In this paper, we presented an ultra-wideband multiple-input multiple-output (MIMO) antenna system with high element-isolation for the application in 5G metal-frame smartphones. We proposed T-shaped and C-shaped slots on the metal frame generating four resonances to enhance the bandwidth. What's more, we introduce modified H-shaped slots between each antenna-element to improve the elementisolation of MIMO antenna system. As a result, the MIMO antenna system has a wide bandwidth of 58% ranging from 3.3 to 6 GHz and the element-isolation is over 18 dB crossing the effective frequency band. Thanks to the decent element-isolation, the envelope correlation coefficient (ECC) between each antennaelement is below 0.05 providing a reliable anti-interference for the MIMO antenna system. In addition, the measured radiation efficiencies of the MIMO antenna system are higher than 40%. At last, we analyze the effects caused by user's hands and head to guarantee the robustness of the MIMO antenna system in practical applications. INDEX TERMS 5G communication, sub-6 GHz, ultra-wideband, high isolation, metal frame.
In this article, a high-gain square patch antenna with reconfigurable broadside and bidirectional beams under operation of TM20 and TM21 modes is proposed. Initially, two open slots are loaded to the edges in two opposite sides of the radiating patch so as to reshape the current distribution of TM21 mode, by which its four-beam radiation pattern is transformed into the desired broadside beam. With this arrangement, the resonant frequency of TM21 mode can additionally get reduced towards that of TM20 mode. By utilizing a simple feeding network with four p-i-n diode switchers, TM20 and TM21 modes can be further excited with common-mode and differential feeding schemes, respectively, thus bringing out switchable broadside and bidirectional patterns. The simulated and measured results are found in good agreement, both demonstrating that the antenna achieves an overlapping bandwidth of 7.3% in a range from 2.35 to 2.54 GHz, and the measured peak gains as high as 10.4 and 9.6 dBi for the broadside and bidirectional states, respectively.
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