NLTL Frequency Chirp Through Dynamic Bias of Inductor Cores

Nonlinear transmission lines (NLTL) have demonstrated the ability to convert a low-frequency video pulse into a narrowband RF packet whose frequency may vary from pulse to pulse. Synchronous wave magnetic NLTLs achieve this via a DC current bias prior to the launch of a video pulse which sets the subsequent shock velocity and thus the RF frequency. This paper explores the idea that a dynamic (time-varying) bias waveform can yield NLTL RF output with a chirp frequency characteristic by varying the shock velocity along the length of the line. A low power NLTL was utilized to prototype the concept using 1 kV-3 kV input drive, 0-150 V bias waveform, and 0-1 A DC bias current. The center frequency output of the low power NLTL ranges from 120 MHz-260 MHz, which varies with bias current and drive voltage, and has RF pulse widths between 50 ns and 300 ns. The optimization of the input waveform required to produce a chirp output waveform and experimental characterization of various dynamic bias waveforms on a low power test bed are described.