A method and device for radar target feature recognition based on fast interference scanning with optical delay

Abstract

The present invention discloses a method and apparatus for radar target feature recognition based on fast interference scanning with optical delay. The apparatus mainly includes an antenna unit, an electro-optical converter, an optical delay numerically controlled scanning device, an optical combiner, a photodetector, and a power feature analysis device. The apparatus rapidly scans the delay amounts of two signals through an optical delay line, calculates the power of the combined signal through photoelectric conversion and linear power detection, and realizes the fast recognition of the target radar signal features by observing the relationship between the combined power and the delay amount. This method can not only be used to measure the azimuth of the target signal, but also measure the frequency and spectral features of the signal. Therefore, the device of the present invention can be applied to the detection of radar targets with different modulation systems in different electromagnetic environments.

Description

Technical Field

[0001] The present invention belongs to the field of optoelectronic technology, and particularly relates to a method and device for radar target feature recognition based on fast interference scanning with optical delay. Background Art

[0002] With the development of electronic technology in military applications, electronic countermeasure has gradually become a direct combat means for offense and defense, and is active on the stage of modern warfare. The basic means of electronic countermeasure are electronic reconnaissance, interference and destruction. Among them, electronic reconnaissance is mainly realized through radar detection technology. Radar analyzes the received electromagnetic waves to achieve rapid identification of targets. In recent years, in order to counter reconnaissance and anti-jamming, the modulation patterns and modulation parameters of radar signals have the characteristics of time-varying, fast and large range, which brings great difficulties to the reconnaissance and identification of electronic countermeasures.

[0003] In order to adapt to different combat conditions, scientific research personnel have been continuously exploring methods for quickly and accurately identifying the azimuth and spectral characteristics of radar targets. Multi-beam amplitude comparison direction finding and interferometer direction finding are two of the most widely used direction finding technologies. Multi-beam amplitude comparison direction finding determines the angle of arrival of the signal by using the relative amplitude of the signals received by the adjacent beams of the main lobe. However, this method has high requirements for the beams. To prevent the side lobes of adjacent beams from causing non-linearity to the amplitude comparison curve, it is necessary to ensure that the two beams are close enough, so that the gain of the adjacent beam coverage points is higher than the highest side lobes of the two beams, or use the design of beam width and beam position to eliminate the influence of side lobes. At the same time, as the frequency of the received signal changes, the axis angle of the antenna beam will deviate, resulting in a change in the angle corresponding to the maximum beam value. The principle of interferometer direction finding is to use the relationship between the path difference of the signal arriving at two antennas and the angle of arrival of the signal, and identify the phase difference between the two received signals through a phase discriminator to calculate the angle of arrival of the signal. Compared with multi-beam amplitude comparison direction finding, although this method has a simple structure and does not need to consider complex beam design, there are problems of mirror image ambiguity and phase ambiguity. The measured phase difference can only be within ±π, and the results beyond the phase measurement range will be unreliable. To solve the problem of mirror image ambiguity, the influence caused by the symmetric incoming waves on both sides of two single baselines can be eliminated by using two non-parallel baselines. To solve the problem of phase ambiguity, the method of using long and short baselines can be used, with short baselines ensuring a large angle measurement range and long baselines ensuring high angle measurement accuracy. Although scientific research personnel have made many optimizations and designs to improve the direction finding accuracy and detection range of the two methods, both the multi-beam amplitude comparison method and the interferometer method only focus on the estimation of the target azimuth. In the future, facing the complex battlefield electromagnetic environment and radar radiation sources with diverse systems, a method that can detect both the target azimuth and identify the target characteristics is needed. Therefore, it is of great significance to explore a method that can simultaneously measure the azimuth and spectral characteristics of radar targets. Summary of the Invention

[0004] In view of the above, the present invention provides a method and device for radar target feature recognition based on optical delay rapid interference scanning.

