A broadband high-efficiency leaky-wave antenna design method and structure based on a low-loss anti-resonance hollow waveguide

Abstract

The application discloses a kind of based on low-loss anti-resonance hollow waveguide broadband high-efficiency leaky-wave antenna design method and structure, its technical scheme includes: first based on anti-resonance principle design single dielectric wall hollow waveguide;Further introduce second dielectric wall optimization form double dielectric wall anti-resonance hollow waveguide, significantly enhance the transverse restraint to electromagnetic energy in air cavity by cascading reflection effect, realize super low loss transmission;Finally, etching periodic radiation slot in the upper layer metal plate of double dielectric wall hollow waveguide, construct leaky-wave antenna with frequency scanning function.The application uses air as main transmission medium, fundamentally reduces dielectric loss, so that the antenna has ultra-low transmission loss and ultra-high radiation efficiency in wide frequency band, while the structure is simple, process compatibility is strong, only through standard PCB process can be realized, can be widely used in 5G / 6G communication, millimeter wave radar, terahertz imaging and other high-performance wireless systems.

Description

Technical Field

[0001] This invention relates to the field of microwave and millimeter-wave antenna technology, specifically to a design method and structure for a broadband high-efficiency leaky wave antenna based on a low-loss anti-resonant hollow waveguide. Background Technology

[0002] With the rapid development of fifth-generation (5G) and future sixth-generation (6G) mobile communication, millimeter-wave radar, terahertz imaging and other technologies, the operating frequency of radio frequency front-ends is constantly climbing to the millimeter-wave and even terahertz bands. As the core components of the system, waveguides and antennas need to simultaneously meet the requirements of low transmission loss, wide operating bandwidth, lightweight structure and flexible beam control capability, which poses a severe challenge to traditional waveguide structures.

[0003] In the microwave and millimeter-wave bands, metallic waveguides (such as rectangular and circular waveguides) can achieve low transmission loss and high power capacity due to the strong confinement of electromagnetic waves by their metal walls. However, traditional metallic waveguide structures are bulky and cumbersome, making them difficult to adapt to the miniaturization, lightweighting, and planar integration requirements of modern radio frequency front-ends, thus limiting their application in space-constrained scenarios such as airborne and spaceborne applications.

[0004] In order to overcome the integration problem of metal waveguides, various planar transmission lines have emerged, such as microstrip lines, coplanar waveguides (CPWs) and substrate integrated waveguides (SIWs). Among them, SIWs replace the sidewalls of traditional rectangular waveguides by fabricating two rows of metallized vias on a dielectric substrate, realizing a quasi-planar waveguide structure. It has the advantages of low profile, easy processing and easy integration with planar circuits, and is widely used in leaky antenna design. However, such planar structures face severe dielectric loss problems at high frequencies. Taking SIW as an example, its electromagnetic energy is mainly concentrated in the dielectric substrate, and the dielectric loss (tanδ) of the substrate increases significantly with increasing frequency. Reference [1] provides a detailed theoretical analysis and experimental verification of the loss of SIWs. In the Ka-band, the simulated transmission loss for a Rogers 6002 substrate with a height of 0.508 mm (εr = 2.94, tanδ≈ 0.0012) is approximately 0.15–0.2 dB / cm, while for a Rogers 5880 substrate with a height of 0.508 mm (εr = 2.2, tanδ≈ 0.0009), the simulated transmission loss is approximately 0.1–0.15 dB / cm. In the U-band, the simulated transmission losses increase to 0.2–0.25 dB / cm and 0.15–0.2 dB / cm, respectively. This inherent loss severely degrades the system link budget, limiting the application of planar transmission lines in high-performance millimeter-wave systems.

[0005] Leaky-wave antennas (LWAs), as a type of traveling wave antenna, convert guided waves into radiated waves by introducing periodic or uniform discontinuities along the waveguide structure, thereby achieving radiation characteristics such as frequency scanning. Planar transmission line-based leaky-wave antennas, such as SIW leaky-wave antennas, have attracted considerable attention due to their simple structure, ease of integration, and ability to achieve wide-angle beam scanning. A typical SIW leaky-wave antenna usually has periodic slots etched on the upper metal surface, achieving continuous scanning from back to front using the fundamental frequency or the -1st spatial harmonic. However, as mentioned earlier, the dielectric loss of SIWs increases sharply at high frequencies. This loss not only reduces antenna efficiency but also makes it difficult to improve antenna gain.

[0006] The anti-resonant effect was first proposed in the field of optics and successfully applied to low-loss optical waveguides. In 1986, Duguay and Kokubun et al. proposed the concept of anti-resonant reflecting optical waveguide (ARROW), which uses a Fabry-Perot resonator composed of high and low refractive index dielectric layers to confine the light field to the low refractive index core layer through the principle of interference destructive, thereby significantly reducing transmission loss[2]. Since then, structures such as photonic crystal fiber and terahertz waveguide based on the anti-resonant effect have been widely studied, confirming their great potential in broadband low-loss transmission. At present, there are no public reports of the successful application of this type of waveguide to leaky antenna design, especially in the research of broadband high-efficiency beam scanning antennas.

[0007] The most common leaky wave antenna scheme is the periodic slot antenna based on SIW. The typical structure of this type of antenna includes upper and lower metal layers, a dielectric substrate, SIW sidewalls composed of two rows of metallized vias, and periodic transverse slots etched on the upper metal surface. For example, the SIWLWA proposed in reference [3] uses SIW to transmit the TE10 mode and excites fast wave radiation through the periodic slots to achieve frequency scanning. However, the operating bandwidth of this type of antenna is limited by the single-mode bandwidth of SIW, and the radiation efficiency is limited by the high-frequency loss of the dielectric substrate. As mentioned above, the transmission loss is large in the millimeter wave band, which leads to the radiation efficiency of leaky wave antennas based on this being limited to between 72% and 95%, which is difficult to meet the stringent requirements of high gain and high efficiency for millimeter wave long-distance communication.

