How do you calculate parabolic dish gain?
A parabolic dish has gain G = eap(πD/λ)², where D is diameter and eap the aperture efficiency (typically 0.55–0.70), and a half-power beamwidth of about 70λ/D degrees.[1][2] A 1.0 m dish at 12 GHz with 65% efficiency has about 40.1 dBi gain and a 1.75° beamwidth.
What is the geometry of a paraboloid?
A paraboloid of revolution satisfies r² = 4fz, where f is the focal length. Rays from the focus reflect parallel to the axis, and all path lengths from the focus to a plane across the aperture are equal, producing a uniform-phase aperture. The depth is d = D²/(16f), and the half-angle subtended at the feed is θ0 = 2·arctan(D/(4f)).[2]
How should the feed illuminate the dish?
The feed pattern should fall to about −10 dB at the rim; a sharper taper wastes aperture, a weaker taper spills energy past the rim, increasing noise and sidelobes. Corrugated horns provide symmetric, low cross-polar illumination.[3][1]
How do surface errors and wind affect performance?
Ruze showed that random surface errors of rms value ε reduce gain by exp[−(4πε/λ)²].[4] Pointing error matters too: with a 1.75° beamwidth, a 0.5° pointing error costs roughly 1 dB (using the Gaussian approximation 12(θ/θ3dB)² dB).[5]
Frequently asked questions
What is the gain of a 60 cm dish at 11 GHz?
About 34–35 dBi with 60–65% efficiency.
Does doubling diameter double gain?
It quadruples gain (+6 dB) and halves beamwidth.
Why are mesh dishes possible?
A mesh with openings smaller than about λ/10 reflects almost like a solid surface.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “Antenna Theory and Design, 3rd ed.”. W. L. Stutzman and G. A. Thiele, Wiley. 2012.
- “Antenna Theory: Analysis and Design, 4th ed.”. C. A. Balanis, Wiley. 2016.
- “Microwave Horns and Feeds”. A. D. Olver, P. J. B. Clarricoats, A. A. Kishk and L. Shafai, IEE/IEEE Press. 1994.
- “Antenna Tolerance Theory — A Review”. J. Ruze, Proceedings of the IEEE, vol. 54, no. 4, pp. 633-640. April 1966.
- “Satellite Communications Systems, 5th ed.”. G. Maral and M. Bousquet, Wiley. 2009.