Lesson 3 : Section 3 : Mason Plot

Section 3: Mason Plot

The plotting program is hopefully fairly intuitive. You can resize the window to resize the plot.

Figure 3.13: Initial plot when using Mason Plot

Add the text S_2_2 on a second line below S_1_1 as shown in Figure 3.14. Click the refresh button.

Figure 3.14: Adding a second plot

To get the image in Figure 3.15, follow these five steps.

1. Click on Rect as a Plot Type, and click Refresh.
2. Change the Freq Unit to GHz, and click Refresh
3. Change the Start Freq to 0.5, the Stop Freq to 2, and the Step Freq to 0.1, and click Refresh
4. Change the Y Step to 10, and click Refresh

Figure 3.15: Displaying the logarithmic scale in the plot program

This plot shows the transmission line does a good job of matching the 50Ώ source impedance to the 100Ώ load impedance.

Of note is the difference between the Plot Types "Rect" view and the "Arg" view. These are both rectangular plots, however the "Log" view will plot phase as being only between +/- 180 degrees, while the "Arg" view will unwrap in degrees.

The equation that can be used in this program may be fairly involved, as shown in Figure 3.16. A full description (and most up to date list) of what can be used in equations is at: http://sites.google.com/site/circuitmason/wiki/muparser.

Figure 3.16: Insertion loss calculation

The blue line is the insertion loss, how much energy is burned up in the transmission line; the flat 0dB line means no power was burned up in our lossless transmission line. The red line relates the actual power delivered to the load [note: Mason adjusts the S-Parameters to make up for the difference in source and load impedance]. The difference between the power delivered to the load, and the power burned up in the transmission line, is the amount of power that was reflected back to the source.

Also of note is the difference between the Plot Types "Log" view and the "Arg" view. These are both rectangular plots, however the "Log" view will plot phase as being only between +/- 180 degrees, while the "Arg" view will unwrap in degrees.