High focusing characteristic near field antenna based on symmetric rectangular leaky waveguide

Abstract

This invention discloses a near-field antenna with high focusing characteristics based on a symmetrical rectangular leaky waveguide, relating to the field of microwave antenna technology. It includes a first short leaky waveguide unit and a second short leaky waveguide unit, both with identical structures and synchronized feed phases. The electric field vector polarization directions of the first and second short leaky waveguide units at a preset focal point S are also consistent. Through coherent superposition of symmetrical beams, the field strength amplitude at the focal point is significantly enhanced, resulting in a significant improvement in detection sensitivity. When applied to non-destructive testing of composite materials, a stronger incident field can excite stronger defect scattering signals, thereby enabling the detection of deeper and smaller internal defects. The symmetrical structure naturally compensates for the directional deviation of the unidirectional leaky wave antenna, resulting in a more uniform distribution of the focused spot in both the longitudinal and lateral directions, thus improving the spatial resolution of the detection.

Description

Technical Field

[0001] This invention relates to the field of microwave antenna technology, and in particular to a near-field antenna with high focusing characteristics based on a symmetrical rectangular leaky waveguide. Background Technology

[0002] Microwave near-field focusing technology refers to the use of antenna structure design, field distribution modulation, or signal processing to create a highly concentrated "focused spot" of microwave energy in the near-field region. The core objective is to achieve high energy density and high spatial resolution field distribution control at close range. In recent years, microwave near-field focusing technology has seen increasingly widespread applications in daily life. In medical settings, the focused beam can precisely target diseased tissue, enabling microwave thermotherapy. In security and public safety, millimeter-wave and submillimeter-wave imaging systems utilize near-field focusing characteristics to perform concealed object detection and high-resolution security imaging without contacting the target and while protecting privacy. Compared to lens antennas and reflector antennas, leaky-wave antennas (LWA) offer advantages such as low profile, simple structure, and ease of integration, making them an important candidate for near-field focusing.

[0003] Taking the field of non-destructive testing (NDT) as an example, in recent years, non-metallic materials have been widely used in various fields. However, during production, processing, and use, they are easily affected by various factors, resulting in damage and defects. Failure to detect and repair these problems in a timely manner will threaten the material performance and safety, and even endanger the safety of engineering structures. Therefore, effective methods are needed to detect these defects. Microwave-based NDT technology is an ideal choice because microwave signals can penetrate non-metallic materials and interact with their internal structure, making it very practical for the testing of various non-metallic materials. This technology does not generate ionizing radiation and does not require a coupling agent, making it a non-contact testing method. In particular, microwave near-field testing technology is widely used in the testing of various non-metallic materials due to its high sensitivity and excellent resolution.

[0004] In microwave detection, the sensitivity and spatial resolution of the detector directly depend on the focusing performance of the antenna. To form a high-energy-density "focused spot" in the near-field region, researchers have proposed various solutions. The paper "Microwave Near-Field Focusing Properties of Width-Tapered Microstrip Leaky-Wave Antenna" proposes a microstrip leaky-wave antenna with a tapered width. While it achieves focusing, the high dielectric loss of the microstrip structure at high frequencies limits its penetration capability in thick-walled material detection. The paper "Near-field leaky-wave focusing antenna with inhomogeneous rectangular waveguide" proposes a focusing antenna based on a rectangular waveguide, utilizing the variation in the waveguide's wide-wall height to control the phase. Compared to microstrip lines, waveguide structures have extremely low loss and high power capacity, making them more suitable for high signal-to-noise ratio detection. However, existing waveguide antennas mostly employ unidirectional traveling-wave structures, which, while achieving focusing, have the following limitations:

[0005] Field strength limitation: Since it is a unidirectional traveling wave radiation, the energy decays exponentially along the propagation direction, and only the contribution of the radiation field on one side is utilized, so the increase in electric field strength at the focal point is limited.

[0006] Larger size: In order to obtain sufficient phase accumulation and aperture efficiency, antennas are usually long, making it difficult to balance increasing field strength and reducing antenna size. Summary of the Invention

[0007] The purpose of this invention is to design a near-field antenna with high focusing characteristics based on a symmetrical rectangular leaky waveguide in order to solve the above problems.

[0008] The present invention achieves the above objectives through the following technical solutions:

[0009] High-focusing near-field antennas based on symmetrical rectangular leaky waveguides include:

[0010] First short leaky waveguide unit;

[0011] The second short-leaking waveguide unit; the first short-leaking waveguide unit and the second short-leaking waveguide unit have the same structure, and the first short-leaking waveguide unit and the second short-leaking waveguide unit are arranged in a mirror symmetrical manner. The shortest distance L1 between the first end of the first short-leaking waveguide unit and the first end of the second short-leaking waveguide unit is greater than 0. The feeding phase of the first short-leaking waveguide unit and the second short-leaking waveguide unit is synchronized. The electric field vector polarization direction of the first short-leaking waveguide unit and the second short-leaking waveguide unit at the preset focus S is consistent.

