A near-field focused circularly polarized radial line slot array antenna and its design method

Abstract

This invention discloses a near-field focusing circularly polarized radial slot array antenna and its design method. Based on a single-layer radial waveguide, the antenna employs direct feeding via coaxial probes. The focal position and circular polarization direction are adjusted by modifying the slot pair layout and slot orientation. Etching helical slots improves the antenna's radiation performance, and loading short-circuit probes suppresses the influence of higher-order modes. This invention addresses the limitations of existing technologies, such as the application scenarios of ring-distributed slot pairs, the difficulty in implementing electromagnetic algorithm analysis, and the low radiation efficiency of existing near-field focusing antennas. This invention achieves near-field focusing characteristics not yet present in existing radial slot array antennas, reducing the structural complexity of existing near-field focusing antennas and improving antenna efficiency.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic field and microwave technology, and further relates to a near-field focusing circularly polarized radial slot array antenna and its design method in the field of wireless power transmission technology. The antenna designed in this invention can improve the efficiency of electromagnetic focusing in wireless power transmission systems and has the characteristics of controllable focus and adjustable circular polarization. Background Technology

[0002] In engineering practice, antenna design focuses on far-field radiation characteristics and efficiency. Traditional antennas are unsuitable for communication applications in the near-field radiation region due to power divergence and high sidelobes. However, near-field focusing antennas are needed to meet the requirements of certain specific situations. For example, in microwave hyperthermia, the antenna needs to raise the temperature of diseased tissue without affecting surrounding healthy biological tissue. In wireless power transmission systems, transmitting antennas often need to be small in size, highly efficient, have stable transmission rates, and be able to power multiple devices simultaneously. Traditional radial slot antennas, with their low profile, high gain, and low loss, have broad application prospects in satellite communication and deep space exploration. However, most current radial slot array antenna designs focus on beam control, feed structure design, and rapid numerical analysis. Existing near-field focusing radial slot array antennas are axially linearly polarized rather than tangentially circularly polarized, which limits their application scenarios; or they are based on complex double-layer radial slot array antennas, which lack advantages in terms of ease of manufacturing and cost.

[0003] The paper "On the Near-Field Shaping and Focusing Capability of a Radial Line Slot Array" (IEEE Transactions on Antennas and Propagation, Vol. 62, No. 4, pp. 1991-1999, April 2014) by Mauro Ettorre et al. proposes a near-field focusing radial line slot array antenna and its design method. This near-field focusing antenna employs a ring-shaped slot pair layout, and the polarization of the radiated electromagnetic waves is axial / linear polarization along the antenna normal, rather than traditional circular or linear polarization, thus limiting its application scenarios. The design method derives the antenna aperture field distribution through Fast Fourier Transform (FFT) and designs the size and position of the slot pairs using alternating projection and the method of moments (MoM), achieving high computational efficiency and accuracy. Antennas designed using this method can significantly focus energy. However, a remaining drawback is the need to write code related to FFT, alternating projection, and MoM, making implementation relatively difficult.

[0004] The University of Electronic Science and Technology of China (UESTC) has proposed an inward-facing zero-order Hankel leaky-wave antenna for near-field focusing in its patent application, "Inward Zero-Order Hankel Leaky Wave Antenna for Near-Field Focusing" (Application No.: CN201710103235.7, Publication No.: CN 1068485821 A). This antenna primarily consists of a radial waveguide. Inside the radial waveguide, a circular metal plate parallel to the bottom plate is arranged radially, dividing the radial waveguide into upper and lower dielectric layers. A gap is provided between the edge of the circular metal plate and the inner wall of the radial waveguide, forming an annular slit along the circumference of the radial waveguide. The upper dielectric surface of the radial waveguide has an impedance surface structure for exciting the leaky wave mode. This antenna can achieve different wavenumbers (TE and TM) leaky waves using different impedance surfaces, and different broadband planar periodic structures can be used to eliminate residual waves at the antenna center. The antenna has advantages such as small size and adjustable efficiency. However, this antenna still has some shortcomings. First, because it is based on a double-layer radial waveguide, its structure is complex and its manufacturing cost is high. Second, the sidelobe level in the focusing region of this antenna is high, and the influence of higher-order modes is not considered, thus failing to achieve optimal radiation efficiency. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a near-field focusing circularly polarized radial slot array antenna and its design method. The main problems solved are: First, the use of annular distributed slots to fix the polarization of the radial slot array antenna limits its application scenarios. Second, the complex principle and high manufacturing cost of the double-layer radial slot antenna structure. Third, the high focal region sidelobe level, low radiation efficiency, and high-order mode influence of the near-field focusing Hankel leaky wave antenna. Fourth, the difficulty in implementing electromagnetic algorithm analysis techniques.

