Microstrip antenna structure, design method and millimeter wave radar

Abstract

The application provides a microstrip antenna structure, a design method and a millimeter wave radar. The microstrip antenna structure comprises an antenna main body, the antenna main body comprises a top copper sheet, a dielectric substrate and a bottom copper sheet, at least two groups of comb-shaped antennas and a group of electromagnetic bandgap structures between each two adjacent groups of comb-shaped antennas are formed on the top copper sheet through etching. The electromagnetic bandgap structure comprises a plurality of interconnected electromagnetic bandgap units, the opening directions of two adjacent electromagnetic bandgap units are opposite, a previous electromagnetic bandgap unit is conformally designed with a radiation sheet on one side of a first group of comb-shaped antennas, and a subsequent electromagnetic bandgap unit is conformally designed with a radiation sheet on the other side of a second group of comb-shaped antennas, so as to produce a wave-limiting function on adjacent and conformally designed radiation sheets. The application does not need to increase the size of a circuit board, can realize the bandgap characteristic by only changing the structure or distribution of the EBG, saves space and is flexible in application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of antenna design, and relates to a band gap structure, in particular to a microstrip antenna structure, a design method and a millimeter wave radar. BACKGROUND

[0002] Electromagnetic wave propagation control technology, microwave engineering technology, and antenna design and optimization technology are important components of modern communication technology. Electromagnetic wave propagation control technology mainly controls the propagation of electromagnetic waves through artificially designed structures to achieve the desired effect. Microwave engineering technology is a technology that studies and applies electromagnetic waves in the microwave frequency band, and is widely used in communication, radar, navigation and other systems. Antenna design and optimization technology is to improve the performance of the antenna, including improving the radiation efficiency, gain, directivity, etc.

[0003] One of the trends of automotive millimeter wave radar is to develop towards low cost and miniaturization. Miniaturized radar faces the trend of antenna aperture reduction, and the physical distance between TX antenna and RX antenna is reduced, which leads to poor TRX antenna isolation, affecting signal quality. The common practice to improve TRX antenna isolation is to increase the physical distance between TRX antennas. The disadvantage of this approach is that the use area of high frequency board material is large, and the overall radar physical size is large, which is not conducive to miniaturization and cost reduction.

[0004] In existing technologies, the electromagnetic band gap (EBG, Electromagnetic Band Gap) structure is a commonly used technology that forms a high impedance by periodically arranging units to block the propagation of electromagnetic waves. The application of EBG structure in antenna design can significantly improve the performance of the antenna, such as reducing the side lobe and side lobe by suppressing surface waves, reducing the mutual coupling between array elements, improving the port isolation, thereby improving the radiation efficiency and gain of the antenna. In addition, EBG structure is also used to improve the electromagnetic compatibility (EMC, Electromagnetic Compatibility) of the antenna system, by suppressing unwanted electromagnetic interference (EMI, Electromagnetic Interference), improving the radiation pattern of the antenna.

[0005] Although existing EBG structures play an important role in antenna design, there are still some problems. First, traditional EBG structures are usually composed of a single unit, and their impedance characteristics and bandgap frequencies are fixed, which cannot meet the needs of different application scenarios. Second, when adjusting the impedance characteristics and bandgap frequencies of existing EBG structures, the size and shape of the unit need to be changed, which increases the complexity of design and manufacturing. Then, existing EBG structures and antenna structure designs are independent, and need to maintain a certain physical distance from the antenna, occupying a large area, which restricts the arrangement of antenna arrays and the size of radars. Finally, existing EBG structures still have room for improvement in suppressing electromagnetic interference and improving antenna performance. SUMMARY

[0006] The present application provides a microstrip antenna structure, a design method and a millimeter wave radar, which are used to solve the problems of fixed impedance characteristics and bandgap frequencies of traditional EBG structures and how to improve the antenna isolation.

[0007] In a first aspect, the present application provides a microstrip antenna structure, which comprises an antenna main body, the antenna main body comprising a top copper skin, a dielectric substrate and a bottom copper skin, at least two groups of comb-shaped antennas and a group of electromagnetic bandgap structures between each adjacent two groups of comb-shaped antennas being formed on the top copper skin by etching, each group of the comb-shaped antennas comprising a feed line and a plurality of groups of radiation patches arranged on the feed line, wherein the width value of the radiation patch decreases in turn from the center to both ends of the comb-shaped antenna; the electromagnetic bandgap structure comprises a plurality of interconnected electromagnetic bandgap units, the opening direction of adjacent two electromagnetic bandgap units is opposite, a previous electromagnetic bandgap unit is conformally designed with a radiation patch on one side of a first group of comb-shaped antennas, and a subsequent electromagnetic bandgap unit is conformally designed with a radiation patch on the other side of a second group of comb-shaped antennas, for producing wave limiting on adjacent and conformally designed radiation patches; each electromagnetic bandgap unit comprises at least one group of first rectangular structures and at least one group of second rectangular structures, the first rectangular structures and the second rectangular structures are alternately distributed and connected end to end, wherein the first rectangular structure is arranged perpendicular to the feed line, and the length and width of the first rectangular structure are fixed values; the second rectangular structure is arranged parallel to the feed line, the width of the second rectangular structure is a fixed value, the length of the second rectangular structure is a variable, and changes according to the width change of the conformally designed radiation patch; and at least one via is arranged on the second rectangular structure; the electromagnetic bandgap structure and the bottom copper skin are electrically connected through the via.

[0008] In an implementation form of the first aspect, the via is arranged at the transverse center of the second rectangular structure and is fine-tuned according to a preset value of longitudinal offset, and the via radius is arranged according to the processing process requirement.

[0009] In an implementation form of the first aspect, the pitch of the via is in a range of 0.3mm to 1.2mm, and the smaller the better; and the dielectric constant of the dielectric substrate is 3.0-3.2.

[0010] In an implementation form of the first aspect, the EBG unit comprises two groups of the first rectangular structure and two groups of the second rectangular structure, the two groups of the first rectangular structure and the two groups of the second rectangular structure are alternately arranged and connected end to end; the second group of the second rectangular structure of a previous EBG unit is connected to the first group of the first rectangular structure of a next EBG unit; or the EBG unit is in an S-shaped structure, comprising three groups of the first rectangular structure and two groups of the second rectangular structure, the three groups of the first rectangular structure and the two groups of the second rectangular structure are alternately arranged and connected end to end; the third group of the first rectangular structure of a previous EBG unit is connected to the first group of the first rectangular structure of a next EBG unit.

