A metamaterial electrically scanned antenna

Abstract

An embodiment of the present invention discloses a metamaterial electrically scanned antenna, which includes a dielectric plate, a first microstructure array, and a second microstructure array. The first microstructure array and the second microstructure array are respectively disposed on the upper and lower surfaces of the dielectric plate; the first microstructure array includes a plurality of first microstructures, and the second microstructure array includes a plurality of second microstructures; a first diode is disposed on each first microstructure, and capacitance values of the plurality of first diodes disposed on the plurality of first microstructures are all within a preset range. Therefore, antenna grating lobes or sidelobes can be effectively reduced or eliminated.

Description

Technical Field

[0001] The present invention relates to the technical field of antennas, and particularly to a metamaterial electrically scanned antenna. Background Art

[0002] Among multiple radiation oscillators of an array antenna, there may be a situation where the distance between two adjacent radiation oscillators is too large, that is, there is a relatively large gap between two adjacent radiation oscillators; this will result in the generation of more antenna side lobes or grating lobes. Due to the large number of antenna side lobes or grating lobes and the dispersion of energy, the radiation energy of the main lobe of the antenna will be reduced, resulting in a low gain in the direction of the main lobe of the antenna.

[0003] Existing methods for reducing side lobes or eliminating grating lobes of an array antenna mainly involve designing and optimizing the amplitude-phase distribution of antenna dipoles and the array arrangement method, etc. When the form of the antenna array is determined, there are bottlenecks in the design and optimization for reducing side lobes or grating lobes. Summary of the Invention

[0004] To solve the above technical problems, an aspect of an embodiment of the present invention provides a metamaterial electrically scanned antenna, which includes:

[0005] A dielectric plate;

[0006] A first micro-structure array; and

[0007] A second micro-structure array; wherein, the first micro-structure array and the second micro-structure array are respectively arranged on the upper and lower surfaces of the dielectric plate; the first micro-structure array includes a plurality of first micro-structures, and the second micro-structure array includes a plurality of second micro-structures; a first diode is arranged on each first micro-structure;

[0008] The capacitance values of the plurality of first diodes arranged on the plurality of first micro-structures are all within a preset range.

[0009] Further, in the above-mentioned metamaterial electrically scanned antenna, the capacitance values of the plurality of first diodes arranged on the plurality of first micro-structures are all within 1 pF to 1.2 pF.

[0010] Further, in the above-mentioned metamaterial electrically scanned antenna, the capacitance values of the plurality of first diodes arranged on the plurality of first micro-structures are all equal.

[0011] Further, in the above-mentioned metamaterial electrically scanned antenna, the capacitance values of the plurality of first diodes arranged on the plurality of first micro-structures are all equal to 1.1 pF.

[0012] Further, in the above-mentioned metamaterial electrically scanned antenna, the plurality of first diodes arranged on the plurality of first micro-structures are respectively used to receive a plurality of first voltages, so that the capacitance values of the plurality of first diodes arranged on the plurality of first micro-structures are all within a preset range.

[0013] Furthermore, in the above-mentioned metamaterial electrically scanned antenna, the multiple first microstructures are respectively arranged corresponding to the multiple second microstructures.

[0014] Furthermore, the metamaterial electrically scanned antenna further includes a waveguide feed, and the dielectric plate, the first microstructure array, and the second microstructure array are arranged on the waveguide feed;

[0015] A second diode is arranged on each second microstructure; when the capacitance value of each second diode is a first preset capacitance value, the corresponding second microstructure is in the 1 state, and when the capacitance value of each second diode is a second preset capacitance value, the corresponding second microstructure is in the 0 state; the beam direction of the metamaterial electrically scanned antenna is changed by changing the 1 state or 0 state of each of the multiple second microstructures.

[0016] Furthermore, in the above-mentioned metamaterial electrically scanned antenna, when the capacitance value of the second diode is the first preset capacitance value, the second diode is in a conducting state, so that the corresponding second microstructure emits or receives electromagnetic waves; or

[0017] When the capacitance value of the second diode is the second preset capacitance value, the second diode is in a cut-off state, so that the corresponding second microstructure stops emitting or receiving electromagnetic waves.

[0018] Furthermore, in the above-mentioned metamaterial electrically scanned antenna, both the first diode and the second diode are varactor diodes.

