We are plotting both S11 on a smith chart and a rectangular plot. In this project, please see the graphs Normalized and S11. Using the equation above, the characteristic impedance of the line is 37.42 ohms. From either approaches, this value is 28 ohms. This impedance can be read from the smith chart where the response crosses the real axis or from the minimum or maximum of the Input Impedance graph. Then we read what the impedance is at quarter wavelength. We know that ZL in this case is 50 ohms, due to the port impedance setting. Where Zc is the characteristic impedance of the quarter wavelength line, ZL is the load impedance and Zo is the impedance you are matching to. Notice the marker on the Normalized plot is crossing the real axis at 11.6 GHz so in this example, we have met these criteria.įrom impedance matching theory, you can calculate the characteristic impedance of a quarter wave transformer, by this equation: The most important aspect of this approach is that we want to simulate either a long enough line or high enough in frequency such that the line is quarter wavelength a frequency simulated. The Input Impedance plot is looking at the impedance looking into port 1 of the schematic.

The Normalized graph is showing the s-parameters of the line on a smith chart. In the project, please see the graphs Normalized and Input Impedance. Techniques 2 and 3 are discussed in more detail below. Set the port impedances on either side of the line to be a variable and tune or optimize the impedance until the line is perfectly matched, the value of the port impedances is the characteristic impedance of your line. Then using the quarter wavelength transformer equation, calculate the characteristic impedance of the line.ģ. Determine the impedance looking into one side of the line at the frequency where the line is quarter wavelength long. This approach will not work if you are only given s-parameters and have to determine the impedance only from the frequency response of the line.Ģ. Please select Tools > TXLine to access this software. TXLINE is a free addition to AWR software that allows the user to enter geometry and calculate impedance or vice-versa. The AWR design environment has several ways you can calculate a line's characteristic impedance.ġ. This example will demonstrate with a CPW line, but the approach is general and can be applied to any transmission line structure, such as microstrip, stripline, coax, etc. This example will show users several ways of determining the characteristic impedance of a transmission line. Transmission Line Characteristic Impedance Where To Find This Example Download Project

Quarter wave transformer smith chart