Novel non-line-of-sight target detection method and system

Abstract

The invention discloses a novel non-line-of-sight target detection method and system. The non-line-of-sight target detection method comprises the steps that a ground radar transmits a signal to an airborne relay system; the relay system receives and amplifies a transmitting signal of the radar, and forwards the enhanced transmitting signal to a to-be-detected target; the to-be-detected target receives the enhanced emission signal and generates an echo signal; the relay system receives and amplifies the target echo signal, and forwards the enhanced echo signal to the ground radar; and the ground radar processes the received enhanced target echo signal so as to realize non-line-of-sight target detection. The non-line-of-sight target detection system comprises a ground radar, an airborne relay system and a to-be-detected target. According to the invention, the airborne relay system is used for enhancing radar emission signals and target scattering echo signals, the radar detection range is expanded, and non-line-of-sight targets shielded by high-rise buildings in the urban environment can be detected.

Description

Technical Field

[0001] The invention belongs to the technical field of radar signal processing and relates to a novel non-line-of-sight target detection method and system. Background Art

[0002] Traditional radar detection methods are for line-of-sight targets, that is, there are no obstacles between the radar and the target. For non-line-of-sight targets, it is difficult for electromagnetic waves to penetrate multiple layers of obstacles to obtain target information, resulting in the failure of traditional line-of-sight target detection methods. In urban environments, due to the obstruction of buildings, the radar transmission signal cannot propagate to the target in a straight line, resulting in the inability of UAV targets and ground vehicle targets behind the buildings to be effectively detected by the radar. Therefore, how to accurately obtain target information and realize non-line-of-sight target detection for obscured non-line-of-sight targets has become one of the technical problems that need to be solved at present.

[0003] Existing non-line-of-sight target detection technologies mainly include penetration detection technology and multipath detection technology. Penetration detection technology uses the transmission characteristics of electromagnetic waves to obtain information about non-line-of-sight targets by processing radar echoes that penetrate obstacles. Multipath detection technology uses multipath components such as reflection and diffraction of electromagnetic waves to detect hidden targets in corner non-line-of-sight scenarios. When electromagnetic waves penetrate multiple layers of obstacles or thicker buildings, the energy of the electromagnetic waves is severely attenuated, resulting in poor detection results. In multipath detection technology, the energy of electromagnetic waves is also attenuated after being reflected by the wall, and it will be interfered by multiple reflection signals between walls, resulting in false targets in the detection results. Whether it is transmission detection technology or multipath detection technology, the energy of electromagnetic waves is greatly attenuated during the propagation process, resulting in a limited non-line-of-sight detection range.

[0004] The non-line-of-sight detection technology of targets is mainly used in specific non-line-of-sight scenarios, and due to the attenuation of the energy of electromagnetic waves during transmission, reflection and diffraction, the current application scenarios of this non-line-of-sight detection technology are relatively small. For long-distance aerial drone targets and ground vehicle targets blocked by buildings, the signal-to-noise ratio of the echo signal received by the radar in the penetration detection technology and multipath detection technology is very small, and effective non-line-of-sight target detection cannot be achieved. Summary of the invention

[0005] The present invention aims to solve the technical problem in the prior art that the energy of electromagnetic waves is severely attenuated during transmission, reflection and diffraction, resulting in a limited detection range. The present invention provides a new non-line-of-sight target detection method and system, and the technical solution adopted is:

[0006] A novel non-line-of-sight target detection method comprises the following steps:

[0007] S1. Ground radar transmits signals to the airborne relay system;

[0008] S2, the relay system receives and amplifies the transmission signal, and forwards the enhanced transmission signal to the target to be detected;

[0009] S3, the target to be detected receives the enhanced transmission signal and generates a target echo signal;

[0010] S4, the relay system receives and amplifies the target echo signal, and forwards the enhanced target echo signal to the ground radar;

[0011] S5. The ground radar processes the received enhanced target echo signal to achieve detection of non-line-of-sight targets.

