## 2 Basic Principles  
IPL serves as a key indicator for evaluating electromagnetic interference defined in Equation (1):  
\[IPL=P_{T}-P_{R} \tag{1}\]  
where \(P_{T}\) denotes the transmit power and \(P_{R}\) denotes the received power (in dBm). IPL can be equivalently expressed as the scattering parameter \(S_{21}\) between the antenna ports in Equation (2):  
\[IPL=|S_{21}|=\frac{|V_{2}|}{|V_{1}|}=20\log(\frac{|V_{2}|}{|V_{1}|}) \tag{2}\]  
Note that the magnitude \(|S_{21}|\) is used in this equation, as the negative sign in \(S_{21}\) indicates the signal direction, while the positive magnitude represents the loss. This approach ensures that negative \(S_{21}\) values are treated as positive losses in the calculation. Additionally, the use of the 20 log form is appropriate because CST exports \(S_{21}\) as a voltage-wave ratio, which requires logarithmic conversion to express the result in decibels. To assess whether high power PEDs can cause electromagnetic interference to the onboard antenna, the \(IPL_{target}\) is defined in Equation (3):  
\[IPL_{target}=P_{T}+MEF-P_{threshold} \tag{3}\]  
where \(P_{threshold}\) denotes the interference threshold of the receiving antenna and \(MEF\) denotes the front door multiple equipment factor. To compute the cumulative effects from multiple devices, the spurious emission value for each device is first weighted proportionally to its linear interference coupling value. The results for all devices are then summed and normalized to the single PED worst-case contribution to arrive at the cumulative effects. When the sources have equal magnitude, the worst-case contribution from a single PED corresponds to the location with the lowest IPL value. The interference coupling value \(C_{i}\) is calculated from the IPL at the same source location, as described in [23]:  
\[C_{i}=10^{-IPL/10} \tag{4}\]  
Thus, the maximum power coupled from seat \(n\) to the receiving antenna can be expressed as follows:  
\[P_{R}^{n}=P_{T}^{n}\cdot C_{i}^{n} \tag{5}\]  
By summing all \(P_{R}^{n}\) and normalizing by the maximum value \(P_{R}^{\max}\), the \(MEF\) for \(N\) devices is defined as follows:  
\[\text{MEF}=(\sum_{N}P_{R}^{n})/(P_{R}^{n})^{\max}=(\sum_{N}P_{T}^{n}\cdot C_{i }^{n})/(P_{T}^{n}\cdot C_{i}^{n})^{\max} \tag{6}\]  
If \(P_{T}\) is identical for all transmitting sources, it can be normalized out and Equation (6) becomes  
\[\text{MEF}=\sum_{N}(C_{i}^{n}/C_{i}^{\max});n=1,...,N \tag{7}\]Alternatively, the normalized coupling factor \(\left\langle C_{i}^{n}\right\rangle\) and the normalized IPL \(\left\langle IPL^{n}\right\rangle\) can be defined as follows:  
\[ \begin{split}\left\langle IPL^{n}\right\rangle&=IPL^{n }-IPL^{\min},\text{ and}\\ \left\langle C_{i}^{n}\right\rangle&=C_{i}^{n}/C_{i }^{\max}=10^{-\left\langle IPL^{n}\right\rangle/10}\end{split}  \tag{8}\]  
It can be shown that  
\[\text{MEF}_{\text{dB}}=10\log_{10}(MEF)=10\log_{10}(\sum_{N}(C_{i}^{n})) \tag{9}\]  
If the IPL is lower than \(IPL_{target}\), it means the energy received by the antenna exceeds the interference threshold, which may result in electromagnetic interference to the GPS antenna. Conversely, if the IPL is greater than \(IPL_{target}\), interference with the antenna is unlikely. For example, a certain type of mobile phone connected to the TianTong satellite operates with an uplink frequency of 1980-2010 MHz and a downlink frequency of 2170-2200 MHz. When the satellite communication function is activated, the device transmits at a peak power of 2 W within this frequency band, which is close to the GPS L1 band. When the satellite communication function is activated, the device transmits at a peak power of 2 W within this frequency band, which is close to the GPS L1 band. The GPS antenna operates at 1575.42 \(\pm\) 10 MHz, with an interference threshold \(P_{threshold}\) of \(-120.5\) dBm, as specified by ICAO Annex 10 [24]. Sensitive receivers can be disrupted by spurious emissions, which may overlap with the receiver's operating band and significantly degrade performance.