[0008] To overcome dielectric loss, the most similar solution to the present invention is to propose a leaky antenna based on an air-filled planar transmission line design. The core idea is to hollow out the dielectric in the energy transmission channel and use air as the main transmission medium, thereby significantly reducing transmission loss while retaining the planar configuration. Currently, typical air-filled waveguide structures include: substrate integrated slab waveguide (SISW)[4], air-filled substrate integrated waveguide (SIW)[5], air-filled substrate integrated coaxial line (SICL)[6], and substrate integrated suspension line (SISL)[7].

[0009] However, the aforementioned air-filled structures generally suffer from the following limitations: they typically require precise alignment and lamination processes on multilayer dielectric substrates to form a closed air cavity, resulting in a relatively cumbersome manufacturing process with high precision requirements. Furthermore, the interconnection transition structures between the multilayer dielectrics are complex, increasing design difficulty and manufacturing costs to some extent. In addition, publicly reported research on how to extend these low-loss hollow transmission lines to the field of beam-scanning antennas remains relatively limited.

[0010] Based on the most similar existing technical solution mentioned above, the main disadvantages are as follows: (1) High dielectric loss limits the radiation efficiency of leaky antennas: Existing leaky antennas based on dielectric-filled planar transmission lines (such as SIW) mainly concentrate their electromagnetic energy in the dielectric substrate. In the millimeter-wave band, dielectric loss increases sharply, which generally limits the radiation efficiency of the antenna. This inherent defect severely restricts the system link budget and cannot meet the requirements of millimeter-wave long-distance communication for high-efficiency and high-gain antennas.

[0011] (2) Existing air-filled structures have complex processes and high manufacturing costs: Although existing air-filled planar transmission lines (such as air-filled SIW, SICL, SISL, etc.) can reduce dielectric loss, their implementation usually relies on the precise alignment and lamination process of multilayer dielectric substrates, which requires the formation of a closed air cavity. This multilayer composite structure has high requirements for processing accuracy and a complicated process flow, resulting in increased manufacturing costs and decreased yield, which is not conducive to large-scale promotion and application and low-cost integration with standard planar circuits. Moreover, there are few publicly reported studies on the extended application of the above-mentioned low-loss hollow transmission lines in the field of beam scanning antennas, and related technical solutions still need to be explored. Summary of the Invention

[0012] In view of the shortcomings of the prior art, the present invention aims to address the following: (1) A high-efficiency leaky antenna based on air transmission is provided: It aims to fundamentally overcome the high-frequency dielectric loss problem of dielectric-filled planar transmission lines, use air as the main transmission medium, and combine anti-resonance effect to achieve efficient confinement of electromagnetic energy, so that the leaky antenna can achieve a radiation efficiency of more than 90% in the millimeter-wave broadband, which is significantly better than the existing planar leaky antenna scheme.

[0013] (2) A low-cost antenna solution with simplified structure and compatible process is provided: It aims to get rid of the dependence of existing air-filled structures on multi-layer precision lamination process, adopts a double dielectric wall structure, and can be realized by single-layer standard PCB process, which greatly simplifies the production process, reduces manufacturing costs, and improves the integration capability with planar circuits.

[0014] (3) The first realization of the function extension of the leaky wave antenna of the anti-resonant hollow waveguide: It aims to extend the anti-resonant effect from simple waveguide transmission to the design of radiating devices. By introducing a periodic slot radiation structure on the double dielectric wall anti-resonant hollow waveguide, a leaky wave antenna with frequency scanning function was successfully constructed, filling the technical gap of this type of new waveguide structure in the field of antenna application.

[0015] (4) A broadband, low-loss leaky antenna operating platform is provided: This platform aims to enhance the confinement of the transverse electromagnetic field through the cascaded anti-resonance effect of the double dielectric walls, achieving stable low transmission loss (0.0034 dB / mm) over a wide bandwidth (relative bandwidth > 50%), thus providing an ideal waveguide foundation for the realization of high-performance beam-scanning antennas. To achieve the above objectives, the technical solution adopted by this invention is as follows: Firstly, a broadband high-efficiency leaky antenna design method based on a low-loss anti-resonant hollow waveguide includes the following steps: S1. Design of a single-dielectric-walled anti-resonant hollow waveguide: Based on the principle of anti-resonance reflection, a single-dielectric-walled hollow waveguide is constructed, consisting of a parallel metal plate and a high-dielectric-constant dielectric wall. S2. Optimized design of double dielectric wall anti-resonant hollow waveguide: Based on the single dielectric wall structure of S1, a second dielectric wall is introduced to construct a double dielectric wall hollow waveguide; S3. Leakage antenna design based on double dielectric wall hollow waveguide: Based on the double dielectric wall hollow waveguide optimized in S2, a periodic rectangular slot array is introduced into the upper metal plate.

[0016] Furthermore, S1 further includes: determining the relationship between the dielectric wall thickness and the working wavelength through theoretical derivation, selecting a suitable dielectric material and air cavity width, realizing low-loss transmission in the fundamental mode anti-resonance state, and verifying its transmission characteristics and field confinement capability.

[0017] Furthermore, the method for determining the thickness of the medium wall is as follows: The high dielectric constant dielectric wall is considered as a transverse Fabry-Perot resonant cavity; by reasonably designing the dielectric wall thickness t1, the phase delay generated by the electromagnetic wave traveling back and forth once inside the dielectric wall is reduced. Satisfying the anti-resonance condition: ; Where, k yd Let be the transverse wavenumber in the dielectric wall, and a (a = 1, 2, 3, …) be the anti-resonance order; in this case, the dielectric wall can achieve strong field confinement. Conversely, when the phase delay satisfies the resonance condition, the dielectric wall exhibits high transmission and significant energy leakage. Therefore, the relationship between the optimal dielectric wall thickness ta and the operating wavelength λ0 is: ; Where λ0 is the wavelength at the center of free space, ε r is the relative permittivity of the dielectric wall.

