Terahertz series-fed beam forming network antenna and design method

Abstract

The invention provides a terahertz series-fed beam forming network antenna and a design method, and belongs to the technical field of antenna design, and the design method comprises the following steps: determining the size and position of a radiation slot based on a waveguide slot array, and introducing an artificial surface plasmon structure and an open stop band suppression structure; designing a series-fed beam forming network, and calculating the length of a waveguide transmission line to provide a required phase difference; the size parameters of the structures of all parts of the antenna are optimized, aperture field distribution of a target antenna is achieved, a series-fed beam forming network and an artificial surface plasmon structure are adopted, the design of the passive two-dimensional beam scanning antenna in the terahertz frequency band is achieved, and the antenna design method can be applied to beam scanning of any frequency band and has wide application prospects. Beam scanning of any two-dimensional space is designed, the designed antenna can achieve the beam scanning range of-25 degrees to 35 degrees and the beam scanning range of-50 degrees to 50 degrees on the plane of the pitch angle and the plane of the azimuth angle respectively, and the antenna is high in efficiency and compact in structure.

Description

Technical Field

[0001] This invention belongs to the field of antenna design technology, specifically relating to a terahertz series-fed beamforming network antenna and its design method. Background Technology

[0002] Terahertz (THz) waves, with their unique advantages such as wide bandwidth and high resolution, have shown great application potential in fields such as next-generation high-speed wireless communication, high-precision radar imaging, non-destructive testing, and spectral analysis. Achieving flexible and efficient beam scanning is key to improving the application capabilities of terahertz systems in scenarios such as dynamic target tracking and space multiple access.

[0003] Among various beamforming techniques, series-feed networks are considered a highly efficient feeding scheme suitable for high-frequency, highly integrated antenna systems due to their compact structure, simple feeding network, and relatively low loss. Compared to parallel-feed networks, series-feed networks avoid complex power distribution branches, reduce transmission path differences, and are beneficial for achieving lower insertion loss and higher radiation efficiency in the terahertz band.

[0004] However, existing terahertz antenna designs based on series-feed networks face significant challenges in achieving two-dimensional beam scanning. The topological characteristics of series-feed networks inherently limit their phase progression mechanism to a single dimension, meaning traditional designs can only achieve one-dimensional scanning for linear or curved arrays. Forcing a two-dimensional extension typically requires complex cascaded feed structures or multi-level power dividers, completely contradicting the original design principles of series-feed networks, which prioritize compactness and low transmission loss. At the scanning mechanism level, traditional frequency scanning methods deeply bind beam pointing to the operating frequency band. This characteristic makes it unsuitable for modern communication systems that require flexible beamforming or multi-beamforming at fixed frequencies. Furthermore, in practical terahertz band implementations, the combination of micrometer-level fabrication precision requirements and electromagnetic field complexity makes any complex feed structure highly susceptible to problems such as high-order mode excitation, parasitic radiation, and impedance mismatch, directly leading to antenna efficiency degradation and limited scanning range. The patent with publication number CN120784611A provides a full-space scanning terahertz leaky antenna. It adopts an artificial surface plasmon polarization (SSPP) structure and combines copper additive manufacturing process to design a feeding part, an antenna body part and an absorption part. It uses a leaky antenna array, SSPP transmission line and series feeding network, but does not provide the design method.

[0005] Therefore, there is an urgent need in the current technological field for an innovative series-fed beamforming network topology and its supporting design method to solve the core problem that existing terahertz antennas are unable to achieve efficient, flexible, and structurally simple two-dimensional spatial beam scanning. This invention aims to overcome the above-mentioned shortcomings and provide a terahertz antenna solution that achieves two-dimensional beam scanning at a fixed frequency, with a compact structure, low loss, and a clear design method. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a design method for a terahertz series-fed beamforming network and antenna for two-dimensional spatial beam scanning. Employing a series-fed beamforming network and an artificial surface plasmon (SPP) structure, it achieves the design of a passive two-dimensional beam scanning antenna in the terahertz band. This antenna can achieve beam scanning ranges of -25° to 35° and -50° to 50° in the elevation and azimuth planes, respectively, exhibiting high efficiency and a compact structure.

[0007] To achieve the above objectives, the present invention first provides a design method for a terahertz series-fed beamforming network antenna, comprising the following steps: Based on waveguide slot arrays, the size and location of radiation slots are determined, and artificial surface plasmon structures and open stopband suppression structures are introduced. Design a series-feed beamforming network and calculate the length of the waveguide transmission line to provide the required phase difference; Optimize the dimensional parameters of each part of the antenna structure to achieve the aperture field distribution of the target antenna.

[0008] Furthermore, a leaky wave antenna array was designed, the size and location of the radiation slots were determined, and an artificial surface plasmon structure was introduced, including: Low-frequency surface plasmons are constructed by periodically etching grooves on a metal surface; By applying continuous boundary conditions at the interface between a semi-infinite free space and a semi-infinite metallic conductor, the electromagnetic waves of a subwavelength one-dimensional groove array in a semi-infinite free space and a semi-infinite metallic conductor are solved; the dispersion relation of the subwavelength one-dimensional groove array is obtained. Incident wave TM polarization and along x For directional transmission, the dispersion relation for a subwavelength one-dimensional groove array is:

[0009] in, d For the periodicity of the groove structure, h For groove depth, a The width of the groove. k 0 is the wavenumber in vacuum. k sspp aUnder condition <<1, the following parameters are derived based on the equivalent medium theory:

[0010]

[0011] in, ε x Let be the relative permittivity in the x-direction. ε y Let be the relative permittivity in the y-direction. ε z Let be the relative permittivity in the z-direction. μ x Let be the relative permeability in the x-direction. μ y Let be the relative permeability in the y-direction. μ z Let be the relative permeability in the z-direction.

