Antenna Structure

Abstract

The present application provides an antenna structure, which includes a substrate, a radiation part, an impedance transformation part, a feeding part and a reference ground; the radiation part, the impedance transformation part and the feeding part are sequentially and grounded on the first surface, and the reference ground is arranged on the second surface; the radiation part is symmetric about the first connection line, and the reference ground is symmetric about the first connection line; the distance between the projection of the side of the reference ground far from the fourth side on the first surface and the side of the radiation part far from the third side is not less than a preset threshold, and the radiation part and the reference ground form the radiation body of the antenna structure; the impedance transformation part is used to transform the impedance of the radiation body so as to achieve impedance matching when the antenna structure is connected to a coaxial cable. The antenna structure of the present application can still meet the requirements of high gain under the condition of small antenna size, is convenient for installation and use, and is easy to popularize.

Description

Technical Field

[0001] This application relates to the technical field of antennas, and particularly to antenna structures. Background Art

[0002] V2X (Vehicle to Everything) is a technology for vehicles to interact with everything outside, which can be understood as connecting vehicles with everything outside into a network. From the perspective of the current vehicle networking, V2X has broad and narrow definitions. Broad V2X refers to the general term for all networks connected to vehicles, and narrow V2X is a low-latency and highly reliable ultra-long-range communication technology. The technical characteristics of narrow V2X are: ultra-long-range sensors, which are technologies that achieve perception through radio wave propagation. In V2X, X is a variable, which can be replaced by V, I, P, and N, etc., namely vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), vehicle-to-pedestrian (V2P), and vehicle-to-internet (V2N), etc.

[0003] V2X is a necessary technology for vehicle autonomous driving. It can make up for the weaknesses of single-vehicle intelligence and is the most important part of autonomous driving. V2X is a communication technology. Compared with in-vehicle sensors, it is not affected by weather conditions. For example, in sandy weather, heavy rain, or thick fog, the function of in-vehicle cameras will be weakened, but V2X can still work normally, can obtain information without dead angles and through obstacles, form an interconnection with the vehicle operating environment, and communicate information. At the same time, it can also obtain intelligent capabilities through a remote large platform to complete autonomous driving.

[0004] The realization of V2X technology is inseparable from the development of V2X antennas. Current V2X antennas can be divided into two categories, namely passive V2X antennas and active V2X antennas. Among them, passive V2X antennas include unit antennas and array antennas. Unit antennas are small in size, convenient for installation and use, but the antenna gain is low, while array antennas have high gain, but are large in size and inconvenient for installation and use. How to balance small antenna size and high antenna gain has become a research hotspot for antennas.

[0005] Therefore, there is an urgent need to design an antenna structure to solve the problems existing in the prior art. Summary of the Invention

[0006] The purpose of this application is to provide an antenna structure that can still meet the requirements of high gain when the antenna size is small, is convenient for installation and use, and is easy to promote.

[0007] The purpose of this application is achieved by adopting the following technical solutions:

[0008] An antenna structure, the antenna structure includes a substrate, a radiation part, an impedance transformation part, a feeding part and a reference ground. The substrate has a first surface and a second surface opposite to each other in the thickness direction, a first side and a second side opposite to each other in the width direction, a third side and a fourth side opposite to each other in the length direction, and a first connection line connecting the third side and the fourth side;

[0009] The radiation part, the impedance transformation part and the feeding part are sequentially and grounded on the first surface, and the reference ground is arranged on the second surface;

[0010] The radiation part is symmetric about the first connection line, and the reference ground is symmetric about the first connection line;

[0011] The distance between the projection of the side of the reference ground far from the fourth side on the first surface and the side of the radiation part far from the third side is not less than a preset threshold value. The radiation part and the reference ground form the radiation body of the antenna structure;

[0012] The impedance transformation part is used to transform the impedance of the radiation body so as to achieve impedance matching when the antenna structure is connected to a coaxial cable;

[0013] The feeding part is used to feed the antenna structure.

