Quasi-single-mode circular waveguide conical horn antenna, radar and communication device

Abstract

The invention discloses a quasi-single-mode circular waveguide conical horn antenna, a radar and a communication device. The quasi-single-mode circular waveguide conical horn antenna comprises a circular waveguide section and a conical horn section. Conductor loss is reduced by remarkably increasing the diameter of the circular waveguide, and axial periodic annular grooves are formed in the inner wall of the circular waveguide to form a spatial mode filter and a selective attenuation high-order mode, so that high radiation efficiency and high mode purity are realized at the same time in a millimeter wave frequency band. And the conical horn section adopts an index profile to realize high-directionality radiation. The antenna structure effectively solves the technical problems of large loss and impure mode in a millimeter wave high-frequency band in the traditional design.

Description

Technical Field

[0001] This invention relates to the field of radar measurement, specifically to a quasi-single-mode circular waveguide conical horn antenna, radar, and communication device. Background Technology

[0002] Conical horn antennas are widely used in satellite communications, radio astronomy, radar, and measurement systems due to their simple structure, strong directivity, and wide bandwidth. In the millimeter-wave band, traditional rectangular waveguide horns suffer from problems such as low polarization purity and poor symmetry; while circular waveguide horns naturally possess a symmetrical structure, facilitating circular or dual polarization, and are relatively easy to fabricate. However, circular waveguides contain several degenerate modes (such as TE...). 11 TM 01 TE 21 If higher-order modes cannot be effectively suppressed, it will lead to antenna pattern distortion, deterioration of cross-polarization, and reduced efficiency. Especially in the millimeter-wave high-frequency band (such as 122.5 GHz), dimensional tolerances and surface roughness have a significant impact on mode purity, making stable single-mode transmission extremely challenging. In existing technologies, the diameter of the circular waveguide is usually reduced to meet the single-mode condition, but this increases conductor loss and manufacturing difficulty; or complex structures such as mode filters and dielectric loading are used, but these introduce additional losses and bandwidth limitations. Summary of the Invention

[0003] (I) Technical Solution

[0004] To address the aforementioned technical problems, this invention provides a quasi-single-mode circular waveguide conical horn antenna, a radar, and a communication device.

[0005] In a first aspect, a quasi-single-mode circular waveguide conical horn antenna is provided, comprising:

[0006] A circular waveguide section, having a circular cross-section, is used to transmit electromagnetic waves. The inner wall of the circular waveguide section is provided with axially periodically distributed annular grooves or annular protrusions, configured to selectively attenuate higher-order modes and transmit electromagnetic waves within the operating frequency band. 11 Main model;

[0007] The conical horn section, whose throat is smoothly connected to the exit end of the circular waveguide section, is used to convert the waveguide mode into a free space wave and achieve directional radiation.

[0008] Let the target operating frequency of the antenna be f, and the corresponding free space wavelength be λ. The geometric dimensions of the circular waveguide section and the conical horn section satisfy the following relationship:

[0009] The inner wall diameter of the circular waveguide segment is D1 = k1·λ, where 3.5 ≤ k1 ≤ 5; the length of the circular waveguide segment is L1 = k2·λ, where 20 ≤ k2 ≤ 40; the throat inner wall diameter of the conical horn segment is D2 = D1; the horn mouth inner wall diameter of the conical horn segment is D3 = k3·λ, where 30 ≤ k3 ≤ 40; the length of the conical horn segment is L2 = k4·λ, where 100 ≤ k4 ≤ 150; the groove depth of the annular groove or the protrusion height of the annular protrusion is h = k h ·λ, where 0.05≤k h ≤0.15; the axial periodicity d=k of the annular groove or annular protrusion. d ·λ, where 0.25≤k d ≤0.5.

[0010] Furthermore, the inner wall profile of the conical trumpet segment is an exponential curve, and its curve equation satisfies:

[0011]

[0012] Where r(z) is the radius at the axial position z; R t =D² / 2, where R is the radius of the throat; a =D3 / 2, where D is the diameter radius, and k is the shape constant, with a value ranging from 2 to 3.

[0013] Furthermore, the inner wall surface roughness Ra of the circular waveguide section (1) and the conical horn section (2) is ≤0.2μm, and is coated with a silver or gold coating of 3 to 5μm thickness.

[0014] As a preferred embodiment of this application, the circular waveguide section has a diameter D1 of 10 mm and a length L1 of 80 mm; the conical horn section has a throat diameter D2 of 10 mm, a horn mouth diameter D3 of 80 mm, and a length L2 of 320 mm; and the total axial length of the antenna is 400 mm.

[0015] In a second aspect, a radar is provided, comprising the quasi-single-mode circular waveguide conical horn antenna of the first aspect.

[0016] Thirdly, a communication device is provided, comprising the quasi-single-mode circular waveguide conical horn antenna described in the first aspect.

