Stable dual-beam metasurface antenna array based on broadband positive phase

Abstract

This invention discloses a stable dual-beam metasurface antenna array based on broadband positive phase, belonging to the field of antenna technology. This invention applies it to the design of a series-fed dual-beam metasurface antenna array; by employing two types of metasurface antenna elements, two adjacent resonant modes can be excited, enabling the metasurface antenna elements to achieve positive phase response over a wide frequency range, offsetting the phase lag caused by the long-line effect of the series-fed transmission line, and solving the inherent defect of beam scanning with frequency in traditional series-fed arrays. This invention realizes a dual-beam metasurface antenna array through a dual-port microstrip line feeding network and multiple series-fed metasurface antenna elements. Simulation and experimental results show that the proposed metasurface antenna array maintains beam angle stability over a wide relative bandwidth. Compared with existing designs, it has advantages such as broadband stable beam pointing, compact structure, simple configuration, and low insertion loss, and has strong application potential in compact broadband wireless communication systems.

Description

Technical Field

[0001] This invention relates to the field of antenna technology, specifically to a metasurface antenna array, and more particularly to a stable dual-beam metasurface antenna array based on broadband positive phase. Background Technology

[0002] With increasingly scarce spectrum resources, multi-beam antennas have received widespread attention and application. Through spatial diversity multiplexing, they can expand the spatial coverage of wireless communication systems. In existing multi-beam antenna schemes, parallel-fed antenna arrays typically achieve fixed beam pointing through beamforming networks. However, the required beamforming networks suffer from large physical size and non-negligible insertion loss, making them unsuitable for compact device scenarios. Series-fed arrays, on the other hand, can achieve beam control by adjusting the periodic spacing of the radiating elements. Compared to parallel-fed arrays, they are simpler in structure and have a lower profile, allowing for dual-beam radiation through a compact design. However, series-fed antennas have an inherent drawback of being affected by long-line effects, causing their beam pointing to shift significantly with frequency, making them unsuitable for broadband applications. To suppress long-line effects and alleviate frequency scanning problems, existing technologies have introduced positive phase response methods, such as using anomaly group delay phase shifters to achieve positive phase response and offset the phase lag caused by long-line effects. However, this introduces significant insertion loss, which severely affects antenna radiation efficiency. Leaky wave antenna arrays can achieve wide-angle beam scanning, but their broadband frequency offset effect is also severe, making it impossible to achieve stable beam pointing under broadband conditions.

[0003] In addition, metasurface-based series-fed antenna schemes replace phase shifters with equivalent circuits of metasurface antennas, avoiding additional insertion loss. However, they can only excite a single resonant mode, and the relative bandwidth of the positive phase response is difficult to exceed 10%, resulting in an extremely narrow operating bandwidth for the stable beam, which cannot meet the application requirements of broadband wireless communication systems. Existing series-fed patch antenna arrays with dual-beam capability also suffer from the problem of narrow operating bandwidth, failing to balance broadband operation, stable beam pointing, and compact structural design. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing series-fed metasurface antenna arrays, such as narrow stable beam operating bandwidth (typically <10%), high insertion loss due to the need for additional phase shifters, complex structure, and difficulty in achieving stable broadband dual-beam radiation. This invention provides a stable dual-beam metasurface antenna array based on broadband positive phase. Through a dual RLC series-loaded equivalent circuit design, combined with two types of metasurface antenna elements to excite dual adjacent resonant modes, this invention fundamentally cancels the negative phase lag of the series-fed transmission line, suppresses frequency scanning effects, and simultaneously achieves low insertion loss and a compact structure, thus realizing stable dual-beam radiation over a wide bandwidth.

[0005] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0006] A stable dual-beam metasurface antenna array system based on broadband positive phase employs a double-layer substrate stacked structure, consisting of, from top to bottom: a metasurface radiating layer, a metal ground plane layer, and a feed network layer. The metasurface radiating layer contains multiple cascaded-fed metasurface antenna elements; the feed network layer contains a dual-port symmetrical folded microstrip line feed network, which is used to provide phase-consistent feed signals to the multiple metasurface antenna elements.

