A circularly polarized microstrip antenna, an OBU device, and vehicle glass

Abstract

The present application discloses a circularly polarized microstrip antenna, an OBU device and vehicle glass, comprising an insulating dielectric plate and a ground plate arranged on the back of the insulating dielectric plate, and a radiation layer arranged on the front of the insulating dielectric plate; a slot groove is provided on the ground plate, and the slot groove divides the ground plate into a first ground plate and a second ground plate, and the first ground plate and the second ground plate are respectively used to be electrically connected to a feeding element; the slot groove is used to electrically connect the radiation layer to the feeding element; an OBU device comprises the above-mentioned circularly polarized microstrip antenna and an OBU control device, and the circularly polarized microstrip antenna is electrically connected to the OBU control device through a feeding element; the present application arranges the radiation layer and the slot groove so that the circularly polarized microstrip antenna can be separated from the hardware circuit, thereby facilitating the adaptation of the circularly polarized microstrip antenna to different places of use; and the radiation layer has a simple structure and is easy to industrialize.

Description

Technical Field

[0001] The present invention relates to the field of intelligent transportation equipment, and in particular to a circularly polarized microstrip antenna, an OBU device, and vehicle glass. Background Art

[0002] ETC (Electronic Toll Collection), a fully automated electronic toll collection system, is a service feature of the Intelligent Transportation System. It is particularly suitable for toll booths on highways and bridges. Car owners simply install an ETC onboard unit (OBU) on their vehicle's windshield and pre-deposit a fee. This allows them to pass through toll booths without having to pay or stop. This system collects tolls per vehicle in less than two seconds, and its toll lanes have a capacity 5 to 10 times greater than manual toll lanes.

[0003] In May 2019, China accelerated the construction of ETC toll stations, aiming for ETC usage to exceed 90%. Stable and reliable communication between ETC toll station equipment and on-board ETC units increases the first-pass success rate for vehicles. Antenna failure prevents the on-board electronic tag from receiving data, resulting in ETC transaction interruption or failure. Therefore, it is crucial to balance the performance and reliability of ETC antennas. In addition to ETC antennas, the integration of 5G, in-vehicle FM / DTV antennas and automotive glass is becoming a trend in automotive antenna design.

[0004] Most current OBUs have antennas and hardware circuits installed in a black box, and then the entire OBU is attached to the car's front windshield. This has the following main disadvantages:

[0005] (1) The OBU is installed on the inner surface of the glass: It is difficult to avoid the influence of glass on the antenna performance and the aesthetics. It is necessary to find a suitable location on the glass to install the OBU box.

[0006] (2) The antenna part of the OBU is installed on the outer surface of the glass: Although the influence of the glass on the antenna performance is avoided, the antenna will be affected by the external environment and is easily corroded, which will affect the service life and performance, and is not aesthetically pleasing.

[0007] (3) Due to limitations in panel material and thickness, windshield assembly processes, and other factors, existing OBU antenna technology cannot be separated from the housing and directly sandwiched between two panes of glass. Therefore, the antenna and vehicle glass are separate and not integrated. Typically, an additional OBU unit with an antenna must be installed on the vehicle glass after installation. Summary of the Invention

[0008] To solve the above problems, the present invention provides a circularly polarized microstrip antenna, an OBU device, and vehicle glass. Through the reasonable arrangement of the radiation layer and the slot, the circularly polarized microstrip antenna can be set separately from the hardware circuit, thereby conveniently adapting the circularly polarized microstrip antenna to different usage locations; the radiation layer structure is simply designed and the process is easy to implement.

[0009] To achieve the above-mentioned objectives, the technical solution adopted by the present invention includes: a circularly polarized microstrip antenna, comprising an insulating dielectric plate and a ground plate arranged on the back side of the insulating dielectric plate, and a radiating layer arranged on the front side of the insulating dielectric plate; a slot is provided on the ground plate, and the slot divides the ground plate into a first ground plate and a second ground plate, and the first ground plate and the second ground plate are respectively used to electrically connect to a feeding element; the slot is used to electrically connect the radiating layer to the feeding element.

