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 field of microwave technology, in particular to a broadband transition structure from a coaxial cable to a coplanar waveguide.

Background technique

With the development of 5G and millimeter wave technology, semiconductor devices continue to develop towards high frequency and miniaturization. The above-mentioned trend also makes the performance requirements of the thin film probe card test system continue to increase, and ultra-wideband, low loss, and high isolation have become the main indicators of the thin film probe card test system. As an important part connecting thin film probes and test equipment, the PCB adapter board realized by broadband transition structure directly affects the quality of the entire thin film probe card test system.

The traditional PCB adapter board generally uses a single coplanar waveguide that transmits quasi-transverse electromagnetic waves to complete the main signal transmission task, and realizes the signal transfer between the test instrument and the thin film probe card by matching SMA connectors. However, the use of the above-mentioned PCB adapter board has problems such as narrow bandwidth and high loss, so it is mostly suitable for test scenarios below the 20GHz frequency band. In addition, the semi-open coplanar waveguide transmission line structure has problems such as low isolation and signal crosstalk in a multi-chip test environment, which affects the accurate characterization of chip performance.

Contents of the invention

In view of the related technical problems of narrow bandwidth, high loss, and low isolation in the above-mentioned traditional PCB adapter board, the purpose of the present invention is to provide a broadband transition structure capable of realizing broadband, low loss, and high isolation.

In order to achieve the above object, the present invention provides the following technical solutions: a broadband transition structure from a coaxial cable to a coplanar waveguide, including a coplanar waveguide transmission line and a coaxial cable, and the coplanar waveguide transmission line includes layers of A metal layer and a dielectric layer, the metal layer is formed with a central conductive strip and ground conductive strips distributed on both sides of the central conductive strip, and the coaxial cable includes an outer conductor, an inner conductor, and a and the intermediate dielectric layer between the inner conductor, the coplanar waveguide transmission line is provided with a groove as deep as the dielectric layer, one end of the coaxial cable is embedded in the groove, and the The inner conductor at the end protrudes out of the groove and overlaps and is electrically connected to the central conducting strip, and the ground conducting strip is electrically connected to the outer conductor.

This application uses a semi-rigid cable as the main transmission channel of the signal, uses the extension inner conductor to cascade with the central conduction band of the coplanar waveguide transmission line, and controls the relative position of the semi-rigid cable and the coplanar waveguide transmission line through the groove. , Low loss, high isolation performance transition technology.

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

In one embodiment of the present application, the width of the central conductive strip is equal to the width of the ground conductive strip.

In one embodiment of the present application, the groove is collinear with the central axis of the central conductive strip.

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

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

In one embodiment of the present application, the groove depth 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, there are several one-to-one correspondences between the coplanar waveguide transmission lines, the coaxial cables, and the grooves, and the central conductive strips of each of the coplanar waveguide transmission lines are arranged in parallel along the left and right directions. cloth, each of the coaxial cables and the grooves are respectively arranged along the central axis of the corresponding central conductive band.

In one embodiment of the present application, two adjacent coaxial cables share one grounding conductor strip.

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 connected to the central conduction band.

In one embodiment of the present application, the through holes are arranged in multiple rows along the direction of the central conductive strip.

Compared with the prior art, the broadband transition structure provided by the technical solution of the present invention uses a semi-rigid coaxial cable to complete the main signal transmission task, and completes the external output of the signal through the coplanar waveguide transmission line. The semi-rigid cable has the characteristics of broadband, low loss and phase stability, which meets the performance requirements of the high-frequency probe card test system. At the same time, its closed structure for transmitting transverse electromagnetic wave mode provides high performance for the multi-chip probe card test system Performance Guarantee of Isolation. In addition, the technical solution of the present invention provides a good welding environment through the design of the extension part, so that the inner conductor and the central conductive band maintain good and low-loss electrical contact.

Description of drawings

Fig. 1 is the three-dimensional schematic view of the broadband transition structure provided by the present invention;

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

Fig. 3 is the return loss and insertion loss simulation figure of embodiment 1 provided by the present invention;

FIG. 4 is a simulation diagram of adjacent channel isolation in Embodiment 1 provided by the present invention.

in:

1. Top layer grounding strip; 2. Dielectric layer; 3. Bottom grounding strip; 4. Metallized through hole;

5. Central conduction band; 6. Outer conductor; 7. Inner conductor; 71. Extension; 8. Intermediate dielectric layer; 9. Groove; 10. Coplanar waveguide transmission line; 20. Semi-rigid cable; 21. Horizontal section.

Implementation

In order to describe the technical content, structural features, goals and effects of the invention in detail, the technical solutions in the embodiments of the application will be described below in conjunction with the accompanying drawings in the embodiments of the application. Obviously, the described embodiments are only the present invention. Claim some of the examples, not all of them. In the following description, for purposes of explanation, numerous specific details are set forth to provide detailed illustrations of various exemplary embodiments, or modes, of implementing 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 differ, but are not necessarily exhaustive. For example, the specific shape, configuration, and characteristics of an exemplary embodiment may be used or implemented in another exemplary embodiment without departing from the inventive concept.

