## 2 Methodology
### Fifth-Generation Base Station Measurement Campaign  
Figure 4 illustrates the setup for measuring near-field electromagnetic radiation emitted by a 5G base station using a spherical coordinate system. The 5G base station antenna, referred to as the Antenna Under Test (AUT), is positioned at the center of the spherical space and acts as the radiation source. A measurement probe is placed on the surface of this hypothetical sphere to detect the electric field strength at a radial distance \(r\). In this coordinate system, \(r\) denotes the distance from the antenna to the probe, \(\theta\) represents the elevation (or polar) angle measured from the vertical axis, and \(\phi\)--although not shown--typically indicates the azimuthal angle around the \(z\)-axis. The Cartesian axes (\(x,y\), and \(z\)) are included to correlate spherical coordinates with actual spatial directions. The radiation pattern is illustrated with arrows showing the general direction of wave propagation. This configuration is used to assess electromagnetic field levels in the near-field zone, allowing for the spatial mapping of electric field strength \(E\) based on the angular position and distance, which aids in analyzing the antenna's performance. Figure 3: Measurement of the on-site 5G base station in the Lekki region. One of the main challenges to the rollout of 5G new radio (NR) is the extensive application of technological innovations like massive MIMO (multiple-input and multiple-output) and beamforming. The electric field in the distant field near 5G base stations shown in Figure 2 can be determined using the following [27; 28; 29]. \[E=\sqrt{377\frac{P_{T}G_{T}(\theta,\phi)}{4\pi R^{2}}}, \tag{1}\]  
\(E\) is the electric field intensity (in volts per meter, V/m). \(P_{T}\) is the transmitted power (in watts). \(G_{T}(\theta,\phi)\) is the gain of the transmitting antenna in the direction \((\theta,\phi)\). \(R\) is the distance from the antenna to the observation point (in meters). The value of 377 is the intrinsic impedance of free space (\(\eta_{0}\) = 377 \(\Omega\)), and \(4\pi R^{2}\) represents spherical spreading in free space. This section presents the method used for the environmental monitoring of electromagnetic radiation at 5G base stations. Measurements were conducted at multiple 5G base stations across six regions in Lagos, Nigeria: Ikeja, Lagos Island, Ikoyi, Lekki, and Ajah. Furthermore, three major operators--MTN, Global Communication, and Airtel--are active in these areas. The active bands of the 5G base stations are shown in Table 1.  
The 5G base station measurement data for the Lekki region is presented in Figure 3. We used the PMM (Narda) EMR-300 (Narda, Pfullingen, Germany), a frequency-selective radiation meter, as our testing device. This equipment was chosen for its ability to monitor the frequency range within the probe's response. This capability enables the device to accurately capture and display electromagnetic radiation from 5G base stations, showing the spectrum distribution of contributions across different frequencies. SRM-3006 (Narda, Pfullingen, Germany), offers a typical instrumental accuracy of \(\pm 1.5\) dB across most of its operating range. For highest confidence, careful calibration, spatial resolution, and \begin{table}
\begin{tabular}{c c} \hline \hline
**Network Operator** & **Frequency (MHz)** \\ \hline MTN & 35,000 \\ \hline Globalcom & 32,000 \\ \hline Airtel & 26,000 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Network providers of 5G base stations with individual active bands. Figure 4: Setup for measuring near-field electromagnetic radiation in various regions. environmental control are essential to minimize total uncertainty and improve model-matching reliability. Furthermore, measurement accuracy depends significantly on the probe used: Isotropic E-field probes (e.g., EF 0691, EP-601(Narda, Pfullingen, Germany)) offer omnidirectional sensitivity, which is crucial for averaging over three spatial axes.