Metasurface circularly polarized antenna

Abstract

The invention discloses a metasurface circularly polarized antenna, which belongs to the technical field of wireless communication, and comprises a metasurface, the metasurface comprises a plurality of first metasurface units and a plurality of second metasurface units which are arranged in an array, and the first metasurface units are located on the peripheries of the second metasurface units; the second metasurface unit is of a symmetrical structure formed by cutting the first metasurface unit; the dielectric substrate comprises an upper-layer dielectric substrate and a lower-layer dielectric substrate; the driving patch is positioned between the upper-layer dielectric substrate and the lower-layer dielectric substrate; the metal bottom plate is arranged on the lower surface of the lower-layer dielectric substrate; the microstrip feed structure is in non-contact coupling with the driving patch through the coupling gap; through unit array optimization, a phase difference is generated in an orthogonal radiation mode, and circular polarization radiation is realized. A 50-ohm microstrip line is adopted for feeding, and non-contact coupling excitation is carried out through a coupling gap and a driving patch; by means of collaborative design, 31.5% of impedance bandwidth and 20.4% of axial ratio bandwidth are achieved, and the full coverage of the WBAN5.15-5.825 GHz frequency band is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wireless communication technology, and particularly relates to a metasurface circularly polarized antenna. BACKGROUND

[0002] With the rapid development of wireless body area network (WBAN), it puts forward strict requirements on the performance of wearable antennas. The WBAN system usually works in the frequency band of 5.15-5.825 GHz, and needs to support high-speed data transmission of up to 10 Gb / s, so the antenna is required to have wide bandwidth, high gain and circular polarization characteristics. At the same time, the wearable antenna needs to be used in close contact with the human body, and needs to meet the flexible, light and comfortable wearing requirements, and needs to resist the interference of human tissues on the performance of the antenna.

[0003] Although the traditional microstrip antenna can realize basic circular polarization radiation, the impedance bandwidth is usually less than 10%, and the axial ratio bandwidth is insufficient, which is difficult to cover the whole frequency band of WBAN. Due to the limitation of structural design, there are problems of low axial ratio bandwidth, insufficient gain or unbeneficial feed structure for human body conformal, which cannot meet the requirements of wideband transmission and stable circular polarization, and seriously restricts the application effect of WBAN system in health monitoring, motion tracking and other scenes. SUMMARY

[0004] In order to solve the problems of the prior art, the present application provides a metasurface circularly polarized antenna, comprising: A metasurface, the metasurface comprises a plurality of first metasurface units and a plurality of second metasurface units arranged in an array, the first metasurface units are located at the outer periphery of the second metasurface units, and the second metasurface units are symmetric structures cut from the first metasurface units; A dielectric substrate, the dielectric substrate comprises an upper dielectric substrate and a lower dielectric substrate; A driven patch, the driven patch is located between the upper dielectric substrate and the lower dielectric substrate; A metal floor, the metal floor is arranged on the lower surface of the lower dielectric substrate; A microstrip feed structure, the microstrip feed structure is coupled to the driven patch through a coupling gap to excite the driven patch.

[0005] Further, the first metasurface units are divided into 4 groups and symmetrically arranged at the outer periphery of the second metasurface units; The plurality of second metasurface units are symmetrically arranged at the center of the metasurface; The first metasurface units are rectangular structures, and the second metasurface units are rectangular structures cut at least one group of diagonals; The first super surface unit and the second super surface unit form an N*N arranged array, and the four corners of the N*N array remove the corresponding first super surface unit. The first super surface unit is symmetrically arranged. The cutting diagonal parts of the first super surface units are uniformly oriented.

[0006] Further, in the super surface, the distance g between adjacent super surface units is 0.5mm, the width p of the first super surface unit is 13mm, and the projected cutting width C1 of the cutting part of the second super surface unit is 3mm.

[0007] Further, the driving patch is provided with an I-shaped coupling groove, the I-shaped coupling groove is located at the center of the super surface, the width of the end of the I-shaped coupling groove is greater than the projected width of the cutting part of the first super surface unit, the width of the middle of the I-shaped coupling groove is adapted to the first distance between the two second super surface units, and the length of the I-shaped groove is greater than the second distance between the two second super surface units.

