EM-based design optimization of microstrip lines traversing a rectangular gap in the reference plane

A practical EM-based design optimization method to mitigate the negative effects of non ideal return paths for microstrip lines is proposed. Our technique consists of finding the optimal compensation width of the microstrip line above a rectangular gap in the reference plane. By introducing this compensation, distributed effective capacitance above the discontinuity in the reference plane is increased, such that the original inductive effect created by the non-ideal return path is compensated. Highly accurate full-wave EM simulations are used directly to find the optimal compensation width. Resultant S-parameters show a very significant improvement of the interconnect performance at the optimal design, in terms of both transmission and reflections. It is demonstrated that the optimal value of the compensation width is far from that one predicted by first-order quasi-static approximations. Current density distributions on the non-ideal return path are shown before and after compensating the microstrip line, confirming the effectiveness of the proposed technique.