Dual-Wideband MIMO Antenna Using Characteristic Mode Theory for Mobile Terminal Applications

This paper presents a minimum-profile dual-wideband MIMO antenna. Modal analysis using the Theory of Characteristic Modes (TCM) was applied to improve the design through a series of minor modifications to the terminal chassis. A hybrid mode-tracking algorithm was applied to benefit all possible radiating modes in both frequency bands. The phase of the normalized envelope correlation coefficient (NECC) was studied to make the two ports excite the same modes while maintaining minimum coupling and correlation. As a proof of the concept, a dual-wideband (0.8-1GHz, 2.4-3GHz), dual-port MIMO antenna was designed and fabricated on a 150 mm <inline-formula> <tex-math notation="LaTeX">$\times 76$ </tex-math></inline-formula> mm chassis. A simple matching network was designed to match the two ports over the entire frequency range. The impedance matching was less than −6 dB, the isolation between the two adjacent ports was over 12.8 dB, the correlation coefficient between the two adjacent ports <inline-formula> <tex-math notation="LaTeX">$\rho _{S}$ </tex-math></inline-formula> was less than 0.07, the correlation coefficient between the radiation patterns resulting from each port <inline-formula> <tex-math notation="LaTeX">$\rho _{3D}$ </tex-math></inline-formula> was less than 0.185, the average total efficiency was 84%, the peak realized gain was 4.38 dB, and the diversity performance was good, over the entire frequency range. Moreover, two reconfigurable resonant antennas were added to the two short edges of the chassis. By controlling the variable capacitor of a varactor diode and the state of a PIN diode, each resonant antenna can scan the entire upper or lower frequency bands.