# Effect of Buildings on the Radiation Characteristics of MF Broadcast Antennas
## 4 Discussion
The effect of the presence of two (identical) buildings on the radiation pattern of the monopole is examined in Figure 8. Even a casual glance at the plots in Figure 8 suggests that they follow roughly the same trend as those obtained in the presence of a single building, i.e., the height is the most important parameter that determines whether the other parameters (such as the distance between the antenna and the buildings or the relative position of the buildings) affect the radiation pattern significantly. Indeed, when the two buildings are 20 m high, the pattern for \(R=100\) m \(\approx 0.5\lambda\) (blue dotted curve in Figure 8a) almost coincides with the black circle denoting omnidirectional behavior. In Figure 8b, the distance between the antenna and each building is doubled (i.e., \(R=200\) m \(\approx\lambda\)). The latter implies that the distance between the two buildings also changed. However, the blue dotted curve in Figure 8b suggests that the pattern is still almost omnidirectional. As the heights of the buildings increase, the patterns tend to differ significantly from the omnidirectional shape, and the impact of \(R\) on the radiation of the antenna becomes more significant. For example, the blue dashed-dotted curves I Figure 8a,b, which correspond to relatively high buildings (i.e., \(H=60\) m \(\approx 0.3\lambda\)), deviate considerably from the circular shape. In this case, the distances between the two buildings and their relative positions become important because the shape of the radiation pattern is altered. This may be readily verified by comparing the shape of the two blue dashed-dotted curves in Figure 8a,b. Moreover, a comparison between Figure 8a,b, Figures 4a and 5a, respectively, indicates that the deviation of the omnidirectional shape occurs at slightly smaller values of \(H\) when there are two buildings near the antenna (i.e., \(H\approx 0.2\lambda\)) than in the presence of a single building (\(H\approx 0.3\lambda\)). The remarks reported above for the monopole also hold, more or less, for the two-element array The radiation patterns presented in Figure 9 suggest that a building \(50\times 10\times H\) m\({}^{3}\), at a distance 100 m from the antenna, may affect its radiation pattern only for \(H\geq 0.2\lambda\). The other results (including radiation patterns in the presence of two buildings), not shown herein for the sake of brevity, indicate that the radiation characteristics of the array may depend on the parameters \(L\), \(W\), and \(R\) only if the height of the building exceeds the aforementioned critical value (i.e., \(0.2\lambda\)). The latter was found to be slightly greater for the monopole (i.e., \(0.3\lambda\)), but the trend was roughly the same. Table 1 offers a comparison of the study presented herein and pertinent works found in the literature. The first three lines in Table 1 comprise three studies [2; 11; 12], respectively, which, together with the current study, deal with the impact of buildings either on the radiation characteristics of antennas or, more generally, on the far field at MF or HF frequencies. However, ref. [15] deals with the HF band, albeit it focuses on the influence of buildings on direction finding. The familiar result of the present study, i.e., that the height of the buildings is the most important parameter in the distortion of the radiation pattern, was also obtained by other researchers [2; 12]. In addition, the conclusion that the impact on the antenna pattern is greater if the size or height of the blockage is larger than \(\lambda/2\)[2] is not very far from the finding of our study that the effect on the radiation pattern is significant if the height of the buildings is greater than \(0.3\lambda\). The rest of the studies cited in Table 1[4; 6; 13; 29] refer to higher-frequency bands. Thus, a direct comparison between these works and the present study is not possible; the works are included for the sake of completeness.