Termination device

The device is provided with an inner conductor electrically connected to a counterpart central terminal in a counterpart coaxial device, a tubular outer conductor having the inner conductor disposed in the center thereof, said outer conductor being electrically connected to a counterpart outer conductor in the counterpart coaxial device, a grounding conductor electrically connected to the outer conductor, a resistance element provided in the axial direction between the inner conductor and the grounding conductor, and an annular dielectric member provided between the inner conductor and the outer conductor such that the member has the inner conductor passing therethrough and, at the same time, the inner conductor and the outer conductor are spaced apart from each other in the radial direction.

CROSS REFERENCE TO RELATED APPLICATIONS

This Paris Convention Patent Application claims benefit under 35 U.S.C. § 119 and claims priority to Japanese Patent Application No. JP 2016-173072, filed on Sep. 5, 2016, titled “TERMINATION DEVICE”, the content of which is incorporated herein in its entirety by reference for all purposes.

BACKGROUND

Technical Field

The present invention relates to termination devices and, in particular, to a coaxial termination device that can be used for high-frequency bands.

Background Art

Termination devices have been developed for the purpose of minimizing high-frequency signal reflection, preventing noise generation, and the like. For instance, an exemplary conventional termination device is shown in Japanese Patent No. 4331529. This termination device, which is connected to a counterpart coaxial connector in the axial direction, is provided with a first component having a terminal portion that is electrically connected to a counterpart center conductor of the counterpart coaxial connector and an outer conductor portion that is electrically connected to a counterpart outer conductor of the counterpart coaxial connector, and a second component having a grounding conductor portion that is electrically connected to the outer conductor portion of the first component, an intermediate portion that is resiliently connected to the terminal portion of the first component in the axial direction, and a resistance element that is electrically connected to the grounding conductor portion and the intermediate portion and that electrically connects the grounding conductor portion to the counterpart center conductor of the counterpart coaxial connector.

Desirably, the resistance of the termination device in the axial direction should be constant at all times. In the above described termination device example, the sum total of the resistance of the resistance element, the impedance appearing between the terminal portion and the outer conductor portion, and the impedance appearing between the resistance element and the outer conductor portion is desirably maintained at a constant value of, for example, about 50Ω in the axial direction.

However, in the past, there has not been an established technology for solving this problem and attempts to solve the problem have been made by trial-and-error depending on the device. In recent years, improved high-frequency characteristics have been increasingly sought after, while, at the same time, there is also increasing demand for device miniaturization. Accordingly, there exists a need to establish a technology that would solve the above-mentioned problem while satisfying these requirements.

PRIOR ART DOCUMENTS

Patent Documents

SUMMARY

Problems to be Solved by the Invention

The present invention, which is designed to solve such prior-art problems, provides a proven technology for keeping the resistance of a termination device constant in the axial direction. In addition, it is an object of the invention to implement device miniaturization while achieving improvements in high-frequency characteristics. The present disclosure herein is directed to an invention that provides a proven technology for keeping the resistance of a termination device constant in the axial direction. Airspaces formed between the inner conductor and the outer conductor by mutually spacing apart the inner conductor and the outer conductor in the radial direction are disposed adjacent the dielectric member in the axial direction and the diameter of the inner peripheral surface of the outer conductor is expanded in the vicinity of the boundaries between the airspaces and the dielectric member, on the side located closer to the dielectric member than the airspaces in the axial direction.

Means for Solving the Problem

Based on new findings showing that impedance was readily variable in locations where the dielectric constant underwent abrupt changes, the inventors focused their attention on locations in a termination device where such changes were likely to occur, for example, the vicinity of the boundaries between a securing portion made of resin that secured the terminal portion to the outer conductor portion, and airspaces formed between the terminal portion and the outer conductor portion, and, upon performing numerous trial-and-error experiments using simulation equipment, discovered the optimum technology for minimizing the above-described changes as well as a proven technology adapted for device miniaturization.

