Abstract: An improved active integrated antenna(AIA) design method is proposed in this paper. The farfield simulation of AIA is conducted in the transient EM/circuit co-simulation platform of CST with the pre-designed active device module reversely embedded in the EM model. By introducing a virtual zero-impedance port, the active integrated antenna is transformed into an equivalent dual-port device, besides, the characteristics of the active circuit can be calculated more accurately. Based on the previous analytic model, an improved design method of AIA is proposed. The method is used to complete the design of multi-frequency active integrated antenna which satisfies the two constraint criteria of gain equalization and G/T value equalization respectively. An AIA prototype with balanced G/T was fabricated and tested. The measured and simulated results are basically in consistence with each other, and it is verified that the improved design method can design AIA under different criteria, which is of positive significance to restrain design error, improve design efficiency and improve the characteristics of active integrated antenna.