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Concept
Reflector (antenna)
Summary
An antenna reflector is a device that reflects electromagnetic waves. Antenna reflectors can exist as a standalone device for redirecting radio frequency (RF) energy, or can be integrated as part of an antenna assembly.
The function of a standalone reflector is to redirect electromagnetic (EM) energy, generally in the radio wavelength range of the electromagnetic spectrum.
Common standalone reflector types are
corner reflector, which reflects the incoming signal back to the direction from which it came, commonly used in radar.
flat reflector, which reflects the signal such as a mirror and is often used as a passive repeater.
When integrated into an antenna assembly, the reflector serves to modify the radiation pattern of the antenna, increasing gain in a given direction.
Common integrated reflector types are
parabolic reflector, which focuses a beam signal into one point or directs a radiating signal into a beam.
a passive element slightly longer than and located behind a radiating dipole element that absorbs and re-radiates the signal in a directional way as in a Yagi antenna array.
a flat reflector such as used in a Short backfire antenna or Sector antenna.
a corner reflector used in UHF television antennas.
a cylindrical reflector as used in Cantenna.
Parameters that can directly influence the performance of an antenna with integrated reflector:
Dimensions of the reflector (Big ugly dish versus small dish)
Spillover (part of the feed antenna radiation misses the reflector)
Aperture blockage (also known as feed blockage: part of the feed energy is reflected back into the feed antenna and does not contribute to the main beam)
Illumination taper (feed illumination reduced at the edges of the reflector)
Reflector surface deviation
Defocusing
Cross polarization
Feed losses
Antenna feed mismatch
Non-uniform amplitude/phase distributions
The antenna efficiency is measured in terms of its effectiveness ratio.
Any gain-degrading factors which raise side lobes have a two-fold effect, in that they contribute to system noise temperature in addition to reducing gain.
Official source
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