A tunable frequency transmission line pulse forming network circuit for forming a waveform having a spectral content. The pulse forming network circuit comprises a dielectric material; a ground section; a stepped shaped charged section, with the charged section having a plurality of stages including a first stage; a power supply coupled to the pulse forming network circuit for charging the pulse forming network circuit; a switch coupled to the pulse forming network circuit for periodically discharging the pulse forming network circuit; and an antenna coupled to the pulse forming network circuit for propagating a high-power microwave signal from the pulse forming network circuit into the environment. At least the first stage of pulse forming network circuit has one of a tunable magnetic material and a nonlinear magnetic which facilitates adjusting the waveform and the spectral content of the waveform emitted by the pulse forming network circuit into the surrounding environment.