Electromagnetic Investigation of Crosstalk in Bent Microstrip Lines with Partial and Apertured Shielding: Simulations and Measurements

TL;DR

This work analyzes crosstalk between two bent microstrip lines separated by a perforated shield, combining 3D full-wave CST simulations with geometrical diffraction theory and multimodal waveguide analysis to capture effects of shielding and apertures. It experimentally validates the influence of imperfect shielding using VNA measurements up to 20 GHz, and demonstrates how shield height and aperture resonances control NEXT and FEXT beyond conventional circuit models. Key contributions include the first experimental characterization of partial shielding between bent microstrip lines, the identification of waveguide-like behavior due to dielectric regions, and a predictive framework for aperture-induced resonances that informs shielding design. The findings offer practical guidance for reducing EMI in dense PCB layouts by tailoring shield coverage, height, and aperture geometry.

Abstract

This paper presents an electromagnetic investigation of the crosstalk between two bent microstrip lines (MLs) separated by a perforated planar shield. As an extension of our previous study, the effects of various discontinuities in either the MLs or the shield along the coupling path are analyzed through numerical simulations and validated by measurements. The underlying electromagnetic mechanisms are also discussed. Furthermore, multimodal wave theory in a rectangular waveguide is applied to predict crosstalk behavior when the shield contains an aperture. This study aims to conceptually elucidate complex crosstalk phenomena that are difficult to model using circuit theory, and successful predictions of crosstalk behavior are presented for different problem cases.

Figures (6)

• Figure 1: (a) Geometry and (b) a sample of fabricated PCBs of two bent MLs implemented on a Rogers RO4003C substrate, and symmetrically separated by a copper made shield with an aperture (with the height of 1 mm).
• Figure 2: The experimental setup used for the crosstalk measurement while the VNA is measuring two-ports scattering parameters. This configuration is set for NEXT measurement of the fabricated PCB with a solid copper made shield while the other two SMA ports are terminated with 50 $\Omega$ standard loads.
• Figure 3: Scattering parameters of the proposed geometry without the shield, modeled using the dimensional parameters in Table \ref{['tab1']}. In the first case, the MLs are terminated at the port locations indicated in Fig. \ref{['fig1']}, while in the second case, they are terminated at both ends of the CL on both lines. The measured results correspond to the first case.
• Figure 4: Scattering parameters of the proposed geometry under three shielding configurations without the aperture. Case 1: full shield implemented as specified in Table \ref{['tab1']}. Case 2: shield covering only the dielectric region. Case 3: shield covering only the air region, with the same height as in Case 1 and grounded at both ends.
• Figure 5: Simulated and measured crosstalk of the proposed geometry in Fig. \ref{['fig1']}(a) without an aperture, as a function of shield height $h$, at $f = 2$ GHz and $f = 5$ GHz.