Square- and Rectangular-Ring Vertex-Bar Slow Wave Structures for High-Efficiency Wide Bandwidth TWTs

In this article, novel square-ring vertex-bar (SRVB) and rectangular-ring vertex-bar (RRVB) slow wave structures (SWSs) are proposed to develop high-efficiency wide bandwidth traveling wave tubes (TWTs). High-frequency characteristics including dispersion, interaction impedance, and transmission of these novel slow wave circuits are analyzed. It is shown that both the SRVB and RRVB possess the advantages of flatter dispersion and higher interaction impedance of the fundamental space harmonic of the forward wave in comparison with the traditional circular ring-bar (RB) SWS. Beam–wave interaction study of SRVB TWT with a pencil beam and RRVB TWT with a sheet beam is carried out. The particle-in-cell (PIC) simulations predict that with the beam voltage of 15.7 kV and beam current of 0.23 A, the maximum output power of the SRVB TWT and the RRVB TWT can reach 616 and 695.6 W, respectively. Both the SRVB TWT and RRVB TWT can produce larger output power, higher differential small-signal gain, and wider 3-dB bandwidth than the RB counterpart. The SRVB TWT is superior to the RRVB TWT for its stability against backward-wave oscillations but with relatively small output power.