[0014] The beneficial effects of this technical solution are as follows: Both the radiator and the reference ground are symmetric structures, which can meet the symmetry requirements of the antenna structure and achieve omnidirectional radiation in the horizontal plane;

[0015] By arranging the radiation part and the reference ground on two opposite surfaces respectively, compared with the way of arranging the radiation part and the reference ground on the same surface, when the size of the substrate is limited, the arrangement ways of the radiation part and the reference ground can be flexible and diverse, and the spatial arrangement is more flexible and compact;

[0016] During the use of the antenna structure, it needs to be connected to the terminal through a coaxial cable. By setting the impedance transformation part, the impedance of the radiation body formed by the radiation part and the reference ground can be transformed so as to achieve impedance matching when the antenna structure is connected to the corresponding coaxial cable. The antenna structure has a high gain and can still meet the requirements of high gain when the antenna size is small, which is convenient for installation and use and is easy to promote.

[0017] In some optional embodiments, the radiation part includes a first end adjacent to the third side, a second end connected to the impedance transformation part, and an intermediate part located between the first end and the second end;

[0018] In the direction from the fourth side to the third side, the first end portion has a gradually decreasing width structure, wherein the width of the side of the first end portion adjacent to the third side is smaller than the width of the side of the first end portion connected to the middle portion;

[0019] In the direction from the third side to the fourth side, the second end portion has a gradually decreasing width structure, wherein the width of the side of the second end portion connected to the impedance transformation portion is smaller than the width of the side of the second end portion connected to the middle portion.

[0020] The beneficial effects of this technical solution are as follows: The first end portion and the second end portion of the radiation portion can be gradually decreasing width structures. On the one hand, such gradually decreasing width structures can adjust the resonance frequency of the radiation portion, and on the other hand, they can achieve impedance transformation of the radiation portion.

[0021] In some alternative embodiments, the first end portion and the second end portion are trapezoidal, and the middle portion is rectangular.

[0022] The beneficial effects of this technical solution are as follows: The first end portion and the second end portion can be set as trapezoidal. Compared with gradually decreasing structures of regular shapes such as arcs and grooves or other irregularly shaped gradually decreasing structures, trapezoidal machining is simpler and more convenient in industry.

[0023] In some alternative embodiments, the upper base, lower base, and waist of the first end portion are 7 mm, 9 mm, and 1.07 mm respectively, the upper base, lower base, and waist of the second end portion are 0.85 mm, 9 mm, and 4.39 mm respectively, and the length and width of the middle portion are 14 mm and 9 mm respectively.

[0024] The beneficial effects of this technical solution are as follows: The dimensions of each part of the radiation portion can be set according to actual needs (the size of the substrate itself) to meet specific dimensional requirements.

[0025] In some alternative embodiments, the reference ground includes a first part far from the fourth side, a second part adjacent to the fourth side, and a connecting part located between the first part and the second part;

[0026] In the direction from the fourth side to the third side, the first part has a gradually decreasing width structure, wherein the width of the side of the first part far from the fourth side is smaller than the width of the side of the first part connected to the connecting part;

[0027] The distance between the projection of the side of the first part far from the fourth side on the first surface and the side of the second end portion far from the third side is not greater than a preset threshold.

[0028] The beneficial effects of this technical solution are as follows: The first part of the reference ground can be a structure with a gradually decreasing width. On the one hand, this structure with a gradually decreasing width can adjust the resonance frequency of the reference ground, and on the other hand, it can achieve impedance transformation of the reference ground.

[0029] In some alternative embodiments, the first part is trapezoidal, and the connecting part and the second part are rectangular;

[0030] The length of the connecting part is less than the length of the second part, and the width of the connecting part is less than the width of the second part.

[0031] The beneficial effects of this technical solution are as follows: The first part can be set as trapezoidal. Compared with tapered structures with regular shapes such as arcs and grooves or other irregular-shaped tapered structures, trapezoidal machining is simpler and more convenient in industry;

[0032] The width of the connecting part can be less than the width of the second part. Since the reference ground is a symmetric structure, two relatively small steps will be formed at the junction of the connecting part and the second part, thereby further adjusting the resonance frequency of the reference ground.

[0033] In some alternative embodiments, the upper base, lower base, and waist of the first part are 0.85 mm, 9 mm, and 4.39 mm respectively, the length and width of the connecting part are 7 mm and 9 mm respectively, and the length and width of the second part are 12 mm and 10 mm respectively.

