Millimeter wave ultra wide band substrate integrated coaxial line antenna array based on laminated metasurface

Abstract

The invention discloses a millimeter wave ultra-wideband substrate integrated coaxial line antenna array based on a laminated metasurface. The ultra-wideband antenna array comprises a coplanar waveguide-to-substrate integrated coaxial line switching structure, a one-to-eight power divider based on a substrate integrated coaxial line structure, a butterfly coupling slot and a laminated metasurface antenna, after being fed in by the coplanar waveguide, energy is transmitted to the substrate integrated coaxial line power divider through the blind hole structure, and is uniformly distributed to eight channels in the substrate integrated coaxial line power divider; and then, the energy is coupled and fed to the laminated metasurface antenna through the coupling slot. The antenna can stably work in the frequency range of 15.84 GHz-49.15 GHz, the return loss (S11) is always lower than 10 dB, and the corresponding relative bandwidth is 102.5%. In a target working frequency band, the maximum peak gain of the antenna can reach 18.58 dBi, and the antenna has excellent ultra-wideband characteristics and good radiation performance.

Description

Technical Field

[0001] This invention relates to the application field of ultra-wideband antennas, and in particular to a millimeter-wave ultra-wideband substrate integrated coaxial antenna array based on a stacked metasurface. Background Technology

[0002] With the continuous evolution of wireless communication, radar sensing, and imaging technologies, various systems are increasingly demanding higher data rates, larger capacities, and higher sensing accuracy. The millimeter-wave band, due to its abundant available spectrum resources and excellent spatial resolution, has become an important research direction for high-speed communication and precision detection systems. Among these, ultra-wideband antennas operating in the millimeter-wave band play a crucial role in achieving high-speed data transmission, high-resolution imaging, and high-precision target detection.

[0003] To fully utilize the abundant spectrum resources of the millimeter-wave band, various broadband antenna structures have been proposed, such as magnetoelectric dipole antennas, resonant cavity slot antennas, horn antennas, and patch antennas. Among them, broadband metasurface antennas are attracting widespread attention due to their advantages such as low profile, high design flexibility, and ease of fabrication. Furthermore, their unique multimode excitation characteristics can simultaneously excite multiple resonant modes, thereby significantly extending the impedance bandwidth and improving overall radiation performance.

[0004] However, most traditional metasurface antennas employ a single-layer homogeneous metasurface structure, whose inherent singular electromagnetic characteristics impose certain limitations, making it difficult to exceed 40% impedance bandwidth. Therefore, the concepts of non-uniform metasurfaces and stacked metasurface structures have been proposed. However, existing non-uniform metasurface antennas are mostly designed using elements with different patterns or sizes, resulting in high structural complexity. Research on stacked metasurfaces is currently limited, and most designs require the introduction of air layers, with research primarily focused on the microwave band. Extending this to millimeter-wave band array antennas typically faces challenges such as increased fabrication complexity and limited feed structure bandwidth. Therefore, exploring design methods for stacked metasurfaces in the millimeter-wave band is crucial for realizing high-performance ultra-wideband antennas. Summary of the Invention

[0005] The purpose of this invention is to provide a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on stacked metasurfaces, which offers a new solution to the problems of limited bandwidth, complex structure, and difficulty in millimeter-wave array integration of existing metasurface antennas, and elucidates the realization mechanism of its ultrawideband characteristics in principle.

[0006] To solve the aforementioned technical challenges, the present invention adopts the following technical solution: a millimeter-wave ultra-wideband substrate-integrated coaxial antenna array based on a stacked metasurface, comprising an ultra-wideband feed network based on a substrate-integrated coaxial structure, a stacked metasurface structure serving as a radiation aperture, and an equivalent circuit model of the antenna element; the ultra-wideband feed network based on the substrate-integrated coaxial structure comprises a first dielectric substrate, a first metal structure printed on the bottom of the first dielectric substrate, an adhesive layer, a second dielectric substrate, a second metal structure printed on the bottom of the second dielectric substrate, a third metal structure printed on the top of the second dielectric substrate, metal blind vias distributed on the second dielectric substrate, and metal through-holes distributed on the first dielectric substrate, the adhesive layer, and the second dielectric substrate; the stacked metasurface structure comprises a third dielectric substrate, a fourth metal structure printed on the top of the third dielectric substrate, a fourth dielectric substrate, and a fifth metal structure printed on the top of the fourth dielectric substrate. The third metal structure is etched with U-shaped slots and eight butterfly-shaped slots; the fourth metal structure consists of eight 3×3 metasurface arrays and a first spacer, with spacing between adjacent 3×3 metasurface arrays; the fifth metal structure consists of eight 4×4 metasurface arrays and a second spacer, with spacing between adjacent 4×4 metasurface arrays; eight first mechanical holes are opened on both sides of the first dielectric substrate, adhesive layer, second dielectric substrate, third dielectric substrate, fourth dielectric substrate, first metal structure, third metal structure, first spacer, and second spacer to facilitate mechanical assembly; two second mechanical holes are opened on the first dielectric substrate, adhesive layer, second dielectric substrate, first metal structure, and third metal structure; the equivalent circuit model of the antenna unit consists of a port model, an equivalent model of the transmission line extension, a cavity model, a slot model, a transformer model to represent the coupling effect, a 3×3 metasurface equivalent model, and a 4×4 metasurface equivalent model.

