## 2 Materials and Methods
### EMFs from 5G Base Stations Relative to Distance  
The second part of the analysis explored the potential inverse correlation between EMF measurements around 3.5 GHz and the distance to 5G BS. As the distance from a BS increased, the strength of the electric field decreased due to the propagation characteristics of electromagnetic waves. In free space, the electric field strength diminished following an inverse law, meaning that the electric field strength dropped proportionally to 1/d, where d is the distance from the source, as described by the Friis transmission equation [14]. Signal propagation in real-world environments is influenced by various factors, including obstacles, terrain, and weather conditions. When signals encounter barriers, they undergo phenomena such as reflection, refraction, and diffraction, which lead to scattering and attenuation of the signal strength. The complexity of path loss behavior in these scenarios is modeled by empirical models, such as the Okumura-Hata model [15] and the COST 231 Walfisch-Ikegami model [16]. A current trend in research is the increasing use of AI in various fields. Path loss and EMF prediction models are no exception to this trend [8; 9; 17]. These models commonly use the distance from BS antennas as an input variable (or \"feature\"). Combined with other features, such as transmitted antenna power, line-of-sight (LOS) or non-line-of-sight (NLOS) conditions, and more, these inputs help predict the target values accurately. Antennas for 2G, 3G, and 4G BS were engineered to consistently cover sectors within a hexagonal cellular network layout. These antennas maintain an almost stable radiation pattern regardless of the traffic load. The inverse relationship between distance and the E-field has been examined in many works, especially for previous generations of cellular technologies [18]. In contrast, 5G BS primarily broadcast signals, such as the synchronization signal block (SSB), which are typically transmitted periodically in different directions. It is of interest to explore whether the varying radiation pattern from a 5G BS, without forcing traffic to the measuring spot, still leads to a decrease in the recorded electric field strength as the distance increases. For the analysis, it was crucial to determine the distance between each measurement spot and the BS that include 5G antennas. To this end, we gathered information about the coordinates of 5G antennas and loaded it, along with the measurement coordinates, into the QGIS software (Desktop version 3.34.3) [19]. For each spot, we independently calculated the distance from that spot to the nearest 5G BS. Additionally, we calculated the average distances from each spot to the two closest, three closest, four closest, and five closest 5G BS. This study utilized data from the Hellenic Telecommunications and Post Commission (EETT) database [12], which contains the locations of all BS antennas. Moreover, specific information relating only to the locations of 5G BS was used. The first 5G antenna in Greece was installed in June 2019. By March 2024, more than 500 5G BS had been installed all over Greece. Figure 2 depicts the monthly number of 5G BS installed in Greece, starting from 2019. The spot measurements across four different environments were conducted over the period from May 2023 to January 2024. The last column of Table 1 containsthe information on how many 5G BS at 3.5 GHz were in operation in each environment during the measurements. Since no 5G BS were installed in the municipality of Thermi, the suburban environment of Central Macedonia was excluded from the analysis.