Bandwidth-Enhanced 5G Mobile Phone Antenna Pair With Tunable Electric Field Null

In this communication, a bandwidth-enhanced antenna pair with a tunable electric field (
$E$
-field) null for the fifth-generation (5G) mobile phone application is presented. The proposed antenna pair is composed of a stub-loaded inverted-F antenna (IFA) and a simple feeding network. The stub-loaded IFA can obtain a wider impedance bandwidth and a feeding network is designed to excite the orthogonal dipole mode and adjust the
$E$
-field null position. By adjusting the phase shifter in the feeding network, the
$E$
-field null can be moved to the feeding position of the IFA, achieving excellent isolation performance. A sub-6 GHz antenna pair is simulated and shows an isolation of better 16.5 dB within the N78 (3.3–3.8 GHz) band. By arranging the proposed antenna pair along two long edges of the ground plane, an
$8\times 8$
multiple-input multiple-output (MIMO) system is designed, fabricated, and measured. The measured results show that the MIMO system could achieve isolation of better than 19.5 dB and envelope correlation coefficients (ECCs) of lower than 0.03. The measured total efficiencies are greater than 43% for each port. The proposed antenna reveals a novel decoupling strategy for wider bandwidth while retaining the isolation performance and compact size based on a pair of orthogonal mode.