A Compact Wideband Omnidirectional Circularly Polarized Implantable Antenna for Capsule Endoscopy System

This letter presents a compact wideband omnidirectional circularly polarized (CP) implantable antenna for the capsule endoscopy system in the 2.4 GHz industrial, scientific, and medical (ISM: 2.4 GHz to 2.48 GHz) band. The proposed antenna achieves CP property in all orientations of the omnidirectional radiation plane. By adopting arc structures and introducing parasitic patches, the size of the antenna is effectively reduced to π × (4.9)<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> × 0.835 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>, the −10 dB impedance bandwidth (IBW) is extended to 23.8% and the 3 dB axial ratio bandwidth is widened to 6.1% when simulated in a homogeneous muscle phantom. Additionally, the antenna is integrated into a capsule-type device and implanted in a realistic human phantom, exhibiting stable omnidirectional and CP performance. Experiments were conducted in minced pork with a measured IBW of 23.57%. The omnidirectional CP radiation pattern was verified by experimentally establishing a communication link. The proposed antenna offers a reliable candidate for establishing a robust communication link for the capsule endoscopy system.