[0012] Furthermore, the introduction of an on-stopband suppression structure includes: Based on the impedance mismatch analysis of the operating frequency corresponding to the beam side-firing of the terahertz series-fed beamforming network antenna, a series-parallel composite circuit structure is adopted in the equivalent circuit of the leaky antenna element, and components with complementary reactance are loaded at the same time. Based on the circuit structure, a circular slot is introduced into the linearly polarized leaky antenna. The circular slot cuts the transverse current of the waveguide, which is equivalent to parallel loading.

[0013] Furthermore, the design of the series-fed beamforming network and the calculation of the waveguide transmission line length to provide the required phase difference include: Two adjacent periodic leaky wave arrays are connected end to end by a transmission line to form a series-fed beamforming network, and the feeding method between the arrays is serial. The electromagnetic wave input at the input port is transmitted through the first-stage leaky antenna to the input port of the next-stage leaky antenna via the waveguide transmission line at the bottom layer. The phase difference between two adjacent leaky antenna stages is determined by the length of a single leaky antenna. L 1. Length of the bottom delay line L 2. Antenna-bottom delay line interconnection structure length L The phase difference introduced by the transmission line, determined by the three factors, is expressed as follows:

[0014] in, λ c It is the cutoff wavelength of the waveguide. λ This refers to the wavelength corresponding to the operating frequency, and the calculation relationship is as follows: λ c = 2 W ,W This is the length of the wide side of the waveguide.

[0015] Furthermore, by analyzing the dispersion characteristics of the two different transmission lines at the top and bottom layers of the antenna, and combining the radiator loading method, the aperture amplitude and phase distribution are derived, resulting in the antenna array factor and frequency sweep range, including: Based on a simplified model of the antenna array, the antenna array includes m × n Unit, in x and y The spacing in the directions are respectively d x and d y Its array factor F ( θ , φ ) is represented as:

[0016] in, I MN and a MN These represent the amplitude and phase of the Mth and Nth radiators, respectively. Each leaky antenna in the antenna is fed in series from start to finish, and the amplitude of each leaky antenna will attenuate sequentially. The attenuation component includes the radiation attenuation of the element. A rad _ IJ and waveguide transmission line attenuation A wg The amplitude of the Mth and Nth radiators I MN The expression is:

[0017] For the phase distribution of the array elements, the phase delay introduced by the bottom waveguide transmission line of the antenna is:

[0018] in, l wg It is the length of the waveguide transmission line. λ c It is the cutoff wavelength of the waveguide. x The phase delay between adjacent slots in the direction is:

[0019] In the formula, the additional 180° is achieved through alternating left and right radial slits. β Let be the propagation constant of the SSPP transmission line. For the SSPP transmission line in the antenna, it is expressed as:

[0020] in, k It is the wavenumber in free space. p It is the period length of the SSPP unit. a and h These are the width and height of the metal plate, respectively. Based on the above formula, different frequencies and their corresponding array factors are calculated.

[0021] Further optimization of the dimensional parameters of each part of the antenna structure includes: The initial parameters of the terahertz series-fed beamforming network antenna are set, and the single-pole and multi-stage antenna arrays are optimized using simulation software to obtain the antenna array. The phase difference required by the series-fed beamforming network is calculated, and the length of the single leaky antenna L1, the length of the bottom delay line L2, and the length of the interconnection structure of the bottom delay line of the antenna L3 are optimized to obtain the total length of the delay line and the width of the inner wall of the waveguide of the series-fed network.

[0022] Furthermore, based on the above design method, this invention can also provide a terahertz series-fed beamforming network antenna, which has a multi-layer structure, consisting of, from top to bottom: a radiating array, a waveguide cavity, an SSPP structure, a waveguide bottom, a series-fed beamforming network, and the waveguide bottom of the series-fed beamforming network; a plurality of slotted radiating apertures are uniformly opened on the radiating array to form a radiating aperture array, and OSB suppression apertures are located at the slotted radiating apertures, with the diameter of the OSB suppression apertures being larger than the width of the slotted radiating apertures and smaller than the length of the slotted radiating apertures; circular OSB suppression apertures are set on the radiating slots, and the entire antenna array extends out of the waveguide opening; transmission vias are opened on both sides of the SSPP structure and the waveguide bottom; a twisted waveguide is set in the series-fed beamforming network, using a quarter-circular metal wall transition.

[0023] Furthermore, the radiating array has a length of 20.5 mm, a width of 19.55 mm, and a thickness of 0.75 mm; the slit radiating aperture has dimensions of 0.06 mm × 0.5 mm × 0.05 mm; the OSB suppression aperture has a radius of 0.08 mm and a height of 0.05 mm; the SSPP slit has dimensions of 0.045 mm × 0.6 mm × 0.2 mm; the waveguide aperture has dimensions of 0.1 mm × 0.71 mm × 0.7 mm; and the waveguide cavity thickness is 0.1 mm. Furthermore, SSPP slits are made in the SSPP structure, with one SSPP slit directly below each row of slit radiation holes. There is a raised structure in the middle of the bottom of the SSPP slit. The SSPP structure consists of two layers, with the upper layer being 0.2mm thick and the lower layer being 0.1mm thick.

[0024] Furthermore, in a column along the length of the radiating array, two adjacent slotted radiating apertures are located on either side of the center line of the column, and the two adjacent slotted radiating apertures overlap by a set length in the length direction. The center of the OSB suppression aperture is located on the center line of the slit radiation aperture along its length, and the OSB suppression aperture is offset towards the waveguide opening on the slit radiation aperture.

