A low sidelobe array antenna for vital sign monitoring radar

Abstract

This invention belongs to the field of millimeter-wave antenna array technology and discloses a low-sidelobe array antenna for a vital signs monitoring radar. From top to bottom, it comprises: an array antenna structure, a dielectric substrate layer, and a metal ground plane. The array antenna structure is located on the upper surface of the dielectric substrate layer. The metal ground plane, the upper surface metal of the dielectric substrate layer, and a ring of metallized vias penetrating the upper surface metal of the dielectric substrate layer, the dielectric substrate layer, and the metal ground plane constitute a substrate integrated waveguide resonant cavity. One end of the substrate integrated waveguide resonant cavity is connected to a first microstrip line through a converging, tapered structure. The two sidewalls of the substrate integrated waveguide resonant cavity are alternately connected to a second microstrip line through coplanar waveguides. The second microstrip line is connected to an array element. This invention uses a substrate integrated waveguide as a feed network to feed the microstrip patch, achieving vertical polarization while maintaining a low sidelobe level in the horizontal plane. This reduces the difficulty of low-sidelobe design, lowers the losses caused by the feed network, and offers high scalability.

Description

Technical Field

[0001] This invention belongs to the field of millimeter-wave antenna array technology, specifically relating to a low sidelobe array antenna for a vital signs monitoring radar. Background Technology

[0002] Antennas are essential components of various military and civilian radio systems, including electronic communications, navigation, radar, and meteorological monitoring. With the radio spectrum becoming increasingly congested, the low-frequency band of the microwave band is approaching saturation. To further improve the transmission rate of wireless communication and the resolution of radar, the millimeter-wave band has gradually become a research focus. Due to the development of microwave and millimeter-wave integration technology and the urgent need for low-profile antennas in space technology, microstrip antennas have attracted great interest. However, microstrip antenna elements generally have low gain, making them difficult to adapt to various application scenarios. Therefore, it is often necessary to arrange microstrip antenna elements into arrays to obtain higher gain. Besides gain, sidelobe level is an important indicator of an antenna. In radar technology, to improve the antenna's anti-interference and anti-ground clutter performance, the sidelobe level must be as low as possible.

[0003] Microstrip array antennas typically come in two types: series-fed and parallel-fed. Series feeding, due to its shorter feed lines, effectively reduces feed line losses and increases antenna radiation efficiency. Series feeding controls the current amplitude by adjusting the width of each microstrip patch, thus achieving low sidelobe levels. However, this method only allows for rough calculations of the width of each microstrip patch using empirical formulas, which is inaccurate and often requires extensive adjustments. Parallel feeding, on the other hand, uses microstrip lines of varying widths to precisely control the current amplitude, achieving a low sidelobe design. However, parallel feeding introduces an additional microstrip line feed network, increasing the overall antenna array area and introducing additional losses, which are particularly significant in the millimeter-wave band.

[0004] When using a vital signs monitoring radar to monitor various indicators of patients in hospital beds, the reflected echoes from other patients constitute clutter and are undesirable interference. This necessitates that the radar antenna possess a narrow beam and low sidelobe level in the horizontal plane. Furthermore, to minimize the influence of the ground on the antenna, vertical polarization should be chosen. However, a vertically polarized series-fed microstrip antenna does not meet the requirements of a narrow beam and low sidelobe level in the horizontal plane; a vertically polarized parallel-fed microstrip antenna suffers from very high losses in its microstrip feed network. Therefore, a low-sidelobe array antenna for vital signs monitoring radar has become a crucial and valuable research focus. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention provides a low sidelobe array antenna for vital sign monitoring radar, which achieves low sidelobes while also having low loss.

[0006] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0007] A low sidelobe array antenna for a vital signs monitoring radar comprises, from top to bottom: an array antenna structure, a dielectric substrate layer, and a metal ground plane. The array antenna structure is located on the upper surface of the dielectric substrate layer. The metal ground plane, the upper surface metal of the dielectric substrate layer, and a ring of metallized vias penetrating the upper surface metal of the dielectric substrate layer, the dielectric substrate layer, and the metal ground plane constitute a substrate integrated waveguide resonant cavity. One end of the substrate integrated waveguide resonant cavity is connected to a first microstrip line through a convergent gradient structure. The two sidewalls of the substrate integrated waveguide resonant cavity are alternately connected to a second microstrip line through coplanar waveguides. The second microstrip line is connected to an array element.

[0008] Furthermore, the array unit is a 1*2 microstrip patch array.

[0009] Furthermore, the spacing between adjacent coplanar waveguides on the same side of the substrate integrated waveguide resonant cavity is one waveguide wavelength.

[0010] Furthermore, the characteristic impedance of the first microstrip line is 50 ohms, and the characteristic impedance of the second microstrip line is 70 ohms.

[0011] Furthermore, the coplanar waveguides at different positions in the substrate integrated waveguide resonant cavity have different lengths, and the lengths of the coplanar waveguides at different positions are axially symmetric about the central array unit.

