Passive Reconfigurable Triple-Wideband Antenna for LTE Tablet Computer

A passive reconfigurable triple-wideband tablet computer antenna for the LTE operation in the low band of 698 ~ 960 MHz, middle band of 1710 ~ 2690 MHz, and high band of 3400 ~ 3800 MHz is presented. The antenna mainly acts like an inverted-F antenna (IFA) at frequencies in the LTE low and middle bands and like a loop antenna at frequencies in the LTE high band. The reconfigurable IFA/loop antenna is achieved without active switch circuits and occupies a small volume of 10 ×35 ×3 mm³. The antenna is obtained by first configuring the radiating arm of an IFA to be folded and coupled to the device ground plane through a distributed capacitor. Then, the IFA´s shorting and feeding strips are respectively loaded with an inductor and a capacitor. This leads to good excitation of a resonant mode generated in the LTE low band with the radiating arm length of the IFA only about 0.16 wavelength at 800 MHz. By further aided using a high-pass matching circuit integrated within the antenna, a wide low band is obtained for the antenna. The IFA´s first two higher-order modes can also be excited in the middle band. Owing to the distributed capacitor between the IFA´s radiating arm and the device ground plane, the two higher-order modes can lead to a wide middle band for the antenna. At frequencies in the LTE high band, the antenna mainly acts like a loop antenna operated at its one-wavelength loop mode, which contributes to a wide high band for the antenna. Triple-wideband operation covering the LTE operation is hence obtained. Details of the proposed antenna are described, and experimental results are presented. Working principle of the antenna acting like an IFA and a loop antenna at different frequencies is discussed.