JP2008159312A - Connection structure of coaxial cable and coaxial connector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance general applicability of a connector so as not to cause a large amount of reflection of a signal, even if coaxial cable and connector having different characteristic impedances are connected with each other. <P>SOLUTION: The terminal of the coaxial cable is connected to the coaxial connector, the center conductor of the coaxial cable is connected to the inner conductor terminal of the coaxial connector, and a shielding layer coated on the center conductor of the coaxial cable through an insulating material is connected to the outer conductor terminal of the coaxial connector. The characteristic impedance of the coaxial connector is lower than the characteristic impedance of the coaxial cable, a high impedance forming part is provided in the shielding layer on the connector connecting side of the coaxial cable to raise the characteristic impedance of the connector connecting part by equilibrating it with the low impedance of the connector, and to bring it close to the characteristic impedance of the coaxial cable. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a connection structure between a coaxial cable and a coaxial connector, and more specifically, to reduce signal reflection when a coaxial cable and a coaxial connector having different characteristic impedances are connected.

Conventionally, high-frequency coaxial cables have been used to transmit high-frequency electrical signals to printed circuit boards for control built in electrical devices such as car navigation systems, televisions, and radios installed in automobiles.
Generally, the coaxial cable has an insulator between a central conductor formed by twisting a plurality of metal wires as a transmission path for an electric signal and the like and a shield layer formed of a braided wire knitted with the plurality of wires. It has a coaxial structure in which the outer periphery is covered with an insulating sheath, and the shield layer covers the center conductor, so that the structure is suitable for high-frequency signal transmission.

A coaxial connector is used to connect the coaxial cable to the control printed circuit board or another coaxial cable, and the applicant of this type is disclosed in Japanese Patent Application Laid-Open No. 2003-297493 (Patent Document 1) and the like. Coaxial connectors are provided.
The coaxial connector includes an inner conductor terminal connected to the central conductor of the coaxial cable, an outer conductor terminal connected to the shield layer and electromagnetically shielded by covering the outer periphery of the inner conductor terminal, and the inner conductor terminal and the outer conductor terminal. Each terminal is individually connected to the center conductor and shield layer that are exposed by peeling off the insulation and sheath of the coaxial cable end. The

  Signal reflection occurs if the characteristic impedance of the coaxial cable that transmits a high-frequency signal and the coaxial connector connected to the end of the coaxial cable do not match. For example, a coaxial cable having a characteristic impedance of 50Ω has a characteristic impedance of 50Ω. A coaxial connector is connected, and a coaxial cable having a characteristic impedance of 75Ω is connected to a coaxial cable having a characteristic impedance of 75Ω to match the characteristic impedance.

  However, as described above, when the coaxial connectors having the characteristic impedance suitable for the characteristic impedance of the coaxial cable are connected to each other, a coaxial connector must be provided for each coaxial cable having a different characteristic impedance, which increases the number of parts. At the same time, design and evaluation are required for each coaxial connector, which requires a great deal of labor, cost, and time.

JP 2003-297493 A

  The present invention has been made in view of the above problems, and it is possible to share the same type of coaxial connector so that no large signal reflection occurs even when a coaxial cable is connected to coaxial connectors having different characteristic impedances. It is an issue.

In order to solve the above problems, as a first invention, a terminal of a coaxial cable is connected to a coaxial connector, a central conductor of the coaxial cable is connected to an inner conductor terminal of the coaxial connector, and the central conductor of the coaxial cable is connected to the central conductor. A shield layer covered with an insulator is connected to the outer conductor terminal of the coaxial connector, and the characteristic impedance of the coaxial connector is lower than the characteristic impedance of the coaxial cable,
A high impedance forming portion is provided in the shield layer on the connector connection side of the coaxial cable, and the characteristic impedance in the connector connection portion is increased by averaging with the low impedance of the connector, which is close to the characteristic impedance of the coaxial cable. A connection structure between a coaxial cable and a coaxial connector is provided.