[0007] The metasurface antenna element is based on the equivalent circuit design of dual RLC series loading, and its radiation region is equivalent to the structure of two independent RLC parallel resonant networks connected in series.

[0008] Metasurface antenna elements include two types: the first type is a solid patch element, and the second type is a patch element with etched slots. These two types of elements correspond to two parallel RLC branches in the equivalent circuit, which are used to excite two adjacent resonant modes, enabling the metasurface antenna element to generate a positive phase response over a wide frequency range, canceling the inherent negative phase hysteresis of the series feed transmission line, and achieving beam angle stability.

[0009] To optimize the above technical solution, the specific measures also include:

[0010] The total series impedance of the equivalent circuit with dual RLC series loading is ;in, and These are the input impedances of two parallel RLC resonant networks. The resonant frequencies of the two RLC branches are close to the center operating frequency of the antenna array, which work together to generate a wideband positive phase response.

[0011] The metal ground plane is etched with coupling slots corresponding to the metasurface antenna elements and half-wavelength slots symmetrically distributed on both sides of the metasurface radiating layer. The coupling slots are used to couple the feed energy from the feed network layer to the metasurface radiating layer, and the half-wavelength slots are used to reduce the beamwidth in the low-frequency band and reduce beamwidth fluctuations in the operating frequency band.

[0012] Multiple metasurface antenna elements are connected in series via folded microstrip lines. The folded microstrip lines adopt a symmetrical bending structure, and their length and characteristic impedance are matched with the target beam angle. This is used to control the radiation phase difference between adjacent metasurface antenna elements and match the input impedance of each element, ensuring that the feed phase of the two ports is consistent, thus achieving symmetrical dual-beam radiation.

[0013] Solid surface mount units use square, round, or rectangular surfaces; surface mount units with etched slots have H-shaped, U-shaped, or L-shaped slots.

[0014] Solid surface mount units and etched slotted surface mount units are arranged in an alternating pattern with a row between them.

[0015] The coupling groove can be a rectangular groove, a dumbbell-shaped groove, or a stepped groove.

[0016] The metasurface radiating layer consists of four metasurface antenna elements arranged longitudinally, each of which is a 3×3 patch element array.

[0017] Transmission coefficient within the operating frequency band of the antenna array The phase of the beam deflection is kept consistent with the beam scanning phase condition over a wide bandwidth, thereby achieving a stable beam deflection angle within the band. .

[0018] Beam deflection angle The determined The phase condition is:

[0019]

[0020] In the formula, For free space wavenumber, The spacing between array cells, It represents the spatial harmonic order.

[0021] The present invention has the following beneficial effects:

[0022] First, this invention proposes a broadband positive phase response method. Based on the design of a metasurface antenna element using a dual-parallel RLC equivalent circuit, two adjacent resonant modes are excited by two types of metasurface antenna elements, which greatly expands the relative bandwidth of the positive phase response. This fundamentally solves the beam frequency scanning problem of traditional series-fed arrays and achieves stable beam pointing over a wide bandwidth.

[0023] Secondly, this invention eliminates the need for additional phase shifters and complex beamforming networks. It achieves positive phase response through the equivalent circuit of the metasurface antenna element itself, avoiding additional insertion loss and significantly simplifying the antenna structure, thus realizing a compact design.

[0024] Third, the antenna array of the present invention achieves good impedance matching and port isolation within a wide operating frequency band, with a small beam angle fluctuation range, stable in-band gain, and low cross-polarization level, thus achieving stable dual-beam radiation in a wide bandwidth.

[0025] Fourth, the present invention adopts a double-layer substrate design, which has a simple structure and mature processing technology. It does not require a complex multi-layer cascade structure, has low manufacturing cost, and is easy to mass-produce. It has great application potential and promotion value in compact broadband wireless communication systems and multi-beam MIMO communication systems. Attached Figure Description

[0026] Figure 1 is a graph showing the reflection phase of two types of metasurface antenna elements in the embodiments of the present invention as a function of frequency;

[0027] Figure 2 is a schematic diagram of the overall structure of the stable dual-beam metasurface antenna array proposed in the embodiment of the present invention;

[0028] Figure 3 is a schematic diagram of the functional partitioning of the metasurface antenna unit in an embodiment of the present invention.

