A coaxial solid state nonlinear pulse forming line with an exponentially tapered ferrite composite core

The need to optimize size, weight, and power of high-power microwave (HPM) systems has motivated the development of solid-state HPM sources, such as nonlinear transmission lines (NLTLs), which utilize gyromagnetic precession or dispersion to generate RF. One recent development implemented the NLTL as a pulse forming line (PFL) to form a nonlinear pulse forming line (NPFL) system that substantially reduced the system's size by eliminating the need for a separate PFL; however, matching standard loads can be challenging. This paper describes the development of a tapered NPFL using an exponentially tapered composite based ferrite core containing 60% nickel zinc ferrite (by volume) encased in polydimethylsiloxane (PDMS) and encapsulated in a 5% barium strontium titanate shell. The tapers exponentially change the line's impedance from a 50 Ω standard HN connection to 25 Ω before tapering back to 50 Ω. We characterized the core behavior by obtaining magnetization curves and ferromagnetic resonance measurements. The rise time (10%-90%) of the pulse decreased from ∼6 ns for 5 kV charging voltage to 1.8 ns for 15 kV charging voltage. Under unbiased conditions, the system generated HPM with a center frequency of ∼850 MHz with a 3 dB bandwidth of 125 MHz. Magnetic biases of 15 and 25 kA/m increased the modulation depth and decreased the center frequency to ∼500 MHz for 15 kV charging voltage.