Four-feed-source four-polarization holographic metasurface antenna based on position weighted impedance superposition

Abstract

The invention provides a four-feed-source four-polarization holographic metasurface antenna based on position weighted impedance superposition, which comprises a radiation array and four feed sources, and is characterized in that the radiation array comprises M * N radiation units which are periodically arranged and are provided with I-shaped gaps in an etching manner and are of a circular patch structure; the radius of the radiation unit is determined by the maximum equivalent scalar impedance obtained by performing weighted impedance superposition on tensor surface impedance distribution obtained when single polarized electromagnetic waves are generated by taking different feed sources as centers; the inclination angle of two transverse arms of the I-shaped gap relative to the X axis is the same as the propagation direction of electromagnetic waves corresponding to the maximum equivalent scalar impedance. According to the holographic metasurface antenna, the utilization efficiency of the radiation unit on the surface waves is effectively improved through the position weighted impedance superposition method, interference among different polarization components is reduced, the defect that the aperture efficiency is low due to the fact that a traditional impedance superposition method is adopted by the holographic metasurface antenna is overcome, and the aperture efficiency of the holographic metasurface antenna is improved by exciting the four feed sources respectively. And generation of four kinds of polarized electromagnetic waves is realized.

Description

Technical Field

[0001] The present invention belongs to the field of microwave technology, and relates to a holographic metasurface antenna, specifically to a four-feed four-polarization holographic metasurface antenna based on position-weighted impedance superposition, which can be used in technical fields such as space wireless communication and radar detection. Technical Background

[0002] Electromagnetic metasurfaces are composed of periodically arranged artificial electromagnetic structures with sub-wavelength dimensions. By controlling the structural parameters of the metasurface, flexible regulation of electromagnetic waves can be achieved. As a type of electromagnetic metasurface, holographic metasurfaces refer to the optical holographic principle. The distribution of the interference field is calculated based on the source field and the target field, and then the interference field is recorded in the form of impedance distribution through the holographic metasurface. When the holographic metasurface is excited by the source field, the reproduction of the target field can be realized. Polarization is one of the basic properties of electromagnetic waves. In a complex wireless communication channel, an antenna with multi-polarization characteristics can avoid polarization mismatch problems, thereby improving the efficiency of the transceiver antenna and providing a more stable and efficient communication connection in a complex signal environment.

[0003] For holographic metasurfaces, the impedance distributions corresponding to target beams with different polarization modes can be superimposed to generate beams with multiple polarization modes on the same radiation surface. When generating electromagnetic waves with different polarization modes, the existing multi-feed multi-polarization holographic metasurface antennas usually adopt the method of direct impedance superposition. For example, in the patent application with the application publication number CN117220030 A and the name "A dual-frequency dual-polarization multi-functional holographic structural metasurface antenna", a dual-frequency dual-polarization multi-functional holographic structural metasurface antenna is disclosed. The antenna includes a holographic impedance modulation surface and a low-profile surface wave emitter. The holographic impedance modulation surface includes a grounded dielectric substrate and a metal holographic pattern. By selecting the feeding ports, the generation of low-frequency - vertical polarization, low-frequency - horizontal polarization, high-frequency - vertical polarization, and high-frequency - horizontal polarization beams of the antenna can be realized. This invention can work independently in two frequency bands and has excellent beamforming ability and multi-polarization frequency scanning ability in their respective frequency bands. However, since this invention uses the direct impedance superposition method when calculating the impedance distribution of the holographic metasurface, the utilization rate of the surface waves generated by the feed source by the holographic metasurface is relatively low, and the generated beams are greatly interfered by the clutter components excited by other polarization beam components, thereby affecting the improvement of the antenna aperture efficiency. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art, and propose a four-feed four-polarization holographic metasurface antenna based on position-weighted impedance superposition, aiming to improve the aperture efficiency of the holographic metasurface antenna while generating electromagnetic waves with multiple polarization modes.

