Description varix 200/varix 14 (DECT)
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2 Planning a cordless communications network
I
n the ideal case, the characteristic
antenna field pattern is a torus
("doughnut") centred on the (vertical)
antenna (cf. figure 2.18). In this case,
it would be a special torus with an
internal diameter of zero. The external
torus diameter represents the horizon-
tal range, and the height of the torus
represents the vertical range. This
antenna pattern causes the vertical
range to be lower than the horizontal
range.
Fig. 2.18
The antenna characteristics of an omnidirectional antenna cause the vertical range to be
lower than the horizontal range (cf. Figure 2.18). In practical applications, the vertical wave
propagation attenuation is even greater because ceilings and floors are normally thicker than
walls.
However, depending on the respective site, the actual range may differ greatly from the theo-
retical value and can only be determined precisely by carrying out on-site measurements.
2.9.5
Polarisation and down-tilt
Polarisation
Polarisation, in the description of the propagation of an electromagnetic field, is the term
used to describe the direction of the electrical field vector. The magnetic field vector is always
orthogonal to the electrical field vector. Both components are in a common plane which is, in
turn, orthogonal to the propagation direction (Poynting’s vector) of the energy. In RF communi-
cations engineering, two polarisation modes are mainly used:
Linear polarisation
The electrical field vector remains in the same plane and only varies in amplitude (absolute
value) between a positive and a negative peak value. This can be either a vertical or a hori-
zontal plane (vertical or horizontal polarisation). The spatial diagram of such a field would
be a sine-wave line in the respective plane.
omnidirectional
antenna
