High Repetition Rate Microwave Modulation

Several important emerging applications require efficient, high-speed high-duty-cycle, amplitude modulation of high levels of microwave power, with low cost and small size-and-weight. The modulation frequency and average power required for these applications are far beyond the capabilities of existing technology. MRC proposes to research and develop two alternative methods of achieving square-wave modulation at rates as high as MHz and beyond. One proposed method uses innovative variations of RF pulse-compression techniques demonstrated by the linear accelerator community to achieve such modulation at efficiencies in the vicinity of 90%. This approach uses a CW microwave source and RF cavities to chop up, delay, and stack pulses, resulting in peak output power much higher than that of the source (e.g., about triple for 33% duty cycle operation). The other approach, aimed primarily at extremely-efficient crossed-field microwave devices (CFDs), achieves modulation efficiencies above 96% using relatively low-cost pulsed-power components, by essentially reducing the problem to modulation of the tube's dynamic impedance alone. MRC will be assisted in this endeavor by Litton Systems, Inc., which is sufficiently interested in the potential of this project to provide support during Phase I free of charge. In addition to the requirement for this technology in the DoD HPM community, there is substantial need for highly -efficient, low-cost, high-speed AM modulation of high microwave power in applications such as radar, especially airborne radar. AM modulation currently involves more expensive modulators or very inefficient linear microwave amplifiers that draw considerable power during the off cycle.