Low-Axis-Ratio Circularly Polarized Vortex Wave Design Method Based on Circular Array Antenna

Abstract

This invention discloses a low-axial-ratio circularly polarized vortex wave design method based on a circular array antenna, mainly addressing the problems of complexity and low antenna axial-ratio performance in existing low-axial-ratio circularly polarized vortex wave design methods. The scheme is as follows: Any element in the circular array is selected as the initial phase element, and the remaining elements on the array are numbered sequentially; all elements are rotated sequentially to generate the phase gradient required for the vortex beam, and the target field data M on the sampling receiving plane is extracted; the axial ratio R is calculated based on M. A The process involves drawing an antenna axial ratio distribution diagram; for antennas whose axial ratio distribution diagram does not meet the low axial ratio requirement, the rotation angle of the initial phase element is changed, and the remaining elements are rotated sequentially to make the array meet the required phase gradient. The antenna cross-polarization pattern is then drawn, and the antennas corresponding to the rotation angles of the elements with cross-polarization isolation greater than 15dB in the pattern are identified, thus completing the low axial ratio antenna design. This invention is simple to implement, achieves good low axial ratio results, and can be used for vortex electromagnetic wave design in wireless communication and radar detection.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication technology, and specifically relates to a low-axis-ratio circularly polarized vortex wave design method, which can be used for the research and design of vortex electromagnetic wave generators in wireless communication and radar detection. Background Technology

[0002] With the rapid development of wireless communication technology, spectrum resource occupancy is increasing daily, and communication capacity is approaching the Shannon limit. Improving spectrum resource utilization has become a focus of attention. Orbital angular momentum technology, as a multiplexing technique, can improve spectrum utilization. Vortex electromagnetic waves carrying orbital angular momentum have a helical phase structure, which is related to the modal values ​​of the orbital angular momentum they carry. Different angular momentum modes are orthogonal to each other, so theoretically, the modal values ​​are infinite. Therefore, the modal values ​​of the orbital angular momentum carried by vortex electromagnetic waves provide additional degrees of freedom for electromagnetic control. Consequently, vortex electromagnetic waves carrying orbital angular momentum have been extensively studied due to their potential to expand the capacity of microwave and optical communication channels.

[0003] A vortex electromagnetic beam carrying a topological charge of l has a phase factor. The phase wavefront exhibits a spiral shape. The field strength distribution of a single-mode vortex electromagnetic wave has a "donut" shape, with a very weak, near-zero field strength in the central region along the propagation axis, maintaining this characteristic throughout propagation. As the propagation distance of the vortex electromagnetic wave increases, the radius of the weak field strength region also increases. The larger the topological charge *l*, the larger the radius of the central region with zero light intensity. Axial ratio is an important performance indicator of a circularly polarized antenna, representing the purity of circular polarization. The bandwidth with an axial ratio not exceeding 3 dB is defined as the circular polarization bandwidth of the antenna. It is an important indicator for measuring the overall gain difference of the antenna in different directions. In their 2018 article in High Power Laser and Particle Beams, Jing Hong et al. proposed "A Low Axis Ratio Circular Polarized Antenna Design for Airborne Radiation Field Measurement". This design achieves the effect of low axis ratio by sequentially rotating the trapezoidal radiating element by 90 degrees. However, since the feed position and the phase center of the element will be offset during rotation, the design of the feed network needs to be added, which increases the complexity of the design. At the same time, the feed phase deviation of the element will also have a significant impact on the circular polarization performance. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the prior art by proposing a low axial ratio circularly polarized vortex wave design method based on a circular ring array antenna, so as to reduce the design difficulty of low axial ratio antennas and improve the axial ratio performance of circularly polarized antennas.

[0005] To achieve the above objectives, the present invention provides a low axial ratio circularly polarized vortex wave design method based on a circular ring array antenna, comprising the following steps:

[0006] 1) Select any one element in the circular array as the initial phase element M0, and number the remaining elements in the circular array sequentially in a counterclockwise direction as M1, M2, ..., M0. m-1 Array units M0 to M m-1 The phase gradient required to generate the vortex beam is generated by rotating sequentially, and the target field data M of the vortex beam in the sampling and receiving plane is extracted, where m is the number of units contained in the circular array.

