CN116315554A - Broadband transition structure from coaxial cable to coplanar waveguide - Google Patents

Abstract

The invention relates to the technical field of microwaves, in particular to a broadband transition structure from a coaxial cable to a coplanar waveguide, which comprises a coplanar waveguide transmission line and a coaxial cable, wherein the coplanar waveguide transmission line comprises a metal layer and a dielectric layer which are laminated from top to bottom, a central conduction band and grounding conduction bands distributed on two sides of the central conduction band are formed on the metal layer, the coaxial cable comprises an outer conductor, an inner conductor and an intermediate dielectric layer positioned between the outer conductor and the inner conductor, a groove which is deep as the dielectric layer is formed on the coplanar waveguide transmission line, one end part of the coaxial cable is embedded in the groove, the inner conductor of the end part extends out of the groove and is mutually overlapped and electrically connected with the central conduction band, and the grounding conduction band is electrically connected with the outer conductor. The broadband transition structure has the signal transmission performance of ultra-broadband, low loss and high isolation, and is suitable for a high-frequency-oriented probe card test system.

Description

Broadband transition structure from coaxial cable to coplanar waveguide

Technical Field

The invention relates to the technical field of microwaves, in particular to a broadband transition structure from a coaxial cable to a coplanar waveguide.

Background

With the development of 5G and millimeter wave technologies, semiconductor devices are continuously developed toward high frequency and miniaturization. The trend also makes the performance requirements of the thin film probe card testing system continuously improved, and ultra-wideband, low loss, high isolation and the like become main indexes of the thin film probe card testing system. The PCB adapter plate realized by adopting the broadband transition structure is used as an important component for connecting the film probe and the testing equipment, and the quality of the whole film probe card testing system is directly influenced by the performance of the PCB adapter plate.

The traditional PCB adapter plate generally adopts a single coplanar waveguide for transmitting quasi-transverse electromagnetic waves to complete main signal transmission tasks, and realizes signal transfer between a test instrument and a thin film probe card in a mode of matching with an SMA connector. However, the PCB adapter plate has the problems of narrow bandwidth, high loss and the like, so that the PCB adapter plate is mostly applicable to test scenes below 20GHz frequency bands. In addition, the semi-open coplanar waveguide transmission line structure has the problems of low isolation, signal crosstalk and the like in a multi-chip test environment, and the accurate representation of chip performance is affected.

Disclosure of Invention

Aiming at the related technical problems of narrow broadband, high loss, low isolation and the like of the traditional PCB adapter plate, the invention aims to provide a broadband transition structure capable of realizing broadband, low loss and high isolation.

In order to achieve the above purpose, the present invention provides the following technical solutions: the utility model provides a coaxial cable to broadband transition structure of coplanar waveguide, includes coplanar waveguide transmission line and coaxial cable, the coplanar waveguide transmission line includes metal level and the dielectric layer of from the top down range upon range of, the metal level on be formed with central conduction band and the earthing conduction band of distributing in central conduction band both sides, coaxial cable include outer conductor, inner conductor and be located outer conductor with intermediate dielectric layer between the inner conductor, the coplanar waveguide transmission line on seted up the recess down to the dielectric layer, coaxial cable's one end embedding in the recess, just the inner conductor of tip stretch out the recess outside with central conduction band overlap joint each other and electric connection, earthing conduction band with outer conductor electric connection.

The semi-rigid cable is adopted as a main transmission channel of signals, the epitaxial inner conductor is used for cascading with the central conduction band of the coplanar waveguide transmission line, the relative positions of the semi-rigid cable and the coplanar waveguide transmission line are controlled through the grooves, and the semi-rigid cable and the coplanar waveguide transmission line are transition technology with broadband, low loss and high isolation performance.

In one embodiment of the present application, the end portion has a horizontal section, and a lower portion of the horizontal section is embedded in the groove.

In one embodiment of the present application, the width of the center conduction band is equal to the width of the ground conduction band.

In one embodiment of the present application, the groove is collinear with the central axis of the central conduction band.

In one embodiment of the present application, the inner conductor is collinear with a central axis of the central conduction band.

In one embodiment of the present application, the groove width of the groove is smaller than the diameter of the coaxial cable.

In one embodiment of the present application, the groove depth of the groove is equal to the sum of the wall thicknesses of the outer conductor and the intermediate dielectric layer.

In one embodiment of the present application, the coaxial cable and the groove include a plurality of coplanar waveguide transmission lines, the coaxial cables and the grooves, where the central guide strips of the coplanar waveguide transmission lines are arranged in parallel along the left-right direction, and the coaxial cables and the grooves are respectively arranged along the central axis of the corresponding central guide strip.

In one embodiment of the present application, two adjacent coaxial cables share one ground strap.

