Analysis of microstrip crossovers using the nonorthogonal finite-difference time-domain method

Multilayered monolithic microwave integrated circuits (MMIC) have been proposed with a view to reducing the size and increasing the degree of integration of the MMIC. It has been demonstrated that new circuit configurations can be realized and the design capability can be improved. By the use of a multilayered MMIC, the circuit can be laminated so that the circuit size can be made smaller. However, since the circuit is laminated, qualitative evaluation of the crosstalks between the upper and lower transmission lines becomes important. Most of the previous analyses on the microstrip line crossover focused on the case where the two lines cross orthogonally. In this research, the finite-difference time-domain (FD-TD) method applicable to an arbitrary coordinate system is used for the analysis of the crosstalk when two transmission lines cross at an arbitrary angle. First, the FD-TD method that can be applied to an arbitrary coordinate system is summarized. Next, it is confirmed that the results of the present analysis for a single microstrip line do not depend on the mesh shape and that the present analysis results agree with those by other methods for a microstrip bend with an arbitrary angle. Finally, a three-dimensional crossover of micro-strip lines with an arbitrary angle is analyzed. the normalized frequency characteristics, cross-angle dependence, and the interdistance dependence of the s parameters are presented.