[0012] In one embodiment of the present invention, step S1 comprises:

[0013] The ground radar transmits a linear frequency modulation pulse signal, which is expressed as:

[0014]

[0015] In formula (1), rect[]] is a rectangular function, K is the frequency modulation slope and K = B w / T p , where B w is the signal bandwidth, T p is the pulse duration of the linear frequency modulated pulse signal, f c is the carrier frequency of the signal.

[0016] In one embodiment of the present invention, step S2 comprises:

[0017] The relay system receiving the transmission signal is represented as follows:

[0018]

[0019] In formula (2), P t is the transmitting power of the ground radar, For ground radar The transmitting antenna gain in the direction, For the airborne relay system to receive Directional receiving antenna gain, is the azimuth and elevation angle of the airborne relay system relative to the ground radar, L p1 is the power propagation loss from the ground radar to the airborne relay system, λ is the wavelength of the radar signal, and Δτ1 is the time delay corresponding to the transmission of the radar signal to the airborne relay system;

[0020] The transmission signal forwarded by the relay system to the target to be detected is expressed as:

[0021]

[0022] In formula (3), η represents the power gain factor of the airborne relay system, Transmit for the relay system The transmission gain of the directional signal, is the azimuth and elevation angle of the target relative to the airborne relay system, L p2 is the power transmission loss from the airborne relay system to the target, and Δτ2 is the delay corresponding to the transmission of the relay amplified signal from the airborne relay system to the target.

[0023] In one embodiment of the present invention, step S3 comprises:

[0024] The echo signal generated by the target to be detected is expressed as:

[0025]

[0026] In formula (4), σ is the scattering cross-sectional area of ​​the target.

[0027] In one embodiment of the present invention, step S4 comprises:

[0028] The relay system receives the echo signal, which is represented as:

[0029]

[0030] In formula (5), L p3 is the power propagation loss from the target to the airborne relay system, Δτ3 is the time delay corresponding to the target scattered signal being transmitted to the airborne relay system;

[0031] The echo signal forwarded by the relay system received by the ground radar is expressed as:

[0032]

[0033] In formula (6), L p4 is the power propagation loss from the airborne relay system to the ground radar, Δτ4 is the time delay corresponding to the target echo signal enhanced by the airborne relay system being transmitted to the ground radar;

[0034] Therefore, the echo signal of the target to be detected received by the ground radar is expressed as:

[0035]

[0036] In formula (7), P r is the target echo power received by the ground radar, R1 is the slant distance between the ground radar and the airborne relay system, R2 is the slant distance between the airborne relay system and the target, and c is the speed of light;

[0037] The target echo is expressed as follows after removing the carrier frequency:

[0038]

[0039] The echo power of the ground radar receiving the non-line-of-sight target is expressed as:

[0040]

[0041] In formulas (8) and (9), P t is the radar transmitting power, is the radar antenna gain, is the antenna gain of the relay receiving radar signal, is the antenna gain of the relay transmitting signal to the target, σ is the scattering coefficient of the target, η is the power amplification factor of the relay, λ is the wavelength, R1 is the radial distance from the radar to the airborne relay, and R2 is the radial distance from the airborne relay to the target.

[0042] In one embodiment of the present invention, in step S5, a pulse Doppler radar processing method is used to perform target detection;

[0043] The pulse Doppler radar echo signal processing process includes: echo data preprocessing, pulse compression, moving target display, Doppler filtering, target detection, and target parameter estimation.

[0044] In one embodiment of the present invention, the target Doppler frequency acquired in the target parameter estimation is composed of the Doppler frequency of the relay system relative to the ground radar and the Doppler frequency of the target to be detected relative to the relay system.

