A Hybrid Fractal-Based Conformal Capsule Antenna With UWB and High-Gain Characteristics for WCE Applications

This paper presents a novel hybrid fractal capsule antenna for wireless capsule endoscopes (WCE) operating at industrial, scientific, and medical (ISM) 0.915 GHz and 2.45 GHz, wireless medical telemetry services (WMTS) 1.4 GHz. Crucially, the prototype reduces the size to 12.8 mm × 7 mm, achieving a 58.2% diminution in overall volume relative to the currently employed 15 mm × 10 mm capsules. The capsule antenna is conformally integrated onto the outer wall of the substrate and encapsulated with a biocompatible superstrate. Validated within a homogeneous muscle phantom and subsequently corroborated experimentally, the proposed antenna achieves ultra-wideband operation and high gain (-17.7 dBi@915 MHz; -12.2 dBi@1.4 GHz; -16.1 dBi@2.45 GHz). Leveraging the synergistic integration of two distinct fractal topologies, the antenna exhibits an ultrawide contiguous bandwidth of approximately 2.11-octave bandwidth (return loss < -10 dB), covering all target bands. Benefiting from a propagation path loss consistently below 40 dB across these spectral windows, the system secures exceptionally high transmission efficiency. Moreover, the specific absorption rate meets IEEE exposure limits. The antenna's concomitant miniaturization and high-gain architecture not only render the capsule readily ingestible but also substantially broaden its clinical utility.