# Analysis of Electromagnetic Interference Effects of 5G Signals on Radio Altimeters
## 1 Introduction  
Countries worldwide are currently assigning mid-band spectrum resources to facilitate the advancement of fifth-generation (5G) mobile communication systems. Some of these frequency bands are in close proximity to the operational frequency band (4200 MHz-4400 MHz) of the radio altimeter (RA) [1]. The RA is the only sensor utilized in civil aviation aircraft to measure the distance between the aircraft and the ground during the takeoff, approach, and landing phases. It not only provides pilots with accurate altitude information but also provides a key information input for systems such as the Instrument Landing System (ILS) and the Terrain Awareness and Warning System (TAWS) [2]. If an error in the output of the flight altitude triggers a series of abnormalitiesin the onboard systems, it could lead to catastrophic events during the high-risk phase of aircraft landing. Due to the low power level of the echo signals received by the RA receiver, typically on the order of 0.001 mW, the RA receiver is highly sensitive and susceptible to interference from adjacent band 5G signals. Given the 25- to 30-year service life of civil aircraft, many currently operational planes are equipped with outdated RA receivers that lack adequate electromagnetic shielding [3]. With the extensive deployment and use of 5G mobile communication systems, RAs are facing the issue of interference from 5G base stations, which poses a potential threat to flight safety [4]. Therefore, it is crucial to conduct research on the electromagnetic susceptibility of RAs to 5G signals to enhance their compatibility and ensure the safety and reliability of civil aviation. Currently, relevant research primarily investigates the effects of interference signals on radio receivers through theoretical, simulation, and experimental approaches [5; 6; 7]. [PERSON] et al. [8] employed the power-series method to analyze the interference mechanism associated with the nonlinear effects of radio receivers. However, their study was confined to the analysis of single-frequency interference signals and did not address scenarios involving multi-frequency interference. [PERSON] et al. [9] employed the vector method to investigate the blocking interference mechanism induced by out-of-band multi-frequency signal interference at the receiver. They constructed a mathematical model for evaluating the effects of interference and validated this model through experimental results. In cases of poor receiver linearity, this method may not accurately represent the effects of interference on receiver performance [10]. As a type of radio receiver, RA receivers experience interference from multi-frequency subcarriers when subjected to 5G signals. Research on the mechanisms underlying this interference effect remains insufficient. One study summarized the effects of RA receivers under out-of-band electromagnetic interference and proposed evaluation indicators for assessing interference effects [11]. However, it did not address scenarios involving 5G signal interference, and the proposed receiver indicators are difficult to measure. [PERSON] et al. [12] conducted simulations and experiments to investigate the impact of 5G interference signals on the sweep bandwidth distortion of RA operating signals. However, they did not consider the actual state of the radio frequency (RF) front-end, which cannot fully represent the real situation of the entire receiver in an electromagnetic interference environment. [PERSON] et al. [13] utilized advanced design system (ADS) simulation software to model the output spectrum of an RA receiver subjected to interference from airborne shortwave radio signals, demonstrating the effectiveness of this method for analyzing the electromagnetic interference mechanism through experimental validation. Several studies have injected 5G interference signals into RA receivers to experimentally investigate the impact of these signals on the output performance of RA systems, thereby determining the interference threshold of RA receivers [14].