Since TWTs are bidirectional devices, reflected signals can create oscillations inside the tube. This is why attenuators are essential—they reduce the effect of reflected waves while causing minimal loss to the forward-moving signal. The traveling-wave tube(TWT ), also known as the traveling-wave ampli er(TWA fi ) or traveling-wave tube ampli er(TWTA is a widely used ampli er in satellite communications and radar. It was invented by Andrei Haeff around 1933 as a graduate. The problem is aggravated by the very close coupling of the slow-wave circuits. A helical TWT consists mainly of a slow-wave structure (helix) and an electron gun.