[0005] To achieve the above object, the technical solution adopted by the present invention includes a radiation array 1 and four feeders 2. The radiation array 1 includes M×N radiation units 11 arranged periodically, where M≥20 and N≥20. The radiation array 1 is divided into four regions in the XOY plane of the three-dimensional coordinate system, and the four feeders 2 are arranged at the central positions of the four regions. The radiation unit 11 adopts a circular patch structure etched with an "I"-shaped slot. The radius r of the m×n-th radiation unit mn is obtained by weighted superposition of the tensor surface impedance distributions corresponding to the single-polarized electromagnetic waves generated with different feeders as the centers to obtain the maximum equivalent scalar impedance determined, and the inclination angle of the two transverse arms of the "I"-shaped slot relative to the X-axis is the same as the propagation direction of the corresponding electromagnetic wave ; by exciting the four feeders respectively, electromagnetic waves of four polarizations corresponding to different feeders are realized.

[0006] As an optimization, the radiation array 1 further includes a dielectric substrate 12 and a metal floor 13 printed on its lower surface; the M×N radiation units 11 are printed on the upper surface of the dielectric substrate 12.

[0007] As an optimization, the radius r of the m×n-th radiation unit mn , and the calculation formula is:

[0008]

[0009] A = -3.8581×10 -9

[0010] B = -4.966×10 -6

[0011] C = -2.4353×10 -3

[0012] D = -0.54201

[0013] E = -44.933

[0014] where A, B, C, D, and E are constants related to the shape of the radiation unit respectively.

[0015] As an optimization, the constants A, B, C, D, and E related to the shape of the radiation unit are determined by function fitting of the relationship curve between the radius of the radiation unit and the corresponding maximum equivalent scalar impedance.

[0016] As an optimization, for the m×n-th radiation unit, the maximum equivalent scalar impedance at its position has the calculation formula:

[0017]

[0018] where \(j\) is the imaginary unit, and \(\eta\) 0 is the wave impedance in vacuum, are the impedance responses of the electric field in the X direction to the currents in the X and Y directions respectively, is the impedance response of the electric field in the Y direction to the current in the Y direction, and \(\theta\) mn is the propagation direction of the electromagnetic wave on the \(m\times n\)th radiation element, and \(\theta\) mn \(\in[-180^{\circ}, 180^{\circ}]\).

[0019] As an optimization, the impedance responses of the electric field in the X direction to the currents in the X and Y directions, and the impedance response of the electric field in the Y direction to the current in the Y direction and The calculation formulas are respectively:

[0020]

[0021] where \(P_{imn}\) is the radiation weight value of the \(m\times n\)th radiation element corresponding to the \(i\)th feed source, and are the impedance responses of the electric field in the X direction to the currents in the X and Y directions when a single-polarized electromagnetic wave is generated with the \(i\)th feed source as the center, is the impedance response of the electric field in the Y direction to the current in the Y direction when a single-polarized electromagnetic wave is generated with the \(i\)th feed source as the center, is the distance between the \(m\times n\)th radiation element and the \(i\)th feed source, \(x\) mn and \(y\) mn are the abscissa and ordinate of the \(m\times n\)th radiation element respectively, \(x\) i and \(y\) i are the abscissa and ordinate of the \(i\)th feed source respectively, and \(i\in[1,4]\).

[0022] As an optimization, the impedance responses of the electric field in the X direction to the currents in the X and Y directions, and the impedance response of the electric field in the Y direction to the current in the Y direction when a single-polarized electromagnetic wave is generated with the \(i\)th feed source as the center and The calculation formulas are respectively:

[0023]

[0024] where \(F\) and \(G\) are the average impedance and modulation depth of the holographic metasurface antenna respectively, \(\theta\) i and respectively represent the elevation angle and azimuth angle of the beam generated when the \(i\)th feed source is separately excited, \(k\) t is the wave vector when the electromagnetic wave propagates on the radiation element, \(k\) 0is the wave vector in free space.

[0025] As an optimization, the feeder 2 adopts a monopole antenna structure.

