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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.

Nonlinear transmission lines (NLTLs), which exhibit permittivity as a function of electric field and/or permeability as a function of magnetic field strength, are of increasing importance for sharpening pulses to less than 100 ps and serving as radio frequency (RF) sources; however, NLTLs often are not easily modified to achieve different output parameters. One method under investigation involves combining nonlinear dielectric [barium strontium titanate (BST)] and/or magnetic [nickel zinc ferrite (NZF)] inclusions to tune the NLTL properties by adjusting the inclusion loading fractions. This article focuses on measuring the nonlinear permeability and magnetic loss tangent of composites comprising various volume loadings of NZF or NZF and BST inclusions encapsulated in a silicon matrix. We measured the relative permeability from 1 to 4 GHz using a coaxial airline while biasing the samples in an external dc magnetic field from 0 to 171 kA/m. The permeability decreased from 1 to 4 GHz for each volume fraction but increased with increasing magnetic field strength at low-magnetic field strengths with sufficient NZF volume loading. The magnetic loss tangent of the composites increased with increasing frequency and/or NZF volume fraction but was suppressed by increasing the external magnetic field strength. Adding BST to NZF composites did not cause a significant change in permeability compared to NZF alone, based on an analysis of variance (ANOVA) and multiple comparison test. These results elucidate the frequency dependence of NZF volume loading at microwave frequency and provide initial information for simulating NLTLs and examining more comprehensive RF system behavior.