CN107959112A - A kind of cupulate super wide band plane single pole sub antenna with ladder open-circuit structure floor - Google Patents

Abstract

The invention discloses a cup-shaped ultra-wideband planar monopole antenna with a stepped open-circuit structure floor, which consists of a dielectric substrate, a cup-shaped feed source terminal printed on the dielectric substrate, a coplanar waveguide feeder line, a stepped open-circuit structure floor and an external connection The coaxial joint constitutes. The lateral size of the cup-shaped feed terminal gradually decreases from top to bottom, thus forming radiation bands of different frequencies, making the antenna have ultra-wideband characteristics. The use of the stepped open-circuit structure floor can make the antenna resonate at low frequencies and reduce the design size of the antenna. The upper end of the stepped open-circuit structure floor adopts a ladder structure to further adjust the impedance matching, and the rectangular floor at the lower end of the stepped open-circuit structure floor is rounded. The processing can further broaden the impedance bandwidth of the antenna. The working frequency band of this antenna is 2.9GHz～13GHz, the design size is 20mm×20mm, the radiation characteristics and gain characteristics are good, and it is suitable for ultra-wideband wireless communication systems.

Description

A cup-shaped ultra-wideband planar monopole antenna with a stepped open circuit structure floor

technical field

The invention relates to the technical field of wireless communication antennas, in particular to a cup-shaped ultra-wideband planar monopole antenna with a stepped open-circuit structure floor, which is suitable for ultra-wideband wireless communication systems.

Background technique

With the rapid development of wireless communication technology, the wireless communication system is required to have wider bandwidth and higher communication frequency, and the original communication frequency domain can no longer meet the demand. Ultra-wideband technology has the characteristics of large capacity and high speed, which can be used for short-distance large-capacity high-speed transmission and radar detection, and can effectively solve the contradictions and problems faced by modern communication systems. The planar antenna has the advantage of being easy to integrate and can meet the miniaturization requirements of the UWB communication system. In order to achieve a wider impedance bandwidth in the early antennas, the overall size of the antenna was larger. In order to facilitate the integration of ultra-wideband antennas, it is necessary to design an antenna with a smaller size and a wider impedance bandwidth. This makes the research focus shift from expanding the bandwidth to multi- Function and miniaturization design. The ultra-wideband planar slot antenna is to open a wide slot on the floor. The slot structure generally adopts an approximately elliptical or approximately rectangular slot. The radiation and feeding part are similar to the design of the monopole antenna. The coplanar waveguide feeding and wide slot In combination, a wider impedance bandwidth can be obtained by adjusting the impedance matching by using a special geometric combination structure, and the notch characteristic can also be realized through a special structural design. The ultra-wideband planar monopole antenna is widely used and has a relatively simple structure. Through a certain design, a wide impedance bandwidth and omnidirectional radiation characteristics can be obtained. The planar monopole antenna is generally composed of a radiating unit, a floor, a feeder and a dielectric substrate. The radiating unit can be a combination of circular, elliptical, rectangular, or a special geometric structure, so that the surface current of the radiating unit forms resonance to obtain ultra-wideband response. The size of the radiating element determines the minimum operating frequency of the antenna. Usually, the maximum size of the radiating element is about a quarter wavelength corresponding to the minimum operating frequency of the antenna. Optimizing the structure of the radiating element can reduce the size of the antenna and widen the impedance bandwidth. The radiation unit of the planar monopole antenna fed by the coplanar waveguide, the feeder and the floor are on the same plane, which can make the overall structure of the antenna more compact and easy to integrate with other circuits. A wide impedance bandwidth can be obtained by using a rectangular slot, and the impedance matching can be optimized by adjusting the structure and size of the feed terminal. For example, non-patent document 1 discloses ultra-wideband antennas with rectangular slot circular feed, trapezoidal feed, and polygonal slot square feed. , the slot structure adopts a rectangular or polygonal slot structure, the feed unit adopts a circular or trapezoidal shape, and is fed through a coplanar waveguide. The impedance bandwidth of the three antennas covers the ultra-wideband frequency range, but the design size is 40mm×30mm, which is relatively large . Reasonable design of the structure of the monopole can obtain a wide impedance bandwidth. For example, non-patent document 2 discloses a sector-shaped printed ultra-wideband antenna, which is composed of a sector-shaped radiating unit, a rectangular floor and a coplanar waveguide feeder. Adjust the size of the sector Radiation bands of different frequencies are formed from the top edge to the bottom edge of the fan-shaped structure, thereby obtaining ultra-broadband characteristics. The design size of the antenna is 35mm×30mm. Based on the current cutting principle, cutting off the weaker part of the radiating element current can make the antenna surface current concentrate on the lower edge of the radiating element and near the antenna feeder, thereby widening the impedance bandwidth of the antenna. For example, non-patent literature 3 discloses three new types of ultra-wideband planar single The pole antenna adopts rectangular, hexagonal and pentagonal radiating elements, feeds through rectangular coplanar waveguide, cuts off the weak current part of the radiating element and the floor, and further improves the bandwidth and size of the antenna. The design size of the antenna is 25mm×28mm, and the overall size is still relatively large. Therefore, there is an inherent contradiction between the bandwidth of the antenna and the design size, and it is necessary to further optimize the structure of the radiation unit and the floor, so that the antenna can meet the ultra-wideband characteristics and further reduce the design size.

