### I. Introduction

### II. Target Space and Environment

*S*-parameter of FR4 is measured in the X-band using WR90 coaxial-to-waveguide adaptor probes. Since the real wall cannot be made to the desired size, it is assumed that the probes are in contact with the wall, as shown in Fig. 3(a). Fig. 3(b) shows the real part of the permittivity derived using the NRW method from the simulated

*S*-parameters. When the thickness is thin, the effect of the error is not large, and when the thickness is sufficiently thick, there is a period in the results. That is, it seems that the real part of the permittivity can be estimated by taking the average of the results of the NRW algorithm.

*S*-parameter measurement results for the real wall, it is estimated that the concrete wall of the target structure has a relative permittivity of about 4.44. Since this value its similar to that in the CST simulation tool’s library [20], it is expected that the results of analyzing and simulating electromagnetic waves using this library are sufficiently reasonable. Therefore, the real part of the relative permittivity of the concrete wall is assumed to be 4.4, and the electrical conductivity of the concrete wall is 0.032 S/m. In addition, we calculate the power attenuation from Room1 to Hallway using this permittivity. The calculation method is based on a ray tracing technique, and we set the number of reflections to 1, since convergence properties have been verified through sufficient simulations. First, we calculate the received power under the assumption that all the walls are made of concrete. After this, to consider the real building structure, additional attenuation is applied to the propagating waves based on the ratio of the conductor areas (i.e., doors and columns) to the total wall area. Fig. 4 shows that the calculation results are sufficiently reasonable, compared to the measurement results, and we use the electrical characteristics employed at this time to analyze the propagation characteristics in this paper.

### III. Theoretical Approach, Measurement, and Simulation

### 1. The Theoretical Approach

*S*is the surface area of the target structure,

*u*

*is the relative wall permeability, σ is the wall conductivity,*

_{r}*f*is the used frequency,

*a*

*is the radius of the wall area, T*

_{wall}*is the transmission coefficient of concrete. and*

_{w}*c*is the speed of light. T

*is determined by the electrical properties of concrete, such as permittivity, permeability, and electrical conductivity, but we deal with it as a dielectric material. This equation was devised by referring to the equation used to calculate the MCCS of the aperture in the PWB method. In the PEPWB method, the electromagnetic waves in a cavity propagate through the apertures and walls that they can penetrate. To express the MCCS of a wall in Eq. (2), the wall seems like an aperture, but it is represented by an aperture with the electrical characteristics of the building material, as shown in Fig. 6(b). Therefore, when using the PEPWB method, the target structure is represented by a topological diagram, as shown in Fig. 7. Also, a two-ray ground reflection model was used to calculate the received power at the reference point and the input power propagating into large structures [21]. The result of this model is affected by the transmitted power, the gain of the antenna used in the measurement, the electrical properties of the ground, the distance between the transmitter and the receiver, the heights of the transmitter and the receiver, and the angle of incidence. The results of the PEPWB and PWB methods inside Room1 and Hallway are shown in Fig. 8 along with the simulation results of Wireless Insite. From Fig. 8, two notable points can be seen. The first is that the results of the PEPWB method have higher received power than those of the PWB method in the two target spaces. The second concerns the difference between the results of the PEPWB method and the PWB method for each of the two target spaces. The reason for the first point is that the PEPWB method, unlike the PWB method, considers electromagnetic waves that penetrate the concrete wall. Therefore, the results of the PEPWB method show higher received power. The reason for the second point can be understood by looking at the structural characteristics of the two target spaces. In the wall between the exterior and Room1, the areas where electromagnetic waves can propagate are the concrete walls and windows. Comparing the areas occupied by the concrete wall and the window in the wall, the area occupied by the window is larger than that occupied by the concrete wall in Room1. That is, when electromagnetic waves propagate into Room1, more electromagnetic waves are expected to propagate through the window because even when considering the electromagnetic waves propagating into the concrete wall, there is no considerable change. However, it is different in the case of Hallway. The wall between the two target spaces consists of concrete walls and columns, steel doors, and glass on the doors. Among the several areas, those where electromagnetic waves can propagate are the concrete wall and the glass door, and the concrete wall occupies more area than the door. Therefore, the difference between the PEPWB method and the PWB method in Hallway is larger than that in Room1.*

_{w}### 2. Measurement and Simulation

### IV. Influence of External Environmental Factors on Electromagnetic Wave Propagation

### V. Results and Discussion

^{2}, and the total area of the trees is 27.91 m

^{2}. The actual sizes of the trees are listed in Table 1. Comparing the area of the concrete walls and windows with the area of six trees, the trees occupy about 70% of the area that can be penetrated by the electromagnetic waves. Therefore, the resulting vegetation area of 70% shown in Fig. 14 is coupled with that of the theoretical approach.