When the service area is elongated and the base station Antenna is in the center of the area, a horizontally collinear antenna works well.
It produces a figure eight pattern. The sharpness of the Nulls can be reduced by a special design to fill in the side areas.
A horizontally collinear antenna consists of two vertical radiators spaced at
horizontal distance of a wavelength/2. This causes the radiation to cancel in
the directions of undesired coverage and to reinforce in the desired
directions. By special design, the sharp nulls can be reduced somewhat to provide some
side coverage as needed.