As described above, according to the present invention, when a coaxial connector having a characteristic impedance lower than that of the coaxial cable (hereinafter referred to as a connector) is connected to the end of the coaxial cable and the characteristic impedance is locally reduced, The shield layer on the connector connection side is provided with a high impedance forming portion that further increases the characteristic impedance. When the high impedance forming portion is provided in this way, the characteristic impedance of the connector connecting portion can be increased by combining with the low characteristic impedance on the connector side and averaging.
Therefore, without changing the central conductor and the connector of the coaxial cable, the characteristic impedance at the connector connecting portion can be brought close to the characteristic impedance of the coaxial cable, thereby preventing a large signal reflection at the connector connecting portion. Thus, by sharing the connector, the number of parts can be reduced, and labor, cost, and time for new design and evaluation can be made unnecessary.

The high impedance forming part of the shield layer is
The shield layer is partially expanded at the terminal on the connector connection side, an insulator sleeve for adjusting characteristic impedance is inserted between the expanded shield layer and the insulator, and / or
Change the insulator to a material with a low relative dielectric constant,
The shield layer is partially opened.

As described above, the first means for providing the high impedance forming portion includes inserting an insulator sleeve for adjusting characteristic impedance between the shield layer and the insulator on the side connected to the outer conductor terminal of the connector, Is partially expanded.
In this case, it is preferable that the dielectric constant of the insulator sleeve is 2.3 to 2.4, and the material for forming the insulator sleeve is preferably polyethylene or the like.
Since the characteristic impedance Z of the coaxial cable is expressed by the following equation 1, when the outer diameter d1 of the central conductor and the relative dielectric constant ε of the insulator are constant, the characteristic impedance Z is increased when the inner diameter d2 of the shield layer is increased. Becomes higher. For example, the characteristic impedance Z ′ when the inner diameter d2 of the shield layer is doubled is larger than the characteristic impedance Z as shown in Equation 2. Specifically, when the insulator is polyethylene having a relative dielectric constant of 2.3, the outer diameter of the central conductor is d1 = 0.26 mm, and the inner diameter of the shield layer is d2 = 1.70 mm, the characteristic impedance is 74Ω. On the other hand, when the inner diameter of the shield layer is 3.40 mm, which is twice as large as d2, the characteristic impedance is 102Ω.

In the second means, the insulator between the central conductor and the shield layer is changed to a material having a low relative dielectric constant.
Examples of the material having a low relative dielectric constant include ethylene tetrafluoride and the like, and the relative dielectric constant is preferably about 2.0.
As can be seen from Equation 1, the characteristic impedance Z can be increased by reducing the relative dielectric constant ε of the member interposed between the central conductor and the shield layer.

The third means partially opens the shield layer.
When an opening is provided in the shield layer, the portion where the opening is provided is substantially the same as the inner diameter of the shield layer is increased, and the characteristic impedance of the portion can be increased.

  Any one of the first to third means for providing the high impedance forming unit may be used alone, or a required means may be combined.

Furthermore, an opening is provided in the cylindrical outer conductor terminal on the connector side connected to the shield layer of the coaxial cable, the characteristic impedance on the connector side is increased, and the characteristic impedance on the connector side is made the characteristic impedance of the coaxial cable. You may use together the means to approach.
Similar to the coaxial cable, the connector also has a characteristic impedance that increases as the outer conductor terminal becomes larger. Therefore, when the outer conductor terminal is provided with an opening, the portion provided with the opening substantially increases the outer conductor terminal. The characteristic impedance of the part can be increased. The opening of the outer conductor terminal of the connector can be easily provided by post-processing.