Citation list

non-patent literature

Non-Patent Document 1: Le Yongbo, Design and Research of Printed Slot Antenna, Master Thesis of Harbin Engineering University, 2012:21-33.

Non-Patent Document 2: Wang Chen, Research on multi-band/broadband/circularly polarized printed antennas and arrays, doctoral dissertation of Xidian University, 2013: 41-44.

Non-Patent Document 3: Wang Lingmin, Research and Design of Miniaturized Planar Ultra-Wideband Antennas, Master Thesis of Jilin University, 2015:13-18.

Contents of the invention

The purpose of the present invention is to provide a cup-shaped ultra-wideband planar monopole antenna with a stepped open circuit structure floor, ultra-wideband, omnidirectional radiation, stable gain, small size, easy to integrate in radio frequency circuits, and meet ultra-wideband wireless communication system requirement.

The technical solution of the present invention is: a cup-shaped ultra-wideband planar monopole antenna with a stepped open-circuit structure floor, consisting of a dielectric substrate (1), a cup-shaped feed terminal (2) printed on the dielectric substrate (1) , a coplanar waveguide feeder (3), a stepped open-circuit structure floor (4) and an external coaxial joint (5), characterized in that:

a. The cup-shaped feed terminal (2) is a cup-shaped metal patch, which is composed of a semi-circular ring and a sector. The center O1 of the semi-circular ring is located on the central axis of the dielectric substrate ( ₁ ). Located inside the semi-circular ring, the fan-shaped center _O2 is located at the center of the upper end of the coplanar waveguide feeder (3), the two ends of the fan-shaped are located on the outer circumference of the semi-circular ring, and the lower end of the cup-shaped feed terminal (2) is connected to the coplanar waveguide The upper ends of the feeder (3) are connected;

b. The coplanar waveguide feeder (3) is a rectangular conduction strip with a characteristic impedance of 50Ω, the upper end of the coplanar waveguide feeder (3) is connected to the lower end of the cup-shaped feeder terminal (2), and the coplanar waveguide feeder ( 3) The lower end is externally connected with a coaxial joint (5);

c. The ladder open-circuit structure floor (4) is composed of a rectangular floor, an extended guide strip and a ladder structure. The rectangular floor is located at the lower end of the medium substrate, and with O1 as the center _of the circle, draw a section of arc with a radius of R4 _. For the rectangular floor The two ends of the cup-shaped feed terminal (2) are used for chamfering. The stepped structure is located on the upper end of the dielectric substrate. The stepped structure is formed by superimposing three rectangles of different sizes. The extended conduction bands are located on both sides of the dielectric substrate. The rectangular floor and The ladder structure is connected by extending the conductive strips, and the floor (4) of the ladder open circuit structure is symmetrical to both sides of the coplanar waveguide feeder (3);

d. The coaxial connector (5) is located on the central axis of the lower end of the dielectric substrate (1), and the coaxial connector (5) is connected to the two lower edges of the coplanar waveguide feeder (3) and the floor of the stepped open circuit structure (4) respectively connect.

