A wideband fixed-beam leaky-wave antenna with filtering characteristics

Abstract

The application belongs to the field of millimeter wave point-to-point communication, and particularly relates to a broadband fixed-beam leaky-wave antenna with filtering characteristics. The substrate integrated coaxial transmission structure is used to feed the leaky-wave structure at both ends. Since the substrate integrated coaxial transmission is quasi-TEM wave, the phase constant β changes little in a wide frequency band range, so that a fixed radiation beam can be obtained in a certain frequency band range. The counter-phase signals are fed at both ends of the leaky-wave structure to combine two beams into a main beam. When the two beams deviate from the wide-side radiation by a certain angle, they can still combine into a beam with good radiation, so that the bandwidth corresponding to the fixed radiation beam is further widened. On this basis, a plurality of radiation matching units are sequentially arranged on the metal strip along the length direction of the metal strip, so that the fixed-beam leaky-wave antenna has the characteristics of keeping the angle of the radiation beam unchanged, high gain, high efficiency and low sidelobe in a wide bandwidth.

Description

Technical Field

[0001] This invention belongs to the field of millimeter-wave point-to-point communication, specifically relating to a broadband fixed-beam leaky-wave antenna with filtering characteristics. Background Technology

[0002] Leaky wave antennas (LWAs) are defined as traveling wave antennas whose radiation patterns vary at different frequencies. They have simple feeding structures and can easily achieve narrow beams by controlling the leakage rate and antenna length. Compared with phased array antennas, they have advantages such as low cost, simple geometry, and wide bandwidth. In fact, the frequency-dependent beam scanning characteristics of leaky wave antennas can be understood as an inherent fundamental property of modal dispersion. In naturally occurring dispersive media, dispersion constraints can be represented by the Kramer-Kroning relation and the Bode relation, i.e., linear response functions with real and imaginary parts related to the frequency.

[0003] By studying and utilizing the frequency-dependent beam scanning characteristics of leaky-wave antennas, a real-time spectrum analyzer and radar sensor were realized. However, frequency-dependent beam scanning characteristics are not suitable for point-to-point communication and high-capacity broadband communication.

[0004] Several works have been conducted to mitigate angular dispersion effects and reduce the beam angle as it scans with frequency: generating low-dispersion fast waves in waveguide structures, using multilayer gold cover plates, forming gas-filled hollow waveguides using bulk silicon microelectromechanical systems (MEMS) microfabrication techniques, and creating a slot on its upper surface to achieve a slowly varying dispersion curve in a fixed beam radiation range of 55–67 GHz; another work reports an integrated waveguide leaky-lens antenna on a gas-filled substrate, which achieves a fixed beam of 60° ± 2° within 28.6% of the fractional bandwidth by optimizing the dispersion curve through appropriate parameters. Other works have implemented broadband directional beam leaky-lens antennas using dispersion compensation mechanisms; however, in design, dielectric lenses integrated in long-slot leaky-lens antennas are very bulky and require all-metal structures and / or complex manufacturing / assembly processes. They may not be suitable for planar system integration with other active / passive components, nor for mass production using standard / mature low-cost PCB processes.

[0005] One effective method for fixing the radiation beam is a quasi-TEM mode fixed-beam leaky antenna, where the radiation angle can be limited to a small area in the front quadrant or end-fire region because the ratio between the propagation constant β and the free-space wave number k is almost constant.

[0006] Chinese patent CN110581363A discloses a fixed-beam leaky antenna with customizable emission angle. The leaky antenna includes a gap ridge waveguide, a triangular metal prism, and a transmission-type phase gradient surface structure. It mitigates the characteristic of rapid frequency scanning of the radiated beam of existing leaky antennas, fixes the radiated beam within a small angle range over a large bandwidth, and can customize the required fixed beam angle range according to requirements. Its advantages are high flexibility, while its disadvantages are large size, expensive and complex processing, and complex assembly.