[0007] 2) Based on the target field data M, calculate the axial ratio R of the antenna on the sampling and receiving plane. A Draw the antenna axial ratio distribution diagram;

[0008] 3) Observe whether the axial ratio within the region of the vortex beam planar annular field intensity in the axial ratio distribution diagram satisfies R. A Low aspect ratio requirement <3dB:

[0009] If the requirements are met, the design of the low-axis-ratio circularly polarized vortex beam will be completed.

[0010] If the requirements are not met, then change the rotation angle of the radiation element M0, which is determined as the initial phase element. And rotate M1, M2, ..., M in sequence. m-1 To make the circular array satisfy the phase gradient required for vortex waves, thereby changing the axial ratio performance of the array antenna;

[0011] 4) Draw different rotation angles Observe the corresponding 3D and 2D cross-polarization patterns of the array antennas and find the element rotation angle that makes the cross-polarization isolation on the main lobe of the vortex beam greater than 15dB. at this time The corresponding array antenna is the designed low axial ratio antenna.

[0012] This invention uses an initial phase element as a reference, and changes the rotation angle of the initial phase element and then sequentially changes the rotation angle of the remaining array elements to change the overall phase gradient of the array antenna. This not only reduces the design difficulty of low axial ratio antennas and improves the axial ratio performance of circularly polarized antennas, but also improves the effect of changing the antenna axial ratio. That is, the effect of low axial ratio can be achieved by simply rotating the angle of the metal patch of the element. It can be widely used in array antennas that generate vortex beams by rotating the angle of the element. Attached Figure Description

[0013] Figure 1 This is a flowchart illustrating the implementation of the present invention;

[0014] Figure 2 This is a schematic diagram of the ring array antenna in this invention;

[0015] Figure 3 This is a schematic diagram illustrating the principle of rotating the initial phase unit angle in this invention;

[0016] Figure 4 This is a diagram showing the axial ratio distribution of each OAM mode of the vortex wave when the initial phase is 0 in this invention.

[0017] Figure 5 This is the 3D cross-polarization pattern of the antenna when the initial phase increases in this invention;

[0018] Figure 6 This is a diagram showing the axial ratio distribution of each OAM mode of a low axial ratio vortex wave designed using this invention. Detailed Implementation

[0019] The following detailed description, in conjunction with the accompanying drawings, provides further explanation of the specific embodiments and effects of the present invention.

[0020] Reference Figure 1 The implementation steps for this example are as follows:

[0021] Step 1: Extract the target field data M of the vortex beam within the sampling and receiving plane.

[0022] 1.1) Select any one element in the circular array antenna as the initial phase element M0, and number the remaining elements in the circular array sequentially in a counterclockwise direction as M1, M2, ..., M0. m-1 , where m is the number of cells contained in the annular array;

[0023] 1.2) Using the initial phase array unit M0 as a reference, the units M1, M2, ..., M... m-1 The phase gradient required to generate a vortex beam is generated by rotating sequentially.

[0024] 1.3) Set up a sampling receiving plane in the beam direction at a distance L from the aperture surface of the array antenna, with a size of D*D, where L=20*λ, λ is the wavelength, and the size of D is determined by the intersection of the line connecting the outer 3dB point of the vortex beam divergence angle α in the array antenna pattern and the center point of the array antenna aperture surface with the sampling receiving plane.

[0025] 1.4) The target field data M of the vortex beam in the sampling receiving plane is directly extracted using HFSS simulation software.

[0026] Step 2: Calculate the axial ratio R of the antenna on the sampling and receiving plane based on the target field data M. A Draw the antenna axial ratio distribution diagram.

[0027] 2.1) Based on the known electric field amplitude and phase (E) in the horizontal polarization of the target field data M. xA E xP) and the amplitude and phase of the electric field in the vertical direction of polarization (E) yA E yP ), calculate the left-hand circularly polarized wave F of the antenna respectively. L and right-hand circularly polarized wave F R :

[0028]

[0029]

[0030] 2.2) From the left-hand circularly polarized wave F L and right-hand circularly polarized wave F R Calculate the axial ratio R of the antenna. A :

[0031]

[0032] 2.3) Based on the antenna axial ratio R in 2.2) A The calculation results are used to plot the axis ratio distribution of each OAM mode, as shown below. Figure 4 As shown in the figure. The distribution is as follows. Figure 4 The effect of using black and white areas to distinguish the aspect ratio is shown, with the black area representing R. A <3dB, the white area indicates R A >3dB.

