Electrostatic Solution for Broadside-Coupled Striplines in a Shield

Broadside-coupled striplines in a shield are basic guiding structures in coupled transmission line (CTL) cells that are important in EMI/EMC applications [1]–[3]. The CTL cells exhibit good performance in terms of field uniformity and bandwidth. The CTL cells consist of uniform and tapered sections. Higher-order TE and TM wave propagation along the uniform section was studied in [4]. Higher-order modes for offset striplines in a shield were studied in [5]. However, for the accurate estimation of field distribution in the CTL cells, an understanding of dominant TEM mode in the uniform section is also needed. It is therefore of practical interest to rigorously analyze TEM wave transmission along the uniform section of CTL cells. The TEM wave in the uniform section is governed by Laplace’s equation for the electrostatic potential Φ. While Helmholtz’s equation was used in [5] for higher-order mode analysis, Laplace’s equation will be used here for the TEM wave analysis. The purpose of this letter is to solve Laplace’s equation for broadside-coupled striplines in a shield using the mode-matching method [4], [5]. The analysis follows next.