Electrically tunable frequency klystron

A device is developed which enables to tune electrically the frequency of low power reflex klystrons, in a large bandwidth and with low inertia. This device uses a peculiar characteristic of gaseous plasmas. Indeed a discharge in a low pressure gas behaves as a dielectric for transmission of microwaves; the dielectric coefficient is a function of electron density, then of discharge current. The resonance frequency of a cavity in which a plasma tube is set can then be modified by changing the discharge current. The study was carried on in X band from a reflex klystron equipped with an external cavity. A tube is introduced into this cavity and the klystron oscillation frequency is controlled by the current of the discharge. A 300 Mc/s frequency tuning of the klystron has been reached, this band being covered with an approximately 200 µs time constant. Noise temperature of the klystron is not changed by plasma.