[0018] Furthermore, S2 further includes: By optimizing the air gap between the two walls and maintaining the uniformity of the wall thickness of each layer, the reflected waves from the multi-layer interface are superimposed in phase, which further enhances the transverse field confinement, reduces transmission loss, and widens the effective working bandwidth.

[0019] Furthermore, S3 further includes: Based on the theory of leaky wave antennas, the slot period is set to control the correspondence between the beam scanning angle and the frequency, and the slot size is optimized to achieve high radiation efficiency.

[0020] Furthermore, the method for setting the correspondence is as follows: Appropriate selection of gap period p s This ensures that only the fundamental wave is radiated, while other higher spatial harmonics are in a slow wave state, thereby ensuring a pure single-beam scan within the operating frequency band. The relationship between the radiation angle θ (measured from the side direction) and the free space wavenumber k0 is as follows: ; Where β is the phase constant of the fundamental mode.

[0021] Secondly, a broadband high-efficiency leaky antenna structure based on a low-loss anti-resonant hollow waveguide is provided, comprising: The upper metal plate has periodically arranged radial slots etched on it; The lower metal plate is arranged parallel to the upper metal plate. An intermediate dielectric wall layer is disposed between an upper metal plate and a lower metal plate, and includes at least one pair of high dielectric constant dielectric walls extending longitudinally. The dielectric walls and the upper and lower metal plates together form an air cavity, which serves as the main transmission channel for electromagnetic waves. The dielectric wall includes a first dielectric wall and a second dielectric wall, with an air gap between them to form a double dielectric wall anti-resonant structure, which is used to confine electromagnetic energy within the air cavity to achieve low-loss transmission.

[0022] Furthermore, the first and second dielectric walls have equal thicknesses and satisfy the anti-resonance condition to achieve high reflection and confinement of transverse electromagnetic waves.

[0023] Furthermore, the radiation slots are rectangular slots, arranged at equal intervals along the longitudinal direction, and the slot period, slot length and width are optimized to achieve high radiation efficiency and impedance matching over a wide frequency band.

[0024] Furthermore, the antenna is provided with a feed port and a matching load port at both ends. The feed port adopts a coaxial probe coupling structure, with the probe extending into the air cavity to realize the conversion from coaxial mode to hollow waveguide mode.

[0025] The beneficial effects of this invention are: (1) Double dielectric wall anti-resonant hollow waveguide structure: a quasi-planar hollow waveguide composed of parallel metal plates and double high dielectric constant dielectric walls. The first and second dielectric walls are separated by an air gap to form a cascaded anti-resonant reflection cavity. By utilizing the in-phase superposition effect of multi-layer interface reflected waves, the transverse binding ability of electromagnetic energy in the air cavity is significantly enhanced, realizing ultra-low loss transmission.

[0026] (2) Engineering design method for anti-resonance condition: Based on the transverse Fabry-Perot resonance model, the thickness of the dielectric wall is precisely designed using formulas to satisfy the first-order anti-resonance condition (a = 1), thereby achieving high impedance reflection characteristics of the dielectric wall in the target frequency band. This method extends the optical anti-resonance principle to the design of waveguide structures in the microwave and millimeter-wave frequency bands, providing a theoretical basis for the engineering design of this type of hollow waveguide.

[0027] (3) Implementation of a periodic leaky wave antenna based on the novel low-loss hollow waveguide: A periodic rectangular slot array is introduced into the upper metal plate of the double dielectric wall anti-resonant hollow waveguide, and frequency scanning radiation performance is achieved by utilizing the fundamental wave radiation of the fundamental mode (quasi-TEM mode). This design is the first to propose an anti-resonant hollow waveguide and extends it from a simple waveguide structure to a radiating device, filling the technological gap of this type of novel hollow waveguide structure in the field of antenna applications.

[0028] (4) Integrated low-loss radiation structure: The low-loss waveguide structure and the periodic radiation structure are integrated into the same planar configuration. Air is used as the main transmission medium to fundamentally and significantly reduce the dielectric loss. At the same time, efficient radiation is achieved through periodic gaps, so that the antenna has excellent performance of ultra-low transmission loss (0.0034 dB / mm) and ultra-high radiation efficiency (>94%) in a wide frequency band.

[0029] (5) Quasi-planar process compatible structure: The dielectric layer in this invention adopts a solution based entirely on standard PCB process, without the need for multi-layer dielectric precision lamination or metallized through-hole array. The entire antenna can be manufactured by conventional dielectric board processing and metal plate etching, which greatly simplifies the process flow, reduces manufacturing costs, and improves the integration capability with planar RF front-end circuits. Attached Figure Description

[0030] The present invention includes the following figures: Figure 1 The flowchart illustrates the steps of the leaky antenna design method of this invention. The flowchart shows three core steps: S1 single-walled anti-resonant hollow waveguide design, S2 double-walled anti-resonant hollow waveguide optimization design, and S3 leaky antenna design based on double-walled hollow waveguide.

[0031] Figure 2 This is a three-dimensional exploded view of the leaky antenna of the present invention. The figure shows the upper metal plate, the middle dielectric wall layer, the lower metal plate, the radiation slot, the air cavity, the feed port, and the matching load port. The dielectric wall layer consists of two dielectric walls, forming a longitudinally extending air transmission channel.

[0032] Figure 3 : Schematic diagram of the antenna's cross-sectional structure. The diagram shows the geometric dimensions of each part, the arrangement of periodic slots along the propagation direction, the slot period, slot length, slot width, and the total length of the antenna.

