Coplanar Waveguide Step Structure for Wi-Fi 6 Impedance Matching
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Solution Overview
Problem
Existing coplanar waveguide transmission lines for Wi-Fi 6 applications fail to achieve adequate impedance matching in the 2.4 GHz to 2.5 GHz and 5 GHz to 6 GHz frequency bands, resulting in high reflection coefficients and poor test performance for Wi-Fi 6 chips.
Innovation Solution
A coplanar waveguide transmission line design featuring a step structure with a rectangular groove forming a defected ground structure, combined with metallized through holes for enhanced grounding, to achieve impedance matching in the Wi-Fi 6 frequency band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a step structure is used for impedance matching, then the transmission line can be designed with simple geometry, but the reflection coefficient S11 remains high (15 dB at 2.4 GHz, 10 dB at 5 GHz) failing to meet EVB requirements
Solution Approach 1:
The transmission line is divided into multiple segments with different impedance characteristics. Specifically, it includes a first transmission line segment with characteristic impedance Z0, a second transmission line segment with characteristic impedance Z1, and a third transmission line segment with characteristic impedance Z2, where Z0 < Z1 < Z2. This segmentation allows progressive impedance transformation to achieve better matching across the Wi-Fi 6 frequency band.
Solution Approach 2:
Different segments of the transmission line are designed with locally optimized impedance values. The first segment near the SMA connector has lower impedance (Z0), the middle segment has intermediate impedance (Z1), and the segment near the chip has higher impedance (Z2). This local quality variation enables effective impedance matching across the broadband frequency range.
2Manufacturing precision
If the center conductor strip width is reduced from first segment to second segment, then a step structure is formed for impedance transformation, but processing errors and electromagnetic losses degrade actual test performance
Solution Approach 1:
The transmission line maintains continuous signal transmission through three progressively transitioning impedance segments rather than a single abrupt step. This continuous transformation reduces signal reflection and electromagnetic loss while maintaining manufacturing feasibility, as each segment can be fabricated with standard precision tolerances.
Solution Approach 2:
The characteristic impedance parameter is changed progressively across three segments (Z0 → Z1 → Z2) rather than maintaining a single impedance value. This parameter transformation allows the transmission line to adapt to different impedance requirements at different locations, improving both matching accuracy and reducing energy loss.
3Adaptability or versatility
If a single-branch or dual-branch load matching is used, then the transmission line can achieve impedance matching at specific frequencies, but it fails to provide adequate matching across the entire Wi-Fi 6 frequency band (2.4 GHz and 5 GHz)
Solution Approach 1:
The three-segment transmission line structure serves multiple frequency bands (both 2.4 GHz and 5 GHz Wi-Fi 6 bands) simultaneously. By carefully selecting the impedance values Z0, Z1, and Z2 along with the segment lengths, the structure achieves broadband impedance matching across different frequency ranges, making it universally applicable to Wi-Fi 6 applications.
Data Source
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AI summary
The present disclosure provides a coplanar waveguide transmission line, including a first dielectric substrate, a center conductor strip, and two ground conductor strips. The first dielectric substrate has a first surface and a second surface opposite to each other. The center conductor strip and the ground conductor strips are stacked and fixed to the first surface. The center conductor strip includes a first segment and a second segment. A width of the first segment is greater than a width of the second segment, so that the first segment and the second segment form a step structure, to realize impedance matching. A rectangular groove recessed toward the second surface is defined in the first surface, and a part of the center conductor strip is stacked and fixed to a side, distal from the second surface, of the rectangular groove to form a defected ground structure. The present disclosure further provides a design method for impedance matching in a coplanar waveguide transmission line. Compared with the prior art, the technical solution provided by the present disclosure has a good impedance matching and good transmission index.