Changes

The simplest RF circuit analysis type in [[RF.Spice]] is the "AC Frequency Sweep" Test. As mentioned earlier, this is identical to the AC frequency sweep test of [[B2.Spice A/D]]. The only difference here is that the frequency-domain models of [[Multiport Networks|multiport networks]] and transmission line segments or components are added to the analog or mixed-mode simulation of your circuit. Just as in [[B2.Spice A/D]], the AC Test is run from the Test Panel of the Toolbox.

Just as in low frequency circuits, RF circuits must be excited using a voltage or current source. However, in order to ensure a successful RF circuit simulation, your source must be a single-frequency (sinusoidal) AC source. Remember that in [[B2.Spice A/D]] circuits, you must specifically designate a source to operate as an AC source for all [[tests]] of the AC type. The RF Menu of [[RF.Spice]] provides two additional types sources: the AC voltage source with the keyboard shortcut "Alt+V" and the AC current source with the keyboard shortcut "Alt+I". These sources are identical to the regular voltage and current sources of [[B2.Spice A/D]], whose "Use" checkboxes in the AC section of their source property dialog are automatically checked.

[[File:RFAC3.png|thumb|600px| A more realistic version of the previous RF circuit including connecting transmission line segments.]]

You can use Generic T-Line segments or physical transmission line types to connect the various RF parts and devices in your circuit. The opposite figure shows the same simple RF circuit of the previous figure, but containing two T-line segments, one connecting the source to Port 1 of two-port N1 and the other connecting Port 2 of N1 to the resistive load. Note how the negative input and output pins of both T-line segments have been grounded. Lossless transmission line segments cause a phase shift of the propagating signal, while lossy [[Transmission Lines|transmission lines]] also cause additional signal attenuation.