Backward-wave oscillator
（重定向自Carcinotron）
![Miniature O-type backward-wave oscillator tube produced by Varian in 1956. It could be voltage-tuned over an 8.2 - 12.4 GHz range and required a supply voltage of 600V.](/Images/godic/202501/03/Backward_wave_oscillator2954.jpg")
![Backward wave oscillator at Stockholm University operating in the Terahertz range](/Images/godic/202501/03/Backward-wave_Oszillator-Stockholm2954.jpg")
![(a) Forward fundamental space harmonic (n=0),
(b) Backward fundamental](/Images/godic/202501/03/Space-harmonics.svg2954.png")
![Schematic of an M-BWO](/Images/godic/202501/03/M-bwo.svg2954.png")
A backward wave oscillator (BWO), also called carcinotron (a trade name for tubes manufactured by CSF, now Thales) or backward wave tube, is a vacuum tube that is used to generate microwaves up to the terahertz range. It belongs to the traveling-wave tube family. It is an oscillator with a wide electronic tuning range.