A wideband decoupling method using bezel-coupled loop-type isolator for smartwatch MIMO applications

Abstract

Abstract This paper presents a novel decoupling technique for two-element multiple-in multiple-out (MIMO) antennas for smartwatch applications with floating metallic bezel. The radiating elements consist of embedded loop-type ground-radiation antennas and operate at the 2.45 GHz Bluetooth/Wi-Fi bands. An isolator, consisting of a loop-type structure with a lumped capacitor, is attached externally to the ground plane such that wideband isolation between the antennas has been achieved. It is demonstrated that the small-sized isolator is coupled with the large-sized bezel surrounding the ground plane, where the bezel operates as a low-Q decoupler between the antenna elements producing wideband isolation property. Accordingly, optimized results can be obtained by controlling the location of the isolator, the gap between the isolator and the bezel, and the loaded capacitor. Simulation and measured results have been presented to validate the design performance. The measured −10 dB impedance bandwidth of both antenna elements is more than 210 MHz, whereas the isolation bandwidth is 770 MHz with reference to 20 dB. The envelop correlation coefficient is <0.1 in the operating band. Furthermore, the proposed technique is versatile regardless of the angular separation of the antenna elements on the circular ground plane, which makes it a good candidate for smartwatch MIMO applications in practical scenarios.