[0012] The beneficial effects of this invention are as follows: through the coherent superposition of symmetrical beams, the field strength amplitude at the focal point is significantly enhanced, resulting in a significant improvement in detection sensitivity. When applied to nondestructive testing of composite materials, a stronger incident field can excite a stronger defect scattering signal, thereby enabling the detection of deeper and smaller internal defects; the symmetrical structure naturally compensates for the directional deviation of the unidirectional leaky wave antenna, making the distribution of the focused spot more uniform in the longitudinal and lateral directions, thus improving the spatial resolution of the detection; compared to a single antenna of full length L, this invention uses two short leaky waveguide units of length L', ensuring a stronger effective radiated energy intensity while maintaining the same overall physical length of the antenna; this invention retains the low-loss and high-power capacity characteristics of rectangular waveguides, making it particularly suitable for applications such as aerospace where extremely high signal-to-noise ratio requirements are present. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the high-focusing near-field antenna based on a symmetrical rectangular leaky waveguide according to the present invention;

[0014] Figure 2 This is a simulation curve of the reflection coefficient (S11) parameter of the antenna array described in the embodiment of the present invention within the operating frequency band;

[0015] Figure 3 The diagram shows the energy distribution in the z-direction at 27 GHz when x = 175 mm.

[0016] Figure 4 This is a diagram showing the electric field distribution of a focusing antenna. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0018] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0019] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0020] In the description of this invention, it should be understood that the terms "upper," "lower," "inner," "outer," "left," "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used to facilitate the description of this invention and to simplify the description, and are not intended to 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.

[0021] Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0022] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, terms such as "set" and "connection" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0023] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0024] High-focusing near-field antennas based on symmetrical rectangular leaky waveguides include:

[0025] First short leaky waveguide unit;

[0026] The second short-leaking waveguide unit; the first and second short-leaking waveguide units have the same structure and are arranged in a mirror-symmetric manner. The shortest distance L1 between the first end of the first short-leaking waveguide unit and the first end of the second short-leaking waveguide unit is greater than 0. The feeding phases of the first and second short-leaking waveguide units are synchronized. The electric field vector polarization directions of the first and second short-leaking waveguide units at the preset focal point S are consistent, so that the two electromagnetic waves undergo coherent constructive superposition. The amplitude E of the total electric field intensity is the scalar sum of the independent electric field intensities of the two units, thereby improving the focusing gain.

[0027] The waveguide wide-wall height h(Z) varies nonlinearly with the longitudinal position Z to satisfy the phase synchronization condition at the preset focus S; the first short-leaking waveguide unit and the second short-leaking waveguide unit are excited at the same time, and the two electromagnetic waves generated are coherently superimposed at the preset focus S to form an enhanced focusing electric field.

[0028] Symmetrical Array Architecture: This invention breaks away from the traditional "single waveguide long line" design of waveguide antennas, employing two waveguides with identical structures as sub-units. These two sub-units are arranged in a mirror-symmetric manner about a preset focal plane (the normal plane where the focal point is located). This symmetry eliminates the focusing point asymmetry problem caused by unidirectional wave leakage from a physical structural perspective.

[0029] Coherent superposition enhances field strength: According to the principle of electromagnetic wave superposition, at a preset focal point, the beams from two directions are in perfect phase and coherently superimpose. If the electric field amplitudes of the two elements at the focal point are both E0, the total electric field strength amplitude after superposition is 2E0. This means that, with the total input power remaining constant, this invention can significantly increase the energy density at the focal point, thereby greatly enhancing the scattered echo signal from tiny defects.

[0030] The waveguide wall height at the first end of the first short leaky waveguide unit is less than the waveguide wall height at the second end of the first short leaky waveguide unit; the waveguide wall height at the first end of the second short leaky waveguide unit is less than the waveguide wall height at the second end of the second short leaky waveguide unit; the phase constant β of the rectangular waveguide changes with the wall height h(Z), thereby dynamically adjusting the radiation angle of the leaky wave.

[0031] Let the positional change from the second end of the first short-drain waveguide unit to the first end of the first short-drain waveguide unit and the positional change from the second end of the second short-drain waveguide unit to the first end of the second short-drain waveguide unit both be Z. The relationship between the waveguide wide-wall height h(Z) and the positional change Z is as follows: Where A is the basic size factor, B is the angle control factor, k0 is the wave number in vacuum, and β(Z) is the desired phase constant distribution.

