Microstrip antenna structure, design method and millimeter wave radar

Abstract

The invention provides a microstrip antenna structure, a design method and a millimeter wave radar, the microstrip antenna structure comprises an antenna main body, and the antenna main body comprises a top copper sheet, a dielectric substrate and a bottom copper sheet. And at least two groups of comb-shaped antennas and one group of electromagnetic band gap structures between every two adjacent groups of comb-shaped antennas are respectively formed on the top-layer copper sheet through etching. The electromagnetic band gap structure comprises a plurality of mutually connected electromagnetic band gap units, the opening directions of two adjacent electromagnetic band gap units are opposite, the former electromagnetic band gap unit and the radiation sheet on one side of the first group of comb antennas are conformally designed, and the latter electromagnetic band gap unit and the radiation sheet on the other side of the second group of comb antennas are conformally designed. According to the invention, the size of a circuit board does not need to be increased, the band gap characteristic can be realized only by changing the structure or distribution of the EBG, the space is saved, and the application is flexible.

Description

Technical Field

[0001] The present application belongs to the technical field of antenna design and relates to a bandgap structure, and in particular to a microstrip antenna structure, a design method and a millimeter wave radar. Background Art

[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 radiation efficiency, gain, directivity, etc.

[0003] One of the development trends of automotive millimeter-wave radar is to move towards low-cost miniaturization. One trend faced by miniaturized radar is the reduction of antenna aperture and the physical distance between TX antenna and RX antenna, which leads to poor isolation of TRX antenna and affects signal quality. The general practice of high isolation of TRX antenna is to increase the physical distance of TRX antenna. The disadvantage of this practice is that the use area of ​​high-frequency plate is large, and the physical size of the overall radar is large, which is not conducive to miniaturization and cost reduction.

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

[0005] Although the existing EBG structure plays an important role in antenna design, there are also some problems. First, the traditional EBG structure is usually composed of a single unit, and its impedance characteristics and bandgap frequency are fixed, which cannot meet the needs of different application scenarios. Secondly, when adjusting the impedance characteristics and bandgap frequency of the existing EBG structure, it is necessary to change the size and shape of its unit, which increases the complexity of design and manufacturing. Then, the existing EBG structure and antenna structure are designed independently, and a certain physical distance must be maintained from the antenna, which occupies a large area and restricts the antenna array layout and radar size. Finally, the existing EBG structure still has room for further improvement in suppressing electromagnetic interference and improving antenna performance. Summary of the invention

[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 frequency of traditional EBG structures and how to improve antenna isolation.

[0007] In a first aspect, the present application provides a microstrip antenna structure, including an antenna body, the antenna body including a top copper sheet, a dielectric substrate and a bottom copper sheet, and etching is performed on the top copper sheet to form at least two groups of comb antennas and a group of electromagnetic band gap structures between each two adjacent groups of comb antennas, each group of the comb antennas includes a feeder and a plurality of groups of radiating plates arranged on the feeder, wherein the width of the radiating plates decreases successively from the center to the two ends of the comb antenna; the electromagnetic band gap structure includes a plurality of interconnected electromagnetic band gap units, the opening directions of two adjacent electromagnetic band gap units are opposite, the front electromagnetic band gap unit is conformally designed with the radiating plate on one side of the first group of comb antennas, and the rear electromagnetic band gap unit is conformally designed with the radiating plate on the other side of the second group of comb antennas. The radiation plate on one side is conformally designed to generate wave limiting for the adjacent and conformally designed radiation plate; each electromagnetic band gap unit includes 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 both fixed values; the second rectangular structure is arranged parallel to the feed line, the width of the second rectangular structure is a fixed value, and the length of the second rectangular structure is a variable, and changes according to the width of the conformally designed radiation plate; and at least one via is arranged on the second rectangular structure; the electromagnetic band gap structure is electrically connected to the underlying copper sheet via the via.

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

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

[0010] In an implementation of the first aspect, the electromagnetic band gap unit includes 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 second group of the second rectangular structures of the previous electromagnetic band gap unit is connected to the first group of the first rectangular structures of the next electromagnetic band gap unit; or the electromagnetic band gap unit has an S-shaped structure, including 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 third group of the first rectangular structures of the previous electromagnetic band gap unit is overlapped and connected to the first group of the first rectangular structures of the next electromagnetic band gap unit.

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

[0012] In an implementation of the first aspect, the radiation plates are cross-distributed on both sides of the feed line, and the distance between adjacent radiation plates is half a wavelength to ensure that the currents of adjacent radiation plates are in the same direction.

