Simulated and Measured Output From a Composite Nonlinear Transmission Line Driven by a Blumlein Pulse Generator

Nonlinear transmission lines (NLTLs) provide a means to generate high-repetition-rate, high-power microwaves with fewer auxiliary systems than conventional sources. They are typically driven by pulse forming networks (PFNs) or Marx generators, and one would intuitively hypothesize that the microwave generation would not depend significantly on the method used to generate the input pulse to the NLTL. This study examines the implications on microwave output by using a Blumlein pulse generator with a 10-ns pulse duration and 1.5-ns rise and fall times to drive coaxial NLTLs produced using composites with nickel zinc ferrite and barium strontium titanate (BST) inclusions. Applying a 30-kV pulse to the composite NLTLs produced frequencies ranging from 1.1 to 1.3 GHz with output powers over 20 kW. The output frequencies increased with increasing volume fraction of BST. Measured results and simulations using LT SPICE showed that Blumlein modulators were insufficient to drive NLTLs to produce high-power oscillations; however, LT SPICE simulations showed that applying a standard PFN to the same NLTL produced the expected oscillations. This difference arises because the mechanism for Blumlein pulse formation cancels the shockwaves responsible for inducing microwave production by the NLTL.