Abstract A new approach for the development of microwave electric-vacuum devices is proposed. It implies extracting output power at two or more frequencies ω, 2ω, …, nω simultaneously while applying input power at fundamental frequency ω. The characteristic feature of these devices is that microwave oscillations at different frequencies are phased. It is possible to obtain output power at frequencies ω and 2ω simultaneously by using double-gap resonator tuned into two multiple frequencies -in-phase one at frequency ω and anti-phase one at frequency 2ω. It is possible to obtain power on four frequencies ω, 2ω, 3ω, 6ω by using electro-dynamic system of two doublegap resonators placed one inside other. It is possible to get power at many multiple frequencies by using special coaxial resonator. Has been created a microwave device producing power on nine multiple frequencies simultaneously. The output pulse of the device has ultra-short duration and super-high repetition frequency equal to the input frequency ω. Multifrequency high power microwave electric vacuum devices can be used in compact accelerators of charged particles