[0013] In an implementation of the first aspect, 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, and the array spacing of the antenna array is set to: the comb antennas and the electromagnetic band gap structure axes are used as their lateral coordinates, arranged horizontally, and the lateral spacing is kept consistent; the larger the lateral spacing is within a range that does not affect the overall size, antenna radiation pattern and wave limiting effect, the better.

[0014] In a second aspect, the present application provides an antenna design method applied to the microstrip antenna structure, the method comprising: setting the dielectric material of the comb antenna and the length and width of each radiating plate, and performing a linear array design based on the determined radiating plates to obtain a group of comb antennas; each group of the comb antennas comprises a feeder and multiple groups of radiating plates arranged on the feeder, wherein the width values ​​of the radiating plates decrease successively from the center to the two ends of the comb antenna; determining an electromagnetic band gap structure conformal to the comb antenna; the electromagnetic band gap structure comprises multiple interconnected electromagnetic band gap units, and the opening directions of two adjacent electromagnetic band gap units are opposite; forming an antenna array using at least two groups of comb antennas and a group of electromagnetic band gap structures between each two adjacent groups of comb antennas; the front electromagnetic band gap unit is conformally designed with the radiating plate on one side of the first group of comb antennas, and the rear electromagnetic band gap unit is conformally designed with the radiating plate on the other side of the second group of comb antennas, so as to generate wave limiting for adjacent and conformally designed radiating plates.

[0015] In an implementation of the second aspect, the step of determining an electromagnetic bandgap structure conformal to the comb antenna includes: designing each electromagnetic bandgap unit to include 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; setting the first rectangular structure perpendicular to the feeder, and the length and width of the first rectangular structure are both fixed values; setting the second rectangular structure parallel to the feeder, 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 plate; and at least one via is provided on the second rectangular structure; the electromagnetic bandgap structure is electrically connected to the underlying copper sheet via the via.

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

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

[0018] (1) 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 the adjacent radiation plate. This structural 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) In the conformal S-type EBG structure of the present application, at least one via is provided on each B structure, and the position and size of the via are set according to specific principles, so that the wave limiting effect generated by the conformal S-type EBG structure is located at the center of the antenna's operating frequency, thereby optimizing the radiation characteristics of the antenna. Compared with the existing EBG structure, this design is simpler and more efficient in adjusting its impedance characteristics and bandgap frequency.

[0020] (3) The conformal S-type EBG structure of the present application can adjust its control of the frequency f0 by changing the size of its patch and the position and number of vias, thereby forming a high impedance characteristic, blocking the propagation of electromagnetic waves, increasing the antenna channel isolation, and further improving the radiation efficiency and gain of the antenna. This characteristic makes the EBG structure of the present invention significantly superior to the prior art in suppressing electromagnetic interference and improving antenna performance.

[0021] (4) The conformal S-type EBG structure of the present application has made a key improvement in the miniaturized layout of the antenna, saving circuit layout area and system cost.

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

[0023] Figure 1 Shown is a structural schematic diagram of the microstrip antenna structure described in an embodiment of the present application.

[0024] Figure 2A Shown is a schematic structural diagram of the electromagnetic bandgap unit described in an embodiment of the present application.

[0025] Figure 2B Shown is a dimension diagram of the electromagnetic bandgap unit described in an embodiment of the present application.

[0026] Figure 3 Shown is a schematic diagram of the center positioning of the electromagnetic bandgap structure described in an embodiment of the present application.

[0027] Figure 4 Shown is a schematic diagram of the via positions of the electromagnetic bandgap structure described in an embodiment of the present application.

[0028] Figure 5 Shown is a schematic diagram of a plate having an electromagnetic band gap structure as described in an embodiment of the present application.

[0029] Figure 6 Shown is a schematic diagram of the radiation plate size of the comb antenna described in an embodiment of the present application.

[0030] Figure 7 Shown is a schematic diagram of the comb antenna structure of the electromagnetic band gap structure described in an embodiment of the present application.

[0031] Figure 8 Shown is a schematic diagram of the comb antenna combination described in an embodiment of the present application.

[0032] Fig. 9 Shown is a schematic diagram of a conformal combination of the electromagnetic bandgap structure described in an embodiment of the present application.

[0033] Fig.10 Shown is a graph of antenna gain variation of the electromagnetic bandgap structure described in an embodiment of the present application.

[0034] Fig.11 Shown is a graph showing the variation of antenna isolation of the electromagnetic bandgap structure described in an embodiment of the present application.

[0035] Fig.12 Shown is a principle flow chart of the antenna design method described in an embodiment of the present application.

