## 3 Results  
Oscillation formation correlated strongly to NLTL impedance in the combined PFL and HPM configuration. We observed weak modulation on the flat tops of the pulses generated using the 10 \(\Omega\) and 25 \(\Omega\) lines and no modulation on the pulses generated using the 50 \(\Omega\) lines. In conjunction with oscillation formation, significant pulse sharpening occurred for all lines. When comparing the highest charging voltage to the lowest for each impedance, the rise time, taken from 10% to 90% of the peak amplitude on the rising edge, decreased by 2.4 ns, 2.7 ns, and 2.5 ns for the 10 \(\Omega\), 25 \(\Omega\), and 50 \(\Omega\) lines, respectively. Observable oscillations formed on the 10 \(\Omega\) line for charging voltages as low as 10 kV, while a charging voltage of 15 kV was required to induce noticeable oscillations for the 25 \(\Omega\) line. Interestingly, strong oscillations form after the initial pulse on the 10 \(\Omega\) line with an RF burst duration of \(\sim\)5 ns.  
Figure 3 details the progression of the output waveform for different charging voltages for the 10 \(\Omega\), 25 \(\Omega\), and 50 \(\Omega\) NLTLs. While pulse sharpening occurs for all NLTL impedances, oscillation formation does not. No oscillations occur for the 50 \(\Omega\) NLTL for any of the charging voltages considered. Reducing the NLTL impedance to 25 \(\Omega\) resulted in observable oscillation formation on the flat top of the pulse. Further reducing the NLTL impedance to 10 \(\Omega\) resulted in oscillations on the flat top of the pulse and after the pulse for charging voltages of 15 kV and higher. The waveform profile presented in Figure 3a is consistent with the results for other 10 \(\Omega\) composite-based NLTLs studied in the combined PFL/HPM source configuration [24].  
Figure 4 shows the power spectrum density analysis on the output waveforms of the 10, 25, and 50 \(\Omega\) lines for a 20 kV charging voltage. For the 10 \(\Omega\) line, lobes are observed primarily at 1.08 and 1.43 GHz with peak power of 48.1 dBW (64 kW) and 39.34 dBW (8.5 kW), respectively. The lobes have bandwidths, which are taken as \(-\)3 dB down, of 76 MHz and 102 MHz. The power spectra for the 25 \(\Omega\) and 50 \(\Omega\) lines are very similar with differences between 500 MHz and 1 GHz. For the 25 \(\Omega\) line, lobes are present at 513 MHz, 762 MHz and 943 MHz that are not present for the 50 \(\Omega\) NLTLs. This difference is attributed to the weak RF modulation in the 25 \(\Omega\) line. Further supporting this argument is the period of the observed modulation for a 25 \(\Omega\) line charged to 20 kV lies between 1.3 and 2 ns, making 500 MHz to 1 GHz the region of interest when looking for power spectrum differences between the 25 \(\Omega\) and 50 \(\Omega\) NLTLs.  
Additionally, the 10 \(\Omega\) NLTL yielded greater power output at frequencies between 1.5 and 2.3 GHz compared to the other NLTL impedances. For example, at 2 GHz, the output of the 10 \(\Omega\) line is 17 dBW, while the outputs of the other lines are \(\sim\!-40\) dBW, a 57 dB difference.  
Figure 3: Output voltage waveforms for the (**a**) 10 \(\Omega\), (**b**) 25 \(\Omega\), and (**c**) 50 \(\Omega\) NLTLs as combined. PFL/HPM sources for different charging voltages.