[0011] In an implementation form of the first aspect, the resonant frequency of the comb antenna is determined according to the length, width and dielectric material of each radiating patch in the comb antenna; the length of the radiating patch is adjusted according to the simulation effect on the basis of the initial patch length, and the width of the radiating patch is adjusted according to the simulation effect on the basis of the initial patch width.

[0012] In an implementation form of the first aspect, the radiating patches are alternately arranged on both sides of the feed line, and the adjacent radiating patches are spaced apart by a distance of half a wavelength to ensure that the currents of the adjacent radiating patches are in the same direction.

[0013] In an implementation form of the first aspect, at least two groups of comb antennas and one group of EBG structures between each adjacent two groups of comb antennas form an antenna array, and the array spacing of the antenna array is arranged as follows: taking the axes of the comb antennas and the EBG structures as the transverse coordinates, the antenna array is arranged in a horizontal row, and the transverse spacing is kept consistent; the larger the transverse spacing is, the better, within a range that does not affect the overall size, antenna pattern and wave limiting effect.

[0014] In a second aspect, the application provides an antenna design method applied to the microstrip antenna structure, the method comprising: setting the dielectric material of the comb-shaped antenna and the length and width of each radiation patch, designing a linear array based on the determined radiation patch to obtain a group of comb-shaped antennas; each group of the comb-shaped antennas comprises a feed line and a plurality of groups of radiation patches arranged on the feed line, wherein the width value of the radiation patch decreases sequentially from the center to the two ends of the comb-shaped antenna; determining an electromagnetic bandgap structure conforming to the comb-shaped antenna; the electromagnetic bandgap structure comprises a plurality of interconnected electromagnetic bandgap units, and the opening directions of two adjacent electromagnetic bandgap units are opposite; forming an antenna array by using at least two groups of comb-shaped antennas and a group of electromagnetic bandgap structures between each adjacent two groups of comb-shaped antennas; the first electromagnetic bandgap unit is conformally designed with the radiation patch on one side of the first group of comb-shaped antennas, and the second electromagnetic bandgap unit is conformally designed with the radiation patch on the other side of the second group of comb-shaped antennas, so as to produce wave limiting on the adjacent and conformally designed radiation patches.

[0015] In an implementation form of the second aspect, the step of determining the electromagnetic bandgap structure conforming to the comb-shaped antenna comprises: designing each electromagnetic bandgap unit to comprise at least one group of first rectangular structures and at least one group of second rectangular structures, the first rectangular structures and the second rectangular structures are alternately distributed and connected end to end; the first rectangular structure is arranged vertically to the feed line, and the length and width of the first rectangular structure are fixed values; the second rectangular structure is arranged parallel to the feed line, the width of the second rectangular structure is a fixed value, the length of the second rectangular structure is a variable, and changes according to the width of the conformally designed radiation patch; and at least one via is arranged on the second rectangular structure; the electromagnetic bandgap structure is electrically connected to the bottom copper skin through the via.

[0016] In a third aspect, the application provides a millimeter wave radar comprising the microstrip antenna structure.

[0017] As described above, the microstrip antenna structure, design method and millimeter wave radar provided by the application have the following beneficial effects:

[0018] (1) The conformal S-shaped EBG structure of the application is composed of a plurality of interconnected EBG units, each unit produces wave limiting effect on the adjacent radiation patch, and this structure design can more accurately control the equivalent capacitance and inductance of the EBG, thereby adjusting its impedance characteristics and bandgap frequency, so that it can better meet the needs of different application scenarios.

[0019] (2) The conformal S-shaped EBG structure of the present application is provided with at least one via hole on each B structure, and the position and size of the via hole are set according to a specific principle, which makes the wave-limiting effect of the conformal S-shaped EBG structure located at the center of the working frequency of the antenna, thereby optimizing the radiation characteristics of the antenna. Compared with the existing EBG structure, this design is simpler and more efficient in adjusting the impedance characteristics and bandgap frequency.

[0020] (3) The conformal S-shaped EBG structure of the present application can adjust the regulation of the frequency f0 by changing the size of the patch and the position and number of the via hole, thereby forming high impedance characteristics, blocking the propagation of electromagnetic waves, increasing the isolation degree of the antenna channel, and further improving the radiation efficiency and gain of the antenna. This feature makes the EBG structure of the present application have significant advantages over the prior art in suppressing electromagnetic interference and improving antenna performance.

[0021] (4) The conformal S-shaped EBG structure of the present application makes a key improvement to the miniaturization layout of the antenna, saves circuit layout area, and saves system cost.

[0022] (5) The design and manufacturing process of the conformal S-shaped EBG structure of the present application is relatively simple, low in cost, and easy to promote and apply. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A structural schematic diagram of a microstrip antenna structure according to an embodiment of the present application is shown.

[0024] Figure 2A A structural schematic diagram of an electromagnetic bandgap unit according to an embodiment of the present application is shown.

[0025] Figure 2B A size labeling diagram of an electromagnetic bandgap unit according to an embodiment of the present application is shown.

[0026] Figure 3 A center positioning schematic diagram of an electromagnetic bandgap structure according to an embodiment of the present application is shown.

[0027] Figure 4 A via hole position schematic diagram of an electromagnetic bandgap structure according to an embodiment of the present application is shown.

[0028] Figure 5 A plate schematic diagram of an electromagnetic bandgap structure according to an embodiment of the present application is shown.

[0029] Figure 6 A radiation patch size schematic diagram of a comb-shaped antenna according to an embodiment of the present application is shown.

[0030] Figure 7 A comb-shaped antenna structure schematic diagram of an electromagnetic bandgap structure according to an embodiment of the present application is shown.

[0031] Figure 8 A combiner diagram of the comb antenna is shown.

[0032] Figure 9 A combiner diagram of the electromagnetic bandgap structure is shown.

[0033] Figure 10 A diagram of the antenna gain variation of the electromagnetic bandgap structure is shown.

