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

Abstract

The present invention belongs to the technical field of radar jamming, and specifically relates to an accompanying forwarding jamming method for FDA-MIMO radar based on phase modulation. The method of the present invention mainly first down-converts the intercepted multi-path aliased signals of the FDA-MIMO radar using the carrier frequency, separates the signals from different transmitting elements by using band-pass filters corresponding to the offset frequencies of the transmitting elements, then performs phase modulation with different magnitudes on each separated signal component, and finally mixes and up-converts the modulated signals and forwards them, 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 an FDA-MIM0 radar accompanying transponder jamming method 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-end signals with a fixed stepped frequency difference and orthogonal to each other, making the beamforming pattern of the antenna have the characteristics of two-dimensional joint of range-angle. This characteristic brings excellent detection performance and anti-main lobe jamming ability to the FDA-MIMO radar. In terms of anti-jamming, the FDA-MIMO radar can utilize the phase difference after true and false targets reach the receiving end to suppress the false target jamming entering the main lobe of the radar. Due to the excellent anti-main lobe jamming ability of the FDA-MIMO radar, it has become very difficult to formulate a jamming scheme against it by using traditional means.

[0003] For a typical FDA-MIMO radar system, it is assumed that the radar system has M transmitting signal ends. The signals transmitted by each transmitting element differ by a stepped 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 stepped frequency of the signal.

[0004] For a traditional accompanying jamming scenario, a target platform at a distance r = r0, θ = θ0 from the FDA-MIMO radar is equipped with a traditional DRFM jamming device, as Figure 1 shown. 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 shown in Equation (1).

[0005]

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

[0007] The jammer fully samples and delays and forwards the radar signal. The signal transmitted by the m-th transmitting element of the FDA-MIMO radar is received by the n-th receiving element of the radar after being forwarded by the jammer. The signal x m，n，j (t) of the false target captured by the receiving end of the radar after being forwarded by the jammer is shown in Equation (2).

[0008]

[0009] where \(t\) n represents the time delay when the false target signal arrives at the \(n\)th receiving array element after leaving the jammer; \(t\) j represents the sum of the time when the jammer modulates the radar signal and the time delay of the jammer. \(t\) j Differences in magnitude will result in differences in the distance between the false target and the real target. The distance between the real target and the false target is denoted as \(\Delta r\), which satisfies After the signal is captured by the radar receiving end, it is processed according to the Figure 2 displayed process. First, it is sent into an analog instrument to be mixed with the carrier frequency \(\exp(j2\pi f_0t)\) 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 accompany interference is shown in Equation (3).

[0010]

[0011] where \(\chi\) j is the complex coefficient obtained after the complex envelope signal is matched filtered. The total of \(m\times n\) output signals obtained on the \(n\) receiving array elements of the radar are represented as a vector \(X\) as shown in Equation (4).

[0012] \(X = [S\) 11 , \(S\) 12 , \(\cdots\), \(S\) 1M , \(S\) 21 , \(S\) 22 , \(\cdots S\) 2M , \(\cdots\), \(S\) 2M T (4)

[0013] The above equation can be expressed as Equation (5)

[0014]

[0015] where represents the Kronecker product, \(a(\theta_0, r_0)\) is the transmit steering vector, and \(b(\theta_0, r_0)\) is the receive steering vector, as shown in Equations (6) and (7) respectively.

[0016]

[0017]

[0018] When performing beamforming, the FDA-MIMO radar uses the vector \(H(\theta_0, r_0)\) to process the filtered \(X\), and its expression is shown in Equation (8).

[0019]

[0020] ​Normalize the sum of the signal components obtained after filtering the FDA-MIMO radar, and denote the result of the normalization as W(θ, r), which represents the average power of the radar signal when it enters the radar receiving array after being reflected by the target. The expression of W(θ, r) is shown in Equation (9).