[0025] Compared with the prior art, the present invention has at least the following beneficial effects: it provides a detailed and effective design method for two-dimensional spatial beam scanning antennas and proposes a terahertz band series-fed beamforming network; the antenna design method can be applied to beam scanning in any frequency band and to design beam scanning in any two-dimensional space; it can realize the design of a passive two-dimensional beam scanning antenna in the terahertz band, which can achieve beam scanning ranges of -25° to 35° and -50° to 50° in the elevation and azimuth planes, respectively, and has high efficiency and compact structure. Attached Figure Description

[0026] Figure 1 The diagram shows the structure of a terahertz series-fed beamforming network antenna design for two-dimensional spatial beam scanning; (a) is a partially enlarged view of the top layer, (b) is a partially enlarged view of the middle layer, and (c) is a partially enlarged view of the bottom series-fed beamforming network.

[0027] Figure 2 A schematic diagram of a dielectric waveguide structure for analyzing the periodic structural field characteristics of a terahertz series-fed beamforming network antenna for two-dimensional spatial beam scanning. Figure 3 A schematic diagram of a one-dimensional structure supporting SSPP for a terahertz series-fed beamforming network antenna design for two-dimensional spatial beam scanning; Figure 4 Dispersion verification curves of a terahertz series-fed beamforming network antenna designed for two-dimensional spatial beam scanning at a=0.2d and h=d. Figure 5 A schematic diagram of the electric field flow direction of a slot array for a terahertz series-fed beamforming network antenna designed for two-dimensional spatial beam scanning. Figure 6 A schematic diagram of an OSB suppression circuit designed for a terahertz series-fed beamforming network antenna for two-dimensional spatial beam scanning. Figure 7 A schematic diagram of the OSB suppression structure for a terahertz series-fed beamforming network antenna design for two-dimensional spatial beam scanning; Figure 8 Before and after comparison of the structure of the loaded OSB for a terahertz series-fed beamforming network antenna design for two-dimensional spatial beam scanning; Figure 9 is a schematic diagram of the topology of a terahertz series-fed beamforming network for two-dimensional spatial beam scanning. Figure 10 shows a schematic diagram of the self-progressive phase shift model of the leaky antenna and a verification diagram of the terahertz series-fed beamforming network antenna design with two-dimensional spatial beam scanning. Figure 11 A simplified schematic diagram of the antenna array for a terahertz series-fed beamforming network antenna design for two-dimensional spatial beam scanning; Figure 12 Two-dimensional result verification diagram for the design of a terahertz series-fed beamforming network antenna for two-dimensional spatial beam scanning; Figure 13 Verification diagram of beam scanning results for a terahertz series-fed beamforming network antenna design for two-dimensional spatial beam scanning; Figure 14(a) is a schematic diagram of the radiating array of the leaky terahertz series-fed beamforming network antenna with two-dimensional spatial beam scanning; Figure 14(b) is a schematic diagram of the waveguide cavity of the leaky terahertz series-fed beamforming network antenna with two-dimensional spatial beam scanning; Figure 14(c) is a schematic diagram of the upper layer of the SSPP structure of the leaky terahertz series-fed beamforming network antenna with two-dimensional spatial beam scanning; Figure 14(d) is a schematic diagram of the lower layer of the SSPP structure of the leaky terahertz series-fed beamforming network antenna with two-dimensional spatial beam scanning; Figure 14(e) is a schematic diagram of the lower bottom of the waveguide of the leaky terahertz series-fed beamforming network antenna with two-dimensional spatial beam scanning; Figure 14(f) is a schematic diagram of the series-fed beamforming network of the leaky terahertz series-fed beamforming network antenna with two-dimensional spatial beam scanning; Figure 14(g) is a schematic diagram of the lower bottom of the waveguide of the series-fed beamforming network of the leaky terahertz series-fed beamforming network antenna with two-dimensional spatial beam scanning.

[0028] Figure 15 This is a schematic diagram showing a partial detail of SSPP.

[0029] In the attached diagram, 1-radiating array, 2-waveguide cavity, 3-slot radiation aperture, 4-OSB suppression aperture, 5-process release aperture, 6-SSPP slot, 7-transmission through-hole, 8-waveguide port, 9-twisted waveguide. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] In the description of this invention, it should be understood that the terms "center", "upper", "lower", "left", "right", "top", "bottom", "inner", "outer", "side", "one end", "one side", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0032] The antenna implemented by the method of this invention mainly consists of two parts, as follows: Figure 1 As shown, the lower layer is a series-fed beamforming network, and the upper layer is a leaky antenna array. The field input to the first leaky antenna on the left passes through the antenna itself and is then transmitted to the first waveguide delay line at the bottom layer. After delay, the second leaky antenna is excited, and so on, thus exciting the entire antenna array. The excitation amplitude of the leaky antenna can be adjusted by changing the position of the slot off the center line, avoiding excessively small amplitude of the end radiator and reducing aperture efficiency. The design method of this invention will be mainly described below.

[0033] This invention first introduces the design method of the leaky wave antenna. Based on the radiation characteristics of the leaky wave antenna itself, it can be divided into two main categories: uniform structure and periodic structure. A uniform structure leaky wave antenna has a uniform or quasi-uniform antenna structure along the wave propagation direction. Uniform structure leaky wave antennas are generally designed based on fast wave waveguide structures, where the dominant mode is fast wave, such as a rectangular waveguide. Therefore, a uniform structure leaky wave antenna operates on the fundamental mode, and the scanning beam only covers the forward quadrant. In contrast, a periodic leaky wave antenna is designed based on a slow wave waveguide structure, on which discontinuous perturbation elements are periodically introduced along the wave propagation direction. Due to the introduction of these discontinuous perturbation elements, an infinite number of spatial harmonics are excited, and these spatial harmonics belonging to the fast wave region leak out the electromagnetic energy they carry.

