An exemplary coupler detector circuit comprises a coupler, a detector circuit, and a harmonic tank. The coupler has a transmission line electromagnetically coupled to a coupled line, and the coupled line has an isolated node and a coupled node. The transmission line may, for example, be a 50 ohm RF line for transmitting RF energy. The detector circuit is connected to the coupled node and is configured to detect a power transmitted along the transmission line. The harmonic tank is connected to the coupled node, and is configured to short to ground at least one harmonic signal transmitted along the coupled node.