[0005] A method and device for radar target feature recognition based on optical delay rapid interference scanning, including an antenna unit, an electro-optic converter, an optical delay numerically controlled scanning device, an optical multiplexer, a photodetector, and a power feature analysis device; the antenna unit is used to receive radar target electrical signals, the electro-optic converter is used to convert electrical signals into optical signals, the optical delay numerically controlled scanning device is used to control the delay amount of optical signals, the optical multiplexer is used to synthesize optical signals, the photodetector is used to convert optical signals into radio frequency signals, and the power feature analysis device is used to calculate the average power of radio frequency signals and analyze radar target features; through the optical delay numerically controlled scanning device by forward scanning and reverse scanning, the radar target signal features are realized according to the power feature analysis device.

[0006] The antenna unit includes, but is not limited to, a multi-beam reflector antenna, a multi-beam lens antenna, and a multi-beam phased array antenna. It is characterized in that: the antenna unit has a plurality of antenna sub-arrays, each antenna sub-array corresponds to an input channel, the baseline length between two adjacent antenna sub-arrays is L, the arrival angle of the electrical signal is θ, the frequency is f, the wave velocity is c, and the delay difference between two antenna sub-arrays receiving the same electrical signal is ΔT = Lsinθ / c, and the phase difference is

[0007] The optical delay numerically controlled scanning device includes N levels of high-speed optical delay lines and an optical delay line controller.

[0008] Further, the N levels of high-speed optical delay lines are divided into two paths, T1 and T2, which respectively correspond to two input channels of adjacent antenna sub-arrays in the antenna unit. The N levels of high-speed optical delay lines include 2N 1x2 high-speed optical switches; according to the connection method of 1x2 to 2x1, two high-speed optical switches form one level of delay unit, with a total of N levels of delay units; the delay amount of each level of delay unit is fixed, and its value is twice that of the previous level of delay unit; the delay amount of the first level of delay unit is Δt, and the delay amount of the i-th level of delay unit is 2 i-1 ×Δt, where i ranges from 1 to N. The high-speed optical switches include, but are not limited to, magnetic optical switches, electro-optic switches, PLZT optical switches, etc.

[0009] Further, the optical delay line controller is used to change the delay amounts of the two paths of N levels of high-speed optical delay lines, T1 and T2; the optical delay line controller changes the delay amount of the i-th level of delay unit through a 1-bit state: 0 represents a delay amount of 0, and 1 represents a delay amount of 2 i-1 ×Δt; the delay amount of a single path of N levels of high-speed optical delay lines is controlled within the range of (0 to 2 N -1)×Δt through the N-bit state to control N delay units, and its resolution is Δt.

[0010] Further, the optical delay numerically controlled scanning device realizes forward scanning by fixing the delay amount of the T2 path to 0 and changing the delay amount of the T1 path within the range of (0 to 2 N -1)×Δt, and realizes reverse scanning by fixing the delay amount of the T1 path to 0 and changing the delay amount of the T2 path within the range of (0 to 2 N -1)×Δt. The optical delay numerically controlled scanning device makes the delay amount change within the range of (-(1 - 2 N ) to 2 N -1)×Δt through forward scanning and reverse scanning.

[0011] Further, the two-way N-stage high-speed optical delay lines T1 and T2 use different wavelengths λ1 and λ2. The optical multiplexer combines the two-way light into one optical fiber through wavelength division multiplexing, and obtains the radio frequency power through the photodetector.

[0012] The electro-optical converter converts the electrical signal into an optical signal. After passing through the optical delay numerically controlled scanning device, the phase difference between the two paths is:

[0013]

[0014] The power characteristic analysis device includes a linear power detector, an analog-to-digital converter, a processor, and a memory. The linear power detector is used to calculate the average power of the radio frequency signal after photodetection; the analog-to-digital converter is used to quantize the average power converted by the linear power detector; the memory is used to store the power value P quantized by the analog-to-digital converter; the processor obtains the characteristics of the radar target according to the change law of the power value P.

