# Typical power reflected off wall/window/wooden shelves etc

For interference purposes, I would like to quantify how much signal power I would receive back when my transmitted signal is reflected off an object (a wall, glass window, wooden shelf) at a distance of d meters and frequency f=c/lambda. In my case, f=900 MHz, d is a few meters.

Intuitively, I would calculate:

$$P_{RX} = P_{TX} G_{TX} \underbrace{\left(\frac{\lambda}{4\pi d}\right)^2}_{\text{fwd loss}} \underbrace{|\Gamma|^2 G_{\rm obj}^2}_{\text{object properties}} \underbrace{\left(\frac{\lambda}{4\pi d}\right)^2}_{\text{reverse loss}} G_{RX}$$

$$\P_{TX}\$$ is the transmit power and $$\G_{TX}\$$, $$\G_{RX}\$$ are the gains of the transmit/receiver antenna. If the object would be an antenna, $$\\Gamma\$$ would describe the "reflection coefficient" and $$\G_{obj}\$$ the antenna gain.

I have seen the concept around the radar cross section $$\\sigma_{\rm rcs}\$$. After doing some math, I arrive at the following relation:

$$\sigma_{\rm rcs} = \frac{\lambda^2}{4\pi} |\Gamma|^2 G_{\rm obj}^2 .$$

which means when I either know object properties $$\\Gamma\$$ and $$\G_{\rm obj}\$$ or $$\\sigma_{\rm rcs}\$$ I could some estimates of reflected signal.

I have not found "typical" values for either of them. What could be typical properties of a wall, window, wooden surface?

PS: I am aware that reality is much more complicated. I really only want to get a ballpark estimate for a simple scenario. Is $$\|\Gamma \,G_{\rm obj}|\$$ typically -3dB, -10dB or -40dB?

• lol. But that's exactly my question. So how much is "very ver little"?
– divB
Commented Dec 10, 2020 at 3:21
• Your listed materials have too much variation for anything meaningful. Wires or pipes in those walls, or metal studs? Not much from the window, but if the screens are aluminum not fiberglass... Commented Dec 10, 2020 at 3:40
• "I really only want to get a ballpark estimate for a simple scenario. Is |ΓGobj| typically -3dB, -10dB or -40dB?" - best way to find out? Measure it. Commented Dec 10, 2020 at 5:08
• @ChrisStratton: 1.) Metal wall (infinite sheet in free space), 2.) Wooden wall (infinite sheet in free space) 3.) Glass, 1cm thick (infinite sheet in free space). Those coefficients must depend on some material properies (and geometry) and that's what I am looking for.
– divB
Commented Dec 10, 2020 at 6:27
• Surely you know what an infinite metal sheet would do. Wood would depend on a lot on the moisture content and frequency. Anyway, we don't do multipart questions. These are things you can look up, but if you're going to overlook the typical construction detail in the previous comment about how metal may or may not be present in walls and windows, the whole thing becomes meaningless. Commented Dec 10, 2020 at 6:28