[0034] Dispersion plots can be used to explain the working mechanism of leaky-wave antennas. The dispersion plot shows how the frequency changes... βd and k The relationship of 0, k 0 represents the wavenumber in vacuum. βd For the propagation direction of the wave along the waveguide structure, per unit distance d The waveguide phase shift represents a quantity related to the waveguide phase constant, and has the following properties in the fast wave region: k 0< β < k 0; there are in the slow wave region β > k 0 or β < k0. Dispersion diagrams provide a graphical reference for the transmission mode of guided waves, allowing for a quick and direct determination of whether any waveguide structure exhibits radiation. Dispersion diagrams are primarily used to explain the dispersive characteristics of periodic structures, but they can also explain the characteristics of leaky wave antennas with uniform structures. When discussing the dispersion diagram of a uniform leaky wave antenna, the unit distance ( d Infinitely smaller than the waveguide wavelength λ g .

[0035] When studying the characteristics of periodic structures, the Fourier expansion in the spatial frequency domain (Floquet spatial harmonic expansion) can be used for analysis. A periodic field can be viewed as a superposition of spatial harmonics, and spatial harmonic theory can be used to effectively analyze the characteristics of periodic structure fields. Figure 2 In a dielectric waveguide structure, discontinuous perturbation elements are periodically introduced along the wave propagation direction (Z-axis), with a period length of [missing information]. P Then the complex phase shift of the zeroth harmonic between adjacent units is: k z0 P =( β - ja ) P In other words, for any one-dimensional periodic structure, the fields of adjacent periodic units differ only by a factor e caused by the complex propagation constant. -jkP Therefore, spatial harmonics can be expressed as follows:

[0036] φ (z) represents the spatial harmonic at position z; P The periodicity of the structure; k z0 The fundamental propagation constant along the Z-direction is a key parameter describing the propagation characteristics of waves in periodic structures, and is usually a complex number. k = β jα ,in β It is the phase constant. α It is the attenuation constant. Where e -j（β jα）P It includes the phase delay and possible amplitude attenuation of the wave propagating within one period.

[0037]

[0038] make:

[0039] A function is a... PA periodic function with period is given by the following Fourier series expansion:

[0040] so:

[0041] in:

[0042] For the first n Subspace harmonics z Directional propagation constant, The variation of the harmonic field in the XOY plane is described. At the interface between the antenna and the air, the propagation constant in the X direction is:

[0043] For a lossless waveguide structure, the phase constant of the periodic structure is:

[0044] The propagation constant in the X direction at the interface is simplified to:

[0045] For a periodic leaky wave antenna to generate a leaky wave, a certain spatial harmonic must be in the fast wave region. For the air-filled waveguide transmission line used in this invention, its electromagnetic wave propagation mode is fast, and its propagation constant is less than the free-space propagation constant, making it difficult to achieve continuous beam scanning in the side-firing direction. To solve this problem, the leaky wave antenna waveguide structure in this invention improves the dispersion characteristics of the transmission line by loading an artificial surface plasmon resonance structure, enabling it to operate in a slow wave mode.

[0046] like Figure 3 The diagram shows a subwavelength one-dimensional groove array structure supporting artificial surface plasmon waves. Low-frequency surface plasmon waves are constructed by periodically etching grooves onto a metal surface. The subwavelength one-dimensional grooves correspond to the SSPP slot 6 in Figure 14. The electromagnetic waves in region I (semi-infinite free space) and region II (semi-infinite metal conductor) of the subwavelength one-dimensional groove array are solved separately. Then, by applying continuous boundary conditions at the interface, the corresponding dispersion relation is obtained.

[0047] Incident wave TM polarization and along x Directional transmission, then for Figure 3 The dispersion relation of a subwavelength one-dimensional groove array can be expressed as:

[0048] in,d For the periodicity of the groove structure, h For groove depth, a The width of the groove. k 0 represents the wavenumber in vacuum. k sspp a Under condition <<1, the following parameters can be obtained according to the equivalent medium theory:

[0049]

[0050] in, ε x Let be the relative permittivity in the x-direction. ε y Let be the relative permittivity in the y-direction. ε z Let be the relative permittivity in the z-direction. μ x Let be the relative permeability in the x-direction. μ y Let be the relative permeability in the y-direction. μ z Let be the relative permeability in the z-direction.

[0051] when a =0.2 d , h = d At times, such as Figure 4 The figure shows the dispersion curve of SSPP corresponding to a subwavelength one-dimensional groove array. It can be seen from the figure that at low frequencies, the dispersion is close to but slightly below that of light, then deviates from light as the frequency increases and eventually tends towards a gradual plasma frequency. Furthermore, the plasma frequency of SSPP is determined by the structure, and the mode dispersion characteristics of SSPP can be easily tuned by simply changing the geometry of the grooves. Therefore, subwavelength one-dimensional groove arrays offer great freedom in designing the artificial surface plasmon dispersion characteristics.

[0052] This antenna design is based on a waveguide slot array. By loading radiating slots onto the surface of the traveling waveguide at the terminal, the current within the waveguide's inner wall is cut off, thus achieving energy radiation. For the fundamental mode TE in a rectangular waveguide... 10The pattern involves a distance of one-quarter of the waveguide wavelength between adjacent antinodes and nodes, and a distance of one-half the waveguide wavelength between two adjacent antinodes or nodes, but the field distribution at adjacent antinodes is opposite. To excite adjacent radiating slots to generate in-phase radiation and achieve a side-firing antenna beam, slots are needed to cut currents with the same propagation direction. Since the waveguide wavelength is often greater than the free space wavelength, setting a slot every other waveguide wavelength would result in excessive spacing between adjacent radiating slots, causing grating lobes in the antenna beam and reducing the main beam gain. To solve this problem, adjacent wide-side slot radiating apertures 3 need to be positioned on both sides of the waveguide centerline, cutting currents with the same direction. The current distribution on the corresponding wide side of the waveguide and the slot positions are as follows: Figure 5 As shown. Under this slot loading method, the spacing between adjacent slot elements is approximately half the waveguide wavelength, avoiding the formation of grating lobes. Furthermore, the distance between the adjacent slot elements at the short-circuit end of the waveguide and the short-circuit point is one-quarter of the waveguide wavelength.

