[0023] The present invention will be further described below in conjunction with the drawings.
[0024] Reference figure 1 The application scenarios of the present invention include: horizontally polarized antenna, vertically polarized antenna, target and interference. The horizontally polarized antenna and the vertically polarized antenna are used to transmit electromagnetic wave signals to the area to be detected to detect targets. The target is used to scatter electromagnetic wave signals. The jammer is used to receive the transmitted signals from the two antennas and delay them before forwarding to achieve the purpose of interference. .
[0025] Reference figure 2 In the above scenario, the specific implementation steps of the present invention for active false target interference identification are as follows:
[0026] Step 1. Transmit electromagnetic wave signals.
[0027] The horizontally polarized antenna emits electromagnetic wave signals to the area to be detected:
[0028] The vertically polarized antenna emits electromagnetic wave signals to the area to be detected:
[0029] Where f h And f v Are the carrier frequencies of the signals transmitted by the horizontally polarized antenna and the vertically polarized antenna, t represents time, and j is an imaginary number, f h = F 0 +cΔf, f v = F 0 +cΔf, c is the frequency selection parameter, c=0,1, f 0 Is the center carrier frequency, Δf is the frequency modulation interval, μ is the frequency modulation slope, g(t) is the rectangular pulse modulation signal, and the value is: g ( t ) = 1,0 ≤ t T e 0 , T e ≤ t ≤ T r , T e Is the pulse width of the transmitted signal, T r Is the pulse repetition period.
[0030] These two electromagnetic wave signals s h (t), s v (t) Mutual orthogonality, its orthogonality can be judged by calculating the cross-correlation integral of two signals at any point in space, the calculation process is as follows:
[0031] ∫ 0 T e s h ( t - τ 1 ) s v * ( t - τ 2 ) dt = A · sin ( πUT e ) πUT e "1"
[0032] among them A = T e exp { j 2 π [ f v τ 2 - f h τ 1 + 0.5 μ ( τ 1 2 - τ 2 2 ) + Uτ 1 ] } , U=Δf+μ(τ 1 -τ 2 ), τ 1 , Τ 2 Respectively represent the delay of the two signals to any point in space, because μ(τ 1 -τ 2 )T e <<1, UT e ≈ΔfT e , So when ΔfT e When it is an integer, the formula "1" is approximately zero, and the two transmitted signals are orthogonal.
[0033] Step 2: Perform matched filtering on the echo signal.
[0034] 2a) Give the specific expression of the echo signal;
[0035] The echo signal contains target, fixed polarization false target interference, and polarization modulation false target interference.
[0036] 2a1) For the slowly fluctuating target in the echo signal, set its azimuth angle as θ s , The distance is r 0 , The round-trip delay is τ 0 = 2r 0 /c, the slow undulating target can be considered that its polarization scattering matrix remains unchanged during the beam scanning, and it is recorded as the horizontal and vertical polarization base S = s hh s hv s vh s vv ;
[0037] 2a2) For fixed polarization false target interference, the polarization mode of interference is h Ji =[h i ,v i ] T , H i Is the horizontal polarization component, v i Is the vertical polarization component and satisfies ||h Ji ||=1, 1≤i≤N s , Then the fixed polarization false target interference vector signal received by the two antennas of the radar is: V Js ( t ) = X i = 1 N s G ( θ i ) β i h Ji T s Ji ( t ) = X i = 1 N s C i h Ji T ( s h ( t - 2 τ i ) + s v ( t - 2 τ i ) ) ,
[0038] Where N s Is the number of fixed polarization false target interference, θ i Is the azimuth angle of the i-th interference, G(θ) is the normalized pattern function of the two antennas, β i Is a constant related to interference retransmission gain and transmission loss factor, τ i Is the delay of the i-th interference, s Ji (t)=γ i (s h (t-τ i )+s v (t-τ i )) is the signal received by the i-th jammer, γ i Is the constant related to the jammer distance, radar transmitting antenna gain, and jammer receiving gain, C i =G(θ i )β i γ i , I=1,2,...,N, N is the total number of active false targets;
[0039] 2a3) For polarization modulation false target interference, the polarization mode of interference is h Ji (t)=[h i (t),v i (t)] T , N s +1≤i≤N, the polarization modulation false target interference vector signal received by the two antennas of the radar is:
[0040] V Jc ( t ) = X i = N s + 1 N G ( θ i ) β i h Ji T ( t ) s Ji ( t ) = X i = N s + 1 N C i h Ji T ( t ) ( s h ( t - 2 τ i ) + s v ( t - 2 τ i ) ) , Where N c Is the number of polarization modulation false target interference;
[0041] 2a4) Obtain the echo signal from 2a1) to 2a3): V(t)=V T (t)+V Js (t)+V Jc (t)+n(t), where V T (t) is the target signal in the echo, n(t) is the channel noise;
[0042] 2b) Two-channel matched filtering is performed on the electromagnetic echo signals received by the horizontally polarized antenna and the vertically polarized antenna respectively;
[0043] In matched filtering, the two matched filters are respectively with The output signal after matched filtering is o(t)=[o hh (t),o hv (t),o vh (t),o vv (t)], where o hh (t), o hv (t) is the output signal after two matched filtering of the horizontally polarized antenna receiving signal, hh and hv represent the hh channel and hv channel of the horizontally polarized antenna, o vh (t), o vv (t) is the output signal after two matched filtering of the vertically polarized antenna receiving signal, vh and vv respectively represent the vh channel and vv channel of the vertically polarized antenna.