[0034] The beneficial effects of this technical solution are as follows: The dimensions of each part of the reference ground can be set according to actual needs (the size of the substrate itself) to meet specific dimensional requirements.

[0035] In some alternative embodiments, the impedance transformation part includes a first transformation part connecting the radiation part, a second transformation part adjacent to the fourth side, and a third transformation part;

[0036] The first transformation part is connected to the second transformation part. The first transformation part is symmetric about the first connection line, and the second transformation part is symmetric about the first connection line;

[0037] The third transformation part is arranged on one side of the second transformation part adjacent to the first side, or the third transformation part is arranged on one side of the second transformation part adjacent to the second side.

[0038] The beneficial effects of this technical solution are as follows: Through the combined setting of the first transformation part, the second transformation part, and the third transformation part, the impedance transformation of the radiation body can be carried out more flexibly.

[0039] In some alternative embodiments, the first transformation part, the second transformation part, and the third transformation part are all rectangular;

[0040] One side of the third transformation part adjacent to the fourth side is flush with one side of the second transformation part adjacent to the fourth side;

[0041] The length and width of the first transformation part are 7 mm and 0.85 mm respectively, the length and width of the second transformation part are 13 mm and 3.8 mm respectively, and the length and width of the third transformation part are 5 mm and 2.7 mm respectively.

[0042] The beneficial effect of this technical solution is that the sizes of the first transformation part, the second transformation part, and the third transformation part can be set according to actual needs (the size of the substrate itself) to meet specific size requirements.

[0043] In some alternative embodiments, the antenna structure is a half-wave dipole antenna, and the operating frequency band of the antenna structure is the V2X frequency band;

[0044] The substrate is rectangular, and the length, width, and thickness of the substrate are 37 mm, 10 mm, and 1 mm respectively.

[0045] The beneficial effect of this technical solution is that the antenna structure can be applied to a half-wave dipole antenna. The characteristic of a half-wave dipole antenna is that the length of the radiation arm of the antenna is half of the wavelength at the antenna resonance frequency. Compared with a common quarter-wavelength dipole antenna (with an impedance of about 73 ohms, which is easy to match with the coaxial line impedance, but has a low gain, only reaching 2.16 dBi), the half-wave dipole antenna has a higher gain, which can reach about 4.0 dBi. However, its input impedance is large and it is difficult to match with the coaxial line impedance. The antenna structure of the present application can solve the problem of difficult impedance matching by setting impedance transformation parts while retaining the advantage of a higher gain. Description of the Drawings

[0046] The present application will be further described below with reference to the drawings and embodiments.

[0047] Figure 1 is a schematic structural diagram of the first surface of an antenna structure provided by an embodiment of the present application;

[0048] Figure 2 is a schematic structural diagram of the second surface of an antenna structure provided by an embodiment of the present application;

[0049] Figure 3 is a voltage standing wave ratio test result diagram of an antenna structure provided by an embodiment of the present application;

[0050] Figure 4 is a radiation pattern of an antenna structure provided by an embodiment of the present application in the horizontal plane;

[0051] Figure 5 is the radiation pattern in the horizontal plane of another antenna structure provided by an embodiment of the present application;

[0052] Figure 6 is the radiation pattern in the horizontal plane of yet another antenna structure provided by an embodiment of the present application.

[0053] In the figure:

[0054] 10. Substrate; 11. First side; 12. Second side; 13. Third side; 14. Fourth side; 15. First connection line;

[0055] 20. Radiation part; 21. First end; 22. Middle part; 23. Second end;

[0056] 30. Reference ground; 31. First part; 32. Connection part; 33. Second part;

[0057] 40. Impedance transformation part; 41. First transformation part; 42. Second transformation part; 43. Third transformation part;

[0058] 50. Feeding part. Detailed implementation manners

[0059] Next, in combination with the accompanying drawings and specific implementation manners, the present application will be further described. It should be noted that, on the premise of no conflict, the following-described embodiments or technical features can be arbitrarily combined with each other to form new embodiments.