[0007] Furthermore, the ultra-wideband power supply network based on the substrate-integrated coaxial cable structure adopts a multi-layer structure in space. Its spatial layout, from bottom to top, includes a first dielectric substrate, an adhesive layer, and a second dielectric substrate, which are attached to each other and stacked vertically. The adhesive layer is disposed between the first dielectric substrate and the second dielectric substrate to achieve a fixed connection between the two. Metal blind vias are distributed inside the second dielectric substrate to achieve electrical connections between metal structures. Metal through-holes penetrate the first dielectric substrate, the adhesive layer, and the second dielectric substrate vertically to achieve electrical connections between metal structures in different layers.

[0008] Furthermore, the stacked metasurface structure adopts a multi-layer structure in space, and its spatial layout from bottom to top is as follows: a third dielectric substrate, a 3×3 metasurface array printed on the top of the third dielectric substrate, a fourth dielectric substrate, and a 4×4 metasurface array on the top of the fourth dielectric substrate, forming a multi-layer dielectric and metasurface combination structure stacked on top of each other to achieve the required electromagnetic coupling and broadband radiation performance.

[0009] Furthermore, the equivalent circuit model of the antenna element is arranged along the signal transmission path as follows: the port model and the extension of the transmission line form a parallel structure. The parallel structure is then connected in parallel with the series structure composed of the cavity model and the slot model. The slot model is connected in parallel with the transformer model used to characterize the coupling effect, and then connected in parallel with the 3×3 metasurface equivalent model. On this basis, it is further connected in parallel with the 4×4 metasurface equivalent model to form an overall equivalent circuit.

[0010] Furthermore, the first dielectric substrate material is Rogers 5880, and the overall structural dimensions are 83mm * 21.9mm * 0.381mm.

[0011] The adhesive layer material is Rogers 4450F, and the overall structural dimensions are 83mm * 21.9mm * 0.1mm.

[0012] The second dielectric substrate material is Rogers 5880, and the overall structural dimensions are 83mm * 21.9mm * 0.381mm.

[0013] The third dielectric substrate material is Rogers 5880, with an overall structural size of 83mm * 21.9mm * 1.016mm, and a cuboid hollow area with a size of 61.3mm * 14.8mm * 1.016mm is formed at the edge.

[0014] The fourth dielectric substrate material is Rogers 5880, with an overall structural size of 83mm * 21.9mm * 1.575mm; and a cuboid hollow area with a size of 61.3mm * 14.8mm * 1.575mm is formed at the edge.

[0015] Furthermore, the first, second, third, fourth, and fifth metal structures are all made of copper with a thickness of 0.035 mm. The dimensions of the first metal structure are 83 mm * 21.9 mm * 0.035 mm. The second metal structure is a signal line of a substrate-integrated coaxial cable, consisting of a three-stage parallel structure, used for the transmission and distribution of radio frequency signals. The third metal structure is etched with U-shaped slots and eight butterfly slots to achieve interlayer transmission. The diameter of the metal blind via is 0.3 mm and the height is 0.381 mm. The diameter of the metal through-hole is 0.3 mm and the height is 0.862 mm, with a spacing of 0.6 mm between adjacent metal through-holes.

[0016] Furthermore, the third metal structure printed on the top of the second dielectric substrate, after being etched with a U-shaped slot, together with the metal blind holes distributed on the second dielectric substrate, constitutes a coplanar waveguide conversion substrate integrated coaxial feeding and switching structure.

[0017] Furthermore, the butterfly-shaped slot has a left-right symmetrical structure, with a width of 0.3 mm at the narrow center, a width of 1.78 mm at the two extended ends, a total length of 6.35 mm, and a distance of 7.3 mm between adjacent butterfly-shaped slots.

[0018] Furthermore, the 3×3 metasurface array has a size of 1.2mm * 1.2mm, a distance of 0.1mm between adjacent units, and a distance of 7.3mm between adjacent 3×3 metasurface arrays.

[0019] The 4×4 metasurface array has a size of 0.68mm * 0.68mm, a distance of 0.73mm between adjacent units, and a distance of 7.3mm between adjacent 4×4 metasurface arrays.

[0020] The dimensions of the first and second gaskets are 11mm * 21.9mm.

[0021] Furthermore, the diameter of the first dielectric substrate, adhesive layer, second dielectric substrate, third dielectric substrate, fourth dielectric substrate, first metal structure printed on the bottom of the first dielectric substrate, third metal structure printed on the top of the second dielectric substrate, and the first mechanical holes on both sides of the pad are 2 mm and the spacing is 5 mm.

[0022] The diameter of the second mechanical holes on the first dielectric substrate, the adhesive layer, the second dielectric substrate, the first metal structure printed on the bottom of the first dielectric substrate, and the third metal structure printed on the top of the second dielectric substrate is 2.2 mm, and the spacing is 9.525 mm.

[0023] Furthermore, the characteristic impedance of the port model is 35Ω.

[0024] Furthermore, the equivalent model of the transmission line extension is composed of the first resistor R. s First inductor L s1 First capacitor C s1 It consists of three parts connected in parallel, with the first resistor R S = 60.3Ω, First inductance L S1 = 0.28nH, First capacitor C S1 =0.1pF.

[0025] Furthermore, the cavity model is composed of a second resistor R. C Second inductor L C Second capacitor C C It consists of three parts connected in parallel, with the second resistor R C = 50.1Ω, second inductor L C = 0.28nH, Second capacitor C C = 0.13pF.

