In this paper, a second-order decoupling design using a resonator and an interdigital capacitor is proposed for an MIMO antenna pair in mobile terminals. The proposed antenna pair consists of an interdigital capacitor and an open loop resonator. By properly combining the responses of the resonator and interdigital capacitor, a second-order decoupling performance can be achieved. Meanwhile, isolation between the two antennas is increased by at least 15 dB within the frequency band of interest, from -5 dB to -20 dB. Moreover, the decoupled antenna pair maintains good impedance matching performance from 2.4 GHz to 2.5 GHz. The proposed decoupled antenna pair and its coupled counterpart have been fabricated and measured. The measured results agree with the simulation ones. The proposed MIMO antenna pair is an eligible candidate for Wi-Fi MIMO applications in the 2.4 GHz band.
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