Metasurface circularly polarized antenna

Abstract

The application discloses a kind of super surface circularly polarized antennas, belong to wireless communication technical field, including: super surface, super surface includes a plurality of first super surface units and a plurality of second super surface units arranged in array, first super surface unit is located in the periphery of second super surface unit, and second super surface unit is the symmetrical structure formed by cutting first super surface unit;Dielectric substrate, dielectric substrate includes upper layer dielectric substrate and lower layer dielectric substrate;Driving patch, driving patch is located between upper layer dielectric substrate and lower layer dielectric substrate;Metal floor, metal bottom plate is arranged on the lower surface of lower layer dielectric substrate;Microstrip feed structure, through coupling gap and driving patch non-contact coupling;By unit array optimization, phase difference is generated in orthogonal radiation mode, and circularly polarized radiation is realized.50 ohm microstrip line feeding is used, and non-contact coupling excitation is realized by coupling gap and driving patch;Synergistic design realizes 31.5% impedance bandwidth, 20.4% axial ratio bandwidth, and full coverage WBAN5.15-5.825GHz frequency band.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and more specifically to a metasurface circularly polarized antenna. Background Technology

[0002] With the rapid development of Wireless Body Area Networks (WBANs), stringent requirements have been placed on the performance of wearable antennas. WBAN systems typically operate in the 5.15–5.825 GHz frequency band and need to support high-speed data transmission rates up to 10 Gb / s. Therefore, antennas must possess wide bandwidth, high gain, and circular polarization characteristics. Simultaneously, wearable antennas must conform to the human body, meeting the requirements of flexibility, lightweight, and comfort, and must resist interference from human tissue on antenna performance.

[0003] While traditional microstrip antennas can achieve basic circular polarization radiation, their impedance bandwidth is usually less than 10% and their axial ratio bandwidth is insufficient, making it difficult to cover the entire WBAN frequency band. Furthermore, due to structural design limitations, they suffer from low axial ratio bandwidth, insufficient gain, or feeding structures that are not conformal to the human body. They cannot simultaneously meet the requirements of broadband transmission and stable circular polarization, which severely restricts the application effect of WBAN systems in scenarios such as health monitoring and motion tracking. Summary of the Invention

[0004] To address the problems of existing technologies, this invention provides a metasurface circularly polarized antenna, comprising:

[0005] A metasurface, comprising an array of a plurality of first metasurface units and a plurality of second metasurface units, wherein the first metasurface units are located on the outer periphery of the second metasurface units, and the second metasurface units are symmetrical structures formed by cutting the first metasurface units;

[0006] A dielectric substrate, wherein the dielectric substrate includes an upper dielectric substrate and a lower dielectric substrate;

[0007] A driving patch, wherein the driving patch is located between the upper dielectric substrate and the lower dielectric substrate;

[0008] A metal floor, wherein the metal base plate is disposed on the lower surface of the lower dielectric substrate;

[0009] The microstrip feeding structure achieves excitation of the driving patch through non-contact coupling with the driving patch via a coupling gap.

[0010] Furthermore, the first metasurface unit is divided into 4 groups and symmetrically arranged on the outer periphery of the second metasurface unit;

[0011] Several second metasurface units are arranged symmetrically at the center of the metasurface;

[0012] The first metasurface unit is a rectangular structure, and the second metasurface unit is formed by cutting at least one set of diagonals from a rectangular structure;

[0013] The first metasurface unit and the second metasurface unit form an N*N array, and the corresponding first metasurface unit is removed from the four corners of the N*N array;

[0014] The first metasurface units are symmetrically arranged;

[0015] The diagonal portions of several of the first metasurface units are all oriented in the same direction.

[0016] Furthermore, in the metasurface, the spacing g between adjacent metasurface units is 0.5 mm, the width p of the first metasurface unit is 13 mm, and the projected cutting width C1 of the cutting portion of the second metasurface unit is 3 mm.

[0017] Furthermore, the driving patch has an I-shaped coupling groove located at the center of the metasurface. The width of the end of the I-shaped coupling groove is greater than the projected width of the cut portion of the first metasurface unit. The width of the middle part of the I-shaped coupling groove is adapted to the first distance between two diagonally opposite second metasurface units. The length of the I-shaped groove is greater than the second distance between two diagonally opposite second metasurface units.

[0018] Furthermore, the length of the I-shaped coupling groove is 11-15 mm.

