Near-field focusing cylindrical lens antenna, active security check imaging system and design method

Abstract

The embodiment of the invention provides a near-field focusing cylindrical lens antenna, an active security inspection imaging system and a design method, and relates to the technical field of millimeter wave lens antennae, and the near-field focusing lens antenna comprises an MIMO rectangular pyramid horn antenna array which comprises transmitting arrays and a receiving array, and the transmitting arrays are arranged at the two sides of the receiving array; the cylindrical lens is arranged on one side of the MIMO rectangular pyramid horn antenna array, the cylindrical lens comprises a focusing curved surface and an aperture surface, the focusing curved surface is located on one side, close to the MIMO rectangular pyramid horn antenna array, of the cylindrical lens, and the aperture surface is arranged opposite to the focusing curved surface; and the scanning reflecting plate is arranged on one side, far away from the MIMO rectangular pyramid horn antenna array, of the cylindrical lens, the scanning reflecting plate is provided with a metal reflecting surface, and the metal reflecting surface can swing at an angle alpha. The embodiment of the invention has larger degree of freedom and dynamic range, hardware cost can be reduced, echo data acquisition time can be shortened, possibility is provided for real-time acquisition and processing of data, and the imaging efficiency can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of millimeter-wave lens antenna design, and in particular to a near-field focusing cylindrical lens antenna, an active security inspection imaging system, and a design method. Background Art

[0002] In related technologies, the research and progress of radar imaging technology has enabled imaging radar systems to not only determine whether there is a target, but also have the ability to realize target recognition based on radar images.

[0003] Traditional solutions for public security screening rely on metal detectors and handheld metal detectors to detect metal objects. Metal detectors only provide a warning but cannot identify or locate targets, while handheld detectors come into contact with the human body, potentially infringing on privacy. Active imaging radar systems, on the other hand, use a transmitter to radiate millimeter waves to illuminate a target. A receiver receives the reflected or scattered waves, then applies a radar imaging algorithm to generate a spatial distribution image of the target's reflectivity. This image captures the reflectivity of each component of the target, enabling accurate imaging and identification.

[0004] However, existing active imaging radar systems suffer from limited degrees of freedom and dynamic range, high hardware costs, and long echo data acquisition times, hindering real-time data collection and processing. Furthermore, the original quasi-optical optical path in existing radar systems is large, has low resolution, and suffers from inefficient space utilization. Summary of the Invention

[0005] This application aims to solve at least one of the technical problems existing in the prior art. To this end, this application proposes a near-field focusing cylindrical lens antenna, an active security inspection imaging system, and a design method, which can improve imaging efficiency and space utilization within the system.

[0006] An embodiment of the first aspect of the present application provides a near-field focusing lens antenna, comprising:

[0007] A MIMO rectangular pyramidal horn antenna array includes a transmitting array and a receiving array, wherein the transmitting array is provided on both sides of the receiving array, the transmitting array is used to radiate electromagnetic waves, and the receiving array is used to receive reflected waves or scattered waves of the target;

[0008] a cylindrical lens disposed on one side of the MIMO rectangular pyramidal horn antenna array, the cylindrical lens comprising a focusing surface and an aperture surface, the focusing surface being located on a side of the cylindrical lens close to the MIMO rectangular pyramidal horn antenna array, and the aperture surface being disposed opposite the focusing surface;

[0009] A scanning reflector is arranged on a side of the cylindrical lens away from the MIMO rectangular pyramidal horn antenna array. The scanning reflector has a metal reflective surface. The metal reflective surface is used to focus the beam emitted by the transmitting array on a fixed imaging plane to form a near-field focused beam. The metal reflective surface swings at an angle α so that the beam emitted by the transmitting array scans the target on the pitch plane.

[0010] Furthermore, the transmitting array has a plurality of transmitting array elements, and the receiving arrays each have a plurality of receiving array elements, and the plurality of transmitting array elements and the plurality of receiving array elements are arranged at intervals along the axial direction of the cylindrical lens.

[0011] Furthermore, a maximum phase difference between any one of the transmitting array element and the receiving array element and its adjacent array element is less than πrad.

[0012] Furthermore, the curve equation of the focusing surface profile of the cylindrical lens is:

[0013] .

