Printed loop antenna with an inductively coupled branch strip for small-size LTE/WWAN tablet computer antenna

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 mm², and is printed on a thin FR4 substrate. The branch strip can cause an additional resonance 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. 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).