Pattern-fed Offset Gregorian reflector

Summary of the dual reflector antennas in Antenna Magus.

The Pattern-fed Offset Gregorian reflector is the 7th dual-reflector included in Antenna Magus and the 4th Gregorian-type reflector antenna template.

Dual-reflector antennas are based on principles that have been used in optical telescopes for centuries, with Cassegrain and Gregorian telescopes dating back to the late sixteen hundreds. Though these antennas share many of the underlying principles of operation with typical single-reflector structures, they offer more design flexibility and are more compact. These advantages, however, come at the cost of an increase in design and manufacturing complexity. The dual-reflector topology allows sub reflector shaping to be used to increase the focus-depth or to optimise illumination for an existing feed antenna and main reflector. By using a dual reflector with an offset feed, aperture blockage can be decreased and mounting on a flat or rotating platform is simplified. There are however some factors like spill-over, radiation pattern asymmetry, feed/sub and main-reflector alignment and other manufacturing complexities that have to be considered when choosing an offset-fed dual reflector topology.

Image of the Pattern-fed Offset Gregorian reflector.

When compared with the Horn-fed Offset Gregorian template, the pattern-fed option reduces simulation time and complexity and makes provision for design based on feed properties such as feed-beamwidth, edge-taper and feed distribution efficiency as illustrated below. Properties of any existing feed antenna can be approximated using the pattern-feed approach, or the desired radiation pattern properties of an ideal feed antenna can be derived from the reflector design. Though a physical feed antenna is not included in the pattern-fed design, assumed antenna dimensions are used to ensure that minimal blockage occurs.

Feed antenna pattern properties accounted for by Antenna Magus when designing the Pattern-fed Offset Gregorian reflector.
3D radiation pattern of the Pattern-fed Offset Gregorian.
Normalised radiation pattern of the Pattern-fed Offset Gregorian dual reflector.
Zoomed view of the normalised radiation pattern.