[0014] Furthermore, the distance between the emission aperture of the emission array and the aperture surface of the cylindrical lens is d in , where d in satisfy:

[0015] ;

[0016] Where λ is the wavelength of the beam, w in is the beam width, d out is the required imaging distance, W out is the desired focus resolution.

[0017] Furthermore, the aperture surface is a plane.

[0018] Furthermore, the size of the aperture surface is D, which satisfies:

[0019] ,

[0020] Among them, W out is the required focus resolution, d out is the required imaging distance, T E is the ratio of the power at the edge of the cylindrical lens to the power on the propagation axis.

[0021] Furthermore, the edge power T E is 15dB, and the aperture D of the cylindrical lens is 0.5378m.

[0022] An embodiment of the second aspect of the present application provides an active security inspection imaging system, including the near-field focusing lens antenna as described above.

[0023] The third aspect of the present application provides a design method for a millimeter-wave active imaging security inspection system, which is applied to the aforementioned near-field focusing cylindrical lens antenna, including the following steps:

[0024] S110, calculating parameters of a smooth inner wall rectangular horn antenna in the near-field focusing lens antenna according to the far-field gain requirement and operating frequency of the near-field focusing lens antenna;

[0025] S120, determining the spacing of the MIMO rectangular pyramidal horn antenna array according to the sampling frequency, and then determining the narrow side value range of the pyramidal horn antenna;

[0026] S130, calculating the near-field gain of the near-field focusing lens antenna obtained in step S110 and step S120 using a fast multi-level sub-method, and deriving an equivalent point source;

[0027] S140, calculating the optical path parameters of the near-field focusing lens antenna according to the imaging distance;

[0028] S150, calculating the internal parameters of the cylindrical lens according to the optical path parameters;

[0029] S160, based on the equivalent point source obtained in step S130, replacing the role of the MIMO rectangular pyramidal horn antenna array in the focusing optical path, using ray-launching geometric optics to calculate the near-field distribution of the imaging plane and analyze its focusing characteristics;

[0030] S170, rapidly swinging the metal reflective surface to enable the metal reflective surface to complete beam scanning at an angle α, and combining the two-dimensional fast imaging algorithm to achieve real-time three-dimensional imaging processing.

[0031] It can be seen from the above technical solutions that the embodiments of the present application have at least the following beneficial effects:

[0032] In the near-field focusing lens antenna provided in the embodiment of the present application, by designing the topological structure of the transmitting array and the receiving array in the MIMO rectangular pyramidal horn antenna array, it is possible to obtain virtual channels far exceeding the number of physical array elements with fewer array elements, thereby obtaining greater degrees of freedom and dynamic range. This not only reduces the hardware cost, but also further shortens the echo data acquisition time, making it possible for real-time data acquisition and processing, and helping to improve imaging efficiency. At the same time, by folding the focusing optical path through the metal reflective surface, the internal space of the system is more fully utilized, which is conducive to achieving a miniaturized design. In addition, by controlling the swing inclination angle of the metal reflective surface, real-time multi-beam scanning on the imaging pitch plane is obtained, which is suitable for the use of people to be measured at different heights, thereby improving the flexibility of the optical path design and the imaging speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0034] Figure 1 A schematic diagram of a focal plane array short-range passive imaging system;

[0035] Figure 2 A schematic diagram of the working principle of a near-field focusing lens antenna provided in one embodiment of the present application;

[0036] Figure 3 This is a schematic diagram of the operation of the emission array and the cylindrical lens in one embodiment of the present application;

[0037] Figure 4 This is a two-dimensional cross-sectional schematic diagram of a cylindrical lens in one embodiment of the present application;

[0038] Figure 5 This is a VSWR (standing wave ratio) simulation diagram of a near-field focusing lens antenna in one embodiment of the present application;

[0039] Figure 6 This is a simulated radiation pattern (E plane) of a pyramidal horn antenna in one embodiment of the present application;

[0040] Figure 7 The simulated radiation pattern (H plane) of the pyramidal horn antenna in one embodiment of the present application;

[0041] Figure 8 This is a focusing effect diagram of an active security inspection imaging system according to an embodiment of the present application. As can be seen from the diagram, the focusing resolution is 20 mm.