[0033] Figure 4 : Schematic diagram of the anti-resonance effect. Includes a magnified view of a partial cross-section of a single-sided dielectric wall, labeled with the incident wave, reflected wave, and transmitted wave, as well as the equivalent transverse transmission line model, used to derive the anti-resonance condition.

[0034] Figure 5 : A magnified side view of the antenna feed port. The figure shows the coaxial probe feed structure and the transition matching region.

[0035] Figure 6The figure shows the simulation results of the transmission loss of the double-dielectric-walled antiresonant hollow waveguide. The horizontal axis represents frequency (GHz), and the vertical axis represents transmission loss (dB / mm). The curve shows that the average transmission loss of the waveguide is approximately 0.0034 dB / mm in the frequency range of 16.39 GHz to 26.92 GHz, verifying the excellent low-loss transmission characteristics of the double-dielectric-walled structure.

[0036] Figure 7 The figure shows the simulation results of the electric field distribution in the double-dielectric-walled anti-resonant hollow waveguide of this invention. The figure includes schematic diagrams of the electric field z-component distribution at two frequency points: 21 GHz and 24 GHz. The figure clearly shows that the electromagnetic energy is tightly confined within the air cavity, and the electric field intensity in the outer region of the dielectric walls is extremely low, verifying the strong field confinement capability of the double-dielectric-walled system.

[0037] Figure 8 The figure shows the simulated S-parameter curves of the leaky-wave antenna of this invention. The horizontal axis represents frequency (GHz), and the vertical axis represents amplitude (dB). The solid line represents |S11| (return loss), and the dashed line represents |S21| (insertion loss). The curves show that in the range of 16 GHz to 27 GHz, |S11| is below -10 dB, indicating that the antenna has good broadband impedance matching characteristics.

[0038] Figure 9 The figure shows the simulation results of the leakage antenna radiation efficiency of this invention. The horizontal axis represents frequency (GHz), and the vertical axis represents efficiency (%). The solid line represents radiation efficiency, and the dashed line represents total efficiency. The curve shows that within the entire 16~27 GHz operating frequency band (relative bandwidth 51.1%), the radiation efficiency is higher than 94%, reaching a maximum of 99%, and the total efficiency is higher than 78%, verifying the antenna's high-efficiency radiation performance.

[0039] Figure 10 Simulation results of the E-plane radiation pattern of the leaky antenna of this invention. The figure shows the beam scanning radiation pattern from 16 GHz to 27 GHz in rectangular coordinates. As the frequency increases from 16 GHz to 27 GHz, the main beam pointing angle smoothly scans from 36° to 64°, achieving a continuous scanning range of 28°, while maintaining the integrity of the main lobe shape and low in-band sidelobe levels. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this application clearer, the following description, in conjunction with specific embodiments and with reference to the appendix, provides further details. Figures 1-10 This application will be described in further detail below.

[0041] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this application should have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and similar terms used in the embodiments of this application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are only used to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0042] Combined with appendix Figures 1-10 This specific embodiment provides a design method and structure for a broadband high-efficiency leaky wave antenna based on a low-loss anti-resonant hollow waveguide. The core structure, working principle, and design method of this antenna will be described in detail below.

[0043] (1) Overall design methodology and technical solution Reference Figure 1 The flowchart shown in this invention illustrates a design method for a broadband high-efficiency leaky antenna based on a low-loss anti-resonant hollow waveguide, comprising the following design steps: S1. Design of a Single-Dielectric-Wall Anti-Resonant Hollow Waveguide: Based on the principle of anti-resonance reflection, a hollow waveguide consisting of a parallel metal plate and a high-dielectric-constant dielectric wall is constructed. The relationship between the dielectric wall thickness t and the operating wavelength is determined through theoretical derivation. A suitable dielectric material (such as Rogers RO3010) and an air cavity width wa (≈ λ0) are selected to achieve low-loss transmission in the fundamental mode anti-resonance state, and its transmission characteristics and field confinement capability are verified.

[0044] S2. Optimized Design of Double-Dielectric-Wall Anti-Resonant Hollow Waveguide: Based on the single-dielectric-wall structure of S1, a second dielectric wall is introduced to construct a double-dielectric-wall hollow waveguide. By optimizing the air gap g between the two walls (g = 2.8 mm in this embodiment) and maintaining the same wall thickness for each layer (t1 = t2 = 1.2 mm), the reflected waves from the multi-layer interfaces are superimposed in phase, further enhancing the transverse field confinement, reducing the average in-band transmission loss to 0.0034 dB / mm, and simultaneously widening the effective operating bandwidth.

[0045] S3. Leaky Wave Antenna Design Based on Double-Dielectric-Wall Hollow Waveguide: Based on the low-loss double-dielectric-wall hollow waveguide optimized in S2, a periodic rectangular slot array is introduced into the upper metal plate. According to leaky wave antenna theory, the slot period ps is set to control the correspondence between the beam scanning angle and frequency, and the slot size is optimized to achieve high radiation efficiency. Finally, a broadband high-efficiency leaky wave antenna with a 28° beam scanning and a radiation efficiency >94% in the 16~27 GHz frequency band is obtained.

[0046] (2) Overall antenna structure Figure 2 This is a three-dimensional exploded view of the leaky wave antenna in this embodiment. As shown, the antenna mainly consists of three layers: an upper metal plate, a middle dielectric wall layer, and a lower metal plate. The upper metal plate is etched with periodically arranged radiating slots; the middle dielectric wall layer contains two center-aligned high-dielectric-constant dielectric walls, each consisting of a first dielectric wall and a second dielectric wall forming a double-wall structure; the upper and lower metal plates and the dielectric walls together form a longitudinally extending air cavity, serving as the main transmission channel for electromagnetic waves. The antenna has a symmetrical structure, extending longitudinally (x-direction), with feed ports and matching load ports (used to connect matching loads to achieve traveling wave operation) at both ends. The thickness of both the upper and lower metal plates is 0.5 mm, typically using good conductors such as brass, with a thickness much greater than the skin depth to ensure low conductor loss. The height of the middle dielectric wall layer is h, determined by the spacing between the upper and lower metal plates. It should be clarified that the terms "single dielectric wall" and "double dielectric wall" used in this invention are defined based on one side of the waveguide structure's axis of symmetry. Among them, a single dielectric wall refers to a waveguide structure that has only a first dielectric wall, while a double dielectric wall refers to a waveguide structure that has both a first dielectric wall and a second dielectric wall.