In one embodiment of the present application, the coplanar waveguide transmission line is provided with a plurality of through holes penetrating through the metal layer and the dielectric layer, and the through holes are not communicated with the central conduction band.

In one embodiment of the present application, the vias are arranged in a plurality of rows along the central conduction band direction.

Compared with the prior art, the broadband transition structure provided by the technical scheme of the invention adopts the semi-rigid coaxial cable to complete main signal transmission tasks, and the signal is output outwards through the coplanar waveguide transmission line. The semi-rigid cable has the characteristics of broadband, low loss and stable phase, meets the performance requirements of a high-frequency-oriented probe card test system, and simultaneously, the semi-rigid cable transmits a closed structure of a transverse electromagnetic wave mode to provide high-isolation performance guarantee for the multi-chip probe card test system. In addition, the technical scheme of the invention provides a good welding environment through the design of the extension part, so that the inner conductor and the central conduction band keep good and low-loss electric contact.

Drawings

FIG. 1 is a schematic perspective view of a broadband transition structure according to the present invention;

FIG. 2 is a schematic cross-sectional view of the broadband transition structure shown in FIG. 1;

FIG. 3 is a simulation graph of return loss and insertion loss of example 1 provided by the present invention;

fig. 4 is a simulation diagram of the isolation between adjacent channels according to embodiment 1 of the present invention.

Wherein:

1. the top layer is grounded to the conduction band; 2. a dielectric layer; 3. the bottom layer is grounded to the conduction band; 4. metallizing the through holes;

5. a central conduction band; 6. an outer conductor; 7. an inner conductor; 71. an extension part; 8. an intermediate dielectric layer; 9. a groove; 10. a coplanar waveguide transmission line; 20. a semi-rigid cable; 21. a horizontal segment.

Description of the embodiments

In order to describe the technical content, constructional features, objects and effects of the invention in detail, the technical solutions of the embodiments of the present application will be described below with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are only some embodiments of the present application, not all embodiments. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a detailed description of various exemplary embodiments or modes of practice of the invention. However, various exemplary embodiments may be practiced without these specific details or with one or more equivalent arrangements. Furthermore, the various exemplary embodiments may be different, but are not necessarily exclusive. For example, the specific shapes, configurations, and characteristics of the exemplary embodiments may be used or implemented in another exemplary embodiment without departing from the inventive concept.

Furthermore, spatially relative terms such as "under … …," "under … …," "under … …," "lower," "above … …," "upper," "above … …," "higher," "side" (e.g., as in "sidewall") and the like are used herein to describe one element's relationship to another element(s) as illustrated in the figures. Spatially relative terms are intended to encompass different orientations of the device in use, operation and/or manufacture in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "under" or "beneath" other elements or features would then be oriented "over" the other elements or features. Thus, the exemplary term "below … …" may include both upper and lower orientations. Furthermore, the device may be otherwise positioned (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

The invention provides a broadband transition structure from a coaxial cable to a coplanar waveguide transmission line, which can realize electromagnetic wave propagation with high frequency, broadband, bottom loss and high isolation, and is particularly suitable for a probe card test system. Hereinafter, the content of the present invention is illustrated with a semi-rigid coaxial cable. Referring to fig. 1-2, the broadband transition structure includes a coplanar waveguide transmission line and a semi-rigid cable. The broadband transition structure provided by the present invention is illustrated in fig. 1 in a dual-channel structure, but readers will understand that the total number of channels of the broadband transition structure can be adaptively changed according to actual requirements, i.e. the specific number of channels does not limit the protection scope of the present invention. Meanwhile, in order to avoid redundancy, a broadband transition structure is described below using a single channel as an example.

The coplanar waveguide transmission line is convenient for linear polarization, circular polarization, dual polarization and multi-band operation due to the characteristics of small volume, light weight and planar structure, so that the coplanar waveguide transmission line is widely applied to modern wireless communication. The present invention utilizes the above-mentioned advantages of coplanar waveguide, and uses it as signal output portion in the broadband transition structure so as to make external equipment butt-joint the broadband transition structure.

Specifically, the coplanar waveguide transmission line can be a metallized coplanar waveguide or a common PCB, and at least comprises a dielectric layer and a metal layer capable of forming a central conduction band and a grounding conduction band. In the illustrated embodiment, the coplanar waveguide transmission line includes a central conduction band 5 at the top, a plurality of top-layer ground conduction bands 1 disposed coplanar with the central conduction band 5 and disposed on the left and right sides of the central conduction band 5, a bottom-layer ground conduction band 3 disposed at the bottom, and a dielectric layer 2 disposed between the top-layer ground conduction band 1 and the bottom-layer ground conduction band 3.

