The concepts of [[Transmission Lines|transmission lines]] and [[Multiport Networks|multiport networks]] are integral to any RF simulation. From a simulation point of view, an RF circuit is made up of a collection of [[Multiport Networks|multiport networks]] that are interconnected via [[Transmission Lines|transmission lines]] segments or components. If the input of your circuit is connected to a source and its output is connected to a load, then you can compute all the voltages and currents at all various circuit nodes, some of which may serve as external or internal ports of your circuit. Or you can calculate the port characteristics of the overall network by designating input and output ports to your RF circuit.
All the RF devices of [[RF.Spice A/D]] can be divided into two groups: devices based on transmission line models, and devices based on multiple networks. [[RF.Spice]]'s transmission line models are based on enhanced versions of SPICE's standard LTRA model. The transmission-line-based devices typically utilize a combination of LTRA and passive RLC models. [[Multiport Networks|Multiport networks]] are characterized and modeled based on their frequency-domain scattering (S) [[parameters]]. The S-[[parameters]] are tabulated as a function of frequency , and their values are interpolated in between the frequency samples. [[RF.SpiceA/D]] performs an AC analysis of these RF devices by converting their S-[[parameters]] to Y-[[parameters]] and using them in conjunction with SPICE’s nodal admittance matrix formalism. The S-parameter-based RF devices of [[RF.Spice A/D]] are primarily intended for use in two types of [[tests]]:
* AC Frequency Sweep Test