[0032] The phase constant distribution β(Z) decreases as the position Z increases, thereby compensating for the change in spatial optical path.

[0033] The relationship between the phase constant distribution β(Z) and the position change Z is as follows: , The coordinates of the preset focus S.

[0034] Both the first and second short-leaking waveguide units have periodic slots on their narrow walls to allow for energy leakage and radiation.

[0035] This embodiment designs a near-field focusing antenna with a center frequency of 27 GHz (Ka band), aiming to solve the problem that existing rectangular leaky waveguides struggle to simultaneously enhance the electric field and reduce antenna size during near-field focusing. A standard rectangular waveguide WR-34 or similar size is selected as the base, with a base width a = 8.5 mm. This is to achieve energy focusing at a distance from the antenna aperture. The required phase distribution is inferred from the position of the waveguide using the principle of holographic interference. Based on the leakage waveguide design theory and a series of formulas, the theoretically calculated phase distribution β(Z) is transformed into the actual geometric dimension distribution h(Z), thus completing the waveguide design. Specifically, this includes the following:

[0036] This invention completes the final modeling by constructing an accurate mapping relationship between the propagation direction Z and the waveguide wide-wall height h in the following manner.

[0037] (1) A rectangular waveguide model with a length of L=70 was constructed. The waveguide was placed along the Z-axis, with a position range of Z=0mm to Z=70mm. The base width a was fixed at 8.5mm, and radiation slots were opened on the narrow wall according to a preset period P. The height of the wide wall of the waveguide was defined as the parameter variable h. Using the parameter scanning function of CST, the variable h was set as the scanning object. The scanning range was set to 5.6 to 8, and the step size was set to 0.2. After the simulation was completed, the far-field radiation pattern corresponding to each h value was viewed and recorded in turn. On the main section of the XZ plane, the angle corresponding to the maximum gain of the main beam was found. The angle between the beam pointing and the waveguide axis was recorded as the deflection angle θ. Thus, a discrete reference table containing 13 sets of data was obtained, as shown in Table 1. This data table directly reflects the ability of the geometric height to control the radiation direction of this specific leaky wave structure at the working frequency.

[0038] Table 1. Correspondence between waveguide wide-wall height and beam deflection angle

[0039]

[0040] (2) Fitting the intermediate characteristic function: The discrete data obtained from the first step of the simulation are used to fit the intermediate characteristic function. Import the data into MATLAB. Using MATLAB's curve fitting tool, an exponential function model is selected to perform nonlinear regression fitting on the relationship between waveguide height and radiation angle. After optimization calculation, the intermediate characteristic relationship between the waveguide wide-wall height h (unit: mm) and the radiation deflection angle θ (unit: radians) is obtained as follows: This formula quantitatively characterizes the phase control characteristics of the waveguide structure at a specific frequency, and the goodness of fit meets the design requirements.

[0041] (3) Phase requirement and geometric mapping According to the near-field focusing principle, the leaked wave at any longitudinal position Z on the waveguide must point to the focal point S. Combining the geometric relationship and the phase constant formula, the ideal radiation angle θ(Z) required at any position Z is derived. Substituting this θ(Z) into the intermediate relationship obtained in the second step, the theoretical numerical sequence of waveguide height variation with position is obtained.

[0042] (4) Gaussian Fitting and Modeling of the Final Geometric Curve: To obtain a mathematically concise analytical expression that facilitates the generation of a smooth surface in modeling software, a second fitting was performed on the theoretical height sequence calculated in the third step using MATLAB. A Gaussian function model was used for approximation to obtain the final waveguide wide-wall height distribution function. The final expression output by MATLAB fitting is as follows: This expression is the definition of the set profile of the waveguide gradient slope in this invention.

[0043] (5) In CST, use the analytical curve function to directly input the Gaussian fitting formula obtained in step four. Define variable Z as a parameter; generate a solid structure with a continuous, smooth, gradually changing slope.

[0044] The height modulation function used in this invention is: .like Figure 1 As shown, the high-gain microwave near-field focusing antenna array proposed in this invention consists of two identical rectangular waveguide radiating elements. The left element is located in the Z=0mm to 70mm interval, and the right element is generated symmetrically about the central plane (Z=100mm) and is located in the Z=130mm to 200mm interval. The lateral dimension of the entire antenna array (from the start point of the left element to the end point of the right element) is 200mm. The preset focal point S is located at Z=100mm and X=175mm. At this time, the distance from the edge of the waveguide radiating position (Z=70mm and Z=130mm) to the focal point is 30mm in the Z direction and 175mm in the X direction. In contrast, the conventional unidirectional long waveguide has a length of 200mm (Z=-100mm to 100mm), and its focal point is set at Z=130mm and X=175mm, maintaining the same relative distance in the Z and X directions as the proposed high-gain microwave near-field focusing antenna array. This invention improves performance by more than doubling the electric field strength amplitude at the relative position while maintaining the same overall physical size and the relative distance between the antenna and the focusing position as traditional long waveguides.

