Bias paraboloid horn antenna for RCS near field test

Abstract

The invention discloses a bias paraboloid horn antenna for RCS near-field testing. The bias paraboloid horn antenna comprises a four-ridge orthogonal mode coupler, a pyramid horn and a bias parabolic box. An output port of the four-ridge orthogonal mode coupler is fixedly connected with a wave port of the pyramid horn, and a radiation port of the pyramid horn is fixedly connected with an incident port of the bias parabolic box; the bias parabolic box is of a waveguide structure provided with a radiation port and comprises a top surface metal plate, a bottom surface metal plate, a straight surface reflection metal plate and a curved surface reflection metal plate, and the top surface metal plate and the bottom surface metal plate are parallel to each other; the top surface metal plate, the bottom surface metal plate, the straight surface reflection metal plate and the curved surface reflection metal plate form a box-shaped structure with two openings, the opening close to the straight surface reflection metal plate is an incident port, and the opening close to the curved surface reflection metal plate is a radiation port. According to the invention, the effective radiation of the beam can be obviously improved, and the complexity of a subsequent algorithm is reduced.

Description

Technical Field

[0001] This invention belongs to the field of antenna technology, specifically relating to a biased parabolic horn antenna for RCS near-field testing. Background Technology

[0002] Radar cross section (RCS) testing is a core component of stealth equipment development and target characteristic research, requiring high-precision electromagnetic scattering data to verify designs and evaluate performance. Traditional far-field testing requires the target-antenna distance to satisfy R ≥ 2D² / λ (where D is the target size and λ is the wavelength), resulting in extremely large testing sites for large aircraft and other targets, leading to high costs and susceptibility to environmental interference. Near-field testing technology collects data from the target's near-field region (3λ... The 10λ) scattered field, after mathematical transformation, yields the far-field RCS, significantly reducing site requirements and becoming the current mainstream solution. However, this technology imposes stringent requirements on the performance of the test antenna: 1. Low sidelobes and high isolation: avoiding interference from the antenna's own sidelobes with the near-field scattered signal and ensuring background noise suppression; 2. Wideband matching capability: covering the resonant frequency band of typical stealth targets; 3. Polarization purity: cross-polarization must be below -30dB to prevent polarization distortion from affecting the analysis of scatterer characteristics.

[0003] For near-field RCS testing, horn antennas are generally used. Horn antennas are widely used in RCS testing due to their high gain and strong directivity, but their inherent limitations restrict the accuracy of near-field testing, such as: 1. Low effective radiation: the directional... Figure 1 Generally, the target is approximately rotationally symmetric, while the target of RCS testing is generally streamlined. This leads to an increase in invalid illumination of the horn antenna's elevation plane, which interferes with the extraction of effective scattered signals. 2. The near-field and far-field transformation algorithm for spherical waves is complex: When the horn antenna illuminates an object in the near field, the wavefront shape is approximately spherical. Therefore, the near-field and far-field transformation algorithm requires the input of the target's three-dimensional scattering distribution information. This process is not only time-consuming but also has high algorithm complexity.

[0004] In conclusion, traditional horn antennas have significant drawbacks when used as near-field RCS testing antennas. Therefore, a more suitable antenna needs to be designed for near-field RCS testing. Summary of the Invention To address the aforementioned problems in the prior art, the present invention provides an offset parabolic horn antenna for RCS near-field testing.

[0005] The technical problem to be solved by this invention is achieved through the following technical solution: This invention provides a biased parabolic horn antenna for RCS near-field testing, comprising: Four-ridged orthogonal mode coupler, square pyramidal horn and biased parabolic box; The output port of the four-ridged orthogonal mode coupler is fixedly connected to the wave port of the square cone horn, and the radiation port of the square cone horn is fixedly connected to the incident port of the biased parabolic box. The biased parabolic box is a waveguide structure with a radiation port. The biased parabolic box includes a top metal plate, a bottom metal plate, a straight reflective metal plate, and a curved reflective metal plate. The top metal plate and the bottom metal plate are parallel to each other. The top metal plate, the bottom metal plate, the straight reflective metal plate, and the curved reflective metal plate form a box-shaped structure with two openings. The opening near the straight reflective metal plate is the incident port, and the opening near the curved reflective metal plate is the radiation port.

