In fact, the radio signal transmitted by the RF connector may encounter many objects in its transmission path and experience additional attenuation depending on the absorption characteristics of the object. There are many types of objects, including stationary objects that absorb RF energy and cause RF attenuation, moving objects and transient objects. Similar to free space propagation loss, higher frequency attenuation is much faster than low frequency. Therefore, 5 GHz RF signals typically have higher attenuation than 2.4 GHz, with a few exceptions.
The table below shows the losses introduced by various objects (or attenuation in dB). Most of the attenuation numbers are given as ranges because the actual value depends on the exact frequency and thickness of the transmission and the specific type of material used. Furthermore, the numbers measured at different locations are not always consistent, as the measurement conditions may vary. In particular, the amount of attenuation of concrete walls is the most controversial. This is because different types of concrete materials are used in different parts of the world, and the thickness and coating differ depending on whether they are used for the floor or the interior or exterior wall. Brick walls typically have attenuation at the lower end of the range shown in the table.
Although trees are good for the environment, they have a significant impact on RF transmission. The attenuation caused by the trees varies significantly depending on the shape and thickness of the leaves. The rule of thumb is that for 5 GHz, the attenuation per meter is about 1.2 dB, and for 2.4 GHz, the attenuation per meter is about 0.5 dB. Another major source of attenuation is water, although it is not a good idea to pass the RF link through water unless it is absolutely necessary. In a three-gallon water bottle placed in a triangle experiment, the 2.4 GHz signal attenuated by about 4 dB, while the 5 GHz signal attenuated by more than 14 dB. However, for frequencies below 10 GHz, rain, snow and fog attenuation is very small. The rain attenuation at 5 GHz is almost insignificant (<1 dB per km).
A human body made of about 70% water also attenuates the RF signal. The 2.4 GHz body attenuation is about 3 dB, and the 5 GHz attenuation is about 5 dB. This in particular makes it very challenging to design dense wireless networks for crowded facilities.