Fluidically Reconfigurable MIMO Antenna With Pattern Diversity for Sub-6-GHz 5G Relay Node Applications

A four-element frequency reconfigurable and pattern diverse multiple-input–multiple-output (MIMO) antenna array for fifth-generation relay node applications is presented to operate in LTE bands 42 (3400–3600 MHz), 43 (3600–3800 MHz), and 46 (5150–5925 MHz). A planar microstrip line-fed monopole antenna is utilized as the MIMO element. The antenna relies on fluidic reconfiguration mechanism to either serve LTE bands 42/43 or 46. It incorporates a substrate milled channel beneath each monopole arm to hold distilled water. The water in the channel perturbs the $E$ -field distribution in the vicinity of the antenna arm and modifies the effective permittivity of the dielectric medium. To realize pattern diversity, adjacent elements are placed orthogonal to each other. Measured prototype exhibits a total active reflection coefficient $|{\text{TARC}}|$ and $|S_{11} |\leq -10$ dB for the high band when the channel is vacant (case 1) and the low band when filled with water (case 2), while minimum isolation is above 19.6 dB. The peak measured gain is ~4.6 and ~2.8 dBi, while the worst case envelope correlation coefficient (ECC) is ~0.004 and ~0.016 for cases 1 and 2, respectively. It measures 82.4 $\times$ 82.4 mm2 and was fabricated on a 1.52-mm-thick substrate of $\epsilon_{r}$ = 3.55.