A Compact Four-Element MIMO/Diversity Antenna With Enhanced Bandwidth

In this letter, a four-element wideband multiple-input–multiple-output (MIMO) configuration consisting of inverted L-monopole antenna (ILA) elements is proposed. An additional low-frequency operating mode arises in the MIMO system due to symmetric arrangement of elements with interconnected ground, apart from the resonance of the isolated ILA. Utilizing this mode, the proposed MIMO antenna operates in wide frequency range of <inline-formula> <tex-math notation="LaTeX">$\text{2.70-4.94}$</tex-math></inline-formula> GHz (impedance bandwidth <inline-formula> <tex-math notation="LaTeX">$=58.6\%$</tex-math></inline-formula>). The proposed four-element MIMO system occupies compact total area of <inline-formula><tex-math notation="LaTeX">$0.13\lambda _{0}^{2}$</tex-math></inline-formula> ( <inline-formula><tex-math notation="LaTeX">$\lambda _{0}$</tex-math></inline-formula> = highest operating wavelength) and has no complex decoupling scheme. Satisfactory interelement isolation (<inline-formula><tex-math notation="LaTeX"> $\geq $</tex-math></inline-formula>11 dB) and directional pattern with average gain <inline-formula> <tex-math notation="LaTeX">$\approx 4$</tex-math></inline-formula> dBi are achieved throughout the operating band of the proposed MIMO antenna. Furthermore, envelope correlation coefficient <inline-formula><tex-math notation="LaTeX"> $< 0.1$</tex-math></inline-formula> and mean effective gain ratio close to 1 are obtained in the working frequencies, confirming satisfactory MIMO/diversity performance.