[0036] Fig.13 Shown is a structural principle diagram of the millimeter wave radar described in an embodiment of the present application.

[0037] Component number description

[0038] 1 Electromagnetic band gap structure

[0039] 11. The first rectangular structure

[0040] 12 Second rectangular structure

[0041] Steps S21 to S23 DETAILED DESCRIPTION

[0042] The following describes the embodiments of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. The present application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints 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 illustrations provided in the following embodiments are only used to illustrate the basic concept of the present application in a schematic manner, and therefore the illustrations only show components related to the present application rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0044] The technical solution in the embodiment of the present application will be described in detail below in conjunction with the drawings in the embodiment of the present application. The present application designs an electromagnetic bandgap structure (EBG) with a small size, which is of great help in improving the TRX isolation and is very useful for use in miniaturized projects to improve the RF performance of the radar.

[0045] See also Figure 1 , which is a schematic diagram of the structure of the microstrip antenna structure described in the embodiment of the present application. Figure 1 As shown, the microstrip antenna structure provided in this embodiment includes an electromagnetic bandgap structure, which can be used in the S-type electromagnetic bandgap structure (EBG) of 77G millimeter-wave radar or automotive millimeter-wave radars in other frequency bands such as 24GHz and 60GHz. The improvement is that the EBG structure improves the antenna isolation. The microstrip antenna structure includes an antenna body, and the antenna body includes a top copper sheet, a dielectric substrate, and a bottom copper sheet. At least two groups of comb antennas and a group of electromagnetic bandgap structures 1 between each two adjacent groups of comb antennas are formed by etching on the top copper sheet.

[0046] Each group of the comb antennas includes a feed line and a plurality of groups of radiation plates arranged on the feed line, wherein the width of the radiation plates decreases successively from the center to the two ends of the comb antenna.

[0047] The electromagnetic band gap structure 1 includes a plurality of interconnected electromagnetic band gap units, the opening directions of two adjacent electromagnetic band gap units are opposite, the front electromagnetic band gap unit is conformally designed with the radiating piece on one side of the first group of comb antennas, and the rear electromagnetic band gap unit is conformally designed with the radiating piece on the other side of the second group of comb antennas, so as to generate wave limiting for adjacent and conformally designed radiating pieces.

[0048] Each electromagnetic bandgap unit includes at least one group of first rectangular structures 11 and at least one group of second rectangular structures 12, wherein the first rectangular structures 11 and the second rectangular structures 12 are alternately distributed and connected end to end, wherein the first rectangular structure 11 is arranged perpendicular to the feeder, and the length and width of the first rectangular structure 11 are both fixed values; the second rectangular structure 12 is arranged parallel to the feeder, the width of the second rectangular structure 12 is a fixed value, and the length of the second rectangular structure 12 is a variable, and changes according to the width of the conformally designed radiation plate; and at least one via is arranged on the second rectangular structure 12; the electromagnetic bandgap structure 1 is electrically connected to the underlying copper sheet via the via.

[0049] See also Figure 2A , which is a schematic diagram of the structure of the electromagnetic bandgap unit described in the embodiment of the present application. Figure 2AAs shown, 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, wherein the first rectangular structures 11 and the second rectangular structures 12 are alternately distributed and connected end to end. Thus, in different embodiments, based on the first rectangular structures and the second rectangular structures, the electromagnetic band gap unit may include Figure 2A There are four combinations shown: (a), (b), (c) and (d).

[0050] In one embodiment, the electromagnetic band gap structure includes a plurality of interconnected electromagnetic band gap units. The electromagnetic band gap unit includes two groups of the first rectangular structures and two groups of the second rectangular structures, the two groups of the first rectangular structures and the two groups of the second rectangular structures are alternately distributed and connected end to end; the second group of the second rectangular structure of the previous electromagnetic band gap unit is connected to the first group of the first rectangular structure of the next electromagnetic band gap unit.

[0051] See also Figure 2B , which shows a unit structure diagram of the electromagnetic bandgap structure described in the embodiment of the present application. Figure 2B As shown in (a), the first rectangular structure is an A structure, the second rectangular structure is a B structure, and the electromagnetic band gap unit includes 2 groups of A structures and 2 groups of B structures, the 2 groups of A structures and the 2 groups of B structures are alternately distributed and connected end to end to form ABAB. The second group of B structures of the previous electromagnetic band gap unit is connected to the first group of A structures of the next electromagnetic band gap unit.

