Closely Spaced Broadband MIMO Differential Filtering Slotline Antenna With CM Suppression

Abstract

This letter proposes closely spaced broadband multiple-input-multiple-output (MIMO) differential filtering slotline antennas. A good impedance matching performance can be obtained by well distributing the resonant frequencies of slotline radiator and dual-mode resonator. Under common-mode operation, the differential antenna does not work because the vertical electrical field is hardly introduced on the slotline radiator. Furthermore, four filtering antenna elements are distributed centrosymmetrically along the center of the substrate. The adjacent two filtering antenna elements are placed perpendicularly with a spacing of 0.05λA. Compared with the single filtering antenna, a filtering performance of the MIMO antenna has no significant change. For demonstration, a MIMO differential filtering antenna is simulated and measured, which has a fractional bandwidth of 25% at 5.2 GHz. The simulated results agree well with measured ones. A low mutual coupling of less than -16 dB and low envelope correlation coefficient of better than 0.01 are obtained.