Pulse sharpening and soliton generation with nonlinear transmission lines for producing RF bursts

Abstract

Nonlinear transmission lines (NLTL) are being designed and built to extend the range of available Ultra-Wide Band (UWB) and High Power RF pulse generation technology, especially in the area of high repetition rate microwave burst generation. The NLTL approach to UWB and RF generation eliminates the need for the electron beam, vacuum system, and magnets required in conventional high power microwave (HPM) sources. Furthermore, the novel waveforms of NLTL generated pulses promise to offer a degree of frequency diversity unseen in current electron beam-driven HPM sources. UWB pulses are obtained using the wave front steepening properties of a transmission line with an amplitude dependent phase velocity. Ferrite loaded NLTLs have a phase velocity that increases with amplitude, so the pulse's voltage peak travels faster than the trough until the rise time is limited by dissipation. The addition of dispersion, which occurs in lumped periodic structures, can lead to the generation of a soliton, or solitary wave, and in some cases a group of solitons, where the dispersion replaces the dissipation as the balancing mechanism of the wave front steepening. Soliton bursts can be extracted from the line and delivered to a load as high power RF energy. A multi-stage system that consists of a pulsed power modulator for converting DC power into a high-voltage nanosecond pulse, a semi-continuous NLTL composed of biased ferrite beads for creating a fast rise-time UWB pulse, and a dispersive, lumped element NLTL that converts the UWB pulses into bursts of RF energy is discussed.