[0053] To improve the impedance mismatch problem at the operating frequency corresponding to the side-firing of the antenna beam and suppress the open stopband (OSB) effect, a complementary reactance loading structure design was applied, ultimately achieving continuous beam scanning from the rear direction through the normal direction to the front direction. The most direct method to make the leaky-wave antenna element reflection-free is to make the radiating element impedance match the main transmission line impedance. The impedance mismatch originates from the series impedance introduced by the transverse slot in the equivalent circuit of the antenna element. Z To compensate for series impedance Z To address the resulting impedance mismatch in the leaky antenna, this invention proposes introducing parallel elements (with admittance of...) at the same location in the antenna element. Y ),like Figure 6 As shown. The new leaky antenna element S The parameter can be calculated using the following formula:

[0054]

[0055]

[0056] P For the period of the structure, e -jβP This is the phase delay propagating within one period. According to the above formula, in order to achieve impedance matching of the antenna element and ensure no reflection between the antenna element and the main transmission line, i.e., S11=0, Z and Y The following relationship should be satisfied:

[0057] Furthermore, the real and imaginary parts of the admittance Y can be written in the following forms:

[0058] In the above formula, Re[Z] / Z0 The condition 1 always holds true when the frequency is far from the slot resonant frequency, meaning that both the real and imaginary parts of the admittance Y are positive. A positive real part indicates energy loss, which can be achieved through radiation, while a positive imaginary part indicates that the component corresponding to admittance Y is capacitive. From the above analysis, it can be seen that using a series-parallel composite circuit structure in the equivalent circuit of the leaky antenna element, along with components with complementary reactance, can effectively suppress OSB in the periodic leaky antenna. The structure proposed in this design method is suitable for leaky antennas operating in the -1st order mode. Such leaky antennas have a large element spacing, resulting in less mutual coupling between elements and simplifying the antenna design process. The longer element spacing also provides sufficient space, allowing the antenna to load other components to achieve more complex and precise electromagnetic control. It should be noted that increasing the element spacing also brings negative effects, such as the overlap of higher-order spatial harmonic bands, which, from the perspective of the antenna array angle, means the appearance of grating lobes. Next, this invention will design a periodic leaky antenna based on an SSPP transmission line using a method of complementary reactance loading to achieve OSB suppression.

[0059] To design a periodic leaky antenna based on the proposed circuit structure, a circular slot is introduced into the linearly polarized leaky antenna, as shown in the structure below. Figure 7 As shown, the transverse current cut by the circular slot in the waveguide is physically equivalent to a parallel loading. Similar to the transverse slot, adjusting the size of the circular slot allows for parallel capacitive loading within the desired frequency band. It's important to note that both the transverse and circular slots in this antenna element can leak electromagnetic energy. To achieve linear polarization radiation and suppress cross-polarization levels, a smaller circular slot and a longer transverse slot are used. The diameter of the circular slot is smaller than its length, and the diameter of the circular slot is larger than its width. Therefore, the antenna's energy is primarily radiated outwards through the transverse slot, and the antenna's main polarization direction is perpendicular to the length of the transverse slot.

[0060] The dispersion and attenuation curves of the leaky wave antenna element with and without circular slot loading were compared, such as Figure 8 As shown in the figure. The results show that loading the circular slot can eliminate the abrupt attenuation within the OSB, achieving a good suppression effect. Open-stopband suppression is achieved by loading the circular slot. The circular slot introduces an additional reflection field. By selecting an appropriate circular slot radius, the reflection amplitude and phase can be adjusted. When the reflection amplitudes of the two slots are approximately the same and the phase difference is 180°, good OSB suppression performance can be achieved. The above is the design method of the leaky wave antenna of this invention.

[0061] The following describes the design of the series-fed beamforming network of this invention. In this invention, two adjacent periodic leaky wave arrays are connected end-to-end via transmission lines, with the feeding method between the arrays being serial. Its topology is shown in Figure 9(a). This feeding network can generate frequency-varying gradient phase differences. By rationally designing the transmission line path difference between adjacent arrays, the required frequency sweep rate is achieved, allowing the beam to perform periodic multiple reciprocating scans on the cascaded surface. Combined with the periodic leaky wave antenna, it jointly realizes the two-dimensional frequency sweep function.

[0062] In series-fed beamforming networks, electromagnetic waves gradually leak into free space along the transmission path, and the electromagnetic energy within the transmission line gradually attenuates. This necessitates strict correlational control of the leakage capability of all elements to maintain a uniform field distribution at the radiating aperture and improve the aperture efficiency of the array antenna. Generally, the size of the radiating element affects its own radiation capability and also determines the leakage capability of the feed line. Therefore, controlling the leakage capability of the element becomes a matter of controlling the element size.

[0063] This leaky antenna provides progressive phase shifting, enabling two-dimensional frequency scanning without increasing the antenna area. A single leaky antenna achieves this through… Z The "V"-shaped antennas are connected end-to-end, achieving re-series connection between leaky wave linear array antennas, as shown in Figure 10. This multi-series connection structure effectively reduces the complexity and area occupied by the feed network, and is widely used in far-field beamforming antennas. Here, the asymptotic phase shift required for two-dimensional frequency scanning is generated using the propagation distance of a single series-fed leaky wave antenna, a process known as "self-asymptotic phase shifting." This self-asymptotic phase-shifting antenna requires a very compact, high-density folded feed network.

