A Wideband Circularly Polarized Implantable Antenna for 915 MHz ISM-Band Biotelemetry Devices

A wideband miniaturized circularly polarized implantable antenna operating at 915 MHz Industrial, Scientific, and Medical (ISM) band is presented and experimentally verified in this letter. Compared with previous work, the patch antenna with the dimensions of π × (4.7)2 × 1.27 mm 3 features a better size reduction. The miniaturization of the proposed antenna is well implemented by cutting several kinds of slots to extend the current path. Moreover, a shorting pin is introduced to lower the resonant frequency and prompt circular polarization (CP) purity. Specific absorption rate is also calculated to consider whether it can meet the safety standards. The simulated results in one-layer cubic skin phantom demonstrates that the impedance bandwidth (BW) of 12.2% and the 3 dB axial-ratio BW of 19.7% can be obtained. Finally, the antenna is measured in the skin-mimicking solution, and the measured BW achieves about 17.5%, which generally agrees with the simulated.