Miniaturized Dual-Band Circularly Polarized Implantable Antenna for Capsule Endoscopic System

Abstract

This study proposes a miniaturized dual-band antenna with a circular-polarization characteristic for a wireless-capsule endoscopic system operating in the industrial, scientific, and medical bands: 915 and 2450 MHz. The proposed capsule device is intended for deep-tissue implantation with the standard dimensions of 26 x 11 mm(2). The key features of the proposed antenna are its CP characteristic at both bands, satisfactory gain values, and a smallest volume (6.5 x 6.5 x 0.05 = 2.11 mm(3)) with a via-less ground plane compared with the state-of-the-art device. The CP wave performance and the miniaturization of the antenna are achieved via the introduction of slots accompanied by meandered line segments in a radiating patch and open-end slots in a ground plane. Furthermore, the proposed antenna offers a reasonable axial ratio (AR) of <3 dB at the desired frequency bands. The circularly polarized radiator attains the AR bandwidths (BWs) of 33.0% and 8.67% and the measured -10 dB impedance BWs of 13.63% and 6.28% at 915 and 2450 MHz, respectively. The measurements of the reflection coefficient and radiation pattern are performed using a fabricated prototype of the proposed antenna system in a saline solution and minced pork. Finally, the safety considerations and link budget calculations are evaluated to analyze the performance of the proposed capsule device. Due to the AR BW, impedance BW, and ease of fabrication, the proposed antenna system is a suitable candidate for use in endoscopic applications.