[0019] Furthermore, the driving patch is square and has a width of 16-20mm (preferably 18mm).

[0020] Furthermore, both the upper dielectric substrate and the lower dielectric substrate are made of felt material, and the relative permittivity of the felt material is εr=1.2 and the loss tangent is tanδ=0.02.

[0021] Furthermore, there is a filling gap between the upper dielectric substrate and the lower dielectric substrate, and the height of the filling gap is 2-4 mm.

[0022] Furthermore, the metal floor is made of nylon conductive cloth material.

[0023] Furthermore, the microstrip feeding structure is a 50-ohm microstrip line.

[0024] The beneficial effects of this invention are:

[0025] Through the synergistic design of metasurface and I-groove driven patch, an impedance bandwidth of 31.5% and an axial ratio bandwidth of 20.4% are achieved, fully covering the 5.15–5.825 GHz operating frequency band of the WBAN system, meeting the requirements of high-speed data transmission and breaking through the narrow bandwidth limitation of traditional microstrip antennas. At the core frequency of 5.5 GHz, the maximum gain of right-hand circular polarization reaches 8.9 dB, far exceeding that of similar flexible antennas, and the circular polarization performance is stable, which can extend the signal transmission distance and reduce multipath interference, ensuring the reliability of data transmission. Felt is used as the double-layer dielectric substrate and nylon conductive cloth is used as the radiation and grounding material to achieve an all-fabric structure with an overall thickness of ≤2 mm. It has excellent flexibility and skin-friendliness, solving the problem of discomfort when wearing traditional rigid substrates. The complete metal ground plane on the lower surface of the dielectric substrate can effectively isolate human body interference. Even if the distance between the antenna and the human body varies within 0–6 mm, the performance remains stable, avoiding the impedance mismatch problem of traditional antennas when close to the human body. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the cross-sectional structure of the metasurface circularly polarized antenna provided by the present invention;

[0028] Figure 2 This is a schematic diagram of the wearable structure of the metasurface circularly polarized antenna provided by the present invention;

[0029] Figure 3 This is a schematic diagram of the improved metasurface circularly polarized antenna structure provided by the present invention;

[0030] Figure 4 This is a schematic diagram of the performance parameters of the metasurface circularly polarized antenna evolution process provided by the present invention;

[0031] Figure 5 This is a schematic diagram illustrating the influence of different parameters provided by this invention on the antenna resonant frequency;

[0032] Figure 6 This is a schematic diagram illustrating the impact of different C1 values ​​on antenna performance provided by the present invention;

[0033] Figure 7 This is a schematic diagram illustrating the impact of different Ls on antenna performance provided by the present invention;

[0034] Figure 8 This is a schematic diagram illustrating the effect of different values ​​of d on antenna performance provided by the present invention;

[0035] Figure 9 This is a schematic diagram of the circular polarization direction of the antenna provided by the present invention;

[0036] Reference numerals: 1 is metasurface, 2 is upper dielectric substrate, 3 is driving patch, 4 is lower dielectric substrate, and 5 is metal ground plane. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0038] See Figures 1 to 9 A metasurface circularly polarized antenna, comprising:

[0039] Metasurface 1, the metasurface includes a plurality of first metasurface units and a plurality of second metasurface units arranged in an array, the first metasurface units are located on the outer periphery of the second metasurface units, and the second metasurface units are symmetrical structures formed by cutting the first metasurface units;

[0040] A dielectric substrate, comprising an upper dielectric substrate 2 and a lower dielectric substrate 4;

[0041] The upper dielectric substrate and the lower dielectric substrate are arranged parallel to each other and with a gap between them;

[0042] A filling gap is provided between the upper dielectric substrate and the lower dielectric substrate, the height of which is 2-4 mm (preferably 3 mm); a fabric material is filled between the upper dielectric substrate and the lower dielectric substrate to achieve an indirect connection between them; wherein, the dielectric substrate uses an aramid paper honeycomb core as the interlayer material.

[0043] Both the upper dielectric substrate and the lower dielectric substrate are made of felt material, and the relative permittivity of the felt material is εr=1.2 and the loss tangent is tanδ=0.02.

