Simultaneous Enhancements of Bandwidth and Isolation of Frame Monopoles Utilizing Elongated Back Cover Patches for Smartphones

The conflict between antenna density and limited frame space in smartphones has led researchers to explore back cover space to alleviate the pressure on terminal frame. Unlike existing studies that focus on developing back cover planar antennas, this work utilizes back cover patch antennas to assist the frame antenna design: The elongated metal patches on the back cover provide new radiative modes and additional coupling paths, thereby improving bandwidth and reducing coupling of the frame monopoles. The proposed strategy is effective for two typical frame antenna configurations, namely back-to-back and back-to-face monopole pairs. Using only 0.5-mm clearances, the measured bandwidth and isolation of the first pair are respectively improved from 200/210 MHz to 330/340 MHz and from 8.2 dB to 15.0 dB with the addition of the 2.5-mm-width elongated back cover patches, while the results of the second pair are improved from 140/170 MHz to 300/290 MHz and from 11.3 dB to 16.5 dB. Simultaneous bandwidth and isolation enhancements utilizing elongated back cover patches significantly improved the performance of the frame antennas. Due to their slender shapes, these patches can be easily integrated into the back cover, demonstrating great practical value for smartphones.