Testing this stub board. I understand S12 is attenuated at 1.79GHz due L=λ/4. So I calculate relative permitivity:
εr = (c / 4Lf)2 = 3.3
But what does (εr) represent in a physics perspective? Is it permitivity of the board dielectric? If so how does the signal interact with the ground plane in this stub?
Second: What is the cause of the reduced S11 reflection at 3.09GHz?