Reconfigurable Structure Reutilization Low-SAR MIMO Antenna for 4G/5G Full-Screen Metal-Frame Smartphone Operation

A multiple-input–multiple-output (MIMO) antenna system for a 4G/5G full-screen metal-frame smartphone with a narrow ground clearance of 2 mm is presented in this letter. The long-term evolution antenna structures (LTEAS) for the 4G communication system are devised on both short-side edges with two ports and different matching circuits. It is fully functional over 698–960 MHz (LTE low band) and 1710–2690 MHz (LTE high band). An RF switch is loaded on the LTEAS to form a reconfigurable LTE low-band antenna structure covering the band of LTE700. Four loop antennas on the long side edge are devised close to the LTEAS. By fully reutilizing the structure of the LTEAS, new loop modes are generated in the 5G band. The 5G antenna structure can cover the spectrum of 3300–4500 MHz. The theory of low specific absorption rate (SAR) is applied to antenna design. The proposed antennas can simultaneously cover a wideband of 4G and 5G with low SAR characteristics for the first time. The proposed MIMO antenna is fabricated and measured. The performances show great potential in the future 4G/5G smartphone application.