Using Fdtd With Spice Analysis Of Microwave Active Circuits

The finite-difference time-domain (FDTD) method is to derive the discrete form of the Maxwell's equations by second-order central difference with the electromagnetic distribution of the Yee space lattice, and computes the value of the electric field and magnetic field in the simulation space by using leapfrog for time derivatives. Some FDTD theories and algorithms applied in modeling microwave circuits with passive and active elements are discussed in the paper: the FDTD modeling algorithms incorporate lumped elements and SPICE software with equivalent circuits.First of all, in this paper, we reviewed the finite-difference time-domain Yee's method. The difference equations, the stability condition, numerical dispersion characteristics, absorbing boundary conditions, incident wave source conditions and the calculation of the frequency-dependent scattering parameters are discussed.Then the traditional method of joining lumped-elements in FDTD. At the same time, the matching circuit, filter circuit, and several other examples of microwave circuits with passive lumped elements are used to verify the accuracy of this method.At last, according to the shortage of the method discussed above, another modeling microwave circuit with lumped elements - method of incorporation SPICE software into FDTD is proposed. A set of protocols is putted forward to control the communication between FDTD method and SPICE software to settle this problem. By using the set of protocols, microwave sub-circuits with random number ports and any complication are modeled easily. At the same time, some examples are given, microwave circuits with passive lumped elements and microwave active circuits as limitr circuit and amplifier circuit, the numerical results can verify the accuracy of this method.