The transit-time effect in a coaxial structure was explored to develop a low-impedance high-power microwave (HPM) source that uses no external magnetic field and no confining foils. This source will work in the 1-20 GHz range and will have a power output of no less than 1 GW. The input will be a low-voltage DC pulse of only 350 kV or less with a flat top of approximately 200 ns. The DC pulse is launched into a coaxial structure that is the diode, the oscillator, and the buncher all in one. The source offers significant improvements in power, repetition rate, size, and efficiency. Because of the coaxial structure, the diode impedance may be reduced to a few ohms thus allowing larger input and output powers. With no foils to erode, the only factor limiting the repetition rate is the ability to maintain an adequate vacuum, and since there is no external magnetic field required, the device is simple, lightweight, and inexpensive. Because of the strong bunching, the efficiency is high. As is the case with all transit-time oscillators, the signal is stable and monochromatic. The device may be used as a buncher or as an oscillator. It is shown that a device based on this concept is indeed possible. In addition, it is shown that the gated emission of electrons, a process basic to high-power RF amplification, is a natural by-product of the mechanism used in this device.
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