[0019] Furthermore, in the above-mentioned metamaterial electrically scanned antenna, second diodes are arranged on both the left side and the right side of each second microstructure simultaneously; or

[0020] Second diodes are arranged on either the left side or the right side of each second microstructure.

[0021] For the above-mentioned metamaterial electrically scanned antenna provided by the embodiments of the present invention, since the capacitance values of the multiple first diodes arranged on the multiple first microstructures are all within a preset range (specifically, for example, the capacitance values of the multiple first diodes arranged on the multiple first microstructures are all equal), antenna grating lobes or side lobes can be effectively reduced or eliminated. Description of the Drawings

[0022] Figure 1 It is a schematic diagram of the microstructure slot array antenna model of the metamaterial electrically scanned antenna of the present invention.

[0023] Figure 2 It is the front view of the metamaterial electrically scanned antenna of the present invention.

[0024] Figure 3 It is the sectional view of the microstructure array layer of the metamaterial electrically scanned antenna of the present invention.

[0025] Figure 4 It is a top view of the microstructure array layer of the metamaterial electrically scanned antenna of the present invention.

[0026] Figure 5 It is a schematic structural diagram of the first microstructure array of the present invention.

[0027] Figure 6 It is a schematic structural diagram of the second microstructure array of the present invention.

[0028] Figure 7 It is a schematic diagram of the waveguide feed structure of the metamaterial electrically scanned antenna of the present invention.

[0029] Figure 8 It is the two-dimensional radiation pattern of the metamaterial electrically scanned antenna of the present invention without loading the grating lobe elimination device.

[0030] Figure 9 It is the two-dimensional radiation pattern of the metamaterial electrically scanned antenna of the present invention when loading the grating lobe elimination device.

[0031] Figure 10 It is the two-dimensional radiation pattern of the metamaterial electrically scanned antenna of the present invention. Detailed implementation manners

[0032] To describe in detail the technical content, structural features, achieved objectives and effects of the technical solution, the following will be described in detail with specific embodiments in conjunction with the accompanying drawings.

[0033] The principle of the metamaterial electrically scanned antenna of the present invention is as follows: The working states of the first microstructure array and the second microstructure array of the metamaterial electrically scanned antenna can be controlled by an FPGA (or a single-chip microcomputer, a computer, etc.). The first microstructure array and the second microstructure array are respectively arranged on the upper and lower surfaces of the dielectric plate. The first microstructure array includes a plurality of first microstructures, such as patch microstructures (as shown in Figure 5 ); The second microstructure array includes a plurality of second microstructures, such as slot microstructures (as shown in Figure 6 ). The plurality of patch microstructures are manifested as a plurality of discrete attached metal structures on the dielectric plate. The plurality of slot microstructures are manifested as a plurality of notches or slots opened on the sheet metal, and the metal is connected.

[0034] Its control principle is as follows: The scanning angle and the corresponding voltage distribution are scanned through computer software programming. An instruction is issued to the computer according to the required scanning angle, and digital-to-analog conversion is implemented through a single-chip microcomputer or FPGA to convert the digital signal into an analog signal, so as to control the on-off state of the voltage across the two ends of the second diode loaded on each slot microstructure (i.e., each second microstructure) of the upper layer of the waveguide feed 1. Feed the wave through the waveguide feed and perform energy transmission within the waveguide limitation range. Each slot microstructure of the second microstructure array radiates or does not radiate energy according to different on-off states, and the energy and phase radiated by each slot microstructure at different positions are different. By controlling the on-off state of the second diode loaded on each slot microstructure of the second microstructure array and the capacitance value of the first diode loaded on each patch microstructure of the first microstructure array, the phase distribution of the radiation surface can be controlled to achieve specified beam scanning. The energy reaching the end is matched and absorbed through impedance matching at the waveguide end to reduce reflection.

[0035] Its beam scanning principle is as follows: The control system outputs a control signal from the computer software to the single-chip microcomputer, and the single-chip microcomputer performs digital-to-analog conversion to control the voltage states loaded across the two ends of all the second diodes. A plurality of second diodes (such as varactor diodes) are respectively loaded on a plurality of second microstructures (such as slot microstructures) of the second microstructure array. The capacitance value (or on-off) of the second diode is controlled by applying a second voltage to each second diode.