[0026] Furthermore, the gap model is composed of a third inductor L S2 Fourth inductor L S3 Third capacitor C S2 A π-type network is formed, in which the third inductor L S2 = 0.23nH, Fourth Inductor L S3 = 4.5nH, Third capacitor C S2 = 0.15pF.

[0027] Furthermore, the transformer model used to represent the coupling effect has a coupling coefficient of N = 0.26.

[0028] Furthermore, the 3×3 metasurface model is composed of three sets of LC resonators connected in parallel, with the two edge sets having identical circuit parameters, the values ​​of which are respectively the fifth inductor L... m1 = 1.3nH, Fourth capacitor C m1 = 1.2pF, Sixth Inductor L m2 = 0.03nH, fifth capacitor C m2 = 0.96pF.

[0029] Furthermore, the 4×4 metasurface model is composed of four sets of LC resonators connected in parallel, wherein the circuit parameters are symmetrical about the center, and their values ​​are respectively the seventh inductor L m3 = 0.64nH, sixth capacitor C m3 = 0.12pF, Eighth Inductor L m4 = 0.06nH and the seventh capacitor C m4 = 0.04pF.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] To address the limitations of existing metasurface antennas, such as limited bandwidth, complex structure, and difficulties in millimeter-wave array integration, this invention proposes, for the first time, an ultra-wideband antenna array operating in the millimeter-wave band, based on a stacked metasurface structure combined with a substrate-integrated coaxial feeding method. This antenna array operates in the frequency range of 15.84 GHz - 49.15 GHz, achieving a relative bandwidth of 102.5%, significantly improving the broadband coverage capability of the antenna array.

[0032] This invention constructs an accurate equivalent circuit model and systematically analyzes its operating characteristics. This model effectively reveals the mechanism by which stacked metasurface structures affect impedance matching and bandwidth expansion, providing a reliable theoretical basis for the engineering design of antenna structures.

[0033] The stacked metasurface structure proposed in this invention can form a more uniform surface current distribution in the high-frequency band, effectively alleviating the radiation pattern deterioration problem caused by the increase of electrical aperture in the high-frequency band of single-layer metasurface structures, thereby improving radiation stability and gain performance over a wide frequency range. Attached Figure Description

[0034] Figure 1 This is a three-dimensional view of a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on a stacked metasurface according to the present invention.

[0035] Figure 2 This invention provides an equivalent circuit model for an antenna element of a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on a stacked metasurface.

[0036] Figure 3 This is a three-dimensional view and design parameters of an antenna element for a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on a stacked metasurface, according to the present invention.

[0037] Figure 4 This is a schematic diagram showing the reflection coefficient and gain of an antenna element in a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on a stacked metasurface, according to the present invention.

[0038] Figure 5 This invention relates to the three design stages of an antenna element for a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on a stacked metasurface.

[0039] Figure 6 This invention presents the input impedance curves of an antenna element in a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on a stacked metasurface, under three design stages.

[0040] Figure 7 This invention presents the reflection coefficient and gain curves of an antenna element in a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on a stacked metasurface under three design stages.

[0041] Figure 8 This is a schematic diagram of the equivalent circuit model of an antenna element of a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on a stacked metasurface, according to the present invention.

[0042] Figure 9 This paper compares the equivalent circuit model and full-wave simulation results of the antenna element of a millimeter-wave ultrawideband substrate integrated coaxial antenna array based on a stacked metasurface according to the present invention under three design stages.

[0043] Figure 10 This invention relates to the electric field distribution in the yoz plane of an antenna element of a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on a stacked metasurface.

[0044] Figure 11 This invention provides a comparison of the E-plane radiation patterns of an antenna element in a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on a stacked metasurface in the second and third stages.

[0045] Figure 12 This paper compares the surface current distribution of an antenna element in a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on a stacked metasurface at 46 GHz in the second and third stages of the present invention.

[0046] Figure 13 This invention presents a simulation model of the feed network for a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on a stacked metasurface, and the simulation results of the transmission and reflection coefficients.

[0047] Figure 14 This invention presents a simulation model of a coplanar waveguide-to-substrate integrated coaxial line transition structure for a millimeter-wave ultrawideband substrate-integrated coaxial line antenna array based on a stacked metasurface, and the simulation results of transmission and reflection coefficients.

[0048] Figure 15 This invention provides a simulation model of the overall structure of the antenna element and the 1×8 array of a millimeter-wave ultrawideband substrate integrated coaxial antenna array based on a stacked metasurface, as well as a physical prototype obtained from its fabrication.

[0049] Figure 16 This paper presents a comparison of the simulation and measured reflection coefficients of the antenna element of a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on a stacked metasurface and a 1×8 array, according to the present invention.

[0050] Figure 17This paper presents a comparison of the simulation and measured gain curves of the antenna element of a millimeter-wave ultrawideband substrate integrated coaxial antenna array based on a stacked metasurface according to the present invention, and a 1×8 array.

[0051] Figure 18 This paper presents a comparison of the normalized radiation patterns of the antenna element of a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on a stacked metasurface at 17 GHz, 20 GHz, 25 GHz, 30 GHz, 35 GHz, 40 GHz, 45 GHz, and 50 GHz, based on simulation and testing.