[0006] The specific approach to achieving the objective of this invention is as follows: Because the antenna of this invention employs a helically distributed slot pair to achieve a near-field focusing effect, the circularly polarized waves radiated by the helically distributed slot pair can receive both circularly polarized waves with the same / different helical directions and linearly polarized waves, overcoming the shortcomings of existing technologies using ring-distributed slot pairs, which have fixed polarization and limited application scenarios. The antenna of this invention uses a radial linear slot array antenna composed of a single-layer radial waveguide. The single-layer plate structure contains only one dielectric layer, avoiding the disadvantages of existing radial linear slot array antennas using double-layer radial waveguide structures, such as complex principles and high manufacturing costs. The antenna of this invention possesses the inherent advantages of high radiation efficiency and low transmission loss of waveguide slot array antennas. Furthermore, by loading a short-circuit probe, the influence of higher-order modes in the antenna is suppressed, solving the problems of high focal sidelobe levels, low radiation efficiency, and the influence of higher-order modes present in existing near-field focusing technologies using Hankel leaky wave antennas. The design method of this invention is implemented through equivalent analysis model simulation and analytical formula calculation, resulting in low code complexity and high antenna design efficiency, solving the problem that existing electromagnetic algorithm analysis techniques are difficult to implement. To achieve the above objectives, the near-field focusing circularly polarized radial slot array antenna of the present invention includes a dielectric substrate, a coaxial feed connector, short-circuit probes, and a metal substrate. The dielectric substrate is a single-sided copper-clad laminate, with a slow-wave material filling the space between the dielectric substrate and the metal substrate. A circular annular slot is etched in the central region of the copper-clad layer of the dielectric substrate, a spiral slot is etched in the outer region of the copper-clad layer, and n pairs of rectangular slots are spirally arranged on the copper-clad layer, the value of n being determined by the antenna focusing position and the antenna aperture size. The antenna is fed from the center of the metal substrate through the coaxial feed connector. The short-circuit probes are located around the circular annular slots and are rotationally symmetrical about the circular annular slots. The number of short-circuit probes is m, the value of m being determined by the dimensions of the coaxial feed connector and the circular annular slots.

[0007] The antenna design method of the present invention includes the following steps:

[0008] Step 1: Determine the aperture field amplitude and phase distribution of the near-field focusing radial line slot array antenna:

[0009] The aperture field amplitude distribution of the antenna is determined based on its radiation characteristics, and the size and position range of the slot pair are determined based on the aperture field amplitude distribution. The aperture field phase distribution of the antenna is determined based on its focusing characteristics. The phase includes the sum of two sets of phases: the radiation phase of the main polarization component determined by the slot length and the transmission phase determined by the radial position. The compensation phase and corresponding movement distance of the rectangular slot pair are determined based on the phase distribution.

[0010] Step 2: Extract the port transmission coefficients and the radiation phase of the principal polarization component from the equivalent analysis model of the radiating element:

[0011] An equivalent analysis model of the periodic boundary is established, consisting of a slot pair, a dielectric plate, an air layer, and a metal base plate. The size of the slot in the equivalent analysis model is corrected according to the range of slot size values ​​determined in step 1. The equivalent analysis model is simulated and the transmission coefficient and radiation phase of the main polarization component of the port are extracted.