[0010] As a preferred technical solution of the present invention: the radiation layer includes a plurality of radiation units and a feeding network, and the feeding network is used to couple the plurality of radiation units with the feeding element.

[0011] As a preferred technical solution of the present invention: the feeding network includes a microstrip power dividing circuit and a phase delay circuit; the microstrip power dividing circuit is electrically connected to multiple radiation units respectively; the microstrip power dividing circuit is used to couple with the feeding element.

[0012] As a preferred technical solution of the present invention: the microstrip power division circuit includes a first T-type impedance matcher, a second T-type impedance matcher, and a third T-type impedance matcher. Preferably, the input end of the first T-type impedance matcher is electrically connected to the output end of the third T-type impedance matcher, and the other output end of the T-type impedance matcher is electrically connected to the second T-type impedance matcher through a phase delay circuit. The slot is used to couple the input end of the third T-type impedance matcher with the feeding element; the output ends of the first T-type impedance matcher and the second T-type impedance matcher are respectively electrically connected to the radiation unit.

[0013] As a preferred technical solution of the present invention: the output ends of the first T-type impedance matcher and the second T-type impedance matcher are respectively provided with two parallel branch lines; the branch lines are electrically connected to the radiation unit.

[0014] As a preferred technical solution of the present invention: the microstrip power division circuit is coupled and connected to the feeding element through a tuning branch node and an umbrella load; the umbrella load is electrically connected to the microstrip power division circuit through a microstrip transmission line, and the tuning branch node is arranged on the microstrip transmission line.

[0015] As a preferred technical solution of the present invention: the distance between the tuning branch node and the umbrella-shaped load is 0.1 mm to 10 mm, preferably 0.5 mm to 2 mm.

[0016] As a preferred technical solution of the present invention: a portion of the horizontal projection of the slot along the thickness direction of the insulating dielectric plate is located between the umbrella-shaped load and the tuning branch node.

[0017] As a preferred technical solution of the present invention: the umbrella opening angle of the umbrella-shaped load is 30° to 50°, and the umbrella radius of the umbrella-shaped load is 3mm to 5mm.

[0018] As a preferred technical solution of the present invention: the structure of the slot is L-shaped, H-shaped, Z-shaped, ring-shaped, or long strip-shaped.

[0019] As a preferred technical solution of the present invention: the structure of the slit groove is L-shaped, including a first slit groove and a second slit groove perpendicular to each other. Preferably, the length of the first slit groove is 5mm~10mm, and the width is 0.5mm~1.0mm, and the length of the second slit groove is 5mm~10mm, and the width is 0.5mm~1.0mm.

[0020] The present application also provides an OBU device, in which the circularly polarized microstrip antenna and the OBU control device can be connected separately through a feeding element, thereby avoiding being concentrated in a black box, solving the problem of being unsightly during use and the need to find a suitable location on the vehicle glass to install the OBU box body.

[0021] To achieve the above object, the technical solution adopted by the present invention includes: an OBU device, including the circularly polarized microstrip antenna described above, and also including an OBU control device, wherein the circularly polarized microstrip antenna is electrically connected to the OBU control device through a feeding element.

[0022] As a preferred technical solution of the present invention: the feeding element is a coaxial line, which includes an inner conductor, an outer conductor and an insulating layer; the outer side of the inner conductor is covered with an insulating layer, and the outer side of the insulating layer is covered with an outer conductor.

[0023] As a preferred technical solution of the present invention: the inner conductor is electrically connected to the first grounding plate, and the outer conductor is electrically connected to the second grounding plate.

[0024] As a preferred technical solution of the present invention: the inner conductor is electrically connected to a feeding point provided on the ground plate, and the distance between the feeding point and the first slot is equal to the distance between the feeding point and the second slot.

[0025] The present application also provides a car antenna. By using the inner layer of glass as the dielectric substrate of the circularly polarized microstrip antenna, a design in which the circularly polarized antenna is sandwiched between the vehicle glass is realized. No additional hard plate is added and the characteristics of the vehicle glass itself are not damaged. There is no need to groove the middle layer during the laminated glass lamination process, thereby realizing the integration of the OBU antenna and the vehicle glass.

