JP2010192987A - Coaxial connector and connection structure between coaxial connector and coplanar waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce discontinuous gaps of a propagation mode on a connection surface between a coaxial connector and a planar waveguide, especially a coplanar waveguide with a rear ground. <P>SOLUTION: An inner conductor distal end portion 121A whose cross-sectional shape is different from that of an inner conductor 111 is formed on a distal end portion of the inner conductor 111 in a coaxial line part 110 to gradually change mode conversion between the coaxial line part 110 and the coplanar waveguide 200 with the rear ground at the inner conductor distal end portion 121A. Further, inner dielectric layers 113, 122 are formed so that characteristic impedances are made identical in an outer conductor 122 and the inner conductor distal end portion 121A of a propagation mode conversion part 120, a center conductor 203 and a surface ground 202 of the coplanar waveguide 200 with the rear ground, and an outer conductor 112 and the inner conductor 111 of the coaxial line part 110 to achieve impedance matching between the coaxial connector 100 and the coplanar waveguide 200 with the rear ground. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a coaxial line, and more particularly to a coaxial connector and a coaxial connector / planar line connection structure used for parallel connection between a coaxial line and a planar line.

  Coaxial lines and planar lines are widely used as transmission lines for high-frequency signals in the microwave band and the millimeter wave band. The coaxial line and the planar line are connected to each other by a conductive material.

  At that time, there is a problem in that the propagation mode does not match at the connection point between the coaxial line and the planar line such as the microstrip line, and undesired reflection occurs. The electric field in the coaxial line has an omnidirectional distribution from the center conductor toward the entire circumference of the outer conductor. On the other hand, the electric field in the microstrip line is distributed downward from the strip conductor to the ground conductor. As a result, the electric field distribution becomes discontinuous at the junction between the two, resulting in undesired reflection and conversion loss.

Patent Documents 1 and 2 disclose inventions related to propagation mode conversion.
The coaxial microstrip conversion connector structure described in Patent Document 1 changes the dielectric layer of the coaxial line from a V shape to a semicircular shape as it approaches the connection surface with the planar line. As a result, the electric field distribution is concentrated in the lower part and approximated to a microstrip line. As a result, the coaxial connector and the microstrip line have the same propagation mode to eliminate the discontinuity.
Moreover, the coaxial microstrip converter described in Patent Document 2 has an eccentric hole in which the insertion hole is shifted upward with respect to the central axis of the inner conductor of the coaxial connector. As a result, the electric field distribution of the coaxial connector is concentrated in the lower part and approximated to a microstrip line.

JP-A-5-235613 JP 2005-236648 A

At present, a coplanar line with a back ground having low dispersion characteristics and low radiation loss is generally used as a high-frequency planar line. The inventions described in Patent Documents 1 and 2 above are specialized for coaxial connector-microstrip line conversion, and the electric field distribution is concentrated in the lower part of the coaxial connector. Therefore, a conversion loss occurs in a structure in which the electric field distribution viewed in a cross section is concentrated between the surface grounds, such as a coplanar line.
An object of the present invention made there is to provide a coaxial connector and a coaxial connector / planar line connection structure capable of reducing the gap of discontinuity in propagation mode at the connection surface of the coaxial connector and the planar line, particularly the coplanar line with the back ground. It is to be.

  For this purpose, the coaxial connector of the present invention includes an inner conductor, an inner conductor tip connected to the tip of the inner conductor and having a cross-sectional shape different from that of the inner conductor, and the outer conductor tip and the outer periphery of the inner conductor. And a dielectric provided between the inner conductor and the outer conductor, and an outer conductor provided on the side, a part in the length direction of the tip of the inner conductor, and the inner conductor and the outer conductor.

  Further, according to the present invention, the coaxial line and the planar line are connected via a line conversion part, the line conversion part is connected to the tip part of the coaxial line, and has an inner conductor tip part having a cross-sectional shape different from the inner conductor. An outer conductor provided on the outer peripheral side of the inner conductor tip, and a dielectric provided between the outer conductor and the inner conductor tip, wherein the dielectric is formed between the outer conductor and the inner conductor tip. A coaxial connector / planar line connection structure may be provided in which the impedance is provided so as to match the impedance of the coaxial line.

