Issue link: https://iconnect007.uberflip.com/i/258943
18 The PCB Design Magazine • February 2014 There are four scenarios for building the con- ductor surface roughness model with and with- out separation of the loss and dispersion effects between the dielectric and conductor surface roughness models 7 : 1) Optimize dielectric model to fit mea- sured and modeled GMS-parameters following the procedure in Figure 1 and do not use any additional conductor roughness model. The di- electric model will include effect of conductor surface roughness. Such model may be suitable for the analysis of a particular transmission line and has to be rebuilt if strip width or line type is changed. This combined model may be accept- able in cases of high-loss dielectrics when the effect of conductor roughness is minimal. This case is similar to the dielectric model identifica- tion described in references 5 and 6, but with rough conductors. 2) Define dielectric model with the data available from the dielectric manufacturer and then identify a roughness model (a roughness correction coefficient) with GMS-parameters following the procedure in Figure 1. This ap- proach works well if a manufacturer has reliable procedure to identify the dielectric properties (most of them do). Wideband Debye models can be defined with just one value of dielectric constant and loss tangent specified at one fre- feature Figure 1: identification procedure for dielectric material and conductor surface roughness model. PCB AND PACkAGING DESIGN UP To 50 GHz continues