[0044] The metasurface is connected to the upper surface of the upper dielectric substrate; the metasurface guides the orthogonal radiation mode to generate a phase difference through structural optimization of the unit array, enabling the antenna to achieve circularly polarized radiation;

[0045] A driving patch 3 is located between the upper dielectric substrate and the lower dielectric substrate;

[0046] The driving patch 3 is a rectangular structure with an I-shaped groove, and is disposed on the lower surface of the upper dielectric substrate; the driving patch is square, with a width of 16-20mm (preferably 18mm); the length of the I-shaped coupling groove is 11-15mm;

[0047] Metal floor 5, the metal base plate is disposed on the lower surface of the lower dielectric substrate; used to isolate human interference and suppress back radiation;

[0048] The microstrip feeding structure achieves excitation of the driving patch through non-contact coupling with the driving patch via a coupling gap.

[0049] It should be noted that the working principle of this antenna element is as follows: the metal ground plane separates the 50-ohm microstrip feed line (microstrip feeding structure) from the antenna radiating part. The electrical signal is input from the 50-ohm microstrip feed line and excites the rectangular driving patch through the coupling gap, thereby realizing the electromagnetic wave radiation characteristics of the antenna. The lower surface of the flexible dielectric substrate is printed with an all-metal reflective surface to suppress the back radiation of the antenna element, thereby effectively reducing the back lobe of the antenna.

[0050] Specifically, the length of the rectangular driver patch is W Width is L , The relative effective dielectric constant of the medium. The equivalent dielectric constant of the medium. This refers to the extension of the patch (i.e., a numerical calculation factor introduced to account for the influence of the dielectric substrate). h 1 represents the thickness of a single-layer dielectric substrate. h 2 represents the thickness of a single-layer aramid paper honeycomb core. W p The width of the 50-ohm microstrip feeder. C At the speed of light, f r Let the center operating frequency of the antenna be the given frequency, and the relationship approximately satisfies:

[0051] ;

[0052] ;

[0053] ;

[0054] ;

[0055] The operating bandwidth of the antenna element BW Equivalent dielectric constant of the medium They are inversely proportional, that is

[0056] ；

[0057] Since the equivalent dielectric constant of the aramid paper honeycomb core layer is close to 1, the equivalent dielectric constant of the hybrid dielectric formed by the top dielectric substrate satisfies:

[0058] ;

[0059] In the formula, h 1 represents the thickness of the top dielectric substrate. h 2 represents the thickness of the aramid paper honeycomb core. Therefore, its mixed equivalent dielectric constant is effectively reduced compared to the equivalent dielectric constant of the top dielectric substrate, thereby improving the operating bandwidth of the antenna unit.

[0060] It is worth noting that, based on the design principle, this antenna unit adopts a structure that combines a rectangular driving patch, a coupling slot, and a 50-ohm microstrip feed line. The entire structure isolates the feed line from the radiating element through a metal ground plane, achieving efficient excitation and good matching, while suppressing back radiation and improving directivity and axial ratio performance.

[0061] The rectangular driving patch serves as the primary radiating structure, and its working mechanism is similar to an open-circuit resonant cavity. When the effective length of the patch... When the wavelength is approximately half that of the operating frequency, resonance occurs, producing strong radiation.

[0062] ;

[0063] in This is the equivalent extension introduced by the extension of the edge electric field, which is calculated as follows:

[0064] ;

[0065] The equivalent dielectric constant of the patch is:

[0066] ;

[0067] To achieve circular polarization, a metasurface structure with rotational symmetry perturbation is loaded above the patch to guide the two orthogonal modes to generate a phase difference, thereby achieving right-hand circular polarization radiation.

[0068] Coupling slots are used to achieve non-contact excitation of the patch by the microstrip feed line. The principle is that the microstrip feed line generates a strong electric field above the ground plane, and the capacitive coupling generated at the slot excites the patch to resonate, equivalent to a capacitive coupling structure. The equivalent capacitance between the slots is:

[0069] ;

[0070] in:

[0071] These represent the width and length of the coupling gap, respectively.

[0072] This is the vertical distance from the ground plane to the patch.

[0073] It is the free space dielectric constant.

[0074] By adjusting the gap size and feeder position, the coupling strength can be controlled, and the input impedance matching and polarization performance can be optimized.