[0042] Reference numerals:

[0043] 1-16, receiving array; 17-24, transmitting array; 25, cylindrical lens; 26, metal reflective surface; 27, fixed imaging plane. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0045] Traditional solutions for public security screening rely on metal detectors and handheld metal detectors to detect metal objects. Metal detectors only provide a warning but cannot identify or locate the target, while handheld detectors come into contact with the human body, potentially infringing on privacy.

[0046] With the research and advancement of radar imaging technology, imaging radar systems can not only determine whether there is a target, but also have the ability to recognize targets based on radar images.

[0047] However, existing active imaging radar systems suffer from limited degrees of freedom and dynamic range, high hardware costs, and long echo data acquisition times, hindering real-time data collection and processing. Furthermore, the original quasi-optical optical path in existing radar systems is large, has low resolution, and suffers from inefficient space utilization.

[0048] See also Figure 1 , Figure 1 A schematic diagram of a focal plane array short-range passive imaging system is shown. In the figure, a new W-band 16-element full-sampling focal plane linear array antenna based on a large-aperture parabola achieves Nyquist sampling of the target area through optimized arrangement of the feed array. The lens antenna profile is determined based on the Gaussian beam method and geometric optics method, and an improved hybrid numerical calculation method is used to accurately analyze the near field of the lens antenna and optimize the lens antenna profile. Applying this optimization design method, a hyperbolic lens antenna and an aspheric lens antenna were designed respectively. Both large-aperture antennas achieved a focused focal spot size of less than 30 mm. However, this passive imaging system has the problems of large size and low resolution.

[0049] In view of this, a first embodiment of the present application provides a near-field focusing lens antenna to effectively solve the aforementioned problems.

[0050] In the embodiment of the first aspect of the present application, by rationally designing the topology of the transmitting arrays 17-24 and receiving arrays 1-16 of the MIMO rectangular pyramidal horn antenna array, a virtual channel far exceeding the number of physical array elements is obtained with a smaller number of array elements, thereby achieving greater degrees of freedom and dynamic range. This not only reduces hardware costs but also further shortens the echo data acquisition time, making it possible to collect and process data in real time. At the same time, the design of the cylindrical lens 25 and the metal reflective surface 26 takes into account the inspection of contraband without contacting the security personnel to be tested, and further fully utilizes the internal space of the system by folding the focusing optical path. Finally, the outgoing beam forms a narrow, uniformly stacked multi-beam on the azimuth plane of the security personnel to be tested that meets the requirements of the Nyquist sampling theorem. Through real-time multi-beam scanning on the pitch plane, a high imaging frame rate and the ability to detect metal objects hidden in the human body are achieved, which is suitable for application in high-throughput active security inspection scenarios.

[0051] See below Figure 2 The near-field focusing lens antenna provided in the embodiment of the first aspect of the present application is described in detail.

[0052] See also Figure 2 As shown, an embodiment of the first aspect of the present application discloses a near-field focusing lens antenna, including a MIMO rectangular pyramidal horn antenna array, a cylindrical lens 25 and a scanning reflector.

[0053] Specifically, the MIMO rectangular pyramidal horn antenna array includes transmitting arrays 17 to 24 and receiving arrays 1 to 16. Transmitting arrays 17 to 20 and transmitting arrays 21 to 24 are respectively arranged on both sides of the receiving arrays 1 to 16. The transmitting arrays 17 to 24 are used to radiate electromagnetic waves, and the receiving arrays 1 to 16 are used to receive reflected waves or scattered waves of the target; a cylindrical lens 25 is arranged on one side of the MIMO rectangular pyramidal horn antenna array, and the cylindrical lens 25 includes a focusing surface and an aperture surface. The focusing surface is arranged close to the MIMO rectangular pyramidal horn antenna array, and the aperture surface is arranged opposite to the focusing surface; a scanning reflector is arranged on the side of the cylindrical lens 25 away from the MIMO rectangular pyramidal horn antenna array, and the scanning reflector has a metal reflective surface 26. The metal reflective surface 26 is used to focus the beams emitted by the transmitting arrays 17 to 24 on a fixed imaging plane to form a near-field focused beam, and the metal reflective surface 26 swings at an angle α so that the beams emitted by the transmitting arrays 17 to 24 scan the target on the pitch plane.

