A Supportive Repeater Jamming Method for FDA-MIMO Radar Based on Phase Modulation

Abstract

The present invention belongs to the technical field of radar jamming, and specifically relates to a support-type repeater jamming method for FDA-MIMO radar based on phase modulation. The method of the present invention mainly obtains the time difference between the arrival of the radar signal at the protected target and the arrival at the jammer through positioning technology. First, the intercepted multi-channel aliased signals of the FDA-MIMO radar are down-converted using the carrier frequency f = f0. The signals from different transmitting elements are separated using band-pass filters corresponding to the offset frequencies of the transmitting elements. Then, different-phase modulations of different magnitudes are performed on the separated signal components. Finally, the carrier signal f0 is modulated into N parts, and the sum of these N carrier signals is used to up-convert the radar offset signals respectively. Finally, the signals are superimposed and forwarded, so as to achieve the purpose of jamming the FDA-MIMO radar.

Description

Technical Field

[0001] The present invention belongs to the technical field of radar jamming, and specifically relates to a support-type repeater jamming method for FDA-MIMO radar based on phase modulation. Background Art

[0002] On the basis of a common phased array radar, a frequency diverse array multiple-input multiple-output radar (FDA-MIMO) introduces transmitting signals at the transmitting end that have a fixed step frequency difference and are orthogonal to each other, making the beamforming pattern of the antenna have the characteristics of two-dimensional joint distance-angle. This characteristic gives the FDA-MIMO radar excellent detection performance and anti-main lobe interference ability. In terms of anti-jamming, the FDA-MIMO radar can use the phase difference after true and false targets reach the receiving end to suppress the false target interference entering the main lobe of the radar. Due to the excellent anti-main lobe interference ability of the FDA-MIMO radar, it has become very difficult to formulate a jamming scheme against it using traditional means.

[0003] For a typical FDA-MIMO radar system, assume that the radar system has M transmitting signal ends, and the signals transmitted by each transmitting element differ by a step frequency Δf. The carrier frequency of the transmitting signal s1(t) of the first transmitting end is set to f0, and it satisfies f0 >> Δf. The carrier frequency of the signal s m (t) transmitted by the m-th transmitting end satisfies f m = f0 + mΔf, where f0 is the signal carrier frequency and Δf is the signal step frequency.

[0004] For a traditional support-type jamming scenario, the jammer and the protected target are in different azimuths, and the jammer is not carried on the platform of the protected target, as Figure 1 shown. Assume that the protected target is located at r = r0, θ = θ0, and the jammer is located at r = r j , θ = θ j ). The radar signal is captured by the jammer after a transmission delay of . The sum of the signals from the M transmitting elements captured by the jammer is forwarded after a time delay of t j and transmitted for t j,n before being captured by the n-th receiving element. The signal is shown in Equation (1).

[0005]

[0006] where A m (t) represents the envelope of the signal transmitted by the m-th transmitting element.

[0007] When the signal is captured by the radar receiving end, according to Figure 2The displayed process is processed as follows. First, it is sent into a simulation instrument to be mixed with the carrier frequency exp(j2πf0t) of the transmitted signal, and then the obtained signal is sampled and converted into a digital signal, and matched filtering is performed using different frequencies. The signal output component obtained after processing the false target signal generated by the accompanying interference is shown in Equation (2).

[0008]

[0009] where χ j is the complex coefficient obtained after matched filtering of the complex envelope signal. The total of m*n output signals obtained on n receiving array elements of the radar are represented as a vector X as shown in Equation (3).

[0010] X = [S 11 , S 12 , …, S 1M , S 21 , S 22 , …S 2M , …, S NM T (3) The above equation can be expressed as Equation (4)

[0011]

[0012] where denotes the Kronecker product, a(θ0, r0) is the transmit steering vector, and b(θ0, r0) is the receive steering vector, as shown in Equations (5) and (6) respectively.

[0013]

[0014]

[0015] In beamforming, the FDA-MIMO radar uses the vector H(θ0, r0) to process the filtered X, and its expression is shown in Equation (7).

[0016]

[0017] Normalize the sum of the signal components obtained after filtering by the FDA-MIMO radar, and denote the result of the normalization as W(θ, r), which represents the average power magnitude of the radar signal when it enters the radar receiving array elements after being reflected by the target. The expression of W(θ, r) is shown in Equation (8).