In order to solve the abovementioned problem, the termination device according to one aspect of the invention is a termination device connected to a counterpart coaxial device, wherein said termination device is provided with: an axially extending inner conductor electrically connected to a counterpart central terminal in the counterpart coaxial device, a tubular outer conductor having the inner conductor disposed in the center thereof, said outer conductor extending in the axial direction and being electrically connected to a counterpart outer conductor in the counterpart coaxial device, a grounding conductor electrically connected to the outer conductor, a resistance element provided in the axial direction between the inner conductor and the grounding conductor, and an annular dielectric member provided between the inner conductor and the outer conductor such that the member has the inner conductor passing therethrough and, at the same time, the inner conductor and the outer conductor are spaced apart from each other in the radial direction, and airspaces formed between the inner conductor and the outer conductor by mutually spacing apart the inner conductor and the outer conductor in the radial direction are disposed adjacent the dielectric member in the axial direction, and the diameter of the inner peripheral surface of a cylindrical member of the outer conductor is expanded in the vicinity of the boundaries between the airspaces and the dielectric member in the axial direction.

In addition, in order to solve the abovementioned problem, the termination device according to another aspect of the invention is a termination device connected to a counterpart coaxial device, wherein said termination device is provided with: an axially extending inner conductor electrically connected to a counterpart central terminal in the counterpart coaxial device, a tubular outer conductor having the inner conductor disposed in the center thereof, said outer conductor extending in the axial direction and being electrically connected to a counterpart outer conductor in the counterpart coaxial device, a grounding conductor electrically connected to the outer conductor, a resistance element provided in the axial direction between the inner conductor and the grounding conductor, and an annular dielectric member provided between the inner conductor and the outer conductor such that the member has the inner conductor passing therethrough and, at the same time, the inner conductor and the outer conductor are spaced apart from each other in the radial direction, and airspaces formed between the inner conductor and the outer conductor by mutually spacing apart the inner conductor and the outer conductor in the radial direction are disposed adjacent the resistance element in the axial direction, and the diameter of the inner peripheral surface of a cylindrical member of the outer conductor is expanded in the vicinity of the boundaries between the airspaces and the resistance element in the axial direction.

It should be noted that the dielectric member may be used as a securing member for securing the inner conductor to the outer conductor. In addition, the resistance element may be a planar resistive substrate.

In the termination device of this aspect, in order to minimize changes in impedance due to abrupt changes in the dielectric constant in the vicinity of the boundaries between the dielectric member and the airspaces in the radial direction, the airspaces are provided such that the diameter of the inner peripheral surface of a cylindrical member of the outer conductor in the vicinity of these boundaries is expanded to thereby make it possible to maintain a constant resistance. In addition, since the outer conductor is formed of metal, it is easier to machine than resin and the like and is also adapted for device miniaturization.

In the termination device of the above-described aspect, it is preferable to adjust the diameter of the inner peripheral surface of a cylindrical member of the outer conductor according to the areas of the resistance element in which the impedances appearing with respect to the outer conductor differ in the axial direction.

Using the termination device of this aspect, it is easy to maintain a constant resistance by minimizing changes in impedance generated by the resistance element and the like.

In addition, in the termination device of above-mentioned aspect, it is preferable for a portion of the pads provided on the resistance element to be covered by at least a portion of the inner conductor in the axial direction, and for the width of the pads in a direction orthogonal to the axial direction to be adjusted separately in the region covered by a portion of the inner conductor in the axial direction and in the region not covered by a portion of the inner conductor in the axial direction.

In the termination device of this aspect, the width of the pads is adjusted to thereby make it possible to minimize changes in impedance and maintain a constant resistance.

Furthermore, in the termination device of the above-mentioned aspect, the width of the pads in a direction orthogonal to the axial direction in the region not covered by a portion of the inner conductor in the axial direction may be smaller than the width of the pads in a direction orthogonal to the axial direction in the region covered by a portion of the inner conductor in the axial direction.

Furthermore, in the termination device of above-mentioned aspect, the resistance element comprises the pads that include the region covered by a portion of the inner conductor in the axial direction and the region not covered by a portion of the inner conductor in the axial direction, and a resistor that is disposed to the side closer to the grounding conductor in the axial direction than said pads, and the width of the pads in a direction orthogonal to the axial direction in the region not covered by a portion of the inner conductor in the axial direction may be equal to the width of the resistor in a direction orthogonal to the axial direction.

DETAILED DESCRIPTION

A preferred embodiment of the present invention will be described below with reference to the accompanying drawings. It should be noted that while only the preferred embodiment is illustrated herein for convenience purposes, it is not intended to be restrictive of the present invention.

FIG. 1shows a centerline cross-sectional view of a termination device used as an example of the present invention. The termination device1extends in the axial direction “α” and includes, for example, a metal connecting portion10with a regular hexagon-shaped cross-section having a relatively short length in the axial direction “α”, a substantially cylindrical metal shell20having a relatively long length in the axial direction “α”, and, furthermore, a first component3inserted and installed inside the shell20, and a second component5inserted and installed inside the first component3.

