Design of a Dual-Polarized Wideband Conformal Loop Antenna for Capsule Endoscopy Systems

This paper presents a dual-polarized conformal loop antenna for capsule endoscopy systems. The antenna is designed on the capsule shell, with two orthogonal counterparts to generate dual-polarized radiation. This design exhibits broad impedance bandwidths of 271 and 247 MHz for each port, covering the entire Medical Device Radiocommunications Service band as well as the 433.05-434.79 MHz Industrial Scientific Medical band. Due to the highly orthogonal current distributions of the proposed structure, an isolation of higher than 33 dB is achieved among the operating frequency bands in measurement. The dual-polarized antenna also shows an omnidirectional radiation property and a low cross-polarization level of around -40 dB, which helps to enhance communication quality, regardless of position and orientation. Whether other electronics and biocompatible coatings are included or an electromagnetic interference shielding is considered, the antenna still presents a robust performance. The cubic tissue phantom model is utilized for the initial design and optimization of the antenna structure. Moreover, the CST voxel human model is applied to study the conformal antenna in a realistic environment. Measurements are implemented using a solid tissue-mimicking phantom, and performances consistent with theoretical predictions are achieved. Finally, the wireless biotelemetry property is evaluated via the calculation of the communication link budget with an external antenna.