At the heart of RF.Spice lie the concepts of [[Multiport Networks|multiport networks]] and RF [[Transmission Lines|transmission lines]]. From a simulation point of view, an RF circuit is made up of a collection of [[Multiport Networks|multiport networks]] that are interconnected via RF [[Transmission Lines|transmission lines]]. 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 the external or internal ports of the circuit (i.e. at the various circuit nodes). Or you can calculate the port characteristics of the overall network by designating input and output ports to your RF circuit.
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==Limitations of RF.Spice==
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The RF circuit analysis performed by RF.Spice is based on the assumption that your distributed RF circuit can be modeled as an interconnected network of multiport devices and transmission line segments and components. This means that all the coupling or crosstalk effects must have been captured by the S-parameter-based models of devices or by the transmission line and discontinuity models used by RF.Spice. Most of these models work satisfactorily at lower frequencies up to several Gigahertz. As the frequency increases, more complex wave radiation and propagation effects start to appear and affect the performance of your circuit. At much higher frequencies in the millimeter wave region of the spectrum, each junction may have to be considered as
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