[0007] Chinese patent CN113316868A discloses a dual-end-fed wide-side leaky antenna in which opposite ends of the leaky structure are fed with an inverted version of a common signal, resulting in a separation of the wide-side frequency from the open stopband. To achieve this, the common signal can be split into two paths of equal length, one including an ideal electrical conductor (PEC) reflector and the other including an ideal magnetic conductor (PMC) reflector. Alternatively, the common signal can be split into two paths differing in length by half a wavelength. Power dividers and feed horns can be used in the corresponding paths. The leaky structure can have a transverse slot whose width increases toward the midpoint of the structure, allowing it to be formed on a single planar portion of a photolithographic structure, for example, by patterning its conductive layer. However, this antenna only achieves wide-side fixed-beam radiation in the 27.5 GHz–28 GHz range and lacks out-of-band filtering characteristics.

[0008] It is evident that existing fixed-beam leaky antennas typically employ an all-metal structure, which involves complex manufacturing or assembly processes and results in a large size. Furthermore, quasi-TEM mode fixed-beam leaky antennas still exhibit a beam outside the operating frequency band corresponding to the fixed radiation beam, thus hindering their application as receiving antennas in millimeter-wave point-to-point communication. Summary of the Invention

[0009] The purpose of this invention is to provide a broadband fixed-beam leaky antenna with filtering characteristics. This antenna is a full-planar quasi-TEM mode leaky antenna with broadband fixed-beam radiation and out-of-band filtering characteristics. It has the advantages of simple manufacturing process, low cost, small size, high gain, high efficiency, and low sidelobes, and is suitable for millimeter-wave point-to-point communication.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A fixed-beam leaky antenna with out-of-band filtering characteristics includes, from top to bottom, the following layers stacked sequentially: a first metal layer, a first dielectric layer, a second metal layer, a second dielectric layer, a third metal layer, a third dielectric layer, a fourth metal layer, and a metal feed layer.

[0012] The first metal layer consists of multiple pairs of radiating patches;

[0013] The first dielectric layer has multiple pairs of first metallized vias.

[0014] The second metal layer has multiple radiation grooves;

[0015] The second dielectric layer is provided with a plurality of second metallized vias, which are arranged in a rectangle;

[0016] The third metal layer has three through matching slots, including two first matching slots and one second matching slot; the second matching slot is located between the two first matching slots, and a metal strip is provided on the line connecting the midpoints of its two wide sides.

[0017] The third dielectric layer has the same structure as the second dielectric layer 4;

[0018] The fourth metal layer has a coupling window at each end, and each coupling window has a coupling patch smaller than the coupling window inside, with one end of the coupling patch connected to the fourth metal layer.

[0019] The metal feed layer is provided with a differential feed transition structure, a first bandpass filter and a second bandpass filter. The input of the differential feed structure is connected to an external excitation structure, and the output is connected to the first bandpass filter and the second bandpass filter respectively.

[0020] Multiple pairs of radiating patches, multiple radiating slots, multiple pairs of first metallized vias, and multiple matching units are arranged in a vertical direction. Two coupling windows and two first rectangular slots are arranged in a vertical direction. The first metal layer, the first dielectric layer, and the second metal layer together constitute a leakage wave structure. The second metal layer, the second dielectric layer, the third metal layer, the third dielectric layer, the metal strip, and the second metallized vias together constitute a substrate-integrated coaxial transmission structure.

[0021] Furthermore, the spacing between the rectangular arrangement of the plurality of second metallized vias, with both ends located on the two long sides and close to the wide side, is reduced to divide the space enclosed by the second metallized vias into five parts, namely the first region, the second region, the third region, the fourth region, and the fifth region, wherein the first region and the fifth region are located at the two ends.

[0022] Furthermore, the first region and the fifth rectangular region correspond to the two coupling slots in the vertical direction, respectively.

[0023] Furthermore, the matching grooves provided on the third metal layer are all rectangular grooves.

[0024] Furthermore, multiple radiation matching units are sequentially arranged along the length of the metal strip, and each radiation matching unit is composed of a metal patch.

[0025] Furthermore, the first and last radiation matching units in the multiple radiation matching units consist of two first metal patches, which are symmetrically arranged on both sides of the metal strip; the multiple radiation matching units between the first and last radiation matching units each consist of four first metal patches, with each pair of first metal patches forming a group, and the two groups of first metal patches are symmetrically arranged on both sides of the metal strip.

[0026] Furthermore, each pair of radiating patches consists of two symmetrical rectangular metal patches, and both coupling windows are trapezoidal coupling windows.