[0045] Figure 2 The simulation results of the reflection coefficient (S11) of the antenna array as a function of frequency are shown. As can be seen from the figure, the amplitude of the S11 curve is about -21dB near the design center frequency of 27GHz, indicating that the segmented symmetrical structure still maintains good impedance matching characteristics, and energy can be effectively fed in and radiated.

[0046] To quantify the focusing effect of this invention, Figure 3 The electric field energy distribution curve along the z-axis at an operating frequency of 27 GHz is presented. Under the same structural dimensions and focal length parameters, the maximum electric field amplitude at the focal point of a conventional long waveguide antenna is approximately... The symmetrical array antenna proposed in this invention achieves a maximum electric field strength amplitude of 52 V / m (approximately 35 dB) at the focal point. Data shows that, under the premise of comparable S11 performance, this invention, through symmetrical coherent superposition technology, more than doubles the electric field strength amplitude at the focal point, thus improving the sensitivity of near-field detection. Furthermore, the peak of the curve precisely appears at Z=100 mm, perfectly consistent with the pre-designed focal position, proving the accuracy of the mapping relationship between the phase constant β(Z) and the waveguide height h(Z). The image exhibits perfect left-right symmetry, which means that the energy distribution of the focused spot in the Z direction is more uniform, which is beneficial for improving the accuracy of imaging decisions.

[0047] Figure 4 This visually illustrates the two-dimensional electric field amplitude distribution cloud map of the antenna array on the XZ plane. The image clearly shows two high-intensity beams emanating from the left and right waveguide elements, converging towards the center at a specific tilt angle. Within the pre-defined focal region... Nearby, the two beams interfered strongly and superimposed, forming a bright spot with highly concentrated energy and a clear outline. The sidelobe levels around this bright spot were low, indicating that most of the energy was effectively concentrated within the main focal spot, further verifying the feasibility and effectiveness of the present invention in achieving high-field-strength near-field focusing using a symmetrical array.

[0048] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A near-field antenna with high focusing characteristics based on a symmetrical rectangular leaky waveguide, characterized in that, include: First short leaky waveguide unit; The second short-leaking waveguide unit; the first short-leaking waveguide unit and the second short-leaking waveguide unit have the same structure, and the first short-leaking waveguide unit and the second short-leaking waveguide unit are arranged in a mirror symmetrical manner. The shortest distance L1 between the first end of the first short-leaking waveguide unit and the first end of the second short-leaking waveguide unit is greater than 0. The feeding phase of the first short-leaking waveguide unit and the second short-leaking waveguide unit is synchronized. The electric field vector polarization direction of the first short-leaking waveguide unit and the second short-leaking waveguide unit at the preset focus S is consistent.

2. The near-field antenna with high focusing characteristics based on a symmetrical rectangular leaky waveguide according to claim 1, characterized in that, The waveguide wide wall height at the first end of the first short leakage waveguide unit is less than the waveguide wide wall height at the second end of the first short leakage waveguide unit; the waveguide wide wall height at the first end of the second short leakage waveguide unit is less than the waveguide wide wall height at the second end of the second short leakage waveguide unit.

3. The near-field antenna with high focusing characteristics based on a symmetrical rectangular leaky waveguide according to claim 2, characterized in that, Let the positional change from the second end of the first short-drain waveguide unit to the first end of the first short-drain waveguide unit and the positional change from the second end of the second short-drain waveguide unit to the first end of the second short-drain waveguide unit both be Z. The relationship between the waveguide wide-wall height h(Z) and the positional change Z is as follows: Where A is the basic size factor, B is the angle control factor, k0 is the wave number in vacuum, and β(Z) is the desired phase constant distribution.

4. The near-field antenna with high focusing characteristics based on a symmetrical rectangular leaky waveguide according to claim 3, characterized in that, The phase constant distribution β(Z) decreases as the position Z increases.

5. The near-field antenna with high focusing characteristics based on a symmetrical rectangular leaky waveguide according to claim 4, characterized in that, The relationship between the phase constant distribution β(Z) and the position change Z is as follows: , The coordinates of the preset focus S.

6. The near-field antenna with high focusing characteristics based on a symmetrical rectangular leaky waveguide according to claim 1, characterized in that, Periodic slots are provided on the narrow walls of both the first and second short-leaking waveguide units.

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