1. Interaction of radiators has an appreciable effect on the noise characteristics of passive as well as active phased antenna arrays. This effect can be rather accurately accounted for with the aid of only one parameter of the radiator array, namely its effective reflection coefficient defined in the transmission mode with excitation of all channels. 2. The sensitivity of a phased antenna array depends on the effective reflection coefficient differently than does the antenna gain. In passive phased antenna arrays, moreover, the sensivity decreases with beam deflection more than does the gain. 3. In active phased antenna arrays there is a theoretical possibility to weaken the dependence of the sensitivity on the scanning angle, viz., by optimizing the parameters of the input stages.