In addition, in this application, terms such as "under", "under", "below", "below", "above", "on", "on ”, “higher”, “side” (for example, as in “side wall”), etc., to describe the relationship of one element to another (other) element as shown in the drawings . 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 "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary term "below" can encompass both an orientation of above and below. In addition, the device may be otherwise positioned (eg, rotated 90 degrees or at other orientations), and such 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, low loss and high isolation, and is especially suitable for a probe card test system. Hereinafter, a semi-rigid coaxial cable is used as an example to illustrate the content of the present invention. Referring to Figure 1-2, the broadband transition structure includes coplanar waveguide transmission lines and semi-rigid cables. Wherein, Fig. 1 illustrates the broadband transition structure provided by the present invention in the form of a dual-channel structure, but readers should understand that the total number of channels of the broadband transition structure can be adaptively changed according to actual needs, that is, the specific number of channels It does not limit the protection scope of the present invention. Meanwhile, in order to avoid redundant description, a single channel is used as an example to describe the broadband transition structure below.

Because of its small size, light weight and planar structure, coplanar waveguide transmission lines are convenient for linear polarization, circular polarization, dual polarization and multi-band operation, so they are widely used in modern wireless communications. The present invention utilizes the above-mentioned advantages of the coplanar waveguide, and applies it as a signal output part in a broadband transition structure, so as to facilitate the connection of external equipment to the broadband transition structure.

Specifically, the coplanar waveguide transmission line can be a metal-backed coplanar waveguide or an ordinary PCB board, which has at least a dielectric layer and a metal layer capable of forming a central conduction band and a grounding conduction band. In the embodiment shown in the figure, the coplanar waveguide transmission line includes a central conductive strip 5 at the top, several top-level grounded conductive strips 1 arranged coplanarly with the central conductive strip 5 and located on the left and right sides of the central conductive strip 5, and a plurality of top ground conductive strips 1 located at the bottom The bottom ground conductive strip 3 and the dielectric layer 2 between the top ground conductive strip 1 and the bottom ground conductive strip 3 .

The central conductive strip 5 and the pair of top layer ground conductive strips 1 both extend back and forth horizontally. The coplanar waveguide transmission line can also be provided with a plurality of metallized through-holes 4 penetrating in the vertical direction, and each top-layer grounded conductive strip 1 and the bottom-layer grounded conductive strip 3 are electrically connected through several metallized through-holes 4 . Further, the above-mentioned plurality of metallized through holes 4 are arranged in multiple rows side by side, and each row of metallized through holes 4 extends forward and backward and is close to the central conductive strip 5 .

In one embodiment, the width of the central conductive strip 5 may be equal to the width of the top ground conductive strip 1 . However, in the embodiment shown in Figures 1 and 2, due to the structure of the twin-axial coaxial cable, the two coaxial cables can share a top-layer grounding conductor, so the width of the top-layer grounding conductor is larger than that of the center conductor width.

The coaxial cable has the characteristics of high bandwidth, low loss and phase stability in terms of electrical performance, which meets the performance requirements of the probe card test system for signal transmission. The present invention utilizes the above-mentioned advantages of the coaxial cable, and applies it as a main electromagnetic wave transmission component in a broadband transition structure. Specifically, a semi-rigid coaxial cable is used in this embodiment, and the semi-rigid cable includes an outer conductor 6 , an inner conductor 7 inside the outer conductor 6 , and an intermediate dielectric layer 8 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 strip 5 in the front-rear direction. The notch of the groove 9 emerges from the top of the coplanar waveguide transmission line. The end of the semi-rigid cable forms a horizontal section 21 extending horizontally, and the lower part of the horizontal section 21 is embedded in the groove 9 . Part of the inner conductor 7 in the horizontal section protrudes outward relative to the outer conductor 6 and the intermediate dielectric layer 8 at the same time (that is, it protrudes forward from the horizontal section, and changing the length of the protrusion can change the working frequency, thereby meeting the needs of various frequency designs. ) and form an extension portion 71 directly in contact with the central conduction strip 5 , the extension portion 71 overlaps with the central conduction strip 5 and forms a stable electrical connection by welding. Understandably, the exposed extension portion 71 provides a good welding space, thereby reducing the probability of poor welding. In some embodiments, the extension part can also be fixedly connected to the central guide strip by various methods such as bonding, hot-melt pressure bonding, fastener connection and the like.