[0017] (ii) Beneficial effects

[0018] First, by significantly increasing the diameter of the circular waveguide section to approximately 4λ, the conductor loss caused by the skin effect is effectively reduced, improving the antenna radiation efficiency and solving the problems of excessive loss in the high-frequency band and the difficulty in manufacturing due to its small size in traditional single-mode waveguides. Second, by incorporating an axially periodic annular groove structure on the inner wall of the enlarged circular waveguide, selective attenuation of the TM signal within a finite length is achieved based on the Bragg scattering principle.01 TE 21 Using higher-order modes, thus enjoying the advantages of large diameter and low loss while ensuring TE 11 The pure transmission of the master mode avoids pattern distortion. Furthermore, the horn section employs a large-aperture exponential profile design, ensuring smooth wavefront transition and high directional radiation. This antenna provides a key hardware component with low loss, pure beam, and high gain for high-performance systems such as satellite communications and millimeter-wave radar in the 122.5 GHz band. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of the present invention.

[0021] Figure 2 This is a cross-sectional view of a circular waveguide segment.

[0022] Figure 3 The figures show the simulated response curves of gain and frequency in the embodiments of this application.

[0023] Figure 4 This is the radiation pattern of the conical horn antenna in the embodiment of this application. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The described embodiments are only some embodiments of the invention, not all embodiments. Based on the embodiments of the invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the invention.

[0025] The principles and structure of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0026] Please see Figure 1 and Figure 2 The quasi-single-mode circular waveguide conical horn antenna of the present invention includes a circular waveguide section 1 and a conical horn section 2. The circular waveguide section 1 has a circular cross-section for transmitting electromagnetic waves. The inner wall of the circular waveguide section is provided with axially periodically distributed annular grooves 1.1, configured to selectively attenuate higher-order modes and transmit electromagnetic waves within the operating frequency band. 11 Main mold; 1.1 The annular groove can be replaced by an annular protrusion of the same size.

[0027] The throat of the conical horn section 2 is smoothly connected to the exit end of the circular waveguide section 1, which is used to convert the waveguide mode into a free space wave and achieve directional radiation. The inner wall surface roughness Ra of the circular waveguide section 1 and the conical horn section 2 is ≤0.2μm, and they are coated with a 3-5μm thick silver or gold coating.

[0028] The parameters of this antenna are described in detail below.

[0029] Let the target operating frequency of the antenna be f, and the corresponding free space wavelength be λ. The geometric dimensions of the circular waveguide section and the conical horn section satisfy the following relationship:

[0030] The inner diameter of the circular waveguide section is D1 = k1·λ, where 3.5 ≤ k1 ≤ 5. In the millimeter-wave band, the skin effect is significant. The larger the waveguide diameter, the lower the conductor loss per unit length. If a traditional single-mode diameter (approximately 1.7λ) is used, the loss will be too high, reducing radiation efficiency. A larger diameter also allows for greater tolerance to machining tolerances (such as ellipticity and roughness). This diameter is much larger than TE. 11 The single-mode cutoff diameter of the modulus (1.71λ) necessarily supports TM. 01 TE 21 Since higher-order modes are transmitted, a suppression structure is needed to filter out redundant modes.

[0031] In this embodiment, the waveguide wall material is a silver-plated layer with a conductivity σ = 6.1 × 10⁻⁶. 7 S / m, wave impedance η Where μ0 and ϵ0 are the free permeability and free permittivity, respectively. These two values ​​are constant. The theoretical basis is the circular waveguide TE. 11 The conductor attenuation constant α of the dominant mode c ;

[0032]

[0033] R s Let be the surface resistance, and 'a' be the radius of the circular waveguide. =1.841, which is TE 11 The Bessel function roots of the modulus. It can be seen that the attenuation constant α... c It is inversely proportional to the radius *a*. Taking 122.5 GHz as an example, λ ≈ 2.45 mm, R... s ≈0.091Ω, we calculated the attenuation constant and the total loss of the circular waveguide section (25λ) for different k1 values, as shown in the table below:

[0034]

[0035] Increasing k1 from 1.3 to 3.5 reduces loss by approximately 62.5% (from 0.16dB to 0.06dB), demonstrating a significant loss advantage. When k1 < 3.5 (e.g., 2.5), although the loss is lower than that of a single-mode waveguide, considering the total loss budget of the entire antenna system (including the horn section), the smaller diameter leads to an excessively high proportion of conductor loss. In this case, further increasing the diameter no longer significantly improves efficiency (e.g., from 3.5 to 5.0, the improvement is only 0.5%).

