how to differentiate filter fron antenna

dilectric reasonator filter. i got s11 tip and s21 tip.
for antenna also i am getting s11 tip and s21 tip.
how can i differentiate wheather the device is working like antenna or filter

Hello,

Just See the Radiation Patterns to differentiate between Antenna & Filter...
& also E & H Fields...

Are you referring to Differential Antenna ? (If not then it is a Single port device which doesn't have S21!)

---manju---