[0026] To achieve the above-mentioned objectives, the technical solution adopted by the present invention includes: a vehicle glass, including the circularly polarized microstrip antenna described above, the vehicle glass is laminated glass, including an inner layer of glass, an intermediate layer and an outer layer of glass connected in sequence, and the insulating dielectric plate of the circularly polarized microstrip antenna is the inner layer of glass.

[0027] As a preferred technical solution of the present invention: the radiation layer of the circularly polarized microstrip antenna is located between the middle layer and the inner layer of glass.

[0028] As a preferred technical solution of the present invention: the horizontal projection area of ​​the radiation layer along the thickness direction of the insulating dielectric plate is less than or equal to the horizontal projection area of ​​the ground plate.

[0029] Compared with the prior art, the present invention has at least the following beneficial effects:

[0030] 1. Through the reasonable setting of the radiation layer and the slot, the circularly polarized microstrip antenna can be set separately from the hardware circuit, which makes it easy to adapt the circularly polarized microstrip antenna to different application scenarios; and the radiation layer structure design is simple and easy to industrialize.

[0031] 2. The circularly polarized microstrip antenna and the OBU control device in the OBU device can be connected separately through the feeding element, thus avoiding being concentrated in a black box, solving the problem of being unsightly during use and the need to find a suitable location on the vehicle glass to install the OBU box.

[0032] 3. By using the inner layer of laminated glass as the dielectric substrate of the circularly polarized microstrip antenna, the circularly polarized antenna is sandwiched between the vehicle glass. This eliminates the need for additional hard plates and does not damage the characteristics of the vehicle glass itself. During the lamination process, there is no need to groove or drill holes in the middle layer, thus enabling the integration of the OBU antenna and the vehicle glass. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the overall structure of the circularly polarized microstrip antenna;

[0034] Figure 2 Schematic diagram of the overall structure of the circularly polarized microstrip antenna 2×4 radiation units;

[0035] Figure 3Schematic diagram of the structure of the circularly polarized microstrip antenna ground plate and radiation unit;

[0036] Figure 4 Schematic diagram of the structure of the feeding element and the circularly polarized microstrip antenna;

[0037] Figure 5 for Figure 4 A partial enlarged schematic diagram;

[0038] Figure 6 for Figure 5 Schematic diagram of the cross-section structure;

[0039] Figure 7 Schematic diagram of the overall structure of vehicle glass;

[0040] Figure 8 is the radiation coefficient diagram of the circularly polarized microstrip antenna;

[0041] Figure 9 is the phi = 0° circular polarization microstrip antenna pattern;

[0042] Figure 10 is the phi=90° circularly polarized microstrip antenna pattern.

[0043] Figures 1 to 7 In: 1. Insulating dielectric plate, 2. Ground plate, 3. Radiating layer, 4. Slot, 5. First ground plate, 6. Second ground plate, 7. Feeding element, 8. Radiating unit, 9. Microstrip power divider circuit, 10. Phase delay circuit, 11. First T-type impedance matcher, 12. Second T-type impedance matcher, 13. Third T-type impedance matcher, 14. Branch line, 15. Tuning branch node, 16. Umbrella load, 17. Microstrip transmission line, 18. First slot, 19. Second slot, 20. Coaxial line, 21. Inner conductor, 22. Outer conductor, 23. Insulation layer, 24. Inner glass layer, 25. Middle layer, 26. Outer glass layer, 27. Sheath, 28. Solder layer, 29. Feeding point. DETAILED DESCRIPTION

[0044] In order to make the purpose and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0045] Example 1