[0047] Figure 3This is a top view of the antenna in this embodiment, including structural diagrams with and without an upper metal plate. The figure clearly shows the geometric relationships and dimensions of each part: the figure shows a periodic slot structure along the propagation direction (x-direction). The radiating slots are rectangular and arranged at equal intervals of periodic ps (ps = 5 mm in this embodiment) along the longitudinal direction of the upper metal plate. The slot length ls and width ws are optimized to achieve good radiation efficiency and impedance matching. In addition, the thicknesses of the first and second dielectric walls are t1 and t2, respectively (which can be independently optimized according to design needs; in this embodiment, they are taken as equal values, t1 = t2 = 1.2 mm), and the spacing between the two rows of dielectric walls is the air cavity width wa (wa = 14.5 mm in this embodiment). The air gap width between the first and second dielectric walls is g (g = 2.8 mm in this embodiment). All dielectric walls are made of Rogers RO3010 high dielectric constant, low loss material (relative dielectric constant εr = 11.2, loss tangent tanδ = 0.0022), and its thickness and dielectric constant together determine the anti-resonant operating frequency band.

[0048] (3) Functions and implementation principles of key components 3.1 Field confinement mechanism of antiresonant hollow waveguide Before delving into the field confinement mechanism of this invention, it is necessary to first clarify the essential difference in waveguide principle between the anti-resonant hollow waveguide proposed in this invention and the traditional dielectric ridge parallel plate waveguide (DRPW) to avoid conceptual confusion. From a structural perspective, the two do share some similarities: both use parallel metal plates at the top and bottom to provide vertical electric wall confinement, with a dielectric layer in between. However, the role of the dielectric layer and the corresponding waveguide mechanism are drastically different: the dielectric ridge of a traditional DRPW does not require a high relative permittivity; electromagnetic waves propagate within and around the dielectric ridge, which itself is the primary transmission channel. The anti-resonant hollow waveguide proposed in this invention is based on a completely different anti-resonance mechanism. In this waveguide, the high-dielectric-constant dielectric wall is not a transmission channel but rather serves as a lateral boundary. By precisely designing the dielectric wall thickness, it suppresses lateral leakage waves, thereby confining electromagnetic energy within the air cavity enclosed by the dielectric wall for transmission. In this structure, the primary transmission medium is air, and the dielectric wall only acts as a boundary, without confining or guiding electromagnetic waves. Based on this fundamental difference, the present invention can achieve low-loss transmission performance in the millimeter-wave band that is unattainable by traditional dielectric ridge structures, laying the foundation for the design of subsequent high-performance leaky wave antennas.

[0049] The waveguide structure of this invention is essentially a hollow waveguide based on the anti-resonance effect. Its working principle can be derived from... Figure 4 The theoretical model of the hollow waveguide with a single dielectric wall is shown below for illustration. Figure 4This is a magnified cross-section of a single-sided dielectric wall and its equivalent transverse transmission line model. When an electromagnetic wave propagates longitudinally (x-direction), its transverse component (y-direction) is reflected and transmitted at the interface between the air cavity and the dielectric wall. The high dielectric constant dielectric wall (ε...) r >>1) This can be considered as a transverse Fabry-Perot resonant cavity. By reasonably designing the dielectric wall thickness t1, the phase delay generated by the electromagnetic wave making one round trip inside the dielectric wall is reduced. Satisfying the anti-resonance condition: ; Where, k yd Let be the transverse wavenumber in the dielectric wall, and 'a' (a = 1, 2, 3, …) be the anti-resonance order. In this case, the dielectric wall can achieve strong field confinement. Conversely, when the phase delay satisfies the resonance condition, the dielectric wall exhibits high transmission, resulting in severe energy leakage. In this embodiment, a first-order anti-resonance (a=1) is selected, so the relationship between the optimal dielectric wall thickness ta and the operating wavelength λ0 is: ; For a center frequency of 22 GHz (λ0 ≈ 13.6 mm) and ε r Using a dielectric material with a thickness of 11.2 mm, theoretical calculations and simulation optimizations show that when the dielectric wall thickness t1 = 1.2 mm, the waveguide can achieve excellent low-loss transmission within the frequency band of interest in this invention.

[0050] To enhance field confinement capability, this invention employs a dual-dielectric-wall structure. For example... Figure 3 As shown, the first and second dielectric walls are separated by an air gap g, forming a cascaded anti-resonant reflective cavity. The reflected waves generated by the multi-layer interfaces are superimposed in phase, further suppressing energy leakage and reducing transmission loss.

[0051] 3.2 Power Supply and Matching Structure To achieve impedance matching from the standard RF coaxial connector to the hollow waveguide, this invention designs a dedicated feed transition structure and impedance matching loop, such as... Figure 5 As shown. Figure 5 This is a partially enlarged side view of the input port of a single dielectric wall waveguide. The feed port uses a 2.92 mm coaxial connector, with its inner conductor (probe) extending into the air cavity to form a probe feed. The top of the probe is flush with the top of the dielectric wall. In this embodiment, the dielectric wall thickness at the port is consistent with that of the main transmission section (t1 = t2 = 1.2 mm).