[0012] Furthermore, the lengths of the second microstrip lines connected by the coplanar waveguides at different positions in the substrate integrated waveguide resonant cavity are not equal, and the lengths of the second microstrip lines are axially symmetric about the central array unit.

[0013] Furthermore, the dielectric substrate layer is made of Taconic RF-35 material with a thickness of 0.254 mm and a dielectric constant of 3.5.

[0014] Furthermore, the dimensions of the substrate integrated waveguide resonant cavity are 2.7mm*18mm, and the length of the gradient line from the first microstrip line to the substrate integrated waveguide resonant cavity is 2mm.

[0015] Furthermore, the microstrip patch has a size of 1.65mm*1.18mm; and the spacing between two microstrip patches in the microstrip patch array is 1.46mm.

[0016] Furthermore, the lengths of the coplanar waveguide from left to right are 0.5mm, 0.63mm, 0.88mm, 1.19mm, 1.25mm, 1.19mm, 0.88mm, 0.63mm, and 0.5mm, respectively; and the lengths of the second microstrip line from left to right are 1.1mm, 0.9mm, 0.6mm, 0.25mm, 0.2mm, 0.25mm, 0.6mm, 0.9mm, and 1.1mm, respectively.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] The low sidelobe array antenna for vital sign monitoring radar of the present invention uses a substrate integrated waveguide as a feed network to feed a microstrip patch, achieving vertical polarization and a low sidelobe level in the horizontal plane. Compared with series-fed arrays, it reduces the difficulty of low sidelobe design; compared with parallel-fed arrays, it greatly reduces the loss caused by the feed network; and the form of using a substrate integrated waveguide as the feed network in the present invention has high scalability. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A cross-sectional view of a low sidelobe array antenna for a vital signs monitoring radar provided by the present invention.

[0021] Figure 2 A top view of a low sidelobe array antenna for a vital signs monitoring radar provided by the present invention;

[0022] Figure 3 The electric field distribution of the low sidelobe array antenna for vital sign monitoring radar provided by the present invention;

[0023] Figure 4 The radiation pattern of a low sidelobe array antenna for a vital signs monitoring radar provided by the present invention.

[0024] Reference numerals: 1-Dielectric substrate layer, 2-Metal ground plane, 3-Metalized via, 4-First microstrip line, 5-Gradualized structure, 6-Substrate integrated waveguide resonant cavity, 7-Coplanar waveguide, 8-Second microstrip line, 9-Array unit. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0026] A low-sidelobe array antenna for vital sign monitoring radar, its structure is as follows: Figure 1 , Figure 2 As shown, from top to bottom, it includes: an array antenna structure, a dielectric substrate layer 1, and a metal ground plane 2. The array antenna structure is located on the upper surface of the dielectric substrate layer 1. The upper and lower metals and a ring of metallized vias 3 constitute a substrate integrated waveguide resonant cavity 6. One end of the substrate integrated waveguide resonant cavity 6 is connected to a first microstrip line 4 through a converging gradient structure 5. The two side walls of the substrate integrated waveguide resonant cavity 6 are alternately transformed into a second microstrip line 8 through coplanar waveguides 7. The spacing between adjacent coplanar waveguides 7 on the same side is one waveguide wavelength. The second microstrip line 8 is connected to an array unit 9, and the array unit 9 is a 1*2 microstrip patch array. Preferably, the characteristic impedance of the first microstrip line 4 is 50 ohms, and the characteristic impedance of the second microstrip line 8 is 70 ohms.

[0027] The coplanar waveguides 7 at different positions of the substrate integrated waveguide resonant cavity 6 have unequal lengths, and their lengths are axially symmetric about the central array unit. The second microstrip lines 8 connected to the coplanar waveguides 7 at different positions of the substrate integrated waveguide resonant cavity 6 also have unequal lengths, and their lengths are axially symmetric about the central array unit.

[0028] More specifically, in this embodiment, as Figure 1 As shown, dielectric substrate layer 1 uses Taconic RF-35 material with a thickness of 0.254 mm and a dielectric constant of 3.5. (As shown...) Figure 2As shown, the substrate integrated waveguide resonant cavity 6 has a size of 2.7mm*18mm, approximately 5 times the waveguide wavelength of the center frequency; the microstrip patch has a size of 1.65mm*1.18mm; in a 1*2 microstrip patch array, the spacing between two microstrip patches is 1.46mm; the length of the gradient line from the first microstrip line 4 to the substrate integrated waveguide resonant cavity 6 is 2mm; the lengths of the coplanar waveguide 7 from left to right are 0.5mm, 0.63mm, 0.88mm, 1.19mm, 1.25mm, 1.19mm, 0.88mm, 0.63mm, and 0.5mm, respectively; the lengths of the second microstrip line 8 from left to right are 1.1mm, 0.9mm, 0.6mm, 0.25mm, 0.2mm, 0.25mm, 0.6mm, 0.9mm, and 1.1mm, respectively.

[0029] like Figure 3 The diagram shows the electric field distribution of the low sidelobe array antenna for vital sign monitoring radar provided by this invention, clearly indicating that each antenna element is in phase. Figure 4 The image shows the horizontal radiation pattern of the low sidelobe array antenna used for vital sign monitoring radar. The curve shows a very low sidelobe level, achieving a sidelobe level greater than 23dB at the center frequency.

