High Data-Rate Hilbert-Curved-Shaped MIMO Antenna With Improved Bandwidth and Circular Polarization for Wireless Capsule Endoscopy

The growing demand for wireless communication in biomedical engineering has opened new research frontiers. This paper introduces an innovative miniaturized ( $4\times 9$ mm2) multiple-input multiple-output (MIMO) circularly polarized (CP) implantable antenna for a wireless capsule endoscopy (WCE) system. The presented device features two Hilbert curve-shaped meandered resonators. The space-filling characteristic inherent in the Hilbert curve contributes to miniaturization and bandwidth enhancement of up to 250 MHz to cover possible detuning between diverse organs. Simultaneously, employing the curve’s inherent natural symmetry and adopting an orthogonal port arrangement led to a noteworthy improvement in isolation up to 27 dB with an enhanced gain of −27.9 dBi. Comprehensive simulation analysis of antenna-integrated WCE systems in homogeneous and hetrogenous environments is conducted in the stomach, small intestine, and large intestine. Without the need for an external decoupling structure, the system demonstrated good MIMO characteristics with isolation of 27 dB. A fabricated prototype has been tested in a saline solution and minced pork. A good match between the measured and simulated results has been observed. At both ports, the axial ratio (