A Design Study of a C-Band Crestatron

Abstract : This memorandum presents a design study of a high power C-band Crestatron Amplifier. While conventional helix traveling-wave tubes (TWT's) are operated in an exponentially growing-wave mode, the Crestatron operates a "beating-wave" regime where three constant-amplitude voltage waves traveling at different phase velocities along the helix beat together to produce power gain. Although inherently lower in gain than a TWT, the Crestatron can produce high power rf over a surprisingly broad frequency range with very good efficiency. In our design example, CHRISTINE 1-D large-signal simulations show that a 5850 volt, 196 mA Crestatron can produce in excess of 250 W of rf power over a frequency span of 3 to 5.5 GHz. When combined with a two-stage depressed collector, the peak efficiency of the Crestatron is ~64% compared with ~50% for a TWT of similar power over this band. The Crestatron is also a higher power density device, with an estimated 40% reduction in length and 25% reduction in mass compared to the TWT. Compact, efficient, high power, high gain transmitters can be realized by combining the Crestatron with a low-noise solid-state driver in a microwave power module (MPM) configuration. Such a system has promising applications in volume- and weight-constrained platforms such as airborne pods and unmanned vehicles.