[0036] When the capacitance value of the second diode is the first preset capacitance value (such as 0.2 pF), the second diode is in a conducting state. At this time, the corresponding second microstructure is in the ON state (i.e., the 1 state), resonates at the antenna center operating frequency, and radiates a relatively large amount of energy outward.

[0037] When the capacitance value of the second diode is the second preset capacitance value (such as 1 pF), the second diode is in a cutoff state. At this time, the corresponding second microstructure is in the OFF state (i.e., the 0 state), does not resonate at the antenna center operating frequency, and radiates a relatively small amount of energy outward (or does not radiate energy outward).

[0038] Its principle of eliminating antenna grating lobes is as follows: By applying a plurality of first voltages to a plurality of first diodes (such as varactor diodes) provided on a plurality of first microstructures (such as a plurality of patch microstructures) of the first microstructure array respectively, and controlling the capacitance values of the plurality of first diodes to be within a preset range (such as within 1 pF to 1.2 pF), the side lobes or grating lobes of the metamaterial electronically scanned antenna can be reduced or eliminated.

[0039] In a specific embodiment, by applying a plurality of first voltages to a plurality of first diodes provided on the plurality of first microstructures respectively, and controlling the capacitance values of the plurality of first diodes to be equal (such as all equal to 1.1 pF), the side lobes or grating lobes of the metamaterial electronically scanned antenna can be reduced or eliminated.

[0040] In the simplified model, we take a single microstructural slot array layer (i.e., the second microstructural array) as an ideal point source and perform phase analysis on it. Figure 1 It is a schematic diagram of the microstructural slot array (i.e., the second microstructural array) model of the metamaterial electrical scanning antenna of the present invention. As Figure 1 shown, assume that the angle between the main radiation beam direction and the waveguide surface is φ, and the distance between different microstructural units (i.e., the second microstructures) is d; then the phase difference between adjacent oscillators (i.e., radiation microstructural units) is: β0·dcos(φ) - β wg ·d, where β0 and βwg are the effective propagation constants of electromagnetic waves in space and in the waveguide respectively; in order to form a combined beam in the far field, the phase difference between oscillators needs to satisfy:

[0041]

[0042] It can be derived that:

[0043]

[0044] According to formula 2, the beam scanning angle φ is related to the distance d of the radiation slots of the microstructure. By programming the computer software to output signals, converting the digital signals into analog signals, and respectively regulating the voltages across all the loaded diodes (i.e., the second diodes loaded on each second microstructure), the on-off control of the diodes is realized. The on-off control of the diodes can regulate the arrangement state of the radiation slots, that is, different d, to achieve beam scanning. It should be noted here that d represents the distance between two adjacent second microstructures in a radiation state (i.e., state 1).

[0045] Figure 2 It is the front view of the metamaterial electrical scanning antenna of the present invention. Figure 3 It is the cross-sectional view of the microstructural array layer of the metamaterial electrical scanning antenna of the present invention. Figure 4 It is the top view of the microstructural array layer of the metamaterial electrical scanning antenna of the present invention. Please refer to Figure 2 , Figure 3 and Figure 4 , the metamaterial electrical scanning antenna 100 includes a waveguide feed 1 and a microstructural array layer 2 provided on the waveguide feed 1. The microstructural array layer 2 includes a dielectric plate 10, a first microstructural array 20, and a second microstructural array 40. The dielectric plate 10 is connected to the first microstructural array 20 and the second microstructural array 40 through metal material layers 12 and 14 plated on the upper and lower surfaces respectively. As Figure 5 shown, the first microstructural array 20 includes a plurality of first microstructures 22, and a first diode 24 is provided on each first microstructure 22.

[0046] As Figure 6As shown, the second microstructure array 40 includes a plurality of second microstructures 42. A second diode 44 is disposed on each second microstructure 42. The plurality of second microstructures 42 are respectively arranged corresponding to the plurality of first microstructures 22.

[0047] In other embodiments, the plurality of second microstructures 42 may not be respectively arranged corresponding to the plurality of first microstructures 22, and a second diode may not be disposed on each second microstructure 42.

[0048] The dielectric plate 10 includes any one or a combination of cyanate ester, epoxy, and quartz fiber prepreg; the dielectric constant is 2 to 4; the thickness is 1 mm to 6 mm. Each first microstructure 22 includes any one or a combination of Au, Ag, Cu, and Al, and the first diode 24 is a varactor diode. Each second microstructure 42 includes any one or a combination of Au, Ag, Cu, and Al, and the second diode 44 is a varactor diode.