According to the present invention, by disposing the inner conductor tip portion having a different cross-sectional shape from the inner conductor of the coaxial line inside the outer conductor, the electric field distribution has a high electric field density in a predetermined plane direction of the inner conductor tip portion. A coaxial connector can be configured.
When such a coaxial connector is connected to a planar line, particularly a coplanar line with a back ground, the mode conversion between the electric field distribution in the coaxial line and the electric field distribution of the coplanar line with the back ground changes stepwise, resulting in conversion loss. Decrease.
Thereby, the gap of discontinuity in propagation mode is reduced, the frequency characteristic is improved, and application at a higher frequency becomes possible.

It is a perspective view of a coaxial connector and a coplanar track with a back ground in the first embodiment of the present invention. It is the top view and side view of a coaxial connector and a coplanar track with a back surface ground in the first embodiment of the present invention. It is a perspective view which shows an inner conductor and an inner conductor front-end | tip part. It is a figure which shows the cross-section electric field distribution of a coaxial line and a coplanar line with a back surface ground. It is the side view and perspective view which show the conventional coaxial connector and the coplanar track | line with a back surface ground. It is a figure which shows the electromagnetic field analysis result of the input reflection characteristic in the structure shown in the 1st Embodiment of this invention, and the conventional structure. It is a perspective view which shows the inner conductor and inner conductor front-end | tip part in the 2nd-4th embodiment of this invention.

  The best mode for carrying out a coaxial line according to the present invention will be described below with reference to the accompanying drawings. However, the present invention is not limited only to these examples.

(First embodiment)
FIG. 1 and FIG. 2 are schematic views showing a coaxial line-coplanar line conversion unit with a back surface ground according to a first embodiment of the present invention, and FIG. FIG. 2 is a side view and a plan view after connection.
As shown in FIG. 1 and FIG. 2, the coaxial line-coplanar substrate / line conversion structure with a coaxial line-back ground that is the first embodiment of the present invention is such that the coaxial connector 100 and the coplanar line 200 with the back ground are connected. It consists of

  In the coplanar line 200 with the back surface ground, the center conductor 203 and the surface ground 202 are provided on one surface side of the planar dielectric layer 201, and the back surface ground 204 is provided on the other surface side. The central conductor 203, the front surface ground 202, and the back surface ground 204 are all formed of a conductor.

On one surface side of the dielectric layer 201, the center conductor 203 and the front surface ground 202 are respectively formed continuously in the signal propagation direction in the back-grounded coplanar line 200. The center conductor 203 is arranged at the center in the width direction of the coplanar line 200 with the back ground. The surface ground 202 is disposed on both sides in the width direction of the central conductor 203 with a certain gap therebetween. Here, the gap between the center conductor 203 and the surface ground 202 is adjusted so that the characteristic impedance becomes a predetermined value Z, for example, 50Ω.
The back surface ground 204 is formed on the other surface side of the dielectric layer 201 so as to cover the entire surface.

  The front surface ground 202 and the back surface ground 204 are electrically connected to each other by through vias 205 penetrating through the dielectric layer 201 arranged in a large number at intervals in the propagation direction.

The coaxial connector 100 includes a coaxial line unit 110 and a propagation mode conversion unit 120.
The coaxial line portion 110 includes an inner conductor 111 having a circular cross section, an outer conductor 112 disposed on the outer peripheral side of the inner conductor 111 at an interval, and an outer conductor 112 to match impedances of the outer conductor 112 and the inner conductor 111. And an inner dielectric layer 113 provided between the inner conductor 111 and the inner conductor 111. The inner conductor 111 and the outer conductor 112 are made of a conductive material.

  Propagation mode conversion unit 120 is provided at the distal end portion of coaxial line portion 110 at the outer peripheral side of inner conductor distal end portion 121A, which is formed of the same material as inner conductor 111, continuously from inner conductor 111, and inner conductor distal end portion 121A. Outer conductor 122 and board mounting protrusion 124.