[0026] As an optimization, for the "I"-shaped slot, its geometric center coincides with the center of the circular patch.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] The present invention obtains the maximum equivalent scalar impedance of each radiation element by weighting and superimposing the tensor surface impedance distributions corresponding to the single-polarized electromagnetic waves generated by different feeders as the center, so that when generating a beam in the polarization mode corresponding to a feeder, the impedance components on the radiation elements closer to the feeder have higher weights, and the weights of the impedance components corresponding to the remaining feeders are reduced, effectively improving the utilization efficiency of the surface waves generated by the feeders by the radiation elements, and at the same time reducing the energy magnitude of the clutter components excited by other polarization beam components, effectively improving the aperture efficiency of the antenna. Description of the Drawings

[0029] Figure 1 is the overall structural schematic diagram of the present invention;

[0030] Figure 2 is the top view of the present invention;

[0031] Figure 3 is the structural schematic diagram of the radiation element of the present invention;

[0032] Figure 4 is the curve graph of the equivalent scalar impedance when the radius of the radiation element and the incident angle of the electromagnetic wave of the present invention change;

[0033] Figure 5 is the fitting relationship graph between the radius of the radiation element adopted in the present invention and the maximum value of the equivalent scalar impedance;

[0034] Figure 6 is the distribution graph of the radius and rotation angle of the radiation elements at different positions of the present invention;

[0035] Figure 7 is the two-dimensional direction graph of the four polarization beams generated by the present invention. Detailed Embodiments

[0036] The following further describes the present invention in conjunction with the drawings and specific embodiments.

[0037] Refer to Figure 1 and Figure 2, the present invention includes a radiation array 1 and four feeders 2. The radiation array 1 includes a dielectric substrate 12 and a metal floor 13 printed on its lower surface. The dielectric substrate 12 is made of F4B material with a relative dielectric constant of 3.5 and a thickness of 2 mm. The radiation array 1 is divided into four regions in the XOY plane of the three-dimensional coordinate system. The four feeders 2 adopt monopole antenna structures and are respectively arranged at the centers of each region to generate beams with four polarization modes: X polarization, Y polarization, left-handed circular polarization, and right-handed circular polarization. The radiation array 1 includes 51×51 periodically arranged radiation units 11 printed on the upper surface of the dielectric substrate 12. The radiation units 11 adopt circular patch structures etched with "I"-shaped slots. The radius r of the m×nth radiation unit mn is the maximum equivalent scalar impedance obtained by weighted superposition of the tensor surface impedance distributions corresponding to the single-polarization electromagnetic waves generated with different feeders as the centers determined, and the inclination angle of the two transverse arms of the "I"-shaped slot relative to the X-axis is the same as the corresponding electromagnetic wave propagation direction .

[0038] The structure of the radiation unit 11 is as shown in Figure 3 . It adopts a circular patch structure etched with an "I"-shaped slot, and the geometric center of the "I"-shaped slot coincides with the center of the circular patch. By weighted superposition of the tensor surface impedance distributions corresponding to the single-polarization electromagnetic waves generated with different feeders as the centers to obtain the maximum equivalent scalar impedance of each radiation unit, the radii of the 51×51 radiation units are determined. The minimum value is 1.05 mm and the maximum value is 1.45 mm. For the "I"-shaped slot, the width of each rectangular slot is 0.3 mm, and the distance between the two transverse arms is 0.9 mm.

[0039] Fitting the radiation unit radius and the maximum equivalent scalar impedance, the relationship between the maximum value of the maximum equivalent scalar impedance and the radiation unit radius after fitting is:

[0040]

[0041] A = -3.8581×10 -9

[0042] B = -4.966×10 -6

[0043] C = -2.4353×10 -3

[0044] D = -0.54201

[0045] E = -44.933

[0046] Among them, A, B, C, D, and E are constants related to the shape of the radiation element respectively.