[0006] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention designs a biased parabolic horn antenna based on a four-ridge orthogonal mode coupler feed. This antenna features a flat beamform, which significantly improves the effective radiation of the beam for streamlined RCS test targets. Furthermore, the wavefront shape of the electromagnetic wave radiated by this antenna approximates a cylindrical wave. For near-field and far-field transformation algorithms when a cylindrical wave illuminates an object, only the two-dimensional scattering distribution information of the target needs to be input, greatly reducing the complexity of subsequent algorithms and making it more suitable for near-field RCS testing.

[0007] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the overall structure of the biased parabolic horn antenna for RCS near-field testing provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure after dividing the integral structure formed by the biased parabolic box and the square pyramid horn according to an embodiment of the present invention; Figure 3 This is a cross-sectional view of the overall structure formed by the biased parabolic box and the square pyramid horn provided in an embodiment of the present invention; Figure 4 This is a three-dimensional structural schematic diagram of a four-ridge orthogonal mode coupler provided in an embodiment of the present invention; Figure 5 This is a top view of the four-ridge orthogonal mode coupler provided in an embodiment of the present invention; Figure 6 This is a side sectional view of the four-ridge orthogonal mode coupler provided in an embodiment of the present invention; Figure 7 This is a split schematic diagram of the four-ridge orthogonal mode coupler provided in an embodiment of the present invention; Figure 8This is a schematic diagram of the output port of the four-ridged orthogonal mode coupler and the wave port of the square cone horn provided in an embodiment of the present invention; Figure 9 It is the VSWR of the two ports of the antenna designed in this invention; Figure 10 This refers to the port isolation of the antenna designed in this invention; Figure 11 This is the 3D far-field radiation pattern of the antenna designed in this invention at 4GHz; Figure 12 This is the 3D far-field radiation pattern of the antenna designed in this invention at 7.2 GHz; Figure 13 This refers to the 3dB beamwidth of the wide beam within the operating frequency range of the antenna designed in this invention. Figure 14 This refers to the 3dB beamwidth of the narrow beam within the operating frequency range of the antenna designed in this invention. Figure 15 This is a schematic diagram of the main polarization and cross polarization of the two ports of the antenna designed in this invention. Detailed Implementation

[0009] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0010] Figure 1 This is a schematic diagram of the overall structure of the biased parabolic horn antenna for RCS near-field testing provided by the present invention, as shown below. Figure 1 As shown, the antenna includes: a four-ridged orthogonal mode coupler 1, a square pyramidal horn 2, and a biased parabolic box 3; the output port of the four-ridged orthogonal mode coupler 1 is fixedly connected to the wave port of the square pyramidal horn 2, and the radiation port of the square pyramidal horn 2 is fixedly connected to the incident port of the biased parabolic box 3.