The inner conductor tip portion 121 </ b> A is formed continuously with the inner conductor 111 of the coaxial line portion 110 and has a cross-sectional shape different from that of the inner conductor 111.
The inner conductor tip 121A protrudes from the end surface X of the connector main body 101 in a block shape at least at a part of its length direction, and when the coaxial connector 100 is connected to the coplanar line 200 with the back surface ground, It is mounted in parallel on the central conductor 203 of the attached coplanar line 200.
As shown in FIG. 3, the inner conductor front end 121 </ b> A has a substantially semicircular cross-sectional shape in a direction orthogonal to the propagation direction in the present embodiment. Here, the inner conductor front end portion 121A having a substantially semicircular cross section has a circular arc surface 121a on the side facing the center conductor 203 of the back-grounded coplanar line 200, and the side away from the center conductor 203 is the surface of the center conductor 203. The plane 121b is substantially parallel to the plane.
The length of the inner conductor tip 121A inside the connector, that is, the dimension from the end surface X of the connector main body 101 to the switching position W between the inner conductor tip 121A and the inner conductor 111 is determined by the coaxial connector 100 and the coplanar line 200 with the back ground. It is preferable to have a length of λ / 10 or more with respect to the effective wavelength λ of the propagating signal. This is because a line length of λ / 10 or more is required to perform mode conversion at the inner conductor tip 121A.

  Further, in the inner conductor tip 121A, in the portion from the switching position W between the inner conductor tip 121A and the inner conductor 111 to the end surface X of the connector body 101, that is, the portion where the inner conductor tip 121A is located in the connector body 101. The outer conductor 122 is formed continuously with the outer conductor 112 of the coaxial line portion 110 on the outer peripheral portion of the inner conductor tip portion 121A, and the coaxial line portion 110 is interposed between the outer conductor 122 and the inner conductor tip portion 121A. The internal dielectric layer 123 is provided continuously to the internal dielectric layer 113.

In the part where the inner conductor tip 121A is located in the connector body 101, the characteristic impedance of the outer conductor 122 and the inner conductor tip 121A is the same as the characteristic impedance of the center conductor 203 and the surface ground 202 of the coplanar line 200 with the back ground. The outer diameter / inner diameter ratio of the outer conductor 122 and the inner conductor tip 121A, in other words, the thickness of the inner dielectric layer 123 is adjusted so that the value Z is, for example, 50Ω.
Further, in the coaxial line portion 110, the outer conductor 112 and the inner conductor 111 have a characteristic impedance such that the outer conductor 112 and the inner conductor 111 have the same value Z as the characteristic impedance of the center conductor 203 and the front ground 202 of the backplane ground coplanar line 200, for example, 50Ω. The outer diameter / inner diameter ratio of 112 and the inner conductor 111, in other words, the thickness of the inner dielectric layer 113 is adjusted.
At this time, when the relative dielectric constant of the dielectric forming the internal dielectric layers 113 and 122 is 1, in the coaxial line portion 110, the outer conductor 112 and the inner conductor 111 whose characteristic impedance is 50Ω as exemplified above are used. The outer diameter / inner diameter ratio is about 2.3. On the other hand, the outer diameter / inner diameter ratio of the outer conductor 122 and the inner conductor tip 121A is about 1.8 when the characteristic impedance at the inner conductor tip 121A is the same 50Ω. Impedance matching can be achieved by adjusting the outer diameter / inner diameter ratio of the outer conductor 112 and the inner conductor 111, and the outer conductor 122 and the inner conductor tip 121A. Here, the outer diameter / inner diameter ratio of the outer conductor 112 and the inner conductor 111 and the outer conductor 122 and the inner conductor tip 121A at an arbitrary dielectric constant can be easily obtained by multiplying this value by the square root of the dielectric constant.

  By the way, the switching position between the outer conductor 112 of the coaxial line portion 110 and the outer conductor 122 of the inner conductor tip portion 121A is the same position as the switching position W between the inner conductor tip portion 121A and the inner conductor 111, or the back surface thereof. The position is preferably shifted to the grounded coplanar line 200 side. This is to suppress the influence of local stray capacitance components at high frequencies due to the discontinuity of the shapes of the outer conductor 112 and the outer conductor 122, and the stray capacitance components can be offset by adjusting the gap. Increasing the width of the gap can be expected to improve the reflection characteristics at higher frequencies. However, on the other hand, low frequency matching becomes worse, so care must be taken when designing.

