Tuning gain and bandwidth of traveling wave tubes using metamaterial beam-wave interaction structures

Abstract

We employ metamaterial beam-wave interaction structures for tuning the gain and bandwidth of short traveling wave tubes. The interaction structures are made from metal rings of uniform cross section, which are periodically deployed along the length of the traveling wave tube. The aspect ratio of the ring cross sections are adjusted to control both gain and bandwidth. The frequency of operation is controlled by the filling fraction of the ring cross section with respect to the period.

Giant amplification in degenerate band edge slow-wave structures interacting with an electron beam

“…Furthermore, the dispersion diagram of the hot structure is slightly perturbed when the average electron beam current is not high 20 . On the other hand, it is completely distorted for large beam currents and synchronism may not explicitly be casted into the form of (10) implying that one may lose the degeneracy and the benefits of the DBE features for amplification. Here we will consider only weak beam currents since this is the case when the advantage is anticipated.…”

“…Here we will consider only weak beam currents since this is the case when the advantage is anticipated. In summary, equation (10) is the main criterion for the design of a DBE electron beam amplifier that can be finely tuned using the dispersion diagram of the hot structure and resonance condition due to a finite length of the SWS. Fine tuning of the electron beam velocity allows for optimizing the gain.…”

“…When seeking for best conditions for the synchronization, researchers proposed a number of periodic structures as SWS such as those comprising coupled cavities 6 or corrugated waveguides 7 . Recently, metamaterial based SWSs have been proposed [8][9][10] by loading a waveguide with subwavelength resonant elements, like ring-bars 11 or split-ring resonators 8 , with the aim of enhancing the interaction impedance and gain accordingly 2,12 . Such periodic SWSs usually operate at frequencies far from the edge of their band gap.…”

“…with (10) for large N. Such value of u0 has been selected in our specific design of the finite length TWT to achieve a giant amplification, without seeking a thorough optimization. In other words, fine tuning of u0 around ωr,d /kd is necessary to maximize the gain but not attempted here for simplicity.…”