[0046] like Figures 1 to 3As shown, this embodiment provides a circularly polarized microstrip antenna, including an insulating dielectric plate 1 and a ground plate 2 arranged on the back side of the insulating dielectric plate 1, and a radiating layer 3 arranged on the front side of the insulating dielectric plate 1; the ground plate 2 reflects the antenna signal and makes the radiation direction outward; the size of the ground plate 2 is preferably 50mm×50mm; a slot groove 4 is provided on the ground plate 2, and the slot groove 4 divides the ground plate 2 into a first ground plate 5 and a second ground plate 6, and the first ground plate 5 and the second ground plate 6 are electrically connected to the feeding element 7 respectively. The setting of the slot groove 4 forms a potential difference between the first ground plate 5 and the second ground plate 6, so that the signal on the microstrip transmission line around the slot groove can be coupled to the ground plate, so that the ground plate generates a potential difference around the slot groove, and energy can be coupled to the radiating layer 3 through the slot groove 4; the setting of the slot groove 4 makes the feeding structure design simple and the process easy to implement. At the same time, adjusting the size of the slot groove 4 has a more obvious effect on adjusting the input impedance, which can be used to adjust the frequency of the circularly polarized microstrip antenna, thereby facilitating the production of circularly polarized microstrip antennas suitable for different scenarios.

[0047] The microstrip power divider circuit 9 is coupled to the feed element 7 via a tuning branch 15 and an umbrella load 16. The umbrella load 16 is electrically connected to the microstrip power divider circuit 9 via a microstrip transmission line 17, on which the tuning branch 15 is disposed. The umbrella load 16 is used to increase the impedance bandwidth. In this application, the umbrella opening angle of the umbrella load 16 is 30° to 50°, and the umbrella radius of the umbrella load 16 is 3mm to 5mm. The arrangement of the umbrella load 16 enables a strong potential difference to be formed between the first ground plate 5 and the second ground plate 6, thereby improving antenna efficiency. The position of the tuning branch 15 affects the resonant frequency of the circularly polarized microstrip antenna. The closer to the umbrella, the lower the resonant frequency tends to move. Conversely, the farther from the umbrella, the higher the resonant frequency tends to move. When the tuning branch 15 is 0.5mm to 2mm away from the umbrella, the resonant frequency of the circularly polarized microstrip antenna meets the requirements for ETC applications.

[0048] The ground plane 2 is preferably made of a printed silver layer or other materials with high radio wave reflection; the radiation layer 3 includes a plurality of radiation units 8 and a feeding network, and the plurality of radiation units 8 are coupled to the feeding element 7 through the feeding network. The feeding network includes a microstrip power dividing circuit 9 and a phase delay circuit 10; the microstrip power dividing circuit 9 is electrically connected to a plurality of radiating elements 8 respectively; the microstrip power dividing circuit 9 is coupled to the feeding element 7; preferably, the microstrip power dividing circuit 9 includes a first T-type impedance matching box 11, a second T-type impedance matching box 12, and a third T-type impedance matching box 13; the two output ends of the first T-type impedance matching box 11 and the second T-type impedance matching box 12 are electrically connected to the radiating element 8 through a microstrip transmission line 17, the input end of the first T-type impedance matching box 11 is electrically connected to the third T-type impedance matching box 13, and the third T-type impedance matching box 13 is electrically connected to the input end of the second T-type impedance matching box 12 through the phase delay circuit 10; the output ends of the first T-type impedance matching box 11 and the second T-type impedance matching box 12 are respectively connected to the 4 The radiating units 8 are electrically connected. According to the needs of the application, for example, when a right-handed signal is received, the length of the microstrip transmission line 17 can be set so that the four radiating units 8 form a phase difference of 90° in the counterclockwise direction, thereby forming a right-handed circular polarization as a whole. That is, after the radio frequency signal is equally divided by the third T-type impedance matcher 13, one path enters the first T-type impedance matcher 11 and is then divided into two. The two paths of signal phase differ by 90° due to the different lengths of the microstrip transmission line 17. The other path passes through the phase delay circuit 10 so that the phase of the radio frequency signal is delayed by 180°. After passing through the second T-type impedance matcher 12, it is divided into two again. The two paths of signal phase differ by 90° due to the different lengths of the microstrip transmission line 17. Therefore, the phases of the four radiating units 8 can be sequentially divided by 90° in the counterclockwise direction. Figure 2 As shown, the first T-type impedance matcher 11 and the second T-type impedance matcher can also be provided with two parallel branch lines 14 at the ends of the microstrip transmission line 17 connected to their output ends, as needed. The branch lines 14 are electrically connected to the radiating elements 8. The provision of the branch lines 14 enables two radiating elements 8 to be provided at each output end of the first T-type impedance matcher 11 and the second T-type impedance matcher 12, thus forming a 2×4 radiating element structure, thereby improving the gain of the antenna and enhancing the antenna's directivity. Optionally, an array structure of multiple groups of radiating elements can also provide the antenna with dual-band characteristics.