[0008] Further, the length of the I-shaped coupling groove is 11-15mm.

[0009] Further, the driving patch is square, and the width is 16-20mm (preferably 18mm).

[0010] Further, the upper layer dielectric substrate and the lower layer dielectric substrate are both made of felt material, the relative dielectric constant εr of the felt material is 1.2, and the loss tangent tanδ is 0.02.

[0011] Further, the upper layer dielectric substrate and the lower layer dielectric substrate have a filling gap therebetween, and the height of the filling gap is 2-4mm.

[0012] Further, the metal floor is made of nylon conductive cloth material.

[0013] Further, the microstrip feed structure is a 50-ohm microstrip line.

[0014] The beneficial effects of the present application are: By the synergistic design of the super surface and the I-shaped slot driven patch, 31.5% impedance bandwidth and 20.4% axial ratio bandwidth are achieved, which can completely cover the working frequency band of 5.15-5.825GHz of the WBAN system, meet the demand of high-speed data transmission, and break through the limitation of narrow bandwidth of the traditional microstrip antenna; the maximum gain of the right-handed circular polarization at the core frequency of 5.5GHz reaches 8.9dB, which is much higher than the similar flexible antennas, and the circular polarization performance is stable, which can prolong the signal transmission distance and reduce the multipath interference, and guarantee the reliability of data transmission; the felt is used as the double-layer dielectric substrate, and the nylon conductive cloth is used as the radiation and grounding material, so that the full fabric structure is realized, the overall thickness is less than or equal to 2mm, the flexibility and skin-friendliness are excellent, and the problem of wearing discomfort of the traditional rigid substrate is solved; the complete metal floor on the lower surface of the lower dielectric substrate can effectively isolate the human body interference, and even when the distance between the antenna and the human body changes within 0-6mm, the performance remains stable, and the impedance mismatch problem of the traditional antenna close to the human body is avoided. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0016] Figure 1 is the cross-sectional structure schematic diagram of the super surface circularly polarized antenna provided by the present application; Figure 2 is the wearing structure schematic diagram of the super surface circularly polarized antenna provided by the present application; Figure 3 is the improved structure schematic diagram of the super surface circularly polarized antenna provided by the present application; Figure 4 is the performance parameter schematic diagram of the evolution process of the super surface circularly polarized antenna provided by the present application; Figure 5 is the schematic diagram of the influence of different parameters on the resonant frequency of the antenna provided by the present application; Figure 6 is the schematic diagram of the influence of different C1 on the performance of the antenna provided by the present application; Figure 7 is the schematic diagram of the influence of different Ls on the performance of the antenna provided by the present application; Figure 8 is the schematic diagram of the influence of different d on the performance of the antenna provided by the present application; Figure 9 is the schematic diagram of the circularly polarized direction of the antenna provided by the present application; The figure mark: 1 is a super surface, 2 is an upper dielectric substrate, 3 is a driven patch, 4 is a lower dielectric substrate, and 5 is a metal floor. DETAILED DESCRIPTION

[0017] In order to make the objectives, technical solutions and advantages of the present application clearer, the embodiments of the present application will be further described in detail below with reference to the drawings.

[0018] Reference is made to Figures 1 to 9 An ultra-surface circularly polarized antenna comprises: An ultra-surface 1, which comprises a plurality of first ultra-surface units and a plurality of second ultra-surface units arranged in an array, the first ultra-surface units being located at the periphery of the second ultra-surface units, and the second ultra-surface units being symmetric structures cut from the first ultra-surface units; A dielectric substrate, which comprises an upper dielectric substrate 2 and a lower dielectric substrate 4; The upper dielectric substrate and the lower dielectric substrate are arranged in parallel with a spacing therebetween; The upper dielectric substrate and the lower dielectric substrate have a filling gap therebetween, the height of the filling gap being 2-4 mm (preferably 3 mm); a fabric material is filled between the upper dielectric substrate and the lower dielectric substrate to achieve indirect connection between the upper dielectric substrate and the lower dielectric substrate; wherein the dielectric substrate uses aramid paper honeycomb core as the material of the interlayer The upper dielectric substrate and the lower dielectric substrate are both made of felt material, the relative dielectric constant of the felt material being εr=1.2, and the loss tangent being tanδ=0.02.