The first component3includes a substantially rod-shaped inner conductor30extending in the axial direction “α”, a substantially cylindrical metal cylindrical member40extending in the axial direction “α”, and an annular dielectric member60disposed inside the cylindrical member40. Meanwhile, the second component5includes a substantially rod-shaped connection terminal50extending in the axial direction “α”, a substantially cylindrical grounding conductor such as, for example, a connecting tube70, and, furthermore, a resistance element such as a resistive substrate2, for example, provided in the axial direction “α” between the connection terminal50and the connecting tube70.

The shell20includes a reduced-diameter tubular member21provided on the front side, an expanded-diameter main body23provided on the rear side, and an annular flange22provided therebetween. A retainer12is fitted into an annular recessed portion14provided in the inner wall of the connecting portion10and extraction of the shell20from the connecting portion10is prevented by making this retainer12collide with the flange22. A securing screw29is installed in the rear end portion of the main body23, thereby preventing the first component3and second component5from falling out of the shell20.

The shell20has a cylindrical holding space25formed therethrough in the axial direction “α”. The holding space25is placed in communication with a through hole13provided in the connecting portion10. The diameter of the anterior inner peripheral surface20A of the holding space25formed by the tubular member21and flange22is set to a relatively small diameter. By contrast, the diameter of the posterior inner peripheral surface20B of the holding space25is set to a relatively large diameter. Threading is formed in the end portion of the holding space25to allow the securing screw29to be secured.

The inner conductor30passes in the axial direction “α” through the center of a holding portion formed by the anterior inner peripheral surface20A of the holding space25. Meanwhile, the cylindrical member40passes in the axial direction “α” through a holding portion formed by the posterior inner peripheral surface20B of the holding space25while being in contact with the inner peripheral surface20B. The shell20and cylindrical member40, as well as the connecting portion10, which is in contact with the shell20, can collectively form the outer conductor of the termination device1.

The dielectric member60may be made, for example, of fluorocarbon resin (PTFE). In order to facilitate the insertion of the dielectric member60into the cylindrical member40, tapers61A,61B are provided at the edges of the rear face b1and front face b2of the dielectric member60. For the same reason, the insertion aperture of the cylindrical member40on the side where the dielectric member60is inserted is provided with tapers62. It should be noted that while the side where the tapers61B are provided is opposite to the side used to insert the dielectric member60, the dielectric member60is a very small component, with a length in the axial direction of the termination device1is less than 2 mm, and therefore the direction of insertion of the dielectric member60is difficult to recognize with the naked eye. For this reason, tapers61A,61B are provided both on the rear face b1and on the front face b2of the dielectric member60to permit insertion using either side without identifying the presence or absence of tapers. However, the tapers61A,61B, and62are not essential.

The dielectric member60has the inner conductor30passing therethrough and, in addition, is disposed between the inner conductor30and the a cylindrical member40of the outer conductor20such that the inner conductor30and outer conductor40are spaced apart in the radial direction “β”. The dielectric member60is used to provide the inner conductor30in the axial direction “α” in the center of the holding space45of the cylindrical member40. In addition, the dielectric member60is used to electrically disconnect the inner conductor30from the cylindrical member40. In order to secure the inner conductor30and the dielectric member60, a portion of the lateral face of the inner conductor30is machined from the opposite side to leave a plate-like portion33in the center, and the space formed by such machining may be filled by an adhesive agent34such as epoxy resin or the like.

The second component5will be described in greater detail with reference toFIG. 2andFIG. 3in addition toFIG. 1.FIG. 2shows a perspective view of the second component5andFIG. 3shows a front elevation view thereof. In the same manner as the inner conductor30, the connection terminal50constituting the second component5extends in the axial direction “α” in the center of the holding space45of the cylindrical member40.

