CHARACTERISTIC IMPEDANCE OF OFFSET COUPLED PAIRS OF STRIP LINES BY THE PRINCIPLE OF SUPERPOSITION FOR INTERCONNECT CAPACITANCE OF IMAGE CONDUCTORS

In this paper, the characteristic impedance calculation method based on an approximate computation formula for the capacitance between the strip conductors presented by the authors, the electric image method, and the method of superposition of conductor systems is extended. A simple calculation method is proposed in which the characteristic impedance of an offset strip line and of offset coupled strip lines with no rigorous solution can be computed much more easily than by the conventional numerical methods. Since this method uses no elements for the model, the computational labor is very small. Therefore, the method is considered extremely effective for optimized circuit design of strip lines and offset coupled strip lines. Also, since the calculation procedure is very simple, it is very fast and accurate calculation for a wide range of parameters is possible. For strip lines and coupled strip lines, infinitely many image conductors appear in principle, and their potential coefficients can be expressed in terms of the sum of an infinite series of Dirichlet type in the mutual capacitances of the strip conductors. The numerical results of characteristic impedance calculations by this method agree well with the approximation for microstrip lines by Schneider and Wheeler and for symmetric strip lines by Hilberg, as well as with the approximations for symmetric coupled microstrip lines, and offset strip lines by the finite element method. Hence, the proposed method is an extremely simple and general one that covers all of the above cases by means of one calculation method. © 1999 Scripta Technica, Electron Comm Jpn Pt 2, 81(12): 27–40, 1998