Page "Radar" Paragraph 135

Symmetric parabolic antennas produce a narrow " pencil " beam in both the X and Y dimensions and consequently have a higher gain.

The NEXRAD Pulse-Doppler weather radar uses a symmetric antenna to perform detailed volumetric scans of the atmosphere.

Spoiled parabolic antennas produce a narrow beam in one dimension and a relatively wide beam in the other.

This feature is useful if target detection over a wide range of angles is more important than target location in three dimensions.

Most 2D surveillance radars use a spoiled parabolic antenna with a narrow azimuthal beamwidth and wide vertical beamwidth.

This beam configuration allows the radar operator to detect an aircraft at a specific azimuth but at an indeterminate height.

Conversely, so-called " nodder " height finding radars use a dish with a narrow vertical beamwidth and wide azimuthal beamwidth to detect an aircraft at a specific height but with low azimuthal precision.