As a second invention, the end of the coaxial cable is connected to the coaxial connector, the central conductor of the coaxial cable is connected to the inner conductor terminal of the coaxial connector, and the central conductor of the coaxial cable is covered with an insulator. A shield layer is connected to the outer conductor terminal of the coaxial connector, and the characteristic impedance of the coaxial connector is higher than the characteristic impedance of the coaxial cable,
A low-impedance forming portion is provided in the shield layer on the connector connection side of the coaxial cable, and the characteristic impedance in the connector connection portion is lowered by averaging with the high impedance of the connector so as to be close to the characteristic impedance of the coaxial cable. The connection structure of the featured coaxial cable and coaxial connector is provided.

  As described above, even when a connector having a higher characteristic impedance than that of a coaxial cable is connected, if a low impedance forming portion is provided in the shield layer of the coaxial cable on the connection side with the connector, a combination with a higher characteristic impedance on the connector side Thus, on average, the characteristic impedance of the coaxial cable and the connector connection portion can be lowered to be close to the characteristic impedance of the coaxial cable, and a large signal reflection can be prevented.

  A low-impedance forming portion in the shield layer removes the insulator on the connector connection side end of the coaxial cable and inserts a thin insulator sleeve for adjusting characteristic impedance or for adjusting characteristic impedance having a high relative dielectric constant It is formed by inserting an insulator sleeve.

  As described above, according to the first invention, when the coaxial cable is connected to the connector having a low characteristic impedance, the high impedance forming portion is provided in the shield layer on the connector connection side of the coaxial cable to further increase the characteristic impedance of the coaxial cable. Since the characteristic impedance of the connector connecting portion is increased on the average with the low characteristic impedance on the connector side, it approaches the characteristic impedance of the coaxial cable, and large signal reflection can be prevented. As a result, a coaxial cable with high characteristic impedance can be connected to a coaxial connector with low characteristic impedance, so the connector can be shared, the number of parts can be reduced, and labor, cost, and time for new design and evaluation are unnecessary. It can be.

  According to the second invention, when the coaxial cable is connected to a connector having a high characteristic impedance, the low impedance forming portion is provided in the shield layer on the connector connection side of the coaxial cable so that the characteristic impedance of the coaxial cable is further reduced. By providing the average impedance with the high characteristic impedance on the connector side, the characteristic impedance of the connection portion with the connector can be lowered, and the reflection of the signal can be prevented by approaching the characteristic impedance of the coaxial cable. As a result, a coaxial cable with low characteristic impedance can be connected to a coaxial connector with high characteristic impedance, so the connector can be shared, the number of parts can be reduced, and labor, cost, and time for new design and evaluation are not required. It can be.

Embodiments of the present invention will be described with reference to the drawings.
1 to 3 show a first embodiment of the present invention.
A connection structure 10 between a coaxial cable and a connector according to this embodiment includes a coaxial cable 20 that constitutes a signal circuit that transmits a signal to an electric device mounted on an automobile, and connects the coaxial cable 20 to another coaxial cable 20 ′. For this purpose, a coaxial connector 30 (hereinafter abbreviated as “connector 30”) is connected.
In the present embodiment, the characteristic impedance of the coaxial cable 20 is 75Ω, while the characteristic impedance of the connector 30 is 50Ω and is connected to the connector 30 having a lower characteristic impedance than the coaxial cable 20.

  The coaxial cable 20 is formed by twisting a plurality of metal strands, a center conductor 21 disposed on the central axis, an insulator 22 covering the outer peripheral surface of the center conductor 21, and a plurality of metal strands. A shield layer 23 formed of a braided wire knitted on the outer peripheral surface of the insulator 22 and a sheath 24 covering the outer peripheral surface of the shield layer 23. The shield layer 23 is coaxially surrounded by the outer periphery of the central conductor 21. Arranged above. The insulator 22 is made of polyethylene having a relative dielectric constant of 2.3.