[0011] Specifically, the bias parabolic box 3 is a metal waveguide structure with a radiation port 30. The bias parabolic box 3 includes a top metal plate, a bottom metal plate, a straight reflective metal plate, and a curved reflective metal plate. The top and bottom metal plates are parallel to each other. The top, bottom, straight, and curved reflective metal plates form a box-shaped structure with two openings. The opening near the straight reflective metal plate is the incident port, and the opening near the curved reflective metal plate is the radiation port. The phase center of the square pyramidal horn 2 is located at the focal point of the curved reflective metal plate. For example... Figure 2 This is a schematic diagram of the structure after dividing the integrated structure formed by the offset parabolic box and the square pyramidal horn, as shown below. Figure 2As shown, the top metal plate 31 and bottom metal plate 32 of the biased parabolic box 3 are horizontally connected to the square cone horn 2. When the integral structure formed by the biased parabolic box 3 and the square cone horn 2 is laterally divided, both the biased parabolic box 3 and the square cone horn 2 are divided into upper and lower parts. For the biased parabolic box 3, the straight reflective metal plate 33, the curved reflective metal plate 34, and the radiation port 30 are all divided into upper and lower parts, and the two long sides of the radiation port 30 are one straight side of the top metal plate 31 and the bottom metal plate 32, respectively. For the square cone horn 2, the two inner sidewalls, the two outer sidewalls, the wave port, and the radiation port are all divided into upper and lower parts, and one inner sidewall 21 of the square cone horn 2 is connected to one side of the straight reflective metal plate 33, while the other inner sidewall of the square cone horn 2 is used to form one side of the radiation port 30 of the biased parabolic box 3. Preferably, the square pyramid horn 2 can be formed by cutting out a horn cavity from a solid cuboid.

[0012] The antenna designed in this invention applies the working principle of a horn reflector antenna, as exemplarily... Figure 3 This is a cross-sectional view of the overall structure formed by the offset parabolic box and the square pyramidal horn, as shown below. Figure 3 As shown, when the phase center is placed at the focal point, the square pyramidal horn 2 emits electromagnetic waves and irradiates the parabolic surface formed by the curved reflective metal plate 34. After being reflected by the parabolic surface, a radiation beam parallel to the +x axis is formed. The maximum radiation direction of the beam is along the +x axis, and the phase center is approximately at the center of the radiation aperture.

[0013] The focal diameter ratio of the antenna designed in this invention ranges from 0.3 to 0.5. Preferably, the focal diameter ratio is 0.5 and the focal length is 115 mm.

[0014] In this invention, the elevation angle of the square cone horn 2 is related to the electric field distribution at the radiating port surface of the biased parabolic box 3. For example... Figure 3 As shown, the elevation angle θ of the square cone horn 2 ranges from 30° to 40°, and preferably, θ is 35°. This makes the electric field distribution on the radiating port surface more symmetrical. Specifically, the elevation angle θ of the square cone horn 2 is the angle between the plane perpendicular to the plane where the radiating port 30 is located and the central axis of the square cone horn 2.

[0015] In this invention, the size of the radiation port of the square cone horn 2 is the same as the size of the incident port of the biased parabolic box 3, that is, the size of the incident port of the biased parabolic box 3 is equal to the size of the horn mouth of the square cone horn 2.

[0016] Preferably, the size of the radiation port 30 of the biased parabolic box 3 is 230mm × 57mm.

[0017] Preferably, the curve function of the curved reflective metal plate 34 is: , This indicates the focal point of the curved reflective metal plate 34.

[0018] In some embodiments, the biased parabolic box 3 and the square cone horn 2 are integrally processed, and, as described above Figure 2 As shown, the structure formed by the biased parabolic box 3 and the square cone horn 2 is composed of two parts, an upper part and an lower part, and the upper and lower parts are as follows: Figure 2 The nested arrangement shown is secured with fasteners (e.g., screws) for a tight connection.

