The various types of capacitor used in modulators all have very different design requirements and require differing dielectric characteristics. These capacitors range from the high voltage storage types used in the classical Pulse Forming Network modulator and in the newer MOSFET modulators to the capacitors used in the actual PFN's, and the newer requirements of the relatively low voltage types and IGBT snubbers, which are both used in the CLW and other solid-state modulators. The capacitor design requirements are discussed and reviewed in conjunction with the advantages and disadvantages of the different types of modulator.