Helical waveguide millimeter wave TWT

It has been demonstrated that the ridge-loaded waveguide circuit is a viable slow-wave circuit for use in TWTs (traveling wave tubes) requiring a forward-wave fundamental mode. Cold test measurements of several circuits at frequencies above 40 GHz demonstrated a range of phase velocities corresponding to beam voltages as low as 10 kV. Interaction impedances from less than one ohm to several hundred ohms were also measured. Test results for a TWT using one of the ridge-loaded circuits correlated well with predicted behavior at the lower phase velocity. An experimental, semitransparent, millimeter-wave TWT was built and tested. The TWT, operating with E/sub w/=24.7 kV, demonstrated output power of 163 W at 42 GHz. The peak electronic efficiency of over 6% (at 42.4 GHz) and the maximum large signal gain of 24 dB (at 43.8 GHz) in an unattenuated circuit length of 2.0 in were close to calculated values. Because of the circuit dispersion, the instantaneous bandwidth was 1.3%. The 20-kV circuit voltage and greater than 20- Omega interaction impedance of this circuit show promise.<
>