[0064] According to the field propagation path diagram 9(b) of the series-fed network, the electromagnetic wave input through the input port passes through the first-stage leaky antenna and is then transmitted to the input port of the next-stage leaky antenna through the waveguide transmission line of the bottom layer. Therefore, the phase difference between two adjacent leaky antenna stages is determined by the length of a single leaky antenna. L 1. Length of the bottom delay line L 2. Length of the antenna bottom layer delay line interconnect structure L 3. Since waveguides are used as waveguide structures in all stages of the transmission lines and antennas, the phase difference introduced by the transmission lines can be expressed as:

[0065] In the formula λ c It is the cutoff wavelength of the waveguide. λ This refers to the wavelength corresponding to the operating frequency, and the calculation relationship is as follows: λ c = 2 W , WThis is the length of the wide side of the waveguide.

[0066] After completing the structural design of each part of the antenna, in order to achieve beam coverage in a specific area, the dispersion characteristics of the two different transmission lines at the top and bottom layers of the antenna can be analyzed, and the aperture amplitude and phase distribution can be derived by combining the radiator loading method. This yields the antenna array factor and frequency sweep range. This calculation method can guide the subsequent antenna array expansion design and meet the requirements of different array sizes and beam coverage ranges. The specific derivation steps are as follows.

[0067] Figure 11 The image shows a simplified model of the antenna array, which includes... m × n Unit, in x and y The spacing in the directions are respectively d x and d y Its array factor F ( θ , φ ) can be represented as:

[0068] in, I MN and a MN These represent the amplitude and phase of the Mth and Nth radiators, respectively. Since each leaky antenna in the antenna is fed in series from start to finish, its amplitude will attenuate sequentially. The attenuation component includes the radiation attenuation of the element. A rad _ IJ and waveguide transmission line attenuation A wg The amplitude of the Mth and Nth radiators I MN The expression is:

[0069] For the phase distribution of the array elements, the phase delay introduced by the bottom waveguide transmission line of the antenna is:

[0070] in, l wg It is the length of the waveguide transmission line. λ c It is the cutoff wavelength of the waveguide. x The phase delay between adjacent slots in the direction is:

[0071] In the formula, the additional 180° is achieved through alternating left and right radial slits. β This is the propagation constant of the SSPP transmission line. For the SSPP transmission line in this antenna, it can be expressed as:

[0072] in, k It is the wavenumber in free space. p It is the period length of the SSPP unit. a and h These represent the width and height of the metal plate, respectively. Based on the above formula, different frequencies and their corresponding array factors can be calculated. To achieve a relatively ideal aperture efficiency, the excitation amplitude of each element in the array was set to 1 in the initial calculations. In the actual structural implementation, this can be achieved through optimization. A rad The value is used to achieve this.

[0073] To demonstrate the feasibility of the above theory, this invention designs a two-dimensional frequency-scanning antenna with an operating frequency of 300-380 GHz and a center frequency of 340 GHz (wavelength approximately 0.882 mm). First, the radiator of the antenna is designed. A high-gain antenna is designed, with an array size of 20.5 mm * 19.55 mm * 0.45 mm, consisting of a 30-stage leaky wave antenna. Each stage of the leaky wave antenna has a width of 0.8 mm. Simulations show a gain of 35 dB. The dimensions of the first-stage leaky wave antenna are 0.8 mm * 15.795 mm * 0.45 mm; the slot size is 0.06 mm * 0.5 mm * 0.05 mm (length approximately half a wavelength), the slot spacing is 0.45 mm (length approximately half a wavelength), and the distance from the short-circuit element slot to the short-circuit point is 0.222 mm (length quarter of the waveguide wavelength). This is the radiating part of the antenna. To ensure radiation, artificial surface plasmons (Spoof Surface Plasmons) are introduced in this design. The polariton (SSPP) structure is located below the radiating slot array, consisting of 0.045mm*0.6mm*0.05mm unit slots spaced 0.09mm apart. To suppress OSB (Out-of-Band) radiation, these unit slots correspond to slot radiation apertures 3 in Figure 14. This invention introduces a circular open-stopband suppression structure at the location of the radiating slots. This open-stopband suppression structure is the OSB suppression aperture 4 shown in Figure 14, with a radius of 0.04-0.08mm. Finally, this stage of leaky wave antenna is replicated to 30 stages. After setting the initial parameters, the optimizer in simulation software can be used to optimize the single-stage and 30-stage antenna arrays. Frequency switching allows for scanning in the elevation plane, followed by the feed network design of this invention to achieve scanning in the azimuth plane.

[0074] To achieve two-dimensional beam scanning, a phase difference needs to be provided to the array surface. In this invention, this is provided through a series-fed beamforming network. As described above, the phase difference between two adjacent leaky antenna stages is determined by the length L1 of a single leaky antenna, the length L2 of the bottom delay line, and the length L3 of the interconnection structure of the bottom delay lines. Therefore, the lengths of L1, L2, and L3 need to be optimized. In this design, to achieve scanning from -50° to 50° in the azimuth plane, the required phase difference is calculated to be ±137.88°. In this invention, a delay line design with a total length of 40mm is used (L1+L2+2L=40mm). The influence of waveguide wall thickness on the transmission phase is also analyzed. The optimized series-fed beamforming network uses a waveguide inner wall width of 0.6mm.

