45-degree polarized array waveguide antenna and system for millimeter wave radar

Abstract

The invention relates to the field of millimeter wave radars, and discloses a 45-degree polarized array waveguide antenna for a millimeter wave radar, which comprises a metal groove layer; a slot array element layer; the slot array element layer and the metal slot layer are connected in a vertical lamination mode; the metal groove layer is provided with a plurality of radiation grooves; radiation grooves with the same number are formed in the metal groove layer at the corresponding positions of the slot array elements; the radiation slot indirectly increases the effective radiation aperture area of the antenna. The invention provides a method for solving the problems of low array pattern sidelobe, low gain and wide beam width of the N-element waveguide array antenna in a miniaturized application scene.

Description

Technical Field

[0001] The present invention relates to the field of millimeter wave radar, and in particular to a 45-degree polarization array waveguide antenna and system for millimeter wave radar. Background Art

[0002] Currently, millimeter-wave radars primarily use microstrip array antennas. Key performance indicators, including bandwidth, gain, beamwidth, and sidelobes, directly determine the radar's detection range, accuracy, and capability. To improve these performance characteristics, engineers and scholars in the field have researched and designed a microstrip comb array antenna. This broadens the bandwidth of traditional resonant microstrip antennas, increases gain, narrows beamwidth, reduces sidelobes, and improves isolation between antenna channels, enabling widespread use of microstrip array antennas in millimeter-wave radars.

[0003] Arrayed waveguide antennas are widely used in next-generation millimeter-wave imaging radars due to their narrow beamwidth, high aperture efficiency, low transmission loss, and high power handling. Millimeter-wave imaging radars employ waveguide antennas in miniaturized systems. Size significantly limits their performance, and the manufacturing process used for arrayed waveguide antennas has higher tolerances than the PCB manufacturing used for traditional microstrip array antennas. The performance of arrayed waveguide antennas directly determines the radar's detection capability. Improving the performance of waveguide antennas within limited size and large process tolerances to meet the requirements of millimeter-wave imaging radars while also adapting them to factory production is a key technical focus in the development of arrayed waveguide antennas for millimeter-wave radars.

[0004] The design of waveguide antenna solutions in the existing technology mainly focuses on the design of the current distribution and radiation pattern function of the array antenna, while ignoring the impact of boundary conditions on the antenna radiation pattern. After the radiation pattern function of a single array element is determined according to the application scenario and the single array element is designed, an appropriate current distribution can be designed through Taylor and Chebyshev distributions in the array antenna to achieve the overall radiation pattern target. This method ignores the size limitation of the array, which, however, restricts the optimization of antenna performance. Under a fixed size, when the radiation pattern function meets the standard, optimizing the current distribution often causes impedance mismatch and leads to bandwidth reduction, while when the current distribution meets the standard, optimizing the radiation pattern function often leads to gain reduction or sidelobe increase. Summary of the Invention

[0005] The main purpose of the present invention is to solve the technical problems of narrow bandwidth, low gain and high sidelobe of existing waveguide array antennas. A 45-degree polarized array waveguide antenna for millimeter wave radar, the 45-degree polarized array waveguide antenna comprising: A metal slot layer; a slot array element layer; the slot array element layer and the metal slot layer are connected in a vertical stacking manner; the metal slot layer is provided with a plurality of radiation slots; the same number of radiation slots are provided in the metal slot layer at positions corresponding to the slot array elements; the radiation slots indirectly increase the effective radiation aperture area of the antenna; the angle between the length direction of the slot array element and the waveguide transmission direction is 45 degrees.

[0006] As a preferred technical solution, the waveguide antenna further includes two transverse slots and one longitudinal slot; the transverse slots are arranged near the radiation slot along the waveguide transmission direction; and the longitudinal slots are arranged near the radiation slot along the tangential direction of the waveguide transmission direction.

[0007] As a preferred technical solution, the two transverse grooves are symmetrical with respect to the waveguide transmission direction.

[0008] As a preferred technical solution, the slot array element layer and the metal slot layer form a layer of metal waveguide.

[0009] As a preferred technical solution, the transverse groove is 15.3 mm long and 1.25 mm wide.

[0010] As a preferred technical solution, the longitudinal groove is 2.65 mm long and 1.45 mm wide.

[0011] As a preferred technical solution, the radiation slot is provided with a transition gradient profile, and the gradient curve of the transition gradient profile is one of a cylindrical curve, a rectangular horn profile, and a trigonometric function curve.

