CN109323634A

CN109323634A - A method for measuring the falling angle of shells based on chirp short-range detection system

Info

Publication number: CN109323634A
Application number: CN201710643908.8A
Authority: CN
Inventors: 赵惠昌; 仝华东; 周冲
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2017-07-31
Filing date: 2017-07-31
Publication date: 2019-02-12

Abstract

The invention discloses a method for measuring the falling angle of a shell based on a linear frequency modulation short-range detection system. Calculate the phase of the highest spectral peak, subtract the phases of the two obtained spectral peaks, and obtain the phase difference of the two-channel difference frequency signals; according to the measured phase difference, use the phase comparison method to calculate the falling angle of the shell. The invention can realize the high-precision measurement of the phase difference, and then can accurately measure the falling angle, and has strong anti-interference performance.

Description

Method based on the linear frequency modulation short-range detecting systematic survey shell angle of fall

Technical field

The present invention relates to short-range detecting technologies, especially a kind of to be based on the linear frequency modulation short-range detecting systematic survey shell angle of fall Method.

Background technique

Currently, linear frequency modulation short-range detecting system is due to the advantages that its is small in size, structure is simple, precision is high, low in cost, It is widely applied in every field.

But the research of linear frequency modulation short-range detecting system angle measurement is seldom, linear frequency modulation short-range detecting system uses Phase comparing method can carry out angle measurement, and the key of phase comparing method is the phase difference for finding out two-way echo-signal, currently, phase difference detection had Balance method, correlation method, since zero-crossing method requires relatively high, poor anti jamming capability to signal-to-noise ratio, correlation method requires strictly whole Periodic sampling, and be difficult to harmonic carcellation interference, therefore, existing phase difference detection method is all difficult to apply to that signal-to-noise ratio is low, precision High, strong real-time system.

Summary of the invention

The purpose of the present invention is to provide a kind of method based on the linear frequency modulation short-range detecting systematic survey shell angle of fall, solutions Certainly linear frequency modulation short-range detecting system surveys angle of fall problem.

Realize the technical solution of the object of the invention are as follows: a kind of based on the linear frequency modulation short-range detecting systematic survey shell angle of fall Method includes the following steps:

Mixing: two-way reception signal is mixed, difference frequency signal is obtained；

FFT method phase difference detection: FFT is done to two-way difference frequency signal, highest spectral peak is searched for, calculates the phase of highest spectral peak Position, the phase of gained two-way spectral peak is subtracted each other, two-way difference frequency signal phase difference is obtained；

It calculates the angle of fall: according to the phase difference measured, calculating the shell angle of fall with phase comparing method.

Compared with prior art, remarkable advantage of the invention are as follows: the present invention is based on linear frequency modulation short-range detecting systematic surveys The high-acruracy survey of phase difference may be implemented in the method for the shell angle of fall, and then can accurately measure the angle of fall, and has stronger anti- Interference.

Detailed description of the invention

Fig. 1 is frequency-time chart of sawtooth phase modulation signal.

Fig. 2 is that FFT method of the invention surveys phase difference broad flow diagram.

Fig. 3 is the schematic diagram that the present invention measures angle of fall value when signal-to-noise ratio is 20dB.

Fig. 4 is the schematic diagram that the present invention measures value error in the angle of fall when signal-to-noise ratio is 20dB.

Fig. 5 is the schematic diagram that the present invention measures angle of fall value when signal-to-noise ratio is 10dB.

Fig. 6 is the schematic diagram that the present invention measures value error in the angle of fall when signal-to-noise ratio is 10dB.

Fig. 7 is the schematic diagram that the present invention measures angle of fall value when signal-to-noise ratio is 3dB.

Fig. 8 is the schematic diagram that the present invention measures angle of fall value error when signal-to-noise ratio is 3dB.

Specific embodiment

A method of based on the linear frequency modulation short-range detecting systematic survey shell angle of fall, include the following steps:

Further, the detailed process of mixing are as follows:

Frequency-time curve of sawtooth phase modulation signal is as shown in Figure 1, be divided into two sections, area for a cycle Between one be formula area, section two be region of disorder.

Transmitting signal frequency expression be

The frequency representation formula of echo-signal is at fuse receiving antenna 1

τ is the delay of echo-signal relative transmission signal, f₀For carrier frequency, Δ F_MFor modulating bandwidth, T_MFor frequency modulation week Phase,t₀For the initial position corresponding time；

Using the π ∫ fdt of relational expression φ=2 of frequency and phase, obtains transmitting signal and receive the instantaneous phase of signal Difference；Within the single linear frequency modulation period, transmitting signal is found out respectively and receives the instantaneous phase of signal；

WhenWhen, difference frequency signal is in formula area, and the phase expression formula for emitting signal is

WhenWhen, difference frequency signal is in irregular area, emits the phase expression formula of signal Are as follows:

Wherein, C is constant；

From the continuity of signal phase:Then

WhenWhen, the phase expression formula for receiving signal is

Then whenWhen, transmitting signal is with the instantaneous phase difference for receiving signal

Δφ₁=| φ_R-φ_T1|=2 π (τ Δ F_Mf_mt+f₀τ-τΔF_Mf_mt₀)

Due to T in real system_mThe signal of formula area part is mainly studied much larger than τ, therefore in signal analysis process.

