## 1 Introduction  
In recent years, the susceptibility and vulnerability of electronic systems threatened by high power electromagnetics (HPEM) such as high-altitude electromagnetic pulse (HEMP), ultra-wide bandwidth (UWB) and high-power microwave (HPM) etc., have been paid more attention from researchers [1, 2]. As antennas of wireless communication systems are usually exposed to free space, the electromagnetic (EM) coupling response of the RF front-end may possibly cause the permanent destruction or performance degradation of RF circuits inside the wireless equipment [3]. Studying how the electromagnetic pulse (EMP) conducts on the RF channel is the key to evaluate the potential risk of multiple HPEM threats faced by the wireless communication system, and it requires the system-level SPICE modelling technology of the RF channel consisting of wireless antenna and RF components etc., considering the HPEM illumination scenarios. The wireless communication system with the L band works on the frequency range of 1 GHz\(\sim\)2 GHz, is widely applied in radar navigation, mobile communication and satellite communication fields facing on a variety of HPEM environments. In practice, the circuit details of the targeted system usually cannot be provided to researchers from the manufacturer due to commercial secrets, which may cause difficulties in circuit modeling and response analysis. Hence, trying to establish the system-level SPICE model of the response coupled on the RF channel according to the measured data of the targeted system, and then using norm theory to analyze these responses excited from multiple HPEM waves to evaluate the potential EM risk suffered by the RF channel, is the main issue in this paper. System-level SPICE circuit modeling of EMP response coupling on the RF channel is the way to study the pulse energy propagation along the RF channel, which mainly consists of the SPICE modeling of antenna HPEM response and RF components. Much effort has been devoted to the equivalent circuits of RF components such as antennas or filters [4; 5; 6; 7; 8; 9; 10; 11]. Antenna response after EMP illumination is mainly calculated by the typical electromagnetic methods such as MoM, FDTD [4; 5], or simulated with commercial software such as CST or HFSS etc. The traditional equivalent circuit model of the dipole antenna was adopted to compute the antenna response after HEMP illumination in [6]. However, this antenna model is narrowband and not suitable for the wide frequency range due to the super wideband feature of EMPs. In [10], an equivalent circuit model for the broadband antenna was established with rational function approximation by the vector fitting (VF) method [12; 13; 14; 15], which is deemed as an efficient method and is particular suitable for SPICE circuit modeling. [PERSON] presents a SPICE model of a paraboloid antenna for receiving based on the Thevenin theorem [11]. It is an efficient way to utilize the Thevenin or Norton theorem to obtain the equivalent circuits of the antenna response illuminated by HPEMs with the VF method, which will be applied to the SPICE model of the RF channel in this paper. However, no existing literatures have been found which focus on the system-level SPICE model of the RF front-end circuits with pyramid horn antenna illuminated by HPEMs. Hence, the system-level SPICE model method with VF method is proposed for the RF channel with a pyramid horn antenna. It is hard to compare the HPEM response after RF components when considering multiple HPEMs due to its complex waveform characteristics, which is the major difficulty of EM risk analysis. In our previous work [16], the electromagnetic sensitivity research of vulnerable components in wireless communication system was studied, the research results demonstrate that norm theory is suitable for the analysis of the HPEM conducted responses based on the physical effect mechanism.