|Image of the Parabolic horn fed reflector with shroud.|
Axisymmetric prime focus paraboloidal reflectors provide a good compromise between performance and cost, but can suffer from high-side lobe levels if designed for high efficiency. Here's a simple, practical, low-cost method is presented for suppressing close-in side lobes to comply with stringent radiation pattern envelope specifications.
The antenna consists of an axisymmetric parabolic reflector and a metallic cylindrical shroud which extends from the rim of the reflector dish. The feed used here is a pyramidal horn antenna designed to give the desired illumination level of the paraboloid edges, e.g. -10 dB. The E- and H-plane beamwidths are approximately equal and the -10 dB beamwidth can be specified.
A variety of other feed antennas may also be used, including simple conical horns, corrugated conical horns, compound box horns and axial-choke horns, to name a few. The Shrouded pattern fed parabolic reflector antenna (already in Antenna Magus) can be designed to substitute the horn feed with a theoretical, simulated or measured pattern. ...
The image below compares the patterns of a parabolic reflector with and without a shroud. The reduction in the spill over radiation is very clear.
|3D gain comparison for a parabolic reflector with and without a shroud.|