[0015] The power P is:

[0016]

[0017] Further simplify equation (2):

[0018]

[0019] For a single-frequency signal, A is the amplitude constant, f is the signal frequency, and the synthesized power is:

[0020]

[0021] Further, according to equation (4), the delay amount corresponding to the power peak is:

[0022]

[0023] According to equations (4) and (5), the power changes periodically with the delay amount, Tk is the delay corresponding to the power peak, and the single-frequency signal frequency is estimated through the delay interval of the power peak:

[0024]

[0025] When , that is, when there is no phase ambiguity, according to Equation (5), the arrival angle of the signal is estimated through the position T 0 of the first power peak point: For any broadband signal, the carrier frequency is f c , and the baseband signal is A(t). After combination, the power is:

[0026] The combined power is:

[0027]

[0028] According to Equation (5), the power changes periodically with the delay. T k is the delay corresponding to the power peak, and the carrier frequency of the broadband signal is estimated through the delay interval of the power peak:

[0029]

[0030] Furthermore, Equation (9) represents the power envelope curve, which is further simplified to:

[0031] E[A(t)+A(t + ΔT + T d )] 2 = E[A(t)] 2 + E[A(t + ΔT + T d )] 2 + 2E[R A (ΔT + T d )] 2

[0032] #(11)

[0033] Furthermore, the power is normalized according to the maximum value; the envelope of the power is obtained through a digital low-pass filter; as shown in Equation (12), the relative value 1 is at the maximum power, and the corresponding delay is As shown in Equation (13), the relative value 0.5 is at the minimum power; the corresponding delay is T r0.5 ;

[0034] max{E[A(t)+A(t + ΔT + T d )] 2}= 4E[A(t)] 2 #(12)

[0035] min{E[A(t)+A(t + ΔT + T d )]2} = 2E[A(t)] 2 #(13)

[0036] Since the power peak envelope is affected by the component represented by Equation (9), the maximum power appears only at the position where the two-way delay difference is 0. Therefore, there is no problem of phase ambiguity in wideband signal detection, and the arrival angle of the signal can be estimated from the delay amount corresponding to the maximum power peak Estimate the arrival angle of the signal:

[0037] When the signal bandwidth is relatively small, the slope change at the maximum power point is not obvious. Take the middle value of the delay amounts T x1 and T x2 at two identical powers at the far end of the envelope curve for estimation

[0038]

[0039] Furthermore, according to the characteristic that the power component outside the signal bandwidth is weak, take the one closest to the center T r1 on the power envelope to estimate the signal bandwidth:

[0040]

[0041] A method for radar target feature recognition based on fast optical delay interference scanning is to change the delay amounts of the two paths of T1 and T2 through the optical delay numerically controlled scanning device, and observe the law of the power change with the delay amount after the two paths are combined, so as to realize the fast analysis of the spectral characteristics and arrival angle of the radar target signal. Among them, the frequency of the single-frequency signal is obtained through the delay amount interval of the power peak, and the arrival angle of the signal is obtained through the delay amount corresponding to the first peak point; the carrier frequency of the wideband signal is obtained through the delay amount interval of the power peak, the arrival angle of the signal is estimated through the delay amount corresponding to the maximum power, and the spectral bandwidth of the wideband signal is estimated through the delay amount span of the main lobe of the power peak envelope. Compared with the traditional radar target detection technology, this method can not only be used to measure the azimuth of the signal, but also measure the spectral characteristics of the signal. Therefore, the device of the present invention is applicable to the detection of radar targets with different modulation systems in different electromagnetic environments. Brief Description of the Drawings

[0042] Figure 1 It is the system structure block diagram of the device of the present invention.

[0043] In the figure: 1 - antenna unit, 2 - electro-optic converter, 3 - optical delay numerically controlled scanning device, 4 - optical combiner, 5 - photodetector, 6 - power feature analysis device, 7 - optical delay line controller, 8 - N-stage high-speed optical delay line, 9 - analog-to-digital converter, 10 - memory, 11 - processor, 12 - linear power detector.

