The filter has only reactive components and so does not absorb any power itself, so power is passed between the diode and the ports without loss. The input signal power to the diode is P in = V I 2 / R 1 The output power from the diode is P out = V R 2 / R 1 So the power gain G P of the amplifier is the square of the reflection coefficient G P = P out P in = V R 2 V I 2 = | Γ Γ | 2