[0030] The working principle of the low sidelobe array antenna for vital sign monitoring radar of the present invention is as follows: The present invention consists of three layers: an array antenna structure, a dielectric substrate layer 1, and a metal ground plane 2. A 50-ohm first microstrip line 4 excites a substrate integrated waveguide resonant cavity 6 through a gradient structure 5. Alternating slots are made on both sides of the cavity wall of the substrate integrated waveguide resonant cavity 6, with the spacing between adjacent slots on the same side being one waveguide wavelength. A coplanar waveguide 7 connects the substrate integrated waveguide to a 70-ohm second microstrip line 8; the second microstrip line 8 excites 1*2 microstrip patch array elements 9. The length of the coplanar waveguide 7 determines the matching state between the substrate integrated waveguide and the second microstrip line 8, that is, it determines the current amplitude of each array element, thereby satisfying the Taylor distribution current amplitude ratio and achieving a low sidelobe level. Moreover, changing the length of the coplanar waveguide 7 alone will not affect the current amplitude of other antennas, but changing the length of the coplanar waveguide 7 will change the phase of the antenna feed port. Therefore, the phase of each array element 9 is kept consistent by changing the length of the second microstrip line 8.

[0031] The low sidelobe array antenna for vital sign monitoring radar of the present invention uses a substrate integrated waveguide as a feed network to feed a microstrip patch, achieving vertical polarization while achieving a low sidelobe level in the horizontal plane; and compared with series feed arrays, it reduces the difficulty of low sidelobe design; compared with parallel feed arrays, it greatly reduces the loss caused by the feed network; and the form of using a substrate integrated waveguide as the feed network in the present invention has high scalability.

[0032] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A low sidelobe array antenna for a vital signs monitoring radar, characterized in that: From top to bottom, the structure includes: an array antenna structure, a dielectric substrate layer (1), and a metal ground plane (2). The array antenna structure is located on the upper surface of the dielectric substrate layer (1). The metal ground plane (2), the upper surface metal of the dielectric substrate layer (1), and a ring of metallized vias (3) penetrating the upper surface metal of the dielectric substrate layer (1), the dielectric substrate layer (1), and the metal ground plane (2) constitute a substrate integrated waveguide resonant cavity (6). One end of the substrate integrated waveguide resonant cavity (6) is connected to the first microstrip line (4) through a convergent gradient structure (5). The two side walls of the substrate integrated waveguide resonant cavity (6) The second microstrip line (8) is connected alternately through the coplanar waveguide (7), and the second microstrip line (8) is connected to the array unit (9); the coplanar waveguide (7) at different positions of the substrate integrated waveguide resonant cavity (6) penetrates the substrate integrated waveguide resonant cavity to different depths, and the depth of the coplanar waveguide (7) at different positions penetrates the substrate integrated waveguide resonant cavity is symmetrical about the central array unit. The length of the second microstrip line (8) connected to the coplanar waveguide (7) at different positions of the substrate integrated waveguide resonant cavity (6) is different, and the length of the second microstrip line (8) is symmetrical about the central array unit.

2. The low sidelobe array antenna for vital sign monitoring radar according to claim 1, characterized in that: The array unit (9) is 1 2. Microstrip patch array.

3. The low sidelobe array antenna for vital sign monitoring radar according to claim 1, characterized in that: The spacing between adjacent coplanar waveguides (7) on the same side of the substrate integrated waveguide resonant cavity (6) is one waveguide wavelength.

4. The low sidelobe array antenna for vital sign monitoring radar according to claim 1, characterized in that: The characteristic impedance of the first microstrip line (4) is 50 ohms, and the characteristic impedance of the second microstrip line (8) is 70 ohms.

5. The low sidelobe array antenna for vital sign monitoring radar according to claim 1, characterized in that: The dielectric substrate layer (1) is made of Taconic RF-35 material with a thickness of 0.254 mm and a dielectric constant of 3.

5.

6. The low sidelobe array antenna for vital sign monitoring radar according to claim 2, characterized in that: The substrate-integrated waveguide resonant cavity (6) has a size of 2.7 mm. The length of the gradient line from the first microstrip line (4) to the substrate integrated waveguide resonant cavity (6) is 2 mm.

7. The low sidelobe array antenna for vital sign monitoring radar according to claim 6, characterized in that: The microstrip patch has a size of 1.65 mm. 1.18mm; in a microstrip patch array, the spacing between two microstrip patches is 1.46mm.

8. The low sidelobe array antenna for vital sign monitoring radar according to claim 1, characterized in that: The lengths of the coplanar waveguide (7) from left to right are 0.5mm, 0.63mm, 0.88mm, 1.19mm, 1.25mm, 1.19mm, 0.88mm, 0.63mm, and 0.5mm, respectively; the lengths of the second microstrip line (8) from left to right are 1.1mm, 0.9mm, 0.6mm, 0.25mm, 0.2mm, 0.25mm, 0.6mm, 0.9mm, and 1.1mm, respectively.

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