The board mounting protrusion 124 is formed of the same material as the outer conductor 122 continuously to the outer conductor 122. The board mounting protrusion 124 is provided so as to protrude from the end surface X of the connector main body 101 of the inner conductor tip 121A in a direction parallel to the inner conductor tip 121A. The board mounting protrusion 124 is separated from the inner conductor tip 121A by a predetermined gap. The board mounting protrusion 124 has a height equal to the thickness of the inner conductor tip 121A (the dimension in the direction perpendicular to the surface of the back-grounded coplanar line 200) and the end surface X of the connector main body 101 of the inner conductor tip 121A. Has a length equal to the projecting length.
The characteristic impedance upon mounting of the substrate mounting protrusion 124 and the surface ground 202 of the portion facing the substrate mounting protrusion 124 on the side of the coplanar line 200 with the back surface ground is the same value Z as described above, for example, 50Ω. As described above, the width and the distance from the center conductor 203 are adjusted.

  FIG. 4 shows an electric field distribution in a cross section orthogonal to the propagation direction of the back-grounded coplanar line 200 in the coaxial line portion 110 and the inner conductor tip portion 121A of the present invention. As shown in FIG. 4A, in the coaxial line portion 110, the electric field distribution is uniform over the entire circumference, whereas, as shown in FIG. 4B, in the inner conductor tip portion 121A having a substantially semicircular cross section. The electric field distribution has a lower density on the upper plane 121b side where the distance to the outer conductor 122 is farther, and the lateral coupling is strongest at the end points where the plane 121b and the arc surface 121a are joined.

  Therefore, mode conversion between the electric field distribution in the coaxial line portion 110 (FIG. 4A) and the electric field distribution in the coplanar line with the back ground (FIG. 4C) is stepwise at the inner conductor tip 121A. Change and reduce conversion loss.

  As a method of manufacturing the structure of the present embodiment, the tip of the cylindrical inner conductor 111 is polished into a semicircular shape before assembly in which the inner conductor 111 of the coaxial line portion 110 is fitted to the outer conductor 112. Thus, it is desirable to form the inner conductor tip portion 121A. Accordingly, the inner conductor tip 121A can be easily formed by machining the cylindrical inner conductor 111 such as cutting or polishing.

  Thereafter, the inner dielectric layers 113 and 122 are formed in the insertion portions opened at both ends of the outer conductor 112 provided on the outer peripheral portion of the inner conductor 111 having the inner conductor tip portion 121A formed at the distal end portion by processing. The connector main body 101 is molded by being housed and fixed via an insulating dielectric, and further by resin molding. The insulating dielectric forming the inner dielectric layers 113 and 122 is formed by a resin insulating member, and the outer diameter thereof is formed to be equal to or slightly smaller than the inner diameter of the outer conductors 112 and 121.

  As described above, the coaxial line portion 110 and the coplanar line 200 with the back surface ground are formed by forming the inner conductor tip portion 121A having a different cross-sectional shape from the inner conductor 111 at the tip portion of the inner conductor 111 of the coaxial line portion 110. The mode conversion between the two changes stepwise at the inner conductor tip 121A, and the conversion loss can be reduced. Such an inner conductor tip 121A is easy to manufacture and provides a sufficient characteristic improvement effect.

  In addition, the characteristic impedance of the outer conductor 122 and the inner conductor tip 121A in the propagation mode conversion unit 120, the characteristic impedance of the center conductor 203 and the front surface ground 202 of the coplanar line 200 with back surface ground, and the outer conductor 112 in the coaxial line unit 110. By forming the inner dielectric layers 113 and 122 so that the characteristic impedance of the inner conductor 111 is equal to that of the inner conductor 111, impedance matching between the coaxial connector 100 and the backplane grounded coplanar line 200 can be achieved.

  Here, since the effect of the structure shown in said 1st embodiment was verified, the result is shown. For comparison, a coaxial connector in which the diameters of the cylindrical inner conductor 111 and the outer conductor 112 are constant as shown in FIG. 5 was used. Here, the board mounting protrusion 124 is made equal to the diameter of the inner conductor 111, and the widths of the board mounting protrusion 124 and the back-grounded coplanar line 200 are adjusted so that the impedance during mounting is 50Ω. It was wider than the embodiment.

