Wideband MIMO Antenna System for Sub-6 GHz Cell Phone

In this paper, a novel MIMO antenna system is proposed and studied for the application of 5G cell phone in the Sub-6 GHz frequency band. The configuration of the designed antenna consists of four resonators operating at the Sub-6 GHz 5G band. Each antenna element is composed of a planar-inverted F antenna (PIFA), a monopole antenna and a slot by defected ground structure (GDS). These four compact resonators are located in four corners, representing a smartphone board in practice. All radiating elements are etched on a low-cost FR4 substrate with an overall size of $150\times 75\times 7\mathrm{mm}^{3}$. Under the impedance matching ($S_{11}\leq$-10dB) of 3.3-5.8 GHz, the designed MIMO antenna has good total efficiency of 55%-87%, sufficient maximum gain of 3.5-6.0 dBi and ports isolation $\leq$-15dB. The bandwidth of the presented antenna covers Sub-6 GHz 5G band of some current research hotspots including n77(3.3-4.2GHz), n78(3.3-3.8GHz), n79(4.4-5.0GHz) and others. The calculated antenna envelope correlation coefficient (ECC) and total active reflection coefficient (TARC) are low over the whole band. Moreover, the proposed design exhibits very small specific absorption rate (SAR) values at the reflection zeros of user-head.