[0027] Furthermore, the metal feed layer is provided with a fourth rectangular slot, the two wide sides of which are chamfered to form a trapezoidal structure similar to the coupling window.

[0028] Furthermore, the differential transition structure is fabricated using CNC machining technology, and both the substrate-integrated coaxial transmission structure and the leakage wave structure are fabricated using PCB substrate machining technology.

[0029] Furthermore, the radiating groove is a bowtie-shaped groove.

[0030] Furthermore, a third metallized through-hole is provided at the middle position of both the first region and the fifth region, and two pairs of fourth metallized through-holes are provided at both ends of the third region. The line connecting the centers of the two pairs of fourth metallized through-holes is parallel to the line connecting the centers of the second metallized through-holes that form the second region or the fourth region.

[0031] By adopting the above technical solution, the present invention has the following advantages:

[0032] 1. The fixed-beam leaky antenna of the present invention integrates two bandpass filters in the path of the feed signal. This achieves out-of-band filtering characteristics without increasing the antenna volume, suppressing radiation beams outside the operating frequency band corresponding to the fixed radiation beam, thus enabling better application in millimeter-wave point-to-point communication. The first bandpass filter is connected at one end to the first output terminal of the differential transition structure, and at the other end to a coupling window at one end of the fourth metal layer, via a coupling window at one end of the fourth metal layer. This method integrates two bandpass filters in the path of the feed signal, suppressing radiation beams outside the operating frequency band corresponding to the fixed radiation beam, thus enabling better application in millimeter-wave point-to-point communication.

[0033] 2. This invention employs a substrate-integrated coaxial cable transmission structure to feed the leaky wave structure at both ends, with the signals fed at both ends being inverse signals. Since the substrate-integrated coaxial cable transmits quasi-TEM waves, it has very weak dispersion characteristics, and its phase constant β changes little over a wide frequency band. Therefore, a fixed radiation beam can be obtained within a certain frequency band. Feeding inverse signals at both ends of the leaky wave structure allows the two beams to be combined into a main beam. Even when the two beams deviate from the wide side radiation by a certain angle, they can still be combined into a beam with good radiation, thereby further widening the bandwidth corresponding to the fixed radiation beam. Based on this, by sequentially arranging multiple radiation matching units along the length of the metal strip, the fixed-beam leaky wave antenna of this invention possesses characteristics such as maintaining a constant angle of the radiation beam over a wide bandwidth, high gain, high efficiency, and low sidelobe.

[0034] 3. The differential transition structure and bandpass filter structure connecting the fixed-beam leaky antenna to the standard waveguide are manufactured using CNC machining technology, while the substrate-integrated coaxial line and leaky structure are manufactured using PCB substrate machining technology. They are assembled using screws and pre-drilled holes in the metal parts and substrate, resulting in low cost and simple assembly. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the overall structure of a fixed-beam leaky antenna with out-of-band filtering characteristics, as shown in the embodiment.

[0036] Figure 2 This is a layered model diagram of a fixed-beam leaky-wave antenna with out-of-band filtering characteristics, as shown in the embodiment.

[0037] Figure 3 This is a schematic diagram of the leaky wave unit structure of a fixed beam leaky wave antenna with out-of-band filtering characteristics in the embodiment.

[0038] Figure 4 This is a schematic diagram of the differential feed transition structure to substrate integrated coaxial line transmission structure of a fixed-beam leaky antenna with out-of-band filtering characteristics, as shown in the embodiment.

[0039] Figure 5 The simulated reflection coefficient of a fixed-beam leaky-wave antenna with out-of-band filtering characteristics is shown in the example.

[0040] Figure 6 The actual gain of the fixed-beam leaky antenna with out-of-band filtering characteristics in the embodiment;

[0041] Figure 7 The simulated radiation efficiency of a fixed-beam leaky antenna with out-of-band filtering characteristics is shown in the example.