[0034] Figure 11 A diagram of the antenna isolation variation of the electromagnetic bandgap structure is shown.

[0035] Figure 12 A principle flowchart of the antenna design method is shown.

[0036] Figure 13 A structure principle diagram of the millimeter wave radar is shown.

[0037] Element number explanation

[0038] 1 electromagnetic bandgap structure

[0039] 11 first rectangular structure

[0040] 12 second rectangular structure

[0041] S21-S23 steps DETAILED DESCRIPTION

[0042] The present application will be described in detail below with specific embodiments, and those skilled in the art can easily understand other advantages and effects of the present application from the disclosure. The present application can also be implemented or applied by different specific embodiments, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0043] It should be noted that the diagrams provided in the following embodiments only illustrate the basic concept of the present application in a schematic manner, and only show the components related to the present application in the diagrams, not the number, shape and size of the components when actually implemented. The actual implementation of each component may be a random change in type, number and proportion, and the component layout pattern may be more complex.

[0044] The technical solutions in the embodiments of the present application will be described in detail below with reference to the drawings in the embodiments of the present application. The present application designs an electromagnetic band gap structure (EBG), which is small in size and is very helpful for improving the TRX isolation degree, and is very beneficial for use in miniaturization projects to improve the radio frequency performance of a radar.

[0045] Please refer to Figure 1 , which shows a structural schematic diagram of the microstrip antenna structure according to the embodiments of the present application. As shown in Figure 1 , the microstrip antenna structure provided by the embodiments includes an electromagnetic band gap structure, which can be used in an S-shaped electromagnetic band gap structure (EBG) of a 77G millimeter wave radar or a 24GHz, 60GHz or other frequency band automotive millimeter wave radar, and the improvement point is the improvement of the EBG structure on the antenna isolation degree. The microstrip antenna structure includes an antenna main body, the antenna main body includes a top copper sheet, a dielectric substrate and a bottom copper sheet, and at least two groups of comb-shaped antennas and a group of electromagnetic band gap structures 1 between each adjacent two groups of comb-shaped antennas are formed on the top copper sheet through etching.

[0046] Each group of the comb-shaped antennas includes a feed line and a plurality of groups of radiation patches arranged on the feed line, wherein the width values of the radiation patches decrease in turn from the center to the two ends of the comb-shaped antenna.

[0047] The electromagnetic band gap structure 1 includes a plurality of interconnected electromagnetic band gap units, the opening directions of adjacent two electromagnetic band gap units are opposite, a previous electromagnetic band gap unit is conformally designed with the radiation patches on one side of the first group of comb-shaped antennas, and a subsequent electromagnetic band gap unit is conformally designed with the radiation patches on the other side of the second group of comb-shaped antennas, so as to generate wave limiting on the adjacent and conformally designed radiation patches.

[0048] Each electromagnetic band gap unit includes at least one group of first rectangular structures 11 and at least one group of second rectangular structures 12, the first rectangular structures 11 and the second rectangular structures 12 are alternately distributed and connected end to end, wherein the first rectangular structures 11 are arranged perpendicularly to the feed line, and the length and width of the first rectangular structures 11 are fixed values; the second rectangular structures 12 are arranged parallel to the feed line, the width of the second rectangular structures 12 is a fixed value, the length of the second rectangular structures 12 is a variable value and changes according to the width of the conformally designed radiation patch; at least one via is arranged on the second rectangular structure 12; and the electromagnetic band gap structure 1 is electrically connected to the bottom copper sheet through the via.

[0049] Please refer to Figure 2A , which shows a structural schematic diagram of the electromagnetic band gap unit according to the embodiments of the present application. As shown in Figure 2AAs shown, each EBG unit includes at least one set of first rectangular structures 11 and at least one set of second rectangular structures 12, which are alternately arranged and connected end to end. Thus, in different embodiments, based on the first rectangular structures and the second rectangular structures, the EBG unit can include Figure 2A As shown, the four combinations of (a), (b), (c) and (d).

[0050] In one embodiment, the EBG structure includes a plurality of EBG units connected to each other. The EBG unit includes two sets of first rectangular structures and two sets of second rectangular structures, which are alternately arranged and connected end to end; the second set of second rectangular structures of a previous EBG unit is connected to the first set of first rectangular structures of a subsequent EBG unit.

[0051] Referring to Figure 2B , a unit structure diagram of the EBG structure according to the embodiments of the present application is shown. As shown in Figure 2B (a), the first rectangular structure is A structure, the second rectangular structure is B structure, the EBG unit includes two sets of A structures and two sets of B structures, which are alternately arranged and connected end to end, forming ABAB; the second set of B structures of a previous EBG unit is connected to the first set of A structures of a subsequent EBG unit.

[0052] In another embodiment, the EBG structure includes a plurality of EBG units connected to each other. The EBG unit has an S-shaped structure, including three sets of first rectangular structures and two sets of second rectangular structures, which are alternately arranged and connected end to end; the third set of first rectangular structures of a previous EBG unit is connected to the first set of first rectangular structures of a subsequent EBG unit.

[0053] As shown in Figure 2B (b), the first rectangular structure is A structure, the second rectangular structure is B structure, the EBG unit has an S-shaped structure, including three sets of A structures and two sets of B structures, which are alternately arranged and connected end to end; the third set of A structures of a previous EBG unit is connected to the first set of A structures of a subsequent EBG unit.

[0054] The first rectangular structure 11 has a first preset length and a first preset width. The second rectangular structure 12 has a second preset length and a second preset width. In Figure 2BTaking (b) as an example, the structure consists of multiple interconnected EBG units 3, each of which produces a wave-limiting effect on adjacent radiating plates. Each EBG unit is an S-shaped structure, each comprising five segments. The five segments are composed of two structures: an A structure with a first preset length of h1 and a first preset width of w1, and a B structure with a second preset length of h2 and a second preset width of w2, connected end to end, i.e., ABABA. In this embodiment, the preset parameters of the A structure are h1 = 1.325 mm and w1 = 0.33 mm, and the preset parameters of the B structure are h2 = 1.5 mm and w2 = 0.27 mm.