[0029] The attached figures are labeled as follows: 1. Metasurface radiating layer; 11. Solid patch unit; 12. Etched patch unit with gaps; 2. Metal ground plane layer; 21. Coupling groove; 22. Half-wavelength slot; 3. Feed network layer; 31. Folded microstrip line. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this application clearer, the application is described and illustrated below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0031] This invention discloses a stable dual-beam metasurface antenna array based on broadband positive phase. The parallel RLC resonant circuit is a typical positive phase response circuit, which can cancel the inherent negative phase hysteresis of the series-fed transmission line. By adopting a dual RLC series loading structure, continuous phase compensation can be achieved in a wider frequency band, thereby realizing stable beam angle scanning.

[0032] A dual RLC series-fed array, from which a periodic cell is extracted, has a period length of... For regional divisions, please refer to [link / reference]. Figure 1 Including the two segments with physical lengths of For the simplified circuit model, the characteristic impedance of each transmission line segment is assumed to be equal to that of the transmission line and the radiating antenna section in the middle. The propagation constant of the transmission line is .

[0033] The radiating antenna section is equivalent to two independent RLC parallel resonant networks connected in series, and its total series impedance is the sum of the impedances of the two branches, i.e. ,in, The input impedance of the first RLC parallel resonant network is... The input impedances of the second RLC parallel resonant network are as follows:

[0034] , (1)

[0035] In the formula, The operating angular frequency, The imaginary unit, These are the radiation resistance, equivalent inductance, and equivalent capacitance of the first RLC branch, respectively. These are the radiation resistance, equivalent inductance, and equivalent capacitance of the second RLC branch, respectively.

[0036] This periodic unit can be equivalent to a cascade of three two-port networks: the left transmission line (S matrix is...) ), total series impedance (S matrix is ), right transmission line (S matrix is The total S matrix is ​​a cascade of the three:

[0037] (2)

[0038] After simplification, the total S matrix of one periodic unit is:

[0039] (3)

[0040] The transmission coefficient of the periodic unit can be obtained from this. for:

[0041] (4)

[0042] Based on the principle of antenna beam scanning, the beam deflection angle Determined by (the angle between the beam pointing and the array normal) The phase condition is:

[0043] (5)

[0044] In the formula, The characteristic impedance of each transmission line segment, The input impedance of the first RLC parallel resonant network is... The input impedance of the second RLC parallel resonant network is... For free space wavenumber, The spacing between array cells, It represents the spatial harmonic order.

[0045] In other words, by independently adjusting two sets of RLC parameters ( and This makes equation (4) possible. The phase remains consistent with the beam scanning phase condition in equation (5) over a wide bandwidth, thereby achieving a stable beam deflection angle within the band. .

[0046] Metasurface antenna elements are divided into two categories: the first is a solid square patch element, and the second is a patch element with an H-shaped slot etched in the center. These two types of elements are arranged in an alternating row, which can precisely excite two adjacent and independent resonant modes, enabling the metasurface antenna element to produce a continuous and flat positive phase response over a wide frequency range. Specifically, in this embodiment, the resonant characteristics of the solid square patch element are mainly determined by the side length of the patch, which is equivalent to the first set of parallel RLC resonant branches; while the patch element with the etched H-shaped slot, due to the additional capacitance effect and current path introduced by the slot, has a lower resonant frequency than the solid square patch of the same size, which is equivalent to the second set of parallel RLC resonant branches. By precisely adjusting the length, width, and position of the H-shaped slot, the frequency of the second resonant mode can be independently controlled, keeping its frequency interval with the first resonant mode within the range of 100~300MHz, forming two adjacent resonant peaks.

[0047] In this embodiment, see Figure 2 The reflection phase of two types of metasurface antenna elements was simulated and analyzed using the Floquet port model. The results show that the resonant frequency of the solid square patch element is approximately 5.1 GHz, exhibiting a positive phase response in the range of 4.9–5.3 GHz; the resonant frequency of the patch element with etched H-shaped slots is approximately 4.9 GHz, exhibiting a positive phase response in the range of 4.7–5.1 GHz. The positive phase response regions of the two adjacent resonant modes overlap and transition smoothly, forming a continuous wide positive phase band of 4.7–5.3 GHz after superposition, which is more than double the positive phase bandwidth of the traditional single resonant structure.