[0033] Step 3: Based on the axial ratio distribution diagram, while satisfying the phase gradient required for vortex waves, change the overall phase of the array to reduce the axial ratio.

[0034] 3.1) Observe whether the axial ratio within the region of the vortex beam planar annular field intensity in the axial ratio distribution diagram satisfies R. A Low aspect ratio requirement <3dB:

[0035] If the requirements are met, the design of the low-axis-ratio circularly polarized vortex beam will be completed.

[0036] If the requirements are not met, proceed to step 3.2);

[0037] 3.2) Change the rotation angle of the radiation element M0, which is determined as the initial phase element. The rotation angle of the initial phase unit M0 according to The pattern changes regularly; this example is set up as follows. θ = 30°, n = 6, that is Varying the angle between 0° and 180° in 30° intervals, execute 3.3);

[0038] 3.3) Using the initial phase array unit M0 as a reference, the remaining units M1, M2, ..., M... m-1Rotate sequentially, according to the rotation angle of the initial phase unit M0. As the angle changes from 0° to 180°, the initial phase of the array changes, affecting the other elements M1, M2, ..., M... m-1 This also results in a phase change, when these units M1, M2, ..., M... m-1 When the rotation angle changes from 0° to 180° in 30° intervals, the required phase gradient of the vortex beam can be satisfied, causing the overall phase of the array to change, and step 4 can be executed.

[0039] Step 4: Plot the cross-polarization pattern of the array antenna and find the element rotation angle corresponding to low axial ratio performance.

[0040] 4.1) Draw different rotation angles The corresponding cross-polarization 3D radiation pattern and cross-polarization 2D radiation pattern of the array antenna, such as Figure 5 As shown;

[0041] 4.2) Observation Figure 5 In the cross-polarization pattern, find the element rotation angle that results in a cross-polarization isolation greater than 15 dB on the main lobe of the vortex beam. at this time The corresponding array antenna is the designed low axial ratio antenna.

[0042] The effects of this invention can be further illustrated by the following simulation examples:

[0043] 1. Simulation conditions

[0044] This invention is implemented using a circular array antenna that generates vortex beams by rotating the element angles. In this example, a dual-ring circular antenna array with alternating array elements is specifically used to generate vortex beams with four different OAM mode values ​​of ±1 and ±2. The simulation software used is HFSS.

[0045] The structure diagram of the ring array antenna is as follows: Figure 2 As shown, it consists of inner and outer rings, each with 16 elements. The inner ring is divided into two groups of eight elements each, which are fed to generate ±1 OAM modes. The outer ring is also divided into two groups of eight elements each, which are fed to generate ±2 OAM modes. The phase difference between adjacent elements of the array antenna corresponding to each OAM mode is different. Find the answer. Figure 2 The array elements marked with circles are the initial phase units M0 of each OAM mode, and the initial phase is set to θ = 0°.

[0046] According to such Figure 3The principle illustrated involves rotating the initial phase cell M0 at an angle. Since the feed point of the cell in this example is located at the cell phase center, no additional phase difference is generated during rotation. Therefore, phase control can be achieved simply by rotating the cell patch. When rotating a cell whose feed point is not located at the cell phase center, a feed network is needed to compensate for the phase difference generated during cell rotation; this is not specifically explained in this example.

[0047] 2. Simulation content:

[0048] Simulation 1: With the initial phase at 0, the circular array antenna is simulated using HFSS to obtain the axial ratio distribution of each mode of the antenna. The results are as follows. Figure 4 As shown.

[0049] from Figure 4 It can be seen that only the vortex beam with mode l = +1 satisfies the axial ratio R within the region of the annular field strength observed in the plane. A The requirement of <3dB is not met, and the axial ratios of the l=-1, l=+2, and l=-2 mode vortex beams are all not satisfied, requiring further low axial ratio design.

[0050] Simulation 2, taking a circular array with vortex mode l=-1 as an example, uses the method of this invention to change the rotation angle of the radiation element M0, which is determined as the initial phase element. And taking the initial phase array unit M0 as the reference, the units M1, M2, ..., M m-1 The phase gradient required to generate vortex waves is generated by rotating sequentially. Varying between 0° and 180° in 30° intervals, for The corresponding circular array antenna was simulated to obtain the antenna's cross-polarization pattern, such as... Figure 5 As shown.