[0019] Figure 4 This is a schematic diagram of the three-dimensional structure of a four-ridge orthogonal mode coupler; Figure 5 This is a top view of a four-ridged orthogonal mode coupler; Figure 6 This is a side sectional view of a four-ridge orthogonal mode coupler; Figure 7 This is a split diagram of a four-ridged orthogonal mode coupler. Also refer to... Figures 4-7 The four-ridge orthogonal mode coupler 1 includes: a housing 11, four ridges 12, and two SMA feed cables 13, wherein each ridge 12 is fixedly disposed inside the housing 11, and the four ridges 12 are orthogonal in shape inside the housing 11, as shown below. Figure 5 As shown, there is a gap 4 between the four orthogonal ridges. (Continue to refer to...) Figure 5 and Figure 6 Each ridge 12 has a first cutting edge 123 and a second cutting edge 124, and the first cutting edge 123 and the second cutting edge 124 are joined to form the cutting edge of the ridge 12. Preferably, the cutting angle of the cutting edge is 90°, which can improve the impedance matching of the coaxial-ridge waveguide conversion section. The first cutting edge 123 and the second cutting edge 124 are formed by chamfering the right-angled cutting edge of the ridge 12 at a 45° angle. (See also...) Figure 2 , Figure 5 and Figure 6 The ridge 12 includes a straight ridge 121 and a tapered ridge 122, and the end of the straight ridge 121 not connected to the tapered ridge 122 is close to the output port of the four-ridge orthogonal mode coupler 1. Exemplarily, the straight ridge 121 and the tapered ridge 122 are integrally formed. The housing 11 and the four ridges 12 of the four-ridge orthogonal mode coupler 1 can be machined separately, and the four ridges 12 can also be machined separately.

[0020] Continue to refer to Figure 7 Each of the four outer walls 110 of the outer casing 11 has a plurality of through holes 101 (e.g., screw holes) penetrating the casing. Correspondingly, each ridge 12 has a plurality of through holes 102 on its side wall 126. Thus, each ridge 12 can be fixed to an inner wall of the outer casing 11 by fasteners such as screws. (Continue to refer to...) Figure 7Each of the two adjacent outer walls 110 of the housing 11 also has a power supply port 111, and through holes (e.g., screw holes) 112A and 112B located on both sides of the power supply port 111. For example, the SMA connector of each SMA power supply cable 13 can be fixed to one outer wall 110 of the housing 11 through the through holes 112A and 112B and fasteners (e.g. screws).

[0021] Continue to refer to Figure 7 Each of the two adjacent outer walls 110 of the housing 11 has a power supply port 111. Correspondingly, each of the two adjacent ridges 12 has a power supply port 103 on its side wall 126. After each SMA power supply cable 13 passes through the power supply port 111 on one of the outer walls 110 of the housing 11 into the interior of the housing 11, it enters the interior of the ridge 12 through the power supply port 103 fixedly installed on the outer wall 110. Then, the coaxial probe on the SMA power supply cable 13 extends out through the hole near the gap 4 of the ridge 12, passes through the gap 4, and is inserted into the interior of the opposite ridge 12 through the hole near the gap 4 on the opposite ridge 12. The SMA connector of the SMA power supply cable 13 is fixed to the outer wall 110 of the housing 11 by fasteners (e.g., screws). For example, as Figure 7 As shown, both ridges 12A and 12B have power supply ports 103 on their sidewalls 126, and both ridges 12A and 12B have power supply ports 111 on their outer walls 110 at their mounting positions inside the housing 11. After an SMA power supply cable 13 passes through the power supply port 111 on one of the outer walls 110 of the housing 11 and then enters the interior of ridge 12A through the power supply port 103 of ridge 12A, which is fixedly mounted on the outer wall 110, the coaxial probe on the SMA power supply cable 13 extends out through a hole near the gap 4 in ridge 12A. Then, it passes through the gap 4 and is inserted into the inside of the ridge 12C through the hole near the gap 4 on the ridge 12C; similarly, after another SMA feed cable 13 passes through the feed port 111 on the other outer wall 110 of the housing 11 into the inside of the housing 11, it enters the inside of the ridge 12B through the feed port 103 of the ridge 12B fixedly installed on the outer wall 110. After the coaxial probe on the SMA feed cable 13 extends out through the hole near the gap 4 on the ridge 12B, passes through the gap 4 and is inserted into the inside of the ridge 12D through the hole near the gap 4 on the ridge 12D.

[0022] For example, refer to Figure 5 When the operating frequency band of the antenna designed in this invention is 4-7.2GHz, the size of the output port and input port of the four-ridge orthogonal mode coupler 1 is 44mm*44mm.

