A design method for a wide-beam cross dipole antenna

Abstract

This invention discloses a design method for a wide-beam cross-dipole antenna, belonging to the field of electromagnetic compatibility and antenna technology. The method includes: designing a vertical coaxial waveguide converter with a stepped waveguide impedance transformation structure; designing the dimensions of the cross-dipole antenna according to its structural characteristics to match the vertical coaxial waveguide converter, then obtaining the beamwidth of the cross-dipole antenna and optimizing its dimensions to widen the beamwidth; connecting the cross-dipole antenna to the vertical coaxial waveguide converter, and using a slotted balun structure on the outer conductor of the vertical coaxial waveguide converter based on the input impedance of the cross-dipole antenna to achieve impedance matching. This invention achieves good in-band matching, reduces the size of the image synthesized aperture reflector, and the antenna not only has wide beam characteristics but also uses a coaxial waveguide converter for feeding at the lower end.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic compatibility and antenna technology, and more specifically, relates to a cross-electrode antenna design with waveguide coaxial conversion suitable for mirror synthetic aperture systems. This cross-electrode antenna with a wide 3dB beamwidth can significantly increase the field of view of the mirror synthetic aperture and reduce the size of the reflector. Background Technology

[0002] With the development of spaceborne microwave radiometer systems, the original real aperture system and synthetic aperture system are difficult to achieve the spatial resolution required for small and medium scale monitoring in geostationary orbit. The proposed mirror synthetic aperture microwave radiation imaging system has improved the spatial resolution, but it has problems such as a small field of view and an excessively large reflector size. In order to solve the current problems, higher requirements are put forward for the beamwidth of the mirror synthetic aperture unit antenna.

[0003] The mirror synthetic aperture (SAP) antenna, by adding a reflector next to the antenna array, can be analogous to placing a mirror antenna symmetrically about the reflector to the real antenna. Both the real and mirror antennas simultaneously receive radiated signals from the scene. Therefore, both direct and reflected signals are within the antenna's main beamwidth. The wider the antenna's beamwidth, the larger the range of reflected signals that can be received, thus allowing for a reduction in the size of the SAP reflector.

[0004] A summary of existing wide-beam antenna research reveals two main techniques. The first technique involves reducing the aperture of the horn antenna to increase its beamwidth. Numerical calculations show that while keeping the length of the pyramidal horn constant, gradually increasing its aperture size to increase the aperture area will decrease the beamwidth. However, once the aperture area reaches a certain value, the beamwidth will actually increase with the increase in aperture size. The second technique is far-field pattern superposition. Since the far-field pattern is related to the antenna's current distribution, introducing a new current into the existing antenna can be considered. This allows the far-field pattern resulting from the new current to be superimposed on the original antenna's far-field pattern, thereby widening the beamwidth by 3dB. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a design method for a wide-beam cross-electrode antenna suitable for mirror-synthetic apertures, achieving good intra-band matching and reducing the size of the mirror-synthetic aperture reflector. This antenna not only has wide-beam characteristics, but also uses a coaxial waveguide converter for feeding at the lower end.

[0006] To achieve the above objectives, the present invention provides a design method for a wide-beam cross-electrode antenna, comprising:

[0007] Design a vertical coaxial waveguide converter, wherein the vertical coaxial waveguide converter adopts a stepped waveguide impedance transformation structure;

[0008] Based on the structural characteristics of the cross dipole antenna, the dimensions of the cross dipole antenna are initialized to match the vertical coaxial waveguide converter. Then, the beamwidth of the cross dipole antenna is obtained, and the dimensions of the cross dipole antenna are further optimized to broaden its beamwidth.

[0009] The cross-dipole antenna is connected to the vertical coaxial waveguide converter. Based on the input impedance of the cross-dipole antenna, a slotted balun structure is used on the outer conductor of the vertical coaxial waveguide converter to achieve impedance matching of the cross-dipole antenna.

[0010] In some alternative implementations, the vertical coaxial waveguide converter employs a stepped waveguide impedance transformation structure. The number of sections of the vertical coaxial waveguide converter is calculated based on the Chebyshev type λ / 4 stepped impedance transformer by calculating the characteristic impedance of the coaxial section of the cross-electrode antenna and the equivalent characteristic impedance of the rectangular waveguide.

