Cn-fdtd Analysis Of Microwave Circuits Including Lumped Elements

The finite-difference time-domain (FDTD) method is one of the most important methods in electromagnetic numerical simulations for its powerful capabilities. However, the FDTD method still has its disadvantages. In this thesis, the intrinsic characteristic of traditional FDTD are successfully improved by a new ideal through studying classical FDTD methodology and foundations of mathematics. The selection of the time steps' size in traditional finite-difference time-domain (FDTD) method is restricted to the Courant-Friedrichs-Levy stability condition. In this paper the three-dimension Crank-Nicolson difference scheme FDTD is introduced.First of all, in this paper, according to the method of joining lumped-elements in traditional FDTD method, we set CN-FDTD difference scheme into lumped-eiements iterative formulas, which proposed a method of CN-FDTD when processing the plane microwave circuit including lumped-elements. Compared with the traditional FDTD method, being out of the CFL conditions of stability, reducing the time step and keeping the accuracy. At the same time, the matching circuit, the left/right hand transmission lines, power divider, and several other examples are used to verify the accuracy of this method. At last, we introduce the application of this method in the designing of microstrip antenna.Then, according to the lumped-network FDTD (LN-FDTD) method, the paper proposes a lumped-network CN-FDTD (LN-CNFDTD) method, using this method can shake off the disadvantage of lumped-elements can not being accurately calculated by any connection in the two-port circuit of LE-FDTD method, it can make FDTD grid combine any linear two-port network. We introduce the iterative formula of the so-called LN-CNFDTD method, and then use the LN-CNFDTD to calculate the limited bandwidth microstrip plane microwave circuit to verify this approach.