Abstract: An extended interaction output circuit interacts with a modulated electron beam and outputs RF electromagnetic energy. The circuit comprises a plurality of linearly disposed cavities each having a gap permitting the traveling therethrough of the modulated electron beam. A first pair of the linearly disposed cavities is coupled by a single side cavity, a second pair of the linearly disposed cavities is coupled by a pair of side cavities radially disposed 180 degrees apart, and a third pair of the linearly disposed cavities is coupled by three side cavities radially disposed 120 degrees apart. The linearly disposed cavities act as an RF filter having successively tapered impedances to reduce reflections of the electromagnetic energy propagating through the circuit. RF energy is extracted from the fourth cavity through four waveguide sections that are radially disposed 90 degrees apart.