The connection terminal50is made up of a base51and a notched member53attached to said base51. The base51includes an expanded-diameter cylindrical main body51A, a narrow-diameter rod-shaped portion51B extending forward of this main body51A, and two substantially D-shaped pinching portions51C provided at the rear end of the main body51A. The distal end51aof the rod-shaped portion51B is tapered. Multiple notched-out portions53aare formed by providing multiple slits in the notched member53and the notched member53is installed in the base51such that the rod-shaped portion51B passes through the center of these notched-out portions53a. Under the action of the securing screw29, the tapered distal end51aof the rod-shaped portion51B exposed beyond the distal end of the notched member53, along with the notched-out portions53adisposed along a rear perimeter of said distal end51a, is threadedly driven in the axial direction “α” and inserted into a hole32(seeFIG. 1) provided in the rear end portion of the inner conductor30. As a result, the inner conductor30and connection terminal50are physically and electrically connected and all of these components can collectively form the inner conducting member of the termination device1. Meanwhile, the rear end of the connection terminal50is secured to the resistive substrate2in the axial direction “α” by the pinching portions51C. The connection terminal50is secured to the resistive substrate2by vertically pinching the front side of the resistive substrate2with the pinching portions51C, in other words, such that at least a portion of the front end of the resistive substrate2is covered thereby. The rear end of the resistive substrate2is inserted and installed in an indentation78provided in the connecting tube70and is connected to ground.

The connecting tube70is disposed such that its lateral surface is in contact with the inner peripheral surface40A in the rear side of the cylindrical member40. As a result, the connecting tube70is electrically connected to the cylindrical member40and is further connected to the connecting portion10and shell20through the cylindrical member40. Tapers71are formed in the connecting tube70in an anterior-to-posterior direction towards the central indentation78. Although the impedance between the connecting tube70and resistive substrate2appears mainly in the radial direction “β”, a constant resistance can be maintained by adjusting the impedance with the help of the tapers71.

A counterpart coaxial apparatus, for example, a counterpart coaxial connector (not shown in the drawing), is connected to the connecting portion10side in the axial direction “α”. At such time, a counterpart outer conductor provided in the counterpart coaxial connector is physically connected to the tubular member21and connecting portion10of the termination device1, and, as a result, is electrically connected to the connecting portion10, shell20, and cylindrical member40constituting the outer conductor. Furthermore, at such time, a counterpart central terminal provided in the counterpart coaxial connector is physically connected to the inner conductor30of the termination device1, in particular, in the vicinity of its distal end31, and, as a result, is electrically connected to the inner conductor30and connection terminal50constituting the inner conducting member.

The outer conductor, in particular, the shell20and cylindrical member40, are mutually spaced apart from the inner conductor30and connection terminal50in the radial direction “β”. As a result, an airspace43A is formed between the inner peripheral surface40B near the center of the cylindrical member40and the inner conductor30, the connection terminal50and the resistive substrate2, and an airspace43B is formed between the inner conductor30and the inner peripheral surface20A of the tubular member21of the shell20. These airspaces43A,43B are both disposed adjacent the dielectric member60in the axial direction “α”. The dielectric constant of the dielectric member60is substantially different from that of the airspaces43A,43B (for example, about double that in the case of the relative dielectric constant of PTFE, from which the dielectric member60is formed), as a result of which the dielectric constant abruptly changes in the vicinity of the boundaries between the dielectric member60and the airspaces43A,43B. As a result of focusing their attention on the fact that impedance was readily variable in locations where the dielectric constant underwent abrupt changes and accumulating experimental results by conducting simulations of the vicinity of the boundaries between the dielectric member60and the airspaces43A,43B, the inventors determined that changes in impedance could be minimized by expanding the diameter of the inner peripheral surface40C of the cylindrical member40in the vicinity of the boundaries between the dielectric member60and the airspaces43A,43B in the axial direction “α”, which, in the present example, is in the vicinity of the boundary b1of the rear face and the airspace43A and the boundary b2of the front face of the dielectric member60and the airspace43B. Although the details of the mechanism are unclear, it is presumed that, as a result of expanding the diameter of the inner peripheral surface40C of the cylindrical member40, airspaces41A,41B are formed by the expanded-diameter portions, and these airspaces41A,41B are used to increase the impedance appearing between the inner conductor30and connection terminal50and the cylindrical member40right before the airspaces43A,43B, thereby allowing for a constant resistance to be maintained. It should be noted that since the cylindrical member40is formed of metal, it is easier to machine than resin and the like and more readily lends itself to sizing. For this reason, this configuration makes it possible to easily perform diameter adjustments despite the small size of the termination device.

Next, the configuration of the resistive substrate2will be described in detail by referring toFIG. 4, in addition toFIGS. 1 to 3.FIG. 4is a schematic plan view of the resistive substrate2.

