Inverse Cosecant Squared Antenna Pattern
Figure 1: Coverage of an inverse cosecant squared diagram (upper) vs. the simple “Fan-beam” (lower diagram)
Figure 1: Coverage of an inverse cosecant squared- diagram (upper) vs. the simple “Fan-Beam” (lower diagram)
Inverse Cosecant Squared Antenna Pattern
ASDE and VTS radar systems use antennas designed to provide inverse cosecant squared coverage and direct energy preferentially towards the surface giving constant gain for targets on the surface.
The coverage diagram shows the antenna pattern of a vessel radar with an inverse cosecant squared antenna pattern in the upper diagram. The antenna is designed to preferentially radiate below 0° (the horizon line) to provide constant detection for targets approaching on the sea surface. The simple Fan-Beam in the lower diagram using the same power leads to losses in the near and far region. A big amount of power is radiated in unwanted directions (e.g. into the air-space).
The antenna of the long-range air and surface coastal surveillance radar Coast Watcher 100 may be mounted upside down. Therefore it provides either a Cosecant Squared or an inverted Cosecant Squared pattern.
