Gain measurement of microwave antenna with heterodyne bichromatic excitation in Rydberg atoms

We propose a scheme for gain measurement of microwave (MW) antenna with heterodyne bichromatic excitation in Rydberg atoms via electromagnetically induced transparency (EIT). The Rydberg-EIT atoms serve as a frequency mixer with a strong locally oscillating MW field and a weak signal field. A large dispersion appears in the EIT windows due to the interference of two sub-EIT systems, which much narrows the transmission spectrum. The locally oscillating MW field could enhance the atomic response to the weak MW signals. The simulation results show that the gain measurement of MW antenna remains good accuracy even for weak MW fields and the minimum detectable MW field strength is about 1/12 of that of common EIT scheme. Other influences on the gain measurement are also investigated.