The cup-shaped feed terminal (2) is a cup-shaped metal patch, which is composed of a semi-circular ring and a sector. The center O1 of the semi-circular ring is located on the central axis of the dielectric substrate ( ₁ ), and the semi-circular ring The distance from the center O ₁ of the circle to the lower edge of the dielectric substrate (1) is R ₃ +L ₂ , the inner diameter R ₂ of the semi-circular ring is 4.1 mm to 4.5 mm, and the outer diameter R ₃ of the semi-circular ring is 5.3 mm to 5.7 mm. The sector is located inside the ring, the center _O2 of the sector is located at the center of the upper end of the coplanar waveguide feeder (3), the distance L2 between _O2 and the lower end of the dielectric substrate is 3.1 mm to 3.5 mm, and the _two ends of the sector are located at the center of the semicircle On the outer circumference, the radius R ₁ of the sector is 5.4 mm to 5.9 mm, and the angle θ of the sector is 115° to 125°.

The length L ₂ of the rectangular conduction strip with a characteristic impedance of 50Ω in the coplanar waveguide feeder ( 3 ) is 3.1 mm to 3.5 mm, and the width W ₂ is 2.2 mm to 2.6 mm.

The ladder open structure floor (4) is composed of a rectangular floor, an extended guide belt and a ladder structure. The width W ₁ of the rectangular floor is 8 mm to 8.5 mm, the length L ₁ is 3.2 mm to 3.6 mm, and the corner cutting arc radius R ₄ is 5.7mm～6mm, the length L3 _of the extended conduction belt is 9.8mm～11.1mm, and the width W3 is 0.8mm～1.3mm. _The ladder structure is formed by superimposing _three rectangles of different sizes, and the length L4 of the upper rectangle is 4.3mm～4.6mm, width W ₄ is 6.7mm～7.2mm, length L ₅ of the middle rectangle is 0.7mm～1mm, width W ₅ is 4.6mm～5mm, length L ₆ of the lower rectangle is 0.7mm～1mm , and the width W ₆ is 3.4mm to 3.8mm.

The effect of the invention lies in that the invention designs a cup-shaped feed source terminal and a stepped open-circuit structure floor with a novel structure. The horizontal size of the cup-shaped feed terminal gradually decreases from top to bottom, thus forming radiation bands of different frequencies, so that the antenna has ultra-wideband characteristics. Adjusting the sector size in the cup-shaped feed terminal can make the frequency band of the antenna move to high direction widening. The use of a stepped open-circuit structure floor can make the antenna resonate at low frequencies, reduce the design size of the antenna, and at the same time adjust the impedance matching characteristics of the antenna at high frequencies. The upper end of the stepped open-circuit structure floor can further adjust the impedance matching. The arc-cutting treatment of the rectangular floor at the lower end of the floor of the open circuit structure can make the antenna surface current concentrate on the lower edge of the radiation unit and near the antenna feeder, and further broaden the impedance bandwidth of the antenna. The invention has the characteristics of low profile, small size, convenient processing, simple structure, easy integration, etc., the working frequency range is 2.9GHz-13GHz, the design size is 20mm×20mm, the radiation characteristics and gain characteristics are good, and it is suitable for ultra-wideband wireless communication systems.

Description of drawings

Fig. 1 is a schematic structural diagram of an embodiment of the present invention.

Fig. 2 is a curve of the measured reflection coefficient S ₁₁ of the embodiment of the present invention.

Fig. 3 is a radiation pattern diagram of the E plane and the H plane when the frequency is 3 GHz according to the embodiment of the present invention.

Fig. 4 is a radiation pattern diagram of the E plane and the H plane when the frequency is 6 GHz according to the embodiment of the present invention.

Fig. 5 is the radiation pattern of the E plane and the H plane when the frequency is 9 GHz according to the embodiment of the present invention.

Fig. 6 is the radiation pattern of the E plane and the H plane when the frequency is 11 GHz according to the embodiment of the present invention.

Fig. 7 is a peak gain diagram at different frequency points according to an embodiment of the present invention.

