An apparatus and a method are for measuring the radiation efficiency of antennas and the communication power of mobile and wireless terminals. The apparatus includes a chamber to enclose the antenna or terminal to be tested. The chamber includes walls of an inwardly reflective material, rendering the walls reflective to electromagnetic waves. The quality of the antenna or terminal is obtained by averaging the power transmitted between the antenna under test and a fixed antenna, or the power received at the fixed antenna when the terminal under test is used as a transmitter. The averaging is done over the measured power for several different positions of moving objects in the chamber and of a moving platform on which the antenna or terminal under test is located. The radiation efficiency or communication power is obtained by relating the measured average levels to those of a reference antenna or a reference terminal of known radiation efficiency or communication power.