[0060] Referring to Figure 1 and Figure 2 , an embodiment of the present application provides an antenna structure, the antenna structure includes a substrate 10, a radiation part 20, an impedance transformation part 40, a feeding part 50 and a reference ground 30. The substrate 10 has a first surface and a second surface opposite to each other in the thickness direction, a first side 11 and a second side 12 opposite to each other in the width direction, a third side 13 and a fourth side 14 opposite to each other in the length direction, and a first connection line 15 connecting the third side 13 and the fourth side 14. The first connection line 15 can be a connection line between the midpoints of the third side 13 and the fourth side 14;

[0061] The radiation part 20, the impedance transformation part 40 and the feeding part 50 are sequentially and grounded on the first surface, and the reference ground 30 is disposed on the second surface;

[0062] The radiation part 20 is symmetric about the first connection line 15, and the reference ground 30 is symmetric about the first connection line 15;

[0063] The projection of the side of the reference ground 30 away from the fourth side 14 on the first surface has a distance from the side of the radiation part 20 away from the third side 13 that is not less than a preset threshold value, and the radiation part 20 and the reference ground 30 form the radiation body of the antenna structure;

[0064] The impedance transformation part 40 is used to transform the impedance of the radiation body so as to achieve impedance matching when the antenna structure is connected to a coaxial cable;

[0065] The feeding part 50 is used to feed the antenna structure.

[0066] Thus, both the radiator and the reference ground 30 are symmetric structures, which can meet the symmetry requirements of the antenna structure and achieve omnidirectional radiation in the horizontal plane;

[0067] By arranging the radiation part 20 and the reference ground 30 on two opposite surfaces respectively, compared with the way of arranging the radiation part 20 and the reference ground 30 on the same surface, when the size of the substrate 10 is limited, the arrangement ways of the radiation part 20 and the reference ground 30 can be flexible and diverse, and the spatial arrangement is more flexible and compact;

[0068] During the use of the antenna structure, it needs to be connected to a terminal through a coaxial cable. By setting the impedance transformation part 40, the impedance of the radiation body formed by the radiation part 20 and the reference ground 30 can be transformed so as to achieve impedance matching when the antenna structure is connected to the corresponding coaxial cable. The antenna structure has a higher gain and can still meet the requirements of high gain when the antenna size is small, which is convenient for installation and use and is easy to promote.

[0069] This application does not limit the preset threshold value. The preset threshold value can be equal to the thickness of the substrate 10. The preset threshold value can be 0.5 - 3 millimeters. In a specific application, the preset threshold value can be 1 millimeter.

[0070] In some embodiments, the feeding part 50 includes a feeding point. The feeding point can penetrate and connect from the first surface of the substrate 10 to the second surface of the substrate 10. A grounding pad can be arranged on the second surface of the substrate 10. When feeding the antenna structure, the inner conductor of the coaxial cable can be connected to the feeding point, and the braided layer of the coaxial cable can be connected to the grounding pad.

[0071] In some alternative embodiments, the antenna structure is a half-wave dipole antenna, and the operating frequency band of the antenna structure is the V2X frequency band;

[0072] The substrate 10 is rectangular, and the length, width, and thickness of the substrate 10 are 37 millimeters, 10 millimeters, and 1 millimeter respectively.

[0073] Therefore, the antenna structure can be applied to a half-wave dipole antenna. The characteristic of a half-wave dipole antenna is that the length of the radiation arm of the antenna is half of the wavelength at the antenna resonance frequency. Compared with a common quarter-wavelength dipole antenna (with an impedance of about 73 ohms, which is easy to match with the coaxial line impedance, but has a low gain and can only reach 2.16 dBi), the half-wave dipole antenna has a higher gain and can reach about 4.0 dBi. However, its input impedance is large and it is difficult to match with the coaxial line impedance. The antenna structure of the present application can solve the problem of difficult impedance matching by setting the impedance transformation part 40, while retaining the advantage of a higher gain.

[0074] The V2X frequency band can be 5.85 - 5.925 GHz.

[0075] Since direct communication between antennas is required during use, and there will be a certain distance between the antenna and the terminal, the antenna and the terminal will be connected by a coaxial line. However, the V2X frequency is relatively high, and the coaxial line will cause obvious losses. Therefore, it is required that the antenna must have as high a gain as possible to overcome the insertion loss of the coaxial line and ensure a relatively long communication distance. At the same time, it is required that the antenna has good omnidirectionality in the horizontal plane.