[0019] The ultra-surface is connected to the upper surface of the upper dielectric substrate; the ultra-surface generates a phase difference by optimizing the structure of the unit array to guide the orthogonal radiation mode, so that the antenna realizes circularly polarized radiation; A driven patch 3, which is located between the upper dielectric substrate and the lower dielectric substrate; The driven patch 3 is a rectangular structure with an I-shaped slot, which is arranged on the lower surface of the upper dielectric substrate; the driven patch is square-shaped with a width of 16-20 mm (preferably 18 mm); the length of the I-shaped coupling slot is 11-15 mm; A metal floor 5, which is arranged on the lower surface of the lower dielectric substrate; for isolating human body interference and suppressing backward radiation; A microstrip feed structure, which is non-contact coupled with the driven patch through a coupling gap to achieve excitation of the driven patch.

[0020] It should be noted that the working principle of the antenna unit is that the metal ground plane separates the 50-ohm microstrip feed line (microstrip feed structure) and the antenna radiation part, the electrical signal is input from the 50-ohm microstrip feed line, and the rectangular driven patch is excited through the coupling gap, so as to realize the electromagnetic wave radiation characteristics of the antenna; the full-metal reflecting surface is printed on the lower surface of the flexible structure of the dielectric substrate, the suppression of the backward radiation of the antenna unit is realized, and thus the back lobe of the antenna is effectively reduced.

[0021] Specifically, the length of the rectangular driven patch is W , the width is L , is the relative effective dielectric constant of the medium, is the equivalent dielectric constant of the medium, is the extension of the patch (i.e. a numerical calculation factor introduced considering the influence of the dielectric substrate), h 1 is the thickness of the single-layer dielectric substrate, h 2 is the thickness of the single-layer aramid paper honeycomb core, W p is the width of the 50-ohm microstrip feed line, C is the speed of light, f r is the center working frequency point of the antenna, which approximately satisfies the relationship: ; ; ; ; The working bandwidth of the antenna unit BW is inversely proportional to the equivalent dielectric constant of the medium , that is ； Since the equivalent dielectric constant of the aramid paper honeycomb core layer is close to 1, the equivalent dielectric constant of the mixed medium composed of the top dielectric substrate satisfies: ; In the formula, h 1 is the thickness of the top dielectric substrate, h 2 is the thickness of the aramid paper honeycomb core, so the mixed equivalent dielectric constant is effectively reduced compared with the equivalent dielectric constant of the top dielectric substrate, so that the working bandwidth of the antenna unit is improved.

[0022] It is worth mentioning that, from the design principle, the antenna unit adopts the structure of rectangular driven patch, coupled slot and 50 ohm microstrip feed line combination, the whole is isolated by the metal ground plane, realizes high efficient excitation and good matching, at the same time, suppresses backward radiation, improves directivity and axial ratio performance.

[0023] The rectangular driven patch is used as the main radiation structure, and its working mechanism is similar to an open resonant cavity. When the effective length of the patch is approximately half of the wavelength of the working frequency, resonance occurs, and strong radiation is generated: ; The equivalent extension introduced due to the edge field expansion is calculated as: ; The equivalent permittivity of the patch is: ; In order to realize circular polarization, a metasurface structure with rotational symmetry disturbance is loaded above the patch to guide two orthogonal modes to produce a phase difference and realize right-handed circularly polarized radiation.

[0024] The coupled slot is used to realize the non-contact excitation of the microstrip feed line to the patch. Its principle is that the microstrip feed line forms a strong electric field above the ground plane, and the capacitive coupling at the slot excites the patch resonance, which is equivalent to a capacitive coupling structure. The equivalent capacitance between the slots is: ; The width and length of the coupled slot are The vertical distance from the ground plane to the patch is The free space permittivity is

[0025] By adjusting the size of the slot and the position of the feed line, the coupling strength can be adjusted to optimize the input impedance matching and polarization performance.

[0026] The antenna uses a standard 50 ohm microstrip line as the feed structure to ensure impedance matching with the radio frequency system. The characteristic impedance of the microstrip line is closely related to its width , substrate thickness and permittivity The design formula is as follows: When : ; When : ;​​​ Since the felt material has a low and stable dielectric constant, in order to maintain a 50-ohm impedance, the width of the feed line needs to be determined by simulation iteration .

