Pulse Modulation of Millimeter Wave Tubes

Various techniques for producing narrow pulse ( f 5 ns) modulation of millimeter wave tubes, such as extended interaction amplifiers, magnetrons, and traveling-wave tubes, are discussed. In order to achieve the narrow pulsewidth, the switch, pulse forming circuitry, as well as the tube interface, must satisfy very stringent requirements. In particular, the switch must operate at kilovolt (kV) levels and must be capable of the following: 1) fast risetime and falltime ( ~1 ns), 2) large peak currents ( ~ SOA), and 3) high pulse repetition frequencies ( ~ 2 X 104 Hz) . The switch techniques described include near term approaches using tube technology (shielded thyratron, planar triode), as well as longer term solid-state approaches (avalanche transistor, optically activated switch). A hybrid approach (thyratron in combination with a ferrite sharpener) is also described. Experimental results representative of each technique are presented. Comparisons and the merits and drawbacks of each technique are discussed.