[0012] Step 3: Establish the correspondence between the port transmission coefficient, the radiation phase and transmission phase of the main polarization component and the size and position of the slots based on the aperture field amplitude and phase distribution of the antenna. Correct the size and radial position of the rectangular slot pairs according to this correspondence to achieve near-field focusing. The correspondence between the rectangular slot pairs corresponds one-to-one with the focusing characteristics of the antenna.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] First, the antenna of the present invention uses a spirally distributed slot pair to achieve a near-field focusing effect. By changing the layout of the slot pair and the orientation of the slots, the focal position and circular polarization direction can be changed, overcoming the shortcomings of the prior art which uses a ring-distributed slot pair with a fixed polarization mode and limited application scenarios. This makes the antenna of the present invention have the advantages of flexible and controllable polarization mode and a wide range of application scenarios.

[0015] Secondly, since the antenna of the present invention is based on a single-layer radial waveguide structure, it overcomes the inherent disadvantages of complex structure and high processing cost of the double-layer radial waveguide structure in the prior art, as well as the disadvantages of high focal sidelobe level, low radiation efficiency and high-order mode influence of the near-field focusing Hankel leaky wave antenna. As a result, the antenna of the present invention has the advantages of simple structure, low processing cost, low focal sidelobe level, high radiation efficiency and low high-order mode influence.

[0016] Third, the design method of the present invention is realized through equivalent analysis model simulation and analytical formula calculation, which overcomes the shortcomings of existing technologies that are not easy to implement based on electromagnetic algorithm analysis technology. This makes the design method of the present invention have the advantages of strong practicality, simple operation and high design efficiency. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a simulation model according to an embodiment of the present invention; wherein, Figure 1 (a) is a top view of the simulation model; Figure 1 (b) is a side view of the simulation model;

[0018] Figure 2 This is a flowchart of the antenna design method according to an embodiment of the present invention;

[0019] Figure 3 This is a graph showing the gap size and radial position according to an embodiment of the present invention; wherein, Figure 3 (a) is a curve of gap length versus coupling factor; Figure 3(b) is a radial position-distance travel curve;

[0020] Figure 4 This is a diagram of the periodic boundary equivalent analysis model according to an embodiment of the present invention;

[0021] Figure 5 This is a diagram showing the distribution of the left-hand circularly polarized electric field intensity across the cross-section of the antenna according to an embodiment of the present invention; wherein, Figure 5 (a) is a distribution diagram of the magnitude of the electric field intensity; Figure 5 (b) shows the phase distribution of the electric field intensity;

[0022] Figure 6 These are longitudinal and cross-sectional power density distribution diagrams of the antenna according to an embodiment of the present invention; wherein, Figure 6 (a) is a yoz surface distribution diagram; Figure 6 (a) is a distribution map of the xoz surface; Figure 6 (c) is a focal plane distribution diagram;

[0023] Figure 7 This is a graph showing the antenna port reflection coefficient of an embodiment of the present invention.

[0024] Figure 8 This is a graph showing the antenna axial ratio of an embodiment of the present invention. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0026] A near-field focusing circularly polarized radial slot array antenna includes a dielectric substrate 1, a coaxial feed connector 2, short-circuit probes 30-33, and a metal substrate 5. The dielectric substrate 1 is a single-sided circular copper-clad laminate. A slow-wave material 4 is filled between the dielectric substrate 1 and the circular metal substrate 5. The thickness of the dielectric substrate 1 is h1, the thickness of the metal substrate 5 is h3, and the thickness of the slow-wave material is h2. The diameter of the dielectric substrate 1, the slow-wave material 4, and the metal substrate 5 is D, and their equivalent dielectric constant is ε. eff h1, h2, and h3 satisfy the formula for the equivalent dielectric constant of a multilayer medium, and the value of D ranges from 300mm to 500mm. ε eff The value range is 1.4-1.8.