[0047] The constants A, B, C, D, and E related to the shape of the radiation element are determined by function fitting of the relationship curve between the radius of the radiation element and the corresponding maximum equivalent scalar impedance. The specific method is as follows: First, simulate the equivalent scalar impedance of the radiation element when the radius varies from 1.05 mm to 1.45 mm and the incident angle of the electromagnetic wave varies from -180° to 180°, to obtain the initial data; then fit the data of the radiation element radius and the maximum equivalent scalar impedance obtained from the simulation, and finally, the functional relationship between the two can be obtained. When the maximum equivalent scalar impedance distribution of the holographic metasurface is determined according to the position-weighted impedance superposition method, the radiation element radius distribution of the holographic metasurface can be obtained according to the functional relationship between the maximum equivalent scalar impedance and the radius obtained by fitting. The simulation and fitting results are referred to Figure 4 and Figure 5 .

[0048] The maximum equivalent scalar impedance The calculation formula is:

[0049]

[0050] Among them, j is the imaginary unit, η 0 is the wave impedance in vacuum, are the impedance responses of the electric field in the X direction to the currents in the X and Y directions respectively, is the impedance response of the electric field in the Y direction to the current in the Y direction, θ mn is the incident direction of the electromagnetic wave on the m×nth radiation element, θ mn ∈[-180°, 180°]. When and are determined, the value of the maximum equivalent scalar impedance only depends on the incident direction θ mn of the electromagnetic wave, corresponding to the incident direction θ mn of the electromagnetic wave is the inclination angle of the two transverse arms of the "I"-shaped slot relative to the X-axis

[0051] The impedance responses of the electric field in the X direction to the currents in the X and Y directions, and the impedance response of the electric field in the Y direction to the current in the Y direction and The calculation formulas are respectively:

[0052]

[0053]

[0054] Among them, P i mn is the radiation weight value of the m×nth radiation unit corresponding to the ith feeder, and are the impedance responses of the electric field in the X direction to the currents in the X and Y directions respectively when generating a single-polarized electromagnetic wave centered on the ith feeder, is the impedance response of the electric field in the Y direction to the current in the Y direction when generating a single-polarized electromagnetic wave centered on the ith feeder, is the distance between the m×nth radiation unit and the ith feeder, x mn and y mn are the abscissa and ordinate of the m×nth radiation unit respectively, x i and y i are the abscissa and ordinate of the ith feeder respectively, i ∈ [1, 4].

[0055] The impedance responses of the electric field in the X direction to the currents in the X and Y directions, and the impedance response of the electric field in the Y direction to the current in the Y direction when generating a single-polarized electromagnetic wave centered on the ith feeder and The calculation formulas are respectively:

[0056]

[0057]

[0058] Among them, F and G are the average impedance and modulation depth of the holographic metasurface antenna respectively, β i 、θ i 、 are the phase of the interference field, the elevation angle, and the azimuth angle of the generated beam respectively when the ith feeder is separately excited, k t is the wave vector when the electromagnetic wave propagates on the radiation unit, k 0 is the wave vector in free space.

[0059] The working principle of the present invention is:

[0060] When the holographic metasurface is excited by the surface wave generated by a single feed, the target beam corresponding to the feed will be generated. Taking the surface waves generated by four feeds located at different positions as the source fields and the beams of X polarization, Y polarization, left-handed circular polarization, and right-handed circular polarization as the target fields, the different holographic metasurface tensor impedance distributions corresponding to the four-position feeds can be calculated. By superimposing the tensor impedance distributions obtained with a single feed as the center on the same aperture, the holographic metasurface can carry the impedance characteristics of all target beams. When the four feeds are excited separately, when the holographic metasurface is excited by the surface wave excitation impedance generated by different feeds and the impedance is superimposed, the generation of beams of four polarization modes corresponding to different feeds can be realized.