Emitting signal with echo-signal is cos (Δ φ by the lower form for being mixed to obtain difference frequency signal_n), then difference frequency signal Expression formula be

cos(Δφ₁)=cos2 π (Δ F_Mf_mτt+f₀τ-τΔF_Mf_mt₀)

=cos2 π (Δ F_Mf_mτt+f₀R/c+f₀R₁/c-τΔF_Mf_mt₀)

Then the received another way signal of antenna 2 is by the expression formula that lower mixing obtains difference frequency signal

cos(Δφ₂)=cos2 π (Δ F_Mf_mτt+f₀R/c+f₀R₂/c-τΔF_Mf_mt₀)

Two-way difference frequency signal phase difference is 2f₀(R₁-R₂)/c, R₁、R₂Respectively receiving antenna 1 and receiving antenna 2 arrive ground Distance, R be transmitting antenna to the distance on ground, c is the light velocity, wherein R₁-R₂=Lsin α, L are antenna spacing, and α is the angle of fall, this Total phase meter of sample, two paths of signals is shown as

For the wavelength for emitting signal；

It can be seen that being mixed under phase offset unanimous circumstances caused by receiving system signal processing itself in two-way Afterwards, the phase difference that two receiving antennas receive signal remains unchanged.Therefore, after low-frequency amplifier, two-way is obtained with phase discriminator Total phase difference φ of signal, to can get angle information α.

Further, the detailed process of FFT method phase difference detection are as follows:

Two paths of signals is sampled first；

Secondly FFT transform is carried out, their phases at peak value spectral line are then found out according to following formula；

X₁(k) and X₂(k) sequence obtained after FFT is done for two-way difference frequency signal；

imag(X₁And real (X (k))₁(k)) imaginary part and real part are respectively indicated；

Finally the phase of two paths of signals is subtracted each other and finds out phase difference:

Total phase difference φ of two paths of signals in order to obtain measures phase difference φ using FFT phase difference detection method, is based on The phase difference detection method of DFT spectrum analysis has good rejection ability to noise and harmonic wave interference, and FFT method is the one of DFT method Kind fast algorithm, FFT method survey the principle of phase difference: sampling first to two paths of signals；Secondly FFT transform is carried out, is then divided Their phases at peak value spectral line are not found out；Finally the phase of two paths of signals is subtracted each other and finds out phase difference；

If the system two-way to be measured is the same as the expression formula of frequency sinusoidal signal are as follows:

In formula, A₁、A₂The respectively amplitude of two paths of signals；f_aFor signal frequency,Respectively two paths of signals initial phase Position.

Although frequency input signal is it is known that for without loss of generality, by f_aIt indicates are as follows:

f_a=(k₀+δ)·f_d

k₀For integer, f_dFor spectral resolution, f_d=f_s/ N, f_sFor sample frequency, N is sampling number, and δ is lobe error system Number, | δ |≤0.5.

With identical sample frequency f_sIn synchronization to s₁(n) and s₂(n) sampled, thus obtained two-way from Sequence is dissipated,

N=0,1,2 ..., N-1

Next, because the processing to two-way discrete series is similar, here with s₁(n) it is illustrated, to s₁(n) DFT change is carried out Get discrete spectrum S in return₁(k), wherein k=0,1,2 ..., N-1.Because of S₁(k) peak value spectral line is in k=k₀Place obtains, according to DFT definition, can obtain:

Ignore the negative frequency component in formula, formula can abbreviation are as follows:

If phase1 indicates S₁(k) in k=k₀The phase at place, then phase1 can be with unified representation are as follows:

Similarly phase2

Phase difference can be obtained

Further, according to formulaThe value of angle of fall α is calculated, L is two receiving antennas in formula Spacing.

The present invention is described in detail combined with specific embodiments below.

Embodiment

The present embodiment uses following system parameter: sine wave FM system, f₀=24G, Δ F_M=50MHz, T_m=4us, day Line spacing L=0.018m, starting distance R=30m, Missile Motion speed v=350m/s preset 30 °~60 ° of angle of fall range.

As shown in Figure 1 and Figure 2, method of the present embodiment based on the linear frequency modulation short-range detecting systematic survey shell angle of fall includes Following steps:

(1) it is mixed: two-way echo-signal being mixed, difference frequency signal is obtained.

(2) FFT method phase difference detection: being FFT to two-way difference frequency signal first, searches for highest spectral peak, calculates highest spectrum The phase at peak subtracts each other the phase of gained two-way spectral peak, obtains two-way difference frequency signal phase difference.

