# Development and Research of a Medium Vertical Dipole Electromagnetic Pulse Simulator
## 4 Experiments and Characteristics Research
### Different Feeding Modes  
As depicted in Figure 6, the voltage waveforms of the pulse source fed into the antenna under different feed modes were obtained through practical measurements. The waveforms in Figure 6a and the red line in Figure 6b are derived from the measured waveform of the electric field near the antenna origin, while the black curve in Figure 6b represents the output voltage waveform of the bottom feed source when it is directly connected to the 50 \(\Omega\) matched load. In Figure 6a, the black curve is the output voltage waveform of the peaking capacitor shown in Figure 1a, which is charged by the DC source and discharges directly into the antenna load. On the other hand, the red curve is the voltage pulse generated by a one-stage pulse compression circuit. In this circuit, a voltage pulse is initially formed by the discharge of a compact Marx generator, then compressed by a peaking capacitor, and finally, fed into the antenna load.  
The above figures demonstrate that the ideal double exponential wave will experience distortion due to the impedance of the antenna and the structure's discontinuity. An example of this is shown by the red curve in Figure 6b. The half-width of the pulse begins to widen at a distance of 14 ns from the starting point of the waveform. One possible reason for this is that the antenna cable becomes a resistance-loaded line at a distance of 1 m from the end of the antenna. To achieve this loading method, 12 resistance chains formed by a series of 5 metallized film resistors with equal resistance values replace the original 24 or 48 metal cables and are uniformly distributed along the circumference on the top supporting ring of the antenna, as shown in Figure 1a. The total resistance of the loaded lines equals the impedance of the antenna, and the end of the antenna is left open. In Figure 6, the distance from the field monitoring point to the antenna cone is 0.5 m, the antenna is 5 m high, the wire length from the antenna cone to its end is nearly 6 m, and the electromagnetic wave's propagation speed in air is approximately 3 \(\times\) 10\({}^{8}\) m/s. Based on the principle of electromagnetic wave transmission, it is estimated that it takes around 38 ns for the terminal reflection of the electromagnetic wave at the end of the antenna to reach the measuring point. As seen in Figure 6, this reflection results in a concave in the waveform at the 40 ns position, followed by a bump after 15.8 ns, which is believed to be caused by the reflection of the current wave along the antenna from the cone to the end. Another depression appears on the waveform after 97 ns, which may be caused by the waveform back to the source reflected back and forth again. In Figure 6a, a pit appears 50 ns after the second wave peak, which is just the same as the length of the feed-in cable connected with the pulse source output terminal in the bottom feed mode. Due to the  
Figure 6: Voltage waveforms from the source in different feeding modes. (**a**) Voltage fed into the antenna over the ground. (**b**) Voltage fed into the antenna under the ground.  
open end of the antenna and the remaining charge on the antenna that cannot be released directly, the time for the waveform to decay to zero at the end of the curve is significantly extended. Overall, it is clear that the discontinuity of the antenna structure and impedance are major factors causing waveform distortion when the ideal double exponential wave is fed into the antenna.