[0045] In one embodiment of the present invention, the Doppler frequency of the ground radar receiving the target to be detected is f d , f d It is expressed as:

[0046] f d =f d1 +f d2 (14)

[0047] In formula (14), f d1 and f d2 f are the Doppler frequency of the airborne relay system relative to the ground radar and the Doppler frequency of the non-line-of-sight target relative to the airborne relay platform, respectively. d1 and f d2 Respectively expressed as:

[0048]

[0049]

[0050] In formula (15) and formula (16), v plat and v target and are the velocity vector of the airborne relay system and the velocity vector of the non-line-of-sight target, respectively. k1 and k2 are the beam vector from the ground radar to the airborne relay platform and the beam vector from the airborne relay platform to the non-line-of-sight target, respectively. k1 and k2 are expressed as:

[0051]

[0052]

[0053] v plat and v target Respectively expressed as:

[0054] v plat =[v plat_x ,v plat_y ,v plat_z ] T (19)

[0055] v target =[v target_x ,v target_y ,v target_z ] T (20)

[0056] [v plat_x ,v plat_y ,v plat_z ] represents the velocity components of the velocity vector of the airborne relay system on the x, y, and z axes respectively, [v target_x ,v target_y ,v target_z ] represents the velocity components of the velocity vector of the non-line-of-sight target on the x, y, and z axes respectively.

[0057] A new type of non-line-of-sight target detection system, comprising: a ground radar, an airborne relay system and a target to be detected;

[0058] The ground radar is used to transmit signals to the airborne relay system;

[0059] The airborne relay system is used to receive the transmission signal, enhance the transmission signal, and forward the enhanced transmission signal to the target to be detected;

[0060] The target to be detected is used to receive the enhanced transmission signal and generate a target echo signal;

[0061] The relay system is used to receive the target echo signal and the enhanced target echo signal and forward it to the ground radar;

[0062] The ground radar is used to process the received enhanced target echo signal.

[0063] In one embodiment of the present invention, the airborne relay system is composed of a transmitting antenna, a receiving antenna and a power amplifier module;

[0064] The relay system receives a transmission signal from a ground radar, amplifies the received transmission signal through the power amplifier, and forwards the amplified transmission signal to a target to be detected through the transmitting antenna.

[0065] Beneficial effects of the present invention:

[0066] 1. The non-line-of-sight target detection method of the present invention utilizes an airborne relay system to enhance the radar transmission signal and the echo signal scattered by the target. The illumination area can be specified to enhance the non-line-of-sight target echo signal and expand the radar detection range. It can detect non-line-of-sight targets (UAV targets and vehicle targets) blocked by tall buildings in urban environments.

[0067] 2. The non-line-of-sight target detection system of the present invention can prevent radar signals from being transmitted through obstacles by deploying an airborne relay platform between the ground radar and the non-line-of-sight target, thereby enhancing the coverage area of ​​the radar signal, reducing signal attenuation, and improving the overall detection capability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 is a flow chart of a novel non-line-of-sight target detection method provided by an embodiment of the present invention;

[0069] Figure 2 is a schematic diagram of a non-line-of-sight scenario provided by an embodiment of the present invention;

[0070] Figure 3 is a schematic diagram of a mathematical model of a non-line-of-sight scenario provided by an embodiment of the present invention;

[0071] Figure 4 is a pulse Doppler radar signal processing flow chart provided by an embodiment of the present invention;

[0072] Figure 5 It is a schematic diagram of a novel non-line-of-sight target detection system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0073] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0074] In urban environments, due to the presence of complex terrain such as buildings and roads, traditional line-of-sight target detection technology often faces problems such as signal obstruction by obstacles, signal energy attenuation, and signal interference, resulting in the inability to effectively detect non-line-of-sight targets. The present invention mainly focuses on non-line-of-sight target detection in urban environments and proposes a new non-line-of-sight target detection method, which can expand the detection range of ground radars, enhance target echo signals, and realize the detection of UAV targets and vehicle targets obscured by buildings.

[0075] See attached Figure 1 , the non-line-of-sight target detection method comprises the following steps:

[0076] S1. Ground radar transmits signals to the airborne relay system;

[0077] S2, the relay system receives and amplifies the transmission signal, and forwards the enhanced transmission signal to the target to be detected;

[0078] S3, the target to be detected receives the enhanced transmission signal and generates a target echo signal;

[0079] S4, the relay system receives and amplifies the target echo signal, and forwards the enhanced target echo signal to the ground radar;

[0080] S5. The ground radar processes the received enhanced target echo signal to achieve detection of non-line-of-sight targets.

[0081] The present invention proposes to use an airborne relay system to enhance and forward radar transmission signals and target scattered echo signals. The scenario diagram is shown in the attached figure. Figure 2 shown.

