Miniaturized Wideband Four-Antenna Module Based on Dual-Mode PIFA for 5G 4 × 4 MIMO Applications

The huge proliferation of the antenna number brought by 5G greatly increases the pressure of the bezels of the 5G terminals. To release the pressure, planar four-antenna module with miniaturization and wideband performance that can be implemented on the back cover is proposed in this article. Four identical dual-mode PIFAs are arranged in a sequentially rotated style and the whole antenna appears in a circular shape. Each antenna element is a slotted quasi-quarter circle with one inner edge shorted and the other two edges left open, and it is coupled fed by an L-shaped microstrip line. A cross line that connects all the four elements together is used to improve the isolation of the neighboring elements. The four-antenna module covering N77 is with the diameter of 30.6 mm and height of 2 mm. The measured results show that for all the four antenna elements, the -6 dB impedance bandwidths cover 3.3-4.2 GHz, all the isolations are better than 9.7 dB, the average total efficiencies are between 36% and 40%, and envelope correlation coefficients (ECCs) are lower than 0.5. To the best of the authors' knowledge, this is the smallest four-antenna module covering 3.3-4.2 GHz.