What is Pulse Droop?

A pulse is a change in the shape of the signal due to sudden transient variations in the amplitude of the signal from its baseline level to a lower or higher level. Ideally, the pulse has a constant power throughout its duration. But there are conditions where this might not be true. In high-power transmitters such as klystron amplifiers, it is unable to maintain full output power during a long pulse which results in pulse droop. Pulse Droop is defined as a reduction in the amplitude between the beginning and end of a pulse. It is usually expressed in dB.

Where L rise is the amplitude level of the pulse where droop starts and L fall indicates the amplitude level of the pulse where droop ends. Both of them are called rising and falling edge respectively.

Pulse droop leads to a decline in the output pulse voltage throughout one pulse. It is caused by the increase in the current during the time duration of the pulse.

Droop Rate is defined as the rate at which the amplitude of the signal pulse decays. It is defined as the difference between the power level at the beginning of the pulse ON time and the power at the end of the pulse ON time, divided by the pulse amplitude. It is expressed in dB/us. A positive droop rate indicates a reducing amplitude level over the sample pulse duration (L rise > L fall) and a negative droop rate indicates an increasing amplitude level over the sample pulse duration (L rise < L fall).