Abstract: The object of the presently disclosed embodiment is to improve heat dissipation and an overall cooling efficiency to raise a peak oscillation output. To achieve the object, there is provided a coaxial magnetron having the following configuration: Around a cathode, vanes and an anode cylinder form an anode resonant cavity, and a cylindrical side body forms an outer cavity. An input side structure having an input part and an upper structure are joined to both ends of the cylindrical side body. One end of the anode cylinder is joined to the input side structure. A groove (or step) for adjusting the distance between the structures and at the both ends is provided, and the groove is joined to the other end of the anode cylinder.

Abstract: The switching element is provided in a state of being electromagnetically coupled to the cavity resonator of the high frequency oscillator; the bias voltage applying terminal is connected to one electrode of the switching element; another electrode of the switching element is electrically connected to the cavity resonator (the anode shell in FIG. 1); the metal plate having a size enough for reflecting an electric wave to be transmitted before and after the switching element in a high-frequency manner is provided at any one end of the switching element; and by applying a bias voltage to the switching element and varying that, a reactance of the switching element is changed and a resonance frequency of the cavity resonator is varied. By this method, an oscillation frequency can be varied greatly relative to a small change in a bias voltage.