[0082] Specifically, the method first transmits a signal to an airborne relay system through a ground radar. The relay system receives the transmission signal of the ground radar and amplifies the received radar transmission signal through a power amplifier in the relay system. After the radar transmission signal is enhanced, it is irradiated to the area to be detected through the transmitting antenna of the relay system. After the target to be detected receives the radar signal forwarded by the relay system, a scattered echo is generated. After receiving the scattered echo signal of the target, the relay system enhances it and forwards it to the ground radar receiver. The echo signal of the target to be detected received by the radar receiver is processed to realize the detection of non-line-of-sight targets.

[0083] The relay system can provide an effective solution in these complex environments and has shown a wide range of application prospects. In the present invention, by deploying an airborne relay platform between the ground radar and the non-line-of-sight target, the radar signal can be transmitted without passing through obstacles, thereby enhancing the coverage area of ​​the radar signal, reducing signal attenuation, and improving the overall detection capability of the system.

[0084] Attachment Figure 2 The corresponding three-dimensional mathematical model is established for the scene, as shown in the attached Figure 3 As shown, it is convenient to analyze the specific representation of the target echo received by the ground radar.

[0085] In one embodiment of the present invention, it is assumed that the ground radar transmits a linear frequency modulation pulse signal, which is expressed as:

[0086]

[0087] In formula (1), rect[·] is a rectangular function, K is the frequency modulation slope and K = B w / T p , where B w is the signal bandwidth, T p is the pulse duration of the linear frequency modulated pulse signal, f c is the carrier frequency of the signal.

[0088] The transmitted signal received by the relay system can be expressed as:

[0089]

[0090] In formula (2), P t is the transmitting power of the ground radar, For ground radar The transmitting antenna gain in the direction, For the airborne relay system to receive Directional receiving antenna gain, is the azimuth and elevation angle of the airborne relay system relative to the ground radar, L p1 is the power propagation loss from the ground radar to the airborne relay system, λ is the wavelength of the radar signal, and Δτ1 is the time delay corresponding to the transmission of the radar signal to the airborne relay system.

[0091] The transmission signal forwarded by the relay system to the target to be detected can be expressed as:

[0092]

[0093] In formula (3), η represents the power gain factor of the airborne relay system, Transmit for the relay system The transmission gain of the directional signal, is the azimuth and elevation angle of the target relative to the airborne relay system, L p2 is the power transmission loss from the airborne relay system to the target, and Δτ2 is the delay corresponding to the transmission of the relay amplified signal from the airborne relay system to the target.

[0094] The echo signal generated by the target to be detected can be expressed as:

[0095]

[0096] In formula (4), σ is the scattering cross-sectional area of ​​the target.

[0097] The echo signal received by the relay system can be expressed as:

[0098]

[0099] In formula (5), L p3 is the power propagation loss from the target to the airborne relay system, and Δτ3 is the time delay corresponding to the target scattered signal being transmitted to the airborne relay system.

[0100] The echo signal forwarded by the ground radar receiving relay system can be expressed as:

[0101]

[0102] In formula (6), L p4 is the power propagation loss from the airborne relay system to the ground radar, and Δτ4 is the time delay corresponding to the target echo signal enhanced by the airborne relay system being transmitted to the ground radar.

[0103] Therefore, the echo signal of the target to be detected received by the ground radar can be expressed as:

[0104]

[0105] In formula (7), P r is the target echo power received by the ground radar, R1 is the slant distance between the ground radar and the airborne relay system, R2 is the slant distance between the airborne relay system and the target, and c is the speed of light.

[0106] The target echo can be expressed as follows after removing the carrier frequency:

[0107]

[0108] The target echo power received by the ground radar can be expressed as:

[0109]

[0110] In formulas (8) and (9), P t is the radar transmitting power, is the radar antenna gain, is the antenna gain of the relay receiving radar signal, is the antenna gain of the relay transmitting signal to the target, σ is the scattering coefficient of the target, η is the power amplification factor of the relay, λ is the wavelength, R1 is the radial distance from the radar to the airborne relay, and R2 is the radial distance from the airborne relay to the target.