[0027] The copper-clad layer 10 of the dielectric substrate has a circular annular slot 13 etched at its center, a spiral slot 11 etched around its perimeter, and n pairs of rectangular slots 12 spirally arranged on the copper-clad layer. The value of n is determined by the antenna focusing position and the size of the antenna aperture. The inner diameter of the circular annular slot is R0, and the outer diameter is R1. The width of the spiral slot is w0. The length of the rectangular slot pair is L, and the width is w. The values ​​of R0 and R1 are mainly determined by the diameter of the inner conductor 20 of the coaxial feed connector. The value of w0 ranges from λ. g / 4-λg / 2,λ g Where λ is the waveguide wavelength, and the value of L ranges from λ0 / 5 to λ0 / 2, where λ0 is the vacuum wavelength, and the value of w is much smaller than L.

[0028] The antenna is center-fed via a coaxial feed connector 2, the diameter of which is R3, determined by the specified specifications of the coaxial feed connector. The short-circuit probes 30-33 are located around the annular slot 13 and are rotationally symmetrical about the annular slot 13. The diameter of the short-circuit probes 30-33 is R4, which is the same as R3.

[0029] The thickness h1 of the dielectric substrate 1 is 1.524 mm. In this embodiment of the invention, the slow-wave material 4 adopts an air layer / dielectric layer hybrid structure, the thickness h2 of the slow-wave material is 1.6 mm, and the thickness h3 of the metal base plate 5 is 2 mm. The diameter D of the dielectric substrate 1, the slow-wave material 4, and the metal base plate 5 is 432 mm, and the equivalent dielectric constant ε is... eff It is 1.55.

[0030] The annular slot 13 is located around the inner conductor 20 of the coaxial feed connector and is circularly symmetrical about the inner conductor 20. By reasonably adjusting the size of the annular slot, it mainly offsets the reactive component introduced by the inner conductor 20 of the coaxial feed connector, facilitating impedance matching of the antenna. The inner diameter R0 of the annular slot 13 is 2.95 mm, and the outer diameter R1 is 3.85 mm.

[0031] The spiral slot 11 is located on the periphery of the rectangular slot pair 12 and is spiral-shaped about the origin of the copper-clad layer 10. The width w0 of the spiral slot is 6.1 mm. The spiral slot etched in the copper-clad layer 10 can further improve the radiation performance of the antenna and improve the port reflection of the antenna.

[0032] The 12 pairs of rectangular slots consist of two long rectangular slots that are perpendicular in direction, have the same radial angle, and are separated by a quarter of the waveguide wavelength. Each pair of rectangular slots constitutes a circularly polarized radiation unit. The length L of the rectangular slot pair ranges from 7.02 mm to 9.82 mm, and the width w is 1 mm.

[0033] The direction of the spiral lines of the distribution trajectory of the rectangular slot pairs 12 and the orientation of the two rectangular slots in each pair determine the circular polarization direction of the antenna. When the spiral lines of the distribution trajectory are arranged counterclockwise, the antenna radiates a circularly polarized wave; conversely, when arranged clockwise, the antenna radiates a right-hand circularly polarized wave. Figure 1 The rectangular slot distribution trajectory spiral is arranged counterclockwise, and the two rectangular slot pairs point in a counterclockwise "V" shape. The antenna radiates a left-hand circularly polarized wave.

[0034] The rectangular slot pair 12 achieves near-field focusing by adjusting the size and position of each rectangular slot pair unit. Furthermore, the rectangular slot pairs have different slot layouts, each corresponding to a different focusing characteristic. Since the focusing distance determines the density of the rectangular slot arrangement, the number of rectangular slot pairs must be less than the antenna aperture. The antenna's focusing distance is 670mm, and the antenna aperture D is 432mm. Therefore, the number of rectangular slot pairs n is 650, and the antenna's center operating frequency is 10GHz.

[0035] The outer conductor 21 of the coaxial probe feed connector is electrically connected to the metal base plate 5, and the inner conductor 20 passes through the slow wave material 4 and is electrically connected to the copper cladding layer 10 of the dielectric substrate.

