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.

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This letter presents a wideband bezel coupled T‐type isolator, decoupling two antenna elements for smartwatch multiple‐input multiple‐out applications. The antenna elements consist of PIFA antennas operating at 2.45 GHz, covering Bluetooth and Wi‐Fi bands. The proposed T‐type isolator has been installed between the antenna elements made by inserting two slits in the bezel separated by 21 mm. The separated segment of the bezel is connected with the circular ground plane by a conducting strip and an inductor. In this way, the slits offer stray capacitance, and the capacitive coupling between the T‐type isolator has been utilized to achieve a wide isolation bandwidth. Meanwhile, the isolation can also be tuned using the gaps of the slits and the inductor. The design performance has been validated in simulations and measurement. The measured impedance bandwidth is higher than 120 MHz whereas the isolation bandwidth is 790 MHz with a maximum isolation higher than 22 dB. The measured envelop correlation coefficient is below 0.01. The proposed design is a good candidate for smartwatch applications.