I need to find out the antenna gain of the WLAN cards in my laptop and phone, as well as the transmitted signal power. I have an Intel® PRO/Wireless 3945ABG in my laptop and an Atheros AR6003 in my phone. Can someone help me with this?
I tried to compute the gain myself, but I've reached a dead end.
I found that the unknown gain of an antenna can be computed with the formula:
Gain - unknown gain (of laptop or phone antenna) ReferenceGain - gain of a reference antenna MeasuredLevel - signal strength (in dBm) from the antenna of unknown gain ReferenceLevel - signal strength (in dBm) from the reference antenna, measured in the same conditions as MeasuredLevel
I did not bother to check your formula. But negative gain is entirely possible. I would bet that the majority of part 15 devices made have negative gain with their built in antennas.
Yes, space-limited antennas can have 0 or negative gain. Laptops' WiFi antennas are most likely in the range of -3 to +3 dBi of gain. You can assume 0 and be OK. A few dB matters not, when the path loss is many tens of dB.
You can't measure antenna gain without putting the antenna into a test chamber with proper methods and instruments.
For proper antennas (not those crammed into a laptop PC), the vendor publishes gain vs. azimuth and elevation plots.