[0052] 3.3 Periodic Leakage Radiation Structure The radiation mechanism of a leaky-wave antenna is based on fundamental wave radiation. By appropriately selecting the slot period ps, only fundamental wave radiation is emitted, while other higher-order space harmonics are in a slow-wave state, thus ensuring a clean single-beam scan within the operating frequency band. The relationship between the radiation angle θ (measured from the side-firing direction) and the free-space beam k0 is: ; Here, β is the phase constant of the fundamental mode. Therefore, as the frequency increases, β increases, and the radiation angle θ changes continuously, realizing frequency scanning of the beam in the forward region.

[0053] In this embodiment, the slit period ps = 5 mm, enabling continuous forward scanning from 36° to 64° within the 16–27 GHz range. The slit length ls and width ws are optimized to ensure a radiation efficiency >94% within the passband.

[0054] 3.4 Antenna Operation Process Combination Figures 2-10 The working process of the antenna of the present invention is described as follows: Signal Input: The RF signal is input from the feed port and coupled into the air cavity through a coaxial probe. The transition matching region ensures that the signal is efficiently and with low reflection converted into the quasi-TEM fundamental mode of the hollow waveguide.

[0055] Low-loss transmission: Electromagnetic waves propagate longitudinally along the air cavity. Due to the anti-resonance condition satisfied by the double dielectric walls, transversely leaking electromagnetic waves are strongly suppressed, and the energy is tightly confined within the air cavity, resulting in extremely low dielectric loss. The average transmission loss within the operating bandwidth is only 0.0034 dB / mm.

[0056] Periodic radiation: When the guided wave propagates to the periodic slot region, the slot acts as a radiation unit, exciting the fundamental wave radiation.

[0057] Frequency scanning: Since the radiation angle is frequency-dependent, the direction of the main beam changes continuously as the input signal frequency changes. For example, the beam points at 36° at 16 GHz and at 64° at 27 GHz, achieving a scanning range of 28°.

[0058] Residual energy absorption: To suppress terminal reflection, a matching load can be connected to the other end of the antenna to absorb the unradiated residual energy, ensuring traveling wave state and good impedance matching.

[0059] 3.5 Main Design Parameters and Implementation Methods Table 1 shows the key design parameters of a preferred embodiment of the present invention. These parameters were obtained through theoretical calculations combined with full-wave electromagnetic simulation optimization and are suitable for millimeter-wave applications near the center frequency of 22 GHz.

[0060] Table 1 shows the optimized structural parameters of the proposed leaky antenna based on a novel anti-resonant hollow waveguide. ;

[0061] It should be noted that the embodiments of the present invention are not limited to the above parameters, and can be adjusted according to the target operating frequency band, scanning range, gain, and other requirements. For example, the anti-resonance passband can be moved by changing the dielectric wall thickness; the scanning slope can be adjusted by changing the gap period; and the size can be optimized by using materials with different dielectric constants.

[0062] Through the above technical solution, combined with full-wave electromagnetic simulation verification, the present invention achieves the following beneficial effects: (1) Ultra-low transmission loss Thanks to the cascaded anti-resonance effect of the dual dielectric walls, electromagnetic energy is efficiently confined within the air cavity, and lateral leakage is significantly suppressed. For example... Figure 6 The simulation curves of transmission loss for single and double dielectric-walled hollow waveguides show that, within a wide bandwidth from 16.39 GHz to 26.92 GHz, the average in-band transmission loss of the double dielectric-walled structure is only 0.0034 dB / mm. Compared with the single dielectric-walled structure, the loss is significantly reduced; compared with the traditional SIW (loss 0.01~0.03 dB / mm), the loss is reduced by an order of magnitude, fully verifying the superiority of the double dielectric-walled anti-resonant structure established in this invention in low-loss transmission. Figure 7 Simulation results of the electric field z-component (Ez) distribution of the double-dielectric-walled anti-resonant hollow waveguide of this invention at frequencies of 21 GHz and 24 GHz are presented. The figures clearly show that the electromagnetic energy is tightly confined within the air cavity, and the electric field intensity outside the dielectric walls and further out is suppressed to extremely low levels. This indicates that the double dielectric walls effectively suppress lateral leakage, verifying its excellent field confinement capability.

[0063] (2) Wideband impedance matching The antenna designed in this invention exhibits excellent broadband matching characteristics in the millimeter-wave band. For example... Figure 8 The simulated S-parameter curves of the antenna shown indicate that the return loss |S11| is below -10 dB in the frequency range of 16 GHz to 27 GHz. This broadband characteristic stems from two aspects: first, the inherent passband-stopband alternating spectral characteristics of the anti-resonant hollow waveguide, which, through proper design, ensures that the target frequency band is within the low-loss passband; second, the careful optimization of the feed transition matching region ensures a smooth mode transition from the coaxial probe to the hollow waveguide.

[0064] (3) Ultra-high radiation efficiency The simulation results of antenna radiation efficiency are as follows Figure 9As shown, the antenna's radiation efficiency consistently exceeds 94% across the entire 16–27 GHz operating frequency band (51.1% relative bandwidth), reaching a maximum of 99%, with an in-band total efficiency exceeding 78%. This performance is significantly superior to traditional SIW leaky wave antennas, fully demonstrating the substantial reduction in dielectric loss due to air transmission. The high-efficiency radiation characteristics make this antenna particularly suitable for applications with stringent link budget requirements, such as millimeter-wave long-distance communication and high-sensitivity radar detection.

[0065] (4) Stable frequency scanning beam Based on the leakage radiation mechanism of periodic slots, this invention achieves continuous beam scanning over a wide bandwidth. For example... Figure 10 The simulated normalized E-plane radiation pattern of the antenna shows that as the operating frequency increases continuously from 16 GHz to 27 GHz, the main beam pointing angle smoothly scans from 36° to 64°, with a total scanning range of 28°. Throughout the scanning range, the main lobe shape remains intact, and the sidelobe levels, except at the low-frequency edges, are all below -10 dB, indicating that the antenna has good directivity and beam quality. The antenna gain fluctuates between 11.4 dBi and 16.4 dBi.

