Using Agilent ADS Smith Utility for Impedance Matching

Match a source with a characteristic impedance of 50Ω to a 100Ω load at 100MHz. (1)

  1. Enter the frequency of 100MHz in the box at the top-left. Let characteristic impedance Z0 stay at 50Ω. Select the load in the lower-right Network Schematic area and enter the value of 100+j*0. Similarly, select the source and enter the value of 50+j*0. You will see the source and load impedances appear on the smith chart as a circle and diamond marker respectively.


  2. We do not want to use a simple 100Ω resistor in parallel with the load to do this matching because then half the source power would be dissipated by the matching network. Instead, we need to use lossless components in the matching network.
  3. Click to select the shunt inductor from the palette on the left. This inductor will appear in the Network Schematic. Start from the load of 100Ω and move the cursor up from the diamond marker. You will notice a dot that moves counter-clockwise on the smith chart. Move up to the contant resistance cycle and click to stop. The corresponding inductor value will be displayed in the Network Schematic.


  4. Click to select the series capacitor from the palette. You will notice that the dot that now follows a different trajectory (the constant resistance circle) in the counter-clockwise direction. Meet the characteristic impedance of the source Z0 of 50Ω and stop. The corresponding series capacitor value will be displayed in the lower right. The loads are now matched and the matching network is displayed. Note in the Network Response that the input reflection coefficient, S11 is lowest at the frequency specification of 100MHz (narrow band match).

  5. Here's another possible solution with a series inductor and a parallel capacitor:


Match a 100Ω load to a 50Ω system at 100MHz using two transmission lines connected in parallel (single stub tuner)

We will use the admittance chart for this case.

  1. Add a series stub


  2. Add a shunt stub



  1. Smith Chart and Matching Network, James Lu
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