[0044] The calculation formula of the matched filter output signal o(t) is as follows:
[0045] o ( t ) = o hh ( t ) o hv ( t ) o vh ( t ) o vv ( t ) = V h ( t ) * h 1 ( t ) V h ( t ) * h 2 ( t ) V v ( t ) * h 1 ( t ) V v ( t ) * h 2 ( t ) = αG 2 ( θ ) s hh Λ 1 ( t - τ 0 ) αG 2 ( θ ) s hv Λ 2 ( t - τ 0 ) αG 2 ( θ ) s vh Λ 1 ( t - τ 0 ) αG 2 ( θ ) s vv Λ 2 ( t - τ 0 ) = X i = 1 N s C i h i Λ 1 ( t - 2 τ i ) X i = 1 N s C i h i Λ 2 ( t - 2 τ i ) X i = 1 N s C i v i Λ 1 ( t - 2 τ i ) X i = 1 N s C i v i Λ 2 ( t - 2 τ i ) + X i = N s + 1 N C i ( h i ( t ) ( s h ( t - 2 τ i ) + s v ( t - 2 τ i ) ) ) * h 1 ( t ) X i = N s + 1 N C i ( h i ( t ) ( s h ( t - 2 τ i ) + s v ( t - 2 τ i ) ) ) * h 2 ( t ) X i = N s + 1 N C i ( v i ( t ) ( s h ( t - 2 τ i ) + s v ( t - 2 τ i ) ) ) * h 1 ( t ) X i = N s + 1 N C i ( v i ( t ) ( s h ( t - 2 τ i ) + s v ( t - 2 τ i ) ) ) * h 2 ( t ) + n o ( t )
[0046] Where V h (t) and V v (t) are the signals received by the horizontally and vertically polarized antennas respectively; n o (t) is the output noise, Λ 1 (t-τ 0 )=s h (t-τ 0 )*h 1 (t), Λ 2 (t-τ 0 )=s v (t-τ 0 )*h 2 (t), because s h (t) and s v The complex envelope of (t) is the same, so the amplitudes of the two matched filter output signals are equal.
[0047] Step 3. Calculate the peak power P;
[0048] Extract the "target" peak value from the matched filter output signal o(t), and calculate the peak power P of each peak where the "target" peak appears. The calculation process is carried out as follows:
[0049] 3a) Simplify the matched filter output signal o(t);
[0050] Since the degree of modulation of the polarization modulation false target is small, it can be an integer M, and the emission pulse width T e Divided into M time periods, the polarization state is considered unchanged in each time period, so the output of the polarization modulation false target interference after matched filtering in the horizontal polarization antenna can be simplified as follows:
[0051] X i = N s + 1 N C i ( h i ( t ) ( s h ( t - 2 τ i ) + s v ( t - 2 τ i ) ) ) * h 1 ( t ) ≈ X i = N s + 1 N X j = 1 M C i h ij ( s h ( t j - 2 τ i ) + s v ( t j - 2 τ i ) ) * h 1 ( t j ) "2"
[0052] Where 0 e , (J-1)T e /M j ≤jT e /M, j=1,2,...,M. According to formula "1", when ΔfT e Is an integer, s h (t) and s v (t) Orthogonal, it can be inferred that when ΔfT e /M is an integer, s h (t j ) And s v (t j ) Is orthogonal, the formula "2" can be simplified as follows:
[0053] X i = N s + 1 N C i ( h i ( t ) ( s h ( t - 2 τ i ) + s v ( t - 2 τ i ) ) ) * h 1 ( t ) ≈ X i = N s + 1 N X j = 1 M C i h ij s h ( t j - 2 τ i ) * h 1 ( t j ) = X i = N s + 1 N C i X j = 1 M h ij χ 1 j ( t j - 2 τ i )
[0054] Let χ 1j (t j -2τ i )=s h (t j -2τ i )*h 1 (t j ), χ 2j (t j -2τ i )=s v (t j -2τ i )*h 2 (t j ), due to s h (t) and s v (t) has the same complex envelope, so |χ 1j (t j -2τ i )|=|χ 2j (t j -2τ i )|;
[0055] Simplify the matched filter output signal o(t) to obtain a new matched filter output signal o(t)':
[0056] o ( t ) ′ = α G 2 ( θ ) s hh Λ 1 ( t - τ 0 ) α G 2 ( θ ) s hv Λ 2 ( t - τ 0 ) α G 2 ( θ ) s vh Λ 1 ( t - τ 0 ) α G 2 ( θ ) s vv Λ 2 ( t - τ 0 ) + X i = 1 N s C i h i Λ 1 ( t - 2 τ i ) X i = 1 N s C i h i Λ 2 ( t - 2 τ i ) X i = 1 N s C i v i Λ 1 ( t - 2 τ i ) X i = 1 N s C i v i Λ 2 ( t - 2 τ i ) + X i = N s + 1 N C i X j = 1 M h ij χ 1 j ( t j - 2 τ i ) X i = N s + 1 N C i X j = 1 M h ij χ 2 j ( t j - 2 τ i ) X i = N s + 1 N C i X j = 1 M v ij χ 1 j ( t j - 2 τ i ) X i = N s + 1 N C i X j = 1 M v ij χ 2 j ( t j - 2 τ i )
[0057] 3b) Extract the "target" peak
[0058] When extracting the "target" peak value, the matched filter output signal t=τ 0 The target is detected at t = 2τ i Interference is detected at place, 1≤i≤N s.