[0052] Figure 19 This paper presents a comparison of the normalized radiation patterns of the H-plane of the antenna element of a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on a stacked metasurface at 17 GHz, 20 GHz, 25 GHz, 30 GHz, 35 GHz, 40 GHz, 45 GHz, and 50 GHz, based on simulation and testing.

[0053] Figure 20 This paper presents a comparison of the normalized radiation patterns of the E-plane of a 1×8 array of a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on a stacked metasurface at 16 GHz, 20 GHz, 25 GHz, 30 GHz, 35 GHz, 40 GHz, 45 GHz, and 50 GHz, based on simulation and testing of the present invention.

[0054] Figure 21 This paper presents a comparison of normalized radiation patterns from simulation and testing of the H-plane of a 1×8 array of a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on a stacked metasurface at 16 GHz, 20 GHz, 25 GHz, 30 GHz, 35 GHz, 40 GHz, 45 GHz, and 50 GHz. Detailed Implementation

[0055] To meet the urgent needs of various millimeter-wave systems for high-speed transmission, high-resolution imaging, and high-precision detection, metasurface antennas, with their multi-mode excitation characteristics and structural advantages such as low profile and high design flexibility, have become an effective technical approach to achieve broadband radiation characteristics.

[0056] However, most traditional metasurface antennas employ a single-layer homogeneous metasurface structure, which inherently limits their single electromagnetic response capability, making it difficult to exceed 40% impedance bandwidth. Therefore, the concepts of non-uniform metasurfaces and stacked metasurface structures have been proposed to improve their broadband characteristics. However, existing non-uniform metasurfaces are mostly structurally complex and difficult to design. Existing broadband stacked metasurface structures are mostly focused on the microwave band and often require the introduction of an additional air layer structure. Extending them to the millimeter-wave band often faces problems such as increased fabrication complexity and limited operating bandwidth of the feed structure. Therefore, there is still a need to propose a metasurface antenna design scheme that is simple in structure, easy to fabricate, capable of achieving ultra-wideband characteristics in the millimeter-wave band, and easy to integrate into the array, in order to solve the problems of bandwidth limitation, structural complexity, and integration difficulties in existing technologies.

[0057] This invention provides a scheme for implementing a millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on a stacked metasurface, the antenna structure being as follows: Figure 1 As shown, this invention mainly consists of an ultra-wideband feeding network based on a substrate-integrated coaxial line structure and a stacked metasurface structure. Energy is fed in through a coplanar waveguide structure, then transmitted to the substrate-integrated coaxial line via a transition structure, and subsequently evenly distributed to eight branches through the feeding network. The stacked metasurface structure is excited through butterfly-shaped coupling slots, ultimately achieving ultra-wideband characteristics. Furthermore, it also proposes… Figure 2 The equivalent circuit model of the antenna unit is shown to illustrate the mechanism by which its broadband characteristics are realized.

[0058] To explore the working principle of this invention, an antenna element was first designed, such as... Figure 3 As shown, the antenna element consists of four dielectric substrates and one adhesive layer. The dielectric substrates used are Rogers 5880, with thicknesses of 0.381 mm, 0.381 mm, 1.014 mm, and 1.575 mm from bottom to top, respectively. The adhesive layer is Rogers 4450F, with a thickness of 0.1 mm. Dielectric substrates I and II, together with the adhesive film and metal layers M1–M3, constitute the substrate-integrated coaxial feed structure. The radiating aperture is achieved through dielectric substrates III and IV, on which 3×3 and 4×4 metasurface arrays are printed, respectively. The unit sizes of the 3×3 and 4×4 metasurfaces are 1.12 mm and 0.8 mm, respectively, with corresponding unit spacings of 0.1 mm and 0.78 mm. Electromagnetic waves are coupled from the substrate-integrated coaxial feed structure to the radiating aperture through the butterfly-shaped slots etched in the upper metal layer of dielectric substrate II, thereby exciting the stacked metasurface structure. The butterfly-shaped slot has a symmetrical structure, with a width of 0.3 mm at the narrow center and 1.6 mm at the wide ends on both sides, and a total length of 6.5 mm. Figure 4The simulation results of the proposed antenna show the reflection coefficient and gain curves. The results demonstrate that the reflection coefficient remains stable within the frequency range of 16.45 GHz – 50.38 GHz. Below this, the relative bandwidth reaches 101.5%. Within the operating frequency band, the antenna's peak gain reaches 9.1 dBi, and the minimum gain is 5.7 dBi.

[0059] like Figure 5 As shown, the proposed stacked metasurface antenna can be analyzed through three design stages. The first stage involves a butterfly slot antenna integrated from a substrate and fed by a coaxial cable. To analyze the impedance matching performance of the antenna, Figure 6 The simulated resistance and reactance curves of the antennas designed at different stages were plotted. Figure 6 This displays the corresponding reflection coefficient and gain curve. For example... Figure 6 As shown in (a), the antenna exhibits a large input impedance at this stage, resulting in poor impedance matching with the feed port. After optimization, this impedance parameter was determined, and the impedance bandwidth was effectively maximized in the final antenna design. Therefore, as... Figure 7 As shown in Figure (a), the reflection coefficient remains constant throughout the entire frequency band. In summary, to address this issue, the second stage introduces a 3×3 metasurface as a radiating aperture, enabling the butterfly-shaped slot to excite the metasurface's resonant mode through electromagnetic wave coupling. This structure significantly reduces the antenna's input impedance, thereby extending the impedance bandwidth to 43.9%. To further expand the antenna's impedance bandwidth, the third stage integrates 4×4 and 3×3 metasurface units to form the radiating aperture, thus constructing a stacked metasurface structure. This structure effectively enhances the impedance matching capability of the antenna elements, achieving a wider ultra-wideband characteristic. Ultimately, the proposed stacked metasurface antenna achieves a relative bandwidth of 101.5%, covering an ultra-wideband range of 16.45 GHz–50.38 GHz.

