Study of the frequency spectrum of a one-dimensional virtual-cathode microwave system

The spectral distribution of oscillations excited in a continuous monoenergetic radially uniform cylindrical beam completely filling a metal waveguide (r{sub b} = R) of finite length L >> R is studied. It is noted that as the beam current increases a range of frequencies appears in which a backward wave exists. The condition for the appearance of this region is the same as the condition for the development of electrostatic instability in the REB (the development of a virkator). It is shown that the amplitude-frequency characteristic for the amplifier of an external signal at the virtual cathode can be represented as a narrow-band filter in which the central transmission frequency as a function of the REB parameters and the electrodynamic structure can be quite different from the beam plasma frequency. The transmission bandwidth also depends on these parameters. Estimates of the field amplification obtained from a linear treatment (with respect to the initial signal level E{sub in}) in the range of the characteristic frequencies of the virkator shows that in the steady regime it reaches several decades. 8 refs., 4 figs.