RF beam width and antenna diameter?

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Discussion Overview

The discussion revolves around the relationship between RF beam width and antenna diameter, exploring the differences in beam patterns between optical lenses and directional RF antennas. It includes theoretical considerations and implications of using multiple antennas.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant suggests that beam width is inversely proportional to the diameter of the parabolic reflector in RF antennas, questioning why RF beams cannot achieve the same parallelism as light beams.
  • Another participant provides a formula for angular divergence, α = 1.22 λ/d, noting the significant difference in wavelength between visible light and RF signals, which affects beam width.
  • A question is raised about the effects of using two directional antennas, specifically whether this would halve the beam width in one plane and how the distance between them might influence this outcome.
  • It is proposed that using multiple parabolic antennas can enhance performance, referencing the Very Large Array (VLA) and suggesting that separation by multiple wavelengths improves results.

Areas of Agreement / Disagreement

Participants express differing views on the implications of antenna design and configuration, with no consensus reached on the effects of using multiple antennas or the comparison between RF and optical beams.

Contextual Notes

The discussion involves assumptions about the behavior of RF and optical systems, as well as the application of diffraction and interference principles, which may not be fully resolved.

ctech4285
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it seems like looking at beam patterns from directional RF antennas the beamwidith is something like inversely proportional to the parabolic reflector diameter. why can you make an almost perfect strait parallel beam of light but not with RF?
 
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The angular divergence of an optical lens and a directional radio antenna is given by

α = 1.22 λ/d radians

where λ is wavelength, and d is antenna diameter.

For visible light, λ ~ 500 nanometers, and for a 3 GHz antenna, λ = 10 cm. Wavelength ratio is 200,000:1.

Bob S
 
what cause this?
what would happen if you use two directional antennas would the beam width be half on one plane? would it make a difference if you place them far apart?
 
Two parabolic antennas are better than one. 27 parabolic antennas separated by multiple wavelengths are better than two. See Very Large Array (VLA) antenna "farm" photo at

http://en.wikipedia.org/wiki/Very_Large_Array

Read about diffraction, interference, and resolving power of lenses (the equation α = 1.22 λ/d radians) in physical (conventional) optics books.

Bob S
 

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