This is an example of impedance matching. Two transmission lines with different characteristic impedances are matched with a shunt stub, a short section of transmission line. This eliminates standing waves in the first line. On the bottom you see the same two lines without impedance matching. The power delivered to the load is graphed for both cases on the bottom. With impedance matching, more power is delivered to the load.
Next: Stub Frequency Response
Previous: Impedance Matching (L-Section)