Quadrilateral Spatial Diversity Circularly Polarized MIMO Cubic Implantable Antenna System for Biotelemetry

This article presents a first of its kind, coplanar waveguide (CPW)-fed 3-D multi-input-multi-output (MIMO) ground radiating cubic antenna (CA), implantable in the human upper arm for biotelemetry applications. The four antenna elements are circular in shape and loaded with a pair of slots to obtain circular polarization (CP). It excites diversified CP radiation in Industrial, Scientific, and Medical (ISM) band 2.45 and 5.8 GHz in orthogonal space to establish communication between the human body moving in random directions and base-station. The overall dimensions of the proposed antenna are 15 x 15 x 15 mm(3). Monitoring circuit PCB is placed at the top, and the bottom side of the cube and central hollow space is filled with a dry solid phantom for impedance matching. The CA is simulated in the vicinity of the canonical arm tissue model in HFSS software and examined in a realistic human model. The far-field gain is -18.5 dB with -32 dB isolation between elements. The CA is fabricated, and measurements are carried out in skin-fat-muscle phantom and minced pork. Simulated results closely match with measured results. The results show that the proposed CA is polarization and 3-D orientation insensitive and provides good MIMO properties. The low SAR value of the CA allows maximum transmit power of 5.81 mW, makes it a suitable choice to transfer high data rate (200 Mb/s) to an external antenna of diverse polarization. These features make CA an attractive solution for real-time healthcare applications.