Compact Dual-Polarized Wideband Antenna With Dual-/Single-Band Shifting for Microbase Station Applications

Abstract

A gain-enhanced wideband multiple-input multiple-output (MIMO) antenna with dual polarization and high isolation is proposed for microbase station application. It includes two mutually orthogonal bowtie dipole radiators, four bowtie parasitic elements with the switch function of ON-/OFF-state, four vertical stubs, and a cavity, which are fed by a pair of 50 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> coaxial cables. Shifting between the dual-band and single-band is realized by the switch. Four resonant frequencies are generated by cooperative operation of the radiators and cavity, and thus two wide bands are formed. C-shaped slots on radiators and switch slots on parasitic elements are analyzed for estimating the impact on resonant frequency and bandwidth, and the vertical stubs improve the impedance matching. The proposed wideband antenna achieves enhanced diversity performance in the MIMO antenna system. As a proof of concept, a prototype of the expanded four-element MIMO antenna is fabricated. Measured results match well with simulated data. When the switch is ON-state, it operates in 1.58–2.77 and 4.71–6.18 GHz with gains of 9.4–11.2 and 9.1–10.9 dBi, and radiation efficiencies of ≥87.5% and ≥87%, respectively. When the switch is OFF-state, it operates in 1.56–2.76 GHz with a gain of 8.9–10.1 dBi and radiation efficiency of ≥88%. Element isolation is ≥35.3 dB, and envelope correlation coefficient (ECC) is ≤0.002. The experiment of the established <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2 \times 2$ </tex-math></inline-formula> MIMO system demonstrates that it can operate with a lower bit error rate (BER), and the design shows enormous potential to be applied as massive MIMO microbase station antennas.