[0054] Among them, the MIMO rectangular pyramid horn antenna array is a MIMO rectangular pyramid horn antenna array arranged along the narrow side based on the Nyquist sampling definition, and radiates electromagnetic waves outward through the aperture surface; in the millimeter wave band, the electromagnetic waves radiated by the antenna can be regarded as a Gaussian beam, so the divergent Gaussian beam quasi-light outside the focal plane of the cylindrical lens 25 can be incident on the cylindrical lens 25; at this time, the metal reflective surface 26 loaded between the cylindrical lens 25 and the fixed imaging plane 27 can fold the optical path of the outgoing beam, so that the outgoing beam is focused on the fixed imaging plane 27, thereby forming a narrow uniformly stacked multi-beam of a certain width on the azimuth plane, and the near-field focused 3dB beam diameter is used as the imaging resolution value.

[0055] Furthermore, the transmitting arrays 17-24 have multiple transmitting elements, and the receiving arrays 1-16 each have multiple receiving elements, and the multiple transmitting elements and the multiple receiving elements are spaced apart along the axial direction of the cylindrical lens 25. It is worth noting that the number of transmitting elements and receiving elements can be set accordingly according to detection requirements.

[0056] In one possible implementation, see Figure 2 Receive arrays 1-16 include 16 receive elements and 8 transmit elements, with the 16 receive elements spaced along a straight line. Four transmit elements are placed at each end of receive arrays 1-16. Placing transmit arrays 17-24 at both ends and receive arrays 1-16 in the middle creates an equivalent virtual array with uniform spatial distribution.

[0057] In this embodiment, see Figure 2 and Figure 3 , the transmitting array 17~24 includes a plurality of transmitting horn antenna elements, and the radiation beam width of the transmitting horn antenna element is W in Gaussian beam, through L 12 The beam is incident on the surface of the cylindrical lens 25 and is focused by the cylindrical lens 25. 23 Arriving at the metal reflective surface 26, the original light path is folded at the metal reflective surface 26, and the outgoing beam passes through L 34 distance, focusing on the fixed imaging plane 27, forming a near-field focused beam of a certain width. The receiver continuously oscillates within the specified range, scanning the target multiple times in real time across the pitch plane using a narrow, uniformly focused multi-beam. Receiver arrays 1-16 include multiple receiving horn antenna elements, which receive reflected or scattered waves from the target and process the echo data using an imaging algorithm to ultimately produce an image of the target. In this embodiment, the target image is an image of a person concealing a dangerous object.

[0058] Furthermore, in near-field focusing cylindrical lens antennas, the spacing of the MIMO rectangular pyramidal horn antenna array must avoid aliasing effects, requiring the phase difference between adjacent transmitting elements or receiving elements to be less than 1 rad. Therefore, as long as the individual elements (including transmitting and receiving elements) are arranged so that the maximum phase difference is less than π rad, the design requirements are met.

[0059] In this embodiment, the maximum phase difference between any one of the transmitting and receiving elements and its adjacent element is less than π rad. In other words, the maximum phase difference between adjacent transmitting elements, between adjacent receiving elements, or between a transmitting element and an adjacent receiving element is less than π rad, thereby preventing aliasing effects.

[0060] Furthermore, the cylindrical lens 25 has a focusing surface, which is located on a side of the cylindrical lens 25 close to the MIMO rectangular pyramid horn antenna array. The curve equation of the focusing surface profile is:

[0061] .

[0062] Furthermore, the distance between the emission aperture of the emission arrays 17 to 24 and the aperture surface of the cylindrical lens 25 is d in , where d in satisfy:

[0063] ,

[0064] Where λ is the wavelength of the beam, w in is the beam width, d out is the required imaging distance, W out is the desired focus resolution.

[0065] Furthermore, the aperture surface is a plane.

[0066] In some embodiments of the present application, the size of the aperture surface is D, which satisfies:

[0067] ,

[0068] Among them, W out is the required focus resolution, d out is the required imaging distance, T E It is the ratio of the power at the edge of the cylindrical lens 25 to the power on the propagation axis.

[0069] In this embodiment, the edge power T E The specific value is 15 dB. According to the above formula, the diameter D of the cylindrical lens 25 is calculated to be 0.5378 m.

