Page 176 - Antennas for Base Stations in Wireless Communications

Advanced Antennas for Radio Base Stations 149

phase shifters with phase-matched cables running to each subpanel.
A schematic illustration of high-gain antennas based on the modular
principle is shown in Figure 4.12.
Subpanel tilt is applied either on a mechanical basis, using a physical
tilting of each subpanel structure, or on an electrical basis, for subpanels
with a means for progressive time delays or phase shifts of the excita-
tion over the length of the subpanel array. Combinations of mechanical
and electrical tilt are also used. For increased flexibility, remote control
of tilt is possible, but for most extended coverage installations, this is not
an essential feature. Tilt applied to individual subpanels is combined
with delay compensations in the feed network to avoid grating lobe
appearing due to the large subpanel separations.
An advantage with individual subpanel mechanical tilt is that it gives
a more compact installation than if the entire structure is mechanically
tilted. This reduces the wind load, resulting in less torque, and provides
an overall antenna configuration that is essentially conformal with
the mounting structure. Similarly, electrical tilt in the feed network
reduces the amount of hardware compared to a solution with electrical

Subpanel

Subpanel

Subpanel

2/3 30º Subpanel

4.7 dB 1:3 30º Subpanel 1:4

1/3 30º Subpanel
Subpanel

Subpanel

Subpanel

(a) (b) (c)
Figure 4.12 Modular high-gain antennas made up of standard sector antennas (subpan-
els), power dividers/combiners, and phase-matched cables