[0061] The holographic metasurface antenna generates multi-polarization beams through the impedance direct superposition method. Essentially, it linearly superimposes and maps the radiation fields of the target beams generated by multiple feeds respectively into the tensor surface impedance distribution under the same aperture, so that the radiation units of the metasurface simultaneously contain the impedance characteristics of all target beams, thereby realizing multi-polarization radiation on the same holographic metasurface. The leakage radiation energy on the holographic metasurface will gradually decrease as the distance from the feed increases. When the surface wave propagates to the edge of the holographic metasurface, its energy will decrease significantly. To effectively improve the energy utilization efficiency of the metasurface units at positions closer to the feed and reduce the energy of the clutter components excited by other polarization beam components, the target beam impedance component on the impedance unit closer to the feed that excites a single target polarization beam has a higher weight, while reducing the weights of the impedance of the other three polarization components, so as to increase the gain of the target beam without changing the aperture, and finally improve the aperture efficiency of the antenna.

[0062] The technical effects of the present invention will be further described in detail below in combination with simulation experiments.

[0063] 1. Simulation conditions and content

[0064] Simulation 1: Use the simulation software CST MICROWAVE STUDIO to simulate the equivalent scalar impedance when the radius of the radiation unit and the incident angle of the electromagnetic wave change in the embodiment of the present invention. The results are as Figure 4 shown;

[0065] Simulation 2: Fit the relationship curve between the maximum value of the equivalent scalar impedance of the radiation unit and the radius of the radiation unit in the embodiment of the present invention. The results are as Figure 5 shown;

[0066] Simulation 3: Simulate the radius size and rotation angle distribution of the holographic metasurface radiation unit in the embodiment of the present invention. The results are as Figure 6 shown;

[0067] Simulation 4: Simulate the two-dimensional radiation patterns of the four polarization modes of the holographic metasurface antenna according to the embodiments of the present invention at a working frequency of 15 GHz, where the pointing angles of the four beams are all 0°, and the results are as Figure 7 shown;

[0068] 2. Analysis of simulation results

[0069] Referring to Figure 4 , the curve of the equivalent scalar impedance is a family of ellipses. The length of the major axis of the ellipse represents the maximum value of the equivalent scalar impedance, and this maximum value increases with the increase of the radius of the radiation element. The direction of the major axis of the ellipse represents the incident angle of the electromagnetic wave corresponding to the maximum equivalent scalar. When the patch radius changes from 1.05 mm to 1.45 mm, the maximum value of the equivalent scalar impedance increases from 263.08 Ω to 336.00 Ω.

[0070] Referring to Figure 5 , the abscissa and ordinate of this figure are the radius of the radiation element and the maximum value of the equivalent scalar impedance respectively. The points marked with "*" in the figure are the initial values of the maximum equivalent scalar impedance obtained when the radius is changed. The solid line represents the curve after fitting the initial values. It can be seen that the maximum equivalent scalar impedance increases with the increase of the radius of the radiation element, and the larger the radius of the radiation element, the faster the maximum equivalent scalar impedance changes with the radius of the radiation element.

[0071] Referring to Figure 6 , the radius and rotation angle distribution of the radiation elements of the holographic metasurface are calculated by weighted superposition of the tensor impedance distributions corresponding to the electromagnetic waves of the four polarization modes. The larger the gradient change of the radius and rotation angle of the metasurface elements closer to the feed source, indicating that the surface waves generated by the feed source are fully utilized.

[0072] Referring to Figure 7 , Figure 7 (a), Figure 7 (b), Figure 7 (c) and Figure 7 (d) are respectively the two-dimensional radiation patterns of the X-polarized beam, Y-polarized beam, left-handed circularly polarized beam and right-handed circularly polarized beam generated by the present invention. The maximum gains of the four polarization beams are 19.06 dBi, 18.01 dBi, 15.67 dBic and 17.95 dBic respectively. It shows that the present invention can generate high-gain radiation of four different polarizations by switching the excitation feed source. The axial ratios of the two circularly polarized beams are both less than 3 dB at their maximum gain pointing directions, and the sidelobe levels of the beams under all polarizations are less than -10 dB, verifying the feasibility of the four-feed four-polarization holographic metasurface antenna designed by the position-weighted impedance superposition method to radiate multiple polarization beams.

