Semi-Flexible Diversified Circularly Polarized Millimeter-Wave MIMO Antenna for Wearable Biotechnologies

This article presents a novel semi-flexible two-port multi-input–multioutput (MIMO) antenna with dual circular polarization (CP) in the millimeter-wave (mm-wave) frequency band (24–31 GHz) for wearable applications in biotechnologies. The radiating circular patch and ground plane are embedded with multiple sectoral slots and moon-shaped slots, respectively, for broad impedance bandwidth and CP property. The $E_{\theta }$ and $E_{\phi }$ fields are also classified as RHCP and LHCP at 27.10 and 29.53 GHz, respectively. The microstrip line feeds the MIMO antenna, which is printed on a semi-flexible substrate with an overall electrical length of $2.9\lambda _{0} \times 1.8\lambda _{0} \times 0.04\lambda _{0}$ at 24 GHz. The antenna is designed for homogeneous space conditions (off-body) with a flat profile. Its on-body performance capability top-up with bending analysis is examined on the surface (chest, hand, and leg) of the anatomical Gustav human body model. Furthermore, the MIMO diversity parameters are also evaluated in the CST Microwave Studio Simulator. Later on, the simulated radiation characteristics are testified through in vitro measurement of the fabricated MIMO antenna in free-space and chest mimicking gel-based phantom. Finally, to ensure human shielding, the SAR analysis is mapped with the communication link margin to select the input power.