[0049] In the embodiment of the present invention, the capacitance values of the plurality of first diodes 24 disposed on the plurality of first microstructures 22 are all within a preset range, which can effectively reduce or eliminate the side lobes or grating lobes of the metamaterial electrically scanned antenna 100.

[0050] As a non-limiting example, the capacitance values of the plurality of first diodes 24 disposed on the plurality of first microstructures 22 are all within 1 pF to 1.2 pF.

[0051] In a specific embodiment of the present invention, the capacitance values of the plurality of first diodes 24 disposed on the plurality of first microstructures 22 are all equal, which can effectively reduce or eliminate the side lobes or grating lobes of the metamaterial electrically scanned antenna 100.

[0052] As a non-limiting example, the capacitance values of the plurality of first diodes 24 disposed on the plurality of first microstructures 22 are all equal to 1.1 pF.

[0053] Therefore, the metamaterial electrically scanned antenna 100 can increase the radiation energy of the main lobe of the antenna, making the antenna radiation energy more concentrated rather than dispersed; making the gain in the main lobe direction of the antenna higher, achieving high directivity of the metamaterial electrically scanned antenna 100.

[0054] Please refer to Figure 6 , in the embodiment of the present invention, a second diode 44 is disposed on the left side of each second microstructure 42. In other embodiments, a second diode 44 may also be disposed on the right side of each second microstructure 42, or second diodes 44 may be disposed on both the left and right sides of each second microstructure 42 simultaneously.

[0055] When the capacitance value of each second diode 44 is the first preset capacitance value, the corresponding second micro-structure 42 is in the 1 state. When the capacitance value of each second diode 44 is the second preset capacitance value, the corresponding second micro-structure 42 is in the 0 state; the beam direction of the metamaterial electrically scanned antenna 100 is changed by changing the 1 state or 0 state of each of the plurality of second micro-structures 42.

[0056] When the capacitance value of the second diode 44 is the first preset capacitance value, the second diode 44 is in the conducting state, enabling the corresponding second micro-structure 42 to transmit or receive electromagnetic waves or enabling the corresponding second micro-structure 42 to radiate a relatively large amount of energy. When the capacitance value of the second diode 44 is the second preset capacitance value, the second diode 44 is in the cut-off state, causing the corresponding second micro-structure 42 to stop transmitting or receiving electromagnetic waves or causing the corresponding second micro-structure 42 to radiate a relatively small amount of energy.

[0057] As a non-limiting example, the first preset capacitance value is 0.2 pF and the second preset capacitance value is 1 pF.

[0058] The specific beam scanning principle is as follows: There can be various forms of the second micro-structure layer and arrangements of the second diodes 44. Let the on state of the second diode 44 be 1 and the off state be 0; when the plurality of second micro-structures 42 are arranged in a 100 cycle, the beam direction of the metamaterial electrically scanned antenna 100 is -11 degrees. When the plurality of second micro-structures 42 are arranged in a 1100100 cycle, the beam direction of the metamaterial electrically scanned antenna 100 is -5 degrees. When the plurality of second micro-structures 42 are arranged in a 1100 cycle, the beam direction of the metamaterial electrically scanned antenna 100 is 1 degree. When the plurality of second micro-structures 42 are arranged in a 110011100 cycle, the beam direction of the metamaterial electrically scanned antenna 100 is 5 degrees. When the plurality of second micro-structures 42 are arranged in a 11100 cycle, the beam direction of the metamaterial electrically scanned antenna 100 is 9 degrees. When the plurality of second micro-structures 42 are arranged in a 111000 cycle, the beam direction of the metamaterial electrically scanned antenna 100 is 14 degrees.

[0059] Please refer to Figure 2 and Figure 7 , where 1 is the waveguide feed, 2 is the micro-structure array layer, 3 is the waveguide feed interface, 4 is the metal cover plate, 5 is the one-to-four waveguide, and 6 is the screw hole.

