A new principle for the design of frequency converters, operating at significantly higher power and efficiency than previous devices, is described in this article. The presented solution is implemented as a particular klystron topology for which a new design criterion is formulated through analytical expressions and a specific design procedure. The described frequency multiplier is suitable for telecommunications, nonlethal weapons, or scientific and medical particle accelerators, where the most interested exploitation is in the field of high gradient particle acceleration and free electron laser (FEL) devices for which no current sources meet the required performance. The frequency converter replaces all the low-level circuitry needed for frequency multiplication, representing a less expensive alternative. The presented structure can offer efficiencies in the range of 50%–60% in the Ka-band with power levels of 20–30 MW without phase noise, sideband generation, jitter, or chirp effects. The proposed principle is also applicable to other bands or power ranges.