A stub is defined as a transmission line whose electrical length is < = 90 degrees. A sketch of an open stub. an OST, and a shorted stub, an SST, is shown below.

OST/SST Stubs                  Calculate the input impedance of open (OST), and shorted                  (SST) stubs.                  Units:  ohms,degrees                  Choose OST/SST (O or S) [<Enter>=Quit] ? _

Here is the output calculation

                Z in = +j 52.024 ohms

Tip: Since  Tan 45 & Cot 45 = +/-1, a 45 degree (eighth-wave) shorted stub whose Z0 is 50 ohms has Z in =  +j 50 and an open stub has Z in = -j 50 ohms. By the same token, a 45 degree (eighth-wave) SST/OST whose Z0 is 30 ohms, has Z in = +j 30 and -j 30, respectively. Make sense?