[0075] Finally, the radiator and feed grid of this invention are connected, and the whole system is optimized to achieve two-dimensional beam scanning. Using the above design method, a set of dispersive phase distributions is designed to achieve frequency scanning beams around the wide side direction. Figure 14 shows a layered schematic diagram of the two-dimensional beam scanning antenna designed in this application, which is a seven-layer structure. (a)-(g) respectively represent the structural schematic diagram of one layer. The entire antenna's radiating array 1 has a length of 20.5 mm, a width of 19.55 mm, and a thickness of 0.75 mm. It includes a slotted radiating aperture 3, an OSB suppression aperture 4, a process release aperture 5, an SSPP slot 6, a transmission through-hole 7, a waveguide port 8, and a twisted waveguide 9. The dimensions of the slotted radiating aperture 3 are 0.06 mm × 0.5 mm × 0.05 mm, the radius of the OSB suppression aperture 4 is 0.08 mm, the height is 0.05 mm, and the dimensions of the process release aperture 5 are 0.15 mm × 0.2 mm × 0.05 mm. The dimensions of the SSPP slot 6 are 0.045mm × 0.6mm × 0.2mm. The waveguide port 8 is the excitation waveguide port extending from the entire antenna array, and its dimensions are 0.1mm × 0.71mm × 0.7mm. Each row of slot radiating apertures 3 is directly opposite a row of SSPP slots 6. Multiple transmission vias 7 are formed on both sides of the SSPP structural layer and the bottom of the waveguide. The dimensions of the transmission vias 7 between layers are 0.1mm × 0.6mm × 0.6mm, enabling the transmission and flow of the electric field between layers. This is also the self-progressive phase shifting mechanism in this invention. An important component; the twisted waveguide 9 is an important part of the series-fed beamforming network, with a thickness of 0.1 mm, which realizes the transmission of energy in the two-stage leaky wave antenna. The twisted waveguide 9 is arranged along the diagonal of the rectangle in which it is located; in a column along the length direction of the radiating array 1, two adjacent slot radiating apertures 3 are located on both sides of the center line of the column, and the two adjacent slot radiating apertures 3 have a set length of overlap in the length direction but do not connect; the center of the OSB suppression aperture 4 is located on the center line of the length direction of the slot radiating aperture 3, and the OSB suppression aperture 4 is biased towards the waveguide opening direction on the slot radiating aperture 3. Figure 14-(a) shows the radiating array 1 of the leaky wave antenna, with a thickness of 0.05 mm. Figure 14-(b) shows the waveguide cavity 2, in which energy is transmitted and radiated, with a thickness of 0.1 mm. Figures 14-(c) and 14-(d) show the SSPP structure in the design of the leaky wave antenna. The processing requirements and design structure are different, and it is divided into two layers. The upper layer has a slot of 0.6 mm × 0.045 mm × 0.2 mm, and the lower layer has two types of slots: a 0.17 mm × 0.045 mm × 0.1 mm slot at the center, and a symmetrical 0.085 mm × 0.045 mm × 0.1 mm slot at a distance of 0.13 mm from the center slot. These two layers are the main parts of the antenna of this invention that ensure slow wave leakage. See also [reference needed]. Figure 15This can be understood as each SSPP slot 6 having two raised structures at its bottom, symmetrical about the centerline, with gaps between the raised structures and the two sides of the SSPP slot 6. The dimensions of the raised structures are 0.13mm × 0.045mm × 0.1mm, and the gap dimensions are 0.085mm × 0.045mm × 0.1mm. Figure 14(e) shows the bottom waveguide of this leaky wave antenna, used to separate the radiator and the feed grid, with a thickness of 0.1mm. Figures 14(a) to 14(e) correspond to... Figure 1 The structure on the left side of the middle section. Figure 14(f) shows the series-fed beamforming network in this invention, with a thickness of 0.1 mm. It is the main body that provides the required phase difference for the radiator. The twisted waveguide 9 is an important part of the series-fed beamforming network, with a thickness of 0.1 mm. It uses a 1 / 4 circular metal wall transition to change the direction of the wave, realizing the transmission of energy in the two-stage leaky wave antenna. To minimize the volume, within the rectangular area it is located in, the twisted waveguide 9 is arranged in a compact diagonal. Figure 14(g) shows the bottom of the waveguide of this series-fed beamforming network, with a thickness of 0.01 mm, ensuring that the energy is transmitted within the waveguide. Figures 14(f) and 14(g) correspond to Figure 1-2 The structure in.

[0076] The array factor and beam direction of this invention at different frequencies are as follows: Figure 12 and Figure 13 As shown, beam scanning ranges of -25° to 35° and -50° to 50° are achieved in the elevation and azimuth planes, respectively, verifying the feasibility of the proposed design. Therefore, this topology can also be used to achieve beam coverage of arbitrary spatial regions.

[0077] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A design method for a terahertz series-fed beamforming network antenna, characterized in that, Includes the following steps: Based on waveguide slot arrays, the size and location of radiation slots are determined, and artificial surface plasmon structures and open stopband suppression structures are introduced. Design a series-feed beamforming network and calculate the length of the waveguide transmission line to provide the required phase difference; Optimize the dimensional parameters of each part of the antenna structure to achieve the aperture field distribution of the target antenna.

2. The design method for a terahertz series-fed beamforming network antenna according to claim 1, characterized in that, The design of a leaky antenna array, the determination of the size and location of the radiating slots, and the introduction of artificial surface plasmon structures include: Low-frequency surface plasmons are constructed by periodically etching grooves on a metal surface; By applying continuous boundary conditions at the interface between a semi-infinite free space and a semi-infinite metallic conductor, the electromagnetic waves of a subwavelength one-dimensional groove array in a semi-infinite free space and a semi-infinite metallic conductor are solved; the dispersion relation of the subwavelength one-dimensional groove array is obtained. Incident wave TM polarization and along x For directional transmission, the dispersion relation for a subwavelength one-dimensional groove array is: in, d For the periodicity of the groove structure, h For groove depth, a The width of the groove. k 0 is the wavenumber in vacuum. k sspp a Under condition <<1, the following parameters are derived based on the equivalent medium theory: in, ε x Let be the relative permittivity in the x-direction. ε y Let be the relative permittivity in the y-direction. ε z Let be the relative permittivity in the z-direction. μ x Let be the relative permeability in the x-direction. μ y Let be the relative permeability in the y-direction. μ z Let be the relative permeability in the z-direction.

3. The design method for a terahertz series-fed beamforming network antenna according to claim 2, characterized in that, Introducing open-band suppression structures includes: Based on the impedance mismatch analysis of the operating frequency corresponding to the beam side-firing of the terahertz series-fed beamforming network antenna, a series-parallel composite circuit structure is adopted in the equivalent circuit of the leaky antenna element, and components with complementary reactance are loaded at the same time. Based on the circuit structure, a circular slot is introduced into the linearly polarized leaky antenna. The circular slot cuts the transverse current of the waveguide, which is equivalent to parallel loading.