The terminals of the insulator 22, the shield layer 23, and the sheath 24 of the coaxial cable 20 are peeled to the required lengths to expose the ends of the center conductor 21 and the shield layer 23 as shown in FIG. . As shown in FIG. 2B, a cylindrical characteristic impedance adjusting insulator sleeve 25 made of tetrafluoroethylene is inserted between the exposed shield layer 23 and the insulator 22, and the insulation By inserting the body sleeve 25, the end of the shield layer 23 is expanded to form a high impedance forming portion 23a, and the high impedance forming portion 23a has a larger diameter than the shield layer 23 in other portions.
In the present embodiment, the dielectric constant of the insulator sleeve 25 is 2.0, which is lower than the dielectric constant of the insulator 22 of the coaxial cable 20. Further, the radial thickness of the insulator sleeve 25 is made the same as the radial thickness of the insulator 22 of the coaxial cable 20, and the axial length is shorter than the axial length of the coaxial connector 30.

  The characteristic impedance Z of the coaxial cable 20 can be expressed by the following formula 1. The portion expanded by inserting the insulator sleeve 25 having a low relative dielectric constant has a lower relative dielectric constant ε and a larger inner diameter d2 of the shield layer than other portions of the coaxial cable 20. Therefore, the characteristic impedance Z is high. In the present embodiment, the characteristic impedance of the coaxial cable 20 is 75Ω, whereas the characteristic impedance of the portion of the coaxial cable 20 where the shield layer 23 is expanded is 90Ω.

The connector 30 connected to the end of the coaxial cable 20 includes an inner conductor terminal 31 connected to the center conductor 21, an outer conductor terminal 32 connected to the shield layer 23, the inner conductor terminal 31 and the outer conductor terminal 32, The dielectric 33 is interposed between the two.
The inner conductor terminal 31 is provided with a cylindrical female terminal portion 31a at one end and a crimp barrel 31b at the other end, and the crimp conductor 31b is crimped to the center conductor 21 so that the inner conductor terminal 31 is centered. The end of the conductor 21 is connected.

  The outer conductor terminal 32 is provided with a square cylindrical female terminal portion 32a at one end and two pairs of crimp barrels 32b and 32c at the other end. As shown in FIG. 2C, these crimping barrels 32b and 32c are respectively crimped to the high impedance forming portion 23a and the sheath 24 of the shield layer 23, and the outer conductor terminal 32 is connected to the end of the shield layer 23. . With the inner conductor terminal 31 and the outer conductor terminal 32 connected to the central conductor 21 and the shield layer 23 of the coaxial cable 20 respectively, the periphery of the inner conductor terminal 31 is covered with the female terminal portion 32a of the outer conductor terminal 32, and electromagnetically Shield to. The crimp barrel 32b that is crimped to the shield layer 23 is longer than a normal one having a characteristic impedance of 50Ω so that it can be crimped to the high impedance forming portion 23a of the shield layer 23.

The dielectric 33 is made of a resin insulating material having a predetermined relative dielectric constant, and has a cylindrical shape covering the female terminal portion 31a of the inner conductor terminal 31 from the front end side to the rear end. The dielectric 33 is thick at the rear end side, the outer peripheral surface is brought into contact with the inner peripheral surface of the female terminal portion 32 a of the outer conductor terminal 32, and the inner conductor terminal 31 is centered on the female terminal portion 32 a of the outer conductor terminal 32. On the other hand, the tip end side is thin, and a gap is provided between the outer peripheral surface of the dielectric 33 and the inner peripheral surface of the female terminal portion 32a of the outer conductor terminal 32 to provide an insertion space for the counterpart terminal.
The connector 30 is housed in a connector housing made of a resin molded product, but is not shown.