[0036] The number of modes N that can propagate in a circular waveguide is approximately proportional to the square of the normalized frequency V:

[0037]

[0038] When k1=5, approximately 30 propagation modes exist within the waveguide. Within a length of 20λ~40λ, the periodic structure still has sufficient "interaction length" to block the main interfering modes (such as TM). 01 ,TE 21 The decay occurs when k1 > 5 (e.g., 6.0). If k1 > 5, the number of modes surges to over 44. A large number of degenerate modes exist in higher-order modes, making it difficult for periodic structures to distinguish and suppress them individually. The increased energy of the residual higher-order modes leads to deterioration of the radiation pattern sidelobes.

[0039] In summary, if k1 < 3.5, the loss advantage is not obvious and the processing difficulty is high. If k1 > 5, the number of higher-order modes is too large, the mode suppression structure will be too complex and difficult to filter out completely within a finite length.

[0040] The length of the circular waveguide segment is L1 = k2·λ, where 20 ≤ k2 ≤ 40; the throat diameter of the conical horn segment is D2 = D1; the inner wall diameter of the horn opening of the conical horn segment is D3 = k3·λ, where 30 ≤ k3 ≤ 40; the length of the conical horn segment is L2 = k4·λ, where 100 ≤ k4 ≤ 150. The inner wall profile of the conical horn segment is an exponential curve, and its curve equation satisfies:

[0041]

[0042] This design allows the wavefront to smoothly transition from a spherical wave to a plane wave, maximizing aperture efficiency. The horn aperture diameter is much larger than the wavelength λ, thus exhibiting high directivity.

[0043] Where r(z) is the radius at the axial position z; R t =D² / 2, where R is the radius of the throat; a =D3 / 2, where D is the diameter radius, and k is the shape constant, with a value ranging from 2 to 3.

[0044] The groove depth of the annular groove or the height of the annular protrusion, h=k h ·λ, where 0.05≤kh ≤0.15; the axial periodicity d=k of the annular groove or annular protrusion. d ·λ, where 0.25≤k d ≤0.5.

[0045] In this embodiment, the periodic annular groove structure on the inner wall of the circular waveguide is essentially a spatial mode filter. Its working principle is based on Bragg scattering and surface impedance modulation theory. By designing the groove depth h and period d, it can selectively affect electromagnetic modes with different propagation constants: strongly attenuating higher-order modes.

[0046] The period d determines which mode the filter targets. When an electromagnetic wave propagates in a periodic structure, if the period satisfies the Bragg reflection condition for a specific mode, that mode will experience strong back-coupling (reflection) or radiation loss. The condition is approximately 2β. mode ·d≈2π·m (m=1,2,...). β mode This is the propagation constant for this mode. TE 11 The propagation constant of the mode is relatively large, and its corresponding Bragg period is approximately 0.5λ. Controlling d below 0.5 (especially in the 0.25λ~0.4λ range) ensures that the TE condition is not met. 11 The reflection condition of the mode is determined to ensure low-loss transmission of the main mode. If k d A period of less than 0.25 indicates an excessively dense period, making the structure approximate a smooth wall for electromagnetic waves (effective medium theory), thus losing its filtering effect. The slot depth determines the "strength" of mode suppression. It controls the coupling coefficient or surface reactance between the dominant mode and higher-order modes. The annular slot alters the boundary conditions of the waveguide's inner wall, effectively introducing a certain surface reactance. The deeper the slot, the stronger the disturbance to the boundary field and the higher the attenuation rate of higher-order modes. If the slot depth is too shallow, the surface disturbance is too weak, and the attenuation constant of higher-order modes is too small. To achieve the desired suppression ratio, an extremely long waveguide section is required, which increases antenna size and conductor loss of the dominant mode. If the slot depth is too deep, the slot itself may form a resonant cavity (similar to a resonator), not only absorbing higher-order modes but also significantly altering the TE signal. 11 The phase velocity and impedance of the master mode lead to increased reflection of the master mode, shift of the phase center, and even excitation of new parasitic modes.

[0047] At around 0.1λ, the groove depth is sufficient to attenuate higher-order modes to noise levels over a short distance (20λ~40λ), while also reducing TE. 11 The influence of mode transmission characteristics is negligible. This applies to satellite ground stations, radio telescope feeds, millimeter-wave imaging systems, etc., in the 122.5 GHz band.

