IFA-Based Metal-Frame Antenna Without Ground Clearance for the LTE/WWAN Operation in the Metal-Casing Tablet Computer

A metal-frame antenna for the long-term evolution/wireless wide area network (LTE/WWAN) operation in the metal-casing tablet computer is presented. The antenna is formed by using two inverted-F antenna (IFA) structures to provide a low band and a high band to, respectively, cover the LTE/WWAN operation in the 824-960 and 1710-2690 MHz bands. The larger IFA has a longer radiating metal strip for the low band, and the smaller IFA has a shorter radiating metal strip for the high band. The two radiating metal strips are configured to be a portion of the metal frame disposed around the edges of the metal back cover of the tablet computer. The projection of the metal frame lies on the edges of the metal back cover, such that there is no ground clearance between the projection and the metal back cover. Furthermore, the feeding and shorting strips with matching networks therein for the two IFAs are disposed on a small dielectric substrate (feed circuit board), which is separated from the system circuit board and the metal back cover. In this case, there is generally no planar space of the metal back cover and system circuit board occupied, and the antenna can cover the 824-960/1710-2690 MHz bands. Results of the proposed antenna are presented. An extended study is also presented to show that the antenna's low-band coverage can be widened from 824-960 to 698-960 MHz. The wider bandwidth coverage is obtained when a switchable inductor bank is applied in the larger IFA.