The central conduction band 5 and the pair of top-layer ground conduction bands 1 extend horizontally back and forth. The coplanar waveguide transmission line can be further provided with a plurality of metallized through holes 4 penetrating in the vertical direction, and each top-layer grounding conduction band 1 and the bottom-layer grounding conduction band 3 are electrically connected through a plurality of metallized through holes 4. Further, the plurality of metallized through holes 4 are arranged in a plurality of rows arranged side by side, and each row of metallized through holes 4 extends back and forth and is close to the central conduction band 5.

In one embodiment, the width of the center conduction band 5 may be equal to the width of the top layer ground conduction band 1. However, in the embodiment shown in fig. 1 and 2, two coaxial cables may share a top ground strap due to the dual-axis coaxial cable structure, so that the width of the top ground strap is greater than the width of the center strap.

The coaxial cable has the characteristics of high bandwidth, low loss and stable phase in electrical performance, and meets the performance requirements of the probe card test system on signal transmission. The invention utilizes the advantages of the coaxial cable and uses the coaxial cable as a main electromagnetic wave transmission component in a broadband transition structure. In particular, a semi-rigid coaxial cable is employed in this embodiment, the semi-rigid cable comprising an outer conductor 6, an inner conductor 7 located within the outer conductor 6, and an intermediate dielectric layer 8 located between the outer conductor 6 and the inner conductor 7.

The coplanar waveguide transmission line is provided with a groove 9 aligned with the central conduction band 5 in the front-rear direction. The notch of the groove 9 is exposed from the top of the coplanar waveguide transmission line. The end of the semi-rigid cable forms a horizontally extending horizontal section 21, the lower part of the horizontal section 21 being embedded in the recess 9. The inner conductor 7 of the horizontal section is partially protruded outwards relative to the outer conductor 6 and the middle dielectric layer 8 (i.e. protruded forwards from the horizontal section, the working frequency can be changed by changing the protruded length, and then the requirements of various frequency designs are met), and an extension part 71 in direct contact with the central conduction band 5 is formed, and the extension part 71 and the central conduction band 5 are mutually overlapped and form stable electric connection through welding. It can be appreciated that the exposed extension 71 provides a good welding space, thereby reducing the probability of poor welding. In some embodiments, the outer extension may also be fixedly attached to the central conduction band by various means such as bonding, hot melt lamination, fastener attachment, and the like.

The central conduction band 5 is aligned with the central axis of the corresponding groove 9 in the left-right direction. Further, in order to keep the center conduction band 5 collinear with the axis of the corresponding inner conductor 7 and to ensure that the outer extension and the center conduction band 5 form stable and continuous contact, the groove 9 has a certain groove depth and the inner wall surface of the groove 9 extends horizontally in the front-rear direction. The semi-rigid cable has a total wall thickness (i.e. the radial distance between the inner surface of the intermediate dielectric layer 8 and the outer surface of the outer conductor 6) formed by the outer conductor 6 and the intermediate dielectric layer 8, i.e. the height of the semi-rigid cable relative to the horizontal plane of the lower boundary of the inner conductor 7 on the horizontal plane. The groove depth of the groove 9 is configured to be substantially the same as the total wall thickness described above, regardless of the error. As will be appreciated, when the horizontal segment of the inner conductor 7 is placed in the groove 9, the horizontal segment extends in the front-rear direction as defined by the inner wall surface of the groove 9 such that the axis of the horizontal segment inner conductor 7 is parallel to the axis of the center conduction band 5; the relative height of the outer extension of the inner conductor 7 is defined by the recess 9 such that the outer extension is in continuous contact with the central conduction band 5. The arrangement can effectively avoid the abrupt change of capacitance caused by the relative inclination of the epitaxial part and the central conduction band 5, thereby ensuring the high-frequency impedance matching of the broadband transition structure and finally obtaining the signal transmission performance of ultra-broadband, low loss and high isolation.

Still further, the inner wall surface of the groove 9 may be configured as a curved surface of which the layer matches the outer contour of the outer conductor 6 of the semi-rigid cable. In other embodiments the cross-section of the recess 9 may also be rectangular, polygonal or profiled.

In one embodiment, the groove width of the groove may also be slightly smaller than the diameter of the coaxial cable, and the groove width may be sized to just ensure that the lower surface of the inner conductor is flush with the upper surface of the center conduction band when the coaxial cable is positioned within the groove.

In one embodiment, the intermediate dielectric layer of the coaxial cable is made of a material having a high temperature resistance of about 200 degrees.

When the horizontal section of the semi-rigid cable is partially placed into the groove 9, the outer conductor 6 of the horizontal section is in contact with the plurality of top-layer grounding conduction bands 1 on the coplanar waveguide transmission line. The outer conductor 6 of the semi-rigid cable has excellent battery shielding effect, and the isolation of each channel in the broadband transition structure can be greatly improved through the electric connection between the outer conductor 6 and the grounding conduction band.

