# Radio Frequency Interference, Its Mitigation and Its Implications for the Civil Aviation Industry
## 3 Literature Review
However, interference from DME presents significant challenges to the LDACS sXignal, as the high power of DME signals can substantially degrade communication quality. The proposed methods aim to effectively reduce this interference, thereby ensuring reliable air-to-ground communication. [PERSON] [25] describes an RF front-end combinational filter for airborne V/UHF communication systems which integrates low-pass, high-pass, and band-stop filters, covering a frequency range from 30 to 600 MHz. A specific band-stop filter between 88 and 118 MHz  
Figure 6: RFI monitoring using UAV in study by [PERSON] et al. [22]. Figure 7: RFI on GNSS receivers used by [PERSON] et al. [24]. mitigates interference from commercial FM broadcasts, enhancing communication reliability in software-defined radio (SDR) applications. This design ensures the selection of desired signals while rejecting unwanted interference, preserving signal quality, and improving the overall sensitivity and rejection of interference of the system. Implemented on a Polytetrafluoroethylene (PTFE) Printed Circuit Board (PCB), the filter's compact form factor is suitable for military and defense applications. Comprehensive simulations optimized the filter's performance, and real-world tests closely matched these results, demonstrating effective FM broadcast interference mitigation and high signal integrity. The robust design of the filter improves communication reliability, safety, and operational efficiency in aviation. Figure 8 shows the RF front-end combinational filter used by [PERSON] (2018). [PERSON] (2018) highlights that co-site interference in Aircraft systems arises from several mechanisms, including adjacent channel interference, harmonic frequencies, receiver blocking, intermodulation products, and out-of-band transmission. These issues are particularly prevalent when systems operate across a broad frequency range. To address these challenges, electromagnetic simulation plays a vital role by analyzing the electromagnetic environment and quantifying antenna coupling through S parameters. This study highlights that even modest coordination between systems can significantly improve receiver sensitivity. It underscores the importance of enhancing transmitter electronics and implementing practical mitigation strategies such as narrow bandpass filters and meticulous spectrum management. Ultimately, a thorough understanding of the interference mechanisms, coupled with advanced simulation techniques, leads to effective solutions to optimize communication and sensing systems in Aircraft. Figure 9 shows the co-site interference in an Aircraft system described by [PERSON] (2018). Table 1 provides the signal strength measurements (db). Figure 8: RF front-end combinational filter used by [PERSON] (2018). Figure 9: Co-site interference in Aircraft system used by [PERSON] (2018). [PERSON] [27] describes Intermodulation products (IMPs) arise when multiple signals interact within a non-linear medium, such as electronic components or antennas. This interaction can create new frequencies that are combinations of the original signals, potentially disrupting intended communication or navigation signals. The research highlights that third-order and fifth-order IMPs are particularly troublesome for navigation systems like the ILS and VHF Omnidirectional Range (VOR). These IMPs can produce frequencies that are very close to the primary frequencies used by these systems, thereby increasing the risk of interference. To mitigate these issues, the study emphasizes the need for robust measurement and assessment techniques to identify and evaluate potential conflicts between different communication systems in aviation. This approach aims to ensure that navigational signals remain reliable and safe for Aircraft operations, especially during critical phases such as landing and approach. [PERSON] et al.