Abstract <p>PIC simulation of a promising type of a vircator—a multilayer virpertron with an insert consisting of four dielectric layers with dielectric permittivity decreasing along the beam path—has been carried out. It is shown that a four-layer weakly relativistic virpertron (150 keV, 2 kA) ensures a multivircator mode with a number of virtual cathodes (VCs) no less than four. The electron beam densitogram was calculated; this calculation revealed that the electron beam in the virpertron acquires a complex spatial-wave dynamics, characterized by a forward spatial-charge wave and several VCs. As a result, conditions for the generation of high-power microwave electromagnetic fields in the cavity are formed. The calculated energy spectrogram of the electron beam showed redistribution of electron energy in time: occurrence of a group of runaway electrons and a large group of slow electrons with an energy corresponding to the VCs. Spectrograms of microwave fields in the virpertron were calculated. They have a shape characteristic of a noise-like signal in the range from 1 to 5 GHz.</p>