[0052] In another embodiment, the electromagnetic band gap structure includes a plurality of interconnected electromagnetic band gap units. The electromagnetic band gap unit is an S-shaped structure, including three groups of the first rectangular structures and two groups of the second rectangular structures, the three groups of the first rectangular structures and the two groups of the second rectangular structures are alternately distributed and connected end to end; the third group of the first rectangular structure of the previous electromagnetic band gap unit overlaps and connects with the first group of the first rectangular structure of the next electromagnetic band gap unit.

[0053] like Figure 2B As shown in (b), the first rectangular structure is an A structure, the second rectangular structure is a B structure, and the electromagnetic band gap unit is an S-shaped structure, including 3 groups of A structures and 2 groups of B structures, the 3 groups of A structures and the 2 groups of B structures are alternately distributed and connected end to end; the third group of A structures of the previous electromagnetic band gap unit overlaps and is connected with the first group of A structures of the next electromagnetic band gap unit.

[0054] The length of the first rectangular structure 11 is a first preset length, and the width is a first preset width. The length of the second rectangular structure 12 is a second preset length, and the width is a second preset width. Figure 2B(b) as an example, the structure is composed of a plurality of interconnected EBG units 3, and each EBG unit produces a limiting effect on the adjacent radiation sheet. Each EBG unit is an S-shaped structure, each including 5 segments, and the 5 segments are composed of 2 structures, namely, the A structure with a first preset length of h1 and a first preset width of w1 and the B structure with a second preset length of h2 and a second preset width of w2 connected end to end, that is, ABABA. In this embodiment, the preset parameters of the A structure are h1=1.325mm, w1=0.33mm, and the preset parameters of the B structure are h2=1.5mm, w2=0.27mm.

[0055] In one embodiment, at least one via hole is disposed on the second rectangular structure. The via hole is disposed at the lateral 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 bandgap 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 is a schematic diagram showing the via positions of the electromagnetic bandgap structure described in the embodiment of the present application. Figure 4 As shown, the via hole 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. In addition, the via hole radius is set according to the processing requirements.

[0057] In one embodiment, the spacing 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 practical 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 center of the antenna's operating frequency.

[0059] Furthermore, after the vias are set, the position and number of the vias can be adjusted. By changing the size of the patch and the position and number of the vias, the regulation of the limiting frequency can be changed. This helps to form a high impedance characteristic within 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] Therefore, in the specific application of the conformal S-type electromagnetic bandgap structure, the conformal S-type EBG structure is used to optimize the radiation characteristics of the antenna. Through the wave-limiting effect of the conformal S-type EBG structure, the electromagnetic compatibility (EMC) of the antenna system is improved, the unnecessary 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, and the port isolation is improved, thereby improving the radiation efficiency and gain of the antenna.

[0061] In one embodiment, the resonant frequency of the comb antenna is determined according to the length, width and dielectric material of each radiating plate in the comb antenna. The antenna is a planar structure antenna, and the resonant frequency depends on the physical size of the antenna (such as length, width) and the characteristics of the dielectric material. Therefore, the conformal S-type EBG structure (hereinafter referred to as SEBG) of the comb antenna can adjust its control of the limiting frequency by changing the size of its patch and the position and number of vias, which helps to form a high impedance characteristic within 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 radiation sheet is adjusted based on the initial patch length according to the simulation effect, and the width of the radiation sheet is adjusted based on the initial patch width according to the simulation effect. Fig.11 The antenna isolation shown is taken into consideration.

[0063] See also Figure 5 , which is a schematic diagram of a plate having an electromagnetic band gap structure according to an embodiment of the present application. Figure 5 As shown, select a suitable high-frequency plate. In practical applications, Rogers RO3003 plate is a high-performance PTFE (polytetrafluoroethylene) based ceramic filled composite material. The upper and lower layers are copper and the middle layer is PTFE material. It is very suitable for automotive radar (77GHz), advanced driver assistance systems (ADAS) and 5G wireless infrastructure (millimeter wave) and other applications. In this application, Rogers 3003 plate is selected, the dielectric layer thickness is 0.127mm, the dielectric constant DK=3.08, and the loss factor DF=0.003. In addition, in addition to Rogers 3003 plate, any other suitable plate used to design comb antennas and can realize the technical solution of this application is also within the scope of protection of this application.

[0064] See also Figure 6 , which is a schematic diagram showing the dimensions of the radiating piece of the comb antenna described in the embodiment of the present application. Figure 6 As shown, the length of each radiating piece is L0 and the width is W0. Design a comb antenna with an operating frequency of f0 and determine the sizes of W0 and L0.