[0059] 3c) Calculate the peak power of each peak P=|o(t)'| according to the simplified o(t)' 2.
[0060] Step 4. Calculate the statistical identification quantity id(t).
[0061] Calculate the statistical discrimination id(t) according to the peak power P of each peak, and define w 1 , W 2 Two different extraction vectors for the same target peak, w 1 =[1,0,0,1], w 2 =[0,1,1,0], construct the statistical discriminant quantity as follows:
[0062] id ( t ) = w 1 P w 2 P
[0063] The statistical identification quantity id(t) of target and false target interference is calculated separately as follows:
[0064] 4a) For reciprocal targets, the amplitudes of the two co-polarized components of the polarization scattering matrix of the target are approximately equal, and are much larger than the cross-polarized components, namely |s hh /s vv |=1, and |s hh |>>|s hv | To get After matched filtering, the target output peak power is as follows
[0065] P T =|o(τ 0 )'| 2
[0066] Since the distance between the target and the interference is relatively long, the target is less affected by the interference, so the discrimination statistics in the target distance unit can be approximated as
[0067] id ( τ 0 ) = w 1 P T w 2 P T ≈ | α G 2 ( θ ) s hh Λ 1 ( 0 ) | 2 + | α G 2 ( θ ) s vv Λ 2 ( 0 ) | 2 | α G 2 ( θ ) s vh Λ 1 ( 0 ) | 2 + | α G 2 ( θ ) s hv Λ 2 ( 0 ) | 2 1
[0068] 4b) For the fixed polarization false target interference, the i-th (1≤i≤N s ) The output peak power of a fixed polarization false target interference is
[0069] P Jsi =|o(2τ i )'| 2 , 1≤i≤N s ,
[0070] Since the interference power is much greater than the signal power and noise power, the identification statistics of the i-th fixed polarization false target interference distance unit can be approximated as:
[0071] id ( 2 τ i ) = w 1 P Jsi w 2 P Jsi ≈ | C i h i Λ 1 ( 0 ) | 2 + | C i v i Λ 2 ( 0 ) | 2 | C i h i Λ 2 ( 0 ) | 2 + | C i v i Λ 1 ( 0 ) | 2 = ( | h i | 2 + | v i | 2 ) | Λ 1 ( 0 ) | 2 ( | h i | 2 + | v i | 2 ) | Λ 1 ( 0 ) | 2 = 1
[0072] 4c) For the polarization modulation false target interference, the output peak power of the k-th polarization modulation false target interference is
[0073] P Jci =|o(2τ k )'| 2 , N s +1≤k≤N,
[0074] Since the interference power is much greater than the signal power and noise power, the discrimination statistics of the k-th polarization modulation false target interference range unit can be approximated as:
[0075] id ( 2 τ k ) = w 1 P Jck w 2 P Jck ≈ | C k X j = 1 M h kj χ 1 j ( 0 ) | 2 + | C k X j = 1 M v kj χ 2 j ( 0 ) | 2 | C k X j = 1 M h kj χ 2 j ( 0 ) | 2 + | C k X j = 1 M v kj χ 1 j ( 0 ) | 2 = ( | X j = 1 M h kj | 2 + | X j = 1 M v kj | 2 ) | χ 1 j ( 0 ) | 2 ( | X j = 1 M h kj | 2 + | X j = 1 M v kj | 2 ) | χ 1 j ( 0 ) | 2 = 1
[0076] Step 5. Identify the false target interference and target.