Detailed ways

The specific embodiment of the present invention is: as shown in Figure 1, a kind of cup-shaped ultra-broadband planar monopole antenna with ladder open circuit structure floor, is made of dielectric substrate (1), the cup that is printed on the dielectric substrate (1) Shaped feed terminal (2), coplanar waveguide feeder (3), ladder open circuit structure floor (4) and external coaxial joint (5), it is characterized in that: the described cup-shaped feed terminal (2) is The cup-shaped metal patch is composed of a semi-circle and a sector. The center O ₁ of the semi-circle is located on the central axis of the dielectric substrate (1), the sector is located inside the semi-circle, and the center O ₂ of the sector is located at the common The center position of the upper end of the planar waveguide feeder (3), the two ends of the sector are located on the outer circumference of the semicircle, and the lower end of the cup-shaped feeder terminal (2) is connected to the upper end of the coplanar waveguide feeder (3); the coplanar waveguide The feeder (3) is a section of rectangular conduction band with a characteristic impedance of 50Ω, the upper end of the coplanar waveguide feeder (3) is connected to the lower end of the cup-shaped feeder terminal (2), and the lower end of the coplanar waveguide feeder (3) is externally connected to a coaxial connector (5); the ladder open-circuit structure floor (4) is made up of a rectangular floor, an extended guide strip and a ladder structure, the rectangular floor is located at the lower end of the medium substrate, and with O1 as the center _of the circle, draw a section of radius _R4 arc, to The rectangular floor is corner-cut by the two ends of the cup-shaped feed terminal (2). The ladder structure is located on the upper end of the dielectric substrate. The ladder structure is formed by superimposing three rectangles of different sizes. The floor and the ladder structure are connected through an extended guide strip, and the floor (4) of the ladder open circuit structure is symmetrical to both sides of the coplanar waveguide feeder (3); the coaxial joint (5) is located on the central axis of the lower end of the dielectric substrate (1), The coaxial joint (5) is respectively connected with the coplanar waveguide feeder (3) and the two lower edges of the stepped open-circuit structure floor (4).

The cup-shaped feed terminal (2) is a cup-shaped metal patch, which is composed of a semi-circular ring and a sector. The center O1 of the semi-circular ring is located on the central axis of the dielectric substrate ( ₁ ), and the semi-circular ring The distance from the center O ₁ of the circle to the lower edge of the dielectric substrate (1) is R ₃ +L ₂ , the inner diameter R ₂ of the semi-circular ring is 4.1 mm to 4.5 mm, and the outer diameter R ₃ of the semi-circular ring is 5.3 mm to 5.7 mm. The sector is located inside the ring, the center _O2 of the sector is located at the center of the upper end of the coplanar waveguide feeder (3), the distance L2 between _O2 and the lower end of the dielectric substrate is 3.1 mm to 3.5 mm, and the _two ends of the sector are located at the center of the semicircle On the outer circumference, the radius R ₁ of the sector is 5.4 mm to 5.9 mm, and the angle θ of the sector is 115° to 125°.

The length L ₂ of the rectangular conduction strip with a characteristic impedance of 50Ω in the coplanar waveguide feeder ( 3 ) is 3.1 mm to 3.5 mm, and the width W ₂ is 2.2 mm to 2.6 mm.

The ladder open structure floor (4) is composed of a rectangular floor, an extended guide belt and a ladder structure. The width W ₁ of the rectangular floor is 8 mm to 8.5 mm, the length L ₁ is 3.2 mm to 3.6 mm, and the corner cutting arc radius R ₄ is 5.7mm～6mm, the length L3 _of the extended conduction belt is 9.8mm～11.1mm, and the width W3 is 0.8mm～1.3mm. _The ladder structure is formed by superimposing _three rectangles of different sizes, and the length L4 of the upper rectangle is 4.3mm～4.6mm, width W ₄ is 6.7mm～7.2mm, length L ₅ of the middle rectangle is 0.7mm～1mm, width W ₅ is 4.6mm～5mm, length L ₆ of the lower rectangle is 0.7mm～1mm , and the width W ₆ is 3.4mm to 3.8mm.

