This article presents a simple structure for reducing mutual coupling between two diversity planar monopole antennas for WLAN 5.2/5.8 GHz applications. The structure has two λ/4 (λ-wavelength in the substrate) slots cut into the ground plane between the two monopoles. In 0.5 λo (λo,-wavelength in the air) of the antenna spacing, mutual coupling was -33.3, -21.1 dB at 5.2, 5.8 GHz, respectively. The lowest mutual coupling of -33.3 dB was achieved at 5.2 GHz, which is 20.8 dB improvement over the reference.
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