[0077] 5a) Set the discrimination threshold T h From the analysis of steps 4a) to 4c), it can be known that the discrimination statistics of false target interference is equal to 1 when the interference power is much greater than the signal power and noise power, so the discrimination threshold T is set h Greater than 1, set T during engineering practice h 1.1;
[0078] 5b) Compare the statistical identification quantity id(t) with the identification threshold T h , If id(t)>T h , The peak value is the target peak value, otherwise it is the false target interference peak value to complete target identification.
[0079] The effect of the present invention can be further illustrated by the following simulation:
[0080] 1. Simulation conditions:
[0081] Suppose that both the horizontally polarized antenna and the vertically polarized antenna emit FMCW signals, and the carrier frequency of the signal transmitted by the horizontally polarized antenna is f 0 =1GHz, the carrier frequency of the vertically polarized antenna is f 0 '=1.001GHz, the common parameters of the two transmit signals are bandwidth B=1MHz, pulse width T e =40us, pulse repetition period T r = 200us. Polarization scattering matrix S = 1 0.3 j 0.3 j 0.9 , Target distance R 0 = 15km. The number of Monte Carlo tests in the simulation is 200.
[0082] 2. Simulation content
[0083] Simulation 1, assuming there are 2 fixed polarization false target interference and 1 polarization modulation false target interference, the distances of the three interferences are R=[5km,22km,28km], the polarization state of the fixed polarization false target interference They are left-hand circular polarization and right-hand circular polarization. When processing, take M=10, and the interference signal ratio is fixed at 40dB. The discrimination threshold is T h = 1.1 and 1.2. Simulate the matched filter output waveform of the common polarization channel of two antennas, the result is as follows image 3 Shown. Under different discrimination thresholds, the relationship between the discrimination probability of the target and interference and the output signal-to-noise ratio is simulated, and the results are as follows Figure 4 Shown, where Figure 4 (a) is the discrimination threshold T h = 1.1, the relationship between the discrimination probability of the simulation target and the interference and the signal-to-noise ratio at the output, Figure 4 (b) is the discrimination threshold T h =1.2 The relationship between the discrimination probability of the simulated target and interference and the signal-to-noise ratio at the output.
[0084] Simulation 2. Assuming that there is a left-hand circularly polarized false target interference and a polarization modulation false target interference in the space, the distances are respectively R=[10km,20km], the input interference-to-noise ratio changes from 0 to 40dB, and the discrimination thresholds are respectively Take T h = 1.1 and 1.2. Under different discrimination thresholds, simulate the relationship between the discrimination probability of interference and the input interference-to-noise ratio, and the results are as follows Figure 5 Shown, where Figure 5 (a) is the discrimination threshold T h =1.1, the relationship between the discrimination probability of simulated interference and the interference-to-noise ratio at the input, where Figure 5 (b) is the discrimination threshold T h =1.2 The relationship between the discrimination probability of simulated interference and the interference-to-noise ratio at the input.
[0085] 3. Analysis of simulation results
[0086] From image 3 It can be seen that after the matched filtering, the target and three interference peaks are detected in the common polarization output hh channel of the horizontally polarized antenna and the common polarization output vv channel of the vertically polarized antenna. Compare Figure 4 (a) and Figure 4 (b), it can be seen that the common point of the two figures is that in the case of low signal-to-noise ratio, the target identification probability is lower. When the signal-to-noise ratio is greater than 0dB, the target identification probability is greater than 90%. At 5dB, the target discrimination probability reaches 100%, and both can detect fixed false target interference and polarization modulation false target interference. The difference between the two figures is that when they have the same output signal-to-noise ratio, Figure 4 (a) The identification probability of the target is higher than Figure 4 The identification probability of the target in (b) is large, that is, the identification probability of the target decreases with the increase of the identification threshold.
[0087] Compare Figure 5 (a) and Figure 5 (b), it can be seen that the same point in the two figures is that the interference discrimination probability increases with the input interference-to-noise ratio. At low interference-to-noise ratios, fixed polarization interference and polarization modulation interference can be detected. In addition, the discrimination probability of fixed polarization interference is higher than that of polarization modulation interference. When the interference-to-noise ratio is greater than 15dB, the discrimination probability of both is 100%. The difference between the two figures is that when the input interference to noise ratio is the same, Figure 5 (a) The discrimination probability of interference is higher than Figure 5 In (b), the discrimination probability of interference is small, that is, the discrimination probability of interference increases with the increase of the discrimination threshold.
[0088] Based on the above analysis, the following conclusion can be drawn: the present invention can maintain good performance even under low interference-to-noise ratio, and is not only suitable for fixed polarization false target interference, but also suitable for polarization modulation false target interference.
