# Development and Research of a Medium Vertical Dipole Electromagnetic Pulse Simulator
## 4 Experiments and Characteristics Research
### Resistance Loading on Antenna  
The radiation field waveform produced by small- or medium-sized EMP simulators is inevitably affected by reflection at the end of the antenna due to limitations in the antenna's structure and size. One way to reduce this reflection effect is to load the resistance onto the antenna's current-carrying wires [25; 26]. To study the effect of resistance loading on the radiation characteristics of the antenna, 48 metal wires of the wire-mesh antenna were replaced with 24 tubular long water resistors with a 15 mm diameter. The resistance value  
Figure 10: The radiation field of the simulator on different distances. (**a**) \(E\) waveforms with different distances to the origin of the antenna. (**b**) The rise time of the \(E\) waveforms. Figure 9: The radiation field of the simulator on different angles. (**a**) Distance to the cone point of the antenna is 1 m. (**b**) Distance to the cone point of the antenna is 6 m.  
of the water resistor can be adjusted by changing the conductivity of its internal electrolyte. Figure 11 shows the variations of the radiation field waveform measured at different measuring points in the north direction when the water resistance value is changed. The water resistance value indicated in Figure 11 is the total resistance of the 24 water resistors in parallel, which was measured by the bridge. In Figure 11, it is evident that the radiation field waveform generated by small- or medium-sized EMP simulators is influenced by the reflection at the end of the antenna due to its structure and size limitations. To minimize this reflection effect, a common approach is to load the resistance onto the antenna's current-carrying wires. In this study, 48 metal wires of the wire-mesh antenna were replaced with 24 tubular long water resistors to investigate the impact of resistance loading on the antenna's radiation characteristics. The resistance value of the water resistor was adjusted by modifying the conductivity of its internal electrolyte. The results indicate that, at a distance of 0.5 m from the antenna cone vertex (as shown in Figure 11a), the radiation field waveform closely resembles the ideal double exponential wave without any concave or protruding features caused by antenna end reflection (as shown in Figure 6). When the resistance value increases gradually from 165 \(\Omega\) to 2.1 k\(\Omega\), the radiation field waveform remains unchanged, but the amplitude slightly decreases. However, the amplitude of the radiation field decreases gradually with the increasing resistance loaded onto the antenna at the measuring point of 1 m from the antenna cone vertex. When the resistance value reaches 2.1 k\(\Omega\), a significant distortion appears on the radiation field waveform, and an oscillation occurs at its peak (as shown in Figure 11b). As the measuring point moves outward to 3 m from the antenna cone vertex, the radiation field waveform starts to distort when the resistance value is greater than 460 \(\Omega\), and the pulse width of the waveform is reduced to only a few ns (as shown in Figure 11c). At the 5 m position, none of the resistance values used in the test meet the application's requirements for the waveform width of the radiation field. Nevertheless, the amplitude of the radiation  
Figure 11: Effect of antenna resistance loading on a radiation electric field at different measuring points in the north direction. (**a**) Measure point: (0.5, 0, 0.05). (**b**) Measure point: (1, 0, 0.05). (**c**) Measure point: (3, 0, 0.05). (**d**) Measure point: (5, 0, 0.05). electric field is still decreasing with the increasing load resistance, because the attenuation effect of the resistance on the current passing through the antenna is enhanced with the increase of the resistance value. This leads to different distortions in the radiation field waveform measured at different points.