In wifi modules what does the shield have to protect?

Question

All wifi modules have a shield over the chip but what I’m wondering is if the track to the antenna need to be shielded or is it just the chip that needs shielding ? Thanks Ben

Answer 1

More than likely the shield is preventing any amplified antenna signals coupling back to the Wi-Fi antenna and turning the circuit into a useless oscillator. This is commonly seen in radios of all frequencies and is especially a problem at above a GHz because any short length of track carrying an amplified antenna signal behaves more like a transmissive antenna than at lower frequencies. Just think about the signal gains that are involved in amplifying less than -80 dBm from the antenna.

Answer 2

The shield is there for several reasons:

• Prevent RF signals that are generated inside the WiFi chips (like the local oscillator) from "escaping" and disturbing other devices nearby. An "escaped" signal could also be picked up by the devices's own antenna making it amplify its own signal. That needs to be prevented.

• Prevent RF signals from nearby devices to be able to disturb the reception.

The track to the antenna doesn't need shielding as the antenna is picking up / transmitting the signal anyway. But in order to connect to the antenna there needs to be a track from the shielded part to the antenna so you cannot make a track to the antenna without any shielding.