TIS = Total Isotropic Sensitivity
“…Because of how long the measurement takes, you might ask if we can simply use the receiver sensitivity along with the antenna’s radiation pattern in order to simplify this process. Since when we change polarizations or angles, the only variable is the antenna, it seems we should be able to account for this using just the antenna’s radiation pattern?
Well, the answer is no. The first, and primary reason is that the antenna is picking up noise from all the electronics that make up the system under test that the receiver wouldn’t otherwise be exposed to. As an example, on mobile phones, the antenna receives energy from the memory and the phone’s screen, which is delivered directly to the receiver. This desensitization of the receiver is known as desense. Since the antenna picks up added noise that the receiver otherwise wouldn’t be exposed to, and since the antenna’s efficiency is always less than 1, the TIS will always be worse (higher) than the receiver’s conducted sensitivity.”
TRP = Total Radiated Power
“…The loss of power due to the antenna being away from 50 Ohms is not just related to mismatch loss (i.e. non-matching impedance between radio and antenna) in this situation, but rather because the radio will not put out the same power for every impedance that it connects to. Taken to the extreme, if an open circuit or short circuit is applied across a radio terminals, the radio will output zero power. For an antenna with a VSWR of 3:1, the power output could typically swing by 3 dB (can range between 17 and 23 dBm – yes, the power can actually be higher for a mismatched antenna!)
As a result, the only way to know how the antenna and radio system will perform as a whole is to measure the Total Radiated Power (TRP).”