Digital multi-beam detection method for aerial targets based on terahertz focal plane

Abstract

The present invention proposes a digital multi-beam detection method for aerial targets based on a terahertz focal plane, and the implementation steps are: (1) initializing an aerial target digital multi-beam detection system; (2) obtaining a terahertz echo signal received by an array antenna; (3) obtaining a digital multi-beam signal; (4) obtaining an aerial target digital multi-beam detection result. In the present invention, the array antenna transmits and receives terahertz signals through a terahertz lens array and a beam-forming lens, and the terahertz lens device expands the beam of the array antenna, effectively improving the instantaneous detection range; the array antenna uses digital multi-beam forming technology when transmitting and receiving terahertz signals, controls multiple beams to point to the terahertz lens array in the terahertz lens device, realizes long-term observation of targets in a fixed observation domain, and uses coherent accumulation to improve the signal-to-noise ratio of the echo signal.

Description

Technical Field

[0001] The invention belongs to the technical field of radar target detection and relates to a digital multi-beam detection method for aerial targets based on a terahertz focal plane, which is used for detecting aerial targets in a large range. Background Art

[0002] Terahertz is a section of electromagnetic waves between microwaves and infrared, and the frequency range is usually defined as 0.1THz-10THz. The wavelength of the terahertz frequency band is short, which can realize large time-bandwidth product signals and extremely narrow antenna beams, which is very convenient for high-resolution detection of targets. In the application of terahertz, lenses are very important components, which can realize the expansion and focusing of terahertz waves; target detection is that the radar actively transmits electromagnetic wave signals, receives signals reflected by the target, and then analyzes the echo to obtain target information and realize target detection; digital beamforming technology is to form a beam by performing complex weighted processing on digital signals at the baseband, thereby replacing the part of the traditional phased array antenna that uses analog devices to form beams. Therefore, applying different complex weights to the array antenna can form beams in different directions to achieve coverage of the observation domain; digital multi-beam detection is to perform digital signal processing on the echo signals in the multi-beam coverage area, and detect whether there is a target in the echo signal through a constant false alarm detector;

[0003] In recent years, digital multi-beamforming technology has been increasingly widely used in target detection. For example, the patent with the authorization announcement number CN110161474 B and the name "A method for detecting low-altitude, slow and small targets based on digital beamforming technology" provides a method for detecting low-altitude, slow and small targets based on digital beamforming technology. The method uses a low-altitude defense radar based on digital beamforming technology, and uses digital beamforming technology in the elevation direction to form multiple beams to achieve elevation airspace coverage. Servo is used for mechanical scanning in the horizontal direction to obtain radar echo data of different antenna units, and the echo data is coherently accumulated and constant false alarm detection is performed to obtain the detection results of low-altitude, slow and small targets in the low-altitude defense area. The method controls the low-altitude defense radar to perform mechanical scanning of the low-altitude defense area at a certain rotation speed by servo control. Due to the rotation speed, the instantaneous detection range is small, and the beam of the array antenna stays on the target for a short time, resulting in a small number of pulses accumulated during the coherent accumulation of the echo signal, which in turn affects the improvement of the signal-to-noise ratio of the echo signal. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and propose a digital multi-beam detection method for aerial targets based on terahertz focal plane to solve the technical problems of small instantaneous detection range and low echo signal noise in the prior art.

[0005] To achieve the above object, the technical solution adopted by the present invention includes the following steps:

[0006] (1) Initialize the digital multi-beam detection system for aerial targets:

[0007] Initialization includes a terahertz lens device composed of a square terahertz lens array and a beam-forming lens with overlapping center lines, an array antenna located at the focus position of the beam-forming lens, a digital multi-beam forming module and a constant false alarm detector for airborne targets; the terahertz lens array includes K periodically arranged terahertz lenses; the array antenna is composed of P×Q antenna units arranged periodically and with an array element spacing of d; wherein K≥4, P≥2, Q≥2;

[0008] (2) Obtaining the terahertz echo signal received by the array antenna:

[0009] Obtain the echo signal S(t) of K terahertz pulse signals emitted by the array antenna to the fixed observation domain through the terahertz lens group at time t, and for each echo signal s k (t-τ k ) performs N samplings to obtain the sampled echo signal X received by the array antenna:

[0010] S(t)=[s1(t-τ1), s2(t-τ2),…,s k (t-τ k ), …, s K (t-τ K )] T

[0011] X=[x 11 (n),x 12 (n),…x pq (n),…x PQ (n)] T

[0012] Where N ≥ 2, k = 1, 2...K, p = 1, 2...P, q = 1, 2...Q, s k (t-τ k ) represents the kth echo signal at time t, τ k represents the time delay between the kth transmitted signal and the echo signal, x pq (n) represents the K echo signals received by the array element in the pth row and qth column;

[0013] (3) Obtaining digital multi-beam signals:

[0014] The digital multi-beam forming module is based on the kth echo signal s k (t-τ k ) of the pitch angle θ k , azimuth And the array element spacing d, calculate the weighted vector W of the kth echo signal k and through W k The conjugate transpose of and the sampled echo signal X received by the array antenna calculates the kth beam signal y k (n), K beam signals form a multi-beam signal y(n):

[0015] y(n)=[y1(n),y2(n),…y k (n),…y K (n)] T

[0016] y k (n) = W k H X(n)

[0017]

[0018] Among them, W k H W k The conjugate transpose result of ;

[0019] (4) Obtaining digital multi-beam detection results of aerial targets:

[0020] The constant false alarm detector is based on each beam signal y k (n) Calculate y k (n) detection threshold T k , and judge y k (n) Amplitude y k With T k Does it satisfy y k ≥T k Is it true? If so, then y k (n) has a target, otherwise, y k There is no target in (n).

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. The present invention uses an array antenna located at the focal position of a focusing lens of a terahertz lens device to obtain echo signals of multiple terahertz pulse signals emitted by the array antenna through a terahertz lens array to a fixed observation domain, thereby avoiding the defect of the prior art of using angular mechanical scanning due to being limited by the rotation speed, and effectively broadening the instantaneous detection range.

[0023] 2. The array antenna of the present invention adopts digital multi-beam forming technology when transmitting and receiving terahertz signals, controls multiple beams to point to the terahertz lens array in the terahertz lens device, and realizes long-term observation of the target in a fixed observation domain. The residence time of the beam on the target becomes longer, thereby increasing the number of pulses that can be effectively accumulated, and improving the signal-to-noise ratio of the echo signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a flow chart of the implementation of the present invention;

[0025] Figure 2 is a schematic structural diagram of a terahertz lens device of the present invention;

[0026] Figure 3 It is a schematic diagram of the terahertz lens focusing beam of the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0028] Reference Figure 1 , the present invention comprises the following steps:

[0029] Step 1) Initialize the digital multi-beam detection system for aerial targets:

[0030] The digital multi-beam detection system for aerial targets is initialized, which includes a terahertz lens device consisting of a square terahertz lens array and a beam-forming lens with overlapping center lines, an array antenna located at the focus position of the beam-forming lens, a digital multi-beam forming module and a constant false alarm detector.

[0031] The structure of the terahertz lens array is as follows: Figure 2 As shown, K terahertz lenses are periodically arranged on a terahertz lens substrate, and the focusing lens includes an upper curved surface and a lower curved surface, both of which are spherical surfaces, and the radius of the upper curved surface is smaller than the radius of the lower curved surface, thereby effectively realizing the focusing of the terahertz signal, wherein K=64.

[0032] The beam can be converged to its focal position through the terahertz lens. The normal of each terahertz lens coincides with the normal of the array element of the array antenna, that is, the terahertz lens array and the array element of the array antenna correspond one to one, such as Figure 3 As shown; the terahertz lens substrate is a rectangular three-dimensional structure made of metal or rubber, and the terahertz lens array is uniformly embedded in it; the array antenna is composed of P×Q antenna units arranged periodically and with an array element spacing of d, where P=8 and Q=8.

[0033] Step 2) Obtain the terahertz echo signal received by the array antenna:

[0034] Obtain the echo signal S(t) of K terahertz pulse signals emitted by the array antenna to the fixed observation domain through the terahertz lens group at time t. The number of pulses is 128, and the field of view of the fixed observation domain is not less than 60°×60°. For each echo signal s k (t-τ k ) performs N samplings to obtain the sampled echo signal X received by the array antenna:

[0035] S(t)=[s1(t-τ1), s2(t-τ2),…,s k (t-τ k ), …, s K (t-τ K )] T

[0036] X=[x 11 (n),x 12 (n),…x pq (n),…x PQ (n)] T

[0037]

[0038]

[0039]

[0040] S=[s1(n-n1), s2(n-n2),…s k (nn k ), …s K (nn K )] T

[0041] V=[v 11 (n), v 12 (n),…v PQ (n)] T

[0042]

[0043] Where N ≥ 2, k = 1, 2...K, p = 1, 2...P, q = 1, 2...Q, s k (t-τ k ) represents the kth echo signal at time t, τ k represents the time delay between the kth transmitted signal and the echo signal, x pq (n) represents the K echo signals received by the array element in the pth row and qth column, is the orientation vector matrix, represents the steering vector of the p-th row and q-th column array element receiving the k-th echo signal. The steering vector represents the spatial phase difference between the p-th row and q-th column array element and the 1-th row and 1-th column array element. j represents the imaginary unit, and λ represents the wavelength. S represents the sampling value of the echo signal, s k (nn k ) means s k (t-τ k ) The sampled signal, n k represents the time delay τ k The sampling value of V represents the P×Q-dimensional zero-mean Gaussian white noise vector, v pq (n) represents the zero-mean Gaussian white noise received by the p-th row and q-th column array element.