[0036] The short-circuit probes 30-33 are spaced π / 2 apart, and each probe is electrically connected at both ends to the copper-clad layer 10 of the dielectric substrate and the metal base plate 5, respectively. The specifications of the coaxial feed connector are: operating frequency 0-18GHz, and inner conductor 20 diameter R3 of 1.3mm. Since the inner conductor 20 diameter R3 of the coaxial feed connector affects the antenna's input reactance component and the attenuation rate of higher-order modes, and the inner diameter R0 and outer diameter R1 of the annular slot determine the antenna's input inductive reactance component, after optimization and size adjustment, the inner conductor 20 diameter R3 of the coaxial feed connector is 1.3mm, the annular slot inner diameter R0 is 2.95mm, and the outer diameter R1 is 3.85mm. Therefore, the number of short-circuit probes m is 4. The presence of the short-circuit probes can suppress the influence of higher-order modes of the antenna, balance the antenna's sidelobe level, and improve the antenna's near-field focusing performance to a certain extent.

[0037] Reference Figure 2 The implementation steps of the antenna design method of the present invention will be further described below.

[0038] Step 1: Determine the aperture field amplitude and phase distribution of the near-field focusing radial line slot array antenna.

[0039] The aperture amplitude distribution of the antenna is determined based on the radiation characteristics. Considering the sidelobe level and design complexity, the aperture field amplitude distribution of the antenna is determined to be a uniform amplitude distribution. The size and position range of the rectangular slot pair are then determined based on the aperture amplitude distribution.

[0040] Step 2: Determine the focal position and focal diameter parameters using the following empirical formula:

[0041]

[0042] Where, Δ s Let r0 be the focal diameter, λ0 be the preset focal point position, λ0 be the vacuum wavelength, and L be the maximum size of the antenna. In the embodiments of the present invention, considering both the operating frequency and the operating size, r0 is 1.2m, and Δ sIt is 2λ0.

[0043] Step 3: Determine the range of values ​​for the size and position of the rectangular gap pair according to the following energy coupling formula:

[0044]

[0045]

[0046] Wherein, α is defined as the coupling factor, which is defined as the proportion of leakage energy per unit thickness of radial waveguide. max Set to 20.5 dB / m. ρ max The location of the outermost gap, ρ min The location of the innermost gap, ρ max ρ min The thicknesses are set to 200mm and 36mm respectively.

[0047] The range of values ​​for the size and position of the rectangular gap pair can be obtained from the above formula, such as... Figure 3 (a) shows the curve of the change in gap length versus coupling factor.

[0048] Step 4: Determine the phase distribution of the antenna based on the focusing characteristics.

[0049] The antenna phase consists of the sum of the radiation phase, which is determined by the main polarization component based on the slot length, and the transmission phase, which is determined by the radial position. The compensation phase and corresponding movement distance of the rectangular slot pair are determined based on the phase distribution. To achieve a focused phase distribution of the radiation field, the compensation phase of the slot is calculated.

[0050] Calculate the corresponding distance using the following formula:

[0051]

[0052] Among them, S ρa S' represents the uncorrected distance between radially adjacent gaps a and b. ρa k represents the corrected distance between gaps a and b. b k a ρ represents the waveguide phase constant representing the positions of slits b and a before correction. b ρ a The radius represents the position of gaps b and a before correction, r0 represents the preset focal position, and λ represents the radius of the original position of gaps b and a. g π represents the waveguide wavelength, and π represents pi.

[0053] The moving distance of the rectangular gap pair can be obtained from the above formula, such as... Figure 3 (b) shows the radial position-distance travel curve.

[0054] Step 5: Extract the port transmission coefficient and the radiation phase of the main polarization component from the equivalent analysis model of the radiating element.

[0055] An equivalent analysis model of the periodic boundary is established, consisting of a slot pair, a dielectric plate, an air layer, and a metal base plate. The size of the slot in the equivalent analysis model is changed according to the range of slot size determined in step 1. The equivalent analysis model is simulated and the transmission coefficient and radiation phase data of the main polarization component of the port are extracted.