[0060] To further elucidate the bandwidth enhancement mechanism of stacked metasurfaces, this invention constructs... Figure 8 The equivalent circuit model is shown. The equivalent circuit of the first-stage slot antenna consists of three parts: the slot structure, the substrate-integrated coaxial cavity, and the extended substrate-integrated transmission line. The slot structure can be approximated as a π-type equivalent network. For example... Figure 9 As shown, the results obtained from the equivalent circuit model calculated by the Advanced Design System show good agreement with the full-wave simulation results of HFSS.

[0061] In the second stage, the coupling between the slot and the metasurface is approximated using an equivalent model of a transformer structure, while the metasurface structure itself is characterized by parallel inductance and capacitance to reflect its resonant contribution. The capacitance effect mainly originates from the edge capacitance caused by electromagnetic coupling between adjacent metasurface units, while the inductance effect corresponds to the current path formed between the metasurface and the ground plane. To simplify the model, the metasurface units along the y-axis are divided into three groups, each represented by a resonant branch. The contribution of the intermediate region can be approximated using the following expression:

[0062]

[0063]

[0064] Among them, C m1 and L m1 This represents the resonance contribution of the central region of the 3×3 metasurface. Parameters d9 and d... 10 ε0 represents the unit cell size of the 3×3 metasurface and the distance between adjacent units, respectively. ε0 is the vacuum permittivity, ... r h1 and h2 represent the relative permittivity and thickness of substrate III, respectively. φ0 is the free-space permeability. Meanwhile, due to the weakened electromagnetic coupling in the edge region, its corresponding resonance contribution is lower than that in the central region. Therefore, in the second stage, the metasurface structure and the slot structure together form a parallel equivalent network, significantly improving the matching with the port characteristic impedance and thus achieving effective expansion of the antenna bandwidth. Similarly, in the third stage, the units of the 4×4 metasurface along the y-axis are divided into four symmetrical groups, forming a parallel equivalent structure together with the bottom 3×3 metasurface. In this stage, the units in the central region of the 4×4 metasurface consist of two groups, and their corresponding resonance contribution is correspondingly reduced. Therefore, the corresponding resonance contribution can be updated to the following form:

[0065]

[0066]

[0067] Among them, C m3 and L m3 This represents the resonance contribution of the central region of the 3×3 metasurface. k is the distribution coefficient, taken as 0.5 here. The parameter d... 11 and d 12 ... Figure 8The parallel topology shown effectively improves the impedance matching between the antenna and the feed port, thereby significantly widening the impedance bandwidth of the antenna element and achieving ultra-wideband characteristics. In summary, by sequentially introducing two layers of metasurface structure on top of the slot antenna, a two-stage parallel impedance tuning mechanism is established in the antenna element, introducing additional resonance contributions. This method significantly improves the impedance matching of the feed port, greatly expands the impedance matching bandwidth, and ensures consistent matching characteristics across the ultra-wideband frequency range, ultimately achieving superior ultra-wideband performance.

[0068] To more intuitively demonstrate the working mechanism of stacked metasurfaces, Figure 10 The electric field distributions under three characteristic modes are presented. These modes are all extracted from the frequency point where the real part of the antenna input impedance reaches its peak and the imaginary part is zero in the third stage. It can be seen that at 20 GHz, the electric field in the yoz plane is mainly concentrated on both sides of the butterfly-shaped slot and the bottom metasurface, and the directions are basically consistent, corresponding to the TM... 10 Typical distribution characteristics of the mode. At 36 GHz, the electric field in the yoz plane is deflected in the central region, and the electric field direction on both sides is opposite to that at the center, corresponding to an anti-phase TM. 20 The electric field distribution characteristics of the mode. At 46 GHz, the electric field in the yoz plane undergoes two significant deflections along the y-axis. The electric field direction in the central region is opposite to that in the two side regions, forming three continuous alternating polarity regions, corresponding to TM. 30 Typical distribution of the mode. Therefore, the proposed stacked metasurface antenna is excited by TM. 10 Mode, Inverted TM 20 Pattern and TM 30 This mode enables stable axial radiation over an ultra-wide frequency range.

[0069] Furthermore, when the second stage operates in high-frequency mode, the antenna's electrical dimensions are correspondingly larger due to the relatively high operating frequency. In this case, the overall radiation pattern of the antenna is determined by the interaction between the in-phase and out-of-phase surface current components, as shown in the following equation:

[0070]

[0071] in, This represents the overall radiation pattern of the antenna. The antenna is operating at TM. 10 The radiation pattern at time represents a n The amplitude of the current components on the upper surface of the antenna is represented by d, and the spacing between these current components is represented by k. yLet be the wavenumber along the y-axis. Due to the large electrical dimensions of the antenna, significant mutual cancellation occurs between the surface currents in different regions of the antenna, resulting in... Figure 11 The radiation pattern shown has deteriorated. For easier visual understanding, Figure 12 Figure (a) shows the surface current distribution of the metasurface in the second stage. It can be seen that the current is mainly concentrated at the patch edges. Furthermore, the y-axis current component at the edge of the central patch is almost completely canceled out by the opposite current on the adjacent patches in the x-axis direction. In contrast, the current amplitude at the edges of the patches in the outer region is significantly greater than the opposite current on their adjacent patches, resulting in partial current cancellation. Therefore, the radiation pattern on the yoz plane shows a significant deterioration.

