A Conformal Circularly Polarized Antenna for Wireless Capsule Endoscope Systems

A conformal circularly polarized (CP) capsule antenna, designed for ingestible wireless capsule endoscope (WCE) systems at industrial, scientific, and medical (ISM) band (2.4-2.48 GHz), is presented. The antenna consists of a rectangular loop, an asymmetric U-shaped strip, and a protruding L-shaped stub printed on the top of the dielectric substrate. The CP wave is generated by the corner-fed U-shaped strip protruding into the rectangular slot. Further, by adjusting the size of the U-shaped strip and the L-shaped stub, the 3 dB axial-ratio (AR) band can be fully covered by the 10 dB impedance band. The simulated 10 dB impedance bandwidth (BW) and 3 dB ARBW are 31.58% and 13.11%, respectively. The simulated results show that the overlapped impedance BW and ARBW are from 2.28 to 2.6 GHz, which completely covers the 2.4 GHz ISM band. The measured 10 dB impedance BW is 39.21%. Finally, the radiation performance, safety consideration, and link budget of the antenna are examined and characterized. Owing to the broad overlapped impedance BW and ARBW, the minimized in-capsule foot print, and ease of fabrication, the designed antenna is a capable candidate for a WCE system.