[0044] Step 3) Obtain digital multi-beam signal:

[0045] The digital multi-beam forming module is based on the kth echo signal s k (t-τ k ) of the pitch angle θ k , azimuth And the array element spacing d, calculate the weighted vector W of the kth echo signal k and through W k The conjugate transpose of and the sampled echo signal X received by the array antenna calculates the kth beam signal y k (n), the role of the weighted vector is to make the beam of the array antenna point to the direction of the kth echo when it receives the echo, so that the received echo signal is maximized. K beam signals form a multi-beam signal y(n):

[0046] y(n)=[y1(n),y2(n),…y k (n),…y K (n)] T

[0047] y k (n) = W k H X(n)

[0048]

[0049] Among them, W k H W k The conjugate transpose of .

[0050] Step 4) Obtain the digital multi-beam detection results of aerial targets:

[0051] The beam signal accumulates 128 pulses and performs fast Fourier transform processing between pulses to achieve coherent accumulation operation, which increases the beam signal noise ratio by 128 times. k (n) Calculate y k (n) detection threshold T k , and its calculation formula is:

[0052]

[0053] Determine y k (n) Amplitude y k With T k Does it satisfy y k ≥T k Is it true? If so, then y k (n) has a target, otherwise, y k (n) does not contain a target, where α represents the threshold factor, P fa represents the false alarm probability, P fa =10 -6 .

Claims

1. A digital multi-beam detection method for aerial targets based on terahertz focal plane, characterized in that: The steps include: (1) Initialize the digital multi-beam detection system for aerial targets: Initialization includes a terahertz lens device consisting of a square terahertz lens array with overlapping center lines and a beam-forming lens, an array antenna located at the focus position of the beam-forming lens, a digital multi-beam forming module and a constant false alarm detector for airborne target digital multi-beam detection; the terahertz lens array includes K periodically arranged terahertz lenses; The array antenna is composed of P×Q antenna units arranged periodically and with an array element spacing of d; wherein K≥4, P≥2, Q≥2; (2) Obtaining the terahertz echo signal received by the array antenna: Obtain the echo signal S(t) of K terahertz pulse signals emitted by the array antenna to the fixed observation domain through the terahertz lens array at time t, and for each echo signal s k (t-τ k ) performs N samplings to obtain the sampled echo signal X received by the array antenna: S(t)=[s1(t-τ1),s2(t-τ2),···,s k (t-τ k ),···,s K (t-τ K )] T X=[x 11 (n),x 12 (n),···x pq (n),···x PQ (n)] T Where N ≥ 2, k = 1, 2...K, p = 1, 2...P, q = 1, 2...Q, s k (t-τ k ) represents the kth echo signal at time t, τ k represents the time delay between the kth transmitted signal and the echo signal, x pq (n) represents the K echo signals received by the array element in the pth row and qth column; (3) Obtaining digital multi-beam signals: The digital multi-beam forming module is based on the kth echo signal s k (t-τ k ) of the pitch angle θ k , azimuth And the array element spacing d, calculate the weighted vector W of the kth echo signal k and through W k The conjugate transpose of and the sampled echo signal X received by the array antenna calculates the kth beam signal y k (n), K beam signals form a multi-beam signal y(n): y(n)=[y1(n),y2(n),···y k (n),···y K (n)] T y k (n)=W k H X(n) Among them, W k H W k The conjugate transpose result of ; (4) Obtaining digital multi-beam detection results of aerial targets: The constant false alarm detector is based on each beam signal y k (n) Calculate y k (n) detection threshold T k , and judge y k (n) Amplitude y k With T k Does it satisfy y k ≥T k Is it true? If so, then y k (n) has a target, otherwise, y k There is no target in (n).

2. The digital multi-beam detection method for aerial targets based on terahertz focal plane according to claim 1 is characterized in that: The array antenna described in step (2) receives the sampled echo signal X, and the K echo signals x received by the array element in the pth row and qth column pq (n), and the calculation formulas are: S=[s1(n-n1),s2(n-n2),···s k (n-n k ),···s K (n-n K )] T V=[v 11 (n),v 12 (n),···v PQ (n)] T in, is the orientation vector matrix, represents the steering vector of the p-th row and q-th column array element receiving the k-th echo signal, j represents the imaginary unit, λ represents the wavelength, S represents the sampling value of the echo signal, s k (nn k ) means s k (t-τ k ) The sampled signal, n k represents the time delay τ k The sampling value of V represents the P×Q-dimensional zero-mean Gaussian white noise vector, v pq (n) represents the zero-mean Gaussian white noise received by the p-th row and q-th column array element.

3. The digital multi-beam detection method for aerial targets based on terahertz focal plane according to claim 1 is characterized in that: The detection threshold T described in step (4) k , and its calculation formula is: Among them, α represents the threshold factor, P fa represents the false alarm probability, P fa <1.

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