As shown in FIG. 3, the connector 30 connected to the terminal of the coaxial cable 20 is connected to a connector 40 connected to the terminal of another coaxial cable 20 ′.
The other coaxial cable 20 ′ has the same configuration as the coaxial cable 20 and has a characteristic impedance of 75Ω.
The connector 40 connected to the end of the coaxial cable 20 ′ includes an inner conductor terminal 41 and an outer conductor terminal 42, and has a characteristic impedance of 50Ω. The inner conductor terminal 41 is provided with a male terminal portion 41a at one end, and a crimping barrel 41b provided at the other end is crimped and connected to the center conductor 21 of the coaxial cable 20 ′. The outer conductor terminal 42 is provided with a square cylindrical female terminal portion 42a having an outer shape smaller than the female terminal portion 32a of the outer conductor terminal 32 of the connector 30 at one end, and two sets of crimp barrels 32b and 32c provided at the other end. Are crimped to the shield layer 23 and the sheath 24 of the coaxial cable 20 ′.

When these connectors 30 and 40 are fitted, the male terminal portion 41a of the inner conductor terminal 41 of the connector 40 is inserted and connected to the female terminal portion 31a of the inner conductor terminal 31 of the connector 30, and the outer conductor of the connector 30 is connected. The inner surface of the female terminal portion 32a of the terminal 32 is connected to the outer surface of the female terminal portion 42a of the outer conductor terminal 42 of the connector 40, and the central conductors 21 of the coaxial cables 20 and 20 ′ and the shield layer 23 are connected to each other. Is done.
The outer conductor terminal 32 of the connector 30 and the outer conductor terminal 42 of the connector 40 are provided with a locking structure for locking each other, but illustration thereof is omitted in FIG.

In this way, the shield at the connection portion of the coaxial cables 20 and 20 'with the connectors 30 and 40 is provided with a portion having a low characteristic impedance of 50Ω and a portion having a high characteristic impedance of 90Ω adjacent to each other. The characteristic impedance at the connector connecting portion can be increased and brought close to 75Ω which is the characteristic impedance of the coaxial cables 20 and 20 ′, and a large signal reflection can be prevented. Thereby, since the coaxial cable 20 and the connector 30 having different characteristic impedances can be connected, the versatility of the connector 30 can be improved, the number of parts can be reduced, and labor, cost, and time for new design and evaluation can be reduced. Can be made unnecessary.
In the present embodiment, the high impedance forming portion 23a is provided only in one coaxial cable 20, but the high impedance forming portion may also be provided in the other coaxial cable 20 ′ connected to the coaxial cable 20.
In this embodiment, the coaxial cables are connected to each other by a connector. However, the coaxial cable may be connected to a connector mounted on the substrate and connected to a conductor pattern on the substrate.

FIG. 4 shows a second embodiment of the present invention.
In the present embodiment, the insulator 22 on the inner peripheral side of the shield layer 23 at the portion where the crimp barrel 32b of the outer conductor terminal 32 of the connector 30 is crimped is peeled off, and the exposed central conductor 21 and shield layer 23 are exposed. A cylindrical insulator sleeve 25 having the same inner diameter and outer diameter as the insulator 22 is inserted between them. Whereas the relative dielectric constant of the insulator 22 is 2.3, the dielectric sleeve 25 is formed of ethylene tetrafluoride so that the relative dielectric constant is 2.0, and the relative dielectric constant of the insulator sleeve 25 is The portion where the insulator sleeve 25 is provided with a smaller dielectric constant than that of the insulator 22 is used as a high impedance forming portion.

According to the above configuration, the characteristic impedances of the parts close to the connector having a low characteristic impedance can be increased, and on average, the characteristic impedances of these parts can be brought close to the characteristic impedance of the coaxial cable 20 to prevent a large signal reflection. can do.
In this embodiment, the outer diameter of the insulator sleeve 25 is the same as that of the insulator 22. However, the outer diameter of the insulator sleeve 25 is made larger than that of the insulator 22, and a high impedance forming portion is provided in the shield layer 23. It may be provided.
In addition, since other configurations and operational effects are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.