[0018]

[0019] where When r j + Δr ≠ r0 or θ j ​When θ ≠ θ0, the normalized value W(θ, r) of the signal processing of the FDA-MIMO radar is less than 1, and the interference signal is suppressed by the receiving-end beamforming technology. It can be seen that it is very difficult to formulate an interference scheme for the FDA-MIMO radar by using traditional means. Summary of the Invention

[0020] In view of the above problems, the present invention proposes a support-type repeater interference method for FDA-MIMO radar based on phase modulation.

[0021] The technical solution of the present invention is as follows:

[0022] A support-type repeater interference method based on phase modulation, and the scheme includes the following steps:

[0023] S1. Use the carrier signal A dn exp[j2πf0(t - t dn )] to perform down-conversion on the multiplexed radar signals received by the jammer

[0024] S2. Filter the signals respectively through band-pass filters with a center frequency of mΔf to obtain the offset frequency signals of each transmitting array element.

[0025] S3. Obtain the time difference Δt between the arrival of the radar signal at the protected target and the arrival at the jammer through the positioning technology, and then perform phase modulation with different magnitudes on each separated signal component, and perform phase modulation on the offset frequency of the m-th transmitting array element. The magnitude of the adjusted phase is

[0026] S4. For all N receiving array elements at the radar receiving end, modulate the up-conversion carrier signal into N copies, superimpose these N up-conversion signals, use them to perform up-conversion on the radar offset signal mΔf respectively, and finally superimpose and forward the signals.

[0027] The beneficial effect of the present invention is that the method of the present invention mainly obtains the time difference between the arrival of the radar signal at the protected target and the arrival at the jammer through the positioning technology. First, perform down-conversion on the intercepted multiplexed radar signals of the FDA-MIMO radar using the carrier frequency f = f0, separate the signals from different transmitting array elements by using band-pass filters corresponding to the offset frequencies of the transmitting array elements, then perform phase modulation with different magnitudes on each separated signal component, and finally modulate the carrier signal f0 into N copies, use these N carrier signals to perform up-conversion on the radar offset signal mΔf respectively, and finally superimpose and forward the signals, so as to achieve the purpose of interfering with the FDA-MIMO radar. Description of the Drawings

[0028] Figure 1 It is a support-type interference scenario diagram.

[0029] Figure 2 It is the signal processing flow of the receiving end of the FDA-MIMO radar.

[0030] Figure 3 It is the modulation signal flow of the jammer in the support jamming scenario.

[0031] Figure 4 It is the interference effect diagram after the traditional delay and forwarding of the support jammer.

[0032] Figure 5 It is the interference effect diagram of the support jammer after phase modulation and then delay and forwarding. Specific implementation mode

[0033] The following combines the attached drawings and simulation examples to describe in detail the technical principle and scheme of the present invention:

[0034] The present invention is divided into four parts, namely the down-conversion of radar multiplex signals, the separation of radar signals, the phase modulation of radar signals, and the phase modulation of up-converted carrier signals. As Figure 3 shown, the specific method of the present invention is:

[0035] S1. Use the carrier signal A dn exp[j2πf0(t - t dn )] to perform down-conversion on the multiplexed radar signals received by the jammer.

[0036] The multiplexed radar signals received by the jammer are:

[0037]

[0038] Mix with A dn exp[j2πf0(t - t dn )] to obtain the down-converted signal as shown in Equation (10).

[0039]

[0040] Among them, the subscript M in X M,j (t) represents the sum of m transmitted signals, and the subscript j represents the jth jammer. A m represents the envelope of the signal transmitted by the mth transmitting array element, rect() is the rectangular function, and T is the duration of the radar signal pulse. t dn is the time difference between the down-converted signal and the reference signal of the radar, and A dn is the amplitude of the down-converted signal.

[0041] S2. Filter the signal through M band-pass filters with center frequencies of mΔf respectively, where m = 0, 1, 2…, M - 1, to obtain the offset frequency signals of M transmitting array elements. The offset frequency signals of each transmitting array element are obtained as shown in Equation (11).

[0042]

[0043] S3. Obtain the time difference Δt between the arrival of the FDA-MIMO radar signal at the protected target and at the jammer through positioning technology, then perform phase modulation of different magnitudes on each separated signal component, perform phase modulation on the offset frequency of the m-th transmitting array element, and the magnitude of the adjusted phase is

[0044] Denote the sum of the system positioning time, modulation signal time, and delay time as t j , t j,m =t m +Δt, t m is the transmission time for the m-th transmitting array element to reach the target. It can be seen from formula (11) that after time delay, the frequency offset mΔf of the radar signal can generate a phase difference, and the magnitude is equal to It can be known from formula (8) that the additional phase difference carried by the false target will cause the interference signal to be suppressed by the beamforming technology at the receiving end of the FDA-MIMO radar. Therefore, it is necessary to perform phase modulation of magnitude on the frequency offset of each transmitting array element, and the phase modulation result of the m-th signal is shown in formula (12).