4. The design method for a terahertz series-fed beamforming network antenna according to claim 1, characterized in that, Designing a series-feed beamforming network and calculating the waveguide transmission line length to provide the required phase difference includes: Two adjacent periodic leaky wave arrays are connected end to end by a transmission line to form a series-fed beamforming network, and the feeding method between the arrays is serial. The electromagnetic wave input at the input port is transmitted through the first-stage leaky antenna to the input port of the next-stage leaky antenna via the waveguide transmission line at the bottom layer. The phase difference between two adjacent leaky antenna stages is determined by the length of a single leaky antenna. L 1. Length of the bottom delay line L 2. Antenna-bottom delay line interconnection structure length L The phase difference introduced by the transmission line, determined by the three factors, is expressed as follows: in, λ c It is the cutoff wavelength of the waveguide. λ This refers to the wavelength corresponding to the operating frequency, and the calculation relationship is as follows: λ c = 2 W , W This is the length of the wide side of the waveguide.

5. The design method for a terahertz series-fed beamforming network antenna according to claim 1, characterized in that, By analyzing the dispersion characteristics of two different transmission lines at the top and bottom layers of the antenna, and combining this with the radiator loading method, the aperture amplitude and phase distribution are derived, resulting in the antenna array factor and frequency sweep range, including: Based on a simplified model of the antenna array, the antenna array includes m × n Unit, in x and y The spacing in the directions are respectively d x and d y Its array factor F ( θ , φ ) is represented as: in, I MN and a MN These represent the amplitude and phase of the Mth and Nth radiators, respectively. Each leaky antenna in the antenna is fed in series from start to finish, and the amplitude of each leaky antenna will attenuate sequentially. The attenuation component includes the radiation attenuation of the element. A rad _ IJ and waveguide transmission line attenuation A wg The amplitude of the Mth and Nth radiators I MN The expression is: For the phase distribution of the array elements, the phase delay introduced by the bottom waveguide transmission line of the antenna is: in, l wg It is the length of the waveguide transmission line. λ c It is the cutoff wavelength of the waveguide. x The phase delay between adjacent slots in the direction is: In the formula, the additional 180° is achieved through alternating left and right radial slits. β Let be the propagation constant of the SSPP transmission line. For the SSPP transmission line in the antenna, it is expressed as: in, k It is the wavenumber in free space. p It is the period length of the SSPP unit. a and h These are the width and height of the metal plate, respectively. Based on the above formula, different frequencies and their corresponding array factors are calculated.

6. The design method for a terahertz series-fed beamforming network antenna according to claim 1, characterized in that, Optimizing the dimensional parameters of each part of the antenna structure includes: The initial parameters of the terahertz series-fed beamforming network antenna are set, and the single-pole and multi-stage antenna arrays are optimized using simulation software to obtain the antenna array. The phase difference required by the series-fed beamforming network is calculated, and the length of the single leaky antenna L1, the length of the bottom delay line L2, and the length of the interconnection structure of the bottom delay line of the antenna L3 are optimized to obtain the total length of the delay line and the width of the inner wall of the waveguide of the series-fed network.

7. A terahertz series-fed beamforming network antenna, characterized in that, Based on the design method described in any one of claims 1-6, the structure is a multi-layer structure, consisting of the following from top to bottom: a radiating array, a waveguide cavity (2), an SSPP structure, a waveguide bottom, a series-fed beamforming network, and the waveguide bottom of the series-fed beamforming network; a plurality of slotted radiation holes (3) are uniformly opened on the radiating array (1) to form a radiation hole array, and an OSB suppression hole (4) is located on the slotted radiation hole (3). The diameter of the OSB suppression hole (4) is greater than the width of the slotted radiation hole (3), and the diameter of the OSB suppression hole (4) is less than the length of the slotted radiation hole (3); a circular OSB suppression hole (4) is set on the radiating slot, and the entire antenna array extends out of the waveguide opening (8); transmission through holes (7) are opened on both sides of the SSPP structure and the waveguide bottom; a twisted waveguide (9) is set in the series-fed beamforming network, and a quarter-circular metal wall is used for transition.

8. The terahertz series-fed beamforming network antenna according to claim 7, characterized in that, The radiation array has a length of 20.5 mm, a width of 19.55 mm, and a thickness of 0.75 mm; the slit radiation aperture (3) has dimensions of 0.06 mm × 0.5 mm × 0.05 mm; the OSB suppression aperture (4) has a radius of 0.08 mm and a height of 0.05 mm; the SSPP slit (6) has dimensions of 0.045 mm × 0.6 mm × 0.2 mm; the waveguide port (8) has dimensions of 0.1 mm × 0.71 mm × 0.7 mm; and the waveguide cavity (2) has a thickness of 0.1 mm.

9. The terahertz series-fed beamforming network antenna according to claim 8, characterized in that, SSPP slits (6) are opened on the SSPP structure. Each row of slit radiation holes (3) is directly opposite a row of SSPP slits (6). There is a raised structure in the middle of the bottom of the SSPP slits (6). The SSPP structure is two-layered, with the upper layer having a thickness of 0.2 mm and the lower layer having a thickness of 0.1 mm.

10. The terahertz series-fed beamforming network antenna according to claim 7, characterized in that, Two adjacent slit radiation apertures (3) in a column along the length of the radiation array are located on both sides of the center line of the column, and the two adjacent slit radiation apertures (3) have a set length of overlap in the length direction; The center of the OSB suppression aperture (4) is located on the center line of the length direction of the slit radiation aperture (3), and the OSB suppression aperture (4) is biased towards the waveguide port direction on the slit radiation aperture (3).

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