Then, the electromagnetic analysis results of the input reflection characteristics of the coaxial line-back ground ground coplanar line conversion structure were compared between the configuration in the first embodiment shown in FIGS. 1 and 2 and the configuration shown in FIG. The results are shown in FIG.
As shown in FIG. 6, it can be seen that the insertion loss is improved in the high frequency band from 55 GHz to 80 GHz.

(Second Embodiment)
In the first embodiment, the inner conductor tip 121A has a semicircular cross section, but hereinafter, the second to fourth embodiments show modifications thereof. In the following embodiments, the same reference numerals are given to the same components as those in the first embodiment, and the description thereof is omitted.
In the second embodiment, as shown in FIG. 7A, the thickness of the inner conductor tip 121B (the dimension in the direction orthogonal to the surface of the back-grounded coplanar line 200) is equal to the inner conductor of the coaxial connector 100. It is formed smaller than the radius of 111.
The diameter of the outer conductor 122 of the propagation mode conversion unit 120 is smaller than that of the first embodiment because impedance matching is achieved by the ratio with the diameter of the inner conductor tip 121B.

  The width of the gap of the propagation mode converter 120 is wider than that of the first embodiment by the increase of the stray capacitance. Other configurations are the same as those in the first embodiment.

  By processing as described above, the same effect as that of the first embodiment can be obtained, and discontinuity at the connection end due to the difference in height between the coaxial line portion 110 and the substrate line can be further reduced. Can do. Further, since the width of the chord portion of the inner conductor tip 121B is shorter than the diameter of the inner conductor 111, the width of the central conductor 203 to be mounted can be reduced, and the structure can be downsized.

  In addition, the width of the chord portion of the inner conductor tip 121B is further reduced so that the electric field distribution seen in the cross section is more concentrated in the lower part than in the lateral direction of the coaxial line part 110, thereby reducing the microstrip. The present invention can also be applied to connection with a planar line that is dominantly coupled to the back surface ground 204 such as a line.

(Third embodiment)
In the third embodiment, as shown in FIG. 7B, not only the upper part of the inner conductor tip part 121C but also the lower part has a planar part 120d.
The diameter of the outer conductor 122 of the inner conductor tip 121C is smaller than that of the first embodiment because impedance matching is performed by the ratio with the diameter of the inner conductor tip 121C.

  The width of the gap of the propagation mode converter 120 is wider than that of the first embodiment by the increase of the stray capacitance. Other configurations are the same as those in the first embodiment.

In the structures shown in the first and second embodiments, the electric field distribution remains in the lower portions of the inner conductor tip portions 121A and 120B in order to match the propagation mode with the coplanar line 200 with back ground.
On the other hand, in this embodiment, in order to improve the connection between the coplanar line having no back surface ground and the coaxial connector, which is mainly used in a semiconductor substrate or the like, electric field coupling in the lateral direction of the inner conductor tip 121C is performed. It has a stronger structure.

  With the configuration as described above, it is possible to make the electric field distribution in the coaxial line portion 110 coincide with that of the coplanar line as compared with the first embodiment. Further, the discontinuity at the connection end Y and the mounting workability are improved by making the contact surface of the planar line and the inner conductor tip 121C substantially coincide.

(Fourth embodiment)
In the first to third embodiments, the shape change between the inner conductor 111 and the inner conductor tip portions 121A, 121B, 121C is discontinuous.
Therefore, as shown in FIG. 7C, in the inner conductor tip portion 121D of the fourth embodiment, the tapered surface is formed so that the cross-sectional area of the shape change with the inner conductor 111 is gradually reduced. 125, which is continuous.
Correspondingly, the diameter of the outer conductor 122 of the inner conductor tip 121D is continuously reduced so that the characteristic impedance is maintained at 50Ω.

  By adopting the above-described configuration, discontinuity due to shape change can be eliminated and the generation of stray capacitance can be suppressed, so that the characteristics of the entire band can be further improved.

(Other embodiments)
The coaxial line-planar line conversion structure of the present invention is not limited to the above-described embodiments described with reference to the drawings, and various modifications can be considered within the technical scope thereof.
For example, in the inner dielectric layers 113 and 123 filled in the outer conductors 112 and 122, by appropriately selecting the relative dielectric constants of the inner conductor layers 113 and 123, the inner conductors 111 and It is also possible to keep constant the characteristic impedance with the inner conductor tip portions 121A, 121B, 121C, 121D. In this case, the inner dielectric layer 123 in the outer conductor 122 of the inner conductor tips 121A, 121B, 121C, and 121D has a relative dielectric constant that is about twice as high as that of the inner dielectric layer 113 filled in the outer conductor 112. It is necessary to have a rate.
Further, the planar line including the coplanar line with the back surface ground is not limited to a single substrate, but can be applied to a multilayer substrate.
In addition to this, as long as it does not depart from the gist of the present invention, the configuration described in the above embodiment can be selected or changed to another configuration as appropriate.