[0070] An active security inspection imaging system includes the near-field focusing lens antenna as described above, and has all the technical effects of the aforementioned near-field focusing lens antenna, which will not be repeated here.

[0071] A design method for a millimeter-wave active security inspection imaging system, applied to the aforementioned near-field focusing cylindrical lens antenna, includes the following steps:

[0072] S110, calculating parameters of a smooth inner wall rectangular horn antenna in the near-field focusing lens antenna according to the far-field gain requirement and operating frequency of the near-field focusing lens antenna;

[0073] In this embodiment, the parameters of the rectangular horn antenna include: the long side of the rectangular waveguide is a1, the short side is b1, and the horn aperture size is a1×b1.

[0074] S120, determining the spacing of the MIMO rectangular pyramidal horn antenna array according to the sampling frequency, and then determining the narrow side value range of the pyramidal horn antenna;

[0075] In this embodiment, the spacing of the MIMO rectangular pyramidal horn antenna array typically requires that the phase difference between adjacent transmitting and receiving elements be less than 1 rad to avoid aliasing. Therefore, the array arrangement is determined as long as the maximum phase difference between the elements (including both transmitting and receiving elements) is less than 1 rad. Furthermore, in this embodiment, the arrangement of transmitting arrays 17-24 at both ends and receiving arrays 1-16 in the middle achieves a spatially uniformly distributed equivalent virtual array.

[0076] S130, calculating the near-field gain of the near-field focusing lens antenna obtained in step S110 and step S120 using a fast multi-level sub-method, and deriving an equivalent point source;

[0077] S140, calculating the optical path parameters of the near-field focusing lens antenna according to the imaging distance;

[0078] In this embodiment, the optical path parameters of the quasi-light in the near-field focusing lens antenna include the beam waist size on both sides of the lens antenna object and image, the object distance, the image distance, and the lens antenna aperture size.

[0079] S150, calculating the internal parameters of the cylindrical lens 25 according to the optical path parameters;

[0080] In this embodiment, the internal parameters of the cylindrical lens 25 include curve parameters of the focusing surface, the aperture D of the aperture plane, and the thickness of the cylindrical lens 25 .

[0081] S160, based on the equivalent point source obtained in step S130, replacing the role of the MIMO rectangular pyramidal horn antenna array in the focusing optical path, using ray-launching geometric optics to calculate the near-field distribution of the imaging plane and analyze its focusing characteristics;

[0082] S170 , rapidly swinging the metal reflective surface 26 to enable the metal reflective surface 26 to complete beam scanning at an angle α, and combining with a two-dimensional fast imaging algorithm to achieve real-time three-dimensional imaging processing.

[0083] The following describes in detail the near-field focusing lens antenna, active security inspection imaging system, and design method of the embodiment of the present application using a specific embodiment. It should be noted that the following embodiment is only an exemplary description and should not be understood as limiting the embodiment of the present application.

[0084] See also Figure 2 and Figure 3 As shown, the near-field focusing cylindrical lens antenna provided in this embodiment includes MIMO rectangular pyramidal horn antenna arrays 1-24, a cylindrical lens 25, a metal reflective surface 26, and a fixed imaging plane 27. The MIMO rectangular pyramidal horn antenna arrays 1-24 include transmitting horn antenna elements 17-24 and receiving horn antenna elements 1-16. The radiation beam width of the transmitting horn antenna elements 17-24 is W in Gaussian beam, through L 12 The beam is incident on the surface of the cylindrical lens 25 and is focused by the cylindrical lens 25. 23 After reaching the metal reflective surface 26, the original optical path is folded and the outgoing beam passes through L 34 The metal reflective surface 26 is focused on the fixed imaging plane 27 to form a near-field focused beam with a certain width. The angle is continuously swung, and a narrow uniformly focused multi-beam is projected onto the pitch and elevation directions of the fixed imaging plane 27 to perform multiple real-time scans of the target. The receiving horn antenna elements 1 to 16 synchronously receive the reflected or scattered waves of the target, and then the imaging algorithm is used to process the echo data, and finally an image of the dangerous object hidden in the human body is obtained.

[0085] The specific parameter design of the near-field focusing cylindrical lens antenna in this embodiment is described below.