FIG. 5 shows a third embodiment of the present invention.
In the present embodiment, as in the first embodiment, the shield layer 23 of the coaxial cable 20 is not enlarged to provide the high impedance forming portion 23a, but the outer conductor of the connector 30 as shown in FIG. Cut the shield layer 23 between the parts to be crimped by the crimp terminals 32b and 32c of the terminal 32, or partially cut out the shield layer 23 to provide an opening 23b as shown in FIG. Yes.

According to the above configuration, when the opening 23b is provided in the shield layer 23, the portion where the opening 23b is provided is substantially the same as the inner diameter d2 of the shield layer 23 is increased, and the portion where the opening 23b is provided is high. The characteristic impedance can be increased as the impedance forming portion.
As a result, the characteristic impedances of the parts close to the connector having a low characteristic impedance can be increased, and on average, the characteristic impedances of these parts can be brought close to the characteristic impedance of the coaxial cable 20 to prevent a large signal reflection. it can.
In addition, you may provide the high impedance formation part which provided the opening of the high impedance formation part of this embodiment, and the high impedance formation of 1st Embodiment adjacent to the shield layer.
In addition, since other configurations and operational effects are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.

6 and 7 show a fourth embodiment of the present invention.
In this embodiment, the connector 30 connected to the coaxial cable 20 in which the high impedance forming portion 23a is provided in the shield layer 23 as in the first embodiment is different from that in the above embodiment, as shown in FIG. In addition, a required portion of the outer conductor terminal 32 of the connector 30 is cut and raised, or as shown in FIG. 7B, the required portion of the outer conductor terminal 32 is partially cut away to provide an opening 32d.

According to the above configuration, like the coaxial cable 20, the connector 30 also has a characteristic impedance that increases as the outer conductor terminal 32 becomes larger. Therefore, when the outer conductor terminal 32 is provided with the opening 32d, the portion where the opening 32d is provided. Is substantially the same as increasing the outer shape of the outer conductor terminal 32, and the characteristic impedance of the portion can be increased.
In addition, you may connect the connector 30 of this embodiment to the coaxial cable of 2nd, 3rd embodiment.
In addition, since other configurations and operational effects are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.

FIG. 8 shows a fifth embodiment of the present invention.
In the present embodiment, contrary to the above-described embodiment, the connector 30 having a characteristic impedance higher than that of the coaxial cable 20 is used while the characteristic impedance of the coaxial cable 20 is 50Ω and the characteristic impedance of the connector 30 is 75Ω.

  The insulator 22 on the inner peripheral side of the shield layer 23 where the crimp barrel 32 b of the outer conductor terminal 32 of the connector 30 is crimped is peeled off, and the insulator is provided between the exposed central conductor 21 and the shield layer 23. A characteristic impedance adjusting insulator sleeve 25 ′ thinner than 22 is inserted to form a low impedance forming portion 23 c in which the shield layer 23 is partially reduced in diameter. In the low impedance forming portion 23c, the inner diameter d2 of the shield layer 23 is smaller than other portions, so that the characteristic impedance is lowered. In the present embodiment, the insulator sleeve 25 ′ is made of polyvinyl chloride, and the relative permittivity of the insulator sleeve 25 is set to 3.5, which is higher than the relative permittivity of the insulator 22, and the low impedance forming portion 23c The characteristic impedance is 35Ω.

According to the above configuration, the characteristic impedance of the coaxial cable 20 can be reduced by averaging the low-impedance characteristic portion at the connector connecting portion by providing the high-impedance portion having a high characteristic impedance of 75Ω and the low-impedance portion having a low characteristic impedance of 35Ω. Can be close to 50Ω, and large reflection of the signal can be prevented.
In the present embodiment, the insulator sleeve 25 ′ is thinner than the insulator 22, and the low impedance forming portion 23c has a diameter smaller than that of the shield layer 23 in other parts. It is also possible to form the insulator sleeve 25 ′ with the outer diameter of the insulator 22 by using a material whose ratio is higher than the relative dielectric constant of the insulator 22.
In addition, since other configurations and operational effects are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.

