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62 DESIGN007 MAGAZINE I APRIL 2021 on menu driven user-defined structures. e structures are simple transmission line circuits with configurations most used. e microstrip transmission line is a very common RF struc- ture that is modeled using MWI-2019 and has proven to have accurate results, as compared to measured circuit performance. e soware will solve for impedance, insertion loss, effec- tive dielectric constant, wavelength, propaga- tion delay, phase angle, and more. e microstrip structure in MWI-2019 so- ware yields results based on the closed form equations defined from a well-known paper published by Hammerstad and Jensen [2] . e basic procedure in this paper will solve for effective Dk, impedance, and insertion loss. e insertion loss calculation is a summation of dielectric loss and conductor loss. For fre- quencies greater than a few GHz, the conduc- tor loss results need to be augmented for the effects of the copper surface roughness and specifically the roughness at the substrate-cop- per interfaces of the microstrip circuit. ere are many different routines which can be used to account for copper roughness and the rou- tine that works best for the type of closed form equations used in MWI-2019 is the Hall- Huray [3] model. is model allows MWI-2019 to account for the additional losses associated with roughened copper across a very wide range of frequencies. Another item to consider with microstrip, and especially when using closed form equa- tions, is transmission line dispersion. Micro- strip circuits are known to be dispersive and basically dispersion is due to the fields of the propagating waves using both air and dielec- tric. Air will have no dispersion and the dielec- tric material will have dispersion. e disper- sion associated with the dielectric material is essentially stating that the dielectric constant will change, given a change in frequency. is does not happen with air, and due to these differences, the microstrip transmission line will have different wave behavior at different frequencies—aside from the expected wave property changes with frequency, such as high frequency waves having shorter wavelength as an example. ere is an excellent dispersion routine for microstrip from a paper by Deibele and Beyer [4] but considering how the closed form equations work with MWI-2019 so- ware, a procedure by Kirschning and Jansen [5] has proven to be more accurate. As a quick and general summary for soware using closed form equations, they are much faster for generating results as compared to field solving, and they can be relatively accu- rate, but the accuracy is sometimes dependent upon special considerations for items related to copper surface roughness and dispersion for some models. ere are other potential issues to consider for closed form equation soware, however, the more accurate field solving so- ware has its own set of issues to be considered. A Field Solver Conversation ere are two types of field solvers: 2D and 3D field solvers. e 2D field solvers are best to use when the designer is considering a stand- alone circuit configuration on a parallel plate structure, such as a filter design on a PCB. However, if a designer would like to model the connector transition to the PCB which has the filter, then a 3D field solver would be best to use. e filter, itself on the PCB, is a parallel plate structure and 2D field solving will gener- There are other potential issues to consider for closed form equation software, however, the more accurate field solving software has its own set of issues to be considered.