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

[0066] See also Figure 7 , which is 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 in total, 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, and the array spacing of the antenna array is set to: the comb antennas and the electromagnetic band gap structure axes are used as their lateral coordinates, arranged horizontally, and the lateral spacing is kept consistent; the larger the lateral spacing is, the better within a range that does not affect the overall size, antenna radiation pattern and wave limiting effect.

[0068] See also Figure 8 , which is a schematic diagram of the comb antenna combination described in the embodiment of the present application. Figure 8 As shown in the figure, the comb antenna and the SEBG structure axis are arranged horizontally (i.e., the longitudinal coordinates are consistent) with the same lateral spacing, which is dx. The larger the dx value is within the specified range, the better. However, if the value is too large, it will affect the overall size, and if the value is too small, it will affect the antenna radiation pattern and the wave limiting effect. A balance needs to be considered between the two.

[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 Fig. 9 , which is a schematic diagram of a conformal combination of the electromagnetic bandgap structure described in the embodiment of the present application. Fig. 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 sheet of the adjacent antenna ( Fig. 9 The two bold radiating sheets in the middle) form a conformal relationship.

[0071] See also Fig.10 , which shows the antenna gain variation diagram of the electromagnetic bandgap structure described in the embodiment of the present application. Fig.10 As shown, the solid line (with SEBG structure, horizontal angle) and the dotted line (without SEBG structure, horizontal angle) of the wide beam change basically the same, and the solid line (with SEBG structure, vertical angle) and the dotted line (without SEBG structure, vertical angle) of the narrow beam change basically the same within the FOV (the FOV of the horizontal angle is generally required to be around ±75°, and the FOV of the vertical angle is generally required to be around ±10 degrees). Fig.10 By comparing the changes in the gain pattern of the comb antenna after adding the SEBG structure, it can be seen that the SEBG structure has very little effect on the antenna's pattern.

[0072] See also Fig.11 , which shows the change of antenna isolation of the electromagnetic bandgap structure described in the embodiment of the present application. Fig.11 As shown, the solid line is the SEBG structure, and the dotted line is the SEBG structure. Fig.11 The changes in the isolation of the comb antenna before and after adding the SEBG structure were compared. Especially in the antenna working frequency band of 76G to 77G, the absolute value of the longitudinal isolation is larger, and the isolation is greatly optimized.

[0073] The application of EBG structure in antenna design can significantly improve the performance of the antenna, for example, by suppressing surface waves to reduce back lobes and side lobes, reduce mutual coupling between array elements, and improve port isolation, thereby improving the radiation efficiency and gain of the antenna.

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

[0075] The problems of fixed impedance characteristics and bandgap frequency of traditional EBG structures are solved. By designing an S-shaped EBG structure that is conformal to the antenna, the required area is greatly reduced, which is conducive to miniaturized antenna design and array design.

[0076] By adjusting the size of the S-type EBG structure and the position of the grounding hole, the limiting frequency can be adjusted to optimize the radiation characteristics of the antenna. By setting vias on the B structure and confirming the position of the vias according to the via spacing dr and longitudinal offset hr, the limiting frequency can be accurately controlled and debugging is convenient.

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

[0078] See also Fig.12 , which is a flow chart showing the principle of the antenna design method described in the embodiment of the present application. Fig.12 As shown, this embodiment provides an antenna design method, which is applied to the microstrip antenna structure, and the method specifically includes the following steps:

[0079] S21, setting the dielectric material of the comb antenna and the length and width of each radiating piece, and performing linear array design based on the determined radiating pieces to obtain a group of comb antennas; each group of the comb antennas includes a feeder and multiple groups of radiating pieces arranged on the feeder, wherein the width of the radiating piece decreases from the center to the two ends of the comb antenna. Specifically including steps S211 to S213.

[0080] S211, choose the right high-frequency sheet material. Rogers RO3003 sheet material is a high-performance PTFE (polytetrafluoroethylene)-based ceramic-filled composite material, with the upper and lower layers of copper and the middle layer of PTFE material. It is very suitable for applications such as automotive radar (77GHz), advanced driver assistance systems (ADAS) and 5G wireless infrastructure (millimeter wave). In this design, Rogers 3003 sheet 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, design a comb antenna with an operating frequency of f0 and determine the dimensions of W0 and L0. The calculation principle of the radiating patch antenna is as follows:

[0082] Assuming the effective length of the radiating antenna is Le, we have

[0083] L e =λ g / 2 (1-1)

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

[0085]

[0086] Where 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] From this, the actual length L of the radiation sheet can be calculated:

[0090]

[0091] In the formula, c represents the speed of light in vacuum; f0 represents the antenna operating frequency; ΔL represents the length of the equivalent radiation gap, and

[0092]

[0093] The width W of the radiation sheet can be calculated by the following formula:

[0094]

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

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

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

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

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

[0100] S213, based on the radiation unit (radiator), perform a linear array comprehensive design. According to the principle of electromagnetic wave interference, an antenna system composed of two or more basic unit antennas with the same appearance structure and physical size arranged in an artificial pattern is called an array antenna. The basic antenna unit that constitutes the antenna array is called a radiation element (or radiation plate). Arranging the radiation elements in a straight line can be called a linear array.

