# Building Penetration Losses at 3.5 GHz: Dependence on Polarization and Incidence Angle
## 3 Experimental Set-Up  
### Measurement System and Procedure  
The measurement system was based on a Keysight FieldFox N9913A portable vector network analyser (VNA). Two Electro-Metrics EM-6952 linearly polarized log-periodic antennas were connected to the VNA ports. These wideband antennas cover all the frequency range of our experiment and exhibit a 70\({}^{\circ}\) 3-dB E-plane beamwidth. During the measurements, we placed both antennas on tripods, at the same height, in opposite positions at each side of the building facades of the School of Telecommunication Engineering at the University of Vigo. The antennas pointed at each other. The distance from the antennas to the beam penetrating point on the facade was 1.5 m, enough to guarantee that the far-field conditions were met. The far-field distance was calculated as 2D\({}^{2}\)/\(\lambda\), where D is the maximum antenna dimension and \(\lambda\) is the wavelength. For the range of frequencies considered in our experiment, the maximum far-field distance is 1.1 m. The radius of the illuminated zone in the facade for a distance of 1.5 m is around 1.05 m, given the antennas' 3 dB beamwidth. The height of the antennas above the ground was chosen to avoid the main beam of the antenna illuminating the ground, covering then the first Fresnel zone, of which the radius is 0.274 m, for the lowest frequency in the range (3 GHz).  
Measurements were taken at normal incidence (\(\theta\) = 0\({}^{\circ}\)) as well as at \(\pm\)15\({}^{\circ}\), \(\pm\)30\({}^{\circ}\), \(\pm\)45\({}^{\circ}\) and \(\pm\)60\({}^{\circ}\) incidence angles, as shown in Figure 5, for vertical (perpendicular) and horizontal (parallel) polarizations of the electric field. To determine the antenna positions, a 1.5 m radius semicircle was drawn on the floor. The centre of the semicircle was at the facade, just below the beam-centre penetrating point. The antenna positions over the semicircle for the different incident angles were then calculated by simple trigonometric operations. The antenna was pointed at the beam-centre penetration point on the facade by using a laser pointer.  
The S\({}_{21}\) parameter was obtained by frequency sweeping from 3 GHz to 4 GHz. A time-gating technique [22] was applied to remove contributions from any multipath component and keep only the data related to propagation through the direct path across the facade. This technique consists of performing an inverse Fourier transform (iFFT) on the measured  
Figure 5: Schematic representation of measurement procedure, with the antennas configured to 30\({}^{\circ}\) incidence angle measurements.  
frequency response to obtain the impulse response of the radio channel. The radiowave propagating directly through the facade is identified by its delay, and the rest of the contributions due to reflection on other objects present in the nearby objects are filtered out. Thus, the building penetration losses through the building facade can be measured on site and the effect of the rest of the scatterers removed from the measurements.  
As an example, Figure 6 shows the amplitude and phase of a measured S\({}_{21}\) parameter as a function of frequency.  
The result of performing the IFFT to the above result is shown in Figure 7, where the different multipath contributions can be identified by their delays as far as the propagation path differs by more than 30 cm. The contribution corresponding to the path through the facade is plotted in red.