[0045]

[0046] S4. For all N receiving array elements at the radar receiving end, the jammer modulates the carrier signal required for upconversion into N copies, and uses the sum of these N carrier signals to perform upconversion on M radar offset signals x m,d (t) respectively, and then superimposes and forwards the M signals.

[0047] In the support jamming scenario, the jammer and the protected target are not at the same angle, and the time delay vector t j,n of the interference signal arriving at the n-th receiving array element of the radar is also different from the time delay vector of the real target echo arriving at the n-th receiving array element of the radar. Although the time delays in the time delay vector are very small, since the reference carrier frequency f0 of the radar is often very large, when these time delays are combined with the reference carrier frequency f0 of the radar, it will cause the phase characteristics of the interference signal to be different from those of the real target echo, so that the interference signal is suppressed during beamforming. Therefore, in the support jamming scenario, in addition to performing phase modulation on the stepped frequency mΔf of the signal transmitted by the radar array element, it is also necessary to perform phase modulation on the reference carrier frequency f0 of the radar. It can be known from formula (1) that the phase difference between the false target and the real target caused by the reference frequency of the radar signal is of magnitude as shown in formula (13).

[0048]

[0049] As can be seen from Equation (13), the phase difference between the signal of each transmitting array element after being relayed by the jammer and the echo of the real target is related to the serial number n of the receiving array element where the signal arrives. Therefore, a fixed phase cannot be modulated onto the reference carrier signal f0 of a certain transmitting array element. Regarding the difference brought by the carrier frequency f0, the carrier signal used in upconversion can be modulated into N parts and superimposed to obtain x m,up (t) is as follows:

[0050]

[0051] where t up is the time difference value between the reference clock of the jammer and the reference clock of the radar during upconversion, A up is the amplitude of the upconverted signal, and l represents the l-th part of the N parts of carrier signals.

[0052] Use x m,up (t) to perform upconversion on M radar offset signals x m,d (t) respectively. The result of upconverting the m-th signal is shown in Equation (15).

[0053]

[0054]

[0055] The jammer superimposes and forwards the M upconverted signals, and the final forwarded signal is shown in Equation (16)

[0056]

[0057] The signal Y M,n (t) received by the n-th receiving array element of the FDA-MIMO radar receiver after propagation is shown in Equation (17).

[0058]

[0059] where is a basic phase term. After the above signal passes through the Figure 3 shown receiving-end processing flow, the signal output component obtained after processing the false target signal generated by this method is shown in Equation (18).

[0060]

[0061] where χ is the complex coefficient after complex envelope signal matched filtering.

[0062] The signal vector X of the false target created by the jammer is represented by the transmitting steering vector and the receiving steering vector, as shown in Equation (19).

[0063]

[0064] a(θ0, r0) and b(θ0, r0) are shown in equations (20) and (21) respectively.

[0065]

[0066]

[0067] It can be obtained through equation (8) that the result W(θ, r) of the FDA-MIMO radar after normalization processing is shown in equation (22).

[0068]

[0069]

[0070] When the jammer and the target are both in the far field of the radar, the angle difference between the jammer and the target under support jamming usually satisfies Δθ = |θ j - θ0| < 1°. Taking the target at a distance of 300 km from the radar and the jammer at a distance of 3 km from the target as an example, at this time, the angle difference Δθ between the jammer and the target is approximately 0.5°. At this time Substituting it in, the result of beamforming W(θ, r) ≈ N 2 > 1. Therefore, the enemy's FDA-MIMO radar cannot suppress the false target signal generated by this jammer.

[0071] Simulation example

[0072] In the support scenario, simulations and comparisons are carried out on the support jamming based on phase modulation and the traditional retransmission jamming to verify the jamming effect of this kind of jamming. Parameter settings: There are 15 array elements for both transmitting and receiving of the FDA-MIMO radar. The carrier frequency f0 of the signal at the transmitting end is 1 GHz, the stepped frequency Δf is 1500 Hz, the signal pulse width τ is 100 μs, the sampling frequency f s = 10 GHz, the wavelength λ of the radar signal carrier frequency is 3 m, and the spacing between the transmitting array element and the receiving array element is half a wavelength, that is, 1.5 m.

