Part of proper grounding on the PCB includes the metallic components such as a display, shield cans and mechanical supporting structures which may cause loss of radiation if not properly grounded. Antenna signal can couple to these components, particularly if there is gap between the PCB and the metallic component. These gaps can create a high-loss, non-radiating resonance in or out of the band which lowers the antenna efficiency. Close-to-band resonances are especially harmful. It may even appear that antenna matching is improved due to these resonances, but in the worst case, they can reduce the radiation significantly.