Worst Case Prediction of Shielding Effectiveness of Board Level Shields

A method is proposed to predict the worst case shielding effectiveness of a board level shield (BLS). This method estimates the shielding effectiveness (SE) of the shield below and above the first resonance of a cavity formed by the BLS. The apertures of the BLS are modelled as antennas with known radiation efficiency. The estimation of the maximum field inside the cavity is used to calculate the magnetic currents driving the antennas above the first resonance of the cavity. Below the first resonance the field inside the cavity is estimated using the resonant LC circuit model. An approximated formula for the radiation of the uniformly placed apertures is developed. The worst case prediction is validated by the full wave simulation and also in measurement on a real BLS