Embodiment: The specific manufacturing process is as described in the embodiment. Choose FR4 epoxy resin dielectric substrate, dielectric constant ε _r = 4.4, thickness h = 1.6mm, metal layer thickness 0.04mm, coaxial joints adopt standard SMA joints. The dielectric substrate has a length L=20mm and a width W=20mm. The horizontal size of the cup-shaped feed terminal gradually decreases from top to bottom, thus forming radiation bands of different frequencies, so that the antenna has ultra-wideband characteristics. Adjusting the sector size in the cup-shaped feed terminal can make the frequency band of the antenna move to high direction widening. The cup-shaped feed terminal is composed of a semi-circular ring and a sector. The inner diameter R ₂ of the semi-circular ring is 4.3mm, and the outer diameter R ₃ of the semi-circular ring is 5.5mm. The sector is located inside the ring, and the center of the sector is O ₂ is located at the center of the upper end of the coplanar waveguide feeder. The distance L ₂ from O ₂ to the bottom _of the dielectric substrate is 3.3mm. is 120°. In the coplanar waveguide feeder, the length L ₂ of the rectangular conduction strip with a characteristic impedance of 50Ω is 3.3 mm, the width W ₂ is 2.5 mm, and the gap g between the rectangular conduction strip and the floor is 0.45 mm. The use of a stepped open-circuit structure floor can make the antenna resonate at low frequencies, reduce the design size of the antenna, and at the same time adjust the impedance matching characteristics of the antenna at high frequencies. The upper end of the stepped open-circuit structure floor can further adjust the impedance matching. The arc-cutting treatment of the rectangular floor at the lower end of the floor of the open circuit structure can make the antenna surface current concentrate on the lower edge of the radiation unit and near the antenna feeder, and further broaden the impedance bandwidth of the antenna. The floor with stepped open circuit structure is composed of a rectangular floor, an extended guide strip and a ladder structure. The width W ₁ of the rectangular floor is 8.3mm, the length L ₁ is 3.4mm, the radius R ₄ of the cut corner arc is 5.9mm, and the length L ₃ of the extended guide strip is 10.3mm, width W ₃ is 1.2mm, the ladder structure is formed by superposition of three rectangles of different sizes, the length L ₄ of the upper rectangle is 4.5mm, the width W ₄ is 6.9mm, and the length L ₅ of the middle rectangle is 0.9 mm, width W ₅ is 4.8mm, length L ₆ of the lower rectangle is 0.9mm, width W ₆ is 3.6mm.

Use a vector network analyzer to test the reflection coefficient of the antenna. The variation curve of the reflection coefficient S ₁₁ with frequency is shown in Figure 2. The impedance bandwidth of the reflection coefficient S ₁₁ less than -10dB is 2.9GHz to 13GHz, and the -10dB impedance bandwidth of the antenna is completely covered. The frequency band specified by the ultra-wideband system is 3.1GHz to 10.6GHz, and multiple resonance points are formed in the frequency band, resulting in an ultra-wideband response. The resonance points are located at 3.1GHz, 6.7GHz, and 9.4GHz, and the corresponding resonance peak intensities are respectively - 26.8dB, -46.6dB, -34.2dB, which can meet the working requirements of the antenna.

Test the radiation pattern of the E-plane and H-plane at the four frequency points of 3GHz, 6GHz, 9GHz, and 11GHz to verify the radiation characteristics of the antenna. The measured pattern is shown in Figure 3, Figure 4, Figure 5, and Figure 6. . It can be seen from the figure that the radiation pattern of the antenna is approximately "8" in the E plane, the pattern in the low frequency range of the H plane is approximately circular, and the pattern in the high frequency range is approximately elliptical. There is a certain distortion in the radiation pattern at 11GHz, but it is similar to the intermediate frequency on the whole. The main reason is the high-order mode in the antenna slot and the influence of the unequal phase distribution electric field. Therefore, the antenna is omnidirectional in the entire frequency band, the radiation characteristics are relatively stable, and the antenna has a relatively wide lobe, reflecting ultra-wideband characteristics, and has good omnidirectionality, which fully meets the needs of ultra-wideband communication systems.

The peak gain curves of the test antenna at different frequency points in the frequency band are shown in Figure 7. The test results show that the peak gain is 1.89dBi at 3GHz, 6.4dBi at 6GHz, 7.8dBi at 9GHz, and 6.1dBi at 11GHz. The peak gain of the antenna varies with The change of frequency shows an overall upward trend, and the change of peak gain in the high frequency band shows a downward trend. The reason for the decline is that the antenna pattern is distorted in the high frequency band. The change range of peak gain is 1.88dBi～8dBi. Reasonable, indicating that the antenna has good gain performance in the working frequency band.