[0086] The parameters of the pyramidal horn antenna in the near-field focusing lens antenna include: the rectangular waveguide has a long side a1 and a short side b1, the horn aperture size is a1×b1, and the gain calculation formula is:

[0087] ;

[0088] Where, It represents the aperture efficiency of the rectangular horn antenna, which is approximately 0.5 when designed for optimal gain.

[0089] In near-field focusing lens antennas, the spacing of MIMO rectangular pyramidal horn antenna arrays typically requires a phase difference of less than 1 rad between adjacent transmitting and receiving elements to avoid aliasing. Therefore, the array elements (including both transmitting and receiving elements) can be arranged and placed as long as the maximum phase difference is less than 1 rad. Furthermore, in this embodiment, an arrangement with transmitting arrays 17-24 at both ends and receiving arrays 1-16 in the middle achieves a spatially uniformly distributed equivalent virtual array.

[0090] In this embodiment, the beam width w of the pyramidal horn antenna feed of the near-field focusing lens antenna is in The quasi-optical path parameters of the near-field focusing lens antenna include the beam waist size on both sides of the lens antenna object and image, object distance, image distance, and lens antenna aperture size. The beam radius at the cylindrical lens 25 is unique, and the beam width w of the pyramidal horn antenna feed is known. in , required imaging distance d out and the required focus resolution w out It can be determined according to actual application requirements. In this way, the distance d of the incident beam can be determined by the following formula in .

[0091]

[0092] Next, the internal parameters of the cylindrical lens 25 in the near-field focusing cylindrical lens antenna include the focal length f, the aperture size D, and the hyperbolic profile equation. The focal length f is determined by the following formula:

[0093]

[0094] For a standard hyperbolic collimating cylindrical lens, the coordinate zero point is taken as the midpoint of the surface, and the hyperbolic equation of the cylindrical lens 25 cross section is:

[0095]

[0096] In order to obtain the curve parameters of the cylindrical lens 25, it is necessary to first determine the lens aperture D. Considering the truncation effect of the cylindrical lens 25 on the Gaussian beam, the ratio of the edge power of the cylindrical lens 25 to the power on the propagation axis is defined as (dB). Given a cylindrical lens with an aperture of 25:

[0097]

[0098] Considering the compromise between the focusing accuracy of cylindrical lens 25 and the lens volume, the edge power is taken (dB)=15dB, so D=0.5378m.

[0099] Take the midpoint of the lens surface as the origin of the coordinate system, and the two-dimensional cross-sectional curve is as follows: Figure 4, the equation is:

[0100]

[0101] The lens thickness is:

[0102]

[0103] Substitution =1.5, D, f, all the parameters are calculated as:

[0104]

[0105] Therefore, the curve equation of the cylindrical lens 25 is obtained as follows:

[0106]

[0107] like Figure 5 As shown, Figure 5 The VSWR (standing wave ratio) simulation diagram of the near-field focusing lens antenna of this embodiment is given in Figure 5 It can be seen that its operating bandwidth is relatively wide, so that the VSWR is less than or equal to 2 in the frequency band of 85-115 GHz.

[0108] like Figure 6 and Figure 7 As shown, Figure 6 The simulated radiation pattern (E plane) of the pyramidal horn antenna of this embodiment is given in FIG. Figure 7 The simulated radiation pattern (H plane) of the pyramidal horn antenna in this example is given. Figure 5 and Figure 6 It can be seen that the pyramidal horn antenna of this embodiment has good directional radiation characteristics.

[0109] Figure 8 FIG shows the focusing effect diagram of the active imaging system of this example. Figure 7 It can be seen that the focusing resolution is 20mm, which has high resolution and good focusing characteristics, meeting the requirements of the active imaging system.

[0110] In summary, the near-field focusing lens antenna of this embodiment has a small overall size, high internal space utilization of the system, and is conducive to achieving a miniaturized design; and the bandwidth reaches 30GHz, with good broadband characteristics, which can achieve high-throughput data acquisition; in addition, the focusing characteristics of this embodiment are good, which can improve the resolution of the focused scanning beam and can meet the accuracy requirements of the active imaging system for detecting hidden dangerous objects.

[0111] In the description of this application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0112] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of such features. Throughout this application, unless otherwise specified, "plurality" means two or more.

