Understanding the Path of Radio Waves (particularly 900 MHz & 2.4 GHz)

[Underhill]

I'm interested in how to understand exactly how radio waves will propagate in a particular situation. I know that they are absorbed by metal and water, pass through other materials albeit with loss of power, and reflect or bounce off of surfaces as well.

How do I know whether a radio wave will reflect off of something or not? How do I know, for either a LOS or NLOS link, how much of the waves that reach the target have (1) reflected off of surfaces or (2) traveled straight through the air or (3) traveled straight through objects (e.g., walls)?

I am specifically interested in the propagation of 900 MHz and 2.4 GHz radio waves.

(Or should this question be posted in a Physics forum?)

 

[marcusl]

This is a complicated subject. It is possible to model transmission through a material, and reflections from it, using electromagnetic theory--if you know the material properties (complex permitivity, and magnetic permeability). Diffraction around edges is also important, and much harder to solve for exactly. In the real world, such modeling is nearly impossible due to the huge number of surfaces (buildings, hills, roads) and other obstacles such as trees.

As a result, approximate models geared toward the general environment (rural, suburban or urban) are used. One of the most common is the COST 231 model, but you can search on "mobile propagation channel models" to find many more.

A result of reflections is multipath fading--that is, multiple waves traveling different path lengths interfere constructively and destructively. For mobile communications, the result is time-varying signal fading. You can search Rayleigh fading and Rician fading to learn more.

 

[skeptic2]

Unless you are working on a thesis or dissertation your best bet would be to find a propagation prediction program. Have you done any internet searches for propagation prediction software?