[0075] The antenna uses a standard 50-ohm microstrip line as its feed structure to ensure impedance matching with the RF system. The characteristic impedance of the microstrip line is related to its width. substrate thickness and dielectric constant Closely related, the design formula is as follows:

[0076] when :

[0077] ;

[0078] when :

[0079] ;

[0080] Because the felt material has a low and stable dielectric constant, the feed line width needs to be determined through simulation iterations to maintain a 50-ohm impedance. .

[0081] The operating bandwidth of the antenna and the equivalent dielectric constant of the medium Inversely proportional. Using aramid paper honeycomb core as the interlayer material, its equivalent dielectric constant is close to 1. Together with the top flexible substrate, it forms a composite dielectric with the following mixed dielectric constant:

[0082] ;

[0083] in:

[0084] , The dielectric constant and thickness of the top flexible dielectric layer;

[0085] , The equivalent dielectric constant and thickness of the honeycomb core layer.

[0086] A lower mixed dielectric constant helps to broaden the impedance bandwidth of the antenna and improve its performance.

[0087] See Figure 3 The parameter table for antenna structure b is as follows:

[0088]

[0089] Based on the fact that wearable antennas operate around the human body, the antenna is placed in a way that... Figure 2Simulations were performed using a three-layer model. The thicknesses of each model were 2mm, 8mm, and 20mm, respectively. The dimensions of the human tissue model needed to be adjusted according to the antenna size, as a large human model would require excessive simulation time, while a small model would fail to accurately simulate the effects of human loading. Generally, the distance between the edge of the human model and the edge of the antenna needs to be greater than a quarter wavelength to eliminate the influence of model size on antenna performance. The antenna designed in this application has a -10dB reflection coefficient bandwidth covering the 4.58–6.67GHz frequency band and an axial ratio bandwidth of 4.93–6.05GHz. A fabric material with a thickness of d=3mm was filled between the antenna and the human model to simulate clothing in a real-world wearing scenario.

[0090] like Figure 3 The diagram illustrates the evolution of the antenna. Antenna 1 is a stacked antenna with a parasitic array, featuring slotted drive patches. Antenna 2 places an improved metasurface on top of the patch antenna to broaden its impedance and axial ratio bandwidths. Its metasurface structure is an improvement on 4×4 rectangular patch elements. Elements at the four corners of antenna 1 are removed to adjust higher-order modes within the passband and eliminate gain nulls. The rectangular slots are modified into I-shaped slots, and the diagonals of the four central elements of the metasurface are chamfered.

[0091] like Figure 4 As shown, by comparing the performance parameters of antenna 1 and antenna 2, it can be seen that both the axial ratio bandwidth and impedance bandwidth have been greatly improved.

[0092] pass Figure 5 The S11 images for different parameters show that the initial resonant frequency of the antenna is determined by the width p of the metasurface elements and the spacing g between the elements. As the width p decreases or the spacing g increases, the resonant frequency of the antenna will shift towards higher frequencies.

[0093] The width wp of the microstrip patch antenna also determines the antenna's resonant frequency, having the same effect as the width p of the metasurface element on the antenna's resonant frequency. After simulation optimization, the width p, spacing g of the metasurface element, and the width wp of the microstrip patch antenna were determined to be 13mm, 0.5mm, and 18mm, respectively.

[0094] from Figure 6 As can be seen, c1 has almost no effect on the impedance bandwidth of the antenna, but the minimum values ​​of the two axial ratios will shift accordingly. This shows that c1 has a significant impact on the axial ratio performance of the antenna, and the effect is best at 3mm.

[0095] Figure 7The effect of Ls on antenna performance is shown in the figure. As can be seen from the figure, the impedance bandwidth increases continuously with increasing Ls. However, the axial ratio performance gradually deteriorates with increasing Ls. Therefore, to balance impedance bandwidth and axial ratio bandwidth, selecting ls = 13mm yields the optimal performance.

[0096] Due to human movement, the distance between the antenna and the human body changes. Therefore, the antenna performance under different distances d (where d is the distance between the antenna and the human body model) was studied. Figure 8 As shown in the figure, the antenna exhibits stable impedance and axial ratio performance under different d values. This is mainly because the proposed antenna has a complete ground plane, reducing the influence of the human body model on the antenna performance.

[0097] Figure 9 The circular polarization pattern of the antenna at a frequency of 5.5 GHz is presented. The gain of right-hand circular polarization is much greater than that of left-hand circular polarization. The maximum gain of right-hand circular polarization is 8.9 dB, which achieves good cross-polarization performance.

