JP4257782B2 - Measurement and evaluation method for high frequency characteristics of coaxial cable - Google Patents

Description

  The present invention relates to a method for measuring and evaluating high-frequency characteristics of a coaxial cable, and more particularly to a method for measuring and evaluating high-frequency characteristics of a coaxial cable using a high-frequency characteristic measuring and evaluating apparatus such as a network analyzer and TDR (Time Domain Reflectometry).

  Recently, coaxial cables are being used for antenna wiring of personal digital assistants, wiring for connecting an LCD and a CPU, etc. in response to an increase in information amount and high-speed transmission. In addition, due to the downsizing and thinning of information equipment terminals and notebook computers, coaxial cables are required to have higher performance and smaller diameters, and various improvements have been studied.

  Here, when measuring and evaluating the high-frequency characteristics of this type of coaxial cable, the existence of known literature has not been confirmed, but at the actual manufacturing site, connectors are connected to both ends or one end of the coaxial cable, and the connectors are connected. The high frequency characteristics are measured and evaluated by connecting to a high frequency characteristic measuring and evaluating apparatus such as a network analyzer and TDR.

  A connector used for such an application is usually composed of a pair of male and female structures. For example, a coaxial cable in which one male connector is connected to a high-frequency characteristic measurement and evaluation device and the other female connector measures and evaluates the characteristic. Connected to.

  In this case, the coaxial cable exposes the central conductor and the shield conductor and inserts them into the connector housing as they are, so that the coupling nut and the shield conductor that are fitted in the housing are electrically connected. In this way, the center conductor is projected to the center of the coupling nut.

  However, such a conventional method for measuring and evaluating high frequency characteristics has the following problems.

  In the conventional high-frequency characteristic measurement and evaluation method described above, the connector to be attached to the coaxial cable is used in accordance with the diameter of the coaxial cable. For example, in the case of a thin coaxial cable incorporated in a small information terminal device or the like In the past, it was usual to design and manufacture a dedicated connector, attach it, and then measure and evaluate it.

  In such a measurement evaluation method, accurate measurement and evaluation of the high frequency characteristics of the coaxial cable could not be performed without a dedicated connector. However, the development of a dedicated connector requires a lot of cost and time, so in the characteristic evaluation at the development stage of the coaxial cable, it has been necessary to deal with existing connectors with different diameters.

  When connectors with different diameters were used, impedance matching was difficult to achieve in the same state, and accurate cable characteristic evaluation could not be performed. In addition, a metal sleeve can be inserted into the ground portion of the connector to improve such inconsistencies, but it is a costly and time consuming process because it is performed manually by skilled workers such as sleeve processing, mounting, and soldering. was there.

  The present invention has been made in view of such conventional problems, and its purpose is to measure and evaluate the high-frequency characteristics of a coaxial cable that can be accurately measured and evaluated without using a dedicated connector. It is to provide a method.

In order to achieve the above object, the present invention provides a method for measuring and evaluating a high-frequency characteristic of a coaxial cable including a center conductor, an insulating coating layer, and a shield conductor. Is cut at right angles to the longitudinal direction, and then the measurement conductor provided at one end of the contact probe is brought into contact with the center conductor and the shield conductor exposed at the cut end face of the coaxial cable, and the contact A method for measuring and evaluating the high-frequency characteristics of the coaxial cable by connecting a high-frequency characteristic measurement and evaluation device such as a network analyzer or a TDR measuring device to the other end of the probe , wherein the coaxial cable is cut vertically. Before, a solidified body is formed by filling and solidifying a thermosetting or solidifying resin such as a thermoplastic resin around the end portion. Cut at right angles to the solidified body by a longitudinal cut end face is held by the fixture so as to be exposed on the upper surface and adapted to mount the fixture in a position adjustable measuring table.

  In the coaxial cable high-frequency characteristic measurement and evaluation method configured in this way, the contact cable used to measure the characteristics of a minute portion such as a semiconductor wafer or a device on a mounting substrate is used to accurately measure the coaxial cable. High frequency characteristics can be measured and evaluated without using a dedicated connector.

  The measurement and evaluation method of the present invention is suitable as a measurement and evaluation method for high-frequency characteristics in a thin coaxial cable having a diameter of 2 mm or less, particularly a thin coaxial cable having a diameter of 1 mm or less.

  In the above-described coaxial cable, in particular, in the case of a small diameter, it is difficult to accurately contact the contact probe by simply cutting, but it is hardened by a solidifying resin and solidified by solidifying. When the resin is cut at right angles to the longitudinal direction, the end face of the coaxial cable can be adjusted to be vertical (angle 90 ° ± 5 °), and the measurement evaluation accuracy can be improved.

