time is:

In the formula, n is the number of phase states, ΔF is the modulation bandwidth, and t _m is the modulation period.

(3) Using Costas frequency hopping coding signal to encode T1(n) code in multi-time, and frequency modulation is performed in each phase sub-pulse of T3(n). The time-domain representation of the frequency-hopping coded Costas signal is u(t):

in,

In the formula, f _n =C _n ·Δf, C is the Costas frequency hopping sequence, and Δf is the frequency interval of the Costas frequency hopping modulation. _TL is the width of each sub-pulse.

(4) The final complex modulation signal waveform is obtained as:

The simulation experiment of the present invention is carried out using MATLAB R2016a software on Intel(R) Xeon(R) CPU E5-1620 v4@3.50GHZ, memory 16GB, and Windows 7 operating system.

Select multi-time coding phase state number n=5, T1(n) code segment number k=9, T3(n) modulation bandwidth ΔF=3MHz, signal carrier frequency 6GHz, pulse duration 30us, coding length 3000, Costas frequency hopping coding The sequence length N=10, the frequency hopping interval Δf=2MHz, and the simulated signal-to-noise ratio is -20dB.

Figure 2(a) shows a folded phase diagram of a multi-time encoded T1(n) code. Figure 2(a) shows a folded phase diagram of a multi-time encoded T3(n) code. In the simulation experiment, the obtained complex modulation waveform is analyzed by using the fuzzy function. Figures 3(a) and 3(b) are three-dimensional ambiguity function diagrams of two multi-time coded Costas frequency hopping signal waveforms. Fig. 4(a) and Fig. 4(b) are the ambiguity function distance section views of the two signal waveforms. Fig. 5(a) and Fig. 5(b) are the ambiguity function velocity sectional views of the two signal waveforms. Fig. 6(a), Fig. 6(b) are two kinds of multi-time coding Costas frequency hopping signal waveform under the signal-to-noise ratio of -20dB anti-jamming performance diagram.

The simulation results show that both the T1(n) code approximated by the frequency waveform and the T3(n) code approximated by the chirp waveform, the signal waveform obtained by the Costas code frequency hopping modulation in the sub-pulse has good performance. From Figure 3(a) and Figure 3(b), it can be seen that both signal waveforms have good ambiguity function performance, and the maximum peak sidelobe levels are -39.54dB and -31.23dB, respectively. Peak sidelobe performance is greatly improved compared to a single modulated signal. It can be seen from Figure 4(a) and Figure 4(b) that the range ambiguity function graphs of the two signal waveforms have very narrow main lobes and very low side lobes, sharp main lobes and good range resolution. From Figure 5(a) and Figure 5(b), it can be seen that the side lobes of the velocity ambiguity function graph of the two signal waveforms are very low, the velocity resolution is very good, and there is no velocity measurement ambiguity, and the width of the main lobe is related to the frequency hopping code used. sequence length. It can be seen from Figure 6(a) and Figure 6(b) that the two signal waveforms have good anti-interference performance when the signal-to-noise ratio is -20dB, and can clearly distinguish the target in the environment of dense noise interference. Compared with the prior art, the present invention adopts the design of signal waveform based on multi-time coding, which is more complicated than the existing single signal or the existing combined signal modulation form, and greatly improves the agility of radar waveform and the low interception performance of radar. .

Claims (4)

1. A low interception radar signal design method based on multi-time coding phase modulation is disclosed. The method is characterized in that: the method comprises the steps of using a frequency modulation basic signal waveform, setting a phase state number, obtaining a multi-time coding phase modulation signal according to a multi-time coding rule, and forming a multi-time coding phase modulation low interception radar signal waveform in a complex modulation form after adopting other frequency modulation forms and setting parameters in each phase sub-pulse. The method comprises the following specific steps:

(1) the frequency modulation base signal waveform to be approximated is selected.

The waveforms of the basic signals are modulated by different frequencies, and multi-time coding phase modulation signals obtained after approximate quantization coding are different. The multi-time code generation relies on a base waveform having a frequency step waveform and a chirp waveform.

The frequency step signal waveform is represented as:

wherein,

f_i∈f＝{f_n|f_n＝f₀+nΔf，n＝0，1，...，N-1}。

in the formula, T_rIs the pulse repetition period, τ is the pulse width, f₀For a signal carrier frequency, Δ f is the stepped frequency interval, and f is the set of N frequencies spaced by Δ f.

The chirp waveform is represented as:

in the formula (f)₀At the center frequency, μ is the chirp rate and τ is the pulse width.

(2) And quantizing the waveform of the selected frequency modulation basic signal into n phase state codes to obtain a multi-time phase code signal T (n).

The multi-time code T1(n) code can be obtained by frequency stepping waveform approximation, and the folding phase of the T2(n) code is expressed relative to time as:

where n is the number of phase states, j is 0, 1, and k-1 is the segment number of the frequency step waveform. k is the number of segments of the multi-time code and T is the entire coding duration.

The multi-time code T3(n) code can be obtained by approximation of the chirp waveform, and the folding phase of the T4(n) code is expressed relative to time as:

where n is the number of phase states, Δ F is the modulation bandwidth, t_mIs the modulation period.

(3) The frequency modulation form adopted in each sub-pulse is selected and corresponding parameters are set. The frequency modulated signal is denoted u (t).

(4) Obtaining a complex modulation signal U (t):

U(t)＝u(t)exp(jφ(t)) 。

2. the method of claim 1, wherein said basic signal waveform of step (1) comprises a frequency step waveform and a chirp waveform.

3. A method for designing a low-interception radar signal based on multi-temporal coded phase modulation according to claim 1, wherein the types of the multi-temporal coded phase signals in step (2) are different, they are derived from the approximation of different types of basic waveforms, and the parameters are different.

4. The method of claim 1, wherein the complex modulation waveform of step (4) is a frequency modulation within each multi-time phase coded sub-pulse, and the complex modulation waveform is a different frequency modulation form that can be adopted.

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