# Development and Research of a Medium Vertical Dipole Electromagnetic Pulse Simulator
## 4 Experiments and Characteristics Research
### Different Angles and Distances  
Figure 9 illustrates the radiation field waveforms measured at different angles around the normal of the cone antenna, with the distance between the monitoring point and the antenna cone point kept constant. The waveforms of the radiation field at different distances from the cone vertex are similar when the position of the monitoring point changes with the angle, except for some variations at the peak of the waveform. The connecting line between the cone point and the FRP supporting column of the antenna is oriented at a 45-degree angle north of west. The measuring point of 0.5 m from the antenna cone vertex is located between the connecting line of the cone vertex and the supporting column, whereas the measuring point of 6 m from the cone vertex is located on the extension line of the connecting line between the cone point and the column. As shown in Figure 9a, three distinct peaks appear at the top position of the radiation field waveform measured at the 0.5 m measuring point from the cone point and 45 degrees north of west. The three peaks become less obvious as the measuring point moves closer to the north or west, and the waveform becomes smoother. However, a clear double peak is observed on the waveform of the radiation field when the measuring point is at the position of 6 m from the cone point and the direction of west or north. The pulse width of the first peak of the waveform widens as the measuring point moves closer to the direction 45 degrees north of west, and the amplitude of the second peak decreases. The difference in the radiation field waveform is attributed to the reflection of the wave generated at the antenna's FRP supporting column. The rise time of the radiation field waveform is only about 2.5 ns, and its shortest wavelength corresponding to the frequency domain is above 80 cm. However, the diameter of the supporting column is only 20 cm. If the FRP column were an ideal insulating medium, its bulk resistivity would be very large, and its dielectric constant would be about 4.5, resulting in a negligible reflection effect. The reason for the observed effect may be that the cement poured into the hollow FRP column to increase its strength also increases the dielectric constant and body conductivity of the supporting column, enhancing its reflection effect on the radiation field. Figure 10 illustrates the radiation field waveforms measured at different distances from the monitoring point to the cone antenna vertex, with a fixed angle around the normal of the cone antenna perpendicular to the ground (at the direction of north). The amplitude of the radiation field measured at the monitoring point, which gradually moves away from the cone point, decreases with the law of 1/r when the distance r varies from 1 m to 11 m. However, the front edge of the radiation field remains basically unchanged, as depicted in Figure 10b. The rise times of the radiation field waveform measured at different positions are all between 2 and 3 ns by adjusting the working state of the internal switches of the pulse source. Specifically, the rise time of the radiation field measured at the position of 2.8 m from the cone antenna vertex is 2.8 ns, and the half-width of the waveform is 24.8 ns. At the 5 m position, the front edge of the measured radiation field is 2.4 ns, and  
Figure 8: Influence of the antenna end conditions on the radiation field of the simulator. (**a**) Measuring point position: (0.5, 0, 0.02). (**b**) Measuring point position: (5, 0, 0.02). the half-width is 22.8 ns. These measured waveform characteristics conform to the EMP experimental waveform specifications in the IEC61000-2-9 standard [7]. Figure 10a demonstrates that, as the monitoring point moves away from the cone point, the bump appearing on the back edge of the measured waveform of the radiation field gradually disappears. When the distance from the measuring point to the cone point reaches more than 9.5 m, the back edge of the radiation field waveform drops sharply and forms a negative peak.