  In this case, the solidifying resin to be used is preferably a thermosetting resin such as a room temperature curable epoxy resin or an ultraviolet curable resin which does not require heating. After fixing such a curable resin and fixing the coaxial cable, after cutting the curable resin at a right angle and creating an end face, the end face is polished with silica particles or the like in order to measure more accurate high-frequency characteristics. It is desirable to make it flat by polishing with a material.

  Further, a thermoplastic resin such as polyethylene resin (PE) or polypropylene resin (PP) may be used as the solidifying resin, and these resins may be melt-molded and cooled and solidified. When such a flexible thermoplastic resin is used, the end face can be easily cut.

  According to the coaxial cable high-frequency characteristic measurement and evaluation method according to the present invention, the high-frequency characteristic of the coaxial cable can be measured and evaluated without using a dedicated connector.

  Hereinafter, preferred embodiments of the present invention will be described in detail based on examples.

  1 to 4 show an embodiment of a method for measuring and evaluating high frequency characteristics of a coaxial cable according to the present invention. In the measurement evaluation methods shown in these drawings, for example, the high-frequency characteristics of a thin coaxial cable 10 having a diameter of 2 mm or less are measured and evaluated. The thin coaxial cable 10 has a cross section as shown in FIG. In addition, a central conductor 10a, an insulating coating layer 10b, a shield conductor 10c, and a protective coating layer 10d are provided.

  The center conductor 10a is composed of a single wire or a stranded wire such as copper or steel, and an insulating coating layer 10b made of synthetic resin is formed on the outer periphery thereof to have a predetermined thickness. The shield conductor 10b is a braided copper wire or the like, and is formed so as to cover the outer peripheral surface of the insulating coating layer 10b. The protective coating layer 10d is made of, for example, a thermoplastic resin and is formed so as to cover the outer periphery of the shield conductor 10b.

  When measuring and evaluating the high frequency characteristics, microwave transmission and reflection characteristics, etc. of the thin coaxial cable 10 having such a configuration, first, as shown in FIG. The solidified body 12 is formed.

  In FIG. 4, the solidified bodies 12 are formed at both ends of the coaxial cable 10, but the solidified bodies 12 may be formed only at one end depending on the type of high-frequency characteristics to be measured. .

  In the case of the present embodiment, the solidified body 12 is solidified such as thermosetting or thermoplastic resin inside the cylindrical body with the end of the coaxial cable 10 inserted into the center of the hollow cylindrical body of a predetermined length. It is formed by removing the cylindrical body after filling and solidifying the functional resin.

  When the solidified body 12 is formed, next, including the end portion of the coaxial cable 10 and the solidified solidified resin, it is cut at a right angle with respect to the longitudinal direction of the coaxial cable 10 to form a right-angle cut end face 14. To do.

  The right-angle cut end face 14 formed in this way is polished with an abrasive such as silica particles as necessary to form a flatter right-angle cut face. When such a cut end face 14 is formed, the coaxial cable 10 is then detachably clamped and fixed to the fixing jig 16 and placed on the measurement table 18 as shown in FIGS. The position of the measurement table 18 can be adjusted in a two-dimensional direction.

  Then, the measurement terminal 22 provided at one end of the contact probe 20 is brought into contact with the central conductor 10a and the shield conductor 10c exposed on the cut end surface 14 of the coaxial cable 10, respectively.

  In this case, as shown in an enlarged view in FIG. 3, the measurement terminal 22 has a pair of branched contacts 22a and 22b, which are brought into contact with the central conductor 10a and the shield conductor 10c, respectively.

  The contact probe 20 is held by a positioner 24 that can be positioned in a three-dimensional direction, and a cable 26 extended to the rear end of the contact probe 20 has one end connected to the measurement terminal 22 and the other end side Since a high-frequency characteristic measurement / evaluation apparatus (not shown) such as a network analyzer or a TDR measuring device is connected, the measurement / evaluation apparatus is operated to measure and evaluate the high-frequency characteristic of the coaxial cable 10 to which the probe 20 is connected. It will be.

  Now, according to the coaxial cable high frequency characteristic measurement and evaluation method configured as described above, the accurate high frequency characteristic of the coaxial cable 10 can be measured and evaluated without using a dedicated connector.

  Hereinafter, more specific examples of the present invention will be described together with comparative examples.

