Coplanar Waveguide Step Structure With Defected Ground Impedance Matching
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Solution Overview
Problem
The existing coplanar waveguide transmission lines for Wi-Fi 6 technology fail to achieve adequate impedance matching in the 2.4 GHz to 6 GHz frequency bands, resulting in high reflection coefficients and poor test performance for Wi-Fi 6 chip evaluation boards due to their step structure design.
Innovation Solution
A coplanar waveguide transmission line design incorporating a rectangular groove in the dielectric substrate to form a defected ground structure, with adjustable width and length, and additional metallized through holes for improved contact with SMA connectors, enhancing impedance matching and transmission efficiency.
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 structure, but the reflection coefficient is high and impedance matching is inadequate in Wi-Fi 6 frequency bands
Solution Approach 1:
The transmission line is divided into multiple segments with different impedance values (first segment with higher impedance, second segment with lower impedance). This segmentation allows progressive impedance transformation from the connector to the chip, achieving better impedance matching across the Wi-Fi 6 frequency bands while maintaining reasonable structural complexity
Solution Approach 2:
Different segments of the transmission line are designed with different local characteristics (different widths and impedances). The first segment has larger width for higher impedance, while the second segment has smaller width for lower impedance. This local differentiation enables optimized impedance matching for specific frequency bands without requiring complete structural redesign
2Reliability
If the center conductor strip width is reduced for better impedance matching, then the reflection coefficient decreases, but the transmission line dimensions become smaller and more difficult to manufacture
Solution Approach 1:
The conductor strip is segmented into multiple sections with different widths. Instead of using a single narrow strip throughout, the first segment uses a wider strip for easier manufacturing, while the second segment uses a narrower strip for better impedance matching. This segmentation allows the design to achieve both manufacturing feasibility and electrical performance
Solution Approach 2:
The impedance transformation is achieved by changing the geometric parameters (width) of different segments. The first segment has larger width parameters for higher impedance and easier manufacturing, while the second segment has smaller width parameters for lower impedance and better matching. This parameter variation across segments resolves the contradiction between manufacturability and performance
Data Source
AI summary
A coplanar waveguide transmission line and a design method thereof are provided. The coplanar waveguide transmission line includes 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. 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.