This paper presents a new dual-frequency antenna, called an inverted LFL antenna (InvLFL). The InvLFL is made of a thin conducting film. It has a flat structure (card-type structure), where both the radiation elements and the ground plate lie in the same plane. The card-type structure facilitates the use of the InvLFL in PC card devices for personal computers or for use inside mobile phone handsets. Responding to a demand for dual-frequency operation at 2.45 GHz and 5.2 GHz (frequencies used for wireless LAN communications), this paper describes the design process and reveals the radiation characteristics obtained using the finite-difference time-domain method (FDTDM).