Electromagnetic field analysis of waveguide‐microstrip line transition by spatial network method

The waveguide to microstrip line transition has been used widely in the microwave and millimeter wave bands for several radio communication systems. Since transition from solid waveguide to planar microstrip line is involved, the internal field distribution becomes complicated. Moreover, different types are required for different applications, thus the analysis of the transition is generally very difficult. The design of the transition till now has been based purely on the trial-and-error method. For such complex structures, the best way to find the characteristics is via computer simulation. In this paper, the spatial network method, which is excellent for three-dimensional (3-D) transient analysis, is applied to the transition and the possibility of unified simulation of the overall structure is demonstrated. The model of transition used for this analysis is such that microstrip line is inserted perpendicularly to the window as well as to the H-plane of the waveguide working in the TE10 mode. As a result of analysis, the dependence of frequency characteristics on various parameters of the transition shape and its relationship with the complex internal electromagnetic field is clarified. In particular, with the help of simulation of the Poynting power flow, the propagation conditions from the waveguide to microstrip line could be shown successively on the time axis. Thus, we have shown that the simulation based on this method can be used for efficient transition design. The authors wish to thank Mr. Shiomi, Communication Research Lab., of Postal Department, Mr. Kurihara, Fujitsu Research Lab., and Mr. Noguchi, Fujitsu Tohoku Digital Technology, Ltd., for their helpful guidance. Thanks are due also to Associate Prof. N. Yoshida of Hokkaido University for important discussions.