Abstract:The co-simulation of the electromagnetic-field-and-circuits hybrid system was studied by employing the extended finite-difference time-domain (FDTD) algorithm. The extended FDTD’s principle and its iterative formula reflecting the embedment of lumped devices in the FDTD cells were introduced. As a sample,a microstrip double dipole antenna loaded with a lumped matching circuit at its input port, which was an antenna-and-circuit hybrid system, was simulated by the extended FDTD. In the simulation,S₁₁ of this antenna was obtained by using a technique,which directly inserted the microstrip feeding line into a complex frequency shifted perfectly matched layer(CFS-PML) and executed the FDTD program twice.The loaded antenna was fabricated and measured.Results showed that the measurement agrees well with the simulation,and for the antenna,the lumped matching circuit slightly affects its gain and radiation patterns,but varies its resonant frequency and significantly changed its S₁₁ curve.