[0101] In order to achieve the design indicators of antenna gain not less than 15dBi and sidelobe level greater than 18dB, this application designs N = 15 radiating elements to form an array, and the excitation current is Chebyshev weighted according to SLL = 35dB. The wide side size of each radiating piece is proportional to the excitation current, and they are formed into an array W0_arrary = W0*chebwin (N, 35);

[0102] The long side size of each radiation piece constitutes 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, and 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] Radiator number Current Excitation L0_array W0_array Yposition 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 the electromagnetic bandgap structure conformal to the comb antenna includes: designing each electromagnetic bandgap unit to include 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; setting the first rectangular structure perpendicular to the feeder, and the length and width of the first rectangular structure are both fixed values; setting the second rectangular structure parallel to the feeder, 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 sheet; and at least one via is provided on the second rectangular structure; the electromagnetic bandgap structure is electrically connected to the bottom copper sheet via the via. In practical applications, S22 specifically includes steps S221 to S223.

[0110] S221, design an S-shaped EBG structure conformal to the comb antenna: the structure consists of multiple interconnected EBG units, each of which has a limiting effect on the adjacent radiating plate. Figure 2BAs shown in (b), each EBG unit is an S-shaped structure, each including 5 sections, and the 5 sections are composed of 2 structures, namely, the A structure with a length of h1 and a width of w1 and the 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, 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 sheet 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 hole: setting at least one via hole on the B structure, the via hole having a key influence on the limiting frequency of the adjacent radiation plate. Figure 4 As shown, the via is located at 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 is necessary 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 influence effect, the position and size of the via are set according to the following principles: the via is located at 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 size of the patch h1, h2, w1, w2 and the position hr and number of vias, the control of the limiting frequency can be adjusted. This helps to form a high impedance characteristic within a specific frequency range, block the propagation of electromagnetic waves, increase the antenna channel isolation, and thus optimize the radiation characteristics of the antenna. It improves the electromagnetic compatibility (EMC) of the antenna system, suppresses unnecessary electromagnetic interference (EMI), and improves the radiation pattern of the antenna. At the same time, it effectively suppresses surface waves, reduces mutual coupling between array elements, and improves port isolation, thereby improving the radiation efficiency and gain of the antenna.

[0113] S23, using at least two groups of comb antennas and a group of electromagnetic bandgap structures between each two adjacent groups of comb antennas to form an antenna array; the first electromagnetic bandgap unit is designed conformally with the radiating piece on one side of the first group of comb antennas, and the second electromagnetic bandgap unit is designed conformally with the radiating piece on the other side of the second group of comb antennas, so as to generate wave limiting for adjacent and conformally designed radiating pieces. Specifically including steps S231 to S232.

[0114] S231, a comb antenna including a conformal S-type EBG structure such as Fig. 9 As shown, it includes at least M groups of comb antenna structures (M≥2) and corresponding M+1 groups of conformal S-type EBG structures, each S-type EBG structure surrounds the radiation sheet of the adjacent antenna to form a conformal relationship;

[0115] S232, array spacing setting, with the comb antenna and SEBG axis as its horizontal coordinate, arranged horizontally (that is, the longitudinal coordinates are consistent), and the horizontal spacing is consistent, that is, dx. The larger the dx value is within the specified range, the better, but a value that is too large will affect the overall size, and a value that is too small will affect the antenna radiation pattern and the wave limiting effect. In this embodiment, dx = 1.4mm or more. Under the condition that the isolation S21 of comb antenna 1 and comb antenna 2 is the same, when there is no SEBG structure, the dx value is significantly larger. If S21≥35dB@76.5G is to be satisfied, dx must be greater than 3mm. In this embodiment, dx = 1.4mm significantly reduces the dx size, making a key improvement in the miniaturized layout of the antenna.

