What are reflector antennas?
A reflector antenna uses one or more conducting surfaces to collimate the radiation of a smaller feed. Forms range from the flat and corner reflector at VHF/UHF to parabolic prime-focus, offset and dual-reflector Cassegrain (hyperboloidal subreflector) and Gregorian (ellipsoidal subreflector) systems for microwave links, satellite and radio astronomy.[1][2]
How do corner reflectors work?
A dipole in front of two flat conducting sheets meeting at an angle (commonly 90°) is equivalent, by image theory, to an array of the dipole and its images, giving roughly 10–12 dBi of gain for a 90° corner with appropriate spacing.[3][1]
What are the main paraboloid configurations?
| Type | Feature | Trade-off |
|---|---|---|
| Prime focus | Feed at the focal point | Simple; feed and struts block the aperture |
| Offset | Section of paraboloid away from the axis | No blockage; higher cross-polar for linear feeds |
| Cassegrain | Convex hyperboloid subreflector | Feed near the vertex, compact, easy access |
| Gregorian | Concave ellipsoid subreflector | Real intermediate focus; used in large telescopes |
What governs reflector efficiency?
Aperture efficiency is the product of illumination (taper), spillover, phase, blockage, cross-polarization and surface-error efficiencies. An edge taper of about −10 to −12 dB balances taper and spillover losses; surface errors reduce gain by Ruze’s factor exp[−(4πε/λ)²] for rms error ε.[2][4]
Frequently asked questions
What f/D is typical?
Prime-focus dishes often use f/D of 0.25–0.5; offset consumer dishes are typically higher.
Why are offset dishes used for satellite TV?
They avoid feed blockage and let the dish stand nearly vertical, shedding snow and rain.
How accurate must a reflector surface be?
By Ruze’s formula, an rms error of λ/16 costs about 2.7 dB and λ/40 about 0.4 dB.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “Antenna Theory: Analysis and Design, 4th ed.”. C. A. Balanis, Wiley. 2016.
- “Antenna Theory and Design, 3rd ed.”. W. L. Stutzman and G. A. Thiele, Wiley. 2012.
- “Antennas for All Applications, 3rd ed.”. J. D. Kraus and R. J. Marhefka, McGraw-Hill. 2002.
- “Antenna Tolerance Theory — A Review”. J. Ruze, Proceedings of the IEEE, vol. 54, no. 4, pp. 633-640. April 1966.