Claims

1. A four-feed four-polarization holographic metasurface antenna based on position-weighted impedance superposition, comprising a radiation array (1) and four feeds (2), wherein the radiation array (1) comprises M×N radiation units (11) arranged periodically, M≥20, N≥20; characterized in that: The radiation array (1) is divided into four areas in the XOY plane of the three-dimensional coordinate system, and the four feed sources (2) are arranged at the center positions of the four areas; the radiation unit (11) adopts a circular patch structure etched with an "I"-shaped gap; the radius r of the m×nth radiation unit mn It is the maximum equivalent scalar impedance obtained by weighted superposition of tensor surface impedance distributions corresponding to single polarization electromagnetic waves generated with different feed sources as the center. Determine the inclination angle of the two horizontal arms of the "I"-shaped gap relative to the X-axis and The corresponding electromagnetic wave propagation direction The same; by exciting the four feed sources separately, four polarized electromagnetic waves corresponding to different feed sources are realized.

2. The holographic metasurface antenna according to claim 1, characterized in that: The radiation array (1) further comprises a dielectric substrate (12) and a metal floor (13) printed on the lower surface thereof; the M×N radiation units (11) are printed on the upper surface of the dielectric substrate (12).

3. The holographic metasurface antenna according to claim 1, characterized in that: The radius r of the m×nth radiation unit mn , the calculation formula is: A＝-3.8581×10 -9 B＝-4.966×10 -6 C＝-2.4353×10 -3 D＝-0.54201 E＝-44.933 Among them, A, B, C, D, and E are constants related to the shapes of the radiation units.

4. The holographic metasurface antenna according to claim 3, characterized in that: The constants A, B, C, D, and E related to the shape of the radiation unit are determined by performing function fitting on a relationship curve between the radius of the radiation unit and the corresponding maximum equivalent scalar impedance.

5. The holographic metasurface antenna according to claim 1, characterized in that: The maximum equivalent scalar impedance of the m×n radiating element The calculation formula is: Where j is an imaginary unit, η0 is the wave impedance in vacuum, They are the impedance responses of the electric field in the X direction to the current in the X and Y directions, is the impedance response of the electric field in the Y direction to the current in the Y direction, θ mn is the propagation direction of the electromagnetic wave on the m×nth radiation unit, θ mn ∈[-180°, 180°].

6. The holographic metasurface antenna according to claim 5, characterized in that: The electric field in the X direction has an impedance response to the current in the X and Y directions, and the electric field in the Y direction has an impedance response to the current in the Y direction. and The calculation formulas are: Among them, P i mn is the radiation weight value of the m×nth radiation unit corresponding to the i-th feed source, and They are the impedance responses of the electric field in the X direction to the currents in the X and Y directions when a single polarized electromagnetic wave is generated with the i-th feed source as the center. is the impedance response of the electric field in the Y direction to the current in the Y direction when a single polarization electromagnetic wave is generated with the i-th feed source as the center, is the distance between the m×nth radiation unit and the i-th feed source, x mn and mn are the horizontal and vertical coordinates of the m×nth radiation unit, respectively. i and i are the horizontal and vertical coordinates of the i-th feed source, i∈[1,4].

7. The holographic metasurface antenna according to claim 6, characterized in that: When a single polarized electromagnetic wave is generated with the i-th feed source as the center, the impedance response of the electric field in the X direction to the current in the X and Y directions, and the impedance response of the electric field in the Y direction to the current in the Y direction and The calculation formulas are: Where F and G are the average impedance and modulation depth of the holographic metasurface antenna, respectively, and β i ,θ i , are the phase of the interference field, the elevation angle and the azimuth angle of the generated beam when the i-th feed is excited separately, respectively. t is the wave vector of the electromagnetic wave when it propagates on the radiation unit, and k0 is the wave vector in free space.

8. The holographic metasurface antenna according to claim 1, characterized in that: The feed source (2) adopts a monopole antenna structure.

9. The holographic metasurface antenna according to claim 1, characterized in that: The geometric center of the "I"-shaped gap coincides with the center of the circular patch.

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