Design of MIMO Antennas for Ultra-Thin Mobile Handsets

With the overwhelming of the full-screen smart phones, the metal frames around the handsets become thinner, making the antenna design more challenging. In this work, a dual-antenna system is designed for mobile handsets at the low frequency band based on characteristic mode analysis. The overall height of the handset is 2 mm, with a ground clearance of the 2 mm along the rest edges and the 3 mm along the top edge. With two grounding strips and two breaking points along the frame, orthogonal modes are created at the frequency bands around 0.8 GHz. Two uncorrelated antennas are then built by properly exciting the two modes. The main antenna operates from 781 MHz to 904 MHz, whereas bandwidth of the diversity antenna is relatively narrow. The isolations of the two antennas are above 18 dB over the operating band. The antenna is built fully from the thin frame and the chassis, without any additional structure, which makes it applicable to the ultra-thin handsets.