Characterization of a Coaxially-fed MIMO Antenna for n257 mmWave IoT Applications

This work presents the design and characterization of a coaxially-fed multiple-input multiple-output (MIMO) antenna for n257 band low-latency internet-of-things (IoT) applications. The proposed MIMO design offers -10 dB impedance bandwidth from 25.8 to 28.77 GHz, covering the globally designated n257 band. The design of the antenna is compact and architecturally simple and offers peak gain up to 9.8 dBi at a resonant frequency of 27 GHz, with a radiation efficiency of above 95% in the covered spectrum. Furthermore, the design features a compact inter-element spacing of $0.18 \lambda$ and a minimum isolation of 31 dB throughout the operational frequency band. The proposed MIMO antenna has an envelope correlation coefficient (ECC) value below 0.0002 and a mean effective gain (MEG) value less than -3 dB in the entire millimeter-wave (mmWave) n257 band spectrum, which renders it suitable for high-speed IoT applications.