## 4 Workplace for Experiment to Measure Shielding Effectiveness  
The process of calibrating the workspace to measure the efficiency of shielding and reflection involved multiple stages. Both the calibration and the subsequent measurement took place inside a chamber that minimized reflection. The measuring instruments were positioned outside this chamber, ensuring that their emissions did not interfere with the measurement. In this context, the principle of calibration entails aligning the transmitting and receiving antennas so that the latter captures the electromagnetic wave emitted by the former. It is important to note that the receiving antenna can still capture the electromagnetic wave even if it is not perfectly aligned with the transmitting antenna. However, if the alignment is off, the receiving antenna may fail to capture the transmitted electromagnetic wave in the main lobe. This could directly impact the measurement of shielding efficiency, especially when reflections occur, and the incident electromagnetic wave arrives at a different angle. The calibration process involved several steps. Initially, it was necessary to identify the transmitted signal and calculate the signal displayed on the spectrum analyzer. Calibration was achieved by adjusting the position of the receiving antenna both vertically and horizontally--as shown in Figure 3. During these adjustments, it was crucial to monitor the electromagnetic wave's value on the spectrum analyzer. The basis for calibrating the measuring workplace was the radio communication equation, which is described in the following manner [2; 20; 21; 22]:  
\[P_{P}=P_{V}-L_{0}+G_{V}+G_{P} \tag{19}\]  
It is established that \(P_{P}\) represents the received power, \(P_{V}\) denotes the transmitted power, \(L_{0}\) are the free-space losses, \(G_{V}\) is the gain of the transmitting antenna, and \(G_{P}\) is the gain of the receiving antenna. The free-space losses \(L_{0}\) are defined as follows [2; 3]:  
\[L_{0}=20 log\bigg{(}\frac{4\pi r}{\lambda}\bigg{)} \tag{20}\]  
where \(r\) represents the distance of the antenna, and \(\lambda\) is the wavelength, which can be expressed as follows [2; 3]:  
\[\lambda=\frac{c}{f} \tag{21}\]where \(c\) is the speed of wave propagation in a vacuum and \(f^{\prime}\) is the frequency of the wave. Additionally, it is necessary to consider the losses in cables used during calibration, which are included in the additional losses. Formula (20) applies an ideal scenario. In real-world conditions, the free-space losses \(L\) are defined as [2,3]:  
\[L=L_{0}+L_{A} \tag{22}\]  
where \(L_{0}\) represents the free-space losses and \(L_{A}\) represents the additional losses. The additional losses \(L_{A}\) consist of several components, which can be generally expressed for the transmission between two antennas as [2,3]:  
\[L_{A}=L_{FT_{X}}+A_{AG}+A_{RAIN}+L_{POL}+L_{POINT}+L_{FR_{X}} \tag{23}\]  
where \(L_{FTX}\) are the losses between the transmitter output and the transmitting antenna (attenuation in cables, connectors), \(A_{AG}\) represents attenuation caused by the atmosphere and ionosphere, \(A_{RAIN}\) represents attenuation due to rain and clouds, \(L_{POL}\) denotes losses caused by changes in polarization between the transmitting and receiving antennas, \(L_{POINT}\) refers to losses caused by inaccurate aiming of the antenna at the satellite, and \(L_{FRX}\) represents the losses between the receiving antenna and the receiver input. In the case of the calibration described in this chapter, the components \(A_{AG}\), \(A_{RAIN}\), and \(L_{POINT}\) are not applicable [2, 3, 4,21,22]. In this study, two antennas were used for the measurements--the RF spin DRH18-E (RF spin, Hanspaulka, Czech Republic) and the Rohde & Schwarz HF 907 (Rohde & Schwarz, Munich, Germany)--Figures 4 and 5. The RF spin DRH18-E horn ridge antenna, with a wide frequency range of 1 GHz to 18 GHz, is designed for use in measuring the electromagnetic compatibility of components, in the automotive industry, in radio monitoring, and in military applications.