Tunable Multi-Band Mobile Phone Antenna with a Metal Rim for LTE Applications

A novel low-frequency tunable multi-band mobile phone antenna based on a variable capacitor is developed in this paper. The antenna consists of a loop and monopole structures as well as a controlling circuit for the varactor. It utilizes the metal rim of the phone for a maximized antenna aperture size and an enhanced performance. The antenna is developed on an FR-4 PCB board using a 50-Ω pigtail line for test. The measured results show that it achieves a -6 dB bandwidth covering all the LTE/WWAN bands from 700MHz to 2.7GHz. The low-frequency radiation efficiency is more than 30% (-5dB). And it varies from 45% to 77% for the 1.7GHz to 2.7GHz high band. It is featured by a tunable low-band and a fixed high frequency part.