[0023] In some embodiments, reference Figure 6The four ridges 121 located inside the housing 11 form a conical reflective cavity 125 between themselves and the end face of the input port of the housing 11. By designing the reflective cavity 125, the phase of higher-order modes and reflected waves can be suppressed, thereby improving the return loss of the port. Preferably, the reflective cavity 125 is a conical reflective cavity, and the bottom radius of the conical reflective cavity is 13.91 mm and the height is 4.14 mm, thus maximizing the improvement of the return loss of the port.

[0024] In this invention, the function curve of the blade of the gradient ridge 122 is: The sine power function, see reference. Figure 6 , The length of the wide side of the straight ridge 121. Let m be the height of the gradient ridge 122, and m be the exponent. Specifically, the value of m ranges from 1 to 3, where the impedance transformation effect of the gradient ridge 122 of the four-ridge orthogonal mode coupler 1 is best when m=2.

[0025] In this invention, the working principle of the four-ridge orthogonal mode coupler 1 is as follows: two pairs of orthogonal coaxial probes are inserted from the feed port 103 on one side of the ridge 12 to the opposite ridge 12. Through the coupling effect of the equivalent capacitance between the ridges, the electric field on the coaxial probe is coupled to the gap between the ridges. Then the electric field passes through the straight ridge 121 and then to the tapered ridge 122. The impedance is matched to the output port through the tapered ridge 122.

[0026] Figure 8 This is a schematic diagram of the output port of the four-ridged orthogonal mode coupler 1 and the wave port of the square cone horn 2, as shown below. Figure 8 As shown, the output port of the four-ridge orthogonal mode coupler 1 and the wave port of the square cone horn 2 have paired integrated flanges 10 and 20. The integrated flanges 10 and 20 can be fastened together by fasteners (e.g. screws) to realize the connection between the output port of the four-ridge orthogonal mode coupler 1 and the wave port of the square cone horn 2.

[0027] For example, both the four-ridged orthogonal mode coupler 1 and the biased parabolic box 3 can be formed by processing aluminum alloy material.

[0028] The technical effects of the present invention are verified through simulation experiments.

[0029] 1) Simulation content Will Figure 1 The antenna model of the structure is imported into the HFSS software. Then, the materials, excitation, solution mode, boundary conditions, solution domain, etc. are set. Finally, the software simulation is started to obtain the data.

[0030] 2) Simulation results The simulation results obtained after performing the simulation in the above manner are as follows: Figures 9-15 As shown. Figure 9 It is the VSWR of the two ports of the antenna designed in this invention; Figure 10 This refers to the port isolation of the antenna designed in this invention; Figure 11 This is the 3D far-field radiation pattern of the antenna designed in this invention at 4GHz; Figure 12 This is the 3D far-field radiation pattern of the antenna designed in this invention at 7.2 GHz; Figure 13 This refers to the 3dB beamwidth of the wide beam within the operating frequency range of the antenna designed in this invention. Figure 14 This refers to the 3dB beamwidth of the narrow beam within the operating frequency range of the antenna designed in this invention. Figure 15 This is a schematic diagram of the main polarization and cross polarization of the two ports of the antenna designed in this invention.

[0031] The results above show that the antenna designed in this invention has a VSWR of less than 1.8 at both ports within the 4-7.2 GHz operating frequency band, a port isolation greater than 30 dB, and a 3 dB beamwidth greater than 35° for the wide beam and greater than 12° for the narrow beam within the operating frequency band, with a cross-polarization isolation greater than 30 dB. Furthermore, the 3D far-field pattern of the antenna demonstrates that it exhibits a flat beamform.

[0032] In summary, the offset parabolic horn antenna based on a four-ridge orthogonal mode coupler designed in this invention exhibits good VSWR, isolation, and cross-polarization discrimination within its operating frequency band. Furthermore, it features a flat beamform with a 3dB beamwidth greater than 35° for wide beams and a 3dB beamwidth greater than 12° for narrow beams. These characteristics give the antenna the advantages of high effective radiation and a relatively simple near-field to far-field transformation algorithm in RCS near-field testing.

