| As a kind of microwave transmission line with excellent performance and convenient process, the coplanar waveguides are increasingly playing greater role in MMIC circuit. Especially in the millimeter wave band, the coplanar waveguides have the incomparable performance advantages over microstrips. However, the traditional theoretical analysis of coplanar waveguides are usually based on a series of ideal cases, such as the medium substrate is infinite thick and the ground plate infinite wide, which is not the real case. In order to direct the design of the MMIC circuit better, it is necessary to research on the electromagnetic characteristics of the coplanar waveguides under the nonideal circumstances. The finite ground's influences on the electromagnetic characteristics of the coplanar waveguides were exactly researched in this paper.In many numerical calculation methods, the Finite Difference Time Domain (FDTD) was chose as the research method due to the advantages that the information in very wide frequency spectrum could be obtained by single time-domain calculation. The principles and steps of using FDTD analyzing the coplanar waveguides were presented detailedly in this paper. On the division of grids, the heterogeneous grids were adopted to simulate the field intensity microscopicly and the physical structure precisely. The common excitations and the ways they added were systematically studied and two adding ways and applications of the excitation were proposed. About the treatment of the absorbing boundary, we use Perfect Match Layer. In addition, eight types of coplanar waveguides with concrete size were given in this paper and their characteristics impedance, propagation constants and effective dielectric constants were calculated. Then the effect rules of finite ground plate on coplanar waveguides were sum up Finally, the current difficulties of this project were put forward and the prospect of next step work were looked forward to. |
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