[0012] As a preferred technical solution, a metal waveguide wall is provided in the height direction of the outer cross-section of the array antenna, and the cross-sectional height of the metal waveguide wall exceeds the slot array element layer.

[0013] As a preferred technical solution, periodic sensory or capacitive structures are arranged in a staggered manner in the radiation slots.

[0014] The present invention has the following beneficial effects: 1. Existing technologies often increase the array area, the number of array elements, the number of waveguide layers, etc. when improving related performance. However, the present invention maintains the array area and the number of array elements basically unchanged, while achieving a wider bandwidth, higher gain, narrower beamwidth, and higher main and side lobes.

[0015] 2. In the existing technology, the mainstream solutions for 45-degree polarized waveguide array antennas all use substrate integrated waveguides as the transmission line structure. The present invention uses a metal waveguide transmission line structure to achieve 45-degree polarization, reducing manufacturing costs and meeting mass production requirements.

[0016] 3. The depth and size of the metal groove are related to the radiating element. This design of adding the metal groove avoids increasing the process complexity of the antenna. At the same time, chamfers are added to the radiating element and the metal groove to facilitate adaptation to the mechanical processing drawings required for factory manufacturing.

[0017] 4. There is a certain degree of cross-polarization between the transmission signals of the 45° polarized waveguide array antenna designed by the present invention and the horizontally polarized and vertically polarized antennas. Even the transmission signals of the opposite 45° polarized antennas have good cross-polarization isolation, as shown in the attached figure. Figure 8 As shown in the figure, among the coupling degrees of different polarization modes at the same antenna position, the 45-degree polarization has a higher isolation. In millimeter-wave radar applications, it can effectively reduce the electromagnetic interference of other millimeter-wave radar signals and improve the anti-interference performance of millimeter-wave radar. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a three-dimensional schematic diagram of the waveguide array antenna according to embodiment 1 of the present invention; Figure 2 This is a plan view of the waveguide array antenna according to embodiment 1 of the present invention; Figure 3 4 is a longitudinal sectional side view of the waveguide array antenna according to embodiment 1 of the present invention; Figure 4 Schematic diagram of a waveguide array antenna according to embodiment 2 of the present invention; Figure 5 This is a diagram showing the impedance bandwidth simulation results of an embodiment of the present invention; Figure 6 This is the simulation result of the elevation pattern of the antenna array according to the embodiment of the present invention; Figure 7 This is the simulation result of the horizontal radiation pattern of the linear array antenna according to the embodiment of the present invention; Figure 8 : is the in-band gain simulation result of an embodiment of the present invention (theta=0°, phi=0°); Figure 9 This is a simulation diagram of polarization isolation according to Example 3 of the present invention; Figure 10 is the coupling degree between different polarizations in Example 3 of the present invention; Figure 11 This is the preferred first alternative implementation of the present invention; Figure 12 This is a second preferred alternative embodiment of the present invention; Figure 13 This is the third preferred alternative implementation of the present invention.

[0019] Reference numerals: Array element 1, metal slot 2, slot array element 3, radiation slot 4, metal slot 5, longitudinal slot 6, metal slot layer 7, slot array element layer 8, transmitting antenna 9, receiving antenna 10; transition gradient profile 11, metal waveguide wall 12, metal through-hole 13. DETAILED DESCRIPTION

[0020] The terms "first," "second," "third," "fourth," and so on (if any) in the description and claims of the present invention and in the accompanying drawings are used to distinguish similar items and are not necessarily used to describe a particular order or sequential sequence. It should be understood that the terms used in this manner are interchangeable under appropriate circumstances, so that the embodiments described herein can be implemented in an order other than that shown or described herein. In addition, the terms "including," "comprising," "having," and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus that includes a series of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, product, or apparatus.

[0021] In the present invention, Figure 2 The length direction is y, the width direction is x, and the direction perpendicular to the length and width is z.