[0060] The following presents a specific example to illustrate the working principle of the metamaterial electrically scanned antenna 100 of the present invention. Please also refer to Figure 5 , Figure 6 and Figure 7, the width of a single waveguide of the one-to-four waveguide 5 is 22.86 mm, and the height of the waveguide is 10.16 mm. The upper-layer first microstructure array 20 is composed of 24×4 first microstructures (i.e., annular patch microstructures), and the lower-layer second microstructure array 40 is composed of 21×4 second microstructures (i.e., slot microstructures).

[0061] When the metamaterial electrically scanned antenna 100 operates in the radiation state, the capacitance values of the multiple first diodes 24 loaded in the upper-layer first microstructure array 20 are 1.1 pF. By adjusting the capacitance values and arrangement states of the second diodes 44 loaded in each of the second microstructures 42 in the lower-layer second microstructure array 40, scanning at different angles can be achieved. For example, it is stipulated that when the capacitance value of the second diode 44 loaded in the lower layer is 0.2 pF, it is in the 1 state, and when the capacitance value of the second diode 44 loaded in the lower layer is 1 pF, it is in the 0 state. When the multiple second microstructures 42 are arranged in 100 cycles, the beam direction of the metamaterial electrically scanned antenna 100 is -11 degrees. When the multiple second microstructures 42 are arranged in 1100 cycles, the beam direction of the metamaterial electrically scanned antenna 100 is 1 degree. When the multiple second microstructures 42 are arranged in 11100 cycles, the beam direction of the metamaterial electrically scanned antenna 100 is 9 degrees. This waveguide antenna is an array antenna, which is different from the substrate integrated antenna and can form two-dimensional beam scanning. The operating frequency of this antenna is 9.3 GHz; the two-dimensional scanning pattern is as shown in Figure 10.

[0062] The substrate integrated antenna is a one-dimensional antenna and only performs one-dimensional scanning. The substrate integrated antenna is fed by a substrate integrated waveguide, and its overall structure is generally relatively thin and light. This electrically scanned antenna is a waveguide antenna, and its overall structure is generally relatively bulky, but it is easy to be compounded with a multi-layer microstructure to form a feed.

[0063] The antenna part includes a waveguide feed layer and a radiation layer. Figure 7 This is a schematic diagram of the waveguide feed structure of the metamaterial electrically scanned antenna of the present invention. As Figure 7 shown, in the example, feeding is performed by splitting one port into four to supply the energy radiation of the microstructure slots in the radiation layer. The metal cover 4 is used to encapsulate the waveguide. The metamaterial electrically scanned antenna of the present invention is provided with a waveguide feed interface 3 and a series of screw holes 6 with a fixed connection function.

[0064] This scanned antenna comprehensively controls radiation and optimizes the scanning beam by setting a double-layer microstructure array. This scanned antenna has a simple structure and is easy to prepare: the control system can be directly controlled by a single-chip microcomputer or an FPGA. The antenna part is only composed of a waveguide and a radiation metamaterial layer, eliminating unnecessary complex phase shifters and transmission line feed networks. By controlling the arrangement of the radiation slots in the microstructure plane slot array, the radiation phase distribution in the radiation plane is controlled to form different electromagnetic scanning beams.

[0065] Figure 8This is the two-dimensional radiation pattern of the metamaterial electrically scanned antenna 100 of the present invention without loading the grating lobe or sidelobe elimination device (that is, without loading the upper first microstructure array 20). As can be clearly seen from Figure 8 , the antenna without the grating lobe elimination device has a main lobe with a gain of approximately 10 dB, a sidelobe with a gain greater than 5 dB, and another sidelobe with a gain greater than 0 dB. Since the antenna does not load the grating lobe elimination device, the radiation energy is relatively dispersed and not concentrated; the radiation energy of the main lobe of the antenna is small, and the gain in the main lobe direction of the antenna is low.

[0066] Figure 9 This is the two-dimensional radiation pattern of the metamaterial electrically scanned antenna 100 of the present invention when loading the grating lobe or sidelobe elimination device (that is, loading the upper first microstructure array 20). As can be clearly seen from Figure 9 , the antenna with the grating lobe elimination device has a main lobe with a gain of approximately 12.5 dB, and the gains of the other multiple sidelobes are basically less than 0 dB. Since the antenna is loaded with the grating lobe elimination device, the radiation energy is relatively concentrated; compared with the antenna without the grating lobe elimination device in Figure 8 , Figure 9 , the radiation energy of the main lobe of the antenna is larger, the gain in the main lobe direction of the antenna is higher, and the antenna has high directivity.