[0055] In one embodiment, at least one through hole is provided on the second rectangular structure. The through hole is provided at the transverse center of the second rectangular structure and is fine-tuned according to a preset value of the longitudinal offset. Figure 3 , which is a schematic diagram showing the center positioning of the electromagnetic band gap structure described in the embodiment of the present application. Figure 3 As shown, the lateral centers of the two B structures are shown.

[0056] See also Figure 4 , which shows a schematic diagram of the via hole positions of the electromagnetic bandgap structure described in the embodiment of the present application. Figure 4 As shown, the via is located at the lateral center of the B structure and is fine-tuned according to the value of the longitudinal offset. In addition, the via radius is set according to the processing requirements.

[0057] In one embodiment, the pitch of the via holes ranges from 0.3 mm to 1.2 mm; and the dielectric constant of the dielectric substrate is 3.0-3.2.

[0058] In actual applications, when setting vias, at least one via is set on the B structure, and the via has a key influence on the limiting frequency of the adjacent radiation plate. The via is located at the lateral center of the B structure as a whole and is fine-tuned according to the value of the longitudinal offset hr. The via radius R is set according to the processing technology requirements, and is designed to be 0.075mm in this embodiment. The position of the via is confirmed based on the via spacing dr and the longitudinal offset hr, wherein the via spacing dr ≥ 0.3mm, preferably, the via spacing ranges from 0.3mm to 1.2mm and the smaller dr, the better. In this embodiment, based on the processing technology parameters, the via spacing dr is set to 0.3mm, and the longitudinal offset hr is set according to the effect of the limiting frequency, so that the limiting effect generated by the adjusted conformal S-type EBG structure, that is, the adjusted limiting frequency, is located at the working frequency center of the antenna.

[0059] Further, after the via holes are set, the positions and number of the via holes can be adjusted. By changing the size of the patch and the positions and number of the via holes, the regulation of the stopband frequency can be changed. This helps to form high impedance characteristics in a specific frequency range, block the propagation of electromagnetic waves, increase the antenna channel isolation, and thus optimize the radiation characteristics of the antenna.

[0060] Thus, in the specific application of the conformal S-shaped electromagnetic bandgap structure, the conformal S-shaped EBG structure is used to optimize the radiation characteristics of the antenna. Through the stopband effect of the conformal S-shaped EBG structure, the electromagnetic compatibility (EMC) of the antenna system is improved, the unwanted electromagnetic interference (EMI) is suppressed, and the radiation pattern of the antenna is improved. At the same time, the surface wave is effectively suppressed, the mutual coupling between the array elements is reduced, the port isolation is improved, and thus the radiation efficiency and gain of the antenna are improved.

[0061] In an embodiment, the resonant frequency of the comb antenna is determined according to the length, width and dielectric material of each radiating patch in the comb antenna. The antenna is a planar structure, and the resonant frequency depends on the physical size (such as length, width) of the antenna and the characteristics of the dielectric material. Thus, the conformal S-shaped EBG structure (hereinafter referred to as SEBG) of the comb antenna can adjust the regulation of the stopband frequency by changing the size of the patch and the positions and number of the via holes, which helps to form high impedance characteristics in a specific frequency range, block the propagation of electromagnetic waves, increase the antenna channel isolation, and thus optimize the radiation characteristics of the antenna.

[0062] The length of the radiating patch is adjusted based on the initial patch length according to the simulation effect, and the width of the radiating patch is adjusted based on the initial patch width according to the simulation effect. Specifically, the simulation effect is considered according to Figure 11 the antenna isolation shown in the figure.

[0063] Please refer to Figure 5 , which shows a schematic diagram of the plate material of the electromagnetic bandgap structure described in the embodiments of the present application. As Figure 5 shown, a suitable high-frequency plate material is selected. In practical applications, Rogers RO3003 plate material is a high-performance PTFE (polytetrafluoroethylene) based ceramic-filled composite material, with copper on the upper and lower layers and PTFE material in the middle layer, which is very suitable for applications such as automotive radar (77GHz), advanced driver assistance systems (ADAS) and 5G wireless infrastructure (millimeter wave). In this application, Rogers 3003 plate material is selected, with a dielectric layer thickness of 0.127mm, a dielectric constant DK = 3.08, and a loss factor DF = 0.003. In addition, in addition to Rogers 3003 plate material, any suitable plate material for designing a comb antenna and capable of achieving the technical solutions of the present application is also within the scope of protection of the present application.

[0064] Please refer toFigure 6 , which shows the dimensions of the radiating piece of the comb antenna according to the embodiment of the present application. Figure 6 As shown in the figure, each radiating piece has a length of L0 and a width of W0. Design a comb antenna with an operating frequency of f0 and determine the dimensions of W0 and L0.

[0065] In one embodiment, the comb antenna includes radiating plates and a feed line. The radiating plates are cross-distributed on both sides of the feed line, with adjacent radiating plates spaced half a wavelength apart to ensure that the currents in adjacent radiating plates are in the same direction. In practical applications, the radiating plates are rectangular.

[0066] See also Figure 7 , which shows a schematic diagram of the comb antenna structure of the electromagnetic band gap structure described in the embodiment of the present application. Figure 7 As shown, there are 15 radiation plates, numbered N1 to N15, which are cross-distributed on both sides of the feeder.

[0067] In one embodiment, at least two groups of comb antennas and a group of electromagnetic band gap structures between each two adjacent groups of comb antennas form an antenna array. The array spacing of the antenna array is set to: the comb antennas and the electromagnetic band gap structure axes are used as their transverse coordinates, and they are arranged horizontally with the transverse spacing remaining consistent; the transverse spacing is preferably as large as possible without affecting the overall size, antenna radiation pattern, and wave limiting effect.

[0068] See also Figure 8 , which shows a schematic diagram of the comb antenna combination described in the embodiment of the present application. Figure 8 As shown, the comb antenna and the SEBG structure axis are arranged horizontally (i.e., with the longitudinal coordinates aligned) and the lateral spacing consistent, which is dx. Within the specified range, a larger dx value is better. However, a value that is too large will affect the overall size, while a value that is too small will affect the antenna pattern and the wave limiting effect. A balance between the two is necessary.

