A Reconfigurable Metal Rim Antenna With Smallest Clearance for Smartphone Applications

In this paper, a reconfigurable metal rim antenna with a small clearance and compact structure for 4G/5G smartphones is proposed. It consists of the system ground plane and a metal rim with two slits, in which a U-shaped slot of 1 mm (the smallest) clearance is realized between the system ground and metal rim. The theory of characteristic modes is applied to analyze the eigenmodes of the antenna so as to aid the optimum design. The characteristic modes (CMs) in the band of interest are studied, and an inductive coupling exciter is identified as the best since three CMs can therefore be generated in the lower frequency band (0.69-0.96 GHz), and an SP4T switch can be utilized to increase the bandwidth of the whole lower band. A prototype antenna of the optimized design was fabricated. A good agreement was obtained between the measured and simulated results. The 6-dB frequency bands are the lower band (0.69-0.96 GHz), the middle band (1.7- 2.7 GHz), and the higher 5G band (3.4- 3.6 GHz), respectively, and the total efficiencies are over 50% in all these frequency bands. They indicate that the antenna is a very good candidate for smartphone applications.