Initial experimental investigations of intermodulation in a klystron amplifier

Abstract

Summary form only given. The growing importance and heavy user demand for digital communications, in both Defense applications and commercial markets, is driving a need for compact, high power, efficient, microwave amplifiers with good linearity (low signal distortion). The requirement for linearity is becoming even more crucial by the desire to operate individual amplifiers under multitone excitations. An experiment has been configured to investigate the fundamental physics of intermodulation product (IMP) generation in klystron amplifiers (KLAs). A primary purpose of this experiment is to compare experimental measurements with predictions from a new general theory of IMP generation. IMPs result from multi-tone excitation of an amplifier, and are due to nonlinear beating between the drive tones and harmonics of other drive tones in the modulated current of the electron beam. The experiment employs a 1 kW CW Varian 4K35L, 4-cavity klystron amplifier, although it is run pulsed for these initial investigations. The KLA operating voltage and current are /spl sim/6 kV and 0.6 A, respectively. It is designed to amplify signals between 1.7 and 2.4 GHz, depending on mechanical tuning of the cavities. Instantaneous bandwidth is /spl sim/10 MHz. A 2 MHz-spaced, two-tone excitation is generated by two synthesizers. Measurements are made of the radiation spectrum at both the 2nd (intermediate) cavity and the output cavity. Beam-loaded cavity characteristics are determined from experimental measurements and numerical simulations.