[0067] Figure 10 This is the two-dimensional radiation pattern of the metamaterial electrically scanned antenna 100 of the present invention. As shown in Figure 10 , this is the Phi = 0 cross-section pattern of this electrically scanned antenna in different beam scanning states. The ordinate is the gain value, with the unit of dB. The abscissa is the Theta angle (the angle with the Z-axis). The patterns in the figure are the patterns at two scanning angles of -11° and 9°. It can be obtained that the gains at both scanning angles are relatively high, greater than 10 dB, and the sidelobes are relatively low, lower than -10 dB; the purpose of reducing or eliminating the sidelobes of the metamaterial electrically scanned antenna 100 is achieved.

[0068] Those skilled in the art should understand that the above embodiments are only exemplary embodiments, and various changes, substitutions, and alterations can be made without departing from the spirit and scope of the present invention.

Claims

1. A metamaterial electrically scanned antenna, characterized in that, Comprising: A dielectric plate; A first micro-structure array; And A second micro-structure array; wherein, the first micro-structure array and the second micro-structure array are respectively disposed on the upper and lower surfaces of the dielectric plate; the first micro-structure array includes a plurality of first micro-structures, and the second micro-structure array includes a plurality of second micro-structures; a first diode is disposed on each first micro-structure; Wherein, the first micro-structure array is a sidelobe elimination device; the capacitance values of the plurality of first diodes disposed on the plurality of first micro-structures are all within a preset range to effectively reduce or eliminate antenna sidelobes; wherein, the plurality of first micro-structures are all annular patch micro-structures, and the plurality of second micro-structures are all slot micro-structures; The first micro-structure includes two annular patch micro-structures, the first diode is located between the two annular patch micro-structures, and both ends of the first diode are respectively connected to the two annular patch micro-structures; A second diode is disposed on each second micro-structure, and the second micro-structure includes a square ring slot and two parallel line slots located inside the square ring slot, and the two parallel line slots are respectively communicated with the square ring slot through slots; When the capacitance value of the second diode is a first preset capacitance value, the second diode is in a conducting state, so that the corresponding second micro-structure emits or receives electromagnetic waves.

2. The metamaterial electrically scanned antenna according to claim 1, wherein: The capacitance values of the plurality of first diodes disposed on the plurality of first micro-structures are all within 1 pF to 1.2 pF.

3. The metamaterial electric scanning antenna according to claim 1, wherein: The capacitance values of the plurality of first diodes disposed on the plurality of first micro-structures are all equal.

4. The metamaterial electrically scanned antenna according to claim 3, wherein: The capacitance values of the plurality of first diodes disposed on the plurality of first micro-structures are all equal to 1.1 pF.

5. The metamaterial electric scanning antenna according to claim 1, characterized in that: The plurality of first diodes disposed on the plurality of first micro-structures are respectively used to receive a plurality of first voltages, so that the capacitance values of the plurality of first diodes are all within a preset range.

6. The metamaterial electric scanning antenna according to claim 1, characterized in that: The plurality of first micro-structures are respectively disposed corresponding to the plurality of second micro-structures.

7. The metamaterial electric scanning antenna according to claim 1, wherein: The metamaterial electric scanning antenna further includes a waveguide feed, and the dielectric plate, the first micro-structure array and the second micro-structure array are disposed on the waveguide feed; When the capacitance value of each second diode is a first preset capacitance value, the corresponding second micro-structure is in a state of 1, and when the capacitance value of each second diode is a second preset capacitance value, the corresponding second micro-structure is in a state of 0; The beam direction of the metamaterial electric scanning antenna is changed by changing the state of 1 or 0 of each of the plurality of second micro-structures.

8. The metamaterial electric scanning antenna according to claim 7, wherein: When the capacitance value of the second diode is a second preset capacitance value, the second diode is in a cut-off state, so that the corresponding second micro-structure stops emitting or receiving electromagnetic waves.

9. The metamaterial electrically scanned antenna according to claim 7, characterized in that: The first diode and the second diode are both varactor diodes.

10. The metamaterial electric scanning antenna according to claim 1, wherein: Second diodes are simultaneously disposed on the left and right sides of each second micro-structure; or Second diodes are disposed on the left or right side of each second micro-structure.

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