[0022] For ease of understanding, the specific process of the embodiment of the present invention is described below. Figure 1 , an embodiment of a 45-degree polarized array waveguide antenna for millimeter wave radar in an embodiment of the present invention includes: The waveguide array antenna for millimeter-wave radar described in the present invention comprises an n-element waveguide array antenna and a rectangular waveguide feed structure, wherein the n-element waveguide array antenna and the rectangular waveguide feed structure are connected as two waveguide layers. Above the rectangular waveguide feed structure are radiating elements, with spacing equal to one waveguide wavelength. The 45-degree polarized waveguide array antenna utilizes slot radiating elements. The length of the radiating elements is one-half wavelength, depending on the operating frequency, and the width is determined by the array element current distribution. The thickness of the metal slot layer 7 and the slot element layer 8 is determined by the thickness requirements of the manufacturing process. The slot element layer forms a 45-degree angle with the waveguide transmission direction, ensuring that the current distribution forms a 45-degree angle with the rectangular waveguide transmission direction, thereby achieving a 45-degree polarization of the far-field electric field in space. The antenna is designed by adjusting the amplitude and phase of each element in the linear array. Specifically, the amplitude and phase of the radiating element input port, as well as the width and thickness of the radiating element, are analyzed using electromagnetic simulation software. Finally, an appropriate amplitude and phase distribution is selected to synthesize a 45-degree polarized beam.

[0023] Figure 4This is the basic structure of a 45° polarized four-element waveguide array antenna. The four slots form a 45° angle with the waveguide transmission direction, so that the current distribution also has a 45° angle distribution, thereby achieving 45° polarization and obtaining a higher gain and main-to-sidelobe ratio. The radiating metal slot 4 indirectly increases the effective radiation aperture area of the antenna, improves the antenna gain, and avoids the sidelobe elevation caused by the discontinuous impedance transition on the aperture surface.

[0024] Preferably, the radiating metal slots 7 and the slot array element layer 8 are combined into a single metal waveguide, simplifying manufacturing and reducing assembly errors. This design offers advantages such as high gain and a narrow beam, but the current overall radiation pattern's main-to-sidelobe ratio is insufficient to meet millimeter-wave radar requirements.

[0025] Preferably, in order to improve the performance of the array antenna, a radiation metal slot 4 is added above the slot, as shown in the attached Figure 1-3 As shown, the physical aperture of the array element 1 is increased, including increasing the length and width of the radiation metal slot 4, and adding two transverse slots and one longitudinal slot near the radiation slot 4 along the axial and tangential directions of the propagation direction of the waveguide.

[0026] Preferably, the two transverse slots 5 are symmetrical about the waveguide transmission direction to obtain a symmetrical horizontal radiation pattern. The inner wall of the transverse slot 5 and the outer wall of the radiation slot 4 affect the distribution of the tangential surface current and the horizontal near-field electric field, thereby affecting the horizontal beam. Similarly, the inner wall of the longitudinal slot 6 and the outer wall of the radiation slot 4 affect the distribution of the axial surface current and the pitch near-field electric field, thereby affecting the pitch radiation pattern. The slot depth and slot width of the transverse slot 5 and the longitudinal slot 6 affect the main-sidelobe ratio of the radiation pattern, and this influence comes from the suppression of high-order modes and will not cause changes in other performance. This is also the reason why the main-sidelobe ratio performance can be essentially improved. After adding the metal slot 2 structure, it is necessary to perform scanning parameter analysis on the amplitude and phase of the slot array element 3 of each array element 1 again to obtain a new composite radiation pattern. At this time, it can be clearly found that the area of the Shekunnov unit circle of the composite radiation pattern has increased significantly, which means that the gain and sidelobe performance of the array antenna are improved at the same time.

[0027] The 76.5GHz frequency point is used as the design center frequency point. Figure 5-8 As shown in the figure, the bandwidth reaches 10 GHz. At the center frequency of 76.5 GHz, the width of the metal slot 4 should be 0.8 guided wavelengths (about 3.1 mm). To control its radiation pattern and improve the gain, the radiating metal slot 4 is widened by 0.2 guided wavelengths (about 0.9 mm), and two transverse slots 5 with a length of 15.3 and a width of 1.25 mm and a longitudinal slot 6 with a length of 2.65 mm and a width of 1.45 mm are added. After adding the slots, the main-sidelobe ratio is improved from 14 dB to 20 dB, the 3 dB beamwidth in the horizontal direction is narrowed from 72° to 56°, and the gain at the center frequency of 76.5 GHz is increased by 1.2 dBi.

[0028] The antenna 3D pattern is exported as the receiving antenna pattern. Under the same boundary conditions and relative positions, the coupling degree between the receiving antenna pattern and the transmitting antenna pattern with 45° polarization, horizontal polarization, and vertical polarization is analyzed, as shown in the following example: Figure 9 As shown, Figure 9 This example uses receiving antenna 10 (radar antenna) and transmitting antenna 9 (interference antenna). The directional pattern of receiving antenna 10 is the 45° polarization antenna pattern described in Example 1, while the directional pattern of transmitting antenna 9 is the subtended 45° polarization antenna pattern. The horizontal-horizontal and vertical-vertical coupling are analyzed using the same method. The beamwidths of the horizontal and vertical polarization patterns are consistent with the beamwidth of the 45° polarization pattern.

