How does the size of an object affect RF propagation?

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Discussion Overview

The discussion focuses on how the size of an obstructing object influences the propagation of RF transmissions, specifically examining phenomena such as refraction, absorption, reflection, diffraction, and scattering in relation to the object's size compared to the wavelength.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether refraction occurs only in objects larger than the wavelength or if it can also occur in smaller objects.
  • Another participant asserts that refraction will only occur on objects larger than the wavelength, while isolated smaller objects will scatter.
  • It is noted that a regular array of small objects with spacing similar to the wavelength will diffract, and diffraction can also occur at the edges of large objects.
  • A participant mentions their ongoing work on a book about radio propagation, particularly focusing on ionospheric effects, indicating that ionospheric refraction is a macro phenomenon with a large radar cross-section.
  • One participant expresses gratitude for the information provided, indicating that the responses were helpful.

Areas of Agreement / Disagreement

There are competing views regarding the conditions under which refraction occurs, with some participants agreeing that size relative to wavelength is significant, while others provide differing perspectives on scattering and diffraction. The discussion remains unresolved on certain aspects.

Contextual Notes

Participants reference general wave phenomena and suggest looking at other types of waves for broader understanding, but do not resolve the complexities of the interactions between size and RF propagation phenomena.

barry.haworth
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Hi there, can anyone please advise how the size of an obstructing object affects the propagation of an RF transmission? Eg, for instance does refraction only occur in objects that are larger than the wavelength or does it occur in objects smaller than the wavelength? I can find heaps of info about RF propagation but very little on how the various phenomena such as absorption, reflection, refraction, diffraction, scattering etc is affected by the size of an object relative to the wavelength? I would appreciate any and all feedback. Many thanks
 
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Refraction will only occur on objects larger than the wavelength.
Isolated objects smaller than the wavelength will scatter.
A regular array of small objects with spacing similar to the wavelength will diffract.
Diffraction will also occur at the edges of large objects.

These are general wave phenomena, not limited to RF. You might get a better understanding if you also look at other kinds of waves, such as microwaves, visible light, and x-rays. Just don't study water waves too much, they are highly non-linear.
 
barry.haworth said:
Hi there, can anyone please advise how the size of an obstructing object affects the propagation of an RF transmission? Eg, for instance does refraction only occur in objects that are larger than the wavelength or does it occur in objects smaller than the wavelength? I can find heaps of info about RF propagation but very little on how the various phenomena such as absorption, reflection, refraction, diffraction, scattering etc is affected by the size of an object relative to the wavelength? I would appreciate any and all feedback. Many thanks
I just happen to be in the process of writing a book for the ARRL dedicated specifically to radio propagation, especially ionospheric.

But, you've had some good answers here, as ionospheric refraction is a very MACRO phenomenon. The ionosphere, as a whole has a very large "radar cross-section" but can also be extremely lossy...or not.

Stay tuned!

Eric
 
Dear M Quack, thank you for your prompt reply, it was very useful. I appreciate your help!

Many thanks,

Barry
 
Hi Eric, good luck with the book! Would love a copy when you get it published.
Many thanks,
Barry
 

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