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Design and Use of FR-4 CBCPW Lines In Test Fixtures for SMD Components

High frequency/speed designs still predominantly use microstrip lines on relatively cheap FR-4 substrates, despite their relatively poor high frequency performance. One good alternative is to use CBCPW lines (conductor backed co-planar waveguide). Compared to CBCPW, microstrip lines are more susceptible to interference (EMI) and can more easily generate interference themselves. We have designed a number of lines that are used as “ fixtures” to access SMD components and report on their performance. Designs are improved through extensive electromagnetic simulations and potential pitfalls are identified. For the lower GHz range, up to 3 GHz, we also report on the modeling of passive SMD components - capacitors and resistors - where good agreement between measurement and simulation is observed. Finally, we report on use of TDR technique for measurement and modeling and how it compares with VNA-based measurements.

microstrip lines; co-planar waveguide lines; SMD components

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