Changes

[[RF.SpiceA/D]] offers a passive device called Generic T-line with the keyboard shortcut “T”, which is a general purpose frequency-domain transmission line segment model. It is based on the native SPICE LTRA model, but with the following [[parameters]]:

The default [[parameters]] of the Generic T-Line are Z0 = 50 Ohms, eeff = 1, alpha = 0, and len = 10mm. A unit effective permittivity implies a TEM transmission line because √ε_eff = β / k₀, where β is the propagation constant of the transmission line and k₀ = 2πf/c is the free space propagation constant, with f being the frequency in Hertz and c = 3e8 m/s being the speed of light. A zero attenuation constant represents a lossless transmission line. The Generic T-Line device is indeed a two-port network with a 2×2 scattering matrix or four S-parameters: s11, s21, s12 and s22. Obviously, this is a reciprocal and symmetric network, i.e., s11 = s22, and s21 = s12.

Note that N-port networks in [[RF.SpiceA/D]] have schematic symbols with 2N pins. Each pair of pins represents a port. In a similar way, the generic T-line has two ports and four pins. The pins are marked with plus and minus signs. For example, in the figure above, the pins P1+ and P1- together form Port 1. Normally, the negative pins are grounded, and the positive pins are connected to the other parts of the circuit.

{{Note | Proper grounding of the transmission line devices is critical for a successful simulation.}}