## 4 A320 Cabin Interference Path Loss Measurement
### Experiment Results and Analyses  
The signal generator was configured to emit a 5G NR TM1.1 standard waveform with a center frequency of 1.995 GHz and a bandwidth of 20 MHz, simulating the satellite communication frequency band used by the mobile phone. According to the datasheet, the amplifier is specified to have a maximum gain variation of \(\pm 1.5\) dB under a 0 dBm input and a 50 \(\Omega\) load. To verify gain flatness across the relevant frequency band, measurements were taken at three representative frequencies: 1980 MHz, 2000 MHz, and 2020 MHz. The amplifier gain was configured to 46 dB using the control software. The measured output gains at the three frequencies were 53.74 dB, 53.87 dB, and 53.78 dB, respectively. These measurements reflect the total system gain, including contributions from the amplifier, cable and connector losses. The gain variation across the three frequencies was within \(\pm 0.065\) dB, and the 95% confidence interval confirms excellent gain flatness and consistency. These results confirm that the amplifier performs as expected and does not introduce any significant frequency-dependent bias into the measurements. The total transmission power \(P_{total}\) was set to 10 W to prevent the received power from being too low, and the spectrum analyzer's resolution bandwidth (RBW) was set to 1 kHz. All the measurements in this study were conducted with a fixed RBW of 1 kHz. Using the same RBW for all measurements ensures that power readings are comparable and reduces systematic bias. Under these measurement conditions, a statistical analysis was performed on the noise floor of the spectrum analyzer. The calculated mean, standard deviation, and 95% confidence interval are as follows: \(-105.31\) dBm, 0.85 dB, and \(\pm 0.12\) dBm, respectively. This indicates that the spectrum analyzer maintains good stability in its noise floor. Since the power measured by the spectrum analyzer corresponds to the energy within the 1 kHz resolution bandwidth, the energy value \(x\) of the transmitted signal in this bandwidth needs to be calculated using Equation (10):  
\[x=10\log(\frac{P_{total}}{1 mW})-10\log(BW)+10\log(RBW) \tag{10}\]  
By substituting the relevant values into the equation, the transmit power is calculated to be approximately \(-3\) dBm. The difference between the transmit power and the received power represents the IPL value. When the transmitting antenna is positioned at the 2 nd, 17 th and 25 th row of windows, the transmit power of the PED and the measurement results from the spectrum analyzer are shown in Figure 8.  
The cable loss between the spectrum analyzer and the aircraft antenna must be taken into account in the above calculations. The loss of the blue tested cable shown in Figure 7 was measured to be approximately 2 dB. The cable is connected via an adapter to an ARINC 600 SIZE 2 coaxial pin, which interfaces with the \"av  
Figure 7: Signal reception setup. According to product specifications, the insertion loss introduced by these two connectors is 2 dB. The connection between the avionics rack and the GPS antenna is established using internal aircraft cable. Similar setups have been used in previous NASA measurement experiments [28], where the cable loss was not directly estimated. Based on the previously measured 2 dB loss of the blue tested cable, an estimated loss of 5 \(\pm\) 2 dB for the internal aircraft cable is considered acceptable. Therefore, the total loss from the GPS antenna to the spectrum analyzer is around 9 \(\pm\) 2 dB, which is considered a reasonable approximation. When the transmitting antenna was positioned at the left or right side of the fourth window, the average IPL values were determined to be 77.52 dB and 77.15 dB, respectively. This indicates that the placement of PED on either the left or right side of the cabin has a minimal effect on the IPL value. Subsequently, the transmitting antenna was positioned at the right side of the cabin, with its location progressively changing from the front to the back of the cabin.