[0042] Figure 8 As an example, a fixed-beam leaky antenna with out-of-band filtering characteristics is used at 26.8 GHz. Z Normalized simulated radiation pattern at the location;

[0043] Figure 9 As an example, a fixed-beam leaky antenna with out-of-band filtering characteristics at 27 GHz Z Normalized simulated radiation pattern at the location;

[0044] Figure 10 As an example, a fixed-beam leaky antenna with out-of-band filtering characteristics is used at 27.7 GHz. Z Normalized simulated radiation pattern at the location;

[0045] Figure 11 As an example, a fixed-beam leaky antenna with out-of-band filtering characteristics at 28 GHz Z Normalized simulated radiation pattern at the location;

[0046] Figure 12 As an example, a fixed-beam leaky antenna with out-of-band filtering characteristics is used at 28.3 GHz. Z Normalized simulated radiation pattern at the location;

[0047] Figure 13 As an example, a fixed-beam leaky antenna with out-of-band filtering characteristics is used at 28.6 GHz. Z Normalized simulated radiation pattern at the location;

[0048] Figure 14 As an example, a fixed-beam leaky antenna with out-of-band filtering characteristics is used at 29.2 GHz. Z Normalized simulated radiation pattern at the location;

[0049] Figure 15 This is the signal transmission path of a fixed-beam leaky-wave antenna with out-of-band filtering characteristics, as shown in the embodiment.

[0050] Figure label:

[0051] 1 is the first metal layer, 2 is the first dielectric layer, 3 is the second metal layer, 4 is the second dielectric layer, 5 is the third metal layer, 6 is the third dielectric layer, 7 is the fourth metal layer, 8 is the differential transition structure, 9 is the bandpass filter, 10 is the rectangular radiating patch, 11 is the first metallized via, 12 is the radiating groove, 13 is the metal strip, 14 is the outer conductor of the substrate coaxial line, 15 is the first matching shorting post, 16 is the second matching shorting post (third metallized via), and 17 is the coupling patch. Detailed Implementation

[0052] The technical solution of this invention will be described in detail below with reference to the accompanying drawings.

[0053] like Figures 1-4As shown, this embodiment provides a fixed-beam leaky antenna with out-of-band filtering characteristics, which includes a first metal layer 1, a first dielectric layer 2, a second metal layer 3, a second dielectric layer 4, a third metal layer 5, a third dielectric layer 6, a fourth metal layer 7, and a metal feed layer stacked sequentially from top to bottom.

[0054] The first metal layer 1 consists of multiple pairs of radiating patches, each pair of radiating patches consisting of two symmetrical rectangular metal patches. The two coupling windows are trapezoidal coupling windows.

[0055] The first dielectric layer 2 is provided with multiple pairs of first metallized through holes 11.

[0056] The second metal layer 3 has a plurality of radiation slots 12. One side of each radiation slot 12 serves as a radiation structure, and the other side is used to couple the energy transmitted on the substrate integration coaxial line to the radiation patch to increase the radiation coupling amount. In this embodiment, the radiation slot 12 is designed as a bowtie-shaped slot.

[0057] The second dielectric layer 4 has multiple second metallized vias arranged in a rectangle. The x-axis is defined as the long side of the rectangle, and the y-axis as the wide side. The two ends of the rectangle are located on the two long sides, and the spacing between the second metallized vias near the wide side is reduced, dividing the space enclosed by the second metallized vias into five parts: a first region, a second region, a third region, a fourth region, and a fifth region. A third metallized via is located in the middle of both the first and fifth regions. Two pairs of fourth metallized vias are located at each end of the third region, and the line connecting the centers of the two pairs of fourth metallized vias is parallel to the line connecting the centers of the second metallized vias forming the second or fourth region.

[0058] The third metal layer 5 has three through rectangular slots, including two first rectangular slots and one second rectangular slot. The second rectangular slot is located between the two first rectangular slots, and a metal strip is provided along the line connecting the midpoints of its two wide sides. Multiple radiation matching units are sequentially arranged along the length of the metal strip. Each radiation matching unit is composed of metal patches. The first and last radiation matching units are composed of two first metal patches, which are symmetrically arranged on both sides of the metal strip. The multiple radiation matching units between the first and last radiation matching units are each composed of four first metal patches, with each pair of first metal patches forming a group, and two groups of first metal patches are symmetrically arranged on both sides of the metal strip.

[0059] The third dielectric layer 6 has the same structure as the second dielectric layer 4.