[0116] Therefore, the present application reduces the back lobe and side lobe by suppressing the surface wave, reduces the mutual coupling between array elements, and improves the port isolation, thereby improving the radiation efficiency and gain of the antenna. Its advantage is that it does not need to increase the size of the circuit board, and can achieve the bandgap characteristics by only changing the structure or distribution of the EBG, saving space, and being flexible in application, and can even achieve functions that cannot be achieved by general microwave structures.

[0117] The conformal S-type EBG structure of the present application is composed of a plurality of interconnected EBG units, each unit having a limiting effect on the adjacent radiation sheet. This structural 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. In the conformal S-type EBG structure of the present application, at least one via is provided on each B structure, and the position and size of the via are set according to specific principles, so that the limiting effect generated by the conformal S-type EBG structure is 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 its impedance characteristics and bandgap frequency. The conformal S-type EBG structure of the present application can adjust its regulation of the limiting frequency by changing the size of its patch and the position and number of vias, thereby forming a high impedance characteristic, blocking the propagation of electromagnetic waves, increasing the antenna channel isolation, and further improving the radiation efficiency and gain of the antenna. This feature makes the EBG structure of the present invention significantly superior to the prior art in suppressing electromagnetic interference and improving antenna performance. The conformal S-type EBG structure of the present application has made a key improvement in the miniaturization layout of the antenna, saving circuit layout area and system cost. The design and manufacturing process of the conformal S-type EBG structure of the present application is relatively simple, low in 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 the present 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 embodiments. All structural deformations and replacements of the prior art made according to the principles of the present application are included in the protection scope of the present application.

[0120] In the several embodiments provided in the present 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 an indirect coupling or communication connection through some interfaces, devices or modules or units, which can be electrical, mechanical or other forms.

[0121] The modules / units described as separate components may or may not be physically separated, and the components displayed as modules / units may or may not be physical modules, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules / units may be selected according to actual needs to achieve the purpose of the embodiments of the present application. For example, the functional modules / units in the various embodiments of the present application may be integrated into one processing module, or each module / unit may exist physically separately, or two or more modules / units may be integrated into one module / unit.

[0122] Those of ordinary skill in the art should further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0123] See also Fig.13 , which shows the structural principle diagram of the millimeter wave radar described in the embodiment of the present application. Fig.13 As shown, this embodiment provides a millimeter wave radar, and the millimeter wave radar includes the microstrip antenna structure.

[0124] The microstrip antenna structure comprises an antenna body, the antenna body comprises a top copper sheet, a dielectric substrate and a bottom copper sheet, and at least two groups of comb antennas and a group of electromagnetic band gap structures between each two adjacent groups of comb antennas are formed by etching on the top copper sheet, each group of the comb antennas comprises a feeder and a plurality of groups of radiating plates arranged on the feeder, wherein the width of the radiating plates decreases successively from the center to the two ends of the comb antenna; the electromagnetic band gap structure comprises a plurality of interconnected electromagnetic band gap units, the opening directions of two adjacent electromagnetic band gap units are opposite, the front electromagnetic band gap unit is conformally designed with the radiating plate on one side of the first group of comb antennas, and the rear electromagnetic band gap unit is conformally designed with the radiating plate on the other side of the second group of comb antennas. Conformal design is used to generate wave limiting for adjacent and conformally designed radiation plates; each electromagnetic band gap unit includes 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 both fixed values; the second rectangular structure is arranged parallel to the feed line, the width of the second rectangular structure is a fixed value, and the length of the second rectangular structure is a variable, and changes according to the width of the conformally designed radiation plate; and at least one via is arranged on the second rectangular structure; the electromagnetic band gap structure is electrically connected to the underlying copper sheet via the via.

[0125] The descriptions of the processes or structures corresponding to the above-mentioned figures have different emphases. For parts that are not described in detail in a certain process or structure, please refer to the relevant descriptions of other processes or structures.

[0126] The above embodiments are merely illustrative of the principles and effects of the present application and are not intended to limit the present application. Anyone familiar with the technology may modify or change the above embodiments without violating the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed in the present application shall still be covered by the claims of the present application.

