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.