[0111] The propagation delays from the ground radar to the airborne relay system and from the airborne relay system to the target to be detected are expressed as:

[0112] Δτ1=Δτ4=R1 / c (10)

[0113] Δτ2=Δτ3=R2 / c (11)

[0114] The power transmission loss coefficients from the ground radar to the airborne relay system and from the airborne relay system to the target to be detected are expressed as:

[0115]

[0116]

[0117] By processing the echo signal received by the ground radar receiver, the target in the non-line-of-sight area can be detected and the parameters can be estimated. The present invention uses a pulse Doppler radar for target detection. The pulse Doppler radar uses the Doppler effect to estimate the relevant parameters of the target from the echo signal received by the radar. The pulse Doppler radar uses the Doppler frequency information in the echo signal to distinguish the target from the clutter in the Doppler frequency domain.

[0118] The pulse Doppler radar echo signal processing process includes: echo data preprocessing, pulse compression, moving target display, Doppler filtering, target detection, and target parameter estimation. The specific signal processing process is shown in the attached figure. Figure 4 shown.

[0119] From formula (8), we can see that the time delay of the radar receiving the target echo signal relative to the radar transmitting signal consists of two parts, namely the time delay corresponding to the distance between the radar and the airborne relay platform and the time delay corresponding to the distance between the airborne relay platform and the target. The target distance obtained in the target parameter estimation is also composed of the above two distances. In practice, the distance from the ground radar to the airborne relay platform is known. The distance of the target relative to the airborne relay platform can be obtained by subtracting the distance from the radar to the relay platform from the target distance obtained in the target parameter estimation.

[0120] In the present invention, the target Doppler frequency obtained in the target parameter estimation is composed of the Doppler frequency of the relay system relative to the ground radar and the Doppler frequency of the target to be detected relative to the relay system.

[0121] Assume that the Doppler frequency of the target to be detected received by the ground radar is f d , f d It is expressed as:

[0122] f d =f d1 +f d2 (14)

[0123] In formula (13), f d1 and f d2 Respectively expressed as:

[0124]

[0125]

[0126] In formula (14) and formula (15), k1 and k2 are respectively expressed as:

[0127]

[0128]

[0129] v plat and v target Respectively expressed as:

[0130] v plat =[v plat_x ,v plat_y ,v plat_z ] T (19)

[0131] v target =[v target_x ,v target_y ,v target_z ] T (20)

[0132] In practical applications, since the geometric relationship between the airborne relay platform and the ground radar is known, the angle of the target relative to the airborne relay platform can be obtained by estimating the target parameters, and the actual movement speed of the target can be calculated.

[0133] In the complex terrain of the city, the numerous buildings can easily cause obstruction and form non-line-of-sight situations. The airborne relay system can expand the radar detection range, break through the traditional line-of-sight limitations, and improve the detection capabilities of various targets hidden behind urban buildings, such as vehicles and specific facilities. At the same time, the airborne relay system is mobile and can flexibly cover different areas of the city. Compared with the detection method of fixed sites, it can continuously and dynamically monitor non-line-of-sight targets in a more flexible and efficient way and obtain target information in a timely manner. In urban combat scenarios, the airborne relay system can assist in detecting enemy hidden forces, drones, etc., enhance situational awareness, better formulate combat strategies, and ensure the effective implementation of military operations in complex urban environments. There are many types of targets in urban environments, and the airborne relay system can improve the radar's ability to identify small targets or low-reflection targets by enhancing signal quality. The deployment of the airborne relay system can help the radar system capture more reflected signals, improve the clarity of target identification, and avoid target loss due to signal attenuation or obstruction.

[0134] The non-line-of-sight target detection method proposed by the present invention can overcome the detection obstacles caused by high-rise buildings in the city, and can effectively enhance signal propagation, increase the detection range, and enhance the target recognition ability. At the same time, the detection method proposed by the present invention is not affected by the detection scene and has a large detection range. As the requirements for radar detection in the urban environment increase, radar technology combined with airborne relay systems will provide more reliable solutions for urban security, urban combat, traffic management, unmanned driving and other fields.