[0076] Therefore, the present application adopts a half-wave dipole antenna with a relatively high gain as the antenna structure to further improve the antenna gain, and the radiation part 20 and the reference ground 30 adopt a symmetric structure to meet the requirement of omnidirectional radiation in the horizontal plane.

[0077] In some embodiments, the substrate 10 can be a PCB board (printed circuit board). The material of the PCB board can be polytetrafluoroethylene (FR4), its relative dielectric constant can be 4.4, and the loss tangent is 0.02. The PCB board can be a double-sided copper clad board, and the copper thickness can be 1 ounce.

[0078] The antenna structure can be provided with a plastic housing according to the installation and use requirements, and different specifications of coaxial lines can be used to connect to the antenna structure.

[0079] In some embodiments, the substrate 10 is rectangular. The first side 11 and the second side 12 can be the longer sides of the rectangle, with a length of 37 mm. The third side 13 and the fourth side 14 can be the shorter sides of the rectangle, with a length of 10 mm. The first connection line 15 can be the connection line between the midpoints of the third side 13 and the fourth side 14.

[0080] In some alternative embodiments, the radiation part 20 includes a first end 21 adjacent to the third side 13, a second end 23 connected to the impedance transformation part 40, and an intermediate part 22 located between the first end 21 and the second end 23;

[0081] In the direction from the fourth side 14 to the third side 13, the first end portion 21 has a tapered width structure, wherein the width of the side of the first end portion 21 adjacent to the third side 13 is smaller than the width of the side of the first end portion 21 connected to the middle portion 22;

[0082] In the direction from the third side 13 to the fourth side 14, the second end portion 23 has a tapered width structure, wherein the width of the side of the second end portion 23 connected to the impedance transformation portion 40 is smaller than the width of the side of the second end portion 23 connected to the middle portion 22.

[0083] Thus, the first end portion 21 and the second end portion 23 of the radiation portion 20 can be of a tapered width structure. This tapered width structure can, on the one hand, adjust the resonance frequency of the radiation portion 20, and on the other hand, achieve impedance transformation of the radiation portion 20.

[0084] In some alternative embodiments, the first end portion 21 and the second end portion 23 are trapezoidal, and the middle portion 22 is rectangular.

[0085] Thus, the first end portion 21 and the second end portion 23 can be set as trapezoidal. Compared with tapered structures of regular shapes such as arcs and grooves or other irregular-shaped tapered structures, trapezoidal machining is simpler and more convenient in industry.

[0086] In some alternative embodiments, the upper base, lower base, and waist of the first end portion 21 are 7 mm, 9 mm, and 1.07 mm respectively, the upper base, lower base, and waist of the second end portion 23 are 0.85 mm, 9 mm, and 4.39 mm respectively, and the length and width of the middle portion 22 are 14 mm and 9 mm respectively.

[0087] Thus, the dimensions of each part of the radiation portion 20 can be set according to actual needs (the size of the substrate 10 itself) to meet specific dimensional requirements.

[0088] In some alternative embodiments, the reference ground 30 includes a first part 31 away from the fourth side 14, a second part 33 adjacent to the fourth side 14, and a connecting part 32 located between the first part 31 and the second part 33;

[0089] In the direction from the fourth side 14 to the third side 13, the first part 31 has a tapered width structure, wherein the width of the side of the first part 31 away from the fourth side 14 is smaller than the width of the side of the first part 31 connected to the connecting part 32;

[0090] The projection of the side of the first part 31 away from the fourth side 14 on the first surface is not greater than a preset threshold distance from the side of the second end 23 away from the third side 13.

[0091] Thus, the first part 31 of the reference ground 30 can be a width-tapering structure, which can, on the one hand, adjust the resonant frequency of the reference ground 30 and, on the other hand, achieve impedance transformation of the reference ground 30.

[0092] In some alternative embodiments, the first part 31 is trapezoidal, and the connecting part 32 and the second part 33 are rectangular;

[0093] The length of the connecting part 32 is less than the length of the second part 33, and the width of the connecting part 32 is less than the width of the second part 33.

