Keysight ADS – Short Circuit Terminated Ideal Transmission Line

Using ADS, a parameter sweep can be used to confirm the results of a short circuited transmission line. The input impedance of a transmission line is given as

input.png

When the line is terminated by a short circuit, ZL = 0 and the equation reduces to only the imaginary part of the numerator. For integer multiples of the wavelength, the input impedance is equal to zero. At odd multiples of a quarter wavelength, the input impedance becomes infinite and looks like an open circuit.

The following circuit is constructed to test the results. A parameter sweep with the variable theta (the electrical length) is used.

schem.PNG

The results are shown below. As expected, the reactance alternates between inductive and capacitive for different electrical length values. The reactance is infinite at quarter wavelength multiples and zero at integer multiples of the wavelength. The current is shown to be lagging the voltage by 90 degrees. The major conclusion to be made is that a transmission line does not behave like a lumped element circuit because voltages and currents are different at different lengths along the line.

results