In pulsed radar transmitters, the modulator is the key interface to the vacuum electronic device. Modern modulators use the series connection of semiconductors for high voltage switches. Stacked IGBTs are used for high current and low repetition rate applications, and stacked MOSFETs are used for low current and high repetition rate. For reliable operation, a series stacked switch needs to have voltage balance during static and dynamic conditions. One approach to achieve this balance is to use voltage grading resistors and capacitors. However, if poorly selected, this approach may have high power losses and not be compact Because of the need for compact designs, this paper describes methods to equalize the voltage distribution for each switch. For MOSFET switches, this paper describes modulator design, protection, Miller effect, voltage balance due to parasitic capacitance, and thermal design. For reliable designs over large operating temperature ranges, this paper identifies the need for an integrated design that addresses all of the power losses in the switch and describes a metric for efficient designs, dissipation density ratio.
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