# Development and Research of a Medium Vertical Dipole Electromagnetic Pulse Simulator
## 2 About the EMP Simulator  
Since the 1990s, with the development of information technology in large aviation equipment, surface ships, and wide-area infrastructure, the HEMP threat assessment and simulation test technology has once again attracted the attention of scholars in the fields of nuclear technology and electromagnetic environmental effects. As people's understanding of the mechanism and effects of HEMP has deepened, various countries have begun to develop various types of EMP simulators with faster front edges (1-2 ns) and narrower pulse widths (20-50 ns) [4; 9; 10; 11; 12]. The waveform of the radiation field generated by EMP simulators usually needs to comply with certain test standards [8; 13]. Currently, newer standards such as IEC61000-4-25 specify that the radiation field waveform of the early HEMP environment should be an ideal double exponential waveform with a rise time of 2.5 \(\pm\) 0.5 ns and a half-width of 23 \(\pm\) 5 ns. Within the specified test range, its maximum amplitude can reach 50 kV/m.  
Based on the antenna structure and the polarization direction of the electric field, HEMP simulators are usually classified into three types: a guided-wave simulator, hybrid simulator, and dipole simulator [8]. The dipole-type EMP simulator is an ideal radiation wave simulator that can radiate extremely fast electromagnetic pulses, and the distribution of the radiation field can be accurately predicted through analytical calculations [2; 9]. The common antenna structure of this type of simulator is a metal cone fixed on a conductive plane, which, together with its mirror image in the conductive plane, forms an equivalent electric dipole antenna. The antenna radiates vertically polarized electromagnetic waves outward along the conductive plane. Therefore, it is also commonly referred to as a vertically polarized dipole radiation wave EMP simulator. The electromagnetic waves generated by this type of simulator originate from the apex of the cone and radiate in all directions in the space formed by the cone and the conductive ground plane, providing a large available test space. Therefore, it is very suitable for EMP-related tests of large equipment such as surface ships or aircraft in the start-up state. Simulators with similar antenna structures, such as EMPRESS II and VPD II in the United States, VPD in Germany,and EMIS-III-VPD in the Netherlands, usually have a typical antenna impedance value between 60 \(\Omega\) and 75 \(\Omega\)[8; 9].  
The pulsed power driver used for EMP simulators generally consists of three parts: a primary energy storage unit, a pulse compression unit, and an antenna coupling unit. The Marx generator is a conventional high-voltage pulse-generating device that generates high-voltage electrical pulses through the serial discharge of multiple charged capacitors via multiple gas switches. Due to its many advantages, such as simplicity, reliable performance, easy adjustment, and easy maintenance, it has been widely used as a primary energy storage unit in EMP simulation devices [10; 14; 15]. Especially with the development of a low inductance fast Marx generator, the pulse driver based on the first-stage steepening mode and the Marx generator has been widely used in the small- and medium-sized EMP simulation devices, with output voltage levels ranging from hundreds of kilovolts to megavolts [11; 12; 16]. There are two types of driver source position layouts: above the conductive plane and inside the conical antenna (known as top feed, as illustrated in Figure 1a) and below the conductive plane (known as bottom feed, as shown in Figure 1b).