The voltage standing wave ratio (VSWR) when a 1 GHz signal is transmitted to a communication circuit having the same coaxial cable and connector connection structure as in the first embodiment is calculated by Eagleware-Elanix. Obtained using the software Eagleware GENESYS.
As shown in FIG. 9, in the communication circuit for obtaining the voltage standing wave ratio (VSWR), coaxial cables 20A and 20B having a characteristic impedance of 75Ω are connected by connectors 30 and 40 having a characteristic impedance of 50Ω, respectively. A circuit is provided in which a high impedance forming portion 23a having a characteristic impedance of 90Ω is provided at a position adjacent to the connector 30 of the cable 20A. However, on the calculation software, the characteristic impedance of the connector of the coaxial cable 20A terminal is set to 90Ω, and the characteristic impedance of the connector of the coaxial cable 20B terminal is set to 50Ω. And a circuit having the same characteristic impedance as the circuit provided adjacent to each other.
The setting conditions for the calculation using the calculation software are: the length of the 75Ω portion made of the coaxial cables 20A and 20B is 1 m, the length of the 50Ω portion in the axial direction is Xmm, and the length of the 90Ω portion is in the axial direction. Ymm.
The voltage standing wave ratio (VSWR) when the length Xmm of the 50Ω portion is 0 to 20 mm and the length Ymm of the 90Ω portion is 0 to 20 mm is obtained, and the calculation result is shown in the graph of FIG.

If the traveling wave inside the coaxial cable is Et and the reflected wave is Er, the maximum value Emax and the minimum value Emin of the voltage are expressed by Emax = | Et | + | Er | and Emin = | Et | − | Er |, respectively. be able to. VSWR = Emax / Emin = | Et | + | Er | / | Et | − | Er |.
Therefore, the closer the VSWR is to 1, the smaller the reflected wave, that is, a communication circuit that transmits signals without waste and has good characteristics.

As is clear from FIG. 10, when the connector having a characteristic impedance of 50Ω is X = 5 to 20 mm, it was found that the VSWR can be improved by providing a high impedance forming portion having a characteristic impedance of 90Ω.
In particular, when the connector having a characteristic impedance of 50Ω is X = 5 to 7 mm, it was found that the VSWR can be improved to less than 1.1 by setting the high impedance forming portion having the characteristic impedance of 90Ω to Y = 5 to 15 mm ( In FIG. 10, a region surrounded by a one-dot chain line).

  On the other hand, when the connector having a characteristic impedance of 50Ω is X = 16 to 20 mm, the VSWR is improved only to around 1.4 even if the high impedance forming portion having the characteristic impedance of 90Ω is set to Y = 5 to 15 mm (FIG. 10). Inside, the area surrounded by the two-dot chain line).

The reason why there is no improvement effect when the length of the connector having a characteristic impedance of 50Ω is X = 16 to 20 mm will be described.
The wavelength of electromagnetic waves with a measurement frequency of 1 GHz is about 30 cm in free space. The wavelength inside the coaxial cable is theoretically 1 / √ε times. When ε = 2.3, it is about 0.66 times, that is, about 30 cm × 0.66≈20 cm. For such a transmission signal of 1 GHz, the length X = 16 to 20 mm of the 50Ω connector is about 1/10 of the wavelength, and is not in a state “small enough” with respect to the wavelength. Yes.
In the present invention, by providing minute portions having different characteristic impedance locally, the characteristic impedance is constant on average when viewed from the high-frequency signal to be transmitted. It is effective within the range of “small enough” length. Therefore, when the connector length X cannot be said to be “sufficiently small” compared to the wavelength, there is no effect of adjusting the characteristic impedance. In order to achieve a “sufficiently small” state that exhibits the adjustment effect, it is preferable that the length X of the connector is about 1/40 to 1/30 of the wavelength inside the coaxial cable.