[0072] To address the aforementioned issues, this invention introduces a stacked metasurface structure in the third stage, enabling effective electromagnetic coupling between the two metasurface layers and thus effectively exciting the top 4×4 metasurface. In this structure, the energy received by the top metasurface primarily originates from the TM-mode electromagnetic waves excited by the bottom metasurface. These TM-mode waves can be structurally approximated as quasi-spherical waves, resulting in a continuous and phase-consistent electromagnetic wavefront on the top metasurface. In contrast, the bottom metasurface is directly excited by a local feed, and its phase distribution varies with spatial location. Under these conditions, the electromagnetic field excited by the top metasurface exhibits a highly consistent polarization direction across the entire radiation aperture, resulting in a highly aligned distribution of the top surface current along the y-axis. This consistent surface current enables in-phase far-field superposition within the radiation aperture, significantly enhancing axial radiation energy. Simultaneously, the uniform current distribution effectively suppresses the radiation cancellation effect caused by the out-of-phase current components in the bottom metasurface. Therefore, through this coupling mechanism, the overall radiation performance of the antenna element in the high-frequency band is significantly improved, effectively avoiding the radiation pattern deterioration problem caused by the increased electrical dimensions of traditional single-layer metasurfaces.

[0073] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0074] Example

[0075] Reference Figure 13 Figure (a) shows a schematic diagram of the ultra-wideband power supply network based on substrate-integrated coaxial cable implemented in this invention. This structure consists of three parallel substrate-integrated coaxial cable 1-to-8 power dividers. The simulation results for the reflection coefficient and transmission coefficient are as follows: Figure 13 As shown in Figure (b). The results show that the reflection coefficient is consistently lower than [value missing] within the operating frequency band. The insertion loss is in the range of 0.5 dB to 1.5 dB.

[0076] Reference Figure 14Figure (a) shows the coplanar waveguide-to-substrate integrated coaxial line transition structure. This structure achieves broadband transmission characteristics by etching the top metal layer to form the coplanar waveguide and using vertical blind vias to transfer energy to the substrate integrated coaxial line feeder in the middle layer. The simulated transmission coefficient and reflection coefficient are shown below. Figure 14 As shown in Figure (b), the results indicate that the reflection coefficient is consistently lower than 15-55 GHz in the frequency range. The insertion loss is less than 0.75 dB.

[0077] Reference Figure 15 This describes the overall structure of the antenna element and the 1×8 array. For ease of assembly, extensions are added along the x-axis on both sides of the structure, each equipped with mechanical holes. Including the extensions, the antenna element size increases from 14.5 mm * 8.2 mm to 14.5 mm * 20 mm. Similarly, the overall size of the 1×8 array increases from 21.9 mm * 59.3 mm to 21.9 mm * 83 mm. Furthermore, mechanical holes are provided on both sides of the substrate-integrated coaxial feed line to secure the coaxial adapter. The final fabricated antenna element and 1×8 array prototype are shown below. Figure 15 As shown in Figure (b).

[0078] Reference Figure 16 This section compares the simulated and measured reflection coefficients of the antenna element and the 1×8 array. For the antenna element, the simulated results show... The impedance bandwidth is 17.03 GHz - 51.99 GHz, with a relative bandwidth of 100.1%; while the measured... The impedance bandwidth ranges from 17.5 GHz to 55 GHz, with a relative bandwidth of 103.4%. For a 1×8 antenna array, the simulated... The impedance bandwidth is 15.84 GHz - 49.15 GHz, with a relative bandwidth of 102.5%; while the measured bandwidth range is 16.1 GHz - 48.7 GHz, with a relative bandwidth of 100.6%. It can be seen that the simulation and measured results show a generally consistent trend, but slight differences still exist. These differences are mainly attributed to the mechanical assembly process, i.e., when screws are used to fix the multilayer substrate, tiny air gaps inevitably occur between the layers.

[0079] Reference Figure 17This section compares the simulated and measured gain curves for the antenna element and the 1×8 array. For the antenna element, the simulated gain curve ranges from 4.44 dBi to 10.88 dBi within the operating frequency band, while the measured gain ranges from 4.74 dBi to 10.95 dBi. Due to limitations of the test equipment, the measured gain curve range is 16 GHz - 50 GHz. Overall, the measured results agree well with the simulated results, but there are slight deviations in some frequency bands. These deviations mainly stem from radiation pattern distortion caused by ground effects, which in turn leads to differences in gain. For the 1×8 antenna array, the measured and simulated results agree even better, with the simulated gain range being 10.41 dBi - 18.58 dBi and the measured gain range being 10.64 dBi - 17.83 dBi.

