The directivity of the antenna in (6) is explained with the
maximum directivity in (7) and the pattern model of the omnidirectional
antenna. Equation (7) is a model of the maximum
directivity proposed by McDonald based on a mathematical experimental
model [17]. This model can determine the maximum
directivity of the antenna using HPBW. The pattern model for
the vertical position of the antenna is the model that is required
when the position movement occurs with the same distance as
that of the transmitting and receiving antennas on the xz plane,
as shown in Fig. 6. The pattern model for the omnidirectional
antenna is required to examine this model. The omnidirectional
antennas have pattern characteristics shown by the 2-D pattern
in Fig. 9. Such patterns can be approximated by [17]