[0049] The structure of the slot 4 is L-shaped, H-shaped, Z-shaped, annular, or long. The slot 4 is preferably L-shaped, including a first slot 18 and a second slot 19 perpendicular to each other. As the slot length increases, the resonant frequency decreases, while the change caused by adjusting the slot width is not obvious. In order to ensure low backward radiation, this application selects a thinner width. The length of the first slot 18 is 5mm to 10mm, preferably 8.5mm, and the width is 0.5mm to 1.0mm, preferably 0.8mm. The length of the second slot 19 is 5mm to 10mm, preferably 7.5mm, and the width is 0.5mm to 1.0mm, preferably 0.8mm. A portion of the horizontal projection of the slot 4 along the thickness direction of the insulating dielectric plate 1 is located between the umbrella-shaped load 16 and the tuning branch node 15. Specifically, when the L-shaped slot 4 structure includes a first slot 18 and a second slot 19 that are perpendicular to each other, the horizontal projection of the second slot 19 along the thickness of the insulating dielectric plate 1 is preferably located between the umbrella-shaped load 16 and the tuning branch 15. This allows energy to be coupled to the radiating layer 3 through the second slot 19. Adjusting the size of the slot 4 also significantly adjusts the input impedance. Therefore, properly arranging the L-shaped slot for matching the feed structure can make the microstrip antenna design more flexible, simplify the process, and facilitate industrialization.

[0050] Example 2

[0051] like Figures 4 to 6As shown, the present application also provides an OBU device, including the aforementioned circularly polarized microstrip antenna and an OBU control device, wherein the circularly polarized microstrip antenna is electrically connected to the OBU control device via a feed element 7. The circularly polarized microstrip antenna and the OBU control device in the OBU device can be separately connected via the feed element 7, thereby avoiding being concentrated in the same OBU black box. This solves the problem of unsightly appearance during use and the need to find a suitable location on the vehicle glass to install the OBU box. The feed element 7 is preferably a coaxial line 20, which includes an inner conductor 21, an outer conductor 22, and an insulating layer 23. The outer side of the inner conductor 21 is coated with an insulating layer 23, the outer side of the insulating layer 23 is coated with an outer conductor 22, and the outer side of the outer conductor is coated with a sheath 27. The inner conductor 21 is electrically connected to the first grounding plate 5, and the outer conductor 22 is electrically connected to the second grounding plate 6; wherein, the inner conductor 21 is electrically connected to a feeding point 29 provided on the grounding plate 2, and the distance between the feeding point 29 and the first slot 18 is equal to the distance between the feeding point 29 and the second slot 19. Preferably, the feeding point 29 is 2.2 mm away from the first slot and the second slot, so that the position of the feeding point 29 can be easily confirmed and easily welded. A solder layer 28 is added to the outer conductor 22 and the first grounding plate 5, and the distance between the solder layer 28 and the first slot 17 is preferably 0.2 mm, and the distance from the end of the second slot 4 is preferably 2.4 mm; the setting of the solder layer 28 can protect the coaxial line 20 while also ensuring that the outer conductor 22 of the coaxial line 20 is in full contact with the printed silver layer, i.e., the grounding plate 2, provided on the insulating dielectric plate 1, so as to achieve both process and performance insurance. The coaxial line is provided by reasonably setting the position between the inner conductor, the outer conductor and the L-shaped slot (such as Figure 5 As shown in FIG, the potential difference of the ground plate around the slot can be maximized, thereby improving the antenna efficiency.

