The type of e-cards that have an antenna built into them are cards.

The type of e-cards that have an antenna built into them are contactless cards.

Explanation:

Contactless cards are a type of card that allows to make payments by aproaching it to the reader without having to swipe it or dipping it in the terminal which makes the process easier and faster. These cards process the payment through a radio interface and they can be recognized because they have a symbol that consists of four curved lines in the front. According to this, the type of e-cards that have an antenna built into them are contactless cards.