Claims

1. A microstrip antenna structure, comprising an antenna body, wherein the antenna body comprises a top copper sheet, a dielectric substrate and a bottom copper sheet, wherein at least two groups of comb antennas and a group of electromagnetic band gap structures between each two adjacent groups of comb antennas are formed by etching on the top copper sheet, characterized in that: Each group of the comb antennas comprises a feed line and a plurality of groups of radiation plates arranged on the feed line, wherein the width of the radiation plates decreases successively from the center to the two ends of the comb antenna; The electromagnetic band gap structure comprises a plurality of interconnected electromagnetic band gap units, the opening directions of two adjacent electromagnetic band gap units are opposite, the front electromagnetic band gap unit is conformally designed with the radiating piece on one side of the first group of comb antennas, and the rear electromagnetic band gap unit is conformally designed with the radiating piece on the other side of the second group of comb antennas, so as to generate wave limiting for the adjacent and conformally designed radiating pieces; Each electromagnetic bandgap unit includes 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 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 both fixed values; the second rectangular structure is arranged parallel to the feed line, the width of the second rectangular structure is a fixed value, and the length of the second rectangular structure is a variable, and changes according to the width of the conformally designed radiation sheet; and at least one via is arranged on the second rectangular structure; the electromagnetic bandgap structure is electrically connected to the underlying copper sheet via the via.

2. The microstrip antenna structure according to claim 1, characterized in that: The via hole is arranged at the transverse center of the second rectangular structure and is fine-tuned according to a preset value of the longitudinal offset, and the radius of the via hole is set according to the processing technology requirements.

3. The microstrip antenna structure according to claim 2, characterized in that: The spacing of the via holes ranges from 0.3 mm to 1.2 mm, and the smaller the value, the better; the dielectric constant of the dielectric substrate is 3.0-3.

2.

4. The microstrip antenna structure according to claim 1, characterized in that: The electromagnetic band gap unit includes two groups of the first rectangular structures and two groups of the second rectangular structures, the two groups of the first rectangular structures and the two groups of the second rectangular structures are alternately distributed and connected end to end; the second group of the second rectangular structures of the previous electromagnetic band gap unit is connected to the first group of the first rectangular structures of the next electromagnetic band gap unit; or The electromagnetic band gap unit has an S-shaped structure, including three groups of the first rectangular structures and two groups of the second rectangular structures. The three groups of the first rectangular structures and the two groups of the second rectangular structures are alternately distributed and connected end to end; the third group of the first rectangular structures of the previous electromagnetic band gap unit is overlapped and connected with the first group of the first rectangular structures of the next electromagnetic band gap unit.

5. The microstrip antenna structure according to claim 1, characterized in that: The resonant frequency of the comb antenna is determined according to the length, width and dielectric material of each radiating piece in the comb antenna; The length of the radiation sheet is adjusted based on the initial patch length according to the simulation effect, and the width of the radiation sheet is adjusted based on the initial patch width according to the simulation effect.

6. The microstrip antenna structure according to claim 1, characterized in that: The radiation plates are cross-distributed on both sides of the feed line, and the distance between adjacent radiation plates is half a wavelength to ensure that the currents of adjacent radiation plates are in the same direction.

7. The microstrip antenna structure according to claim 1, characterized in that: 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, and 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, arranged horizontally, and the transverse spacing is kept consistent; the larger the transverse spacing is within the range that does not affect the overall size, antenna radiation pattern and wave limiting effect, the better.

8. An antenna design method, characterized in that: Applied to the microstrip antenna structure according to any one of claims 1 to 7, the method comprising: The dielectric material of the comb antenna and the length and width of each radiating piece are set, and a linear array design is performed based on the determined radiating pieces to obtain a group of comb antennas; each group of the comb antennas includes a feeder and a plurality of groups of radiating pieces arranged on the feeder, wherein the width of the radiating pieces decreases from the center to the two ends of the comb antenna; Determine an electromagnetic bandgap structure conformal to the comb antenna; the electromagnetic bandgap structure comprises a plurality of electromagnetic bandgap units connected to each other, and the opening directions of two adjacent electromagnetic bandgap units are opposite; An antenna array is formed by using at least two groups of comb antennas and a group of electromagnetic bandgap structures between each two adjacent groups of comb antennas; the front electromagnetic bandgap unit is conformally designed with the radiating piece on one side of the first group of comb antennas, and the rear electromagnetic bandgap unit is conformally designed with the radiating piece on the other side of the second group of comb antennas, so as to generate wave limiting for adjacent and conformally designed radiating pieces.

9. The antenna design method according to claim 8, characterized in that: The step of determining an electromagnetic bandgap structure conformal to the comb antenna comprises: Design each electromagnetic band gap unit to include 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 alternately distributed and connected end to end; The first rectangular structure is arranged perpendicular to the feed line, and the length and width of the first rectangular structure are both 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 plate; and at least one via is arranged on the second rectangular structure; the electromagnetic band gap structure is electrically connected to the underlying copper sheet through the via.

10. A millimeter wave radar, characterized in that: The millimeter wave radar comprises the microstrip antenna structure according to any one of claims 1 to 7.

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