Ultracompact Dual-Band Circularly Polarized Antenna for Head Implants

In this communication, a compact, dual-band, circularly polarized implantable antenna is proposed for head implantable biotelemetry devices. The antenna occupies an ultraminiaturized size of$\mathbf {3.5 {\,}\times {\,}3.5 {\,}\times {\,}0.13~{mm}^{3}}$, corresponding to a total volume of$\mathbf {1.59~{mm}^{3}}$, which facilitates integration in space-constrained implantable systems. The miniaturization is achieved by combining a high-permittivity substrate (Rogers RO3010) with a slotted radiator–ground configuration, which elongates the surface current path and reduces the resonant frequency. The design operates at 0.915 and 2.45 GHz and it achieves −10 dB impedance bandwidths of 27.3% and 15.5% with corresponding axial-ratio (AR) bandwidths of 16.4% and 4.1%, confirming circular polarization (CP) at both industrial, scientific, and medical (ISM) bands. In tissue-representative environments, the antenna provides peak realized gains of approximately −30.1 dBiC at 0.915 GHz and −31.9 dBiC at 2.45 GHz. A SAR assessment shows maximum allowable input powers of 2.99 and 3.64 mW at 0.915 and 2.45 GHz, respectively, satisfying FCC and International Commission on Non-Ionizing Radiation Protection (ICNIRP) safety limits, while link-budget analysis verifies reliable short-range telemetry. Overall, the proposed antenna offers a balanced combination of extreme miniaturization, dual-band CP performance, and practical suitability for head-implantable telemetry applications. To the best of the authors’ knowledge, the proposed antenna is among the most compact, dual-band, circularly polarized implantable designs reported in the literature.