[0060] The fourth metal layer 7 has a coupling window at each end, and each coupling window has a coupling patch 17 with a size smaller than the coupling window. One end of the coupling patch 17 is connected to the fourth metal layer 7.

[0061] The structure comprises multiple pairs of radiating patches, multiple radiating slots, multiple pairs of first metallized vias, and multiple matching units arranged vertically. The first and fifth regions on the second dielectric layer 4 and the third dielectric layer 6, and the two coupling windows on the fourth metal layer 7, are vertically aligned with the two first rectangular slots on the third metal layer 5. The first metal layer 1, the first dielectric layer 2, and the second metal layer 3 together constitute a leakage wave structure. The second metal layer 3, the second dielectric layer 4, the third metal layer 5, the third dielectric layer 6, the metal strip 13, and the second metallized vias together constitute a substrate-integrated coaxial line transmission structure, in which the metal strip 13 serves as the inner conductor. The metal walls of the second metallized vias on the second dielectric layer 4 and the third dielectric layer 6 form the outer conductor 14 of the substrate-integrated coaxial line. The metal walls of the fourth metallized vias form first matching short-circuit posts 15, which improve the matching performance when the width of the inner conductor of the substrate-integrated coaxial line remains constant and the outer conductor gradually widens. The metal wall of the third metallized via forms a second matching short post 16, which connects the inner conductor of the substrate integrated coaxial line and the coupling patch 17, and forms a monopole antenna mode with the coupling patch 17, converting the TE wave transmitted by the substrate integrated waveguide into the TEM wave transmitted by the substrate integrated coaxial line, thus achieving simultaneous mode and impedance matching.

[0062] The metal feed layer is provided with a fourth rectangular slot, a differential feed transition structure, a first bandpass filter, and a second bandpass filter. The two wide sides of the fourth rectangular slot are chamfered to form a trapezoidal structure similar to a coupling window, so as to better convert the TE wave transmitted by the substrate integrated waveguide into the TEM wave transmitted by the substrate integrated coaxial line, allowing more energy to be transferred from the metal feed layer to the substrate integrated coaxial line. The differential feed transition structure, the first bandpass filter, and the second bandpass filter are located within the fourth rectangular slot. The input of the differential feed structure is connected to an external excitation structure, and the outputs are connected to the first bandpass filter and the second bandpass filter, respectively.

[0063] In practice, the differential transition structure and bandpass filter structure are fabricated using CNC machining technology, while the substrate-integrated coaxial line and leakage wave structure are fabricated using PCB substrate machining technology. They are assembled using screws and pre-drilled holes in the metal parts and substrate parts, resulting in low cost and simple assembly.

[0064] Figure 5 The simulated reflection coefficient of a fixed-beam leaky-wave antenna with out-of-band filtering characteristics is shown in the example. Figure 5 It can be seen that the reflection coefficient is below -10dB within the operating frequency band, indicating that most of the energy can be radiated into space.

[0065] Figure 6 The actual gain of the fixed-beam leaky antenna with out-of-band filtering characteristics shown in the example is greater than 15 dBi in the operating frequency band, indicating a high gain.

[0066] Figure 7 The simulated radiation efficiency of the fixed-beam leaky-wave antenna with out-of-band filtering characteristics in this embodiment is shown. The antenna's radiation efficiency is greater than 90% in the operating frequency band, indicating that the antenna in this embodiment has high efficiency.

[0067] Figures 8-14 The example shows the normalized simulated radiation patterns of a fixed-beam leaky antenna with out-of-band filtering characteristics at seven different frequencies. Figures 8-14 The radiation pattern shown has all main lobes in the normal direction, indicating that the antenna has good fixed radiation beam characteristics.

[0068] Figure 15 The example illustrates the signal path of a fixed-beam leaky antenna with out-of-band filtering characteristics; the black arrows indicate the signal path. The signal is fed in from the metal feed layer and transmitted from the middle of the leaky antenna to both ends. The two signals are of equal amplitude and out of phase, and are transmitted through the coupling window to the substrate integrated coaxial line. Finally, they are radiated into space through the radiating slot and radiating patch.