[0066] (5) Simple structure and low manufacturing cost This invention eliminates the need for multi-layer dielectric precision lamination and metallized via arrays, allowing for processing solely through conventional dielectric substrate cutting / milling and metal plate etching. The upper and lower metal plates can be made of ordinary brass sheets, while the intermediate dielectric wall is fabricated from a high-dielectric-constant material and directly laminated to the metal plates using nylon screws. The process is simple, with low manufacturing costs, high yield, and easy integration with planar RF front-end circuits, demonstrating promising engineering application prospects.

[0067] (6) High design flexibility The technical solution provided by this invention offers a high degree of design freedom. By adjusting the dielectric wall thickness, the position of the anti-resonance passband can be flexibly moved; by changing the number of dielectric walls on one side (single / double / multiple) and the spacing g, the field confinement strength and transmission loss can be controlled; by setting the slot period ps, the beam scanning slope can be changed; and by optimizing the slot size, radiation efficiency and impedance matching can be balanced. This flexibility allows the antenna of this invention to be quickly customized for different application frequency bands and different scanning range requirements.

[0068] In summary, this invention successfully combines the low-loss characteristics of anti-resonant hollow waveguides with the beam scanning function of leaky wave antennas, achieving for the first time a millimeter-wave planar leaky wave antenna that combines ultra-low transmission loss, wideband impedance matching, ultra-high radiation efficiency, and stable beam scanning. This opens up new avenues for the application of this type of novel low-loss waveguide structure in high-performance wireless systems.

[0069] Compared with the closest existing dielectric-filled substrate integrated waveguide (SIW) leaky antenna, the present invention has the following significant advantages: First, this invention fundamentally solves the inherent problems of high dielectric loss and low radiation efficiency in millimeter-wave planar leaky-wave antennas. This invention uses air as the primary transmission medium, efficiently confining electromagnetic energy within an air cavity through the anti-resonance effect of the double dielectric walls. The average transmission loss within the operating frequency band is only 0.0034 dB / mm, thereby increasing the antenna radiation efficiency to 94%~99%, providing crucial performance assurance for long-distance millimeter-wave communication and high-sensitivity detection.

[0070] Secondly, this invention achieves a wider operating bandwidth and a simpler manufacturing process while maintaining low loss. Compared with existing low-loss structures such as air-filled SIW and SICL, this invention does not require a multi-layer dielectric precision lamination process and can be realized using only a single-layer standard PCB and metal CNC machining. The double-dielectric-walled anti-resonant hollow waveguide itself has a wide operating bandwidth (16~27 GHz, relative bandwidth 51.1%) and excellent impedance matching, avoiding the design difficulties of complex transition structures. While existing air-filled structures can reduce loss, their multi-layer lamination process requires high processing precision, increases costs, and reduces yield, which is not conducive to large-scale application.

[0071] It should be noted that although the double dielectric wall hollow waveguide and the dielectric ridge parallel-plate waveguide (DRPW) and their array structures [8]-

[10] proposed in this invention have certain similarities in macroscopic configuration, that is, both are composed of parallel metal plates and intermediate dielectric layers, but they have essential differences in wave guiding mechanism and belong to completely different technical routes.

[0072] Traditional DRPWs follow the principle of dielectric waveguides, which relies on a dielectric ridge to confine electromagnetic energy within or near the ridge for transmission. In this structure, the dielectric ridge acts as the main transmission channel, and the electromagnetic energy is primarily concentrated in the dielectric material. Therefore, this inevitably introduces high dielectric loss in microwaves, millimeter waves, and higher frequency bands, and the loss problem becomes more pronounced with increasing frequency. In contrast, the anti-resonant hollow waveguide proposed in this invention employs a completely different field confinement mechanism. Its core lies in constructing a transverse Fabry-Perot resonant cavity using a high-dielectric-constant dielectric wall. Through the anti-resonant interference destructive effect, the dielectric wall effectively suppresses transverse leakage waves, thereby efficiently confining electromagnetic energy within the air cavity enclosed by the dielectric wall for transmission. In this structure, the dielectric wall only serves as a boundary, not a transmission channel; the main transmission medium for electromagnetic waves is air, thus effectively solving the dielectric loss problem.

[0073] In summary, this invention, through the innovative combination of a double-dielectric-walled anti-resonant low-loss hollow waveguide and a periodic slot, has for the first time achieved a millimeter-wave planar leaky wave antenna that combines ultra-low loss, wide bandwidth, ultra-high radiation efficiency, beam scanning function, and is simple to manufacture and low in cost. Its overall performance is significantly better than that of existing similar technologies.

[0074] The above embodiments have provided a detailed description of the technical solutions of the present invention. Obviously, the present invention is not limited to the described embodiments. Based on the embodiments of the present invention, those skilled in the art can make various changes, but any changes that are equivalent or similar to the present invention fall within the scope of protection of the present invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

