Investigation of Half Rectangular-Ring Helix Slow Wave Structure for W-Band Wide Bandwidth High-Efficiency TWTs

The half rectangular-ring helix (HRRH) slow wave structure (SWS), which evolves from the rectangular helix (RH), is proposed to develop a high-efficiency wide bandwidth millimeter-wave traveling-wave tube (TWT). The comprehensive advantages of the HRRH SWS are lower phase velocity and higher interaction impedance in comparison with the RH and the planar helix with straight-edge connections (PH-SECs) SWS with the same dimensions. The particle-in-cell (PIC) simulation shows that, at a beam voltage of 6450 V, a beam current of 0.03 A, the maximum output power of 42.2 W, corresponding to a differential small-signal gain of 1.43 dB/mm, and an electron efficiency of 21.8% can be obtained for the HRRH TWT at 95 GHz. The output power, differential small-signal gain, and electron efficiency of the HRRH TWT are considerably enhanced compared with the RH TWT in a wide frequency range of 60–115 GHz under the same electrical parameters.