[0027] The operating bandwidth of the antenna is inversely proportional to the equivalent dielectric constant of the medium The aramid paper honeycomb core is used as the sandwich material, and its equivalent dielectric constant is close to 1. The composite medium is composed of the top layer of flexible substrate, and the mixed dielectric constant is as follows: ; Wherein: 、 : the dielectric constant and thickness of the top layer of flexible medium 、 : the equivalent dielectric constant and thickness of the honeycomb core layer

[0028] The lower mixed dielectric constant helps to widen the impedance bandwidth of the antenna and improve the performance.

[0029] Referring to Figure 3 The parameter table of the b antenna structure is as follows:

[0030] Based on the wearable antenna working around the human body, the antenna is placed in the three-layer model as shown in Figure 2 The thickness of each model is 2mm, 8mm and 20mm respectively. The size of the human tissue model needs to be adjusted according to the size of the antenna, because the human model is too large and needs to consume a lot of simulation time, and too small cannot accurately simulate the influence of human loading. Generally speaking, the distance between the edge of the human model and the edge of the antenna needs to be greater than one-quarter wavelength, so that the size of the model can be eliminated. The -10dB reflection coefficient bandwidth of the antenna designed in this application can cover the 4.58-6.67GHz frequency band, and the axial ratio bandwidth is 4.93-6.05GHz. The fabric material with a thickness of d=3mm is filled between the antenna and the human model to simulate the clothing in the real wearing scene.

[0031] As shown in Figure 3 , it is the evolution process of the antenna. Antenna 1 is a laminated antenna of a parasitic array, and the driving patch is processed with a slot. Antenna 2 places an improved metasurface above the patch antenna to widen the impedance bandwidth and axial ratio bandwidth of the antenna. The metasurface structure is improved from a 4x4 rectangular patch unit, and the units in the four corners of antenna 1 are removed. The purpose is to adjust the high-order mode in the passband to eliminate the gain zero point, and the rectangular slot is improved to an I-shaped slot, and the diagonals of the four units in the center of the metasurface are cut.

[0032] As Figure 4 shown in FIG. 8, by comparing the performance parameters of antenna 1 and antenna 2, it can be seen that the axial ratio bandwidth and the impedance bandwidth have been greatly improved.

[0033] By Figure 5 the S11 images corresponding to different parameters, it can be observed that the initial resonant frequency of the antenna is determined by the width p of the metasurface unit and the spacing g between the units. As the width p decreases or the spacing g increases, the resonant frequency of the antenna will shift towards high frequency.

[0034] The width wp of the microstrip patch antenna also determines the resonant frequency of the antenna, which has the same effect on the resonant frequency of the antenna as the width p of the metasurface unit. After simulation optimization, the width p of the metasurface unit, the spacing g, and the width wp of the microstrip patch antenna are determined as 13 mm, 0.5 mm, and 18 mm, respectively.

[0035] From Figure 6 it can be seen that c1 has little effect on the impedance bandwidth of the antenna, but the two axial ratio minima will move accordingly, so c1 has a greater impact on the axial ratio performance of the antenna, and the effect is best at 3 mm.

[0036] Figure 7 The effect of Lson the performance of the antenna is given. As can be seen from the figure, as Lsincreases, the impedance bandwidth increases continuously. However, as Lsincreases, the axial ratio performance gradually deteriorates. Therefore, in order to balance the impedance bandwidth and the axial ratio bandwidth, selecting ls=13mm can obtain the optimal performance.

[0037] Due to the movement of the human body, the distance between the antenna and the human body will change. Therefore, the performance of the antenna under different d (the distance between the antenna and the human body model is d) is studied as shown in Figure 8 . As can be seen from the figure, the antenna has stable impedance performance and axial ratio performance under different d. This is mainly because the proposed antenna has a complete floor, reducing the influence of the human body model on the performance of the antenna.

[0038] Figure 9 The circular polarization pattern of the antenna at a frequency of 5.5Ghz is given, and the right-handed circular polarization gain is much larger than the left-handed circular polarization gain. The maximum gain of the right-handed circular polarization is 8.9dB, achieving good cross-polarization performance.

