  A new frequency converter, operating at significantly higher power and
efficiency than previous devices, is described in this paper. The proposed
device is implemented as a klystron structure where a new design principle is
used. New analytical formulas and a specific design procedure are proposed. The
klystron frequency multiplier can be suitable for telecommunications and
non-lethal weapon, scientific and medical particle accelerators while the most
interested exploitations are in the field of high gradient particle
acceleration and FEL devices for which no performant sources exist. The
advanced klystron multiplier can replace all the low level circuitry for
frequency multiplication as a less expensive alternative. Efficiencies in the
range of 60% in the K-band range with power levels of 30 MW are possible
without phase noise, sideband generation, jitter or chirp effects. The
presented design principle is applicable to other bands or power levels.
