It becomes essential to improve electromagnetic interference (EMI) shielding for high-speed, sensitive RF electronic devices when packaged in a shielding metal enclosure. The shielding effect by transmission (SET) was evaluated for 13 metal plates, which were considered as shielding unwanted EM waves. Most of the \(\mathrm S_{21}\) measurements for metals showed a similar high reflection performance at 6 GHz. However, when a 6-GHz low-noise-amplifier (LNA) was packaged in an aluminum die-casting (ADC) mold and covered with a high-SET metal lid, a sharp peak in \(\mathrm S_{21}\) at 5.2 GHz was observed. It was confirmed that the internal output signal radiated from the output signal pin between the PCB and the ADC, caused by impedance mismatch, was reflected at the bottom of the lid, propagated, and changed the total phase by 5 \(\pi\) , and was incident on the input stage of the LNA, causing resonant oscillation at 5.2 GHz. When the iron-based EM wave shielding (EMWS) sheet was attached to the metal lid bottom, the shielding effect by absorption (SEA) was increased by about 10 dB, and the sharp peak on the \(\mathrm S_{21}\) curve disappeared. This phenomenon was also investigated during the EVM evaluation for 64-QAM-OFDM transmission. When the LNA package was covered with an ADC lid, the EVM increased by approximately 10 dB due to increased quadrature error (Quad-Err). When the LNA package was covered with an ADC/EMWS lid, the EVM and Quad-Err were substantially suppressed. It is essential to shield electronic devices from both external and internal EMI by using high-SEA and SET materials to achieve high-quality QAM-OFDM transmission.