[0094] Thus, the first part 31 can be set as trapezoidal. Compared with tapering structures of regular shapes such as arcs and grooves or other irregular-shaped tapering structures, trapezoidal machining is simpler and more convenient industrially;

[0095] The width of the connecting part 32 can be less than the width of the second part 33. Since the reference ground 30 is a symmetric structure, two opposite small steps will be formed at the junction of the connecting part 32 and the second part 33, thereby further adjusting the resonant frequency of the reference ground 30.

[0096] In some alternative embodiments, the upper base, lower base and waist of the first part 31 are 0.85 mm, 9 mm and 4.39 mm respectively, the length and width of the connecting part 32 are 7 mm and 9 mm respectively, and the length and width of the second part 33 are 12 mm and 10 mm respectively.

[0097] Thus, the dimensions of each part of the reference ground 30 can be set according to actual needs (the size of the substrate 10 itself) to meet specific dimensional requirements.

[0098] In some alternative embodiments, the impedance transformation part 40 includes a first transformation part 41 connecting the radiation part 20, a second transformation part 42 adjacent to the fourth side 14, and a third transformation part 43;

[0099] The first transformation part 41 is connected to the second transformation part 42. The first transformation part 41 is symmetric about the first connection line 15, and the second transformation part 42 is symmetric about the first connection line 15;

[0100] The third transformation part 43 is disposed on the side of the second transformation part 42 adjacent to the first side 11, or the third transformation part 43 is disposed on the side of the second transformation part 42 adjacent to the second side 12.

[0101] Thus, through the combined setting of the first transformation unit 41, the second transformation unit 42, and the third transformation unit 43, the impedance transformation of the radiation body can be performed more flexibly.

[0102] In some alternative embodiments, the first transformation unit 41, the second transformation unit 42, and the third transformation unit 43 are all rectangular;

[0103] One side of the third transformation unit 43 adjacent to the fourth side 14 is flush with one side of the second transformation unit 42 adjacent to the fourth side 14;

[0104] The length and width of the first transformation unit 41 are 7 mm and 0.85 mm respectively, the length and width of the second transformation unit 42 are 13 mm and 3.8 mm respectively, and the length and width of the third transformation unit 43 are 5 mm and 2.7 mm respectively.

[0105] Thus, the sizes of the first transformation unit 41, the second transformation unit 42, and the third transformation unit 43 can be set according to actual needs (the size of the substrate 10 itself) to meet specific size requirements.

[0106] In a specific application, the above antenna structure is simulated and analyzed using HFSS software, and the voltage standing wave ratio of the antenna structure is obtained as Figure 3 shown, and the radiation direction of the antenna structure in the horizontal plane is as Figures 4 - 6 shown.

[0107] Among them, Figure 4 is the antenna radiation pattern when the operating frequency of the antenna structure is 5.9 GHz, Figure 5 is the antenna radiation pattern when the operating frequency of the antenna structure is 5.85 GHz, Figure 6 is the antenna radiation pattern when the operating frequency of the antenna structure is 5.925 GHz.

[0108] It can be seen that the voltage standing wave ratio of the antenna structure within the V2X operating frequency band (5.85 - 5.925 GHz) is less than 1.6, the gain of the antenna structure is about 4 dBi, and it is omnidirectional radiation in the horizontal plane.

[0109] In Figures 3 - 6 , VSWR refers to the voltage standing wave ratio, Freq refers to the frequency, Theta refers to the angle with the Z-axis, Gain refers to the gain, and Realized Gain Total refers to the actual gain.

[0110] As Figure 3As shown, at point m3, the operating frequency of the antenna structure is 5.8500 GHz, and the voltage standing wave ratio of the antenna structure is 1.5570; at point m4, the operating frequency of the antenna structure is 5.900 GHz, and the voltage standing wave ratio of the antenna structure is 1.3868; at point m5, the operating frequency of the antenna structure is 5.9250 GHz, and the voltage standing wave ratio of the antenna structure is 1.3077.

[0111] This application is described from the perspectives of purpose of use, effectiveness, progress, and novelty. Its practical progressiveness meets the functional enhancement and usage requirements emphasized by the patent law. The above description and drawings of this application are only preferred embodiments of this application and do not limit this application. Therefore, all those that are similar or identical to the structure, device, features, etc. of this application, that is, all equivalent substitutions or modifications made according to the scope of the patent application of this application, shall fall within the scope of protection of the patent application of this application.