[0069] In one embodiment, the first preset length and the first preset width of the first rectangular structure are fixed values, the second preset width of the second rectangular structure is a fixed value, and the second preset length of the second rectangular structure is a variable, which is adjusted according to the width change of each radiating plate in the comb antenna.

[0070] See also Figure 9 , which is a schematic diagram of a conformal combination of the electromagnetic bandgap structure described in the embodiment of the present application. Figure 9 As shown, the conformal combination includes at least M groups of comb antenna structures (M≥2) comb antenna 1, comb antenna 2 and corresponding M+1 groups of conformal S-type EBG structures (S-type EBG structure 1, S-type EBG structure 2, S-type EBG structure 3), each S-type EBG structure surrounds the radiation piece of the adjacent antenna (Figure 9 The two bold radiating patches are in a conformal relationship.

[0071] Please refer to Figure 10 , which shows the antenna gain variation diagram of the electromagnetic bandgap structure described in the embodiments of the present application. As shown in Figure 10 , the solid line (with SEBG structure, horizontal angle) and the dashed line (without SEBG structure, horizontal angle) of the wide beam vary basically the same, and the solid line (with SEBG structure, vertical angle) and the dashed line (without SEBG structure, vertical angle) of the narrow beam vary basically the same within the FOV (the FOV of the horizontal angle generally requires about ±75°, and the FOV of the vertical angle generally requires about ±10°), Figure 10 Comparing the gain pattern variation of the comb-shaped antenna after adding the SEBG structure, it can be seen that the SEBG structure has little effect on the antenna pattern.

[0072] Please refer to Figure 11 , which shows the antenna isolation variation diagram of the electromagnetic bandgap structure described in the embodiments of the present application. As shown in Figure 11 , the solid line is with SEBG structure, and the dashed line is without SEBG structure, Figure 11 Comparing the isolation variation of the comb-shaped antenna before and after adding the SEBG structure, especially in the frequency range of 76G-77G of the antenna operating frequency, the absolute value of the longitudinal isolation value is larger, and the isolation is greatly optimized.

[0073] The application of the EBG structure in the antenna design can significantly improve the performance of the antenna, such as reducing the side lobe and the sidelobe by suppressing the surface wave, reducing the mutual coupling between the array elements, improving the port isolation, and thus improving the radiation efficiency and gain of the antenna.

[0074] Compared with the prior art, the present application mainly solves the following technical problems:

[0075] The problem of fixed impedance characteristics and bandgap frequency of the traditional EBG structure is solved, and by designing the S-shaped EBG structure, the antenna is conformal, which greatly reduces the required area and is beneficial to the design of small-sized antenna and array.

[0076] By adjusting the size of the S-shaped EBG structure and the position of the grounding hole, the control of the wave limiting frequency is realized, so as to optimize the radiation characteristics of the antenna. By setting the via hole on the B structure and confirming the position of the via hole according to the via hole distance dr and the longitudinal offset hr, the precise control of the wave limiting frequency is realized, and the debugging is convenient.

[0077] Through the wave limiting effect of the conformal S-shaped EBG structure, the present application effectively suppresses the surface wave, reduces the mutual coupling between the array elements, and improves the port isolation, thereby improving the radiation efficiency and gain of the antenna.

[0078] Please refer toFigure 12 , shows the principle flowchart of the antenna design method described in the embodiments of the present application. As shown in Figure 12 , the embodiments provide an antenna design method applied to the microstrip antenna structure, and the method specifically includes the following steps:

[0079] S21, setting the dielectric material of the comb-shaped antenna and the length and width of each radiation sheet, designing a linear array based on the determined radiation sheet to obtain a set of comb-shaped antennas; each set of the comb-shaped antennas includes a feed line and a plurality of sets of radiation sheets arranged on the feed line, wherein the width value of the radiation sheet decreases sequentially from the center to both ends of the comb-shaped antenna. Specifically, it includes steps S211 to S213.

[0080] S211, selecting a suitable high-frequency board material. Rogers RO3003 board material is a high-performance PTFE (polytetrafluoroethylene) based ceramic-filled composite material, with copper on both upper and lower layers and PTFE material in the middle layer, which is very suitable for applications such as automotive radar (77GHz), advanced driver assistance system (ADAS) and 5G wireless infrastructure (millimeter wave). In this design, Rogers 3003 board material is selected, with a dielectric layer thickness of 0.127mm, a dielectric constant DK = 3.08, and a loss factor DF = 0.003.

[0081] S212, designing a comb-shaped antenna with a working frequency f0 and determining the W0 and L0 dimensions. The calculation of the radiation sheet antenna is based on the following principles:

[0082] Assuming that the effective length of the radiation sheet antenna is Le, then

[0083] L e =λ g / 2 (1-1)

[0084] In the formula, λg represents the guided wave wavelength, and

[0085]

[0086] In the formula, λ0 represents the free space wavelength; ε e represents the effective dielectric constant, and

[0087]

[0088] In the formula, εr represents the relative dielectric constant of the medium; h represents the thickness of the dielectric layer; and W represents the width of the radiation sheet.

[0089] Thus, the actual length L of the radiation sheet can be calculated as

[0090]

[0091] where c represents the speed of light in vacuum; f0represents the operating frequency of the antenna; ΔL represents the length of the equivalent radiating slot, and has

[0092]

[0093] The width W of the radiating patch can be calculated by the following formula,

[0094]

[0095] Substituting the dielectric constant εr=3.08 of Rogers 3003 and the speed of light c=3*10^8 m / s into formula (1-6) gives the initial patch width

[0096] W=1.37 mm (1-7)

[0097] Substituting εr=3, h=0.127 mm, f0=76.5 GHz into formula (1-1)-(1-6) gives the initial patch length

[0098] L=1.13 mm (1-8)

[0099] The width and length of the radiating patch of the comb antenna scheme adopted in the present application are different from those of the microstrip patch antenna, and can be adjusted according to the simulation results. The calculation method of the optimal radiating patch length L0 and the microstrip antenna L is similar, which determines the resonant frequency of the radiating patch. The width W0 needs to be as narrow as possible to reduce the excitation of low-order modes, but W0 is too narrow, which will lead to a decrease in the operating bandwidth of the antenna. In this example, L0=1.125 mm and W0=0.75 mm.

