The signal is sent to the 50 Ω termination resistor, R1. Because of load matching, the signal is dissipated safely with a minimum amount of back reflections. In this way the amplifier will still operate at 50% of capacity. Also, if the destination of the amplified signal is off line (for example a damaged antenna), the amplified signal will travel backwards through the coupler to the termination R2 to ground safely without damaging the amplifier.