[0048] A metal ground plane is placed beneath the metasurface antenna elements, with coupling slots etched on it. These slots are fed by dual-port microstrip lines to power the metasurface antenna elements. Multiple metasurface antenna elements are connected in series via folded microstrip lines to generate a pre-defined radiating beam. Symmetrically distributed half-wavelength slots are etched on both sides of the metal ground plane of the antenna array to reduce beamwidth in the low-frequency band, minimize beamwidth fluctuations within the operating frequency band, and optimize beam radiation performance.

[0049] In this embodiment, see Figure 3 The overall structure employs a double-layer substrate stacked structure, consisting of a metasurface radiating layer 1, a metal ground plane layer 2, and a feed network layer 3, from top to bottom. The metasurface radiating layer 1 comprises four metasurface antenna elements arranged longitudinally, each being a 3×3 patch element array. The metasurface antenna elements can be in various patch forms, such as square, circular, or rectangular patches, and the resonant frequencies of both types of metasurface antenna elements are close to the center operating frequency of the antenna array. In this embodiment, a 3×3 metasurface antenna element composed of two types of hybrid metasurface antenna elements and a dual-port symmetrical folded microstrip line feed network are used.

[0050] See Figure 3 In this embodiment, the metasurface antenna element mainly includes square patch elements and H-shaped slot patch elements. Feed energy enters from the dual-port feed port of the feed network layer 3, and is gradually transferred along the folded microstrip line 31 to the coupling slot 21 of the metal ground plane layer 2. Subsequently, the energy is transferred to the upper metasurface antenna element through electromagnetic coupling, and finally radiated into free space through the metasurface antenna element. The metasurface antenna element uses square patch elements and H-shaped slot patch elements arranged in alternating rows, enabling the metasurface antenna element to generate a positive phase response over a wide frequency range, offsetting the negative phase lag of the series feed transmission line, and achieving beam angle stability. (Reference) Figure 2 Each metasurface antenna element is divided into three consecutive functional regions along the series feed direction, including a transmission region located at both ends of the element and an antenna radiation region located in the middle of the element. In this embodiment, H-shaped slotted patch elements and square patch elements are arranged alternately to excite two adjacent resonant modes with a frequency difference of 200MHz, thereby forming a dual parallel RLC equivalent circuit and achieving a broadband positive phase response.

[0051] In this embodiment, the metal ground plane 2 is used to enhance the front-to-back ratio of the antenna, improve the radiation pattern characteristics, and provide a common ground reference surface for the metasurface radiating layer 1 and the feed network layer 3. The metal ground plane 2 is etched with coupling slots 21 corresponding to the four metasurface antenna elements, and four sets of symmetrically distributed half-wavelength slots 22 on both sides of the array. The coupling slots 21 are used to achieve electromagnetic coupling between the feed network and the metasurface radiating layer, transferring feed energy to the upper metasurface antenna elements; the symmetrical half-wavelength slots 22 on both sides are used to reduce the beamwidth in the low-frequency band, reduce beamwidth fluctuations within the operating frequency band, and optimize beam radiation performance. The coupling slots 21 can be in the form of rectangular slots, dumbbell-shaped slots, stepped slots, etc., to couple feed energy to the upper metasurface radiating layer.

[0052] In this embodiment, the feeding network layer 3 mainly includes folded microstrip lines 31. Four metasurface antenna elements are connected in series via folded microstrip lines 31. The length and characteristic impedance of the folded microstrip lines 31 are optimized according to the target beam angle. By adjusting the electrical length of each segment of the folded microstrip line, the radiation phase difference between adjacent metasurface antenna elements is precisely controlled, while matching the input impedance of each element, thereby generating a radiation beam with a preset direction. The coupling slot 21 on the metal ground plane layer 2 is fed and excited by the lower dual-port folded microstrip lines 31, and the energy is transferred to the upper metasurface radiation layer 1 through electromagnetic coupling, realizing the series feeding of the metasurface antenna elements. Specifically, the folded microstrip lines 31 adopt a symmetrical bending structure to ensure that the feeding phase of the two ports is consistent, realizing symmetrical dual-beam radiation.

