Multi-Band Coupled-Fed Antenna for 4G LTE, Sub-6G, and WLAN Frequency Bands in Various Electronic Devices

This paper proposes a multi-band coupled-fed antenna (MBCFA) design for 4G LTE, Sub-6G, and WLAN frequencies, suitable for electronic devices with different sizes and fully metallic backplates. The MBCFA structure can be replicated on the fully metallic backplates of laptops, tablets, or smartphones to form a multi-input multi-output (MIMO) antenna system. Each MBCFA at different positions on laptops and tablets exhibits similar resonance characteristics, highlighting its high robustness and stability. The proposed MBCFA is manufactured using low-cost FR4 material. The overall size of MBCFA is 70 mm
$\times12.5$
mm and an FR4 thickness of 0.8 mm, the measured reflection losses within the -6dB range are 740–990 MHz (250 MHz bandwidth), 1380–2640 MHz (1260 MHz bandwidth), and 4250–7330 MHz (3080 MHz bandwidth). The MBCFA’s isolation levels in the 4G LTE frequency band are below -16 dB, while the remaining frequency bands have isolation levels below -20 dB. The maximum antenna gain is approximately 5 dBi, and the optimal antenna efficiency is 60%. The Equivalent Coupling Coefficient (ECC) for all frequency bands is below 0.5. Given the excellent antenna characteristics described above, the proposed multi-band coupled-fed antenna is an outstanding candidate for laptop, tablet, and smartphone antennas.