Traveling wave tubes are rapidly evolving to provide unprecedented power level in comparison to solid state devices in the millimeter waves region of the spectrum (80 – 300 GHz) thus enabling a wide range of applications.
Wireless communications, imaging, security, plasma diagnostics, healthcare and many others will gain substantial features if high power in the millimeter wave region would be available from compact sources.
The development of fabrication technologies is proving crucial for introducing new topologies and structures for millimeter wave vacuum electronic devices, compatible with the dimensions dictated by the short wavelength that poses substantial challenges due to tight tolerances and surface quality.
This review paper will provide an overview of the principles, evolution and state of the art of one of the most widely utilized vacuum electronic devices, the traveling wave tube (TWT). The wide band, high gain features of TWTs make those devices the most promising solutions for high power at millimeter waves and THz frequencies.