[0052] Furthermore, the umbrella-shaped load 16 preferably has an opening angle of 40° and a length of 4mm; the tuning branch 15 is preferably 0.5mm to 2mm away from the umbrella-shaped load 16, more preferably 0.8mm, at which point the resonant frequency of the circularly polarized microstrip antenna is around 5.8GHZ, meeting the universal ETC frequency, and thus achieving the best performance of the circularly polarized microstrip antenna. The umbrella-shaped load 16 of the radiation layer 3 has an opening angle of 40° and a length of 4mm; the tuning branch 15 is 0.8mm away from the umbrella-shaped load 16, at which point the resonant frequency of the circularly polarized microstrip antenna is around 5.8GHZ, as shown in FIG. Figure 7 As shown in the antenna reflection diagram, at 5.8 GHz, the reflection coefficient S11 of the circularly polarized microstrip antenna is -22.9 dB, with good impedance matching, and S11 can meet the requirements in the entire working frequency band of ETC. Figure 8 and Figure 9The simulation diagram of the circularly polarized microstrip antenna shown in the figure shows that the 3dB lobe width is less than 70° at both phi = 0° and phi = 90°, meeting the ETC standard design requirements for OBU antennas. The antenna gain still reaches 5dBi, ensuring reliable communication between the OBU and toll collection equipment in ETC applications.

[0053] Example 3

[0054] like Figure 7 As shown, the present application also provides a vehicle glass, including the circularly polarized microstrip antenna of Example 1, the vehicle glass is a laminated glass, including an inner layer of glass 24, an intermediate layer 25 and an outer layer of glass 26 stacked in sequence, and the insulating dielectric plate 1 of the circularly polarized microstrip antenna is the inner layer of glass 24; the material of the intermediate layer 25 is preferably polyvinyl butyral (PVB), and can also be selected from polycarbonate (PC), sound insulation PVB, shading tape PVB, thermal control PVB, ethylene vinyl acetate (EVA), thermoplastic polyurethane (TPU), ionomer, thermoplastic material, polybutylene terephthalate (PBT), polyethylene vinyl acetate (PET), polyethylene naphthalate (PEN), polyvinyl chloride (PVC), polyvinyl fluoride (PVf), polyacrylate (PA), polymethyl methacrylate (PMMA), polyurethane (PUR) and their combinations.

[0055] The radiating layer 3 of the circularly polarized microstrip antenna is located between the outer glass 26 and the inner glass 24, preferably between the intermediate layer 25 and the inner glass 24. Positioning the radiating layer 3 on the outer side of the inner glass 24 reduces the glass's influence on the circularly polarized microstrip antenna without compromising the glass's inherent reliability. The ground plane 2, designed on the inner side of the vehicle's inner glass, shields the antenna from the effects of objects within the vehicle. Preferably, the horizontal projection area of ​​the radiating layer 3 along the thickness of the insulating dielectric plate is less than or equal to the horizontal projection area of ​​the ground plane 2. This design improves the gain of the circularly polarized microstrip antenna and facilitates control of its directivity. By directly using the inner glass 24 as the dielectric substrate for the circularly polarized microstrip antenna, the antenna is sandwiched between the vehicle's glass, eliminating the need for additional rigid panels and protecting the glass's inherent properties. Furthermore, the intermediate layer 25 does not require slots or holes during the assembly process, thus achieving integration of the OBU antenna and the vehicle's glass.

[0056] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A circularly polarized microstrip antenna, characterized in that: The invention comprises an insulating dielectric plate, a ground plate provided on the back of the insulating dielectric plate, and a radiation layer provided on the front of the insulating dielectric plate; the ground plate is provided with a slot groove, the slot groove divides the ground plate into a first ground plate and a second ground plate, the first ground plate and the second ground plate are respectively used for electrically connecting to the feeding element; The slot is used to electrically connect the radiation layer and the feeding element; The radiation layer includes multiple radiation units and a feeding network, wherein there are more than four radiation units, and the feeding network is used to couple the multiple radiation units with the feeding element; the feeding network includes a microstrip power dividing circuit and a phase delay circuit; the microstrip power dividing circuit is electrically connected to the multiple radiation units respectively; the microstrip power dividing circuit is used to couple with the feeding element; the microstrip power dividing circuit is coupled with the feeding element through a tuning branch node and an umbrella load; the umbrella load is electrically connected to the microstrip power dividing circuit through a microstrip transmission line, and the tuning branch node is arranged on the microstrip transmission line.

