Traveling-wave tube efficiency degradation due to power absorbed in an attenuator

Traveling-wave tubes will oscillate if sufficient power is reflected at the input and the output of the tube; that is, if the loop gain is more than unity. As most tubes have large forward gain and matches (or loads) have some reflection, protection against oscillation is usually provided by return or backward loss. In most tubes the loss will be bilateral with the loss in the forward direction both absorbing power and reducing the rate of gain. The power absorbed subtracts from the power output and reduces the efficiency. This report presents the efficiency reduction due to power absorbed in the attenuator.