DESCRIPTION OF SYMBOLS 100 Coaxial connector 101 Connector main body 110 Coaxial line part 111 Inner conductor 112 Outer conductor 113 Inner dielectric layer 120 Propagation mode conversion part 121A, 121B, 121C, 121D Inner conductor front-end | tip 122 Outer conductor 123 Inner dielectric layer 124 Protrusion for board | substrate mounting Portion 125 Tapered surface 200 Coplanar line 201 with back surface ground Dielectric layer 202 Surface ground 203 Center conductor 204 Back surface ground 205 Through-via

Claims (14)

An inner conductor, an inner conductor connected to the tip of the inner conductor and having a cross-sectional shape different from that of the inner conductor; and an outer conductor provided on the outer periphery of the inner conductor tip and the inner conductor;
A part of the inner conductor tip in the length direction and a dielectric provided between the inner conductor and the outer conductor;
A coaxial connector comprising:   2. The coaxial connector according to claim 1, wherein the dielectric is provided so that an impedance between the inner conductor tip and the outer conductor matches an impedance between the inner conductor and the outer conductor. .   The dielectric provided between the inner conductor tip and the outer conductor has a higher dielectric constant than the dielectric provided between the inner conductor and the outer conductor. Item 3. The coaxial connector according to Item 2.   The thickness of the dielectric between the inner conductor tip and the outer conductor is smaller than the thickness of the dielectric between the inner conductor and the outer conductor. Coaxial connector.   The inner conductor tip is characterized in that the electric field distribution has a low density on the side facing the plane line to be connected and is strongly coupled in a direction parallel to the surface of the plane line. The coaxial connector according to any one of claims 1 to 4.   6. The coaxial connector according to claim 1, wherein a cross-sectional shape of the tip end portion of the inner conductor is set so as to concentrate an electric field in a direction orthogonal to the axial direction of the inner conductor. .   7. The inner conductor front end portion has a semicircular shape in a sectional view in which a side facing a plane line to be connected is convex and a side away from the plane line is a plane. The coaxial connector described in 1.   The thickness of the said inner conductor front-end | tip part in the direction orthogonal to the surface of the planar line used as connection object is made less than the radius of the said inner conductor, The one in any one of Claim 1 to 6 characterized by the above-mentioned. Coaxial connector.   The said inner conductor front-end | tip part is formed in the side facing the plane track | line used as a connection object, and the side spaced apart from the said plane track | line, respectively, and is formed by the plane. Coaxial connector.   10. The coaxial connector according to claim 1, wherein the coaxial connector has a tapered shape in which a cross-sectional area gradually decreases from the inner conductor toward the tip of the inner conductor.   The length of the inner conductor tip in the axial direction inside the outer conductor is λ / 10 or more with respect to an effective wavelength λ of a signal propagated through the coaxial connector. The coaxial connector according to any one of the above. A coaxial line and a planar line are connected via a line conversion unit,
The line converter is
An inner conductor tip connected to the tip of the coaxial line and having a cross-sectional shape different from that of the inner conductor; and an outer conductor provided on the outer peripheral side of the inner conductor tip;
A dielectric provided between the outer conductor and the inner conductor tip,
The coaxial connector / planar line connection structure is characterized in that the dielectric is provided so that an impedance between the outer conductor and the tip of the inner conductor matches an impedance of the coaxial line.   13. The coaxial connector / planar line according to claim 12, wherein the inner conductor distal end protrudes from a coaxial connector provided at an end of the coaxial line and is attached to the conductor of the planar line. Connection structure.   14. The coaxial according to claim 12, wherein the inner conductor tip has a cross-sectional shape set so as to concentrate an electric field in a direction orthogonal to the axial direction of the inner conductor of the coaxial line. Connector / plane line connection structure.

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