[0044] Figure 2.a It is the graph of the combined power change of the single - frequency signal for the T1 - path delay scan

[0045] Figure 2.b It is the graph of the combined power change of the single - frequency signal for the T2 - path delay scan

[0046] Figure 3.a It is the spectrum graph of the QPSK signal

[0047] Figure 3.b It is the graph of the combined power change of the QPSK signal for the T1 - path delay scan

[0048] Figure 3.c It is the graph of the combined power change of the QPSK signal for the T2 - path delay scan Specific implementation manner

[0049] In order to describe the present invention more specifically, the technical solutions of the present invention will be described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0050] As Figure 1 shown, a device system for radar target feature recognition based on optical delay fast interference scanning includes an antenna unit 1, an electro - optical converter 2, an optical delay numerically controlled scanning device 3, an optical combiner 4, a photodetector 5, and a power feature analysis device 6. Among them, the optical delay numerically controlled scanning device 3 includes two N - stage high - speed optical delay lines 8 and an optical delay line controller 7; the power feature analysis device 6 includes an analog - to - digital converter 9, a memory 10, a processor 11, and a linear power detector 12.

[0051] The antenna unit 1 is connected to the electro - optical converter 2 through a radio frequency line; the electro - optical converter 2, the optical delay numerically controlled scanning device 3, the optical combiner 4, and the photodetector 5 are sequentially connected through optical fibers; the photodetector 5 is connected to the power feature analysis device 6 through a radio frequency line. Inside the optical delay numerically controlled scanning device 3, the optical delay line controller 7 controls the two N - stage high - speed optical delay lines 8 through two N - bits wide data buses. The power feature analysis device 6 sends a scanning control instruction to the optical delay line controller 7 through a control bus.

[0052] In this embodiment, the N - stage high - speed optical delay lines 8 are divided into two paths, T1 and T2, and T1 and T2 respectively correspond to two input channels of adjacent antenna sub - arrays in the antenna unit 1. Each of T1 and T2 paths contains 2N 1x2 high - speed optical switches: according to the connection method of 1x2 to 2x1, two high - speed optical switches form a first - stage delay unit, with a total of N - stage delay units; the delay amount of each stage of delay unit is fixed, and its value is twice that of the previous - stage delay unit; the delay amount of the first - stage delay unit is Δt, and the delay amount of the i - th stage delay unit is 2 i-1×Δt, where i ranges from 1 to N. The processor 11 sends an optical delay scanning control instruction to the optical delay line controller 7. The optical delay line controller 7 changes the delay amount of the i-th stage delay unit through a 1-bit state: 0 represents a delay amount of 0, and 1 represents a delay amount of 2 i-1 ×Δt; The delay amount of the single-channel N-stage high-speed optical delay line is controlled within the range of (0 to 2 N -1)×Δt through the states of N bits to control N delay units, and its resolution is Δt. The T1 path and the T2 path respectively adopt different wavelengths λ1 and λ2; The optical multiplexer 4 uses wavelength division multiplexing to combine two optical signals with different wavelengths into one optical signal, and converts the optical signal into a radio frequency signal through the photodetector 5. Inside the power characteristic analysis device 6, the linear power detector 12 is used to calculate the power of the radio frequency signal. The analog-to-digital converter 9 quantifies the power and sends it to the processor 11 through the data bus. The processor 11 stores the quantified data in the memory 10 through the data bus and the address bus. The processor obtains the characteristics of the target signal according to the variation law of the power value with the delay amount.

[0053] In this embodiment, to more conveniently illustrate the method of using this device for radar target feature recognition, the test results of single-frequency signal delay scanning are described: When the baseline length L of the two antenna subarray channels is 0.5 m, the target signal frequency is 200 MHz, and the signal arrival angle is 30°, the delay difference between the two paths is approximately 833.3 ps; As shown in Figure 2a, fix the optical delay of the T2 path to 0 and let the optical delay of the T1 path scan within the range of 0 to 10230 ps; As shown in Figure 2a, the delay amount of the first power peak is 834 ps, and the arrival angle of the signal arcsin(0.5004)≈30° is calculated according to Equation (7); The delay amount of the second power peak is 5834 ps, with a delay amount of 5 ns from the first power peak. The frequency of the signal is calculated to be 200 MHz according to Equation (6); As shown in Figure 2b, fix the optical delay of the T1 path to 0 and the optical delay of the T2 path scans within the range of 0 to 10230 ps; As shown in Figure 2b, the first power peak is -4167 ps (relative to the T1 path), with the same interval of 5 ns as the first power peak in Figure 2a, which coincides with the target signal period.