[0021]

[0022] When the position of the false target is different from that of the protected target, that is, when Δr≠0, 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. It can be seen that it is very difficult to formulate an interference scheme for the FDA-MIMO radar using traditional means. Summary of the Invention

[0023] In view of the above problems, the present invention proposes an accompanying forwarding interference method for FDA-MIM0 radar based on phase modulation.

[0024] The technical solution of the present invention is as follows:

[0025] An accompanying forwarding interference method based on phase modulation, the scheme includes the following steps:

[0026] 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.

[0027] S2. Filter the signals through band-pass filters with center frequencies of mΔf respectively to obtain the offset frequency signals of M transmitting array elements.

[0028] S3. Perform phase modulation with different magnitudes on the M separated signal components, and perform phase adjustment on the offset frequency of the m-th transmitting array element, and the magnitude of the adjusted phase is ψ m =-2πmΔft j .

[0029] S4. Superimpose the M phase-modulated signals and perform up-conversion and forwarding.

[0030] The beneficial effect of the present invention is that the method of the present invention mainly first performs down-conversion on the intercepted multiplexed radar signals of the FDA-MIMO radar using the carrier frequency, separates the signals from different transmitting array elements using band-pass filters corresponding to the offset frequencies of the transmitting array elements, then performs phase modulation with different magnitudes on each separated signal component, and finally mixes and up-converts the modulated signals and forwards them, so as to achieve the purpose of interfering with the FDA-MIMO radar. Brief Description of the Drawings

[0031] Figure 1 It is a figure of the syndrome interference scenario.

[0032] Figure 2 It is the signal processing flow of the FDA-MIMO radar.

[0033] Figure 3 It is the modulation signal flow of the jammer under the syndrome interference scenario.

[0034] Figure 4 It is the interference effect diagram after the traditional delay and forwarding of the syndrome jammer

[0035] Figure 5 It is the interference effect diagram of the syndrome jammer after phase modulation and then delay and forwarding. Specific implementation mode

[0036] The following combines the accompanying drawings and simulation examples to describe in detail the technical principle and solution of the present invention:

[0037] The present invention is divided into four parts, namely multi-channel signal down-conversion, signal separation, phase modulation, and up-conversion and forwarding. As Figure 3 shown, the specific method of the present invention is:

[0038] S1. Use the carrier signal A dn exp[j2πf0(t - t dn )] to perform down-conversion on the multi-channel overlapping radar signals received by the jammer:

[0039] The multi-channel overlapping radar signals captured by the jammer are as shown in Equation (10).

[0040]

[0041] Among them, the subscript M in X M (t) represents the sum of M transmitted signals. 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.

[0042] Mix with A dn exp[j2πf0(t - t dn )] to obtain the down-converted signal as shown in Equation (11).

[0043]

[0044] Among them, 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.

[0045] S2. Filter the signal through a band-pass filter with a center frequency of mΔf, where m = 0, 1, 2, …, M - 1, to obtain the offset frequency signals x m，d (t) of the M transmitting array elements as shown in Equation (12).

[0046]

[0047] S3. Perform phase modulation with different magnitudes on each separated signal component.

[0048] Assume that after receiving the radar signal, the jammer will fully sample and delay-forward the radar signal. Denote the total modulation time of the radar signal by the jammer and the time delay of the jammer as t j . It can be obtained from Equation (2) that after time delay, a phase difference will be generated for the offset frequency mΔf of the radar signal, and its magnitude is equal to . It can be known from Equation (9) that the additional phase difference carried by the false target can cause the interference signal generated by the jammer to be successfully suppressed. Therefore, it is necessary to perform phase adjustment on the offset frequency of the m-th transmitting array element, and the magnitude of the adjusted phase is to cancel the additional phase of the false target. The phase modulation result of the m-th signal is shown in Equation (13).

[0049]

[0050]

[0051] S4. Mix the modulated signals and perform up-conversion for forwarding.

[0052] Superimpose and up-convert and forward the M phase-modulated signals. The superimposed signal is shown in Equation (14).

