## 3 A320 Cabin Interference Path Loss Simulation  
### Model Design and Simulation Setting  
This research constructs a 1:1 simulation model of the A320 aircraft, as shown in Figure 1. In order to simplify the model, the cockpit, wings, cargo, and other external structures were omitted during the model design process. This approach not only simplifies the model but also reduces the number of mesh cells and shortens the simulation time.  
The A320 cabin model is 23.50 m in length and has a fuselage width of 3.95 m. The aircraft is equipped with windows, main cabin doors, and emergency exits on both sides of the fuselage. Both the PED and the GPS antenna are modeled as half-wave dipole antennasto simulate the emission source. The GPS antenna is positioned on the upper surface of the aircraft near the front cabin door. Discrete ports are assigned to both the PED and GPS antennas, as shown in Figure 1. The half-wave dipole antenna used in this study has a length of L = 86.28 mm and a diameter of D = 0.75 mm. The center frequency is set to 1.575 GHz, which matches the operating frequency of the GPS antenna. The gap between the two dipole conductors is set to L/200, and the simulated \(S_{11}\) parameter is shown in Figure 2. It is important to ensure that the operating frequency range of the dipole antenna covers the simulation frequency range of 1500-1600 MHz described in the next section. Similarly, if the simulation frequency band is changed, the length of the dipole antenna should be adjusted according to the new center frequency.  
Furthermore, Figure 3 shows the radiation patterns of the half-wave dipole antenna used in this study on the two principal planes (0 and 90\({}^{\circ}\)). When the frequency is set to 1.575 GHz, the antenna's main lobe gain is 2.08 dBi, and the main lobe is directed at 90\({}^{\circ}\).  
Studies [11] have shown that when the aircraft fuselage is modeled as a perfect electric conductor (PEC) with open windows, and another model uses an air fuselage with dielectric windows, the simulation results are similar. Although using a finer mesh can improve accuracy, an excessively fine mesh greatly increases the number of mesh cells and lengthens the simulation time. Studies [11] have also shown that when the mesh size is smaller than \(\lambda/8\), further refinement has little effect on accuracy but significantly increases the simulation time. The mesh settings used in the simulation are listed in Table 1.  
Figure 1: A320 aircraft cabin model.  
Figure 2: \(S_{11}\) of half-wave dipole antenna.  
In this study, the structure is configured as a \"PEC fuselage with open windows\". The entire model is constructed as a \"shell\" model in CST, with all six boundaries of the bounding box set to \"open (add space)\". The accuracy parameter for the time domain solver is set to \(-40\) dB, which serves as a relative energy threshold commonly used to determine convergence in full-wave electromagnetic simulations. This value is not an absolute power unit (such as dBm), but a normalized criterion based on the system's initial excitation.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Mesh Properties** & **Mesh Settings** \\ \hline \multirow{4}{*}{Maximum cell} & Cell per wavelength: \\  & near to model: 8; far from model: 8 \\  & Cell per max model box edge: \\  & near to model: 20; far from model: 20 \\ \hline Minimum cell & Fraction of maximum cell near to model: 20 \\ \hline Mesh cells & 41,987,280 \\ \hline \hline \end{tabular} Note: All simulations were performed on a PC platform with Intel(R) (Intel, Santa Clara, USA) Xeon(R) Gold 6242R CPU @ 3.10 GHz (two processors) with 512 GB RAM using the mesh settings detailed in Table 1.  
\end{table}
Table 1: Mesh setting for A320 cabin model  
Figure 3: Radiation patterns of antenna. (red line: Farfield Gain; light blue line: Main lobe direction; dark blue: 3 dB Angular width)