The central guide strip 5 is aligned with the central axis of the corresponding groove 9 in the left-right direction. Further, in order to keep the axis of the central conductive strip 5 and the corresponding inner conductor 7 collinear and to ensure stable and continuous contact between the extension and the central conductive strip 5, the groove 9 has a specific groove depth and the groove 9 The inner wall surface of the inner wall extends horizontally along the front-to-back direction. The semi-rigid cable has a total wall thickness formed by the outer conductor 6 and the intermediate dielectric layer 8 (that is, the radial distance between the inner surface of the intermediate dielectric layer 8 and the outer surface of the outer conductor 6), the total wall thickness is the semi-rigid The cable is placed on the horizontal plane at the height of the lower boundary of the inner conductor 7 relative to the horizontal plane. The groove depth of the groove 9 is configured approximately the same as the above-mentioned overall wall thickness, regardless of tolerances. It can be understood that when the horizontal section of the inner conductor 7 is placed in the groove 9, the horizontal section is limited by the inner wall surface of the groove 9 and extends along the front-to-back direction, so that the axis of the inner conductor 7 in the horizontal section is aligned with the central conductive strip 5 The axes are parallel; the relative height of the extension of the inner conductor 7 is limited by the groove 9, so that the extension and the central conductive strip 5 maintain continuous contact. The above settings can effectively avoid the abrupt change in capacitance of the epitaxial part and the central conduction band 5 due to the relative inclination, thereby ensuring the high-frequency impedance matching of the broadband transition structure, and finally obtaining ultra-wideband, low-loss and high-isolation signal transmission performance.

Still further, the inner wall surface of the groove 9 may be constructed as a curved surface conforming to the outer contour of the outer conductor 6 of the semi-rigid cable. In other embodiments, the cross section of the groove 9 may also be rectangular, polygonal or shaped.

In one embodiment, the width of the groove can be slightly smaller than the diameter of the coaxial cable, and the width of the groove is just enough to ensure that the lower surface of the inner conductor and the center of the inner conductor are maintained when the coaxial cable is in the groove. The upper surface of the conduction strip is flush.

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

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

When the broadband transition structure is in use, the signal propagates along the inner conductor 7 in the transverse electromagnetic wave mode; thereafter, the transition from the transverse electromagnetic wave mode to the quasi-transverse electromagnetic wave mode is completed at the horizontal section of the inner conductor 7, and the inner conductor and the central conduction band The transition is completed at the contact point; finally, the coplanar waveguide transmission line completes the signal transmission in the quasi-transverse electromagnetic wave mode. In the probe card test system, the signal enters the semi-rigid cable from the testing machine, is transmitted to the coplanar waveguide through the inner conductor connected with the central conduction tape, and finally enters the object under test through the film probe connected to the coplanar waveguide. The present invention is a broadband low-loss transition structure, which is suitable for any suitable signal transmission scene requiring low loss, broadband and high isolation performance.

In order to verify the performance of the broadband transition structure provided by the present invention, the present invention provides the following implementation 1 and the performance simulation diagram of this embodiment (see FIGS. 3-4 ).

Embodiment 1: A dual-channel broadband transition structure as shown in Figure 1, the dielectric layer of the transition structure adopts MEGTRON6R5775G substrate (dielectric constant is 3.71, loss angle is 0.002), the intermediate dielectric layer adopts polytetrafluoroethylene, and the intermediate dielectric The length of the layer is 65mm, the length of the extension of the inner conductor is 0.5mm, and the distance between adjacent channels (that is, the distance between two central conduction bands) is 1.5mm. The central guide strip, outer conductor, and inner conductor are made of ordinary copper material, which is stretched to make a semi-rigid cable with a diameter of 0.8mm. The PCB is made of metal copper material that has undergone anti-oxidation treatment.

Fig. 3 is the schematic diagram of the return loss and insertion loss of the above-mentioned embodiment 1. It can be seen from the figure that the insertion loss of the broadband transition structure of the above-mentioned embodiment 1 decreases with the increase of the frequency in the range of 0-40 GHz, but always Better than 1.8dB; the matching of the broadband transition structure of the above-mentioned embodiment 1 is a V-shaped trend in the range of 0-40GHz passband with frequency, and its lowest value occurs at about 18GHz, which is -44dB, and its highest value occurs at Around 40GHz, it is -22dB, that is, the matching of the broadband transition structure is always better than -22dB in the passband in the range of 0-40GHz.

Fig. 4 is the channel isolation response simulation diagram of the above-mentioned embodiment 1. It can be seen from the figure that the channel isolation of the broadband transition structure of the above-mentioned embodiment 1 rises with the increase of the frequency in the range of 0-8GHz passband, and in There is a slight fluctuation in the 8-40GHz passband but maintained below -30dB, that is, the channel isolation of the transition structure in the 0-40GHz passband is always better than -30dB.

The basic principles, main features and advantages of the present invention have been shown and described above. Those skilled in the industry should understand that the present invention is not limited by the above-mentioned embodiments. What are described in the above-mentioned embodiments and the description only illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have For various changes and improvements, the protection scope of the present invention is defined by the appended claims, description 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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