Circularly Polarized Dual-Mode Wearable Implant Repeater Antenna With Enhanced Into-Body Gain

A wearable stripline-fed circularly polarized dual-patch antenna structure that exhibits enhanced into-body gain is presented. The antenna is designed for body-surface repeater solutions and it addresses the problem of marginal into-body deep tissue communication links, where power consumption is of the utmost importance and system link efficiency is critical. Under realistic operation conditions, the antenna's circular polarization (CP) successfully mitigates implant orientation and polarization mismatch. Polarization loss for linear antennas can be up to 16 dB in anechoic environments and as much as 12.5 dB in a realistic multipath environment, as demonstrated by measured co- and cross-polar forward path gain between implanted and linearly polarized surface antennas. To overcome the body-isolating effect of an antenna ground plane and to produce an effective off-body mode, a novel dual-aperture stripline feed was developed which also improves the body-mounted antenna radiation efficiency. The antenna provides a 0 dBi off-body gain while still maintaining excellent into-body performance. The into-body link was shown to exhibit CP with a maximum isolation of only 1.5 dB between co- and cross-polar measurements in the 2.36-2.4 GHz band. All measurements were carried out using an accurate, next-generation layered phantom tested representative of a wide range of the population.