The trend of microwave circuits has been toward highly integrated systems. Most design tools for circuits are based on the fundamental circuit theory using the S matrix combined with the harmonic-balance method. Consequently, the electromagnetic effect is ignored or approximated at best. Therefore, the extended finite-difference time-domain(FDTD) method combined with the equivalent circuit simulation had been presented. However, it takes very long times to analyze any circuits. In this paper, we propose a novel extended FDTD method to reduce calculation resources. We investigate its efficiency to compare with the conventional extended FDTD method or measurements, consequently, it is confirmed that the proposal method is required calculation resources less than 10% compared with the conventional method. We also show that the proposal method is able to analyze characteristics of the active integrated antenna(AIA) which are practicably impossible to analyze by using the conventional method. Copyright 2006 IEICE.