[0100] S213, based on the radiating unit (radiating patch), a linear array synthesis design is performed. According to the principle of electromagnetic wave interference, an antenna system composed of two or more basic unit antennas with the same external structure and physical size arranged according to artificial rules is called an array antenna. The basic antenna unit that constitutes the antenna array is called a radiating element (or radiating patch). The case where the radiating elements are arranged in a straight line can be referred to as a linear array.

[0101] In order to achieve the design index of an antenna gain not less than 15 dBi and a sidelobe level greater than 18 dB, the present application designs N=15 radiating units for arraying, and the excitation current is weighted according to SLL=35 dB. The width of each radiating patch is proportional to the excitation current, and is constructed into an array W0_array=W0*chebwin(N, 35);

[0102] The length of each radiating patch is constructed into an array L0_array=repmat(L0, 1, N);

[0103] The Y coordinate (vertical coordinate) position of each radiation piece constitutes the array Yposition;

[0104] like Figure 7 As shown, the antenna consists of two parts: a radiating plate and a feed line. The radiating plates are cross-distributed on both sides of the feed line. The distance between adjacent radiating plate units is half a wavelength, which can ensure that the currents of adjacent radiating plates are in the same direction.

[0105] Figure 7 The middle rectangular part is the radiation plate. There are 15 radiation plates in total, numbered N1 to N15. The middle part is the feeder. The parameter settings of each radiation plate are shown in Table 1.

[0106] Table 1 Radiator parameter setting table

[0107] Radiation sheet number Current excitation L0_array W0_array Y position N1 0.1749 1.125 0.131 0.8 N2 0.2588 1.125 0.194 2.03 N3 0.4093 1.125 0.307 3.29 N4 0.5757 1.125 0.432 4.58 N5 0.7386 1.125 0.554 5.9 N6 0.8759 1.125 0.657 7.25 N7 0.9677 1.125 0.726 8.62 N8 1 1.125 0.75 10.02 N9 0.9677 1.125 0.726 11.46 N10 0.8759 1.125 0.657 12.91 N11 0.7386 1.125 0.554 14.36 N12 0.5757 1.125 0.432 15.8 N13 0.4093 1.125 0.307 17.21 N14 0.2588 1.125 0.194 18.57 N15 0.1749 1.125 0.131 19.86

[0108] S22, determining an electromagnetic bandgap structure conformal to the comb antenna; the electromagnetic bandgap structure includes a plurality of interconnected electromagnetic bandgap units, and the opening directions of two adjacent electromagnetic bandgap units are opposite.

[0109] In one embodiment, the step of determining an electromagnetic bandgap structure conformal to the comb antenna includes: designing each electromagnetic bandgap unit to include at least one first rectangular structure and at least one second rectangular structure, with the first and second rectangular structures alternately spaced and connected end to end; positioning the first rectangular structures perpendicular to the feeder, with both the length and width of the first rectangular structures being fixed; positioning the second rectangular structures parallel to the feeder, with the width of the second rectangular structures being fixed and the length of the second rectangular structures being variable, and varying according to the width of the conformally designed radiating plate; and providing at least one via in the second rectangular structure; and electrically connecting the electromagnetic bandgap structure to the underlying copper sheet via the via. In practical applications, S22 specifically includes steps S221 to S223.

[0110] S221, design an S-type EBG structure conformal to the comb antenna: the structure consists of multiple interconnected EBG units, each EBG unit has a limiting effect on the adjacent radiation piece. Figure 2BAs shown in (b), each EBG unit is an S-shaped structure, each including 5 segments, which are composed of 2 structures, namely, an A structure with a length of h1 and a width of w1 and a B structure with a length of h2 and a width of w2 connected end to end, namely ABABA. Among them, the first preset length h1 and the first preset width w1 of the A structure are fixed values. In this embodiment, w1 = 0.33mm and h1 = 1.325mm; in the B structure, the second preset width w2 is fixed, such as w2 = 0.27mm, and the second preset length h2 is a variable, which is adjusted according to the change of the radiation plate width W0_array to achieve the best wave limiting effect. The spacing between adjacent B structures is approximately λ g / 2.

[0111] S222, setting a via: setting at least one via on the B structure, which has a key impact on the limiting frequency of the adjacent radiation plate. Figure 4 As shown, the via is located in the lateral center of the B structure as a whole and is fine-tuned according to the longitudinal offset hr value. The via radius R is set according to the processing requirements (R = 0.075mm in this example). The position of the via is confirmed based on the via spacing dr and the longitudinal offset hr, wherein the smaller the via spacing dr, the better, and it needs to meet the processing requirements. In this embodiment, dr = 0.3mm. The via has a key influence on the limiting frequency of the adjacent radiating plate. In order to achieve the best effect, the position and size of the via are set according to the following principles: the via is located in the lateral center of the B structure as a whole and is fine-tuned according to the longitudinal offset hr value. The longitudinal offset hr is set according to the effect of the limiting frequency, so that the limiting effect (limiting frequency) generated by the adjusted conformal S-type EBG structure is located at the operating frequency center f0 of the antenna.

[0112] S223, adjust the position and number of vias: By changing the patch dimensions h1, h2, w1, w2, and the position and number of vias hr, the control of the limiting frequency can be adjusted. This helps to form a high impedance characteristic within a specific frequency range, blocking the propagation of electromagnetic waves, increasing antenna channel isolation, and thus optimizing the antenna's radiation characteristics. This improves the antenna system's electromagnetic compatibility (EMC), suppresses unwanted electromagnetic interference (EMI), and improves the antenna's radiation pattern. It also effectively suppresses surface waves, reduces mutual coupling between array elements, and improves port isolation, thereby enhancing the antenna's radiation efficiency and gain.

[0113] S23: Forming an antenna array using at least two groups of comb antennas and an electromagnetic bandgap structure between each adjacent group of comb antennas; the preceding electromagnetic bandgap unit is conformally designed to be a radiating element on one side of the first group of comb antennas, and the following electromagnetic bandgap unit is conformally designed to be a radiating element on the other side of the second group of comb antennas, thereby limiting the adjacent conformally designed radiating elements. This specifically includes steps S231 and S232.

