This study aims to simplify the diversity gain measurement in a reverberation chamber since the conventional method requires two extra antennas: a transmitting antenna and a reference antenna with known radiation efficiency. By incorporating the one- or two-antenna method for the radiation efficiency measurement in a reverberation chamber and taking advantage of the enhanced backscattering effect, the proposed method in this letter does not need extra antennas, and only the antenna under test is enough to complete the measurement. A virtual antenna is introduced to help understand the proposed method. The measurement results obtained from the proposed method show a good match with the results obtained from the conventional method; preconditions and limitations of the proposed method are also identified and discussed.