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I once read that waves of higher frequency (such as around 1 GHz range and higher) have difficulty passing through water (or other liquids/solids).

Today, when I saw a cellphone tower, I wondered: "how are these towers able to transmit signals even when it's raining, or when its foggy?". I assume that when it's raining, a large surface area of the antenna will probably be covered with water. When it's foggy, there are lots of water droplets in the air that will block the path of the tower's waves.

My question is: what is the physics explanation of how electromagnetic waves of low vs high frequency are interacting with matter, and why higher frequency waves are better absorbed by matter than lower frequency (such as AM radio waves). I searched online for this, but had difficulty finding a well-explained physics explanation.

Then using that explanation, how are the high frequency cellphone tower waves still able to pass through the water? Is it just that the towers have a lot of power so although some energy is absorbed, a lot of energy is still able to pass through?

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    $\begingroup$ "I once read that waves of higher frequency (such as around 1 GHz range and higher) have difficulty passing through water", you read something that is untrue, or at least it is untrue without qualifications. Below 10GHz, and especially below 6GHz rain attenuation is essentially irrelevant to the link-budget. $\endgroup$ – hyportnex Aug 26 '19 at 19:38
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Cell links are affected a little by rain, but an electromagnetic wave is not significantly scattered by objects much smaller than its wavelength. Even frequencies such as $5\mathrm{GHz}$ have a wavelength of $60\mathrm{mm}$, while a raindrop might be a tenth the size. When wavelength and obstacle become comparable in scale, "Mie scattering" becomes significant. Millimeter wave links at $60\mathrm{GHz}$, for example, can suffer $20$ to $30\mathrm{dB/Km}$ (i.e. less than $1\text{%}$ makes it through a kilometer of rain) of loss in heavy rain.

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  • $\begingroup$ Hi Kent, thanks for your answer. When you say "objects much smaller than its wavelength", what counts as an "object"? If we consider water molecules as objects, I'm sure a radio wavelength is larger. However, maybe if we consider a large blob of water stuck to an antenna, the blob may sometimes be similar in size to the wavelength? $\endgroup$ – F16Falcon May 15 '20 at 20:19
  • $\begingroup$ "Object" would be anything not transparent to radio. It could be dielectric, conductive, or some of both. My description was about propagation in far field, away from antenna. Close to an antenna, a film of dielectric (such as water) much thinner than the wavelength causes a small change in impedance but should not be a problem. Water is also weakly conducting but a thin film, again, should not be a problem. $\endgroup$ – Kent Nickerson May 16 '20 at 16:57

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