Ultrafast millimeter wave amplitude modulator for reflectometry of plasma

Summary form only given. In modern pulsed radar and amplitude modulation reflectometry of fusion plasma the high speed PIN switches and PIN attenuators are used. They provide the amplitude modulation to several hundred MHz and pulses with a pulse duration of 1-3 ns. The resolution in the measurement of the distances to the plasma strongly depend on the speed of the modulators. An ultrafast varactor amplitude modulator has been designed for the use in pulsed radar and AM reflectometry over the millimeter band. The modulator provides the speed of the amplitude modulation of 5 GHz and pulses of 0.2 ns with ON/OFF ratio of 25-30 dB for a single diode and 35-40 dB for the two diode modulator. Insertion losses are 1.5-2 dB. It can operates with a source which has an output in the CW mode to a few watts. The modulator has a narrow frequency band <1 GHz, but in reflectometers which use sources working at fixed frequencies it is not regarded as a disadvantage, because each source can be supplied with an individual modulator. The modulator provides a linear change of the output signal with change of the bias voltage from zero to 15 V and can be used as an electrical tuning attenuator