[0114] S231, a combiner antenna comprising a conformal S-shaped EBG structure as shown in Figure 9 As shown, it comprises at least M groups of combiner antenna structures (M≥2) and corresponding M+1 groups of conformal S-shaped EBG structures, each S-shaped EBG structure surrounding the radiating patch of the adjacent antenna to form a conformal relationship;

[0115] S232, the array spacing is set to be horizontal arrangement (i.e. consistent in longitudinal coordinate) with combiner antenna and SEBG axis as its transverse coordinate, and the transverse spacing is kept consistent, i.e. dx. The greater the value of dx within the specified range, the better, but too large value will affect the overall size, and too small value will affect the antenna pattern and wave limiting effect. In this embodiment, dx≥1.4mm. Under the condition that the isolation degree S21 of combiner antenna 1 and combiner antenna 2 is the same, without SEBG structure, the value of dx is obviously large. If S21≥35dB@76.5G is required to be met, dx needs to be greater than 3mm. In this embodiment, dx=1.4mm, which significantly reduces the size of dx, and makes a key improvement to the miniaturization of the antenna layout.

[0116] Therefore, the present application reduces the back lobe and side lobe by suppressing surface waves, reduces the mutual coupling between array elements, improves the port isolation, and thus improves the radiation efficiency and gain of the antenna. Its superiority lies in that it does not need to increase the size of the circuit board, but only needs to change the structure or distribution of EBG to realize the bandgap characteristics to save space, flexible application, and even can realize the function that general microwave structure cannot achieve.

[0117] The conformal S-type EBG structure of the present application is composed of multiple interconnected EBG units, each of which produces a wave-limiting effect on adjacent radiating patches. This structural design allows for more precise control of the EBG's equivalent capacitance and inductance, thereby adjusting its impedance characteristics and bandgap frequency to better meet the needs of different application scenarios. In the conformal S-type EBG structure of the present application, each B structure is provided with at least one via, and the position and size of the via are set according to specific principles. This ensures that the wave-limiting effect produced by the conformal S-type EBG structure is centered around the antenna's operating frequency, thereby optimizing the antenna's radiation characteristics. Compared to existing EBG structures, this design is simpler and more efficient when adjusting its impedance characteristics and bandgap frequency. By varying the size of its patches and the position and number of vias, the conformal S-type EBG structure of the present application can adjust its control of the wave-limiting frequency, thereby forming a high impedance characteristic, blocking the propagation of electromagnetic waves, increasing antenna channel isolation, and further improving the antenna's radiation efficiency and gain. This characteristic makes the EBG structure of the present invention significantly superior to existing technologies in suppressing electromagnetic interference and improving antenna performance. The conformal S-shaped EBG structure of this application has made a key improvement to the miniaturization layout of the antenna, saving circuit layout area and system cost. The design and manufacturing process of the conformal S-shaped EBG structure of this application is relatively simple, low-cost, and easy to promote and apply.

[0118] The protection scope of the antenna design method described in the embodiment of the present application is not limited to the execution order of the steps listed in this embodiment. All solutions implemented by adding, reducing, or replacing steps in the prior art based on the principles of the present application are included in the protection scope of the present application.

[0119] The electromagnetic band gap structure described in the embodiments of the present application can implement the antenna design method described in the present application, but the implementation device of the antenna design method described in the present application includes but is not limited to the structure of the electromagnetic band gap structure listed in the present embodiment. All structural deformations and replacements of the prior art made according to the principles of the present application are included in the scope of protection of the present application.

[0120] In the several embodiments provided in this application, it should be understood that the disclosed structural devices or methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of modules / units is only a logical function division. There may be other division methods in actual implementation. For example, multiple modules or units can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or modules or units, which can be electrical, mechanical or other forms.

[0121] The modules / units described as separated components may or may not be physically separated, and the components shown as modules / units may or may not be physical modules, that is, may be located in one place, or may be distributed to multiple network units. Part or all of the modules / units can be selected according to actual needs to achieve the purpose of the embodiments of the present application. For example, the functional modules / units in each embodiment of the present application can be integrated in one processing module, or each module / unit can be physically present alone, or two or more modules / units can be integrated in one module / unit.

[0122] Those of ordinary skill in the art should further realize that the units and algorithm steps of the examples described in combination with the embodiments disclosed herein can be realized in electronic hardware, computer software, or a combination of both. In order to clearly illustrate the interchangeability of hardware and software, the components and steps of the examples have been described in the above description in a general manner. Whether the functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0123] Please refer to Figure 13 , which shows the structure schematic diagram of the millimeter wave radar described in the embodiments of the present application. As shown in Figure 13 , the present embodiment provides a millimeter wave radar, which comprises the microstrip antenna structure described.

[0124] The microstrip antenna structure comprises an antenna main body, the antenna main body comprises a top layer of copper, a dielectric substrate and a bottom layer of copper, at least two groups of comb-shaped antennas and a group of electromagnetic bandgap structures between each two adjacent groups of comb-shaped antennas are formed on the top layer of copper by etching, each group of the comb-shaped antennas comprises a feed line and a plurality of groups of radiation patches arranged on the feed line, wherein the width of the radiation patches decreases sequentially from the center to the two ends of the comb-shaped antenna; the electromagnetic bandgap structure comprises a plurality of interconnected electromagnetic bandgap units, the opening direction of two adjacent electromagnetic bandgap units is opposite, a previous electromagnetic bandgap unit is conformally designed with the radiation patches on one side of the first group of comb-shaped antennas, and a subsequent electromagnetic bandgap unit is conformally designed with the radiation patches on the other side of the second group of comb-shaped antennas, so as to produce wave limiting for adjacent and conformally designed radiation patches; each electromagnetic bandgap unit comprises at least one group of first rectangular structures and at least one group of second rectangular structures, the first rectangular structures and the second rectangular structures are alternately arranged and connected end to end, wherein the first rectangular structures are arranged perpendicular to the feed line, and the length and width of the first rectangular structures are fixed values; the second rectangular structures are arranged parallel to the feed line, the width of the second rectangular structures is a fixed value, the length of the second rectangular structures is a variable value, and changes according to the width of the conformally designed radiation patches; at least one via is arranged on the second rectangular structure; the electromagnetic bandgap structure and the bottom layer of copper are electrically connected through the via.