[0056] Periodic boundary equivalent analysis model, such as Figure 4 As shown in the simulation model, the length S of the equivalent analysis model ρ The width of the equivalent analysis model is set to a fixed value of 20mm. Set to 13.5mm.

[0057] Step 6: Establish the correspondence between port transmission coefficient, main polarization component radiation phase, transmission phase, and radiation slot size and location based on the antenna aperture field amplitude and phase distribution.

[0058] Since the length of the radiating slot determines the amount of energy coupled from within the radial waveguide, the slot length is correlated with the port transmission coefficient and the radiation phase of the main polarization component. Similarly, since the position of the radiating slot determines the transmission phase within the radial waveguide, the slot position is correlated with the transmission phase. Thus, the slot size and position parameters of the near-field focusing circularly polarized radial slot array antenna are obtained. By changing the slot size and radial position according to this correspondence, near-field focusing can be achieved; different correspondences correspond to different focusing characteristics.

[0059] Step 7: Construct a radial slot array antenna, and use scripts to automatically model and simulate the radiating slots to obtain the power density distribution and field distribution results.

[0060] Figure 5 This is the distribution of the left-hand circularly polarized electric field at a distance of one vacuum wavelength from the antenna in an embodiment of the present invention; wherein, Figure 5 (a) shows the magnitude distribution of the electric field; Figure 5 (b) shows the phase distribution of the electric field. From Figure 5 As can be seen in (a), the radiation field achieves a uniform amplitude distribution. Figure 5 As can be seen in (b), the radiation field phase achieves a focused phase distribution.

[0061] Figure 6 This is a power density distribution diagram of the longitudinal section and focal plane of the radial line slot array antenna according to an embodiment of the present invention; wherein, Figure 6 (a) and Figure 6(b) Power density distribution diagrams for the antenna's yoz and xoz cross sections, respectively. The horizontal axis ranges from -90mm to 90mm, and the vertical axis ranges from 600mm to 1000mm. The shades of color represent the magnitude of power density, and the point with the maximum power density is the focal point. Therefore, there is one focal point in the diagram, located near 670mm. Due to the field propagation factor, the actual focusing position deviates somewhat from the preset focal point r0; that is, the actual focusing position lies between the antenna aperture plane and the preset focal point. Figure 6 (c) shows the power density distribution at the antenna focal plane, with both the horizontal and vertical axes ranging from -90mm to 90mm. Figure 6 (c) shows a focal point at the center of the cross-section with a focal width of 2.48λ0.

[0062] Figure 7 The port reflection coefficient curve of the radial line slot array antenna in this embodiment of the invention shows that the antenna achieves good impedance matching in the range of 9GHz-11GHz, with a -15dB impedance bandwidth of 13.5%.

[0063] Figure 8 The diagram shows the axial ratio curve of the radial slot array antenna according to an embodiment of the present invention. The axial ratio is less than 1dB in terms of side-firing, indicating good circular polarization performance of the antenna.