[0135] The present invention also provides a novel non-line-of-sight target detection system. Figure 5 The non-line-of-sight target detection system includes: a ground radar, an airborne relay system and a target to be detected.

[0136] The ground radar is used to transmit signals to the airborne relay system; the airborne relay system is used to receive the transmitted signal, enhance the transmitted signal, and forward the enhanced transmitted signal to the target to be detected; the relay system is used to receive the echo signal, enhance the echo signal and forward it to the ground radar; the relay system is used to process the echo signal received by the ground radar; the target to be detected is used to receive the enhanced transmitted signal and generate an echo signal.

[0137] In the present invention, the airborne relay system is composed of a transmitting antenna, a receiving antenna and a power amplifier module. The relay system receives the transmitting signal of the ground radar, amplifies the received transmitting signal through the power amplifier, and forwards the enhanced transmitting signal to the target to be detected through the transmitting antenna.

[0138] The present invention enhances the signal irradiated by the radar to the target through an airborne relay system, and at the same time enhances the echo signal scattered by the target, so as to expand the detection range of the ground radar. In an urban environment, due to the obstruction of buildings, the radar signal cannot be directly transmitted to the target to be detected. At present, the reflection, diffraction and transmission of electromagnetic waves on the surface of the building are mainly used to realize non-line-of-sight target detection. However, the reflection, diffraction and transmission of electromagnetic waves on the surface of the building will cause the attenuation of the electromagnetic wave energy, resulting in a small radar detection range. The detection scene is mostly limited to indoors or scenes with relatively fixed building distribution, and it is impossible to effectively detect the target behind the multi-story building. At the same time, the non-line-of-sight detection method based on multipath detection technology will produce multipath ghost interference, affecting the detection of the real target. The method proposed by the present invention uses an airborne relay system to realize the enhancement and forwarding of the signal between the radar and the target, solves the problem of limited detection range caused by energy loss of electromagnetic waves due to reflection and transmission, and realizes the detection of drone targets and vehicle targets blocked by buildings.

[0139] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A novel non-line-of-sight target detection method, characterized in that: Includes steps: S1. Ground radar transmits signals to the airborne relay system; S2, the relay system receives and amplifies the transmission signal, and forwards the enhanced transmission signal to the target to be detected; S3, the target to be detected receives the enhanced transmission signal and generates a target echo signal; S4, the relay system receives and amplifies the target echo signal, and forwards the enhanced target echo signal to the ground radar; S5. The ground radar processes the received enhanced target echo signal to achieve detection of non-line-of-sight targets.

2. A novel non-line-of-sight target detection method according to claim 1, characterized in that: The step S1 comprises: The ground radar transmits a linear frequency modulation pulse signal, which is expressed as: In formula (1), rect[·] is a rectangular function, K is the frequency modulation slope and K = B w / T p , where B w is the signal bandwidth, T p is the pulse duration of the linear frequency modulated pulse signal, f c is the carrier frequency of the signal.

3. A novel non-line-of-sight target detection method according to claim 1, characterized in that: The step S2 comprises: The relay system receiving the transmission signal is represented as follows: In formula (2), P t is the transmitting power of the ground radar, For ground radar The transmitting antenna gain in the direction, For the airborne relay system to receive Directional receiving antenna gain, is the azimuth and elevation angle of the airborne relay system relative to the ground radar, L p1 is the power propagation loss from the ground radar to the airborne relay system, λ is the wavelength of the radar signal, and Δτ1 is the time delay corresponding to the transmission of the radar signal to the airborne relay system; The transmission signal forwarded by the relay system to the target to be detected is expressed as: In formula (3), η represents the power gain factor of the airborne relay system, Transmit for the relay system The transmission gain of the directional signal, is the azimuth and elevation angle of the target relative to the airborne relay system, L p2 is the power transmission loss from the airborne relay system to the target, and Δτ2 is the delay corresponding to the transmission of the relay amplified signal from the airborne relay system to the target.

4. A novel non-line-of-sight target detection method according to claim 1, characterized in that: The step S3 comprises: The echo signal generated by the target to be detected is expressed as: In formula (4), σ is the scattering cross-sectional area of ​​the target.

