==RF Circuit Analysis==
RF circuit analysis, by nature, is an AC analysis that you typically run at high frequencies ranging from tens of Megahertz to tens of Gigahertz. At such high frequencies, the dimensions of your circuit may become comparable in order of magnitude to the wavelength, and wave retardation effect effects start to appear. In other words, your circuit starts to act like a distributed structure rather than a lumped circuit where the signals propagate instantaneously. In the analysis of a low frequency circuit, two nodes that are connected to each other trough a wire are assumed to have equal potential or identical voltages. In RF circuits, the connecting wires indeed act as [[Transmission Lines|transmission lines]], whose lengths play an important role in determining the voltages and current at different point of the circuit.
The RF devices of RF. Spice are characterized and modeled based on their frequency-domain scattering (S) [[parameters]]. The S-[[parameters]] are tabulated as a function of frequency and interpolated in between the frequency samples. RF.Spice performs an AC analysis of these RF devices by converting their S-[[parameters]] to Y-[[parameters]] and using them in conjunction with the SPICEâs nodal admittance matrix formalism. As a result, you can mix RF devices with all the other analog and mixed-mode devices of [[B2.Spice A/D]] in your circuits.