[0051] from Figure 5 It is evident that as the initial phase increases, the cross-polarization isolation on the main lobe of the vortex beam in the antenna's cross-polarization 3D pattern changes. The element rotation angle required to achieve a cross-polarization isolation greater than 15 dB on the main lobe of the vortex beam needs to be identified. Among them when The corresponding array antenna produces the l=-1 mode vortex beam with the best axial ratio performance.

[0052] Simulation 3: Using the method of this invention, for a circular array with vortex modes l=+1, l=-1, l=+2, and l=-2, the simulation shows the optimal vortex beam axial ratio performance. The corresponding antennas, i.e., when simulating the vortex mode l=+1 respectively. When the vortex mode l = -1 When the vortex mode l = +2 When the vortex mode l = -2 The corresponding antennas yielded the axial ratio distribution diagrams for each OAM mode, as shown below. Figure 6 As shown.

[0053] from Figure 6 It can be seen that the axial ratio R of each OAM mode vortex beam is... A The portion less than 3dB can basically cover the annular field strength region of the vortex beam on the observation surface, meaning that after using this invention, each OAM mode can meet the design requirements for low axis ratio.

[0054] The above description is merely a specific embodiment of the present invention and does not constitute any limitation on the present invention. Obviously, those skilled in the art, after understanding the content and principles of the present invention, may make various modifications and changes in form and detail without departing from the present invention. However, these modifications and changes based on the ideas of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. A circularly polarized vortex wave design method with low axial ratio based on a circular ring array antenna, characterized in that, Comprise as follows: 1) select any one unit in the circular array as the initial phase unit , the remaining units on the circular array are numbered in anticlockwise direction as , , …, , the array units to are sequentially rotated to generate the phase gradient required by the vortex beam, and the target field data M of the vortex beam in the sampling receiving plane is extracted, where m is the number of units contained in the circular array; the feeding point of the unit is located at the phase center of the unit; 2) According to the target field data M, calculate the axial ratio of the antenna on the sampling receiving plane , draw the antenna axial ratio distribution map; 3) observing whether the low-axial-ratio requirement of is satisfied in the region of the axial-ratio distribution map where the vortex-beam plane annular field strength is If the requirements are met, the design of low axial ratio circularly polarized vortex beam is completed; If the requirement is not met, the rotation angle of the radiating element determined as the initial phase unit is changed , , , , , and the circular array is sequentially rotated to meet the required phase gradient of the vortex wave to change the axial ratio performance of the array antenna. 4) plot different rotation angles The cross-polar 3D pattern and cross-polar 2D pattern of the vortex wave generated by the corresponding array antenna are observed to find the unit rotation angle that makes the cross-polar isolation on the main lobe of the vortex beam greater than 15 dB At this time The corresponding array antenna is the designed low axial ratio antenna.

2. The method of claim 1, wherein, The target field data M of the vortex beam extracted in the 1) in the sampling receiving plane Is directly extracted by HFSS simulation software.

3. The method of claim 1, wherein, The 2) calculates the antenna in the sampling receiving plane The ratio of the axes on This is achieved as follows: 3a) Calculate the amplitude and phase of the electric field polarized in the horizontal direction from the target field data M and the amplitude and phase of the electric field polarized in the vertical direction , respectively, for the left-hand circularly polarized wave and the right-hand circularly polarized wave of the antenna: ； ； 3b) from a left-handed circularly polarized wave and a right-handed circularly polarized wave calculating the axial ratio of the antenna : 。 4. The method of claim 1, wherein, The change in the 3) determines the rotation angle of the radiating elements which are the initial phase elements and in turn rotates , , the array to meet the required phase gradient, as follows:​ 4a) the rotation angle of the initial phase unit is changed according to the law , , , , where n is an integer, such that the rotation angle is between and ; 4b) With the initial phase unit rotation angle The change in phase causes a change in the initial phase of the array, affecting other elements. , … This also results in a phase change, when these units , … The change in rotation angle and When the change in rotation angle remains consistent, the required phase gradient of the vortex beam can be satisfied.

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