Analysis of Radiated Emissions from a Microstrip Line Covered by an Electromagnetic Shield

This paper studies the effect of a printed circuit board electromagnetic shield on the radiated emissions from a microstrip transmission line passing through it. In this study, full-wave simulations were used to evaluate the radiated emission levels (in terms of the electric field strength modulus <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\vert E\vert$</tex>) at several observation points for both microstrip transmission line configurations with shield and without shield. First of all, the assessment was carried out inside the shield. It was observed that radiated emissions from the microstrip transmission line could increase by more than 40 dB due to the excitation of cavity resonances inside the shield. Furthermore, it was demonstrated that these resonances can also increase reflection levels in the microstrip transmission line, which may lead to distortion of signal integrity in the propagating electrical signals. Next, the radiated emission levels were analyzed outside the printed circuit board shield. It was shown that in some observation points, emissions can be attenuated by the shield, while in others, they may, on the contrary, be amplified. The most significant emission levels increase (by 520 dB) occurs when the observation point is located directly opposite a shield aperture.