A Symmetrical Closed-Loop Conformal Antenna With Wideband for Capsule Endoscope

A symmetrical closed-loop conformal antenna is designed for capsule endoscope at wireless medical telemetry service (608–614 MHz) band and industrial, scientific, and medical (902–918 MHz and 2.4–2.4835 GHz) band. The antenna is compartmentalized into two loops with an inverted-Ω loop and a hollow-T loop by the differential feeding. The antenna has a wideband (|
S
₁₁
| < −10 dB) covering 0.47–1.14 GHz and 1.38–3 GHz. The omnidirectional radiation pattern of the antenna is verified by measurement, and the peak gains are (−15.5, −16.8, and −23.1) dBi for the (611, 915, and 2400) MHz designs, respectively. The antenna possesses excellent environmental tolerance
in vivo
environment test. Moreover, the specific absorption rate value of the antenna can satisfy the IEEE regulations under the limit of 2.42 mW net-input power.