[0069] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A fixed-beam leaky antenna with out-of-band filtering characteristics, comprising, from top to bottom, the following layers stacked sequentially: a first metal layer, a first dielectric layer, a second metal layer, a second dielectric layer, a third metal layer, a third dielectric layer, a fourth metal layer, and a metal feed layer, characterized in that: The first metal layer consists of multiple pairs of radiating patches; The first dielectric layer has multiple pairs of first metallized vias. The second metal layer has multiple radiation grooves; The second dielectric layer is provided with a plurality of second metallized vias, which are arranged in a rectangle; The third metal layer has three through matching slots, including two first matching slots and one second matching slot; the second matching slot is located between the two first matching slots, and a metal strip is provided on the line connecting the midpoints of its two wide sides. The third dielectric layer has the same structure as the second dielectric layer; The fourth metal layer has a coupling window at each end, and each coupling window has a coupling patch smaller than the coupling window inside, with one end of the coupling patch connected to the fourth metal layer. The metal feed layer is provided with a differential feed transition structure, a first bandpass filter and a second bandpass filter. The input of the differential feed structure is connected to an external excitation structure, and the output is connected to the first bandpass filter and the second bandpass filter respectively. Multiple pairs of radiating patches, multiple radiating slots, multiple pairs of first metallized vias, and multiple matching units are arranged in a vertical direction. Two coupling windows and two first rectangular slots are arranged in a vertical direction. The first metal layer, the first dielectric layer, and the second metal layer together constitute a leakage wave structure. The second metal layer, the second dielectric layer, the third metal layer, the third dielectric layer, the metal strip, and the second metallized vias together constitute a substrate-integrated coaxial transmission structure.

2. A fixed-beam leaky antenna with out-of-band filtering characteristics according to claim 1, characterized in that: The rectangular arrangement of the plurality of second metallized vias has its ends located on the two long sides and close to the wide side, with the spacing between the second metallized vias decreasing so that the space enclosed by the second metallized vias is divided into five parts, namely the first region, the second region, the third region, the fourth region and the fifth region, wherein the first region and the fifth region are located at the two ends.

3. A fixed-beam leaky antenna with out-of-band filtering characteristics according to claim 2, characterized in that: The first region and the fifth region correspond to the two coupling windows in the vertical direction, respectively.

4. A fixed-beam leaky antenna with out-of-band filtering characteristics according to claim 1, characterized in that: Multiple radiation matching units are arranged sequentially along the length of the metal strip, and each radiation matching unit is composed of a metal patch.

5. A fixed-beam leaky antenna with out-of-band filtering characteristics according to claim 4, characterized in that: The first and last radiation matching units in the multiple radiation matching units consist of two first metal patches, which are symmetrically arranged on both sides of the metal strip; the multiple radiation matching units between the first and last radiation matching units each consist of four first metal patches, with each pair of first metal patches forming a group, and the two groups of first metal patches are symmetrically arranged on both sides of the metal strip.

6. A fixed-beam leaky antenna with out-of-band filtering characteristics according to claim 1, characterized in that: Each pair of radiating patches consists of two symmetrical rectangular metal patches, with two trapezoidal coupling windows.

7. A fixed-beam leaky antenna with out-of-band filtering characteristics according to claim 1, characterized in that: The metal feed layer is provided with a fourth rectangular slot, the two wide sides of which are chamfered to form a trapezoidal structure similar to the coupling window.

8. A fixed-beam leaky antenna with out-of-band filtering characteristics according to claim 1, characterized in that: The differential feed transition structure is fabricated using CNC machining technology, while the substrate-integrated coaxial transmission structure and the leakage wave structure are both fabricated using PCB substrate machining technology.

9. A fixed-beam leaky antenna with out-of-band filtering characteristics according to claim 1, characterized in that: The radiation groove is a bowtie-shaped groove; the matching grooves on the third metal layer are all rectangular grooves.

10. A fixed-beam leaky antenna with out-of-band filtering characteristics according to claim 2, characterized in that: A third metallized through-hole is provided at the middle position of both the first region and the fifth region. Two pairs of fourth metallized through-holes are provided at both ends of the third region. The line connecting the centers of the two pairs of fourth metallized through-holes is parallel to the line connecting the centers of the second metallized through-holes that form the second region or the fourth region.

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