[0073] The real target is at 200 km and 30 degrees from the radar, and the jammer is at 190 km and 35 degrees from the radar. The signal-to-noise ratio of the real target echo is 20 dB. The false targets generated by direct delay retransmission are located at 210 km, 220 km, 230 km, and 35 degrees, and the signal-to-noise ratio of the false targets is 25 dB. The false targets generated after delay and phase modulation are also located at 210 km, 220 km, 230 km, and 30 degrees, and the signal-to-noise ratio of the false targets is 25 dB. The following simulates and compares the power of the false targets generated by the traditional retransmission jamming and the phase modulation retransmission jamming designed in this paper after passing through the radar beamforming.Figure 4 and Figure 5 are respectively the interference effect diagrams after the conventional delay and forwarding of the support jammer and the interference effect diagrams after phase modulation and then delay and forwarding.

[0074] From Figure 4 it can be seen that in the traditional forwarding mode of the jammer, the three false targets located at 210 km, 220 km, 230 km, and 35 degrees generated are successfully suppressed by the beamforming technology of the FDA-MIMO radar, with a suppression of approximately 140 dB. From Figure 5 it can be seen that in the support jamming scenario, the three false targets generated by the forwarded jamming after phase design at 210 km, 220 km, 230 km, and 30 degrees are not suppressed by the beamforming stage of the FDA-MIMO radar, and since the signal-to-noise ratio of the false targets forwarded by the jammer is higher than that of the echo of the real target, the signal intensity of the false targets at the radar receiving end is also higher than that of the real target echo, achieving the effect of jamming the enemy's FDA-MIMO radar.

Claims

1. A support jamming method based on phase modulation for FDA-MIMO radar is used for the support jamming scenario of the FDA-MIMO radar system. It is defined that the radar system has M transmitting array elements, and the signals transmitted by each transmitting array element differ by a stepped frequency Δf. The carrier frequency of the signal transmitted by the first transmitting array element is f0, and the carrier frequency of the signal transmitted by the m-th transmitting array element is f0+(m - 1)Δf. In the support jamming scenario, the azimuths of the jammer and the protected target are different. It is defined that the radar signal is captured by the jammer after a transmission delay of where r j and θ j represent the position of the jammer, where the subscript j is the number of the jammer, m represents the m-th transmitting array element, and d is the spacing between the transmitting array elements of the FDA-MIMO radar; it is characterized in that the jamming method comprises the following steps: S1. Down-convert the radar multiplex aliased signals received by the jammer using the carrier signal A dn exp[j2πf0(t - t dn )]: The radar multiplex aliased signal received by the jammer is as follows: where X M,j (t) with subscript M represents the sum of m transmitted signals, subscript j represents the j-th jammer, A m represents the envelope of the signal transmitted by the m-th transmitting array element, t is time, rect() is the rectangular function, and T is the duration of the radar signal pulse; With A dn exp[j2πf0(t - t dn )], the down-converted signal obtained is: Among them, A dn is the amplitude of the down-converted signal, and t dn is the time difference between the down-converted signal and the radar reference signal; S2. Filter the signal through a band-pass filter with a center frequency of mΔf respectively to obtain the offset frequency signals x m,d (t) of M transmitting array elements, where m = 0, 1, 2…, M-1: S3. Obtain the time difference Δt between the FDA-MIMO radar signal arriving at the protected target and the jammer through positioning technology, and then perform phase modulation with different magnitudes on each separated signal component to eliminate the phase difference between the interference signal and the protected target signal caused by the stepped frequency mΔf. Specifically: perform phase modulation on the offset frequencies of M transmitting array elements, where the magnitude of the phase adjusted for the m-th one is t j the sum of the modulation time of the jammer on the radar signal and the jammer time delay: where, Δt = t j,m - t m , t j,m is the transmission time for the transmission signal of the m-th transmitting array element to reach the jammer, and t m is the transmission time for the transmission signal of the m-th transmitting array element to reach the protected target; S4. For all N receiving array elements at the radar receiving end, the jammer modulates the carrier signal required for upconversion into N copies to eliminate the phase difference between the interference signal caused by the radar reference carrier frequency f0 and the protected target signal; Modulate N carrier signals and perform superposition to obtain x m,up (t) is as follows: Where A up is the amplitude of the carrier signal, t up is the time difference between the carrier signal and the radar reference signal, and l represents the l-th of N carrier signals; then use x m,up (t) to perform up-conversion on the M radar offset signals x m,d (t) respectively. The result of up-converting the m-th signal is: Finally, the jammer superimposes and forwards the M upconverted signals, and the final signal is:

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