2. The circularly polarized microstrip antenna according to claim 1, wherein: The microstrip power division circuit includes a first T-type impedance matching box, a second T-type impedance matching box, and a third T-type impedance matching box.

3. The circularly polarized microstrip antenna according to claim 2, wherein: The input end of the first T-type impedance matcher is electrically connected to the output end of the third T-type impedance matcher, and the other output end of the third T-type impedance matcher is electrically connected to the second T-type impedance matcher through a phase delay circuit. The slot is used to couple the input end of the third T-type impedance matcher with the feeding element; the output ends of the first T-type impedance matcher and the second T-type impedance matcher are respectively electrically connected to the radiation unit.

4. The circularly polarized microstrip antenna according to claim 2, wherein: The output ends of the first T-type impedance matcher and the second T-type impedance matcher are respectively provided with two parallel branch lines; the branch lines are electrically connected to the radiation unit.

5. The circularly polarized microstrip antenna according to claim 1, wherein: The distance between the tuning branch node and the umbrella-shaped load is 0.1 mm to 10 mm.

6. The circularly polarized microstrip antenna according to claim 1, wherein: A portion of a horizontal projection of the slot along the thickness direction of the insulating dielectric plate is located between the umbrella-shaped load and the tuning branch node.

7. The circularly polarized microstrip antenna according to claim 1, wherein: The umbrella opening angle of the umbrella-shaped load is 30° to 50°, and the umbrella radius of the umbrella-shaped load is 3mm to 5mm.

8. The circularly polarized microstrip antenna according to any one of claims 1 to 7, characterized in that: The structure of the slot is L-shaped, H-shaped, Z-shaped, ring-shaped or long strip-shaped.

9. The circularly polarized microstrip antenna according to claim 8, characterized in that: The slot groove has an L-shaped structure and includes a first slot groove and a second slot groove that are perpendicular to each other.

10. The circularly polarized microstrip antenna according to claim 9, characterized in that: The length of the first slit groove is 5mm-10mm, and the width is 0.5mm-1.0mm. The length of the second slit groove is 5mm-10mm, and the width is 0.5mm-1.0mm.

11. An OBU device, characterized in that: The invention comprises the circularly polarized microstrip antenna according to any one of claims 1 to 10, and further comprises an OBU control device, wherein the circularly polarized microstrip antenna is electrically connected to the OBU control device through a feeding element.

12. An OBU device according to claim 11, characterized in that: The feeding element is a coaxial line, which includes an inner conductor, an outer conductor and an insulating layer; the outer side of the inner conductor is covered with an insulating layer, and the outer side of the insulating layer is covered with an outer conductor.

13. An OBU device according to claim 12, characterized in that: The inner conductor is electrically connected to the first ground plate, and the outer conductor is electrically connected to the second ground plate.

14. An OBU device according to claim 12, characterized in that: The inner conductor is electrically connected to a feeding point provided on a ground plate, and a distance between the feeding point and the first slot is equal to a distance between the feeding point and the second slot.

15. A vehicle glass, characterized in that: The circularly polarized microstrip antenna comprises the circularly polarized microstrip antenna according to any one of claims 1 to 10, wherein the vehicle glass is laminated glass, comprising an inner layer of glass, an intermediate layer and an outer layer of glass stacked in sequence, and the insulating dielectric plate of the circularly polarized microstrip antenna is the inner layer of glass.

16. The vehicle glass according to claim 15, characterized in that: The radiation layer of the circularly polarized microstrip antenna is located between the middle layer and the inner glass layer.

17. The vehicle glass according to claim 16, characterized in that: The horizontal projection area of ​​the radiation layer along the thickness direction of the insulating dielectric plate is smaller than or equal to the horizontal projection area of ​​the ground plate.

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