The connection structure of the coaxial cable and connector of 1st Embodiment of this invention is shown, (A) is sectional drawing of an axial direction, (B) is AA sectional view, (C) is BB sectional drawing It is. (A) Drawing which shows the state which peeled the terminal of a coaxial cable, (B) is a drawing which shows the state which connected the inner conductor terminal of the connector to the coaxial cable, and formed the high impedance formation part, (C) is further It is drawing which shows the state which connected the outer conductor terminal of the connector. It is sectional drawing which shows the state which carried out the connector connection of coaxial cables. It is drawing which shows 2nd Embodiment of this invention. The connection structure of the coaxial cable and connector of 3rd Embodiment of this invention is shown, (A) is sectional drawing of an axial direction, (B) (C) is CC sectional view taken on the line. It is sectional drawing of the axial direction of the connection structure of the coaxial cable and connector of 4th Embodiment of this invention. (A) (B) is a perspective view of the connection structure of the coaxial cable and connector of 4th Embodiment. It is drawing which shows 5th Embodiment of this invention. It is the schematic of an Example. It is a graph which shows the calculation result of voltage standing wave ratio (VSWR).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Connection structure 20 and 20 'of coaxial cable and connector Coaxial cable 21 Central conductor 22 Insulator 23 Shield layer 23a High impedance formation part 23b Opening 23c Low impedance formation part 24 Sheath 25 and 25' Insulator sleeve for characteristic impedance adjustment 30, 40 Connectors 31, 41 Inner conductor terminals 32, 42 Outer conductor terminals 32d Opening 33 Dielectric

Claims (5)

A coaxial cable terminal is connected to the coaxial connector, a central conductor of the coaxial cable is connected to an inner conductor terminal of the coaxial connector, and a shield layer covering the central conductor of the coaxial cable with an insulator is provided to the coaxial connector Is connected to the outer conductor terminal of the coaxial connector, the characteristic impedance of the coaxial connector is lower than the characteristic impedance of the coaxial cable,
A high impedance forming portion is provided in the shield layer on the connector connection side of the coaxial cable, and the characteristic impedance in the connector connection portion is increased by averaging with the low impedance of the connector, which is close to the characteristic impedance of the coaxial cable. Connection structure between coaxial cable and coaxial connector. The high impedance forming part of the shield layer is
The shield layer is partially enlarged at the connector connection end, and an insulator sleeve for adjusting characteristic impedance is inserted between the enlarged shield layer and the insulator, and / or
Change the insulator to a material with a low relative dielectric constant,
The connection structure between the coaxial cable and the coaxial connector according to claim 1, wherein the shield layer is partially opened.   The coaxial cable and the coaxial connector according to claim 2, wherein an opening is provided in the cylindrical outer conductor terminal of the connector connected to the shield layer of the coaxial cable to increase the characteristic impedance on the connector side. Connection structure. A coaxial cable terminal is connected to the coaxial connector, a central conductor of the coaxial cable is connected to an inner conductor terminal of the coaxial connector, and a shield layer covering the central conductor of the coaxial cable with an insulator is provided to the coaxial connector Is connected to the outer conductor terminal of the coaxial connector, the characteristic impedance of the coaxial connector is higher than the characteristic impedance of the coaxial cable,
A low-impedance forming portion is provided in the shield layer on the connector connection side of the coaxial cable, and the characteristic impedance in the connector connection portion is lowered by averaging with the high impedance of the connector so as to be close to the characteristic impedance of the coaxial cable. A connection structure between a coaxial cable and a coaxial connector.   The low impedance forming portion of the shield layer removes the insulator on the connector connection side end of the coaxial cable, inserts a thin insulator sleeve for adjusting characteristic impedance, or adjusts characteristic impedance having a high relative dielectric constant 5. The connection structure between the coaxial cable and the coaxial connector according to claim 4, wherein the insulator sleeve is inserted.

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