The procedure for requesting AWR support has changed. Please read all about
the new AWR product support process.
Starting in version 15, you can synthesize transmission line physical parameters from electrical characteristics.
To demonstrate, see a simple open stub circuit. The frequency at which the stub is 90 degrees will result in a short circuit in the S(2,1) response.
From this geometry, a short is occurring at about 5 GHz.
Right-click on the MLIN element in the stub (ID=TL6) in this example and select Synthesize to display the following dialog.
We want to center the short at 8 GHz. Fill out the form as follows, note that for the Physical column, the Freq parameter is set to 8 GHz and the L parameter is selected to synthesize. On the Electrical side the EL parameter is selected as the synthesis target to achieve.
Clicking the Left arrow 
will then calculate a new value for L as shown below.
Clicking the OK button will change the parameters of the line selected. Notice the line length changed to be approximately 200 mils
The open circuit response is now shifted to 8 GHz.
Note, the short isn't exactly at 8 GHz due to parasitics introduced by the MOPEN and MTEE elements. If you removed those models, the notch would be exactly at 8 GHz.