[0064] The above description is merely an example of the present invention and does not constitute any limitation on the present invention. Any person skilled in the art can conceive of possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, without departing from the spirit and content of the present invention. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A near-field focusing circularly polarized radial line slot array antenna, comprising a dielectric substrate, a coaxial feed connector, a short-circuit probe, and a metal substrate, characterized in that, The dielectric substrate is a single-sided copper-clad laminate, with a slow-wave material filling the space between the dielectric substrate and the metal substrate. A circular annular slot is etched in the central region of the copper-clad layer of the dielectric substrate, a spiral slot is etched in the outer region of the copper-clad layer, and n pairs of rectangular slots are spirally arranged on the copper-clad layer. The value of n is determined by the antenna focusing position and the antenna aperture size. The antenna is fed from the center of the metal substrate through a coaxial feed connector. The short-circuit probes are located around the circular annular slots and are rotationally symmetrical about the circular annular slots. The number of short-circuit probes is m, and the value of m is determined by the dimensions of the coaxial feed connector and the circular annular slots. The design method for the near-field focused circularly polarized radial slot array antenna includes: extracting the port transmission coefficient and the radiation phase of the main polarization component from the equivalent analysis model of the circularly polarized radiating element; and establishing the correspondence between the port transmission coefficient, the radiation phase of the main polarization component, the transmission phase, and the slot size and position based on the amplitude and phase distribution of the antenna. The steps include the following: Step 1: Determine the aperture field amplitude and phase distribution of the near-field focusing radial line slot array antenna: The aperture field amplitude distribution of the antenna is determined based on its radiation characteristics, and the size and position range of the slot pair are determined based on the aperture field amplitude distribution. The aperture field phase distribution of the antenna is determined based on its focusing characteristics. The phase includes the sum of two sets of phases: the radiation phase of the main polarization component determined by the slot length and the transmission phase determined by the radial position. The compensation phase and corresponding movement distance of the rectangular slot pair are determined based on the phase distribution. Step 2, extract the port transmission coefficient and radiation phase of the main polarization component from the equivalent analysis model of the radiating element: establish a periodic boundary equivalent analysis model consisting of slot pairs, dielectric plate, air layer and metal base plate, correct the size of the slot in the equivalent analysis model according to the range of slot size values ​​determined in Step 1, simulate the equivalent analysis model and extract the port transmission coefficient and radiation phase of the main polarization component. Step 3: Establish the correspondence between the port transmission coefficient, the radiation phase and transmission phase of the main polarization component and the slot size and position based on the aperture field amplitude and phase distribution of the antenna. Correct the radial position and size of the rectangular slot pair according to this correspondence to achieve near-field focusing. The correspondence between the rectangular slot pairs corresponds one-to-one with the focusing characteristics of the antenna. The radial position of the modified rectangular slit pair is achieved by the following formula: ； in, This represents the uncorrected distance between radially adjacent gaps a and b. This represents the corrected distance between gaps a and b. , The waveguide phase constants representing the positions of slits b and a before correction. , This represents the radius of the original positions of gaps b and a. Indicates the preset focus position. π represents the waveguide wavelength, and π represents pi.

2. The near-field focusing circularly polarized radial line slot array antenna according to claim 1, characterized in that, The slow-wave material can be any one of the following: low-loss foam, air layer / dielectric layer hybrid structure, or dielectric / metal hybrid periodic structure.

3. The near-field focusing circularly polarized radial line slot array antenna according to claim 1, characterized in that, The annular gap is located around the inner conductor of the coaxial feed connector and is circularly symmetrical about the inner conductor of the coaxial feed connector.

4. A near-field focusing circularly polarized radial line slot array antenna according to claim 1, characterized in that, The spiral-shaped gap is located on the periphery of the rectangular gap pair and is spiral-shaped about the origin of the copper cladding layer.

5. A near-field focusing circularly polarized radial line slot array antenna according to claim 1, characterized in that, The rectangular slot pair consists of two long rectangular slots that are perpendicular in direction, have the same radial angle, and are separated by a quarter of the waveguide wavelength. Each pair of rectangular slots constitutes a circularly polarized radiation unit.

6. A near-field focusing circularly polarized radial line slot array antenna according to claim 1, characterized in that, The direction of the spiral of the distribution trajectory of the rectangular slot pairs and the orientation of the two rectangular slots in each pair determine the circular polarization direction of the antenna. When the spiral of the distribution trajectory is arranged counterclockwise, the antenna radiates a left-hand circularly polarized wave; conversely, when it is arranged clockwise, the antenna radiates a right-hand circularly polarized wave.

7. A near-field focusing circularly polarized radial line slot array antenna according to claim 1, characterized in that, The outer conductor of the coaxial feed connector is electrically connected to the metal base plate, and the inner conductor passes through the slow wave material and is electrically connected to the copper cladding layer of the dielectric substrate.

8. A near-field focusing circularly polarized radial line slot array antenna according to claim 1, characterized in that, The m short-circuit probes are spaced 2π / m apart from each other, and the two ends of each short-circuit probe are electrically connected to the copper cladding layer of the dielectric substrate and the metal base plate, respectively.

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