[0098] The table below illustrates the performance of different circularly polarized antennas in the prior art.

[0099]

[0100] Reference [1], Jiang Zhihong, Cui Zhe, Yue Tao, et al. Application of compact, efficient, fully flexible circularly polarized antenna based on silver nanowires in wireless body area networks [J]. IEEE Transactions on Biomedical Circuits and Systems, 2017, 11(4): 920-932. Flexible circularly polarized radiation was achieved, but the axial ratio bandwidth was low. Reference [2], Morrow R, Agnesens S, Roger H, et al. Circularly polarized cavity-backed wearable antenna based on substrate integrated waveguide technology [J]. Institution of Engineering and Technology Journal of Microwave, Antennas and Propagation, 2018, 12(1): 127-131. It adopts a probe feeding method, which will produce an abrupt feeling in the wearable environment and is not conducive to conformal with the human body. Reference [3], Zu Hao, Wu Bin, Zhang Yu, et al. Low-profile, low-absorption-rate circularly polarized wearable antenna based on highly conductive graphene film [J]. IEEE Antenna & Wireless Propagation Letters, 2020, 19(12): 2354-2358. Compared with this application, the antenna of this application has the characteristics of broadband and high gain. Reference [4], Iqbal A, Smida A, Alazemi AJ, etc. Broadband circularly polarized multiple-input multiple-output antenna for high data rate wearable bio-telemetry devices [J]. IEEE Access Journal, 2020, 8: 17935-17944. It has good broadband characteristics. However, it uses a rigid dielectric substrate, which will bring wearing discomfort in practical applications.

[0101] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A metasurface circularly polarized antenna, characterized in that, include: A metasurface, comprising an array of a plurality of first metasurface units and a plurality of second metasurface units, wherein the first metasurface units are located on the outer periphery of the second metasurface units, and the second metasurface units are symmetrical structures formed by cutting the first metasurface units; The first metasurface unit is divided into 4 groups and symmetrically arranged on the outer periphery of the second metasurface unit; A plurality of second metasurface units are symmetrically arranged at the center of the metasurface; the first metasurface unit is a rectangular structure, and the second metasurface unit is formed by cutting at least one set of diagonals from a rectangular structure. The first metasurface unit and the second metasurface unit form an N*N array, and the corresponding first metasurface unit is removed from the four corners of the N*N array; The first metasurface units are symmetrically arranged; The diagonally cut portions of several of the first metasurface units all face the same direction; In the metasurface, the spacing between adjacent metasurface units is g=0.5mm, the width of the first metasurface unit is p=13mm, and the projected cutting width C1 of the cutting portion of the second metasurface unit is 3mm. The driving patch has an I-shaped coupling groove, which is located at the center of the metasurface. The width of the end of the I-shaped coupling groove is greater than the projected width of the cut portion of the first metasurface unit. The width of the middle part of the I-shaped coupling groove is adapted to the first distance between two diagonally opposite second metasurface units. The length of the I-shaped groove is greater than the second distance between two diagonally opposite second metasurface units. A dielectric substrate, wherein the dielectric substrate includes an upper dielectric substrate and a lower dielectric substrate; A driving patch, wherein the driving patch is located between the upper dielectric substrate and the lower dielectric substrate; A metal floor, wherein the metal floor is disposed on the lower surface of the lower dielectric substrate; The microstrip feeding structure is non-contactly coupled to the driving patch through a coupling gap to excite the driving patch; There is a filling gap between the upper dielectric substrate and the lower dielectric substrate.

2. The metasurface circularly polarized antenna according to claim 1, characterized in that, The length of the I-shaped coupling groove is 11~15mm.

3. The metasurface circularly polarized antenna according to claim 1, characterized in that, The driving patch is square and has a width of 16~20mm.

4. The metasurface circularly polarized antenna according to claim 1, characterized in that, Both the upper dielectric substrate and the lower dielectric substrate are made of felt material, with a relative permittivity εr=1.2 and a loss tangent tanδ=0.

02.

5. The metasurface circularly polarized antenna according to claim 1, characterized in that, The height of the filling gap is 2~4mm.

6. The metasurface circularly polarized antenna according to claim 1, characterized in that, The metal floor is made of nylon conductive cloth material.

7. The metasurface circularly polarized antenna according to claim 1, characterized in that, The microstrip feed structure is a 50-ohm microstrip line.

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