[0039] The following table shows the performance of different circularly polarized antennas in the prior art.

[0040]

[0041] Document [1], Jiang Z, Cui Z, Yue T, et al. Compact, efficient, and fully flexible circularly polarized antenna based on silver nanowires for wireless body area networks[J]. IEEE Transactions on Biomedical Circuits and Systems, 2017, 11(4):920-932. Flexible circularly polarized radiation is achieved, but the axial ratio bandwidth is low. Document [2], Moro R, Agneny S, Roger H, et al. Circularly polarized wearable antenna based on substrate integrated waveguide technology[J]. IET Microwaves, Antennas & Propagation, 2018, 12(1):127-131. It uses probe feeding method, which will produce a sense of strangeness in the wearing environment, which is not conducive to conforming to the human body. Document [3], Zhu H, Wu B, Zhang Y, et al. Low-profile and low specific absorption rate circularly polarized wearable antenna based on highly conductive graphene film[J]. IEEE Antennas and Wireless Propagation Letters, 2020, 19(12):2354-2358. Compared with the present application, the antenna of the present application has the characteristics of wide band and high gain, document [4], Iqbal A, Smida A, Alazemi AJ, et al. Wideband circularly polarized multiple-input multiple-output antenna for high-data-rate wearable bio-telemetry devices[J]. IEEE Access, 2020, 8:17935-17944. It has good wideband characteristics. However, it uses a rigid dielectric substrate, which will bring discomfort in actual application.

[0042] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A metasurface circularly polarized antenna, characterized in that, The application relates to a metasurface, a medium substrate, a driving patch, a metal floor and a microstrip feed structure. The metasurface comprises a plurality of first metasurface units and a plurality of second metasurface units arranged in an array, the first metasurface units are located at the periphery of the second metasurface units, and the second metasurface units are symmetric structures cut by the first metasurface units. The medium substrate comprises an upper medium substrate and a lower medium substrate. The driving patch is located between the upper medium substrate and the lower medium substrate. The metal floor is arranged on the lower surface of the lower medium substrate. The microstrip feed structure is coupled with the driving patch through a coupling gap to excite the driving patch.

2. The metasurface circularly polarized antenna according to claim 1, wherein, The first metasurface units are divided into four groups and symmetrically arranged at the periphery of the second metasurface units. The second metasurface units are symmetrically arranged at the center of the metasurface. The first metasurface units are rectangular structures, and the second metasurface units are rectangular structures cut by at least one group of diagonals. The first metasurface units and the second metasurface units form an N*N array, and the four corners of the N*N array are removed. The first metasurface units are symmetrically arranged. The cutting positions of the first metasurface units are consistent.

3. The metasurface circularly polarized antenna according to claim 2, wherein, In the metasurface, the distance between adjacent metasurface units is g=0.5mm, the width of the first metasurface unit is p=13mm, and the projection cutting width of the cutting position of the second metasurface unit is C1=3mm.

4. The metasurface circularly polarized antenna according to claim 2, wherein, An I-shaped coupling groove is formed on the driving patch, the I-shaped coupling groove is located at the center of the metasurface, the width of the end of the I-shaped coupling groove is greater than the projection width of the cutting position of the first metasurface unit, the width of the middle of the I-shaped coupling groove is adapted to the first distance between two second metasurface units, and the length of the I-shaped groove is greater than the second distance between two second metasurface units.

5. The metasurface circularly polarized antenna according to claim 4, wherein, The length of the I-shaped coupling groove is 11-15mm.

6. The metasurface circularly polarized antenna of claim 1, wherein, The driving patch is square-shaped, and the width is 16-20mm.

7. The metasurface circularly polarized antenna of claim 1, wherein, The upper medium substrate and the lower medium substrate are both made of felt material, the relative dielectric constant of the felt material is epsilon r=1.2, and the loss tangent is tan delta=0.

02.

8. The metasurface circularly polarized antenna of claim 1, wherein, The upper medium substrate and the lower medium substrate have a filling gap, and the height of the filling gap is 2-4mm.

9. The metasurface circularly polarized antenna of claim 1, wherein, The metal floor is made of nylon conductive cloth material.

10. The metasurface circularly polarized antenna of claim 1, wherein, The microstrip feed structure is a 50-ohm microstrip line.

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