[0053]

[0054] Finally, the jammer uses the carrier signal A up exp[-j2πf0(t - t up )] to perform up-conversion on the signal and forward it, and the result is shown in Equation (15).

[0055]

[0056] where t up is the time difference value between the reference clock of the jammer and the reference clock of the radar during up-conversion, and A up is the amplitude of the up-converted signal.

[0057] The signal received by the n-th receiving array element of the FDA-MIMO radar receiver after signal propagation is Y M，n(t) As shown in Equation (16).

[0058]

[0059] The above signal passes through Figure 3 the receiving - end processing flow shown below. The signal output component obtained after processing the false - target signal generated by this method is as shown in Equation (13).

[0060]

[0061] Where χ is the complex coefficient after matched filtering of the complex - envelope signal.

[0062] The signal vector X of the false target created by the jammer is represented by the transmit steering vector and the receive steering vector, as shown in Equation (17).

[0063]

[0064] a(θ0, r0) and b(θ0, r0) are as shown in Equation (18) and Equation (19) respectively.

[0065]

[0066]

[0067] Therefore, the result W(θ, r) of the FDA - MIMO radar normalization process is as shown in Equation (20).

[0068]

[0069] It can be seen that the adjoint - type forwarding interference method designed by this invention cannot be suppressed at the receiving end of the FDA - MIMO radar, achieving the effect of jamming the enemy radar.

[0070] Simulation Example

[0071] In the adjoint scenario, simulation and comparison are carried out on the adjoint - type interference based on phase modulation and the traditional forwarding - type interference to verify the interference effect of this kind of interference. 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 - wavelength, that is, 1.5 m.

[0072] The real target is located at 200 km and 30 degrees from the radar, and the jammer is at the same position as the real target. The signal-to-noise ratio of the real target echo is 20 dB. The false targets generated by direct delay and forward are 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 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. Next, the power of the false targets generated by traditional forward jamming and the phase modulation forward jamming designed in this paper after passing through the radar beamforming are simulated and compared. Figure 4 and Figure 5 are the interference effect diagrams after the conventional delay and forward of the accompany jammer and the interference effect diagrams after delay and forward after phase modulation, respectively.

[0073] From Figure 4 it can be seen that in the traditional forward mode of the jammer, the three false targets located at 210 km, 220 km, 230 km, and 30 degrees are all successfully suppressed by the beamforming technology of the FDA-MIMO radar. The false target at 210 km is suppressed by about 20 dB, the false target at 220 km is suppressed by about 140 dB, and the false target at 230 km is suppressed by about 40 dB.

[0074] From Figure 5 it can be seen that in the accompany jamming scenario, the three false targets generated by the forward 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 because the signal-to-noise ratio of the false targets forwarded by the jammer is higher than the echo of the real target, the signal intensity of the false targets at the radar receiving end is 11 dB higher than the real target echo, achieving the effect of jamming the enemy's FDA-MIMO radar.

Claims

1. A method for accompanying and relaying interference of FDA-MIMO radar based on phase modulation, which is used for the accompanying interference 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 accompanying interference scenario, the jammer is directly mounted on the protected target. It is defined that the radar signal is captured by the jammer after a transmission delay of where r and θ represent the position of the protected target, 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 interference method comprises the following steps: S1. Down-convert the radar multiplex aliased signal received by the jammer using the carrier signal A dn exp[j2πf0(t - t dn )]: The radar multiplex aliased signal captured by the jammer is: where X M (t) with the subscript M represents the sum of M transmitted signals; 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 )] is mixed, and 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. Perform phase modulation with different magnitudes on each of the separated signal components; specifically: perform phase modulation on the offset frequencies of M transmitting array elements, where the phase magnitude 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: S4. Superpose the M phase-modulated signals and up-convert and forward them. The superposed signal is: Finally, the jammer uses the carrier signal A up exp[-j2πf0(t - t up )] to up-convert and forward the signal. The forwarded signal is: Where A up is the amplitude of the carrier signal, and t up is the time difference between the up-converted carrier signal and the radar reference signal.

Images