A magnetron of simplified mechanical construction and including choke structures for harmonic suppression. The structure includes an anode cylinder having a plurality of vanes therein and upper and lower open ends; a cathode within said anode cylinder; a cathode stem air-tightly coupled with the second open end of the anode cylinder for supporting the cathode; and an output section. The output section includes an insulated cylinder having a first end and air-tightly coupled with the first open end of the anode cylinder and a second open end; an electrically conductive annular member coaxial with the insulated cylinder; an electrically conductive metal cap coaxial with the annular member; and an output conductor for conducting microwave energy from the anode cylinder to the cap, the cap and output conductor defining a first choke structure for suppressing second harmonic energy and the annular member defining a second choke structure for suppressing a fourth harmonic component of microwave energy.