Development and testing of high power RF vector modulators

A fan-out RF power distribution system can allow many accelerating cavities to be powered by a single high-power klystron amplifier. High-power vector modulators can perform independent control of amplitudes and phases of RF voltages at the cavities without changing the klystron signal. A prototype high-power RF vector modulator employing a quadrature hybrid and two ferrite phase shifters in coaxial TEM transmission lines has been built and tested for 402.5 MHz. RF properties of the design and results of high power testing are presented.

INTRODUCTION

Figure 1 shows architectures of some simple forms of a vector modulator for high-power operation, consisting of a single or two hybrid junctions and two phase shifters. Traveling waves exist in the phase shifters if two separate hybrids are used. Standing waves are used in the short circuited phase shifters if a single hybrid is used. Figure 1: Vector modulator realization with (a) traveling and (b) standing waves in the phase shifters. Figure 2: Vector modulator responses with respect to two phases: (a) amplitude, (b) phase.