[0029] like Figure 9-10 As shown in the figure, the polarization isolation of 45° polarization is 4-8 dB higher than that of horizontal polarization and vertical polarization. The 45° polarized antenna has a significant improvement in polarization isolation, which can effectively reduce the electromagnetic interference of other millimeter-wave radar signals and improve the anti-interference performance of millimeter-wave radar.

[0030] As a preferred first embodiment, the transition gradient profile between the current distribution structure and the radiation aperture can also be adjusted, such as Figure 11 As shown (taking the cylindrical curve as an example), the gradient curve can use a cylindrical curve, a rectangular horn profile, a trigonometric function curve, etc. to increase the gain and reduce the side lobe, but a certain profile height is required to complete the profile gradient, which is suitable for antenna structures with a higher waveguide profile height.

[0031] As a preferred second embodiment, the beam can also be converged by using a metal waveguide wall in the height direction of the array antenna outer cross section, such as Figure 12 As shown in the figure, the metal waveguide wall is characterized by its cross-sectional height exceeding the slot array element layer. The length and width of the metal wall depend on the required beam width and the relative phase center of the antenna. It can also improve the gain, but will significantly increase the cross-sectional height. It is suitable for antenna structures with high isolation requirements and low cross-sectional height restrictions.

[0032] As a preferred third embodiment, periodic sensory or capacitive structures can be arranged in a staggered manner on the basis of the waveguide array, such as Figure 13 As shown (taking metal through-holes as an example), metal through-holes can adjust the periodic structure of radiation impedance, improve gain and reduce side lobes without increasing manufacturing costs. However, the effect is not obvious when there are fewer array elements. It is suitable for linear array antenna structures with a large number of array elements.

[0033] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A 45-degree polarized array waveguide antenna for millimeter wave radar, characterized in that: The 45-degree polarized array waveguide antenna comprises: Metal slot layer; A slot array element layer; the slot array element layer is connected to the metal slot layer in a vertical stacking manner, and the slot array element layer is provided with a plurality of slot array elements; The metal slot layer is provided with a plurality of radiation slots; The same number of radiation slots are provided at positions corresponding to the slot array elements and on the metal slot layer; the radiation slots indirectly increase the effective radiation aperture area of the antenna; The angle between the length direction of the slot array element and the waveguide transmission direction is 45 degrees.

2. The 45-degree polarization array waveguide antenna for millimeter wave radar according to claim 1, characterized in that: The waveguide antenna further includes two transverse slots and one longitudinal slot; the transverse slots are arranged near the radiation slot along the waveguide transmission direction; and the longitudinal slots are arranged near the radiation slot along the tangential direction of the waveguide transmission direction.

3. The 45-degree polarization array waveguide antenna for millimeter wave radar according to claim 1, characterized in that: The two transverse grooves are symmetrical with respect to the waveguide transmission direction.

4. The 45-degree polarization array waveguide antenna for millimeter wave radar according to claim 1, characterized in that: The slot array element layer and the metal slot layer form a metal waveguide layer.

5. The 45-degree polarization array waveguide antenna for millimeter wave radar according to claim 1, characterized in that: The transverse groove is 15.3 mm long and 1.25 mm wide.

6. The 45-degree polarization array waveguide antenna for millimeter wave radar according to claim 1, characterized in that: The longitudinal groove is 2.65 mm long and 1.45 mm wide.

7. The 45-degree polarization array waveguide antenna for millimeter wave radar according to claim 1, characterized in that: The radiation slot is provided with a transition gradient profile, and the gradient curve of the transition gradient profile is one of a cylindrical curve, a rectangular horn profile, and a trigonometric function curve.

8. The 45-degree polarization array waveguide antenna for millimeter wave radar according to claim 1, characterized in that: A metal waveguide wall is provided in the height direction of the outer cross-section of the array antenna, and the cross-section height of the metal waveguide wall exceeds the slot array element layer.

9. The 45-degree polarization array waveguide antenna for millimeter wave radar according to claim 1, characterized in that: Periodic sensory or capacitive structures are arranged in a staggered manner in the radiation slots.

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