A High-Isolation Building Block Using Stable Current Nulls for 5G Smartphone Applications

Abstract

In this paper, a new design method to enhance the isolation of a two-antenna building block is introduced. Here, a two-antenna building block (Ant 1 and Ant 2) that is composed of a gap-coupled loop antenna (Ant 1) and a loop antenna (Ant 2) is meticulously designed to allow Ant 1 to excite a standing-wave region that can be formed on the structure of Ant 2. To exhibit high isolation (26 dB) between the two antennas, the stable current null point existed in the standing wave region is exploited and designed to fall at the feed point of Ant 2 during the excitation of Ant 1. By employing this proposed building block, a four-port multiple-input multiple-output (MIMO) system and an eight-port MIMO system operating in the long term evolution (LTE) band 42 (3.4-3.6 GHz) are implemented. The proposed four-antenna and eight-antenna MIMO arrays can yield desirable measured isolation of better than 23 dB and 17.9 dB, respectively, over the band of interest, and their respective measured ECCs (envelope correlation coefficients) were lower than 0.032 and 0.075. To further evaluate the MIMO performances of the presented MIMO arrays, their ergodic channel capacities are also investigated.

Keywords

• Fifth-generation (5G) smartphone
• multiple-input multiple-output (MIMO)
• building block
• high isolation