The general form of the instance of a lossless transmission line is the following:

 Note: A lossy transmission line with zero loss may be more accurate than the lossless transmission line due to implementation details.

Parameters

name

Is the name of the component and the initial letter O identifies the lossless transmission lines.

A_node(+), A_node(-)

Are the nodes at port A.

B_node(+), B_node(-)

Are the nodes at port B.

Z0

Z0 is the characteristic impedance.

TD

The transmission delay.

F e NL

F is the frequency and NL is the normalized electrical length of the transmission line with respect to the wavelength in the line at the frequency F.

IC

The (optional) initial condition specification consists of the voltage and current at each of the transmission line ports. Note that the initial conditions (if any) apply 'only' if the UIC option is specified on the .TRAN control line

Description

The length of the line may be expressed in either of two forms. The transmission delay, TD, may be specified directly (as TD=10ns, for example). Alternatively, a frequency F may be given, together with NL, the normalized electrical length of the transmission line with respect to the wavelength in the line at the frequency F. If a frequency is specified but NL is omitted, 0.25 is assumed (that is, the frequency is assumed to be the quarter-wave frequency). Note that although both forms for expressing the line length are indicated as optional, one of the two must be specified.

Note that this element models only one propagating mode. If all four nodes are distinct in the actual circuit, then two modes may be excited. To simulate such a situation, two transmission-line elements are required. The following example simulates a transmission-line inverter. Two transmission-line elements are required since two propagation modes are excited. In the case of a coaxial line, the first line (T1) models the inner conductor with respect to the shield, and the second line (T2) models the shield with respect to the outside world.

Examples

TRANSMISSION-LINE INVERTER
V1   1  0         PULSE(0 1 0 0.1N)
R1   1  2         50
X1   2  0  0  4   TLINE
R2   4  0         50

.SUBCKT TLINE 1 2 3 4
T1   1  2  3  4   Z0=50 TD=1.5NS
T2   2  0  4  0   Z0=100 TD=1NS
.ENDS TLINE

.TRAN 0.1NS 20NS
.END

See also

Lossy Transmission Lines
Lossless Transmission Lines Instance Parameters