The trend of microwave circuits has been toward highly integrated systems. Most design tools for designing microwave circuits mounted the linear or the nonlinear devices adopt the fundamental circuit theory using the S matrix on the frequency domain. The harmonic balance method is also used to correspond to the nonlinear circuit. Therefore, the effect of the electromagnetic field, for example, a mutual coupling between sub-circuits through the space is almost disregarded. To calculate these circuits included its surrounding electromagnetic field, the finite difference time domain method combined with the equivalent circuit simulation had been presented as the lumped element FDTD (LE-FDTD) method. In general, even if an analytical target is a linear circuit, the FDTD method requires very long analytical time. In this paper, we propose an efficient LE-FDTD method to reduce the analytical time. We investigate its efficiency to compare with the conventional LE-FDTD method or measurements, consequently, it is confirmed that the proposal method requires only at analytical time of 1/10 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.