Claims (4)

1. A cup-shaped ultra-wideband planar monopole antenna with a ladder open circuit structure floor, consisting of a dielectric substrate (1), a cup-shaped feed terminal (2) printed on the dielectric substrate (1), and a coplanar waveguide feeder (3), the ladder open circuit structure floor (4) and the external coaxial joint (5) are formed, it is characterized in that: a. The cup-shaped feed terminal (2) is a cup-shaped metal patch, which is composed of a semi-circular ring and a sector. The center O1 of the semi-circular ring is located on the central axis of the dielectric substrate ( ₁ ). Located inside the semi-circular ring, the fan-shaped center _O2 is located at the center of the upper end of the coplanar waveguide feeder (3), the two ends of the fan-shaped are located on the outer circumference of the semi-circular ring, and the lower end of the cup-shaped feed terminal (2) is connected to the coplanar waveguide The upper ends of the feeder (3) are connected; b. The coplanar waveguide feeder (3) is a rectangular conduction strip with a characteristic impedance of 50Ω, the upper end of the coplanar waveguide feeder (3) is connected to the lower end of the cup-shaped feeder terminal (2), and the coplanar waveguide feeder ( 3) The lower end is externally connected with a coaxial joint (5); c. The ladder open-circuit structure floor (4) is composed of a rectangular floor, an extended guide strip and a ladder structure. The rectangular floor is located at the lower end of the medium substrate, and with O1 as the center _of the circle, draw a section of arc with a radius of R4 _. For the rectangular floor The two ends of the cup-shaped feed terminal (2) are used for chamfering. The stepped structure is located on the upper end of the dielectric substrate. The stepped structure is formed by superimposing three rectangles of different sizes. The extended conduction bands are located on both sides of the dielectric substrate. The rectangular floor and The ladder structure is connected by extending the conductive strips, and the floor (4) of the ladder open circuit structure is symmetrical to both sides of the coplanar waveguide feeder (3); d. The coaxial connector (5) is located on the central axis of the lower end of the dielectric substrate (1), and the coaxial connector (5) is connected to the two lower edges of the coplanar waveguide feeder (3) and the floor of the stepped open circuit structure (4) respectively connect. 2. A kind of cup-shaped ultra-wideband planar monopole antenna with ladder open circuit structure floor according to claim 1, it is characterized in that described cup-shaped feed terminal (2) is a cup-shaped metal patch, by a A semi-circular ring and a sector are combined, the center O ₁ of the semi-circular ring is located on the central axis of the dielectric substrate (1), and the distance from the center O ₁ of the semi-circular ring to the lower edge of the dielectric substrate (1) is R ₃ +L ₂ , the inner diameter R ₂ of the semi-circular ring is 4.1mm-4.5mm, the outer diameter R ₃ of the semi-circular ring is 5.3mm-5.7mm, the fan is located inside the ring, and the center O ₂ of the fan is located in the coplanar waveguide feeder (3) At the center of the upper end, the distance L ₂ from O ₂ to the lower end of the dielectric substrate is 3.1mm~3.5mm, the two ends of the sector are located on the outer circumference of the semicircle, the radius R ₁ of the sector is 5.4mm～5.9mm, and the angle θ of the sector It is 115°～125°. 3. A kind of cup-shaped ultra-wideband planar monopole antenna with ladder open circuit structure floor according to claim 1, it is characterized in that the characteristic impedance in the described coplanar waveguide feeder (3) is the rectangular conduction band of 50Ω The length L ₂ is 3.1 mm to 3.5 mm, and the width W ₂ is 2.2 mm to 2.6 mm. 4. a kind of cup-shaped ultra-wideband planar monopole antenna with ladder open circuit structure floor according to claim 1, it is characterized in that described ladder open circuit structure floor (4) is made of rectangular floor, extension conduction band and ladder structure Composition, rectangular floor width W ₁ is 8mm~8.5mm, length L ₁ is 3.2mm~3.6mm, corner cutting arc radius R ₄ is 5.7mm~6mm, extension guide strip length L ₃ is 9.8mm~11.1mm, width W ₃ is 0.8mm to 1.3mm, and the ladder structure is composed of three rectangles of different sizes. The length L ₄ of the upper rectangle is 4.3mm to 4.6mm, and the width W ₄ is 6.7mm to 7.2mm. The length L ₅ is 0.7 mm to 1 mm, the width W ₅ is 4.6 mm to 5 mm, the length L ₆ of the lower rectangle is 0.7 mm to 1 mm, and the width W ₆ is 3.4 mm to 3.8 mm.