[0011] In some alternative implementations, by Calculate the number of sections n in the vertical coaxial waveguide converter, where R is the ratio of the characteristic impedance of the coaxial section to the equivalent characteristic impedance of the rectangular waveguide, and Γ max W is the maximum permissible reflection coefficient within the band. θ The bandwidth is relative, and INT represents the floor function.

[0012] In some alternative implementations, the size of the coaxial waveguide converter is calculated based on the equivalent characteristic impedance of each waveguide segment, using the number of segments in the coaxial waveguide converter. The segments are arranged from left to right, with the rightmost segment being the WR15 international standard waveguide. The dimensions of each step are optimized using the transmission coefficient, including the waveguide inner length, waveguide inner width, and waveguide length of each step, as well as the outer conductor wall thickness. The inner coaxial conductor is longer than the outer conductor.

[0013] In some alternative implementations, the dimensions of the cross-electrode antenna include thickness, length, and width. The thickness of the electrode needs to be consistent with the wall thickness of the coaxial waveguide converter for power feeding. The length and width of the cross-electrode antenna are optimized using HFSS15 to maximize the 3dB beamwidth of the cross-electrode antenna, and the slot structure parameters are adjusted for impedance matching.

[0014] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0015] 1. The antenna has wide beam characteristics, and the coaxial feed end adopts a slotted balun structure to adjust impedance matching.

[0016] 2. It features miniaturization and uses a coaxial waveguide converter for power supply at the lower end, achieving compatibility with existing mirror-based synthetic aperture systems. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a coaxial waveguide converter provided in an embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram of the reflection coefficient and transmission coefficient of a coaxial waveguide converter provided in an embodiment of the present invention;

[0019] Figure 3 This is a schematic diagram of a cross oscillator provided in an embodiment of the present invention;

[0020] Figure 4 This is a front view of a cross-oscillator provided in an embodiment of the present invention;

[0021] Figure 5 This is a top view of a cross-oscillator provided in an embodiment of the present invention;

[0022] Figure 6 This is a schematic diagram of the structure of a cross-electrode wide-beam antenna provided in an embodiment of the present invention;

[0023] Figure 7 This is a cross-oscillator reflection coefficient provided in an embodiment of the present invention;

[0024] Figure 8 This is an embodiment of the invention providing the E-plane and H-plane radiation patterns of a 56GHz cross-electrode wide-beam antenna. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0026] Crossed dipole antenna with wide beamwidth, such as Figure 1 As shown, it consists of a cross-dipole antenna and a coaxial waveguide converter. Firstly, the receiving channel of the mirror-image synthesized aperture experimental system uses waveguide feeding, which is incompatible with the coaxial feeding method used by the cross-dipole. Therefore, to enable the proposed antenna to be used for verification in the experimental system, a coaxial waveguide converter suitable for 50GHz to 60GHz needs to be designed, such as… Figure 1As shown, a stepped waveguide impedance transformation structure is adopted to achieve impedance matching over a wider frequency band. The required number of sections is calculated based on the Chebyshev λ / 4 stepped impedance transformer formula by calculating the characteristic impedance of the coaxial section of the cross-electrode antenna and the equivalent characteristic impedance of the rectangular waveguide.

[0027]

[0028] In the formula, R is the ratio of the characteristic impedance of the coaxial section to the equivalent characteristic impedance of the rectangular waveguide. Γmax W is the maximum permissible reflection coefficient within the band. θ The bandwidth is relative, and INT represents the floor function.

