Small-Size LTE/WWAN Printed Loop Antenna With an Inductively Coupled Branch Strip for Bandwidth Enhancement in the Tablet Computer

The technique of using an inductively coupled branch strip for bandwidth enhancement of a simple printed loop antenna to achieve small size yet multiband operation to cover the LTE/WWAN bands (704-960 and 1710-2690 MHz) in the tablet computer is presented. The antenna´s metal pattern occupies a small area of 10 × 34.5 mm ² and is printed on a thin FR4 substrate. The branch strip is coupled to the loop antenna through a chip inductor. In the antenna´s lower band, the branch strip can cause an additional resonance excited near a resonant mode contributed by the printed loop antenna and thereby greatly widens the antenna´s low-band bandwidth to cover the 704-960 MHz band for the LTE700/GSM850/900 operations. While in the antenna´s higher band, the chip inductor provides a high inductance and limits the excitation of the branch strip, thereby making the branch strip have negligible effects on the high-band operation. In this case, with the printed loop antenna excited in the higher band, the antenna can generate two higher order resonant modes to form a wide operating band for the GSM1800/1900/UMTS/LTE2300/2500 operations (1710-2690 MHz). Details of the proposed antenna are described, and the obtained results of the antenna are presented and discussed.