Computer analysis of microwave planar circuit with impedance matrix

Computation of the wideband frequency characteristics of a microwave planar circuit with arbitrary shape requires computer processing because there are many parameters involved. However, if numerical calculations are carried out by computer from beginning to end, it is difficult to detect the amount of error and the error locations. The present paper resolves this problem. In addition conventional network theory is applied to the planar circuit and a computational method for easy understanding is introduced. To this end, the mode impedance looking at the planar circuit from the transmission line is defined Using this mode inpedance, network theory is employed to derive an expression of the effective impedance of the planar circuit projected on the dominant mode of the transmission line. Once the effective impedance is given,the frequency characteristics (S-matrix) of the circuit can be computed over a wide frequency range. A computer program is developed for this procedure and applied to the analysis of a corner-cut right-angle bend. Potential problematic points of the program are discussed. It is also found that the optimum cut of the right-angle bend can be computed and that the results so obtained agree with those known to date. Finally, it is pointed out that the present method is not only effective for the analysis of planar circuits, but also permits the analysis of higher-order modes of planar circuits.