[0113] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to direct connections, indirect connections through an intermediate medium, or internal communication between two components. Those skilled in the art will understand the specific meanings of these terms in this application based on specific circumstances.

[0114] In the description of this specification, specific features, structures, materials or characteristics may be combined in an appropriate manner in any one or more embodiments or examples.

[0115] It should be understood that although the steps in the flowcharts of the accompanying drawings are shown in sequence as indicated by the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some of the steps in the flowcharts of the accompanying drawings may include multiple sub-steps or multiple stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be executed in turn or alternately with other steps or at least a portion of the sub-steps or stages of other steps.

Claims

1. A near-field focusing lens antenna, characterized in that: include: A MIMO rectangular pyramidal horn antenna array comprises a transmitting array and a receiving array, wherein the transmitting array is provided on both sides of the receiving array; a cylindrical lens disposed on one side of the MIMO rectangular pyramidal horn antenna array, the cylindrical lens comprising a focusing surface and an aperture surface, the focusing surface being located on a side of the cylindrical lens close to the MIMO rectangular pyramidal horn antenna array, and the aperture surface being disposed opposite the focusing surface; A scanning reflector is provided on the side of the cylindrical lens away from the MIMO rectangular pyramid horn antenna array. The scanning reflector has a metal reflective surface. The metal reflective surface is used to focus the beam emitted by the transmitting array on a fixed imaging plane to form a near-field focused beam. The angle is swung so that the beam emitted by the transmitting array scans the target on the pitch plane.

2. The near-field focusing lens antenna according to claim 1, characterized in that: The transmitting array has a plurality of transmitting array elements, and the receiving arrays each have a plurality of receiving array elements. The plurality of transmitting array elements and the plurality of receiving array elements are spaced apart along the axial direction of the cylindrical lens.

3. The near-field focusing lens antenna according to claim 2, characterized in that: The maximum phase difference between any one of the transmitting array element and the receiving array element and its adjacent array element is less than π rad.

4. The near-field focusing lens antenna according to claim 1, wherein: The curve equation of the focusing surface profile of the cylindrical lens is: 。 5. The near-field focusing lens antenna according to claim 1 or 4, characterized in that: The distance between the emission array and the aperture surface of the cylindrical lens is d in , where d in satisfy: ， Where λ is the wavelength of the beam, w in is the beam width, d out is the required imaging distance, W out is the desired focus resolution.

6. The near-field focusing lens antenna according to claim 1, characterized in that: The aperture surface is a plane.

7. The near-field focusing lens antenna according to claim 6, characterized in that: The size of the aperture surface is D, which satisfies: ， Among them, W out is the required focus resolution, d out is the required imaging distance, T E is the ratio of the power at the edge of the cylindrical lens to the power on the propagation axis.

8. The near-field focusing lens antenna according to claim 6, characterized in that: The edge power T E is 15dB, and the aperture D of the cylindrical lens is 0.5378m.

9. An active security inspection imaging system, characterized in that: It comprises the near-field focusing lens antenna according to any one of claims 1 to 8.

10. An antenna design method for a millimeter-wave active security inspection imaging system, applied to the near-field focusing cylindrical lens antenna according to any one of claims 1 to 8, comprising the following steps: S110, calculating parameters of a smooth inner wall rectangular horn antenna in the near-field focusing lens antenna according to the far-field gain requirement and operating frequency of the near-field focusing lens antenna; S120, determining the spacing of the MIMO rectangular pyramidal horn antenna array according to the sampling frequency, and then determining the narrow side value range of the pyramidal horn antenna; S130, calculating the near-field gain of the near-field focusing lens antenna obtained in step S110 and step S120 using a fast multi-level sub-method, and deriving an equivalent point source; S140, calculating the optical path parameters of the near-field focusing lens antenna according to the imaging distance; S150, calculating the internal parameters of the cylindrical lens according to the optical path parameters; S160, based on the equivalent point source obtained in step S130, replacing the role of the MIMO rectangular pyramidal horn antenna array in the focusing optical path, using ray-launching geometric optics to calculate the near-field distribution of the imaging plane and analyze its focusing characteristics; S170, quickly swing the metal reflective surface to complete the metal reflective surface Angle beam scanning is combined with a two-dimensional fast imaging algorithm to achieve real-time three-dimensional imaging processing.

Images