[0048] In this embodiment, the circular waveguide section has a diameter D1 of 10 mm and a length L1 of 80 mm; the conical horn section has a throat diameter D2 of 10 mm, a horn aperture diameter D3 of 80 mm, and a length L2 of 320 mm; the total axial length of the antenna is 400 mm. Compared to traditional single-mode waveguides (approximately 4.2 mm in diameter), the 10 mm diameter increases the conductor surface area, reducing skin effect loss at 122.5 GHz and achieving a radiation efficiency greater than 85%. While this diameter supports multimode transmission, it limits the number of modes to within the range that a periodic structure can handle (approximately 30 modes), avoiding the problem of excessively large diameters leading to overly complex modes that cannot be filtered out, thus ensuring the feasibility of quasi-single-mode transmission. The length L1 provides sufficient interaction distance for the built-in periodic annular slot, ensuring the TM... 01 TE 21 Higher-order modes are attenuated to below -30dB before reaching the horn section, effectively preventing pattern distortion and sidelobe increase. This avoids unnecessary conductor cumulative loss and weight increase caused by excessively long waveguide sections. Figure 4 As shown, the horn aperture diameter is the physical threshold for achieving peak gain. The horn segment length of 320mm ensures a smooth transition of the wavefront from spherical wave to plane wave, and the sufficient tapered length allows for smooth attenuation at the edge of the aperture field distribution, effectively suppressing edge diffraction. Figure 3 The simulated gain-frequency response curves of this antenna structure are shown. Figure 4 The normalized radiated power patterns of the antenna in the E-plane (φ=0°) and H-plane (φ=90°) at an operating frequency of 122.5 GHz are shown.

[0049] Processing parameters:

[0050] Circular waveguide section. Material: Oxygen-free copper. Outer diameter 12mm, inner diameter 10mm, length 80mm. After turning the inner wall, periodic annular grooves are machined with diamond tools: groove depth 0.25mm, period 0.86mm, groove width 0.12mm, approximately 70 grooves in total. The inner wall is plated with 5μm of silver.

[0051] Conical horn section. Machined integrally with the waveguide section or welded in sections. The contour is CNC turned according to an exponential curve, the inner wall is polished to Ra≤0.2μm, and silver-plated to 5μm. The flatness of the horn mouth end face is <λ / 20 (approximately 0.12mm).

[0052] Based on the same inventive concept, this application also provides a radar that uses the above-mentioned high-performance quasi-single-mode circular waveguide conical horn antenna.

[0053] Based on the same inventive concept, this application also provides a communication device that uses the above-mentioned high-performance quasi-single-mode circular waveguide conical horn antenna.

[0054] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A quasi-single-mode circular waveguide conical horn antenna, characterized in that, include: A circular waveguide section, having a circular cross-section, is used to transmit electromagnetic waves. The inner wall of the circular waveguide section is provided with axially periodically distributed annular grooves or annular protrusions, configured to selectively attenuate higher-order modes and transmit electromagnetic waves within the operating frequency band. 11 Main model; The conical horn section, whose throat is smoothly connected to the exit end of the circular waveguide section, is used to convert the waveguide mode into a free space wave and achieve directional radiation. Let the target operating frequency of the antenna be f, and the corresponding free space wavelength be λ. The geometric dimensions of the circular waveguide section and the conical horn section satisfy the following relationship: The inner wall diameter of the circular waveguide segment is D1 = k1·λ, where 3.5 ≤ k1 ≤ 5; the length of the circular waveguide segment is L1 = k2·λ, where 20 ≤ k2 ≤ 40; the throat inner wall diameter of the conical horn segment is D2 = D1; the horn mouth inner wall diameter of the conical horn segment is D3 = k3·λ, where 30 ≤ k3 ≤ 40; the length of the conical horn segment is L2 = k4·λ, where 100 ≤ k4 ≤ 150; the groove depth of the annular groove or the protrusion height of the annular protrusion is h = k h ·λ, where 0.05≤k h ≤0.15; the axial periodicity d=k of the annular groove or annular protrusion. d ·λ, where 0.25≤k d ≤0.

5.

2. The quasi-single-mode circular waveguide conical horn antenna according to claim 1, characterized in that, The inner wall profile of the conical trumpet section is an exponential curve, and its curve equation satisfies: Where r(z) is the radius at the axial position z; R t =D² / 2, where R is the radius of the throat; a =D3 / 2, where D is the diameter radius, and k is the shape constant, with a value ranging from 2 to 3.

3. The quasi-single-mode circular waveguide conical horn antenna according to claim 2, characterized in that, The inner wall surface roughness Ra of the circular waveguide section (1) and the conical horn section (2) is ≤0.2μm, and is coated with a silver or gold coating of 3 to 5μm thickness.

4. The quasi-single-mode circular waveguide conical horn antenna according to claim 3, characterized in that, The circular waveguide section has a diameter D1 of 10 mm and a length L1 of 80 mm; the conical horn section has a throat diameter D2 of 10 mm, a horn mouth diameter D3 of 80 mm, and a length L2 of 320 mm; the total axial length of the antenna is 400 mm.

5. A radar, characterized in that, It includes a quasi-single-mode circular waveguide conical horn antenna as described in any one of claims 1 to 4.

6. A communication device, characterized in that, It includes a quasi-single-mode circular waveguide conical horn antenna as described in any one of claims 1 to 4.

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