Characteristics of a Staggered Double-Elliptical-Groove Circuit for Wide-Band TWT

A novel staggered double-elliptical-groove waveguide (SDEGW) slow wave structure is proposed as an efficient solution to the ultrawideband traveling-wave tube (TWT) at terahertz frequencies. With the groove shape transformed from a rectangle to an ellipse, the characteristics of the circuit have been changed. The frequency of the
$3\pi $
point is largely increased with the same cutoff frequency. This means the available bandwidth between
$2\pi $
and
$3\pi $
is increased and the dispersion of the circuit is reduced. The wide-band amplification characteristics with improved gain flatness have been verified by the particle-in-cell (PIC) simulation at
${G}$
-band. It is shown that the 1-dB bandwidth exceeds 46 GHz, from 217 to 263 GHz, corresponding to a fractional bandwidth of 20%, under a constant input. The elliptical-groove circuit has been successfully fabricated. The measured S parameters are in good agreement with the simulation. In particular, the measured
$\text{S}_{{11}}$
is lower than −20 dB from 208 to 260 GHz.