Claims

1. An antenna structure, characterized in that, the antenna structure includes a substrate, a radiation part, an impedance transformation part, a feeding part and a reference ground. The substrate has a first surface and a second surface opposite to each other in the thickness direction, a first side and a second side opposite to each other in the width direction, a third side and a fourth side opposite to each other in the length direction, and a first connection line connecting the third side and the fourth side; the radiation part, the impedance transformation part and the feeding part are sequentially and grounded on the first surface, and the reference ground is arranged on the second surface; the radiation part is symmetric about the first connection line, and the reference ground is symmetric about the first connection line; the distance between the projection of the side of the reference ground far from the fourth side on the first surface and the side of the radiation part far from the third side is not less than a preset threshold, and the radiation part and the reference ground form the radiation body of the antenna structure; the impedance transformation part is used to transform the impedance of the radiation body so as to achieve impedance matching when the antenna structure is connected to a coaxial cable; the feeding part is used to feed the antenna structure; the impedance transformation part includes a first transformation part connected to the radiation part, a second transformation part adjacent to the fourth side, and a third transformation part; the first transformation part is connected to the second transformation part, the first transformation part is symmetric about the first connection line, and the second transformation part is symmetric about the first connection line; the third transformation part is arranged on the side of the second transformation part adjacent to the first side, or the third transformation part is arranged on the side of the second transformation part adjacent to the second side.

2. The antenna structure according to claim 1, characterized in that, the radiation part includes a first end adjacent to the third side, a second end connected to the impedance transformation part, and an intermediate part between the first end and the second end; in the direction from the fourth side to the third side, the first end is a width-tapering structure, wherein the width of the side of the first end adjacent to the third side is smaller than the width of the side where the first end is connected to the intermediate part; in the direction from the third side to the fourth side, the second end is a width-tapering structure, wherein the width of the side where the second end is connected to the impedance transformation part is smaller than the width of the side where the second end is connected to the intermediate part.

3. The antenna structure according to claim 2, characterized in that, the first end and the second end are trapezoidal, and the intermediate part is rectangular.

4. The antenna structure according to claim 3, characterized in that, the upper base, lower base and waist of the first end are 7 mm, 9 mm and 1.07 mm respectively, the upper base, lower base and waist of the second end are 0.85 mm, 9 mm and 4.39 mm respectively, and the length and width of the intermediate part are 14 mm and 9 mm respectively.

5. The antenna structure according to claim 2, characterized in that, the reference ground includes a first part far from the fourth side, a second part adjacent to the fourth side, and a connecting part between the first part and the second part; In the direction from the fourth side to the third side, the first part has a structure with a gradually decreasing width, wherein the width of the side of the first part away from the fourth side is smaller than the width of the side of the first part adjacent to the connecting part. The distance between the projection of the side of the first part away from the fourth side on the first surface and the side of the second end away from the third side is not greater than a preset threshold.

6. The antenna structure according to claim 5, characterized in that the first part is trapezoidal, and the connecting part and the second part are rectangular; the length of the connecting part is smaller than the length of the second part, and the width of the connecting part is smaller than the width of the second part.

7. The antenna structure according to claim 6, characterized in that the upper base, lower base and waist of the first part are 0.85 mm, 9 mm and 4.39 mm respectively, the length and width of the connecting part are 7 mm and 9 mm respectively, and the length and width of the second part are 12 mm and 10 mm respectively.

8. The antenna structure according to claim 1, characterized in that the first transformation part, the second transformation part and the third transformation part are all rectangular; the side of the third transformation part adjacent to the fourth side is flush with the side of the second transformation part adjacent to the fourth side; the length and width of the first transformation part are 7 mm and 0.85 mm respectively, the length and width of the second transformation part are 13 mm and 3.8 mm respectively, and the length and width of the third transformation part are 5 mm and 2.7 mm respectively.

9. The antenna structure according to any one of claims 1 to 8, characterized in that the antenna structure is a half-wave dipole antenna, and the operating frequency band of the antenna structure is the V2X frequency band; the substrate is rectangular, and the length, width and thickness of the substrate are 37 mm, 10 mm and 1 mm respectively.

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