Example 1

  Junkosha Co., Ltd., small-diameter coaxial cable DFS241 (central conductor silver-plated copper wire 0.05 mm x 7 twist, insulation coating layer 0.42 mm shield 0.05 mm tin-plated copper wire x 3 x 16 braid, characteristic impedance nominal 50Ω), both 1 m The terminal is placed in the center of a hollow cylindrical mold having a thickness of 10 mm and a length of 20 mm from the terminal, and an ultraviolet curable resin (UVcuring 3042 manufactured by ThreeBond) is poured into the mold, and an ultraviolet exposure apparatus (manufactured by Ushio: model: ML) -251D / M) for 20 minutes and cut with a draining cutter so as to be perpendicular to the cable.

  Next, the end portion polished with the solidifying resin was subjected to an end surface polishing treatment with a nano-factor polishing machine (model FACT200) using silica fine particles as an abrasive so as to eliminate end surface irregularities.

  For measurement of high-frequency characteristics, both ends are fixed on the measurement table so that both polished end faces are horizontal, the ground at the tip of the contact probe (pico probe made by GGB) is used as the shield conductor of the coaxial cable, and the probe signal Were brought into contact with the central conductor of the coaxial cable through the XYZ positioners.

  The contact probe is equipped with an APC 3.5mm compatible connector, a digital sampling oscilloscope (Tektronix 11801B Digital Sampling Oscilloscope, manufactured by Tektronix Japan, Inc.) and a vector network analyzer (model 8722ES, manufactured by Agilent Technologies) and an APC 3.5mm connector. Arbitrary connection via a cable attached.

  In the case of TDR measurement, the measurement can be performed with only one end connection. However, when the measurement of the vector network analyzer is performed simultaneously, it is necessary to connect both ends. This time, both ends were connected to a contact probe to measure the network analyzer.

  Next, a TDR measurement method and result using a digital sampling oscilloscope will be described. Measurement was performed by connecting a TDR head of a digital sampling oscilloscope and a contact probe connector.

  In this case, both ends of the coaxial cable are connected to the tip of the contact probe, and data can be obtained regardless of which contact probe is connected to the TDR head.

  As a result, it was confirmed that there was no impedance mismatch (dips) at the connection point between the contact probe and the end face treated coaxial cable. Next, microwave transmission characteristics (S21) and reflection characteristics (S11) were measured using a vector network analyzer.

  As with the TDR measurement, both ends of the cable are connected to contact probes, with one probe connected to network analyzer port 1 and the other connected to port 2 (whichever of the two ends of the coaxial cable is connected). (It may be connected to port 1), and in the frequency range from 500 MHz to 10 GHz, a microwave was inserted, the vertical axis represents attenuation, and the horizontal axis represents frequency data. 5 and 6 show the measurement results.

  As can be seen from the measurement results shown in the figure, the waveform data of the transmission characteristic is a smooth waveform with no ripple, and the reflection characteristic is also good with a small amount of ripple and a large amount of attenuation.

Comparative Example 1

  A small coaxial cable DFS241 manufactured by Junkosha Co., Ltd. used in Example 1 and both terminals having a cable length of 1 m are placed in the center of a mold having a thickness of 10 mm and a length of 20 mm from the terminal, and an ultraviolet curable resin (UVcuring 3042 manufactured by ThreeBond) is used. Pour into the mold, cure for 20 minutes with an ultraviolet exposure device (USHIO ELECTRIC: Model: ML-251D / M), and make a sample cut with a draining cutter so that it is at an angle of 40 ° with the cable did.

  Furthermore, the terminal portion hardened with resin was subjected to an end surface polishing treatment using a silica fine particle as an abrasive with a polishing machine (model FACT200) manufactured by Nano Factor Co., Ltd. so as to eliminate the unevenness of the end surface. (A sample was prepared in the same manner as in Example 1 except that the cut angle of the end face at this time was 40 °.)

  For measurement of high-frequency characteristics, the polished ends are fixed on a measurement table so that they are horizontal, the ground at the tip of the GGB (USA) pico probe is used as the shield conductor of the coaxial cable, and the probe signal is sent to the coaxial cable. The center conductor was brought into contact with each other via an XYZ positioner.

  The contact probe is equipped with an APC 3.5 mm compatible connector, such as a digital sampling oscilloscope (Tektronix 11801B Digital Sampling Oscilloscope, manufactured by Tektronix Japan, Inc.), a vector network analyzer (model 8722ES, manufactured by Agilent Technologies), and APC 3.5 mm. By connecting via a cable with a connector, high frequency characteristics can be measured.

  As a result of TDR measurement using a digital sampling oscilloscope with the same measurement method as in Example 1, the impedance at the connection point between the contact probe and the end-face treated coaxial cable is about 70Ω, and there is an impedance mismatch (dips). I understood. This is thought to be because the signal line was in a semi-open state by cutting the end face portion obliquely.