One of the end regions,2C, of the resistive substrate2is inserted and installed in the indentation78of the connecting tube70and is connected to ground. Pads2B are provided in the other end region of the resistive substrate2, and, furthermore, a resistor2A is provided to the side closer to the connecting tube70in the axial direction “α” than the pads2B. The resistor2A, which is used to adjust the impedance such that the resistance at one end2C of the resistive substrate2is set to zero, is provided in the axial direction “α” in a resistive region42A located directly underneath the tapers71of the connecting tube70.

A portion of the pads2B is vertically pinched between the pinching portions51C of the connection terminal, in other words, covered by the pinching portions51C of the connection terminal. Even after being covered by the pinching portions51C, a small portion,2B′, of the pads2B protrudes from the pinching portions51C in the axial direction “α” as well as in a direction “γ” orthogonal to the axial direction “α”. The connecting member50can be secured to the resistive substrate2by applying solder to the external surface of the pinching portions51C and this overhanging portion2B′.

In the axial direction “α”, the pads2B include a region,42B, that is covered by the pinching portions51C (hereinafter referred to as the “covered region”), and a region,42B′, that is not covered by the pinching portions51C (hereinafter referred to as the “uncovered region”). The resistance values of the covered region42B and the uncovered region42B′ are different, as a result of which the impedance appearing between the resistive substrate2and the outer conductor, in particular, the shell20and the cylindrical member40, is different in the covered region42B and the uncovered region42B′. In this configuration, in order to keep the resistance of the termination device1constant in the axial direction “α”, impedance adjustment is implemented in accordance with this difference by adjusting the diameter of the inner peripheral surface40B of the outer conductor40in the axial direction “α”. As a result of accumulating experimental results by conducting simulations of the vicinity of the boundary b3between the covered region42B and the airspace43A as well as the vicinity of the boundary b4between the covered region42B and the uncovered region42B′ where the dielectric constant was likely to undergo abrupt changes, in the same manner as with the boundaries b1and b2, the inventors determined that changes in impedance could be minimized by respectively expanding the diameter of the inner peripheral surface40Ba and the inner peripheral surface40Bb of the cylindrical member40in the vicinity of the boundary b3in the axial direction “α”, on the side located closer to the covered region42B, and, in addition, in the vicinity of the boundary b4in the axial direction “α”, on the side located closer to the uncovered region42B′. Although the details of the mechanism are unclear, it is presumed that, in the same manner as with the above-described boundaries b1and b2, expanding the diameter of the inner peripheral surface40Ba in the covered region42B and the diameter of the inner peripheral surface40Bb in the uncovered region42B′ makes the airspaces larger, in other words, reduces the dielectric constant and, as a result, increases the impedance appearing between the covered region42B, uncovered region42B′ and the cylindrical member40, thereby allowing for a constant resistance to be maintained. For instance, in this example, the diameter of the inner peripheral surface40Ba of the cylindrical member40of the outer conductor in the covered region42B is set to be slightly larger than the regular diameter of the inner peripheral surface40B and, in addition, the diameter of the inner peripheral surface40Bb of the cylindrical member40of the outer conductor in the uncovered region42B′ is set to be slightly larger than the diameter of the inner peripheral surface40Ba of the cylindrical member40of the outer conductor in the covered region42B.

Instead of changing the diameter of the inner peripheral surface of the cylindrical member40of the outer conductor, or in addition thereto, impedance adjustments may be implemented by adjusting the width of the pads2B in the orthogonal direction “γ” differently depending on whether this is the covered region42B or the uncovered region42B′. In the example illustrated inFIG. 4, the width “e” of the pads2B in the orthogonal direction “γ” in the uncovered region42B′ is set to be slightly larger than the width “d” of the pads2B in the same direction “γ” in the covered region42B. By contrast, in the resistive substrate2′ illustrated inFIG. 5, impedance is adjusted by making the width “f” of the pads2D in the orthogonal direction “γ” in the uncovered region42B′ smaller than the width “e” of the pads2B in the orthogonal direction “γ” in the covered region42B. In such a case, the width “f” of the pads2B in the orthogonal direction “γ” in the uncovered region42B′ can be reduced to a width equal to the width “f” of the resistor2A in the same direction “γ”. What width is required can be easily determined by calculation.

It should be noted that the present invention is not limited to the above-described embodiment and various other modifications are possible. Accordingly, the drawings and descriptions are merely illustrative and not restrictive.

DESCRIPTION OF THE REFERENCE NUMERALS