(3) angle of fall: the phase difference measured according to step 2 is calculated, the shell angle of fall is calculated.

Fig. 3 is predetermined angle and actual measurement angle contrast's figure, it can be seen that predetermined angle and actual measurement in the case where signal-to-noise ratio is 20dB The linear variation of angle, Fig. 4 are the measurement error in the case where signal-to-noise ratio is 20dB, and worst error is 0.18 °, and mean error is 0.04°.Fig. 5 is in the case where signal-to-noise ratio is 10dB, and predetermined angle and actual measurement angle contrast's figure, predetermined angle and actual measurement angle are linear Variation, Fig. 6 are the measurement error in the case where signal-to-noise ratio is 10dB, and worst error is 0.23 °, and mean error is 0.085 °.Fig. 7 be Signal-to-noise ratio is under 3dB, and predetermined angle and actual measurement angle contrast's figure, predetermined angle and the actual measurement linear variation of angle, Fig. 8 are to believe It makes an uproar than for the measurement error under 3dB, worst error is 0.23 °, mean error is 0.863 °.It can be seen that the present invention possess it is higher Angle measurement accuracy and stronger anti-interference.

Claims

1. a method based on linear frequency modulation short-range detection system to measure the falling angle of artillery shell, is characterized in that, comprises the steps:

Mixing: Mix the two received signals to get the difference frequency signal;

FFT method for phase difference detection: perform FFT on two beat frequency signals, search for the highest spectral peak, calculate the phase of the highest spectral peak, and subtract the phases of the two obtained spectral peaks to obtain the phase difference of the two beat frequency signals;

Calculate the falling angle: According to the measured phase difference, use the phase comparison method to calculate the falling angle of the shell.

2. the method based on the linear frequency modulation short-range detection system according to claim 1 to measure the falling angle of the shell, it is characterized in that, the concrete process of frequency mixing is:

The frequency expression of the transmitted signal is

The frequency expression of the echo signal at the fuze receiving antenna 1 is:

In the formula, τ is the delay of the echo signal relative to the transmitted signal, f ₀ is the carrier frequency, _{ΔFM is the frequency modulation bandwidth, T M} _is the frequency modulation period, t ₀ is the time corresponding to the initial position;

Using the relational expression φ=2π∫fdt of frequency and phase, the instantaneous phase difference between the transmitted signal and the received signal is obtained; in a single chirp period, the instantaneous phase of the transmitted signal and the received signal are obtained respectively;

when When the difference frequency signal is in the regular area, the phase expression of the transmitted signal is

when When the difference frequency signal is in the irregular region, the phase expression of the transmitted signal is:

where C is a constant;

It can be known from the continuity of the signal phase: but

when When , the phase expression of the received signal is

then when When , the instantaneous phase difference between the transmitted signal and the received signal is

Δφ ₁ =|φ _R -φ _T1 |=2π(τΔF _M f _m t+f ₀ τ-τΔF _M f _m t ₀ )

The form of the difference frequency signal obtained by down-mixing the transmitted signal and the echo signal is cos(Δφ _n ), then the expression of the difference frequency signal is:

cos(Δφ ₁ )=cos2π(ΔF _M f _m τt+f ₀ τ-τΔF _M f _m t ₀ )

=cos2π(ΔF _M f _m τt+f ₀ R/c+f ₀ R ₁ /c-τΔF _M f _m t ₀ )

Then the expression of the difference frequency signal obtained by the down-mixing of the other signal received by the antenna 2 is:

cos(Δφ ₂ )=cos2π(ΔF _M f _m τt+f ₀ R/c+f ₀ R ₂ /c-τΔF _M f _m t ₀ )

The phase difference between the two beat frequency signals is 2f ₀ (R ₁ -R ₂ )/c, R ₁ and R ₂ are the distances from the receiving antenna 1 and the receiving antenna 2 to the ground respectively, R is the distance from the transmitting antenna to the ground, and c is The speed of light, where R ₁ -R ₂ =Lsinα, L is the antenna spacing, α is the falling angle, and the total phase difference of the two signals is expressed as:

is the wavelength of the transmitted signal.

3. the method based on the linear frequency modulation short-range detection system according to claim 1 to measure the falling angle of the shell, it is characterized in that, the concrete process of FFT method phase difference detection is:

First, sample the two signals;

Secondly, perform FFT transformation, and then find their phase at the peak spectral line according to the following formula;

X ₁ (k) and X ₂ (k) are the sequences obtained after the FFT of the two-path difference frequency signals respectively;

imag(X ₁ (k)) and real(X ₁ (k)) represent the imaginary part and the real part, respectively;

Finally, subtract the phases of the two signals to find the phase difference:

.

4. the method for measuring the angle of drop of the shell based on the linear frequency modulation short-range detection system according to claim 3, is characterized in that, according to formula Calculate the value of the fall angle α, where L is the distance between the two receiving antennas.