5. The novel non-line-of-sight target detection method according to claim 1 is characterized in that: The step S4 comprises: The relay system receives the echo signal, which is represented as: In formula (5), L p3 is the power propagation loss from the target to the airborne relay system, Δτ3 is the time delay corresponding to the target scattered signal being transmitted to the airborne relay system; The echo signal forwarded by the relay system received by the ground radar is expressed as: In formula (6), L p4 is the power propagation loss from the airborne relay system to the ground radar, Δτ4 is the time delay corresponding to the target echo signal enhanced by the airborne relay system being transmitted to the ground radar; Therefore, the echo signal of the target to be detected received by the ground radar is expressed as: In formula (7), P r is the target echo power received by the ground radar, R1 is the slant distance between the ground radar and the airborne relay system, R2 is the slant distance between the airborne relay system and the target, and c is the speed of light; The target echo is expressed as follows after removing the carrier frequency: The echo power of the ground radar receiving the non-line-of-sight target is expressed as: In formulas (8) and (9), P t is the radar transmitting power, is the radar antenna gain, is the antenna gain of the relay receiving radar signal, is the antenna gain of the relay transmitting signal to the target, σ is the scattering coefficient of the target, η is the power amplification factor of the relay, λ is the wavelength, R1 is the radial distance from the radar to the airborne relay, and R2 is the radial distance from the airborne relay to the target.

6. A novel non-line-of-sight target detection method according to claim 1, characterized in that: In step S5, a pulse Doppler radar processing method is used to perform target detection; The pulse Doppler radar echo signal processing process includes: echo data preprocessing, pulse compression, moving target display, Doppler filtering, target detection, and target parameter estimation.

7. A novel non-line-of-sight target detection method according to claim 6, characterized in that: The target Doppler frequency acquired in the target parameter estimation is composed of the Doppler frequency of the relay system relative to the ground radar and the Doppler frequency of the target to be detected relative to the relay system.

8. A novel non-line-of-sight target detection method according to claim 7, characterized in that: The Doppler frequency of the ground radar receiving the target to be detected is f d , f d It is expressed as: f d =f d1 +f d2 (14) In formula (14), f d1 and f d2 f are the Doppler frequency of the airborne relay system relative to the ground radar and the Doppler frequency of the non-line-of-sight target relative to the airborne relay platform, respectively. d1 and f d2 Respectively expressed as: In formula (15) and formula (16), v plat and v target and are the velocity vector of the airborne relay system and the velocity vector of the non-line-of-sight target, respectively. k1 and k2 are the beam vector from the ground radar to the airborne relay platform and the beam vector from the airborne relay platform to the non-line-of-sight target, respectively. k1 and k2 are expressed as: v plat and v target Respectively expressed as: v plat =[v plat_x ,v plat_y ,v plat_z ] T (19) v target =[v target_x ,v target_y ,v target_z ] T (20) [v plat_x ,v plat_y ,v plat_z ] represents the velocity components of the velocity vector of the airborne relay system on the x, y, and z axes respectively, [v target_x ,v target_y ,v target_z ] represents the velocity components of the velocity vector of the non-line-of-sight target on the x, y, and z axes respectively.

9. A new type of non-line-of-sight target detection system, characterized in that: include: Ground radar, airborne relay system and targets to be detected; The ground radar is used to transmit signals to the airborne relay system; The airborne relay system is used to receive the transmission signal, enhance the transmission signal, and forward the enhanced transmission signal to the target to be detected; The target to be detected is used to receive the enhanced transmission signal and generate a target echo signal; The relay system is used to receive the target echo signal and the enhanced target echo signal and forward it to the ground radar; The ground radar is used to process the received enhanced target echo signal.

10. A novel non-line-of-sight target detection system according to claim 9, characterized in that: The airborne relay system is composed of a transmitting antenna, a receiving antenna and a power amplifier module; The relay system receives a transmission signal from a ground radar, amplifies the received transmission signal through the power amplifier, and forwards the amplified transmission signal to a target to be detected through the transmitting antenna.

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