  Next, measurement and evaluation of microwave transmission characteristics (S21) and reflection characteristics (S11) were performed using a vector network analyzer in the same measurement method as in the first specific example. The frequency was scanned from 500 MHz to 10 GHz, and measurement data with the vertical axis representing attenuation and the horizontal axis representing frequency were obtained. 5 and 6 show the measurement results. Large ripples exist in the waveform data of transmission characteristics and reflection characteristics, and accurate measurement and evaluation of high frequency characteristics is impossible.

Comparative Example 2

  Part of the coating on both ends of the cable used in Example 1 was peeled off to expose the central conductor and insulation coating, and then a semi-rigid SMA connector was connected. The SMA connectors at both ends were directly connected to the APC 3.5 mm connector of equipment such as a digital sampling oscilloscope and a vector network analyzer (direct connection is possible because of connector compatibility), and the high frequency characteristics of the cable were measured.

  As a result of TDR measurement using a digital sampling oscilloscope, there was an impedance fluctuation of about 53 to 47Ω for about 1 nanosecond from the connection point. Although I do not know the detailed cause, it is thought that it is caused by impedance mismatch due to heating when the connector is attached.

  Next, measurement and evaluation of transmission characteristics and reflection characteristics were performed using a vector network analyzer. Connect one end of the connector to the network analyzer port 1 and the other end to the port 2 (whichever of the two ends of the coaxial cable may be connected to the port 1). The frequency ranges from 500 MHz to 10 GHz. The measurement data was obtained with the vertical axis representing attenuation and the horizontal axis representing frequency. 5 and 6 show the measurement results. As a result, there was an impedance mismatch in the connector part, so ripples were confirmed in the waveform of the transmission characteristics. Also, the reflection characteristic was larger than that of the example.

  In the above specific example, the high-frequency characteristics of a commercially available flexible small-diameter coaxial cable were measured and evaluated. However, in the present invention, the rigid type, semi-rigid type, semi-flexible type, or other various coaxial cables can be used. It can be applied to high frequency characteristic measurement evaluation.

  According to the coaxial cable high-frequency characteristic measurement and evaluation method according to the present invention, it is possible to measure and evaluate the high-frequency characteristic of the coaxial cable without using a specially designed and manufactured connector. It can be effectively used for measurement evaluation when a thin coaxial cable is manufactured.

  In addition, a printed circuit board, a package, an electronic component, and the like can be directly connected by soldering, welding, conductive adhesive, or the like without using a connector. When considering such applications, the method of the present invention is an indispensable important technology.

It is explanatory drawing of the implementation state of the high frequency characteristic measurement evaluation method in the coaxial cable concerning this invention. It is a principal part enlarged view of FIG. FIG. 3 is an enlarged view of a main part of FIG. 2. It is an external appearance explanatory view of the coaxial cable for evaluation in the measurement evaluation method shown in FIG. It is a graph of the transmission characteristic measured with the measurement evaluation method and comparative example method of the thin coaxial cable concerning the present invention. It is a graph of the reflective characteristic measured with the measurement evaluation method and comparative example method of the thin coaxial cable concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Coaxial cable 10a Center conductor 10b Insulation coating layer 10c Shield conductor 12 Solidified body 14 Cutting end surface 16 Fixing jig 18 Measurement table 20 Contact probe 22 Measurement terminal

Claims (2)

In the high-frequency characteristic measurement evaluation method of a coaxial cable provided with a center conductor, an insulation coating layer, and a shield conductor,
After cutting one end of the coaxial cable, or both ends perpendicular to the longitudinal direction,
With the center conductor and the shield conductor exposed at the cut end surface of the coaxial cable, the measurement terminals provided at one end of the contact probe are brought into contact with each other,
Connect the other end of the contact probe to a high-frequency characteristic measurement / evaluation device such as a network analyzer or a TDR measuring machine,
A method for measuring and evaluating high-frequency characteristics of the coaxial cable ,
Before the coaxial cable is cut vertically, a solidified body is formed by filling and solidifying a thermosetting or solidifying resin such as a thermoplastic resin around the end portion,
The solidified body is cut at right angles to the longitudinal direction, held on a fixing jig so that the cut end face is exposed on the upper surface side, and the fixing jig is placed on a measurement table whose position can be adjusted. To measure and evaluate high-frequency characteristics of coaxial cables. 2. The coaxial cable high-frequency characteristic measurement and evaluation method according to claim 1, wherein the cut end face is polished with an abrasive such as silica particles .

Images