[0075] References [1] F. Parment, A. Ghiotto, T. -P. Vuong, J. -M. Duchamp and K. Wu. Air-Filled Substrate Integrated Waveguide for Low-Loss and High Power-HandlingMillimeter-Wave Substrate Integrated Circuits[J]. IEEE Transactions onMicrowave Theory and Techniques, 2015, 63(4): 1228-1238. [2] Michel Duguay, Yasuo Kokubun, T. Koch, et al. AntiresonantReflecting Optical Waveguides inSiO2-Si Multilayer Structures[J]. AppliedPhysics Letters, 1986, 49: 13-15. [3] X. Li, J. Wang, Z. Li, et al.Archimedean Spiral Slotted Leaky-Wave Antenna[J]. IEEE Transactions on Antennasand Propagation, 2022, 70(5):3208-3222. [4] E. Massoni,M. Bozzi, K. Wu. Increasing Efficiency of Leaky-WaveAntenna by Using Substrate Integrated Slab Waveguide[J]. IEEE Antennas andWireless Propagation Letters, 2019, 18(8): 1596-1600. [5] R. Hong, J. Shi, D. Guan, etal. Wideband and Low-Loss Beam-Scanning Circularly Polarized Antenna Based on Air-Filled SIW[J]. IEEEAntennas and Wireless Propagation Letters, 2021, 20(7): 1254-1258. [6] Y. Zhang, Q. Zhou, F. Zeng, et al. A Compact Dual-CP PlanarMonopulseArray With High Efficiency and Enhanced Sidelobe Suppression[J].IEEETransactions on Antennas and Propagation, 2026: 1-1. [7] N. Yan, K. Ma, H. Zhang, etal. A Novel Substrate IntegratedSuspended Line Wideband Leaky-Wave Antenna[J].IEEE Antennas and WirelessPropagation Letters, 2017, 16: 2642-2645. [8] Zhu R, Zhao Y, Wang J. Abroadband leaky-wave antenna with high efficiency based on dielectric ridged parallel-plate waveguide[J]. IEEEAntennas and Wireless Propagation Letters, 2025, 24(5): 1293-1297. [9] Wang Junhong, Zhu Rui. Three-element leaky wave antenna array structure and design method based on dielectric ridge parallel plate waveguide: China, CN 119764872 B[P]. 2025-10-31.

[10] Wang Junhong, Zhu Rui. Structure and design method of two-element leaky wave antenna array based on half-mode dielectric ridge parallel plate waveguide: China, CN 119786991 B[P]. 2026-02-24.

Claims

1. A design method for a broadband high-efficiency leaky wave antenna based on a low-loss anti-resonant hollow waveguide, characterized in that, Includes the following steps: S1. Design of a single-dielectric-walled anti-resonant hollow waveguide: Based on the principle of anti-resonance reflection, a single-dielectric-walled hollow waveguide is constructed, consisting of a parallel metal plate and a high-dielectric-constant dielectric wall. S2. Optimized design of double dielectric wall anti-resonant hollow waveguide: Based on the single dielectric wall structure of S1, a second dielectric wall is introduced to construct a double dielectric wall hollow waveguide; S3. Leakage antenna design based on double dielectric wall hollow waveguide: Based on the double dielectric wall hollow waveguide optimized in S2, a periodic rectangular slot array is introduced into the upper metal plate.

2. The method according to claim 1, characterized in that, S1 further includes: determining the relationship between the dielectric wall thickness and the working wavelength through theoretical derivation, selecting appropriate dielectric materials and air cavity width, realizing low-loss transmission in the fundamental mode anti-resonance state, and verifying its transmission characteristics and field confinement capability.

3. The method according to claim 2, characterized in that, The method for determining the thickness of the medium wall is as follows: The high dielectric constant dielectric wall is considered as a transverse Fabry-Perot resonant cavity; by reasonably designing the dielectric wall thickness t1, the phase delay generated by the electromagnetic wave traveling back and forth once inside the dielectric wall is reduced. Satisfying the anti-resonance condition: ； Where, k yd Let be the transverse wavenumber in the dielectric wall, and a (a = 1, 2, 3, …) be the anti-resonance order; in this case, the dielectric wall can achieve strong field confinement. Conversely, when the phase delay satisfies the resonance condition, the dielectric wall exhibits high transmission, resulting in severe energy leakage. Therefore, the relationship between the optimal dielectric wall thickness ta and the operating wavelength λ0 is as follows: ； Where λ0 is the wavelength at the center of free space, ε r is the relative permittivity of the dielectric wall.

4. The method according to claim 1, characterized in that, S2 further includes: By optimizing the air gap between the two walls and maintaining the uniformity of the wall thickness of each layer, the reflected waves from the multi-layer interface are superimposed in phase, which further enhances the transverse field confinement, reduces transmission loss, and widens the effective working bandwidth.

5. The method according to claim 1, characterized in that, S3 further includes: Based on the theory of leaky wave antennas, the slot period is set to control the correspondence between the beam scanning angle and the frequency, and the slot size is optimized to achieve high radiation efficiency.

6. The method according to claim 5, characterized in that, The specific method for setting the correspondence is as follows: Select gap period p s This ensures that only the fundamental wave is radiated, while other higher spatial harmonics are in a slow wave state, thereby ensuring a pure single-beam scan within the operating frequency band. The relationship between the radiation angle θ (measured from the side direction) and the free space wavenumber k0 is as follows: ； Where β is the phase constant of the fundamental mode.

7. A broadband high-efficiency leaky wave antenna structure based on a low-loss anti-resonant hollow waveguide, characterized in that, include: The upper metal plate has periodically arranged radial slots etched on it; The lower metal plate is arranged parallel to the upper metal plate. An intermediate dielectric wall layer is disposed between an upper metal plate and a lower metal plate, and includes at least one pair of high dielectric constant dielectric walls extending longitudinally. The dielectric walls and the upper and lower metal plates together form an air cavity, which serves as the main transmission channel for electromagnetic waves. The dielectric wall includes a first dielectric wall and a second dielectric wall, with an air gap between them to form a double dielectric wall anti-resonant structure, which is used to confine electromagnetic energy within the air cavity to achieve low-loss transmission.

8. The structure according to claim 7, characterized in that, The first and second dielectric walls have equal thicknesses and satisfy the anti-resonance condition to effectively confine transverse electromagnetic waves.

9. The structure according to claim 7, characterized in that, The radiation slots are rectangular slots, arranged at equal intervals along the longitudinal direction. The slot period, slot length, and width are optimized to achieve high radiation efficiency and impedance matching over a wide frequency band.

10. The structure according to claim 7, characterized in that, The antenna has a feed port and a matching load port at both ends. The feed port adopts a coaxial probe coupling structure, with the probe extending into the air cavity to realize the conversion from coaxial mode to hollow waveguide mode.

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