Line Coupling, Ground Defect, Port Termination, and Line Parameters Extraction for Coupled Lines with Mixed-mode Stimuli

Some suggested that four-port single-ended scattering S-parameters (simulated or measured) could be converted and used to represent mixed-mode S-parameters; the approach we label here as “SE-matrix converted,” or simply “SE-conv.” SE-conv is often preferred, since the mixed-mode signal sources and probes are not readily or easily available. To employ the SE-conv formulation, two lines have to be loosely coupled. Allan Huynh proposed a different formulation that includes the effect of line coupling. Indeed, the formulation allows SE-conv to closely represent the mixed-mode results using “matched” termination. In true mixed-mode measurement, however, standard, constant references are used. The port termination in simulators is not fully identical to that in measurement. Also in mixed-mode formulation, imperfection in the ground plane was not discussed. In the paper, we first analyze the port termination in simulators, and determine the preferred lumped port terminations for mixed-mode feeding. Secondly, effects of line coupling and imperfection on system ground are studied by comparing SE-conv and standard reference terminated mixed-mode results. Thru the comparison, the benefits of virtual ground, which is supplied only in mixed-mode feeds, can be understood. Finally, line parameters extraction of simulated mixed-mode fed microstrip coupled line is illustrated. The same calculation procedure can be applied to the measured results, which we are working to secure. Currently, we are designing CPLs and associated de-embedding structures for IPD and PCB platforms.