[0080] Reference Figure 18 and Figure 19 A comparison of simulated and measured normalized radiation patterns for the antenna element in the E-plane and H-plane at 17 GHz, 20 GHz, 25 GHz, 30 GHz, 35 GHz, 40 GHz, 45 GHz, and 50 GHz is presented. It can be observed that in the E-plane, the radiation pattern exhibits a certain degree of distortion due to the influence of the ground plane, and this distortion is more pronounced due to the asymmetric feeding structure. In contrast, the perfectly symmetrical H-plane is almost unaffected.

[0081] Reference Figure 20 and Figure 21 A comparison of simulated and measured normalized radiation patterns of a 1×8 array in the E-plane and H-plane at 16 GHz, 20 GHz, 25 GHz, 30 GHz, 35 GHz, 40 GHz, 45 GHz and 50 GHz is presented. It can be observed that due to the higher directivity and radiation gain of the array, the influence of the ground effect is significantly reduced, resulting in good agreement between the simulated and measured results on the two planes.

[0082] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on stacked metasurfaces, characterized in that: The system includes an ultra-wideband feed network (1) based on a substrate-integrated coaxial line structure, a stacked metasurface structure (2) serving as the radiating aperture, and an equivalent circuit model (3) for the antenna element. The ultra-wideband feed network (1) based on the substrate-integrated coaxial line structure consists of a first dielectric substrate (4), a first metal structure (9) printed on the bottom of the first dielectric substrate (4), an adhesive layer (5), a second dielectric substrate (6), a second metal structure (10) printed on the bottom of the second dielectric substrate (6), a third metal structure (11) printed on the top of the second dielectric substrate (6), and distributed on the second dielectric substrate. The metal blind vias (12) on the substrate (6) and the metal through-holes (13) distributed on the first dielectric substrate (4), the adhesive layer (5), and the second dielectric substrate (6) constitute the stacked metasurface structure (2); the stacked metasurface structure (2) is composed of a third dielectric substrate (7), a fourth metal structure (14) printed on the top of the third dielectric substrate (7), a fourth dielectric substrate (8), and a fifth metal structure (15) printed on the top of the fourth dielectric substrate (8); wherein the third metal structure (11) is etched with a U-shaped slot (16) and eight butterfly slots (17); the fourth metal structure (14) is etched with a U-shaped slot (16) and eight butterfly slots (17); the fourth metal structure (15) is etched with a U-shaped slot (16) and eight butterfly slots (17); the fourth metal structure (16) is etched with a U-shaped slot (17) and a butterfly slot (18) and a butterfly slot (19) and a butterfly slot (10) and a butterfly slot (11) and a butterfly slot (12) and a butterfly slot (13) and a butterfly slot (14) and a butterfly slot (15) and a butterfly slot (16) and a butterfly slot (17) and a butterfly slot (19 ...9) and a butterfly slot (12) and a butterfly slot (19) and a butterfly slot (12) and a butterfly slot (19) and a butterfly slot (12) and a butterfly slot (19) and a butterfly 4) It consists of eight 3×3 metasurface arrays (18) and a first spacer (19), with a gap between adjacent 3×3 metasurface arrays (18); the fifth metal structure (15) consists of eight 4×4 metasurface arrays (20) and a second spacer (21), with a gap between adjacent 4×4 metasurface arrays (20); the first dielectric substrate (4), adhesive layer (5), second dielectric substrate (6), third dielectric substrate (7), fourth dielectric substrate (8), first metal structure (9), third metal structure (11), first spacer (19) and second spacer (21) are all open on both sides. There are 8 first mechanical holes (22) to facilitate mechanical assembly; 2 second mechanical holes (23) are opened on the first dielectric substrate (4), adhesive layer (5), second dielectric substrate (6), first metal structure (9) and third metal structure (11); the equivalent circuit model (3) of the antenna unit is composed of port model (24), transmission line extension equivalent model (25), cavity model (26), slot model (27), transformer model (28) to represent coupling effect, 3×3 metasurface equivalent model (29) and 4×4 metasurface equivalent model (30).

2. The millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on stacked metasurfaces according to claim 1, characterized in that: The ultra-wideband power supply network (1) based on the substrate integrated coaxial cable structure adopts a multi-layer structure in space. Its spatial layout includes a first dielectric substrate (4), an adhesive layer (5) and a second dielectric substrate (6) from bottom to top. The three are attached to each other and stacked in the vertical direction. The adhesive layer (5) is disposed between the first dielectric substrate (4) and the second dielectric substrate (6) to realize the fixed connection between the two. Metal blind holes (12) are distributed inside the second dielectric substrate (6) to realize the electrical connection between the metal structure (10) and the metal structure (11). Metal through holes (13) penetrate the first dielectric substrate (4), the adhesive layer (5) and the second dielectric substrate (6) in the vertical direction to realize the electrical connection between the metal structures in different layers.

3. The millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on stacked metasurfaces according to claim 1, characterized in that: The stacked metasurface structure (2) adopts a multi-layer structure in space, and its spatial layout from bottom to top is as follows: a third dielectric substrate (7), a 3×3 metasurface array (18) printed on the top of the third dielectric substrate (7), a fourth dielectric substrate (8), and a 4×4 metasurface array (20) on the top of the fourth dielectric substrate (8), forming a multi-layer dielectric and metasurface combination structure stacked on top of each other.