[0054] In this embodiment, for the convenience of better explaining the method of using this device for radar target feature recognition, the test results of wideband signal delay scanning are described: the baseline length L of the two-antenna subarray channels is 0.5 m, the target signal is a QPSK signal with a carrier frequency of 20 GHz and a bandwidth of 4 GHz, the signal arrival angle is 30°, and the delay difference between the two paths is approximately 833.3 ps; as shown in Fig. 3a, it is the spectrogram of the received electrical signal; as shown in Fig. 3b, the optical delay of the T2 path is fixed at 0, and the optical delay of the T1 path is scanned in the range of 0 to 10230 ps; the delay amount of the maximum power peak is 834 ps, and the arrival angle of the signal arcsin(0.5004)≈30° is calculated according to Equation (10); as shown in Fig. 3b, centered on the maximum power peak, the power peak shows periodic and amplitude-decaying characteristics on both sides: a power wave peak with gradually decaying amplitude is generated at an interval of 50 ps, and the amplitude decays to the lowest at an interval of 250 ps. The carrier frequency is calculated to be 20 GHz according to the delay amount of 50 ps between the power peak delays, and the signal bandwidth is calculated to be 4 GHz according to the delay amount span of 250 ps of the main lobe of the power peak envelope curve. When the received signal bandwidth is narrow, the position of the maximum power peak can also be calculated through the sub-highest power peaks. For example, the center of 734 ps and 934 ps is 834 ps.

[0055] The above description of the embodiments is to enable those of ordinary skill in the art to understand and apply the present invention. It is obvious that those skilled in the art can easily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art based on the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A method for radar target feature recognition based on fast interference scanning with optical delay, characterized in that: The method comprises the following steps: Providing an antenna unit, an electro-optical converter, an optical delay numerically controlled scanning device, an optical combiner, a photodetector, and a power feature analysis device; wherein, the antenna unit is used for receiving radar target electrical signals, the electro-optical converter is used for converting electrical signals into optical signals, the optical delay numerically controlled scanning device is used for controlling the delay amount of optical signals, the optical combiner is used for optical signal synthesis, the photodetector is used for converting optical signals into radio frequency signals, and the power feature analysis device is used for calculating the average power of radio frequency signals and analyzing radar target features; the optical delay numerically controlled scanning device comprises two N-stage high-speed optical delay lines T1 and T2, and an optical delay line controller; the power feature analysis device comprises a linear power detector, an analog-to-digital converter, a processor, and a memory; The optical delay numerically controlled scanning device changes the delay amounts of the optical delay lines T1 and T2 through forward scanning and reverse scanning, and the power feature analysis device observes the law of the power change with the delay amount after the two paths are combined, so as to realize the fast analysis of the spectral features and arrival angles of radar target signals; wherein, the frequency of a single-frequency signal is obtained through the delay amount interval of the power peak, and the arrival angle of the signal is obtained through the delay amount corresponding to the first peak point; the carrier frequency of a broadband signal is obtained through the delay amount interval of the power peak, the arrival angle of the signal is estimated through the delay amount corresponding to the maximum power, and the spectral bandwidth of the broadband signal is estimated through the delay amount span of the main lobe of the power peak envelope.

2. The method according to claim 1, characterized in that, The antenna unit includes, but is not limited to, a multi-beam reflector antenna, a multi-beam lens antenna, and a multi-beam phased array antenna; the antenna unit has a plurality of antenna sub-arrays, and each antenna sub-array corresponds to an input channel; the baseline length between adjacent antenna sub-arrays is L, the arrival angle of the signal is θ, the frequency is f, and the wave velocity is c; when adjacent antenna sub-arrays receive the same signal, the delay difference between the two channels is ΔT, and its value is Lsinθ / c, and the phase difference is 2πfΔT.