[0029] It can be concluded that the number of sections in the coaxial waveguide converter is 3. Based on the equivalent characteristic impedance of each waveguide section, the coaxial waveguide converter can be calculated as follows: Figure 1 As shown, the branch sequence from left to right is as follows: the rightmost branch is the WR15 international standard waveguide. After optimized design of the transmission coefficient, the dimensions of each step are: A1 3.76mm, B1 1.48mm, L1 2.7mm, A2 3.76mm, B2 1.48mm, L2 2.7mm, A3 3.76mm, B3 1.48mm, L3 2.7mm. Here, A represents the inner length of the waveguide, B represents the inner width of the waveguide, L represents the waveguide length, the outer conductor wall thickness is 0.5mm, and the inner conductor of the coaxial waveguide is 1.68mm longer than the outer conductor. Finally, the reflection coefficient and transmission coefficient of the coaxial waveguide converter are obtained as follows: Figure 2 As shown.

[0030] Then, the design of the cross-electrode antenna is carried out, which needs to meet the resonant frequency requirements of the 50GHz to 60GHz frequency band, such as... Figure 3 As shown. A front view of the crossed dipole antenna structure is shown below. Figure 4 As shown, the top view is as follows Figure 5 As shown. Based on the structural characteristics of the crossed dipole antenna, the main dimensions of the dipole are thickness, length, and width. The dipole thickness, for power feeding, needs to be consistent with the thickness of the outer conductor of the coaxial structure. The length and width of the crossed dipole antenna were optimized using HFSS15 to maximize the 3dB beamwidth. Impedance matching was achieved by adjusting the parameters L1 and h2 of the slot structure. The parameters of the crossed dipole antenna were then determined as follows:

[0031] D1=0.5mm, D2=1.6mm, D3=2.6mm, h1=0.5mm, h2=1.04mm, h3=2.6mm, S=2.3mm, W=0.5mm, L1=0.6mm.

[0032] Finally, the cross-electrode and coaxial waveguide converter are connected in HFSS and the design is simulated and optimized as a whole, such as... Figure 6 As shown, the antenna's reflection coefficient is as follows: Figure 7 As shown. The radiation pattern of the wide-beam cross-dipole antenna at 56 GHz is as follows. Figure 8 As shown, the 3dB beamwidth of the cross-electron wide-beam antenna at 56 GHz is 136° and 202.6° in the E-plane and H-plane, respectively.

[0033] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0034] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A design method for a wide-beam cross-electrode antenna, characterized in that, include: A vertical coaxial waveguide converter is designed, which adopts a stepped waveguide impedance transformation structure. By calculating the characteristic impedance of the coaxial part of the cross-electrode antenna and the equivalent characteristic impedance of the rectangular waveguide, the number of sections of the vertical coaxial waveguide converter is calculated according to the Chebyshev type λ / 4 stepped impedance transformer. The size of the coaxial waveguide converter is calculated based on the number of sections and the equivalent characteristic impedance of each waveguide section. The sections are arranged from left to right, with the rightmost section being the WR15 international standard waveguide. The dimensions of each step are optimized by the transmission coefficient, including the inner length, inner width, and length of the waveguide, as well as the outer conductor wall thickness. The inner conductor of the coaxial waveguide is longer than the outer conductor. Based on the structural characteristics of the cross dipole antenna, the dimensions of the cross dipole antenna are initialized to match the vertical coaxial waveguide converter. Then, the beamwidth of the cross dipole antenna is obtained, and the dimensions of the cross dipole antenna are further optimized to broaden its beamwidth. The cross-dipole antenna is connected to the vertical coaxial waveguide converter. Based on the input impedance of the cross-dipole antenna, a slotted balun structure is used on the outer conductor of the vertical coaxial waveguide converter to achieve impedance matching of the cross-dipole antenna.

2. The method according to claim 1, characterized in that, Depend on Calculate the number of sections in a vertical coaxial waveguide converter ,in, R This is the ratio of the characteristic impedance of the coaxial section to the equivalent characteristic impedance of the rectangular waveguide. This represents the maximum permissible reflection coefficient within the band. For relative bandwidth, INT This is for rounding down.

3. The method according to claim 2, characterized in that, The dimensions of the cross-electrode antenna include thickness, length, and width. The thickness of the electrode needs to be consistent with the wall thickness of the coaxial waveguide converter for power feeding. The length and width of the cross-electrode antenna are optimized using HFSS15 to maximize the 3dB beamwidth of the cross-electrode antenna, and the slot structure parameters are adjusted for impedance matching.

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