[0125] The description of the corresponding flow or structure of each of the above figures has its own emphasis, and the parts not described in detail in a certain flow or structure can be referred to the related description of other flows or structures.

[0126] The above embodiments are only illustrative of the principles and effects of the present application, and are not used to limit the present application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical idea of the present application should be covered by the claims of the present application.

Claims

1. A microstrip antenna structure comprising an antenna body, the antenna body comprising a top copper skin, a dielectric substrate and a bottom copper skin, at least two groups of comb-shaped antennas and a group of electromagnetic band gap structures between each adjacent two groups of comb-shaped antennas are formed on the top copper skin by etching, characterized in that: each group of the comb-shaped antennas comprises a feed line and a plurality of groups of radiating patches arranged on the feed line, wherein the width of the radiating patches decreases sequentially from the center to the two ends of the comb-shaped antenna; the electromagnetic band gap structure comprises a plurality of interconnected electromagnetic band gap units, the opening direction of adjacent two electromagnetic band gap units is opposite, a previous electromagnetic band gap unit is conformally designed with a radiating patch on one side of a first group of comb-shaped antennas, and a subsequent electromagnetic band gap unit is conformally designed with a radiating patch on the other side of a second group of comb-shaped antennas, so as to produce wave limiting for adjacent and conformally designed radiating patches; each electromagnetic band gap unit comprises at least one group of first rectangular structures and at least one group of second rectangular structures, the first rectangular structures and the second rectangular structures are alternately distributed and connected end to end, wherein the first rectangular structures are arranged perpendicular to the feed line, and the length and width of the first rectangular structures are fixed values; the second rectangular structures are arranged parallel to the feed line, the width of the second rectangular structures is a fixed value, the length of the second rectangular structures is a variable value, and changes according to the width of the conformally designed radiating patch; at least one via is arranged on the second rectangular structure; the electromagnetic band gap structure and the bottom copper skin are electrically connected through the via. 2.The microstrip antenna structure of claim 1, characterized in that: the via is arranged at the transverse center of the second rectangular structure and is fine-tuned according to a preset longitudinal offset value, and the via radius is set according to the processing requirement. 3.The microstrip antenna structure of claim 2, characterized in that: the spacing of the via is in the range of 0.3mm-1.2mm, and the smaller the better; the dielectric constant of the dielectric substrate is 3.0-3.

2. 4.The microstrip antenna structure of claim 1, characterized in that: the electromagnetic band gap unit comprises 2 groups of the first rectangular structures and 2 groups of the second rectangular structures, the 2 groups of the first rectangular structures and the 2 groups of the second rectangular structures are alternately distributed and connected end to end; the 2nd group of the second rectangular structures of the previous electromagnetic band gap unit is connected with the 1st group of the first rectangular structures of the subsequent electromagnetic band gap unit; or the electromagnetic band gap unit is in an S-shaped structure, comprising 3 groups of the first rectangular structures and 2 groups of the second rectangular structures, the 3 groups of the first rectangular structures and the 2 groups of the second rectangular structures are alternately distributed and connected end to end; the 3rd group of the first rectangular structures of the previous electromagnetic band gap unit is connected with the 1st group of the first rectangular structures of the subsequent electromagnetic band gap unit. 5.The microstrip antenna structure of claim 1, characterized in that: the resonant frequency of the comb-shaped antenna is determined according to the length, width and dielectric material of each radiating patch in the comb-shaped antenna; the length of the radiating patch is adjusted based on the initial patch length according to the simulation effect, and the width of the radiating patch is adjusted based on the initial patch width according to the simulation effect. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 6. The microstrip antenna structure of claim 1, wherein: the radiating patches are arranged on both sides of the feed line with a half-wavelength interval between adjacent radiating patches to ensure that the currents of adjacent radiating patches are in the same direction.

7. The microstrip antenna structure of claim 1, wherein: at least two groups of comb-shaped antennas and a group of electromagnetic bandgap structures between each adjacent two groups of comb-shaped antennas form an antenna array, and the antenna array is arranged in a horizontal row with a consistent lateral interval along the axes of the comb-shaped antennas and the electromagnetic bandgap structures.

8. A method of antenna design, characterized by, The method of any one of claims 1-7, comprising: determining the dielectric material of the comb-shaped antennas and the length and width of each radiating patch, and designing a linear array based on the determined radiating patches to obtain a group of comb-shaped antennas; each group of the comb-shaped antennas comprises a feed line and a plurality of groups of radiating patches arranged on the feed line, wherein the width of the radiating patches decreases from the center to the ends of the comb-shaped antennas; determining an electromagnetic bandgap structure conformal to the comb-shaped antennas; the electromagnetic bandgap structure comprises a plurality of interconnected electromagnetic bandgap units, and the opening directions of adjacent two electromagnetic bandgap units are opposite; forming an antenna array using at least two groups of comb-shaped antennas and a group of electromagnetic bandgap structures between each adjacent two groups of comb-shaped antennas; a first electromagnetic bandgap unit is conformally designed with a radiating patch on one side of a first group of comb-shaped antennas, and a second electromagnetic bandgap unit is conformally designed with a radiating patch on the other side of a second group of comb-shaped antennas to limit the waves of adjacent and conformally designed radiating patches.

9. The antenna design method of claim 8, wherein, The step of determining an electromagnetic bandgap structure conformal to the comb-shaped antennas comprises: designing each electromagnetic bandgap unit to comprise at least one group of first rectangular structures and at least one group of second rectangular structures, wherein the first rectangular structures and the second rectangular structures are arranged alternately and connected end to end; arranging the first rectangular structures perpendicular to the feed line, and the length and width of the first rectangular structures are fixed values; arranging the second rectangular structures parallel to the feed line, the width of the second rectangular structures is a fixed value, the length of the second rectangular structures is a variable value, and the length of the second rectangular structures changes according to the width of the conformally designed radiating patch; at least one via is arranged on the second rectangular structure; and the electromagnetic bandgap structure is electrically connected to the bottom copper layer via the via.

10. A millimeter wave radar, characterized by, The millimeter wave radar comprises the microstrip antenna structure of any one of claims 1-7.

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