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Four-Port Wide-Band Cavity-Backed Antenna with Isolating X-Shaped Block for Sub-6 GHz 5G Indoor Base Stations

Abstract:

A four-port wideband cavity-backed antenna is presented for indoor base stations applications. The antenna is composed of a square open cavity with an X-shaped isolating block and 4 feeding monopoles symmetrically and orthogonally arranged in the aperture of the cavity. A novel methodology based on Characteristic Modes Analysis (CMA) is used for identifying the modes which are contributing to the coupling. As a result of this analysis, an X-shaped isolating block placed at the center of the cavity is proposed for increasing the isolation between ports. A wide-band four-port antenna with unidirectional radiation patterns is obtained with a measured impedance bandwidth ( S11 < -10 dB) ranging from 1.55 to 6 GHz (118%), covering most of the sub-6 GHz 5G bands. The proposed antenna provides four independent radiation patterns, with 16 dB of measured minimum isolation between ports and an efficiency higher than 84%. Multiple-input multiple-output (MIMO) compatibility is confirmed with a 4 × 4 MIMO simulated system with an envelope correlation coefficient (ECC)< 0.5 in different propagation conditions. The antenna is easy to fabricate and presents a compact size of 129.5 × 129.5 × 28.2 mm3 ( 0.68 λ × 0.68 λ × 0.15 λ , at a frequency f =fmin =1.55 GHz). Moreover, the antenna has the advantage of avoiding complex feeding structures with baluns or directional couplers.