A Miniaturized Extremely Close-Spaced Four-Element Dual-Band MIMO Antenna System With Polarization and Pattern Diversity

We propose a miniaturized design of a four-element dual-band multiple-input-multiple-output (MIMO) antenna system. The dual-band function is obtained by etching an "L" slot in the radiating patch. The edge-to-edge elements spacing is only 0.023 lambda(0). A decoupling structure consisting of cross-shaped metal strips shorted to the ground plane using vias is first introduced. Then, metalized walls are used to enhance the isolation level by realizing the pattern diversity. The measured resonant frequencies are centered at 3.5 and 5.7 GHz with bandwidths of 58 and 43 MHz, peak gains of 2.7 and 2.85 dBi, and peak efficiencies of 63% and 65%, respectively. A considerable measured mutual coupling reduction of 10.8 dB in the lower band and 15.6 dB in the upper band is realized. The overall size of the design is 0.41 lambda(0) x 0.41 lambda(0) x 0.04 lambda(0) with minimum isolation levels of 18.4 and 22.7 dB in the lower and upper bands, respectively. The envelope correlation coefficient is lower than 0.08 across both operating bandwidths. The measured results validate the good diversity performance of the MIMO system.