Latest Advancements in High-Power Millimeter-Wave Helix TWTs

The millimeter-wave spectrum, generally considered to range from 30 to 300 GHz, is one of the most actively used spectrums today, with applications such as high-data-rate terrestrial and space communications, radar, and electronic warfare. The helix traveling-wave tube (TWT) amplifier has long been a critical component for enabling modern millimeter-wave systems. This paper presents an overview of several recently developed high-power millimeter-wave helix TWTs which have extended the helix TWT performance envelope. In particular, the power-frequency-bandwidth product for these devices has increased by a factor of 4 to over 100 depending upon the application. These helix TWTs operate at power levels up to 1-kW peak power or 500-W average or continuous-wave power and over frequencies from 18 to 46 GHz, with efficiencies up to 60%. The helix TWT performance improvements discussed here have not only kept pace with improvements in rival technologies such as GaN solid-state power amplifiers but also pushed helix TWTs into competition with traditionally higher power and higher frequency vacuum electron devices such as extended-interaction klystrons and coupled-cavity TWTs. Indeed, the modern high-power millimeter-wave helix TWT offers system engineers a singularly attractive amplifier technology with an outstanding combination of small size, light weight, high efficiency, good linearity, high reliability, and large bandwidth.