3. The method according to claim 1, characterized in that, The N-stage high-speed optical delay lines T1 and T2 respectively correspond to the input channels of two antenna sub-arrays of the antenna unit; the N-stage high-speed optical delay line includes 2N 1x2 high-speed optical switches: in the connection mode of 1x2 to 2x1, two high-speed optical switches form one-stage delay unit, and there are N-stage delay units in total; the delay amount of each stage of delay unit is fixed, and its value is twice that of the previous stage of delay unit; the delay amount of the first-stage delay unit is Δt, and the delay amount of the i-th stage of delay unit is 2 i-1 ×Δt, where i ranges from 1 to N; the high-speed optical switch includes but is not limited to magneto-optical switch, electro-optical switch, semiconductor optical switch, and PLZT optical switch; the switch switching speeds are in the microsecond or nanosecond level respectively.

4. The method according to claim 3, characterized in that, The optical delay line controller is used to change the delay amounts of two N-stage high-speed optical delay lines of T1 and T2. The optical delay line controller changes the delay amount of the i-th delay unit through a 1-bit state: 0 represents that the delay amount is 0, and 1 represents that the delay amount is 2 i-1 ×Δt. The delay amount of a single N-stage high-speed optical delay line is controlled by N bits to control N delay units, so that the delay amount can vary within the range of (0 to 2 N -1)×Δt, and its resolution is Δt.

5. The method according to any one of claims 1, 3, and 4, characterized in that, The optical delay numerically controlled scanning device realizes forward scanning by fixing the delay of the T2 path to 0 and changing the delay of the T1 path within the range of (0 to 2 N -1)×Δt, and realizes reverse scanning by fixing the delay of the T1 path to 0 and changing the delay of the T2 path within the range of (0 to 2 N -1)×Δt; the optical delay numerically controlled scanning device makes the delay T d vary within the range of (-(1 - 2 N ) to 2 N -1)×Δt through forward scanning and reverse scanning.

6. The method according to any one of claims 1, 3, and 4, characterized in that, The two N-stage high-speed optical delay lines T1 and T2 use lights of different wavelengths, and the T1 path and the T2 path correspond to wavelengths λ1 and λ2 respectively; the optical combiner uses the wavelength division multiplexing method to synthesize optical signals of two different wavelengths into the same optical path.

7. The method according to claim 5, characterized in that: The linear power detector is used for calculating the average power of the radio frequency signal converted by the photodetector; the analog-to-digital converter is used for quantifying the average power obtained by the linear power detector; the memory is used for storing the power value P quantified by the analog-to-digital converter; the processor obtains the features of the radar target according to the change law of the power value P with the delay amount. Each time the delay amount T of the optical delay numerically controlled scanning device changes d , the power characteristic analysis device calculates the corresponding power and stores it; After the forward and reverse scans of the optical delay numerically controlled scanning device are completed, extract the power peak P(T k ) and its corresponding delay amount T k ; and based on the power peak P(T k ) and its corresponding delay amount T k obtain the characteristics of the radar target.

8. The method according to claim 7, wherein, When the radar target signal is a single-frequency signal, the period of the single-frequency signal is obtained through the delay amount interval (T k+1 -T k ), and the frequency of the single-frequency signal is calculated; the delay difference ΔT between the two input channels is obtained through the delay amount T 0 corresponding to the first power peak P(T 0 ), and the arrival angle θ of the single-frequency signal is calculated.

9. The method according to claim 7, wherein, When the radar target signal is a broadband signal, the carrier period of the broadband signal is obtained through the delay amount interval (T k+1 -T k ), and the carrier frequency is calculated; the bandwidth of the broadband signal is calculated through the delay amount span of the main lobe of the envelope curve of the power peak, and the delay difference ΔT between the two input channels is obtained according to the delay amount corresponding to the center maximum power , and the arrival angle θ of the broadband signal is calculated.

10. The method according to claim 9, wherein, When the radar target signal is a narrowband signal, calculate the delay corresponding to the center maximum power through the delay amounts corresponding to two equal-power value points on the power peak envelope curve, and according to the delay amount corresponding to the center maximum power obtain the delay difference ΔT between the two input channels, and calculate the arrival angle θ of the broadband signal; obtain the carrier period of the broadband signal through the interval of the power peaks, and calculate the carrier frequency.

Images