[0053] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0054] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if these modifications and variations of the present invention fall within the scope of the claims of this application and their equivalents, this application also intends to include these modifications and variations.

Claims

1. A stable dual-beam metasurface antenna array system based on broadband positive phase, characterized in that, The double-layer substrate stacked structure consists of, from top to bottom: metasurface radiating layer (1), metal ground layer (2) and feeding network layer (3). The metasurface radiating layer (1) contains multiple series-fed metasurface antenna elements. The feed network layer (3) includes a dual-port symmetrical folded microstrip line feed network, which is used to provide phase-consistent feed signals to multiple metasurface antenna elements; The metasurface antenna element is based on the dual RLC series loading equivalent circuit design, and its radiation region is equivalent to the structure of two independent RLC parallel resonant networks connected in series. The metasurface antenna unit includes two types: the first type is a solid patch unit (11), and the second type is a patch unit with etched slots (12). These two types of units correspond to two parallel RLC branches in the equivalent circuit, which are used to excite two adjacent resonant modes, so that the metasurface antenna unit generates a positive phase response in a wide frequency range, cancels the inherent negative phase lag of the series feed transmission line, and achieves beam angle stability.

2. The stable dual-beam metasurface antenna array system based on wideband positive phase according to claim 1, characterized in that, The total series impedance of the equivalent circuit with dual RLC series loading is: ;in, and These are the input impedances of two parallel RLC resonant networks. The resonant frequencies of the two RLC branches are close to the center operating frequency of the antenna array, which work together to generate a wideband positive phase response.

3. The stable dual-beam metasurface antenna array system based on wideband positive phase according to claim 1, characterized in that, The metal floor layer (2) is etched with coupling slots (21) corresponding to the metasurface antenna elements and half-wavelength slots (22) symmetrically distributed on both sides of the metasurface radiating layer (1); the coupling slots (21) are used to couple the feed energy from the feed network layer (3) to the metasurface radiating layer (1), and the half-wavelength slots (22) are used to reduce the beamwidth in the low frequency band and reduce the beamwidth fluctuation in the operating frequency band.

4. The stable dual-beam metasurface antenna array system based on wideband positive phase of claim 1, wherein, Multiple metasurface antenna elements are connected in series via folded microstrip lines (31); the folded microstrip lines (31) adopt a symmetrical bending structure, and their length and characteristic impedance are matched with the target beam angle. They are used to control the radiation phase difference between adjacent metasurface antenna elements and match the input impedance of each element, ensuring that the feed phase of the two ports is consistent, and realizing symmetrical dual-beam radiation.

5. A stable dual-beam metasurface antenna array system based on broadband positive phase according to claim 1, characterized in that, The solid patch unit (11) is a square, round or rectangular patch; the slits of the etched patch unit (12) are H-shaped, U-shaped or L-shaped slits.

6. The stable dual-beam metasurface antenna array system based on wideband positive phase according to claim 1, wherein, The solid patch unit (11) and the etched patch unit (12) are arranged in an alternating pattern with a row spaced apart.

7. The stable dual-beam metasurface antenna array system based on wideband positive phase according to claim 3, characterized in that, The coupling groove (21) is a rectangular groove, a dumbbell-shaped groove, or a stepped groove.

8. The stable dual-beam metasurface antenna array system based on wideband positive phase according to claim 3, characterized in that, The metasurface radiating layer (1) is composed of four metasurface antenna elements arranged in sequence along the longitudinal direction, and each metasurface antenna element is a 3×3 patch element array.

9. The stable dual-beam metasurface antenna array based on wideband positive phase of claim 1, wherein, Within the operating frequency band of the antenna array, the transmission coefficient The phase of the beam deflection is kept consistent with the beam scanning phase condition over a wide bandwidth, thereby achieving a stable beam deflection angle within the band. .

10. The stable dual-beam metasurface antenna array based on wideband positive phase of claim 9, wherein, Beam deflection angle The determined The phase condition is: wherein is the free space wave number, is the array element spacing, is the spatial harmonic order.

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