[0033] It should be noted that 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 technical features indicated. Therefore, features defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0034] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0035] In this specification, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude multiple instances. While different embodiments may describe certain measures, this does not mean that these measures cannot be combined to produce a good effect.

[0036] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A biased parabolic horn antenna for RCS near-field testing, characterized by, The utility model relates to a four-ridge orthogonal mode coupler (1), a square-cone horn (2) and a bias parabolic box (3). The output port of the four-ridge orthogonal mode coupler (1) is fixedly connected with the wave port of the square-cone horn (2), and the radiation port of the square-cone horn (2) is fixedly connected with the incident port of the bias parabolic box (3). The bias parabolic box (3) is a waveguide structure provided with a radiation port, wherein the bias parabolic box (3) comprises a top metal plate (31), a bottom metal plate (32), a straight-face reflecting metal plate (33) and a curved-face reflecting metal plate (34), the top metal plate (31) and the bottom metal plate (32) are parallel to each other, and the top metal plate (31), the bottom metal plate (32), the straight-face reflecting metal plate (33) and the curved-face reflecting metal plate (34) form a box-shaped structure with two openings, wherein the opening close to the straight-face reflecting metal plate (33) is the incident port, and the opening close to the curved-face reflecting metal plate (34) is the radiation port. The phase center of the square-cone horn (2) is located at the focal point of the curved-face reflecting metal plate (34).

2. The biased parabolic horn antenna for RCS near-field testing of claim 1, wherein, The size of the wave port of the square-cone horn (2) is the same as that of the incident port of the bias parabolic box (3).

3. The biased parabolic horn antenna for RCS near-field testing of claim 1, wherein, The size of the radiation port is 230mm*57mm, and the two long edges of the radiation port are a straight edge of the top metal plate (31) and a straight edge of the bottom metal plate (32) respectively.

4. The biased parabolic horn antenna for RCS near-field testing of claim 1, wherein, The square-cone horn (2) and the bias parabolic box (3) are integrally formed.

5. The biased parabolic horn antenna for RCS near-field testing of claim 1, wherein, The focal length-diameter ratio of the parabolic offset box (3) is 0.5, the focal length is 115 mm, and the curve function of the curved surface reflecting metal plate (34) is , represents the focal point of the curved surface reflecting metal plate (34).

6. The biased parabolic horn antenna for RCS near-field testing of claim 1, wherein, The angle between the plane perpendicular to the plane where the radiation port is located and the central axis of the square-cone horn (2) is 35°.

7. The biased parabolic horn antenna for RCS near-field testing of claim 1, wherein, The four-ridge orthogonal mode coupler (1) comprises a shell (11), four ridges (12) and two SMA feeding cables (13), wherein each ridge (12) is fixedly arranged inside the shell (11), the four ridges (12) are in an orthogonal shape inside the shell (11), adjacent two side walls of the shell (11) are provided with feeding ports (111), and each SMA feeding cable (13) is connected with two opposite ridges (12).

8. The biased parabolic horn antenna for RCS near-field testing of claim 1, wherein, Each ridge (12) has a first blade surface and a second blade surface, the first blade surface and the second blade surface are connected to form a blade of each ridge (12), and the opening angle of the blade is 90°.

9. The biased parabolic horn antenna for RCS near-field testing of claim 8, wherein, Each ridge (12) comprises a straight ridge (121) and a gradually-changing ridge (122), one end of the straight ridge (121) not connected with the gradually-changing ridge (122) is close to the output port, and the straight ridges (121) of the four ridges (12) inside the shell (11) together form a reflecting cavity of a cone with the end face of the input port of the shell (11).

10. The biased parabolic horn antenna for RCS near-field testing of claim 8, wherein, ​

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