When the broadband transition structure is in use, signals propagate along the inner conductor 7 in a transverse electromagnetic mode; thereafter, transition from the transverse electromagnetic mode to the quasi-transverse electromagnetic mode is completed at the horizontal section of the inner conductor 7, and transition is completed at the contact of the inner conductor with the center conduction band; and finally, the coplanar waveguide transmission line completes signal transmission in a quasi-transverse electromagnetic wave mode. In the probe card test system, signals enter a semi-rigid cable from a tester, are transmitted to a coplanar waveguide through an inner conductor connected with a central conduction band, and finally enter an object to be tested through a thin film probe connected with the coplanar waveguide. The invention relates to a broadband low-loss transition structure which is suitable for any suitable signal transmission scene requiring low loss, broadband and high isolation performance.

To verify the performance of the broadband transition structure provided by the present invention, the present invention provides the following performance simulation graphs of example 1 and this example (see fig. 3-4).

Example 1: as shown in FIG. 1, in the dual-channel broadband transition structure, a dielectric layer of the transition structure adopts a MEGTRON 6R 5775G substrate (dielectric constant is 3.71, loss angle is 0.002), a middle dielectric layer adopts polytetrafluoroethylene, the length of the middle dielectric layer is 65mm, the length of an epitaxial part of an inner conductor is 0.5mm, and the distance between adjacent channels (namely, the distance between two central conduction bands) is 1.5mm. The central conduction band, the outer conductor and the inner conductor are made of common copper materials, the semi-rigid cable with the diameter of 0.8mm is manufactured through stretching treatment, and the PCB is made of metal copper materials through oxidation prevention treatment.

FIG. 3 is a schematic diagram of the return loss and the insertion loss of the foregoing embodiment 1, and it is understood from the diagram that the insertion loss of the broadband transition structure of the foregoing embodiment 1 decreases with the increase of frequency in the range of 0-40GHz, but is always better than 1.8dB; the matching of the broadband transition structure of the above embodiment 1 takes a V-shaped trend along with the frequency in the range of 0-40GHz passband, the lowest value of which appears at about 18GHz and is-44 dB, and the highest value of which appears at about 40GHz and is-22 dB, i.e., the matching of the broadband transition structure is always better than-22 dB in the range of 0-40GHz passband.

Fig. 4 is a simulation diagram of the channel isolation response of the above-mentioned embodiment 1, and it is clear from the figure that the channel isolation of the broadband transition structure of the above-mentioned embodiment 1 increases with the increase of frequency in the range of 0-8GHz passband, and slightly fluctuates in the range of 8-40GHz passband but is maintained below-30 dB, i.e., the channel isolation of the transition structure in the range of 0-40GHz is always better than-30 dB.

The foregoing has shown and described the basic principles, principal features and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the foregoing embodiments, which have been described in the foregoing embodiments and description merely illustrates the principles of the invention, and various changes and modifications may be made therein without departing from the spirit and scope of the invention, the scope of which is defined in the appended claims, specification and their equivalents.

Claims (10)

1. A broadband transition structure from a coaxial cable to a coplanar waveguide, comprising: the coaxial cable comprises an outer conductor, an inner conductor and an intermediate medium layer positioned between the outer conductor and the inner conductor, a groove reaching the medium layer is formed in the coplanar waveguide transmission line, one end part of the coaxial cable is embedded in the groove, the inner conductor of the end part extends out of the groove to be mutually overlapped and electrically connected with the central conduction band, and the grounding conduction band is electrically connected with the outer conductor.

2. The broadband transition structure according to claim 1, wherein said end portion has a horizontal section, a lower portion of said horizontal section being embedded in said recess.

3. The broadband transition structure of claim 1, wherein a width of the center conduction band is equal to a width of the ground conduction band.

4. The broadband transition structure of claim 1, wherein said grooves are collinear with said central conduction band and a central axis of the inner conductor.

5. The broadband transition structure according to claim 1, wherein the groove width of said groove is smaller than the diameter of said coaxial cable.

6. The broadband transition structure of claim 1, wherein a groove depth of said groove is equal to a sum of wall thicknesses of said outer conductor and said intermediate dielectric layer.

7. The broadband transition structure according to claim 1, comprising a plurality of coplanar waveguide transmission lines, coaxial cables and grooves in one-to-one correspondence, wherein the central guide strips of the coplanar waveguide transmission lines are arranged in parallel in the left-right direction, and the coaxial cables and grooves are respectively arranged along the central axes of the corresponding central guide strips.

8. The broadband transition structure according to claim 7, wherein two adjacent coaxial cables share one of said ground tapes.

9. The broadband transition structure according to claim 1, wherein a plurality of through holes penetrating through the metal layer and the dielectric layer are formed on the coplanar waveguide transmission line, and the through holes are not communicated with the central conduction band.

10. The broadband transition structure of claim 9, wherein said vias are arranged in a plurality of rows along said central conduction band direction.

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