4. The millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on stacked metasurfaces according to claim 1, characterized in that: The equivalent circuit model (3) of the antenna unit is connected in parallel along the signal transmission path as follows: the port model (24) and the equivalent model (25) of the transmission line extension are connected in parallel. The parallel structure is then connected in parallel with the series structure composed of the cavity model (26) and the slot model (27). The slot model (27) is connected in parallel with the transformer model (28) used to characterize the coupling effect, and then connected in parallel with the 3×3 metasurface equivalent model (29). On this basis, it is connected in parallel with the 4×4 metasurface equivalent model (30) to form an overall equivalent circuit.

5. The millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on stacked metasurfaces according to claim 1, characterized in that: The first dielectric substrate (4) is made of Rogers 5880 and has dimensions of 83mm * 21.9mm * 0.381mm; the adhesive layer (5) is made of Rogers 4450F and has dimensions of 83mm * 21.9mm * 0.1mm; the second dielectric substrate (6) is made of Rogers 5880 and has dimensions of 83mm * 21.9mm * 0.381mm; the third dielectric substrate (7) is made of Rogers 5880 and has dimensions of 83mm * 21.9mm * 1.016mm; a cuboid cutout area with dimensions of 61.3mm * 14.8mm * 1.016mm is formed at the edge of the third dielectric substrate (7); the fourth dielectric substrate (8) is made of Rogers 5880 and has dimensions of 83mm * 21.9mm * 0.1mm. 1.575 mm; A cuboid hollow area with dimensions of 61.3 mm * 14.8 mm * 1.575 mm is formed at the edge of the fourth dielectric substrate (8).

6. The millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on stacked metasurfaces according to claim 1, characterized in that: The first metal structure (9), the second metal structure (10), the third metal structure (11), the fourth metal structure (14), and the fifth metal structure (15) are all made of copper with a thickness of 0.035 mm. The first metal structure (9) has dimensions of 83 mm * 21.9 mm * 0.035 mm. The second metal structure (10) is a signal line of a substrate integrated coaxial line, which is composed of a three-level parallel structure and is used to realize the transmission and distribution of radio frequency signals. The third metal structure (11) is etched with a U-shaped slot (16) and eight butterfly slots (17) to realize interlayer transmission. The metal blind hole (12) has a diameter of 0.3 mm and a height of 0.381 mm. The metal through hole (13) has a diameter of 0.3 mm and a height of 0.862 mm, and the spacing between adjacent metal through holes (13) is 0.6 mm.

7. The millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on stacked metasurfaces according to claim 1, characterized in that: After the third metal structure (11) is etched with a U-shaped slot (16), it together with the metal blind hole (12) forms a coplanar waveguide conversion substrate integrated coaxial line feeding and transfer structure.

8. The millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on stacked metasurfaces according to claim 1, characterized in that: The butterfly-shaped slot (17) has a left-right symmetrical structure. The width of its central narrow part is 0.3 mm, the width of the two sides of the unfolded end is 1.78 mm, the total length of the slot is 6.35 mm, and the distance between adjacent butterfly-shaped slots (17) is 7.3 mm.

9. The millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on stacked metasurfaces according to claim 1, characterized in that: The 3×3 metasurface array (18) has a size of 1.2mm * 1.2mm, the distance between adjacent units is 0.1mm, and the distance between adjacent 3×3 metasurface arrays (18) is 7.3mm; the first gasket (19) has a size of 11mm * 21.9mm; The 4×4 metasurface array (20) has a size of 0.68mm * 0.68mm, the distance between adjacent units is 0.73mm, and the distance between adjacent 4×4 metasurface arrays (20) is 7.3mm; the second gasket (21) has a size of 11mm * 21.9mm; The first mechanical hole (22) has a diameter of 2 mm and a spacing of 5 mm; the second mechanical hole (23) has a diameter of 2.2 mm and a spacing of 9.525 mm.

10. The millimeter-wave ultrawideband substrate-integrated coaxial antenna array based on stacked metasurfaces according to claim 1, characterized in that: The characteristic impedance of the port model (24) is 35Ω; The equivalent model (25) of the transmission line extension is composed of the first resistor R. s First inductor L s1 First capacitor C s1 It consists of three parts connected in parallel, with the first resistor R S = 60.3Ω, first inductor L S1 = 0.28nH, first capacitor C S1 = 0.1pF; The cavity model (26) consists of a second resistor R C Second inductor L C Second capacitor C C It consists of three parts connected in parallel, with the second resistor R C = 50.1Ω, second inductor L C = 0.28nH, second capacitor C C = 0.13pF; The gap model (27) is composed of a third inductor L S2 Fourth inductor L S3 Third capacitor C S2 A π-type network is formed, in which the third inductor L S2 = 0.23nH, fourth inductor L S3 = 4.5nH, third capacitor C S2 = 0.15pF; The transformer model (28) used to represent the coupling effect has a coupling coefficient of N = 0.26; The 3×3 metasurface equivalent model (29) consists of three sets of LC resonators connected in parallel, with the two edge sets having the same circuit parameters, the values ​​of which are respectively the fifth inductor L m1 = 1.3nH, fourth capacitor C m1 = 1.2pF, Sixth Inductor L m2 = 0.03nH, Fifth capacitor C m2 = 0.96pF; The 4×4 metasurface equivalent model (30) consists of four sets of LC resonators connected in parallel, wherein the circuit parameters are symmetrical along the center, and their values ​​are respectively the seventh inductor L m3 = 0.64nH, sixth capacitor C m3 = 0.12pF, eighth inductor L m4 = 0.06nH and the seventh capacitor C m4 = 0.04pF.

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